Bhushan Steel ltd. Project for Vocational Training

A complete description of Bhushan Power Plant Layout and operation, describing each and

every steps involving working principles and parts used in the operation of generating

power in the steam boiler using coal as fuel.

5/29/2015

Hirak Jyoti Saha

MNNIT Allahabad

Mechanical Engg.

Batch (2012-2016)

9935715086

Acknowledgement

It is my privilege to undertake the project in Bhushan Steel

Ltd. and successfully get trained in this firm.

I am very much thankful to the HR Department of this

company for giving me the wonderful opportunity to get

training in the power plant sector of the factory.

I am deeply indebted to all the assisted engineers and

technicians for their valuable guidance, keen interest and

encouragement at various stages of my training period.

I acknowledge with thanks the kind of patronage, loving

inspiration and timely guidance, which I have received from my

course co-ordinators. Our technical debates, exchange of

knowledge, skill and venting of infrastructure and insightful

comments during our project work programme helped me to

enrich my experience.

Although leaflet title “Acknowledgement” can’t represents my

true feeling for all these persons. I feel very much thankful to

all of them and also to my PARENTS and BROTHERS for

encouragements and giving me all the moral support required

to all the people who helped me in making this endeavour a

reality.

Hirak Saha

MNNIT Allahabad

Contents:

1. Plant Introduction Thermal Power Plant

Plant Classification

Bhushan Power Plant ltd.

2. Plant Operation Basic Principles

Plant Layout

Main Components

Bhushan Plant Layout

3. Boiler Introduction

Classifications

Boiler Components

Boilers in Power Plants

Boiler Maintenance

4. Turbine Introduction

Principle of Operation

Classifications

Turbines in Bhushan Plant

5. Condenser Introduction

Types

Condensers in Bhushan Plant

6. Deaerator Introduction

Deaerator in Bhushan Plant

7. Valves and Actuators Valves

Actuators

Types

Valves used in Bhushan Plant

Plant Introduction

Article I. Thermal Power Plant

A thermal power station is a power plant in which the prime mover is steam driven.

Water is heated, turns into steam and spins steam turbine which drives an electrical generator.

After it passes through the turbine, the steam is condensed in a condenser and recycled to

where it was heated; this is known as a Rankine cycle

Almost all coal, nuclear, geothermal, solar thermal electrics, and waste incineration

plants, as well as many natural gas power plants are thermal. Natural gas is

frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine can

be used to raise steam, in a combined cycle plant that improves overall efficiency. Power plants

burning coal, fuel oil, or natural gas are often called fossil-fuel power plants. Some biomass-

fueled thermal power plants have appeared also. Non-nuclear thermal power plants, particularly

fossil-fueled plants, which do not use co-generation are sometimes referred to as conventional

power plants.

Combined heat and power plants (CH&P plants), often called co-generation plants,

produce both electric power and heat for process heat or space heating. Steam and hot water

lose energy when piped over substantial distance, so carrying heat energy by steam or hot water

is often only worthwhile within a local area, such as a ship, industrial plant, or district heating of

nearby buildings.

Article II. Plant Classification

A power plant may be defined as a machine or assembly of equipment that generates and

delivers a flow of mechanical or electrical energy. The main equipment for the generation of electric

power is generator. When coupling it to a prime mover runs the generator, the electricity is

generated. The type of prime movers determines, the type of power plants.

Power Plants are classified as:

I. Conventional

a. Steam Turbine Power Plant

b. Diesel Power Plant

c. Gas Turbine Power Plant

d. Hydro-Electric Power Plant

e. Nuclear Power Plant

II. Non-Conventional

a. Geothermal Energy

b. Wind Energy Power System

c. Biogas, Biomass Energy Power System

d. Ocean Thermal and Tidal Energy

Article III. Bhushan Power Plant

Location:

Narendra Pur P.O. Shibapur, Village Meramandali, Dhenkanal, Odisha 759121

Area:

BFPP-2 Power Plant Division

Plant Overview:

The main productions of Bhushan Steel limited are:

Galvanized coils

Galvanized sheet

Galume coils

Galume sheets

Billets

Colour coated sheets

Hardened and Tempered coils

Colour coated tiles

Sponge Iron

Tubes

Cold rolled coils

HFW/ERW pipes

Colled rolled sheets

and 153 by-products of iron

Along with these productions, the plant generates its own power by coal. It produce 300 MW

of power to run the whole industries. The power plant section is divided into 2 divisions.

The 1st division produce power to generate electricity which is transferred to the main grids

of the control system.

The 2nd division produce compressed air along with the electricity which is further utilized in

the cold blast furnace. Here, we will be confined in Division-2 of Bhusuan Power Plant.

