zaid bin farooq - internship report'13

Zaid Bin Farooq

University of

Engineering &

Technology, Taxila.

8th July-2nd August 2013

LALPIR

THERMAL

POWER

PLANT Internship Report ‘13

` INTERNSHIP REPORT - 2013

2


Here I would like to thank Mr. Asad for conveying technical knowledge of Turbine,

Mr. Jaffar for Boiler Area, Mr. Javed Siddiqui and Mr. Usman for BOP, and Mr. Amjad

Javed for Chemical Lab. I would also like to acknowledge the part played by Mr.

Adnan as a whole for helping me understand the basics of Thermal Power Plant.

Last but not the least I would like to mention the contribution of Major Sharukh for

motivating me towards learning as much as possible at Lalpir Thermal Power Plant.

It was really a valuable experience to work with Lalpir team.

3


This report covers the operational aspects of a Power Plant. The report includes

description of Balance of Plant, Boiler, Turbine, Condenser and Chemical Laboratory

in a comprehensive and precise form. Moreover areas such as Cooling Towers and

Mechanical components are also discussed in considerable detail.

4


Table of Contents

Lalpir thermal power plant ........................................................................................................................... 1

Acknowledgements………………………………………………………………………………………

Balance of Plant ............................................................................................................................... 15

Raw Water Intake System ....................................................................................................................... 16

Travelling Band Screen ............................................................................................................................ 17

Pre-Treatment System ............................................................................................................................ 18

(2+2) x Canal Water Pump ...................................................................................................................... 18

Function and Operation: ..................................................................................................................... 18

Specification ........................................................................................................................................ 18

Well Water Pumps Specs. ....................................................................................................................... 19

Settling Basin to Clear Well ..................................................................................................................... 20

CLARIFIER SUPPLY PUMPS ...................................................................................................................... 20

CLARIFIER ................................................................................................................................................ 20

Specifications ...................................................................................................................................... 21

Maintenance of Pumps: ...................................................................................................................... 22

CHEMICAL TREATMENT .......................................................................................................................... 22

Coagulant Dozing: ............................................................................................................................... 22

Polymer Dozing: .................................................................................................................................. 22

Dual Media Filters ................................................................................................................................... 22

Multimedia Filters ................................................................................................................................... 23

Material/Media Used in MMF ............................................................................................................ 24

Osmosis process ...................................................................................................................................... 24

WATER DEIONIZATION PROCESS EXPLAINED ......................................................................................... 29

Ions Commonly Found in Water ............................................................................................................. 31

COOLING TOWERS .................................................................................................... ................................. 37

Natural draft cooling tower .................................................................................................................... 37

Mechanical draft cooling tower .............................................................................................................. 38

WASTE WATER ENVIRONMENTAL STANDARDS ..................................................................................... 39

Hydrogen Generation ............................................................................................................................. 40

5


Feed Water ............................................................................................................................. 40

Safety Precautions for working in the Hydrogen Building ............................................................... 42

Summary of BOP: ........................................................................................................................ 43 Boiler .............................................................................................................................................. 44

INTORODUCTION ......................................................................................................................... 44

Boiler in LALPIR/ PAKGEN ............................................................................................................ 46 Super Heaters ................................................................................................................................. 54 ReHeaters ....................................................................................................................................... 55 Fuel Cycle ....................................................................................................................................... 58 Diesel Cycle .................................................................................................................................... 60 Air Cycle ......................................................................................................................................... 60 Turbine ........................................................................................................................................... 63

Steam Turbine ............................................................................................................................ 63

Gas Turbine ................................................................................................................................ 63

Thermodynamics of Steam Turbine .............................................................................................. 63

Working of a Steam Turbine ........................................................................................................ 64

Rankine Cycle with superheat ...................................................................................................... 64

Types of Steam Turbine ............................................................................................................... 65

Impulse Turbine ...................................................................................................................... 65

Reaction Turbine ..................................................................................................................... 65

Straight Condensing Turbine: ................................................................................................... 68

Straight non condensing Turbine: ............................................................................................. 68

Non automatic-Extraction Turbine, Condensing or Non condensing: .......................................... 68

Automatic-Extract ion Turbine, Condensing or Non condensing: ................................................ 68

Automatic-Extraction- Induction Turbine, Condensing or Non condensing: ................................. 68

Mixed-Pressure Turbine, Condensing or Non condensing: .......................................................... 68

Reheat Turbine: ...................................................................................................................... 68

Parts of Steam Turbine ................................................................................................................ 70

Main Steam Valve (MSV) and Governing Valve (GV) .................................................................. 70

Rotor ....................................................................................................................................... 70

Nozzles .................................................................................................................................... 70

Bearings .................................................................................................................................. 71

6

`

INTERNSHIP REPORT – 2013

Gland Sealing System .......................................................................................................................... 71

Specifications .......................................................................................................................................... 73

Condenser ............................................................................................................................................... 74

Direct Contact Condenser ................................................................................................................... 74

Surface Condenser .............................................................................................................................. 74

Purpose of Condenser ............................................................................................................................. 74

Condenser Cycle ...................................................................................................................................... 74

Reason for Partial Vacuum Inside the Condenser .............................................................................. 75

Steam Ejector .......................................................................................................................................... 75

Non-Condensable Gases in Condenser and their Effects ................................................................... 75

WORKING ............................................................................................................................................ 75

Gland Steam Condenser ......................................................................................................................... 76

Deaerator ................................................................................................................................................ 76

Deaerator Uses: ............................................................................................................. ..................... 77

Scavenging .............................................................................................................................................. 77

WORKING ................................................................................................................................................ 77

CONDENSATE PUMPS ............................................................................................................................. 78

SPECIFICATIONS ............................................................................................................................. ..... 78

FEED WATER HEATERS ............................................................................................................................ 78

TYPES OF FEED WATER HEATER .............................................................................................................. 79

FEED WATER HEATER IN LALPIR ............................................................................................................. 79

BOILER FEED WATER PUMPS .................................................................................................................. 80

BFP AT LALPIR ..................................................................................................................................... 80

Steam Cycle ................................................................................................................................................. 82

Bearing Cooling Water ............................................................................................................................ 82

OIL SYSTEM ............................................................................................................................................. 83

MAIN OIL TANK ....................................................................................................................................... 83

7


Lal Pir (Pvt.) Limited owns and operates Lal Pir Thermal Power station, most efficient power plant in Pakistan, Located near "Muzaffargarh". Against this contribution we make every effort to balance our commitment to country's energy needs with minimizing environmental impacts on land, air and water. Our generating units are fitted with flue gas desulphurisation (FGD) equipment removing 90% of the sulphur dioxide (SO2) from emissions, and work is underway to reduce still further emissions of oxides of nitrogen (NOx). At the same time, by-products of the FGD processes are recycled through their further use in the construction industry.

Lalpir Thermal Power Station was developed in 1997 with the hope of meeting the growing Electricity needs of the Nation followed by PakGen in 1998. Lalpir and PakGen both run on conventional or Rankine cycle. The two units are identical with slight differences in amount of electricity generation. Lalpir and PakGen sell electricity to the Pakistan Water and Power Development Authority (WAPDA), the state-owned utility, under 30-year power purchase agreements.

Plant comprised of different departments: Operation Department

Balance of Plant

Electrical and Instrumentation Department

Mechanical Maintenance Department

Performance Department

8

Lalpir Thermal Power Plant- An

Overview


Thermal power station provides a mechanism to transform energy. The chemical energy that is released from hydrocarbons in fossil fuels, when reaction with oxygen at a high temperature is the input of power plant and the electrical energy delivered by the generator is the output. In a conventional power plant the energy transformations are as follows:

Chemical Heat Mechanical Electrical Energy Energy Energy Energy

In thermal power stations, mechanical power is produced by a heat engine, which transforms thermal energy, often from combustion of a fuel, into rotational energy. Most thermal power stations produce steam, and these are sometimes called steam power stations. About 80% of all electric power is generated by use of steam turbines. Not all thermal energy can be\ transformed to mechanical power, according to the second law of thermodynamics. Therefore, there is always heat lost to the environment. If this loss is employed as useful heat, for industrial processes or district heating, the power plant is referred to as a cogeneration power plant or CHP (combined heat-and-power) plant.

Lalpir/PakGen thermal power plant is Oil fired power plant which burns HSFO (High Sulphur Fuel Oil). HSFO is burned in furnace and the hot combustion gas is used to produce superheated steam in a boiler. The superheated steam is expanded through a steam turbine providing power to drive a generator, which in turns generate electricity. The AES power plant runs on Rankine cycle with reheat.

9

` INTERNSHIP REPORT - 2013 In a real Rankine cycle, the compression by the pump and the expansion in the

turbine are not isentropic. In other words, these processes are non-reversible and entropy is increased during the two processes.

This somewhat increases the power required by the pump and decreases the power generated by the turbine. In particular the efficiency of the steam turbine will be limited by water droplet formation.

As the water condenses, water droplets hit the turbine blades at high speed causing pitting and erosion, gradually decreasing the efficiency of the turbine. The easiest way to overcome this problem is by superheating the steam.

On the Ts diagram above, state 3 is above a two phase region of steam and water so after expansion the steam will be very wet. By superheating, state 3 will move to the right of the diagram and hence produce a dryer steam after expansion.

10


Boiler

The working fluid

completes a cycle as

the liquid leaving

the pump at 4,

called the boiler

feedwater, is heated

to saturation and

evaporated in the

boiler.

=ℎ1−ℎ4

Rankine Cycle

Turbine

Vapor from the boiler at state 1, having an

elevated temp. and pressure expands

through the turbine to produce work and is

then discharged to the condenser at state 2

with relatively low pressure. The work

developed in turbine is

( ) =ℎ3−ℎ4

Pump

The liquid condensate leaving the condenser

at state 3 is pumped from the condenser into

higher pressure boiler. Work done by a

pump is given by:

( ) =ℎ4−ℎ3

Condenser: In the condenser

there is heat transfer

from the vapor to

cooling water flowing

in a separate steam. The vapor condenses

and the temperature

of the cooling water

increases. Steady

state, mass and

energy rate balances

are as following.

INTERNSHIP REPORT - 2013

•Lalpir Pvt Ltd. always puts safety first - for its people, contractors and communities. Ensuring safe operations is the cornerstone of the daily activities and decisions. Everyday Lalpir harnesses one of the world's most powerful forces: electricity. It always puts safety first, and measures success by how safely goals are achieved.

•By acting with integrity one earns the trust of business partners, customers, shareholders, and the people who live in the communities where the firm operates. Maintaining reputation requires a continuous commitment from all to act with the highest standard of integrity in all business decisions.

•Lalpir is committed to protect the investments of its shareholders and to provide financial return and growth. When making business decisions, Lalpir will balance short-term and long term goals in an effort to maximize value to its owner.

•Excellence is both a goal in itself and the way to achieve that goal. Striving for excellence implies continually working to improve ourselves and the business operations.

•At Lalpir Pvt Ltd, we enjoy our work and appreciate the fun of being part of a team

that is making a difference. Having fun through work means knowing that our work at each day has a positive impact. We believe that a workplace that supports respect for one another, teamwork, and diversity of backgrounds and views is a fun workplace.

12


Balance of Plant is responsible for providing treated water according to the need of

the Plant. Considering its importance it plays a vital role in the production of

electricity at Lalpir Power Plant.

General Overview:

Raw water Intake

Settling Basins

Clarrifiers

Dual Media Filters

Multi Media Filters

Reverse Osmosis

Demineralization

Demineralized Water Tank

13


Raw Water Intake System

Raw water at Lalpir Thermal Power Plant comes from 2 sources;

1. Canal Water 2. Well Water

Primary source is Canal water being available from Mid-April to Mid-October.

Secondary source is Well water used in rest of months. Due to the difference in cost,

Canal water is preferred as raw water intake.

Canal Water

Raw Water

Intake

Well Water

Canal Intake to Settling Basin

Canal Water from Canal suction pit (2 trains per unit) passes through

travelling band screen, having 22 baskets. It revolves continuously, so that

water passes through their center. Band screen has the sieve size of 1 mm. Its

purpose is to remove debris, which can choke the flow.

Raw water is then pumped to Settling Basin with the help of canal water pump (2+2) for Lalpir and Pakgen units.

14


Travelling Band Screen

Function and operation: The travelling band screen is designed to prevent the entrance of water pollution into the cooling system, which otherwise could cause mechanical damages. The screen band is conveyed through the chamber continuously. The polluted baskets are cleaned over the floor during the downward travel by the action of a spray water shower which is located above the baskets in the machine covering hood (made of glass fiber reinforced plastic). The screenings which are washed from the baskets are collected in the waste and conveyed to the waste water drain.

Specifications

No. of Baskets 22

Chamber Length 1200mm

Throughput Q0 1600m3/hmin

In bottom Curve 4

Wire Diameter 0,36mm

Mesh Width of Screen fabric 100mm

Pitch of Chain 500mm

Material of Screen Baskets Frame RST 372

Safety precautions: -unauthorized personnel are not allowed to enter. -

main switch must be switched off during any repair.

-be careful of the spray mist while opening the flaps.

15


Pre-Treatment System

The raw water is then pumped to the Settling Basin (2 sets for three units) with the help of canal water pump.

(2+2) x Canal Water Pump

Function and Operation: Two motor driven Canal water pumps are installed for each unit at the Lalpir Power Plant. Each pump is single stage, close impeller, vertical, wet pit type pump. These motor-driven canal water pumps supply the settling basin with Canal water. The stuffing box consisting of gland packing and an adjustable gland follower is provided to seal the pump shaft. All four pumps lubricating oil and rubber bearings at shaft are cooled by cooling water which is supplied from vertically mounted centrifugal lube water pumps which takes there inlet from bore or wells. Two separate storage tanks are used for this purpose. There are two sources to make up the level in these tanks

Two small Makeup pumps located at canal intake. Well pumps A&B for unit-1 and Well water pump A&D

for Unit-2.

Specification

Manufacture GANZ MACHINERY AND ENERGETIC CO., LTD

Model MNM350

Type Centrifugal Vertical Shaft

Pump Speed 1475rpm

Flow Rate 1200 m3/hr

Total Head Required 22mm

Rated Efficiency 80.7%

16


Well Water Pumps Specs.

Manufacturer Weir Pumps Ltd

Type Submersible

No. of Pumps 12+7 (new installed)

Direction of Rotation Anti-Clockwise

Liquid Pumped Well Water

Specific Gravity 1.00

Flow 21.98m3/hr

Total Head 122

Speed 2803rev/min

Pump Efficiency 41% For dry period the continuous demand for water is met with 12 well water pumps having 240m3/hr/pump discharge rate (6 for each unit). Well water contains more dissolved impurities while canal water contains more suspended impurities. Suspended impurities are much easier to separate and more process is cheaper as compared to the dissolved impurities. Hence at Lalpir we prefer Canal water over Well water.

17


Settling Basin to Clear Well

Water from canal pumps through their respective line (PakGen or Lalpir) and then comes to 3 settling basins (1000m3) having common header with the provision of filling any settling basin,and by pass line to cooling tower. Settling basins provide primary settling zone for large suspended particles, sand and silt in canal water hence reducing the cost of coagulation in clarifier, load on filters and providing proper suction for clarifier supply pump. Raw canal and raw well water is fed to an inlet distribution box (3048 × 1828 mm) through settling basin by clarifier supply pump (1050m3/hr). From Clarifier supply pumps raw water goes to Clarifiers (A,B,C) having 2400m3/clarifier storage capacity. Colloidal solids in canal or well water require initial treatment with a chemical having strong ionic properties, such as acid, lime, alum, or ferric sulfate. The latter two will precipitate at neutral pH and produce a gelatinous, flocculent structure which further helps collect extremely small particles. This phenomenon is commonly known as Coagulation. At Lalpir ferric sulfate is used as coagulant which is normally injected at the rate of 20-30 ppm. Polymer (1-2 ppm) is also injected for flocculation of particles. Each clarifier operates at normal flow rate of 1023 m3/hr and maximum flow rate of 1250 m3/hr. The effluent from clarifier goes to clear well (100m3 storage capacities).

CLARIFIER SUPPLY PUMPS

Water from settling basin is pumped to the clarifier through clarifier pumps. A total of 3 pumps of which 2 are used and 1 is stand by.

CLARIFIER

Each clarifier operates at normal flow rate of 1023 m3/hr and maximum flow rate of 1250 m3/hr.

The effluent from clarifier goes to clear well (100m3 storage capacities). Suspended solids in canal or well water require initial treatment with a

chemical having strong ionic properties, such as acid, lime, alum, or ferric sulfate. The latter two will precipitate at neutral pH and produce a gelatinous, flocculent structure which further helps collect extremely small particles. This phenomenon is known as Coagulation.

18


Suspended solids may consist of large solids that can settle by gravity alone without any external aids, and non-settling material, often colloidal in nature. Removal is generally accomplished by coagulation, flocculation and sedimentation. The combination of these three distinct processes is referred to as conventional clarification. This requires also three distinct unit processes:

1. High shear, rapid mix for coagulation; 2. Low shear, high retention time, moderate mixing for flocculation; 3. Liquid-solids separation.

The first step in complete clarification is the neutralization of the electrostatic charges on colloidal particles. Because most of the smaller suspended solids in surface waters carry a negative electrostatic charge, the natural repulsion of these similar charges causes the particles to remain dispersed almost indefinitely. To allow these small suspended solids to agglomerate, the negative electrostatic charges must be neutralized. This is accomplished by using inorganic coagulants (water soluble inorganic compounds), organic cationic polymers or polyelectrolytes. Once the negative charges of the suspended solids are neutralized, flocculation begins. Charge reduction increases the occurrence of particle-particle collisions, promoting particle agglomeration. Portions of the polymer molecules not absorbed protrude for some distance into the solution and are available to react with adjacent particles, promoting flocculation. Bridging of neutralized particles can also occur when two or more turbidity particles with a polymer chain attached come together. It is important to remember that during this step, when particles are colliding and forming larger aggregates, mixing energy should be great enough to cause particle collisions but not so great as to break up these aggregates as they are formed.

Specifications

Manufacture Mitsibishi Heavy Industry

LTD.

Dimensions 400x350mm

Capacity 1100m3hr

Speed 1475rpm

Type Double Suction Discharge

Pump

19


Maintenance of Pumps:

Pumps must not be disassembled unnecessarily unless for periodic inspections, abnormal noise and unexpected behavior.

Ball bearings are applied. Oil is lubricated in bearing to reduce wear and friction and also to prevent

stain and dust.

CHEMICAL TREATMENT

Coagulant Dozing:

Ferric Sulphate is added to Canal water for settling of suspended particles. Coagulation takes place and most of the suspended particles are settled down in the Clarifier. Ferric Sulphate is injected at the rate of 20-30 ppm.

Polymer Dozing:

Polymer is added to the canal water to enhance the settling capacity of the coagulant. Flocks of suspended particles are made and settled down to the bottom. Polymer is dozed at a rate of 1-2 ppm.

There are two types of mixed media filters used at Lalpir

Multimedia Filter

Dual Media Filter

Dual Media Filters

They have two mediums for filtrations, anthracite and filter sand. There is a third layer of gravel also which is just to support the filtering media. The filter is pressure filter type and there are totally eight filters out of which four are for unit-1 while the remaining four are for unit-2. Each of them has a capacity of filtering 300

m3/hr of water.

20


DMF CLEANING/BACKWASHING After 2 hours of running DMF Filters are cleaned/backwashed to remove the suspended particles. Clear well Level should be above 70%.

DRAIN DOWN (5 min) Here the air outlet valve and drain down valves are opened so that any previous reserve is drained because standing water in DMF is rich in silica. Flow rate is 90 m3 /hr.

AIR MIX (5 min) In this step air mix inlet valve (air from the DMF air blowers) and air outlet valve are opened this steps evens the DMF surface same as air scouring. Flow rate is 1380 m3 /hr.

FILL (5 min) In this step service inlet of water and air outlet valve opens in this step DMF fills itself with water. Flow rate is 225 m3 /hr.

BACKWASH (5 min) Here back wash inlet and outlet valves opens and the water goes to Settling Basin. Flow rate is 680 m3 /hr.

RINSE (5 min) Service inlet and rinse outlet valves open and the waste water goes to distribution chamber. Flow rate is 170 m3 /hr. After these steps DMF is ready for service DMF Backwash and clear well overflow goes to settling basin A&B.

Multimedia Filters

Multimedia filters are those which have more than two filtering media. The media used at AES Lalpir are:

1. Garnet 2. Anthracite 3. Filter sand

21


Material/Media Used in MMF

Materials Quantity(m3) mm(average size)

Garnet 1.06 0.35

Anthracite 1.5 0.9-1.0

Filter Sand 1.45 .45-0.55

Fine Gravel 0.5 3.35-1.7

Medium Gravel 0.5 12.7-6.3

Coarse Gravel 1.9 19-12.7

Number of MMF in Aes Lalpir 4\ two for each

Flow Rate of MMF 300m3/hr

Osmosis process

Osmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane. A selectively permeable membrane is one that allows unrestricted passage of water, but not solute molecules or ions. Different concentrations of solute molecules lead to different concentrations of free water molecules on either side of the membrane. On the side of the membrane with higher free water concentration (i.e. a lower concentration of solute), more water molecules will strike the pores in the membrane in a given interval of time. More strikes equates to more molecules passing through the pores, which in turn results in net diffusion of water from the compartment with high concentration of free water to that with low concentration of free water. The key to remember about osmosis is that water flows from the solution with the lower solute concentration into the solution with higher solute concentration. This means that water flows in response to differences in molarity across a membrane. The size of the solute particles does not influence osmosis. Equilibrium is reached once sufficient water has moved to equalize the solute concentration on both sides of the membrane, and at that point, net flow of water ceases.

22


Reverse osmosis process Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Reverse osmosis, however, involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate. Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other substances from the water molecules.

Reverse Osmosis is a water purification technique used to reduce the loading of dissolved solids in solution. In the chemical industries, application of R.O. for treating boiler feed water is growing rapidly because of the rising cost of chemical demineralization and safety concerns associated with handling acid and caustic. A properly designed and operated RO based boiler feed water will reduce the costs and improve water quality.

23


R.O. Membrane Specifications

Number of Elements 72 (36 per R.O. bank)

Membrane Type Spiral wound thin film composite(cpa

Diameter 201.9 mm

Length 1016 mm

Max. Operating Temp. 450 C

Feed water pH range 3,10

Free chlorine Tolerance < 0.1 mg/l

Nominal Permeate flow 1.42 m3 /hr

Nominal Salt rejection 99 %

When high dissolved solids well water is used, then water from multimedia filter is passed through Reverse Osmosis system. Sulphuric acid is also injected in feed water to lower the pH. An anti-scalant solution is also injected in R.O. feed water at constant rate. In the AUTO mode the acid and anti-scalant pumps are started and stopped automatically with R.O. booster pumps. There are three R.O. booster pumps. Usually two pumps are in operation and one is standby. The standby booster pump will not operate unless designated for service by operator. Treated water from R.O. system is directed to R.O. permeate tank.

1. The R.O. system will stop if the level of permeate tank is high and is maintained for preset time. Restart is initiated by operator.

2. Interlocks are provided to shut down R.O. booster pump at low booster pump suction pressure, high booster pump discharge pressure, high R.O. inlet feed temperature and high R.O. permeate pressure.

24


R.O. Storage Tank

R.O. system product water is collected in R.O. storage tank. Demineralizer feed pumps then fed the water from R.O. permeate tank to cation unit. One pump will operate when a cation unit is in service. The other pump will operate when one train is in service or regeneration and other is in service.

The flow of water from multimedia filters to the R.O. storage tank is controlled by the tank level controller.

Interlocks are provided to deactivate the deminerlizer feed pumps on low level in storage tank.

A pump recirculation line to the storage tank is provided for pump protection during low flow demand. If the totalized flow to both the cation units is below the preset minimum, the recirculation valve will open.

Size 1829 mm dia x 2438 mm

Capacity 5 m3

Advantages of Reverse Osmosis: Removes nonionic impurities and dissolved solids. (i.e. organic,silica,bacteria)

Reduction of hazardous chemical storage and handling associated with Ion-exchange.

Reduces loading on ion-exchange systems.

(a) Extends run lengths.

(b) Extends resin life.

(c) Reduce operating costs.

Maintenance of RO Membranes Maintenance of RO membrane is required when any of the following condition occur

Flow decreases 10-15% below rated flow at reference system pressure and

temperature.

Water quality decreases 10-15%

The differential pressure across an R.O. stage increases 10-15%.

25


DEMINERALIZATION SYSTEM

Cation Unit Specification

Quantity 2

Diameter 1829 mm

Straight side 3988 mm

Design Pressure 6.9 kg/cm2

Test Pressure 10.35 kg/cm2

Capacity /Unit 1300 m3

Capacity /Unit 161.2 kgm

Design Basis 124 mg/l

Capacity / m3.Resin 30 kgm/m3

Design flowrate/Unit 65 m3/hr.

Hours Run/Unit –at design flow 20

Resin/Unit 5.375 m3

Resin Bed Depth 2048 mm (app.)

Resin Freeboard 1940 mm (app.)