Plant Operation

The basic theory behind coal thermal power plant is, the steam is produced in high

pressure in the steam boiler due to burning of fuel (pulverized coal) in boiler furnaces. This

steam is further supper heated in a super heater. This supper heated steam then enters into

the turbine and rotates the turbine blades. The turbine is mechanically so coupled with

alternator that its rotor will rotate with the rotation of turbine blades. After entering in turbine

the steam pressure suddenly falls and corresponding volume of the steam increases. After

imparting energy to the turbine rotor the steam passes out of the turbine blades into the

condenser. In the condenser the cold water is circulated with the help of pump which

condenses the low pressure wet steam. This condensed water is further supplied to low

pressure water heater where the low pressure steam increases the temperature of this feed

water, it is again heated in high pressure.

For better understanding we furnish every step of function of a thermal power station as follows,

1) First the pulverized coal is burnt into the furnace of steam boiler.

2) High pressure steam is produced in the boiler.

3) This steam is then passed through the super heater, where it further heated up.

4) This supper heated steam is then entered into a turbine at high speed.

5) In turbine this steam force rotates the turbine blades that means here in the turbine the stored potential energy of the high pressured steam is converted into mechanical energy.

6) After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades and enters into a condenser. 7) In the condenser the cold water is circulated with help of pump which condenses the low pressure wet steam.

8) This condensed water is then further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is then again heated in a high pressure heater where the high pressure of steam is used for heating.

9) The turbine in thermal power station acts as a prime mover of the alternator.

Article I. Basic Principle:

Rankine Cycle When all processes of vapour cycle are ideal, the cycle is an ideal

cycle, called a Rankine Cycle. This is a reversible cycle.

For the steam boiler, this would be a reversible constant pressure heating process of water

to form steam, for the turbine the ideal process would be a reversible adiabatic expansion of

steam, for the condenser it would be a reversible constant pressure heat rejection as the

steam condenses till it becomes a saturated liquid, and for the pump the ideal process would

be the reversible adiabatic compression of this liquid ending at the initial pressure. When all

these four processes are ideal, the cycle is called a Rankine Cycle.

In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pump and

turbine would generate no entropy and hence maximize the net work output. Processes 1-2

and 3-4 would be represented by vertical lines on the T-S diagram and more closely

resemble that of the Carnot cycle. The Rankine cycle shown here prevents the vapor ending

up in the superheat region after the expansion in the turbine, which reduces the energy

removed by the condensers.

The actual vapor power cycle differs from the ideal Rankine cycle because of irreversibilities

in the inherent components caused by fluid friction and heat loss to the surroundings; fluid

friction causes pressure drops in the boiler, the condenser, and the piping between the

components, and as a result the steam leaves the boiler at a lower pressure; heat loss

reduces the net work output, thus heat addition to the steam in the boiler is required to

maintain the same level of net work output

Modified Rankine Cycle Reheat of reheat regenerative steam power cycle

increases its efficiency by increasing the average temperature of heat reception. In-spite of

such an increase in efficiency, reheating increases the irreversibility of feed water heaters by

using superheated steam of a greater temperature difference in the regenerative cycle. This

invention introduces some modifications to the regular reheat regenerative steam power

cycle that reduces the irreversibility of the regenerative process. The invention applies

reversible reheating in addition to the regular reheating and uses smaller temperature

differences across feed water heaters than the regular cycle.

Regenerative-Reheat Cycle 1

Article II. Plant Layout:

The layout of the steam power plant consists of four main circuits. These are:

Coal and ash circuit.

Air and flue gas circuit

Water and steam circuit and

Cooling water circuit

Coal and ash circuit:

Coal from the storage yard is transferred to the boiler furnace by means of coal handling

equipment like belt conveyor, bucket elevator, etc., ash resulting from the combustion of coal

in the boiler furnace collects at the back of the boiler and is removed to the ash storage yard

through the ash handling equipment.

Ash disposal:

The indian coal contains 30% to 40% ash. A power plant of 100MW 20 to 25 tonnes of hot

ash per hour. Hence sufficient space near the power plant is essential to dispose such large

quantities of ash.

Air and flue gas circuit:

Air is taken from the atmosphere to the air preheater. Air is heated in the air preheater by the

heat of flue gas which is passing to the chimney. The hot air is supplied to the furnace of the

bolier.

The flue gases after combustion in the furnace, pass around the boiler tubes. The flue gases

then passes through a dust collector, economizer and pre-heater before being exhausted to

the atmosphere through the chimney. By this method the heat of the flue gases which would

have been wasted otherwise is used effectively. Thus the overall efficiency of the plant is

improved.

Air pollution:

The pollution of the surrounding atmosphere is caused by the emission of objectable gases

and dust through the chimney. The air pollution and smoke cause nuisance to people

surrounding the planet.

Feed water and steam circuit:

The steam generated in the boiler passes through super heater and is supplied to the steam

turbine. Work is done by the expansion of steam in the turbine and the pressure of steam is

reduced. The expanded steam then passes to the condenser, where it is condensed.