Maximum Operating Temperature 40oC

Anion Unit Specification

Quantity 2

Diameter 1829 mm

Straight side 2794 mm

Design Pressure 6.9 kg/cm2

Test Pressure 10.35 kg/cm2

Capacity /Unit 1300 m3

Capacity /Unit 143 kgm

Design Basis 110 mg/l

Capacity / m3.Resin 38.9 kgm/m3

Design flowrate/Unit 65 m3/hr.

Hours Run/Unit –at design flow 20

Resin/Unit 3.68 m3

Resin Bed Depth 1402 mm (app.)

Resin Freeboard 1392 mm (app.)

Maximum Operating Temperature 40 Degree Celsius

26


WATER DEIONIZATION PROCESS EXPLAINED

Deionized water is a type of purified water with mineral ions (salts) removed. These mineral ions include sodium, calcium, iron, copper, chloride, and bromide. Deionized water is created by taking conventional water and exposing it to electrically charged resins that attract and bind to the salts, removing them from the water. Because most of the impurities in water are mineral salts, deionized water is mostly pure, but it does still contain numerous bacteria and viruses, which have no charge and therefore are not attracted to the electrified resins.

The goal of the water purification process is to take raw water and use a method to purify or clean it. When you are trying to explain water purification, you have to know the purpose the water will be used for. There are many methods and each is suitable for certain applications. Mostly water is purified for homes, but there are applications like medical, scientific, industrial and commercial. Each has a water purification process that best suits it. Some of the different methods include, in no particular order, ultra violet light filtration, reverse osmosis, deionization and activated carbon treatment. There are many others, as well. A complete water purification process will remove a whole host of things including algae, suspended particles of organic material, bacteria, viruses, fungi, minerals and metals. The government sets standards as to how many particles may remain and still be safe for human consumption. If you have to know exactly what contaminants are present, you will have to have a sample tested. The source is sometimes a factor in which water purification process is best. Obviously we cannot name them all, but the source could be a river, stream, lake, spring or well. These are only a few. Knowing the source helps experts to identify potential contaminants and choose the right water purification process to get the job done. Deionizers are ion exchange equipment that consists of cationic bed, anionic bed and a combination of both (mixed bed) to meet the requirement of high purity water for process / utility applications. The equipment separately removes the cations and

27

http://www.wisegeek.com/what-is-sodium.htm

http://www.wisegeek.com/what-is-copper.htm


anions in various units that involve usage of strong acid cation, weak acid cation, weak base anion & strong base anion units. The quality and result of deionization process depends on the characteristics of raw water, ratio of its contents, quality of treatment and the capacity of plant. Strong acid cations / weak acid cations are employed to treat all types of cations

from the raw water (Ca++, Mg++, Na+, K+ etc.). A deionizer unit comprises of a MSRL / FRP vessel that is internally fitted with bottom collecting system and inlet distributor and externally with isolation valve and frontal pipe work. The unit is charged with cation resin that is regenerated with acid (HCl / H2SO4) after its exhaustion, usually engineered for once or twice in a day. Mixed Bed (MB) units have found to be suitable for polishing of treated water from

strong base anion unit or RO plant. The unit produces ultra-pure water that is needed for high pressure boiler feed water applications, micro-electronics and semi-conductor industry applications. During this process, the cation and anion resins are mixed in a single vessel and the water is traveled through a resin bed wherein the exchange of ions takes place.

Deionization Process

In the context of water purification, ion-exchange is considered to be a reversible and rapid process wherein the impurity ions present in the hard water are replaced by ions that are released by an ion-exchange resin. The impurity ions are absorbed by the resin, that must be periodically regenerated to restore the earlier ionic form. An ion is an atom or a group of atoms with an electrical charge. Positively-charged ions are known as cations and are usually metals, while the negatively charged ions are known as anions and are usually non-metals. The two most common types of deionization processes are:

1. Two-bed deionization 2. Mixed-bed deionization

28


Ions Commonly Found in Water

Cations: Sodium [Na+], Calcium [Ca++], Magnesium [Mg++], Potassium [K+], Iron [Fe+++], Manganese [Mn++] and Hydrogen [H+]

Anions: Chlorides [Cl-], Sulfates [SO4=], Nitrates [NO3=], Carbonates [CO3=], Silicates [SiO2- ] and Hydroxyl [OH-]

Ion Exchange Resins Modern science has developed materials commonly called “ These resins take the form of little plastic beads made out of styrene cross-linked with divynalbenzene. Once formed, the beads are then either cooked in sulfuric acid to provide negatively charged sulfite sites to make cation resin, or processed in an ammonium salt solution to provide positively charged quaternary ammonium sites foranion resin. It is the charged sites on these resin beads that give them their ion exchange properties. It has been estimated that a cation resin bead half a millimeter in diameter contains more than 280 billion exchange sites.

Cation Resin The sulfite sited cation exchange resin is regenerated with an acid solution. In the acid form (H+), cation resin removes positively charged impurities such as calcium (Ca++), magnesium (Mg++), sodium (Na+) and potassium (K+). The impurities attach themselves to sites on the ion exchange resin, eluting off hydrogen (H+) from the acid regeneration. The resultant liquid is a mixture of acids caused by the association of the H+ hydrogen ion from the resin with all the anionic impurities still in the water.

Anion Resin The resins with the quaternary ammonium sites are called anion resins and are regenerated with caustic soda solution to put them into the hydroxyl [OH-] state. The anion resin is then able to remove negatively charged impurities such as chloride (Cl-), sulfate (SO4=) and carbonate (CO3=). The impurities attach themselves to sites on the ion exchange resin, eluting off the hydroxyl radical (OH-).

29


Deionization

At this point all of the exchangeable anions and cations that were in the water are now held on the cation and anion resins exchange sites. The hydrogen ions [H+] eluted off of the cation resin combine with the hydroxyl ions [OH] eluted off of the anion resin to form pure water.

− 2 This process continues until the resins have a majority of available exchange sites taken up with impurities. When this happens the resin is said to be exhausted. But after the cation resin is treated with acid and the anion is treated with caustic soda the deionizer is ready to operate again. The ability of ion exchange resins to be regenerated and used over and over again makes it a very practical and economical water purification tool.

Cation Regeneration

As soon as all the sites on the cation resin have given up their H+ ion and have taken up cationic impurities, the resin must be regenerated. To regenerate a cation resin column, a 10% hydrochloric acid (HCl) solution or a 4% sulfuric acid (H2SO4) solution is passed through the cation resin. The concentration of hydrogen ions in the acid solution provides the driving force to remove any other cations from the resin in favor or the hydrogen ion (H+).

Anion Regeneration

When the anion resin is loaded up with anionic impurities it is regenerated by passing a 4% caustic soda (NaOH or KOH) solution through it. The concentration of hydroxyl ions in the caustic soda solution provides the driving force to remove the anion impurities from the resin in favor of the hydroxyl [OH-] ion. The resin is once again ready to play its part in deionization.

Separate Bed Deionization

Separate bed or two-bed deionization refers to the fact that the cation resin and the anion resin are in separate tanks. Regeneration is relatively simple, and water quality is frequently around 200,000 ohms/cm3 or 2 ppm.

30


Mixed Bed Deionization

In Mixed bed deionization the cation and the anion resins are mixed after regeneration and placed in the same vessel. The purpose of mixing the resins is to achieve a very high quality deionized water. When the resins are mixed, as the water passes through the resin bed it encounters a cation resin bead, then an anion resin bead, then cation, anion, cation, anion and so forth. The water is deionized then re-deionized continually resulting in an ultra-high purity product. The regeneration of a mixed bed resin complicated by the fact that the resins must first be separated into cation and anion columns, separately regenerated and rinsed then mixed again. This process is more expensive and difficult than separate bed regeneration and mixed bed capacity is typically significantly lower than separate bed deionizers. But the product water from a properly regenerated mixed bed is the highest quality obtainable. Mixed bed deionization will frequently yield a water quality exceeding 18 mega ohms, less than 25 parts per billion.

REGENERATION

When resin has become exhausted, it can no longer remove ions from water. This condition can be corrected by regeneration, a process that uses sulphuric acid for cation as regenerant and sodium hydroxide for anion regeneration.

During normal ion exchange operation, suspended solids from the incoming water become trapped in the resin bed. In addition, the pressure of the incoming water compacts the bed. In order to ensure proper regeneration, trapped solids must be washed from the resin and the resin bed must be expanded so that the regenerant can come into contact with the resin beads. This is accomplished by backwashing the resin beds. During back washing the normal flow of water is reversed. The reverse flow expands the resin bed, creating more space between the beads, and washes away the suspended solids which are sent to waste.

Deionizer Regeneration Chemicals

Cation Regenerant –HCl –H2SO4 –(Never use HNO3) Hydrochloric or Sulfuric Acid is used to regenerate Cation resin. Hydrochloric acid has the advantage of providing higher capacities than Sulfuric, but it is more expensive. Sulfuric acid also has the potential to cause calcium sulfate fouling of the cation resin. If sulfuric acid is to be used for cation regeneration, the water being deionized must be soft, or the sulfuric acid regeneration must proceed step wise, starting at a concentration below 2% and later being raised to 4%. Never use nitric

31


acid HNO3 for cation deionizer regeneration. Combining a nitrate oxidizer with an organic cation resin can, and has, caused rapid exothermic reactions or explosions Anion Regenerant –NaOH –KOH –Soda Ash Sodium Hydroxide is the regenerant of choice for most anion regenerations. While potassium hydroxide can be an excellent regenerant, it usually costs more than the Info 4 equally effective sodium hydroxide. Soda ash can be used weak base anion regenerations as long as the desired water quality can be achieved.

Regeneration In General

During any regeneration procedure, a chemical is being continuously diluted by water and fed into a resin bed. It is the total number of pounds of the chemical put through the bed that determines the capacity of the deionizer. While the exact concentration of chemical can vary with little impact on the quality of the regeneration, maintaining the proper concentration is important because:

• theIfstrength it too high there will either be insufficient contact time or bed channeling.

• If the strength is too low there wi complete regeneration. It is always best to follow the resin manufactures guidelines as to regenerate concentration.

Advantages Some of the important advantages of modern day deionizers include -

1. Easy to use and operate. 2. Low cost per gallon of effluent produced. 3. Quick and efficient production of usable effluent. 4. Superior water purity if the correct resins are used.

32


A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The type of heat rejection in a cooling tower is termed "evaporative" in that it allows a small portion of the water being cooled to evaporate into a moving air stream to provide significant cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere. Evaporative heat rejection devices such as cooling towers are commonly used to provide significantly lower water temperatures than achievable with "air cooled" or "dry" heat rejection devices, like the radiator in a car, thereby achieving more cost effective and energy efficient operation of systems in need of cooling. There is a penalty involved, and that is loss of water which goes up to the cooling tower and is discharged into the atmosphere as hot moist vapor. Under normal operating conditions, this amounts to approximately 1.2% for each 10 F cooling range. Sensible heat that changes temperature is also responsible for part of the coo ling tower’soperation. When water is warmer that the air, there is a tendencyfor the air to cool the water. The air then gets hotter as it gains the sensible heat of the water and the water is cooled as its sensible heat is transferred to the air. Approximately 25% of the sensible heat transfer occurs in the tower while the balance of the 75% cooling is due to the evaporative effect of latent heat of vaporization.

Components of a cooling tower The basic components of a cooling tower include the frame and casing, fill, cold-water basin, drift eliminators, air inlet, louvers, nozzles and fans. These are described below.

Frame and casing Most towers have structural frames that support the exterior enclosures (casings), motors, fans, and other components. With some smaller designs, such as some glass fiber units, the casing may essentially be the frame.

33


Fill Most towers employ fills (made of plastic or wood) to facilitate heat transfer by

maximizing water and air contact.

Cold-water basin The cold-water basin is located at or near the bottom of the tower, and it receives the cooled water that flows down through the tower and fill. The basin usually has a sump or low point for the cold-water discharge connection.

Drift eliminators These capture water droplets entrapped in the air stream that otherwise would be lost to the atmosphere.

Air inlet This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower (cross-flow design) or be located low on the side or the bottom of the tower (counter-flow design).

Louvers Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equalize air flow into the fill and retain the water within the tower. Many counter flow tower designs do not require louvers.

Nozzles These spray water to wet the fill. Uniform water distribution at the top of the fill is essential to achieve proper wetting of the entire fill surface. Nozzles can either be fixed and spray in a round or square patterns, or they can be part of a rotating assembly as found in some circular cross-section towers.

Fans Both axial (propeller type) and centrifugal fans are used in towers. Generally, propeller fans are used in induced draft towers and both propeller and centrifugal fans are found in forced draft towers. Depending upon their size, the type of propeller fans used is either fixed or variable type.

34


TYPES OF COOLING TOWERS

This section describes the two main types of cooling towers: the natural draft and mechanical draft cooling towers.

Natural draft cooling tower

The natural draft or hyperbolic cooling tower makes use of the difference in temperature between the ambient air and the hotter air inside the tower. As hot air moves upwards through the tower (because hot air rises), fresh cool air is drawn into the tower through an air inlet at the bottom. Due to the layout of the tower, no fan is required and there is almost no circulation of hot air that could affect the performance. Concrete is used for the tower shell with a height of up to 200 m. These cooling towers are mostly only for large heat duties because large concrete structures are expensive.

There are two main types of natural draft towers:

Cross flow tower Air is drawn across the falling water and the fill is located outside the tower

35


Counter flow tower Air is drawn up through the falling water and the fill is therefore located inside the tower, although design depends on specific site conditions

Mechanical draft cooling tower

Mechanical draft towers have large fans to force or draw air through circulated water. The water falls downwards over fill surfaces, which help increase the contact time between the water and the air - this helps maximize heat transfer between the two. Cooling rates of mechanical draft towers depend upon various parameters such as fan diameter and speed of operation, fills for system resistance etc. there are mainly two types of mechanical drafts

1. Forced Draft 2. Induced Draft

Forced Draft Forced draft cooling tower are those where the fan or fans are located at the bottom of the tower. Cooling air is pushed up through stack.

36


Induced Draft Induced draft cooling tower are those where the fan or fans are located on top of the tower. Cooling air is pulled up through stack.

At LalPir/PakGen Induced type Cooling Towers are mainly used to condense steam coming from the low pressure turbine to create vacuum and hence act as driving force for steam. Cooling Tower is designed to provide 692mm Hg of Vacuum in the condenser. Initially it was a seven cell Induced draft Cooling Tower but now after modification in 2008, eighth cell has been added.

WASTE WATER ENVIRONMENTAL STANDARDS

37


Hydrogen generation system i s designed to produce 5 normal cubic meters of hydrogen (when measured at 00 C 760 mm of Hg). It can compress and purify 5 normal cubic meters of hydrogen t o a pressure of 175 kg/ cm 2. Hydrogen Gas Generating System consist s of Air Cooled Silicon Rectifier, Transformer and Six Stuart Electrolytic Cells connected in Series

Rectifier Specification

Rated Power 30 KW

Rated AC Voltage 380 +/ - 10

Rated AC Current 58 Amps

Rated Frequency 50 +/ 5%

Number of Phases 3

Rated DC Voltage 15 Volts

Rated DC Current 0 -2000 A

Percent Ripple 5 %

Percent Regulation 1 %

Ambient Temperature 50 0C

Feed Water

When operating at full capacity each of the gas generating system will consume approximately 7.5litre of water per hour. Feed water to the cells must be high purity demineralized or distilled water. Specific conductance of the water should be less than 5 micro ohm/cm. Feed water for the cells is stored in a 50litre polyethylene tank from which it flows by gravity to each of the gas generating system. The tank is fitted with a float valve to automatically maintain and desired water level and level switch to stop the rectifier if the level in the tank is too low.

Hydrogen mist eliminator

The hydrogen gas leaving the cells carries off some of the KOH electrolyte in the form of an entrained mist. Most of this entrainment is removed in the cell gas cooler and is returned to the cells. Some is removed at water seal. The remainder is removed in the mist eliminator.

38


Hydrogen Gas Holder The hydrogen gas after passing through the water seal enters the gas holder. The

hydrogen gasholder is a wet-seal type gasholder with a nominal volume of 30m3. The operating pressure will be approximately 125mm water column. The gasholder is fitted with four level switches for control of the H2 compressors.

Hydrogen Compressor System When any of the compressors is started either on auto or manual mode it will continue running for 30 minutes (provided limit switch not touched min) and then it will stop regardless of the level of gas holder. The compressors are used to

compress the Hydrogen gas to a pressure of 175 kg/cm2.

Hydrogen Purification System The hydrogen at the discharge of the oil lubricated compressors contain the following impurities

1. Oxygen gas, approx. 0.2 percent by volume 2. Water vapor, 100 percent relative humidity at operating conditions. 3. Oil Vapor and oil droplets picked up in the oil lubricated compressors 4. Moisture condensed out of the hydrogen gas as a result of the increase in

pressure The moisture, oil droplets and oil vapor are removed in a series of filter. Two banks of these filters are supplied so that one bank can be in service while the other bank is being standby. The purifier is fitted with inlet and outlet temperature gauges, as well as high and coalescing high temperature switches.

Catalytic purifier The catalytic purifier is used to remove oxygen impurity from the hydrogen gas by causing the oxygen to catalytically combine with hydrogen to form water vapor. When operating properly the purifier should remove oxygen to a residual impurity of less than ten parts per million

After cooler The After cooler is a shell and tube type heat exchanger, with hydrogen flowing on the tube side and cooling water flowing on the shell side. Temperature Gauge at the After cooler outlet indicates hydrogen temperature. From after cooler the hydrogen gas goes to Hydrogen storage bottles through coalescing filters.

39


Storage Room In Hydrogen Storage Building, there are a total of six storage bottles arranged in two banks.

Safety Precautions for working in the Hydrogen Building

Hydrogen gas is a very dangerous gas as it can form an explosive mixture and there is always an explosive hazard present in the Hydrogen Building. The following precautions are necessary while working in the Hydrogen building:

1. Radio and cell phones must be powered off. 2. Spark-less Tools must be used. 3. Care must be taken that no such activity is performed that might result in a

spark.

40


Summary of BOP:

41


INTORODUCTION

A boiler is a closed vessel in which water and other fluid is heated. The heated or

vaporized fluid exits the boiler for use in various processes or heating applications.A

boiler is a device used for transferring heat liberated by combustion of a fuel to

water or steam.

It is a pressure vessel, designed to withstand steam pressure, which can be

dangerous if not properly operated or maintained.Air heater, Economizer and

Superheated fitter to a boiler enables more heat liberated from fuel to be used.Super

heater increase the temperature of steam and are often necessary to render it

suitable for use in a turbine or engine.

Types

There are various types of boilers:

Fire tube Boiler Water tube Boiler Packaged Boiler Fluidized Bed Combustion Boiler Atmospheric Fluidized Bed Combustion Boiler Pressurized Fluidized Bed Combustion Boiler Circulating Fluidized Bed Combustion Boiler Stoker Fired Boiler Pulverized Fuel Boiler Waste heat Boiler Thermic Fluid Heater

42


Fire Tube Boiler In fire tube boiler, hot gases pass through the tubes and boiler feed water in the shell side is converted into steam. Fire tube boilers are generally used for relatively small steam capacities and low to medium steam pressures. As a guideline fire tube boilers have competitive steam rates up to 12,000kg/hr and pressures

upto 18kg/cm2. Water Tube Boiler

In water tube boiler, boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases and converted into steam at the vapour space in the drum. These boilers are selected when the steam demand as well as steam pressure requirements are high as in the case of process cum power boiler

/ power boilers.

Most modern water boiler tube designs are within the capacity range 4,500 –120,000 kg/hour of steam, at very high pressures. Many water tube boilers nowadays are of constr oil and /or gas are to be used as fuel. Solid fuel fired water tube designs are available but packaged

designs are less common.

Features of Water Tube Boilers:

To improve combustion efficiency, forced, induced and balanced draft provisions are used.

Less tolerance for water quality calls for water treatment plant. Higher thermal efficiency levels are possible.

43

` INTERNSH IP REPORT - 201 3

Boiler in LALPIR/ PAKGEN

The boiler is of Mitsubishi Forced Circulation Radiant Reheat type and designed to generate 1,200 ton/hour steam with 541°C steam temperature at super heater outlet and 947.5% ton/hour steam with 541°C steam temperature at re-heater outlet. The design of this type boiler has been employed for many either utility or industrial power station boilers for long years and proven with safe and efficient operation.

Specifications

Steam Flow

(Capacity)

Steam Pressure

Steam Temperature

Steam Temperature

Control Range

Feedwater

Temperature

Ambient Air

Conditions

Others

•Superheater Outlet •Reheat Outlet

•Superheater design •Super heater Outlet

•Reheat Design •Reheat Outlet

•Superheater Outlet •Reheater Outlet •Reheater Inlet

•Super Heater •Reheater

•Economizer inlet

•Air Temperature •Relative Humidity

•Firing System •Draft System

•Fuel (Base Load Carrying) •Ignition and Unit Start-up

1,200 ton/hr 947.46 ton/hr

199 kg/cm2 176 kg/cm2 46 kg/cm2

38.3 kg/cm2

5410 C 5410 C 3350 C

60% to 100% MCR 60% to 100% MCR

278.80 C

250 C

52%

Corner Firing Forced Draft

Heavy Fuel Oil Light Diesel Oil

44

1200 ton/hr

947.46 ton/hr

199 kg/cm2

176 kg/cm2

46 kg/cm2

541 C

541 C

335 C

60 %-100% MCR

60 %-100% MCR

278.8 C

25 C

52%

Corner Firing

LDO

HFO


Primary Flow Path

The LalPir Power Plant oil fired steam generator is forced circulation, forced draft, reheat type boiler. The steam generator has a designed maximum continuous rated steam output of 1,200tons/hour steam flow at 541°C super heater outlet steam temperature and 947.56Tons/hour steam flow at 541°C re-heater outlet steam temperature. The unit has a design steam pressure of 199 kg/cm2 for superheat and of 45 kg/cm2 for re-heater. The steam generator is tilting corner firing units, capable of burning heavy fuel oil.

The Steam Generator System primary flow path begins at the economizer inlet. Feed water flows through the tubes of the economizer and is heated by the combustion gases leaving the furnace. After flowing through the economizer tubes, the feed water enters and mixes with water which is already in the steam drum. The steam drum is located at the top of the boiler. Preheating the feed water in the economizer increases unit efficiency and reduces thermal shock to the steam drum and water wall tubes. The economizer is also equipped with recirculating line which ties the economizer inlet feed water line to the water drum. This line is used to circulate water from the drum through the economizer during startup to prevent boiling in the economizer when feed water flow is low.

Water from the steam drum then flows through down comers to a boiler circulation pump inlet manifold, which provides a positive suction head for the boiler circulation pumps. Boiler water is discharged from the boiler circulation pumps into the water drum, which serves as a distribution header for the water wall tubes. The water drum is located at the bottom of the boiler. In the water wall tubes, the boiler water absorbs heat generated by the combustion of fuel in the furnace region of the boiler.

As the water begins to discharge from the boiler circulation pumps into the water drum, and begins to rise in the water wall tubes. The water rising in the water wall tubes continues to absorb heat and the resulting mixture of steam and water continues up through the tubes to the steam drum.

The steam drum contains equipment to separate the steam from the water, and dry the steam as it leaves the drum. As the steam exits the steam separator, it is dry, saturated steam. The water in the steam drum is returned to the boiler circulation pumps.

The dry, saturated steam leaves the drum and follows one paths. One path forms the steam cold roof from the furnace to the secondary gas pass. The

45


steam flows through the steam cooled roof into a Lower header at the base of the secondary gas pass. This header feeds the steam from the secondary gas pass rear wall into secondary gas pass side walls.

The steam flows upward through these secondary gas pass side walls, into the each secondary gas pass side walls outlet headers.

Leaving the secondary gas pass side walls outlet headers the steam flows to the primary (low temperature) super heater inlet header through four lines. The primary super heater is a radiant that hangs from the top of the furnace in the direct path of the furnace flame.

The steam absorbs radiant heat (exposure to the fireball) and passes through a hanger tube upward on its way to the primary super heater outlet header.

After leaving the primary super heater outlet header, the steam passes down ward to the secondary super heater inlet header. The steam passes through a bank of radiant “Platenand Horizontal”assembliesofthe secondary super heater, upward on its way to the secondary super heater outlet header.

When the steam leaves the secondary super heater outlet header, it enters the two de-super heaters, which are located in the connecting lines between the secondary super heater outlet header and the tertiary super heater inlet header. These de-super heaters maintain the tertiary super heater outlet temperature at the design value during unit operation.

The superheated steam travels from the de-super heaters through two crossover lines to the tertiary super heater inlet header. This header feed the final portion of the convective “Horizont spaced equally across the width of the furnace. The steam passes upward the outlet headers of the tertiary super heater. From this point, the 541°C superheated steam is fed to the high pressure section of the main turbine through outlet steam line.

The steam cycle includes a reheat section. Steam which has passed through the high pressure section of the turbine is reduced in pressure and temperature as it flow through the HP turbine. The steam is then routed back to the boiler to be reheated, thus increasing the overall plant cycle efficiency. Steam returned to the boiler from the high pressure turbine is called "Cold Reheat" steam. This cold reheat steam flow from the HP turbine through the cold reheats steam line to the primary re-heater inlet header.

46


In the steam line prior to the reheat inlet header, there is one reheat de-super heater. The purpose of the re-heater de-super-heater is to reduce the temperature of the reheat outlet steam if the temperature should increase as a result of upsets in the boiler/turbine system.

Leaving the re-heater de-super heater, the steam flow to the primary re-heater inlet header located above the economizer in the secondary gas pass. The steam passes through the convective horizontal assemblies of the primary re-heater and then through the vertical spaced assemblies across the secondary gas pass.

The steam then passes through the rad assemblies of the secondary re-heater before entering the secondary re-heater outlet headers. From this point the 541°C “Hot Reheat”steamispiped to the intermediate pressure sections of the main turbine through hot reheat steam line.

47


Boiler Overview

48


Secondary Flow Path:

The secondary flow paths associated with the Steam Generator System are: Supply Water to the Super Heater and Reheat De-Super Heaters Boiler Chemical Injection Boiler Blow down System Aux. Steam System

List of Major Components

The Steam Generator System consists of the following major components. Economizer Steam Drum Water Wall Tubes Boiler Circulation Pumps Super Heaters Re-Heaters Boiler Control

Economizer

Boiler Economizer or “Basic heat-to-waterrecoveryheat exchanger. At Lalpir, the economizer arrangement is Spiral Finned Tube Type composed of 2 fins/ inch. The purpose of the equipment is to recover waste heat using the established principle of a gas to liquid heat exchanger. The economizer should be a bare, welded, or extruded finned tube coil assembly installed either inside or parallel to the boiler exhaust stack or duct. Feedwater under pressure will circulate in the tubes of the coil and heat will be transferred from the flue gases to the water. Heat is transferred from the exhaust gas to boiler feed water or other heating load. Economizers are selected on a number of parameters.

The amount of saving depends on several items. The existing stack temperature (how much heat can be extracted) The cost of your boiler fuel The hours of operation of your boiler (more hours = more saving) Average boiler firing rate Economizer entering water temperature and flow rate

A rule of thumb is that for every 40F decrease in boiler stack temperature, there is an increase in boiler efficiency of 1%! Total improvements of 3-5% are typical. While this may not sound a lot, it can translate to big savings and short paybacks.

49


Steam Drum

The steam drum is the most important part of a boiler. All the steam and water passes through it. The steam is removed from the water sending the steam-free water back to the boiler system to prevent burnouts. This steam free water allows all liquid levels, chemical feed, and feedwater to be properly controlled. After the steam is removed from the water the steam is purified to be superheated, if necessary, and to perform its demanding tasks.

The most important job of the steam is to ensure that the steam exits the drum as dry as possible and returns the water to the heat source steam free. The reason for this is that any water or moisture that may pass through a steam drum can and will carry solids in it, usually in their dissolved states.

The steam drum also secures natural circulation and/or prevents circulating pump cavitation. This condition can precipitate downstream on other equipment in the system and can be expensive by causing a loss of efficiency or other costly repairs.

Water Drum

If the surface heat transfer in steam boiler may not be enough to produce steam saturation for specific end use, so require additional tubes to increase heat transfer surface. These additional tubes connecting between steam drum and water drum were called steam boiler bank. This is necessary for industrial steam boiler that has low pressure. Steam boiler bank usually consist of steam drum which be typically located on the top, a series of bent connecting tubes on the middle, and water drum on the bottom.

Water drum is a pressure chamber of a drum type located at the lower extremity of a watertube-steam boiler convection bank. The steam drum internals and tube sizes are arranged so that subcooled water travels down the tubes into water drum. From water drum, water is distributed by downcomer to lower drum and then distributed again to the tubes of furnace wall where water is partially converted to steam and returned to the steam drum

Water drum is present only in the bidrum steam boilers and play a less important role such as: a water drum acts like a large header connecting the riser and downcomer tubes of the bank, and it feeds the downcomers to the various evaporator sections. The water drum is always smaller than the steam drum as there are no important internals.

50


Combustion and Firebox

In a steam boiler the firebox or combustion chamber is the area where the fuel is burned, producing heat to boil the water in the boiler. Most are somewhat box-shaped, hence the name. Fuel flows into the burner and is burnt with air provided from an air blower. Burners employed here are not wall mounted but are placed along the walls and are pushed in when fired.

There are four burners with four igniters mounted at four different levels. Hence in total there are sixteen burners with sixteen igniters. The burners fires from four corners of the furnace thus creating a fire ball at

the center of the furnace. The oil igniters are designed for ignition helping combustion of the main burners of the boilers. The main features of the operation of the igniters are given below.The proper ignition requirements

The diesel oil The air for ignition The spark

Max Capacity per Igniters 100 l/hr

Oil Pressure 5 kg/cm

Atomizing Air Pressure 5.5 kg/cm

Flame Detecting System Flame Rod

Corner Firing System

The important thing in designing of these burners is that “the nozzle a

burners is along the tangent of the imaginary circle at the center of the furnace. Jet stream from air and fuel burners produce a cyclone effect in the furnace, through

which atomized fuel can be injected in such an area where the fuel gets the

maximum burning capacity due to availability of excess air and the high

temperature flame zone.

Significance Stable combustion is obtained due to the reason that by the appearance of the

fireball whole furnace becomes like a single big burner. Even heat distribution is obtained due to the fact that revolving flame distributes

the heat evenly to the surroundings of the furnace regardless of the boiler loads and number of the burners in operation.

Less air pollution due the fact that the revolving flame causes less air pollution in the case for NOx.

51


Primary Heater Section

This is the first section of boiler where heat is transferred to the steam passing through primary tubes. The flames heat up the tubes, which in turn heat the fluid (water) inside in the first part of the furnace known as the radiant section. In the chamber where combustion takes place, known as the firebox, the heat is transferred mainly by radiation to tubes around the fire in the chamber. The heating fluid passes through the tubes and is thus heated to the desired temperature. The gases from the combustion are known as flue gases.

Secondary Heater Section

This is the second section where heat is transferred to the steam passing through secondary section tubes. In secondary section preheated steam coming from the primary region is heated more by the flue gases rises from the combustion chamber. The main heat transfer process in this section is through convection heat transfer, and thus more heat is transferred in this section as compared to the primary section and a greater temperature is attained in this section.

Tertiary Heater Section

This is the third section where heat is transferred to the steam passing through tertiary region tubes. In tertiary section preheated steam coming from the secondary region is heated more by the flue gases rising from the combustion chamber primary region and then secondary region. The main heat transfer process in this section is through convection heat transfer. Steam is heated to a temperature of 540oC after passing through tertiary region and its pressure is 176 kg/cm2, steam is then entered into HP turbine. The reason for having three regions of heater transfer for steam is to absorb maximum heat from the flue gases stage by stage.

52


Secondary Reheat

Above tertiary heater region lies the secondary reheat region, this is the next stage of primary reheat region. In this region steam coming from the primary reheat region is heated more to higher temperature. This section heats the reheat steam to 540oC and 40 kg/cm2. The outlet of secondary reheat steam goes to the intermediate turbine. The outlet steam is also called hot reheat.

Primary Reheat

As told before the cycle is a reheat Rankine cycle so steam after expanding in the high pressure turbine is returned to the boiler reheat section where it is heated once again to a temperature of 540oC from 340oC by passing through primary and then secondary reheat regions and is then feed to the intermediate turbine. This reheat process is basically done to increase the efficiency of the plant by using the reaming heat of the flue gases. The steam inlet to the primary reheat region is also called cold reheat steam.

Between periodic boiler cleaning the gas surfaces of the boiler tubes should be kept as clean as practicable. To facilitate this, soot blowers, steam or air operated, are often fitted. They enable the tube surfaces to be cleaned of loose sooty deposits rapidly without shut down of the boiler. To remove these layers from boilers a superheated steam from 3ry SH inlet header is used. At lalpir 2 Rotary soot blowers for gas air heater and 8 longitudinal soot blowers for super heater and 8 longitudinal soot blowers for re-heaters are used.

53


A steam converter is a type of heat exchanger where steam is produced by using the heat of

superheated steam coming from some other source such as boiler. At AES superheat steam from

the boiler is extracted through auxiliary header and supplied to the steam converter where this

steam is used to produce steam from liquid water which further is used to heat the HSFO fuel.

The heating of HSFO fuel is done to increases its fluidity so that it could be flowed easily through

pipes and do not solidify. It should be note here that this type of heat exchanger is of closed type

which means that both the fluids doesn’t mix while exchanging with heat and both the steams

flow in different pipes. the important question which rises here is that why don’t we directly

amuse from the boiler to extract deheat the HSFO, so it is done as a safety measure where if by

chance some of the HSFO leaks into steam pipe this could cause dangerous results. So the flow

pipes for both the steams are kept different, and both steam have different cycles of flow, so by if

any

accident HSFO leaks into the steam pipe during heating it doesn’t ca to the boiler or boiler tubes.

54


Gas Recirculation Fan (GRF) draws gas from a point between the economizer outlet and the air heater inlet and discharges it into the bottom of the furnace outlet. Recirculation gas introduced in the vicinity of the initial burning zone of the furnace is used for steam temperature control, while re circulated gas introduced near the furnace outlet is used for control of gas temperature. In lalpir Gas Recirculation Fan is used to utilize excess oxygen present in the flue gases for combustion. The exhaust gas also increases the specific heat capacity of the mix lowering the peak combustion temperature. Because NOx formation progresses much faster at high temperatures, EGR serves to limit the generation of NOx. NOx is primarily formed when a mix of nitrogen and oxygen is subjected to high temperatures.

55


HFO (Heavy fuel oil) is used as the fuel. There are five HFO tanks located at the plant among which two are used for each unit while the third is the common which can be used to supply fuel to any of the units. HFO is supplied by PSO (Pakistan State Oil) through pipelines.

Initially diesel is used at the startup. There are two diesel tanks which supply to Pakgen and Lalpir each. Diesel is used so that boiler gains sufficient temperature at which the combustion of HFO begins. The tank in which HFO is stored is heated by three Heaters. Two of them are located inside the tanks while the third one is located outside. The two located inside are called Bottom heater and Suction Heater. While third one located outside is called the Discharge heater.

These are not electric heaters but steam heaters. The temperature of the HFO leaving the Tank is almost 62 degrees, while for firing 110 degrees is required this is achieved by discharge heaters which are located outside the tanks.

56


Heating is done so that HFO has gained sufficient temperature before it is pumped into the furnace (Boiler) plus HFO has a high density at low temperatures it starts settling down hence in order to keep its temperature well above room temperature “Tracing”is usedSteam.Before HFO/Diesel is pumped to the boiler it undergoes a process called atomization.

Atomization

Atomization is conversion of bulk liquid into a spray or mist (i.e. collection of drops), often by passing the liquid through a nozzle. Despite the name, it does not imply that the particles are reduced to atomic sizes. This is done so that proper combustion of fuel occurs. Air is used to atomize Diesel while steam is used to atomize HFO. There are 3 HFO transfer pumps (For each unit).Two among the three are in service while one is in standby.

General Overview of Fuel Cycle

Discharge

Trainers HFO

Discharge Header

HFO Pumps Heaters

Suction Trainers

HFO Tanks with suction Heaters

57


There are two diesel tanks located at the plant which supplies to each unit. Capacity

of each tank is around 600 cm3 . From Diesel oil storage tank Diesel passes through

strainer whose function is to remove unwanted particles. From here it is pumped by

the igniter pumps to the igniters in the furnace. Diesel is only used initially for the

firing of the igniters, once burners are turned on, the igniters is turned off and so is

the supply of Diesel. Diesel is also used by Auxiliary Boiler whose function is to

produce steam in order for the heating of the HFO in case the main Boiler is turned

off. There are two Auxiliary boiler Diesel oil pumps, at a time one is working while

other is in standby.

Force Draft fans are employed for the absorption of air. There are basically two types of fans one is called induced draft fan and the other is called forced draft fan .Those employed in the cooling tower are called balance draft fan since they employ both force draft fan plus induced draft force the air out in the atmosphere.

From FDF air flows to the steam air heater where it exchanges heat with the steam

as a result the temperature of the air rises. Then the air is flown through the gas air

heater (GAH) where it exchanges heat with flue gases, this result in more

temperature rise. The air is then blown to the furnace for the purpose of

combustion. The Air fuel ratio is closely monitored. It must be in the range of 12:1. It

represents the ratio between the mass of air and the mass of fuel in the fuel-air

mixture at any given moment. Dampers are employed for the controlling of draft. A

damper is a valve or plate that stops or regulates the flow of air.

The air basically is supplied through the wind box. There are 3 types of air supplied for the combustion of fuel.

1. Primary Air : Air Supplied for the combustion of fuel 2. Auxiliary Air: Excess air supplied for the complete combustion of fuel

3. Over Fire Air: The air is supplied to decrease the temperature of combustion

so as to reduce the amount of NOx and SOx formation.

58

Air Cycle


General Overview of Air Cycle

Air pre-heaters are paramount in maintaining a highly efficient power plant. Such systems provide heat recovery to the unit by cooling the flue gas counter-currently with cool incoming pre-combustion air. Cooling of the flue gas transfers the heat that is necessary both for coal drying and overall boiler efficiency. The air pre-heater is located downstream (flue gas path) of the economizer. There are two primary types of air pre-heaters - regenerative, rotating-type and recuperative, stationary-type. The stationary-type generally is classified as tubular or plate, with more advanced systems using heat pipes. The majority of air pre-heaters used with utility-scale boilers is the regenerative design, which is the type discussed in this report. Two methods are identified for air heater improvement, either singly or in combination:

Limit air heater leakages to 6% of incoming air flow Lower air heater outlet temperature by controlling acid dew point

In Lalpir Thermal Power Plant 2 Air Heaters for each unit is placed so there are total 4 Air Heaters installed.

59


Stack effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, and is driven by buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect is also referred to as the "chimney effect", and it helps drive natural ventilation and infiltration.

Stack effect in flue gas stacks and chimneys

The stack effect in chimneys: the gauges represent absolute air pressure and the airflow is indicated with light grey arrows. The gauge dials move clockwise with increasing pressure. The stack effect in industrial flue gas stacks is similar to that in buildings, except that it involves hot flue gases having large temperature differences with the ambient outside air. Furthermore, an industrial flue gas stack typically provides little obstruction for the flue gas along its length and is, in fact, normally optimized to enhance the stack effect to reduce fan energy requirements.

Large temperature differences between the outside air and the flue gases can create a strong stack effect in chimneys for buildings using a fireplace for heating.

60


A turbine is a rotary mechanical device that extracts energy from a fluid flow and

converts it into useful work. A turbine is a turbo machine with at least one moving

part called a rotor assembly, which is a shaft or drum with blades attached. Moving

fluid acts on the blades so that they move and impart rotational energy to the rotor.

Mainly two types of turbine are used for generating electricity in thermal power

stations.

Steam Turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work. Steam turbines are used for the generation of electricity in thermal power plants, such as plants using coal, fuel oil or nuclear power.

Gas Turbine

A gas turbine extracts energy from a flow of hot gas produced by combustion of gas

or fuel oil in a stream of compressed air. It has an upstream air compressor (radial

or axial flow) mechanically coupled to a downstream turbine and a combustion

chamber in between. "Gas turbine" may also refer to just the turbine element.

Thermodynamics of Steam Turbine

The steam turbine operates on basic principles of thermodynamics using the part of

the Rankine cycle. Superheated vapor (or dry saturated vapor, depending on

application) enters the turbine, after it having exited the boiler, at high temperature

and high pressure. The high heat/pressure steam is converted into kinetic energy

using a nozzle (a fixed nozzle in an impulse type turbine or the fixed blades in a

reaction type turbine). Once the steam has exited the nozzle it is moving at high

velocity and is sent to the blades of the turbine. A force is created on the blades due

to the pressure of the vapor on the blades causing them to move. A generator or

other such device can be placed on the shaft, and the energy that was in the vapor

can now be stored and used. The gas exits the turbine as a saturated vapor (or

liquid-vapor mix depending on application) at a lower temperature and pressure

than it entered with and is sent to the condenser to be cooled

61


Working of a Steam Turbine

A simple explanation would be that a steam turbine uses the energy stored inside the high pressure superheated steam to generate electricity.

High pressure superheated steam is entered in to the turbine from one end. The steam hits the blades of the turbines with high pressure and velocity

which rotates the blades. As steam progresses hitting the blades turn by turn it loses pressure and

temperature as it is giving away its energy to the blades, so it is conventionally said that steam is expanded as it progresses through the turbine blades.

The turbine blades are mounted on a rotor which rotates along with the blades. This rotor attached to the rotor of generator axially and rotates the generator rotor.

The generator then produces electricity.

Rankine Cycle with superheat

Process 1-2: The working fluid is pumped from low to high pressure.

Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor.

Process 3-3': The vapour is superheated.

Process 3-4 and 3'-4': The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur.

Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant pressure to become a saturated liquid.

62


Types of Steam Turbine

To maximize turbine efficiency the steam is expanded, doing work, in a number of

stages. These stages are characterized by how the energy is extracted from them

and are known as either impulse or reaction turbines. Most steam turbines use a

mixture of the reaction and impulse designs: each stage behaves as either one or the

other, but the overall turbine uses both. Typically, higher pressure sections are

impulse type and lower pressure stages are reaction type.

Impulse Turbine The impulse turbine consists basically of a rotor mounted on a shaft that is free to rotate in a set of bearings. The outer rim of the rotor carries a set of curved blades, and the whole assembly is enclosed in an airtight case. Nozzles direct steam against the blades and turn the rotor. The energy to rotate an impulse turbine is derived from the kinetic energy of the steam flowing through the nozzles. The term impulse means that the force that turns the turbine comes from the impact of the steam on the blades. The toy pinwheel can be used to study some of the basic principles of turbines. When you blow on the rim of the wheel, it spins rapidly. The harder you blow, the faster it turns. The steam turbine operates on the same principle, except it uses the kinetic energy from the steam as it leaves a steam nozzle rather than air. Steam nozzles (hereafter referred to as nozzles or stationary blades) are located at the turbine inlet. As the steam passes through a nozzle, potential energy is converted to kinetic energy. This steam is directed toward the turbine blades and turns the rotor. The velocity of the steam is reduced in passing over the blades. Some of its kinetic energy has been transferred to the blades to turn the rotor. Impulse turbines may be used to drive forced draft blowers, pumps, and main propulsion turbines.

Reaction Turbine In the reaction turbine, stationary blades attached to the turbine casing act as nozzles and direct the steam to the moving blades. The moving blades mounted on the rotor act as nozzles. Most reaction turbines have several alternating rows of stationary and moving nozzle blades.

You can use a balloon to demonstrate the kickback or reaction force generated by the nozzle blades. Blow up the balloon and release it. The air will rush out through the opening and the balloon will shoot off in the opposite direction.

63


When the balloon is filled with air, you have potential energy stored in the increased air pressure inside. When you let the air escape, it passes through the small opening. This represents a transformation from potential energy to kinetic energy. The force applied to the air to speed up the balloon is acted upon by a reaction in the opposite direction. This reactive force propels the balloon forward through the air.

You may think that the force that makes the balloon move forward comes from the jet of air blowing against the air in the room, not so.

It is the reaction of the force of the air as it passes through the opening that causes the balloon to move forward.

The reaction turbine has all the advantages of the impulse-type turbine, plus a slower operating speed and greater efficiency. The alternating rows of fixed and moving blades transfer the heat energy of the steam to kinetic energy, then to mechanical energy.

66


Straight Condensing Turbine: All the steam enters the turbine at one pressure, and all the steam leaves the turbine exhaust at a pressure below atmosphere.

Straight non condensing Turbine: All the steam enters the turbine at one pressure, and all the steam leaves the turbine exhaust at a pressure equal to or greater than atmosphere.

Non automatic-Extraction Turbine, Condensing or Non condensing: Steam is extracted from one or more stages, but without means for controlling the pressures of the extracted steam.

Automatic-Extract ion Turbine, Condensing or Non condensing: Steam is extracted from one or more stages with means for controlling the pressures of the extracted steam.

Automatic-Extraction- Induction Turbine, Condensing or Non condensing: Steam is extracted from or inducted into one or more stages with means for controlling the pressures of the extract ion and/or induct ion steam.

Mixed-Pressure Turbine, Condensing or Non condensing: Steam enters the turbine at two or more pressures through separate inlet openings with means for controlling the inlet-steam pressures.

Reheat Turbine: After the steam has expanded through several stages, it leaves the turbine and passes through a section of the boiler, where superheat is added. The superheated steam is then returned to the turbine for further expansion.

65


66


Parts of Steam Turbine

Main Steam Valve (MSV) and Governing Valve (GV)

These are two types of valves disposed between the boiler and the high pressure steam turbine are configured to be super-sized valve devices having a pressure-proof structure, because steam at very high pressures from 176 Kg/cm2g, and at

very high temperatures from 538oC to 5660C. is applied thereto.

These two valves are used to control the flow of steam or shut it down into the turbine the main steam shut-off valve is a valve of an ON-OFF type that immediately supplies the steam toward the high pressure steam turbine when commencing operation, and that immediately shuts off when the load is shut off. In addition, for example, governor valve (steam flow regulation valve) is a valve of control valve type that controls the flow rate by opening a valve body at an arbitrary valve-opening amount in response to a demand of the load and that immediately shuts off the valve body when the load is shut off.

There are two MSV, each allows steam further to two GVs which let steam into the turbine.

Heretofore, the above-described main steam shut-off valve and the governor valve (steam flow regulation valve) are disposed at separate positions before-an inlet of the high pressure steam turbine. However, because both the size of the main steam shut-off valve and the size of the governor valve (steam flow regulation valve) are extremely large, a large space for installing the main steam shut-off valve and the governor valve (steam flow regulation valve) has been required.

Rotor A rotor is the shaft on which the turbine blades are mounted. The movement of the blades causes the motion of rotor axially. Speed of rotor is 3000 Rpm.

Nozzles A nozzle is often a pipe or tube of varying cross sectional area and it can be used to direct or modify the flow of a fluid (liquid or gas). Nozzles are used to control the rate of flow, speed, direction, and/or the pressure of the stream that emerges from them. Nozzles in turbine are mounted at the starting, function of the nozzles is to direct the steam against the blades. Nozzles decrease pressure and increases kinetic energy of the fluid. The blades arrangement inside the turbine is also modified to give it a shape of nozzle type so as to increase the steam velocity as it hits the turbine blades.

67


Bearings A bearing is a device to permit constrained relative motion between two parts, typically rotation or linear movement. Here the relative motion is between the rotor and the casing of the turbine. The rotor of every turbine must be positioned radially and axially by bearings. Radial bearings carry and support the weight of the rotor and maintain the correct radial clearance between the rotor and casing. Axial (thrust) bearings limit the fore-and-aft travel of the rotor. Thrust bearings take care of any axial thrust, which may develop on a turbine rotor and hold the turbine rotor within definite axial positions.

There are a total of six bearings used at Lalpir to support the turbine and generator rotor.

Gland Sealing System Gland seal systems are very important to main and auxiliary turbines. Turbine shafts must exit their casings in order to couple up or connect with the unit that the turbines drive (reduction gears, pumps, etc.) The main and auxiliary gland seal systems enable the turbine to be sealed where the shaft exits the casing; in effect keeping "air out and steam in."

The purpose of gland seal system is to prevent the leakage of air from the atmosphere into turbine casings and prevent the escape of steam from turbine casings into the atmosphere. A labyrinth seal is a mechanical seal that fits around an axle to prevent the leakage of oil or other fluids.

A labyrinth seal is composed of many straight threads that press tightly inside another axle, or inside a hole, so that the fluid has to pass through a long and difficult path to escape.

Sometimes 'threads' exist on the outer and inner portion. These interlock, to produce the long characteristic path to slow leakage. For labyrinth seals on a rotating shaft, a very small clearance must exist between the tips of the labyrinth threads and the running surface.

78


Labyrinth seals on rotating shafts provide non-contact sealing action by controlling the passage of fluid through a variety of chambers by centrifugal motion, as well as by the formation of controlled fluid vortices. At higher speeds, centrifugal motion forces the liquid towards the outside and therefore away from any passages. Similarly, if the labyrinth chambers are correctly designed, any liquid that has escaped the main chamber becomes entrapped in a labyrinth chamber, where it is forced into a vortex-like motion.

This acts to prevent its escape, and also acts to repel any other fluid. Because these labyrinth seals are non-contact, they do not wear out.

The gland sealing system provides low pressure steam to the turbine gland in the final sets of labyrinth packing. This assists the labyrinth packing in sealing the turbine to prevent the entrance of air into the turbine, which would reduce or destroy the vacuum in the associated condenser. Excess pressure (excess gland seal) is removed by the gland seal unloader. Since there are times when steam escapes from the seals, a gland exhaust system is provided.

The gland exhaust system consists of low pressure piping connected to the gland area between the last two outer sets of labyrinths which receives and prevents steam from escaping to the atmosphere. This system collects the steam and directs it to a condenser for further use in the steam plant. Turbines use labyrinth seals due to the lack of friction, which is necessary for high rotational speeds.

69


Specifications

Type •Single reheat condensing tandem two cylinders.

MCR (LALPIR/Pak Gen) •362MW, 365MW

Speed •3000RPM

Direction of Rotation •clockwise (from GV end)

Inlet Pressure •169 kg/cm2

Inlet Temperature •538 0C

Exhaust Pressure •692mmHg

No. of Extractions •8

Blades of HP Turbine •Impulse (1 stage)Reaction (11 Stage)

Blades of IP Turbine •Reaction (10 Stage)

Blades of LP Turbine •Reaction (12 Stage)

70


In systems involving heat transfer, a condenser is a heat exchanger which condenses a substance from its gaseous to its liquid state. In so doing, the latent heat is given up by the substance, and will transfer to the condenser coolant.

Direct Contact Condenser Direct contact condensers condense the turbine exhaust steam by mixing it directly with cooling water. This type of condenser is used where cooling water is of same quality as of condensate, or in other words water chemistry is very good

Surface Condenser Surface condenser is the commonly used term for a water cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations. In this type of condenser cooling water is flooded through tubes and hot steam is showered over it. Surface condenser is used in Lalpir.

Purpose of Condenser

In thermal power plants, the primary purpose of a surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water (referred to as steam condensate) so that it may be reused in the steam generator or boiler as boiler feed water. It is necessary to convert to liquid to pump it.

Condenser Cycle

The steam from the LP turbine is condensed by the cooling water in the tubes. Heat exchange takes place and the heat of steam is taken away by the cooling water inside the tubes and it gets warmed up. The steam is converted to liquid and is collected at the bottom of the condenser called hot well from where it is pumped by the condensate pumps to circulate it back to the boiler. The cooling water inside the tubes is warmed up and travel to the cooling towers located outside where it loses its gained heat to the atmosphere and cools back down and is re-circulated by the CW pumps back to the condenser and the cycle goes on. There is a partial vacuum inside the condenser. This vacuum is created by steam air ejector.

71


Reason for Partial Vacuum Inside the Condenser The low pressure inside the condenser pulls the steam from the LP turbine (where the pressure is high) with more force and thus making LP turbine generating more work. This increases the efficiency of the plant.

Steam Ejector

A steam jet air ejector is device which is connected to the condenser. The main purpose of the air ejector is to create a vacuum inside the condenser plus remove non condensable gases from the condenser.

Non-Condensable Gases in Condenser and their Effects Due to the fact that a surface condenser operates under vacuum, non condensable gases will migrate towards the condenser. The non condensable gases consist of mostly air that has leaked into the cycle from components that are operating below atmospheric pressure (like the condenser). These gases can also result from caused by the decomposition of water into oxygen and hydrogen by thermal or chemical reactions. These gases must be vented from the condenser for the following reasons:

The gases will increase the operating pressure of the condenser. Since the total pressure of the condenser will be the sum of partial pressures of the steam and the gases, as more gas is leaked into the system, the condenser pressure will rise. This rise in pressure will decrease the turbine output and efficiency.

The gases will blanket the outer surface of the tubes. This will severely decrease the heat transfer of the steam to the circulating water.

The corrosiveness of the condensate in the condenser increases as the oxygen content increases. Oxygen causes corrosion, mostly in the steam generator. Thus, these gases must be removed in order to extend the life of cycle components.

WORKING Air ejector is a device that produces vacuum by means of the Venturi effect. In an injector, fluid (liquid or gaseous) flows through a tube which then narrows. When the tube narrows, the fluid's speed increases, and because of the Venturi effect, and its pressure decreases. A low pressure zone is created at this point; this low pressure zone is connected directly with the condenser (relatively high pressure zone) from where gases flow towards this point. The steam used for the air ejector comes from the auxiliary boiler header. The mixture of steam and non condensable gases flow through the venturi tube and is collected inside an air jet ejector tank in which the gases rises above and are evacuated and the steam is mixed with the condensate water coming from the condenser.

72


Gland Steam Condenser

The gland steam condenser is a shell and tube type heat exchanger, horizontally mounted and is equipped with two externally mounted exhaust fans. The function of the gland steam condenser is to condense the leak off gland steam from:

HP, IP and LP turbine cylinder gland seals HP turbine steam chest and IP turbine hot reheat valves

This condensation is done by the exchanging heat with the feed water. The steam heats up the feed water and is condense by giving away its heat.

Deaerator

A deaerator is a device that is widely used for the removal of air and other dissolved gases from the feed water to steam generating boilers. In particular, dissolved oxygen in boiler feed waters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and other metallic equipment and forming oxides (rust). It also combines with any dissolved carbon dioxide to form carbonic acid that causes further corrosion. While dissolved gases and low pH levels in the feed water can be controlled or removed by the addition of chemicals, it is more economical and thermally efficient to remove these gases mechanically. De-aeration is based on two scientific principles. The first principle can be described by Henry's Law. Henry's Law asserts that gas solubility in a solution decreases as the gas partial pressure above the solution decreases.

The second scientific principle that governs de-aeration is the relationship between gas solubility and temperature. Easily explained, gas solubility in a solution decreases as the temperature of the solution rises and approaches saturation temperature. A de-aerator utilizes both of these natural processes to remove dissolved oxygen, carbon dioxide, and other non-condensable gases from boiler feed water. The feed water is sprayed in thin films into a steam atmosphere allowing it to become quickly heated to saturation. Spraying feed water in thin films increases the surface area of the liquid in contact with the steam, which, in turn, provides more rapid oxygen removal and lower gas concentrations. This process reduces the solubility of all dissolved gases and removes it from the feed water. The liberated gases are then vented from the de-aerator.

Along with removing dissolved gases a Deaerator heats up the feed water.

73


Deaerator Uses: 1. Removal of O2 and other non-condensable gases from condensate water 2. Water heating 3. To maintain chemistry 4. To provide a positive suction head to feed pumps 5. Used as a storage tank

Scavenging

It is the process to remove oxygen and free carbon dioxide from feed water. For this purpose we use scavengers like Hydrazine to remove Oxygen and ammonia to remove Carbon Dioxide. One of the most widely used chemical as Oxygen scavenger in high pressure boilers is Hydrazine (N2H4).

N2H4 + O2 2H2O + N2 The products of Hydrazine reaction are inert & volatile. They will not add any dissolved solids in the boiler water.

WORKING

Boiler feed water is showered from the top of the deareater tank and hot steam from the below, as the water comes in contact with hot steam its temperature raises and it release the dissolved gases and settles at the bottom of the deareater in the deaerator storage tank, from where it is sucked by the boiler feed water pumps. The

steam used here is taken from the turbine extraction (5th extraction)

74


CONDENSATE PUMPS

Condensate pumps are pumps used to suck the condensate inside the condenser hot well and discharge it forward to the LP heaters and through steam air ejector, and gland steam condenser. Three condensate pumps (each of 50% capacity, WEIR-FLOWAY), model 21XKH / N, 5 stages, water lubricated vertical canister type discharge condensate to deaerator through 4 Low pressure Heaters. The pumps are equipped with wear ring for bowl and impeller, to prevent leakage of water along the shaft. The seals are supplied with filtered water through the strainers for cooling and lubrication. The seal water is returned into the pump suction.

SPECIFICATIONS These pumps are designed to deliver 520 TPH against a discharge head of 230 m at a discharge pressure of 22.51 Kg/cm2. The design minimum flow is 156 TPH. The total head at rated capacity is 230 m. The available NPSH is -1.2 m.

FEED WATER HEATERS

A feed water heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the involved in steam generation and therefore improves the thermodynamic efficiency of the system This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced back into the steam cycle. In a steam power plant (usually modeled as a modified Rankine cycle), feed water heaters allow the feed water to be brought up to the saturation temperature very gradually. This minimizes the inevitable irreversibly working fluid (water). It should be noted that the energy used to heat the feed water is usually derived from steam extracted between the stages of the steam turbine. Therefore, the steam that would be used to perform expansion work in the turbine (and therefore generate power) is not utilized for that purpose. The percentage of the total cycle steam mass flow used for the feed water heater is termed the extraction fraction and must be carefully optimized for maximum power plant thermal efficiency since increasing this fraction causes a decrease in turbine power output.

75


TYPES OF FEED WATER HEATER

Feed water heaters can also be open and closed heat exchangers. An Open feed water heater is merely a direct-contact heat exchanger in which extracted steam is allowed to mix with the feed water. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the condenser pressure. A deaerator is a special case of the open feed water heater which is specifically designed to remove non-condensable gases from the feed water. Closed feed water heaters are typically shell and tube heat exchangers where the feed water passes throughout the tubes and is heated by turbine extraction steam. These do not require separate pumps before and after the heater to boost the feed water to the pressure of the extracted steam as with an open heater. However, the extracted steam (which is most likely almost fully condensed after heating the feed water) must then be throttled back to the condenser.

FEED WATER HEATER IN LALPIR

There are a total of 8 feed water heaters used at Lalpir/Pakgen.

76


Heater Number Type Extraction Using

Low Pressure Heater 1 Closed Feed Water Heater Extraction No 1 From LP Turbine




Deaerator Heater 5 Open Feed Water Heater Extraction No 5 From IP Turbine

Low Pressure Heater 6 Closed Feed Water Heater Extraction No 6 From IP Turbine

Low Pressure Heater 7 Closed Feed Water Heater Extraction No 7 From HP Turbine

Low Pressure Heater 8 Closed Feed Water Heater Extraction No 8 From HP Turbine

BOILER FEED WATER PUMPS

A boiler feed water pump is a specific type of pump used to pump feed water into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler. These pumps are normally high pressure units that use suction from a condensate return system and can be of the centrifugal pump type or positive displacement type.

BFP AT LALPIR Boiler feed water pump consists of

Booster Pump High Voltage 11 K.V. Motor Main feed Pump

77

` INTERNSH IP REPORT - 201 3

Booster and main pump are driven with same motor. Booster pump is coupled at one end to the motor and main pump coupled is coupled at the other end through reduction gear.

Aux. Lube oil pump provides oil for bearing lubrication. Booster pump and main pump both are horizontal, cartridge type barrel casing pumps. A booster pump is single stage while main pump has six stages.

MAIN PUMP BOOSTER PUMP

Type

Stage

Flow

Suction

Pressure

Discharge

Pressure

RPM

Efficiency

Power

Absorbed

Horizontal, Catridge-type Barrel Casing Pump

6

756

17.2kg/cm2

220.2 kg/cm2

5220 rev/min

82.5%

5068 kW

Horizontal, Catridge type barrel Casing Pump

1

756

9.2kg/cm2

17.2kg/cm2

1480 rev/min

84%

207kW

78

Main Pump Booster Pump


The main steam from the boiler enters the HP turbine at 540oC and 176 Kg/cm2g and expands through the 12 stages of HP turbine and exits at 340oC and 40 Kg/cm2g and it reheated in the boiler to 540oC and 41 kg/cm2g and then feed to the IP turbine where it expands through the 10 stages. After leaving the IP turbine the steam enters the LP turbine where it is expanded more in 6 x 2 = 12 stages. At the end of the LP turbine the steam enters the condenser which is just below the LP turbine. Steam is condensed inside the condenser (shell tube) by the cooling water and is collected at the bottom (Hot Well). Water from the condenser hot well is then forced by the condensate pumps to LP (Low pressure) heater. There are three condensate pumps located in the plant. The pumps are located vertically. While the water flows to the LP heaters it passes through steam jet air ejector whose function is to remove soluble gases and air. After steam jet air ejector water enters into gland steam condenser whose function is to help in condensation. Water is then passed through stages of LP heaters namely LP Heater-1, LP Heater-2, LP Heater-3, and LP Heater-4. This process of passing water through different heater stages is used to preheat the water before it enters the economizer thus increasing the plant efficiency. This heater uses the steam from turbine extractions to heat the water. The condense steam is then flowed back to the condenser hot well. After passing through different LP heater stages the water then enters into deaerator. The function of deaerator is to bring water to saturated temperature to remove oxygen and other soluble gases. The water is then brought to the Deprecator storage tank. From Deaerator storage tank, water is made to pass through stages of HP (High pressure) heaters .This is done by the help of Boiler Feed pumps (BFP). 2 BFP pumps are used for the purpose. Water then passes through HP heaters namely HP Heater-6, HP Heater-7, HP Heater- 8.The function of HP heaters is to help in the process of regeneration which involves the process of adding heat to improve efficiency. From HP heaters the water then enters into the economizer in which the flue gases and water exchange heat.

Bearing Cooling Water

Bearing cooling water is the water required for sealing and cooling purpose on the plant. Lot of spots where it is needed, BCW pumps are working there and its suction comes from cooling water inlet to condenser and discharge goes to cooling water out of condenser which goes to cooling tower.

79


Used in

Air Heaters FDF motors FD Fan Sampling Rack Hydrogen Dryer Condensate Pumps Boiler Feed Pumps BCP Cooler Air Compressers Seal Oil Cooler Vacuum Pump Hydrogen Cooler Stator Water Cooler Lube Oil Cooler Condenser

OIL SYSTEM

Two types of Oil systems are used here; Control Oil System Control oil system is such oil which is utilized for operating servomotors and control devices. The high pressure control oil system discharges from the main oil pump or the full duty Auxiliary oil pump is used to operate the servomotors of main stop valves, governing valves, reheat stop valves, interceptor valves, and the oil operated extraction non-return valves.

Lubrication Oil System Lubrication oil is used for the lubrication of bearings and turning gear. For the lubrication in the different parts of turbine, lubrication oil is used and the pumps used to perform this activity with their preference are listed below.

AOP TOP EOP Jacking Oil Pump Main Oil Pump

MAIN OIL TANK

The main oil tank contains all oil for governing and lubrication systems. It acts as support for all auxiliary pumps, oil ejectors, strainers. Filters, oil vapors extractor and oil coolers.

8080


Oil Cooler Oil cooler are attached with the main oil tank for the cooling of the lubricating oil. They use bearing cooling water for their cooling.

Oil Purifier An oil purifier is attached with the main oil tank for the purification, and removing debris and impurities from the lubricating oil.

Vapor Extractor The vapor extractor is a motor driven centrifugal type turbo-blower mounted on the oil reservoir, designed to extract combustible vapors from the oil reservoir. In addition to extracting oil vapors rising off of the oil in the oil reservoir itself, units having hydrogen cooled generators may have some hydrogen leakage setting into the oil lines which in turn would be carried to the oil reservoir with the oil. The hydrogen would then rise to the top of the oil in the reservoir and be carried off by the vapor extractors as are the oil vapors. As additional function of the oil vapor extractor is to maintain a slight vacuum to prevent leakage of oil vapor outward of the shaft seal.

MAIN OIL PUMP Main oil pump is located on the HP turbine shaft, between the thrust bearing and the over speed trip mechanism. It uses the shaft rotation for rotating its impeller. It is conventional centrifugal type and discharges at a pressure of 22.5-26.7 Kg/cm2 at normal operating speed. This is the main pump which is used for lubricating oil and high pressure oil. It is operational at normal running conditions of the turbine (shaft).

AUXULIARY OIL PUMP Auxiliary oil pump is used to supply both high pressure and bearing oil requirements during the starting and stopping periods when the pressure delivered by the main oil pump is too low for the turbine requirements. It will start automatically any time the turbine is running if the oil pressure in the system drops a specific value.

TURNING OIL PUMP Turning oil pump is used to supply oil to the system for the lubrication when the turbine is on the rotor turning gear during the and stopping periods.

84


EMERGENCY OIL PUMP It is used to supply oil to the system for lubrication when the turbine is on the rotor turning gear during the starting and stopping periods. DC-motor driven emergency oil pump is provided as a backup for the AC-motor one in an emergency case such as Ac power failure. Dc motor driven emergency oil pump will start automatically when the turbine is running if the bearing oil pressure drops.

JACKING OIL PUMP There are two jacking oil pumps, one is A.C. and other is D.C. of 140 Kg/cm2 discharge pressure to supply pressure oil to the jacking oil port of the oil lift type bearings of LP turbine and generator during turning and low speed rolling periods in start-up and shut-down process.

SEAL OIL SYSTEM The function of the seal oil system is to supply oil at a controlled temperature and pressure to the hydrogen seals, preventing leakage of gas from the ends of the rotor shaft from the stator casing. Following are the main parts of the seal oil system;

Seal Oil Filters Seal Oil Coolers Accumulator Station DC Seal Oil Pump AC Seal Oil Pump Seal Oil Tank Vacuum Treatment Plant Loop Seal Chamber Gas Trap Detraining Chamber

Seal Oil Filters: Seal oil filters are being used to filter the seal oil. Seal Oil Coolers: Seal oil coolers are being used to cool the seal oil. Accumulator Station: Accumulator station makes smooth the discharge pressure of seal oil pumps in case of any pressure drop during pump change over. DC Seal Oil Pump: In case of power failure sealing oil is provided by DC seal oil pump. AC Seal Oil pumps: Two seal oil pumps (100% duty each) are supplying seal oil to seal oil system. Seal Oil Tank: The function of seal oil is to provide the suction head for seal oil pumps and to remove the gas accumulated on the top of the tank with the help of vapor extraction fan.

Cooling Water Tests:

A primary consideration for the operation of the cooling tower system is the water quality

of the make-up source. Differing sources present differing challenges. Surface water

sources include lakes, rivers, and streams, while groundwater sources consist of wells or

aquifers. Depending on the location, surface water sources will have seasonal variations

and can carry high levels of suspended silt and debris that cause fouling if not removed by

pre-filtration systems. Groundwater sources don’t have the seasonal variations that

surface water sources have, but depending on the geology of the region, they can have

high levels of dissolved minerals that contribute to scale formation or corrosion in the

cooling system. Recently, water reuse has become popular and many cooling systems are

being supplied reclaimed effluent or discharge water from other processes. While water

reuse is a wise resource option, consideration should be made regarding the quality of the

water and how that will impact the efficient operation of the cooling system, and the

system’s ability to meet the required cooling demand.

Why is Water Used for Cooling?

Several factors make water an excellent Coolant:

•It is normally plentiful, readily available, and inexpensive

•It is easily handled and safe to use

•It can carry large amounts of heat per unit volume, especially compared to air

•It does not expand or compress significantly within normally encountered temperature

ranges

•It does not decompose

Whether the source water is surface, ground, or reuse, in

nature there are a few basic water quality considerations

that should be understood:

•It is easily handled and safe to use

•It can carry large amounts of heat per unit volume, especially

compared to air

•It does not expand or compress significantly within normally encountered temperature ranges

•It does not decompose

pH – pH is a measurement of how acidic or how alkaline a substance is on a scale of 0 to

14. A pH of 7.0 is neutral (the concentration of hydrogen ions is equal to the concentration

of hydroxide ions), while measurements below 7.0 indicate acidic conditions, and

measurements above 7.0 indicate basic or alkaline conditions. The pH scale is logarithmic

(each incremental change corresponds to a ten-fold change in the concentration of

hydrogen ions), so a pH of 4.0 is ten times more acidic than a pH of 5.0 and one hundred

times more acidic than a pH of 6.0. Similarly, a pH of 9.0 is ten times more basic or alkaline

than a pH of 8.0 and one hundred times more alkaline than a pH of 7.0.

Range: 8.2-9.0

Control of pH is critical for the majority of cooling water treatment programs. In general,

metal corrosion rate increases when pH is below recommended ranges. Scale formation

may begin or increase when pH is above recommended ranges. The effectiveness of many

biocides depends on pH; therefore, high or low pH may allow the growth and development

of microbial problems.

Hardness – Hardness refers to the presence of dissolved calcium and magnesium in the

water. These two minerals are particularly troublesome in heat exchange applications

because they are inversely soluble – meaning they come out of solution at elevated

temperatures and remain soluble at cooler temperatures. For this reason calcium and

magnesium-related deposits will be evident in the warmest areas of any cooling system,

such as the tubes or plates of heat exchangers, or in the warm top regions of the cooling

tower where most of the evaporation occurs.

CaH: 400-700 ppm

Hardness levels are usually associated with the tendency of cooling water to be scale

forming. Chemical programs designed to prevent scale can function only when the

hardness level stays within the specified range. Some corrosion control programs require

a certain hardness level to function correctly as corrosion inhibitors, so it is important to

make sure hardness levels are not too low in these programs.

Alkalinity & PO4 – Alkalinity is the presence of acid neutralizing, or acid buffering

minerals, in the water. Primary contributors to alkalinity are carbonate (CO3-2),

bicarbonate (HCO3-), and hydroxide (OH-). Additional alkaline components may include

phosphate (PO4-3), ammonia (NH3), and silica (SiO2), though contributions from these

ions are usually relatively small.

Range:

Metal Alkalinity: 200-300 ppm

Organic PO4: 1.5-2.2 ppm

Alkalinity and pH are related because increases in pH indicate increases in alkalinity and

vice versa. As with pH, alkalinity below recommended ranges increases the chances for

corrosion; alkalinity above recommended ranges increases the chances for scale

formation. When corrosion and scale problems exist, fouling will also be a problem.

Conductivity and TSS – Conductivity is a measure of the ability of water to conduct

electrical current and it indicates the amount of the dissolved solids (TDS) in water. It is a

relative indication of the total dissolved mineral content of the water as higher

conductivity levels correlate to more dissolved salts in solution. Conversely, purified

water has very little dissolved minerals present meaning the conductivity will be very low

Cooling water treatment programs will function within specific ranges of conductivity.

The range will be dependent upon the particular cooling water system’s design,

characteristics, and the type of chemical program.

Range:

Electrical Conductivity: <6500 us/cm

TSS: <30 ppm

Pure distilled water will have a very low conductivity (low minerals) and sea water will

have a high conductivity (high minerals). Dissolved solids present no problem with

respect to the cooling capacity of water, since the evaporation rate of seawater, which has

30,000ppm total dissolved solids, is only 1% less than that of distilled water. The problem

with dissolved solids is that many of the chemical compounds and elements in the water

will combine to form highly insoluble mineral deposits on the heat transfer surfaces

generally referred to as “scale”. The scale stubbornly sticks to the surfaces, gradually

builds up and begins to interfere with pipe drainage, heat transfer and water pressure.

The primary maintenance objective in most circulating water systems is to minimize the

formation of scale deposits and conductivity can be used as the controlling value after the

TDS/conductivity relationship is determined

Iron:

As rain falls or snow melts on the land surface, and water seeps through iron-bearing soil

and rock, iron can be dissolved into the water. In some cases, iron can also result from

corrosion of iron or steel well casing or water pipes. Iron is the fourth most abundant

mineral in the earth’s crust. Soils and rocks may contain minerals very high in iron, so high

in fact.

Iron present in the cooling water can be very harmful for the entire process as iron is the

basic component for rusting and corrosion. Iron, although present in very small amounts

in can cause serious damage to the piping through which it passes during the process.

Range: <2ppm

Why is this Water Chemistry Properties Important in Cooling Water Systems?

These key water chemistry properties have a direct impact on the four main problems of

cooling water systems;

Corrosion

Scale

Fouling

Microbial contamination.

These properties also affect the treatment programs designed to control the problems.

The following four problems are normally associated with cooling water systems.

1. CORROSION

Manufacturing of common metals used in cooling systems, such as mild steel, involves

removing oxygen from the natural ore. Cooling water systems are an ideal environment

for the reversion of the metal to the original oxide state. This reversion process is called

corrosion.

2. SCALE

Minerals such as calcium carbonate, calcium phosphate, and magnesium silicate are

relatively insoluble in water and can precipitate out of the water to form scale deposits

when exposed to conditions commonly found in cooling water systems.

3. FOULING

The deposition of suspended material in heat exchange equipment is called fouling.

Foulants can come from external sources such as dust around a cooling tower or internal

sources such as by-products of corrosion.

4. BIOLOGICAL CONTAMINATION

Cooling water systems provide an ideal environment for microbial organisms to grow,

multiply, and cause deposit problems in heat exchange equipment. Microbial growth can

strongly influence corrosion, fouling, and scale formation, if not controlled properly.

Macro fouling can occur in once-through cooling systems or water intakes in lakes and

rivers. Various species of clams, mussels, and other marine organisms can attach to the

piping, reducing water flow and increasing corrosion.

Scale deposits and corrosion products on tube surfaces reduce heat transfer efficiency,

increase energy costs, and reduce equipment life.

•Possible product yield reduction or even plant shutdown

•Product quality problems and increased product rework

•Environmental compliance problems

•Increased greenhouse gas emissions due to higher energy use

Proper program selection and system control methodology are essential to maximizing

the value of the cooling system to the operation of any facility.

The proper system management to control cooling system stresses will optimize.

What are the Effects of These Problems?

If not properly controlled, these problems can have a direct, negative impact on the value

of the entire process operation. Examples of problems that corrosion, deposition, and

biological fouling can create are as follows:

•Increased maintenance cost

•Equipment repair or replacement cost

•More frequent shutdowns for cleaning and replacement of system components

•Reduced heat transfer efficiency and therefore reduced energy efficiency of the process

being cooled

•Increased fuel costs for power generation plants

•Increased energy consumption by refrigeration chillers

zaid bin farooq - internship report'13

Documents

basics of thermal power

lalpir team

water pumps specs

maintenance of pumps

clarifier supply pumps

raw water intake system

canal water pump

boiler area