The condensate leaving the condenser is first heated in a l.p. water heater by using the

steam taken from the low pressure extraction point of the turbine. Again steam taken from

the high pressure extraction point of the turbine is used for heating the feed water in the H.P

water heater. The hot feed water is passing through the economizer, where it is further

heated by means of flue gases. The feed water which is sufficiently heated by the feed water

heaters and economizer is then fed into the boiler.

Cooling water circuit:

Abundant quantity of water is required for condensing the steam in the condenser. Water

circulating through the condenser may be taken from various sources such as river or lake,

provided adequate water supply is available from the river or lake throughout the year.

If adequate quantity of water is not available at the plant site, the hot water from the

condenser is cooled in the cooling tower or cooling ponds and circulated again.

Plant Layout 1

Article III. Main Components:

Main parts of power plant are:

1. Boiler

2. Electrostatic Precipitator

3. Turbine

4. Condenser

5. Cooling Towers

6. Air Ejector

7. Low Pressure Heater

8. Deaerator

9. High Pressure Heater

10. Boiler Feed Pump.

Boiler : Now that pulverized coal is put in boiler furnace. Boiler is an enclosed vessel in

which water is heated and circulated until the water is turned in to steam at the required

pressure.

Coal is burned inside the combustion chamber of boiler. The products of combustion are

nothing but gases. These gases which are at high temperature vaporize the water inside the

boiler to steam. Some-times this steam is further heated in a super-heater as higher the

steam pressure and temperature the greater efficiency the engine will have in converting the

heat in steam in to mechanical work. This steam at high pressure and temperature is used

directly as a heating medium, or as the working fluid in a prime mover to convert thermal

energy to mechanical work, which in turn may be converted to electrical energy. Although

other fluids are sometimes used for these purposes, water is by far the most common

because of its economy and suitable thermodynamic characteristics.

Electrostatic Precipitator: It is a device which removes dust or other finely divided

particles from flue gases by charging the particles inductively with an electric field, then

attracting them to highly charged collector plates. Also known as precipitator. The process

depends on two steps. In the first step the suspension passes through an electric discharge

(corona discharge) area where ionization of the gas occurs. The ions produced collide with

the suspended particles and confer on them an electric charge. The charged particles drift

toward an electrode of opposite sign and are deposited on the electrode where their electric

charge is neutralized. The phenomenon would be more correctly designated as

electrodeposition from the gas phase.

The use of electrostatic precipitators has become common in numerous industrial

applications. Among the advantages of the electrostatic precipitator are its ability to handle

large volumes of gas, at elevated temperatures if necessary, with a reasonably small

pressure drop, and the removal of particles in the micrometre range. Some of the usual

applications are: (1) removal of dirt from flue gases in steam plants; (2) cleaning of air to

remove fungi and bacteria in establishments producing antibiotics and other drugs, and in

operating rooms; (3) cleaning of air in ventilation and air conditioning systems; (4) removal of

oil mists in machine shops and acid mists in chemical process plants; (5) cleaning of blast

furnace gases; (6) recovery of valuable materials such as oxides of copper, lead, and tin;

and (7) separation of rutile from zirconium sand.

Turbine: Turbine is a rotary mechanical device that extracts energy from a fluid flow and

converts it into useful work. A turbine is a turbomachine 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. Early turbine examples

are windmills and waterwheels.

A steam turbine is a device that extracts thermal energy from pressurized steam and uses it

to do mechanical work on a rotating output shaft. Because the turbine generates rotary

motion, it is particularly suited to be used to drive an electrical generator – about 90% of all

electricity generation in India is by use of steam turbines. The steam turbine is a form of heat

engine that derives much of its improvement in thermodynamic efficiency from the use of

multiple stages in the expansion of the steam, which results in a closer approach to the ideal

reversible expansion process.

Condenser: Steam after rotating steam turbine comes to condenser. Condenser refers here

to the shell and tube heat exchanger (or surface condenser) installed at the outlet of every

steam turbine in Thermal power stations of utility companies generally. These condensers

are heat exchangers which convert steam from its gaseous to its liquid state, also known as

phase transition. In so doing, the latent heat of steam is given out inside the condenser.

Where water is in short supply an air cooled condenser is often used. An air cooled

condenser is however significantly more expensive and cannot achieve as low a steam

turbine backpressure (and therefore less efficient) as a surface condenser.

The purpose is to condense the outlet (or exhaust) steam from steam turbine to

obtain maximum efficiency and also to get the condensed steam in the form of pure water,

otherwise known as condensate, back to steam generator or (boiler) as boiler feed water.

The condensate (water) formed in the condenser after condensation is initially at high

temperature. This hot water is passed to cooling towers. It is a tower- or building-like

device in which atmospheric air (the heat receiver) circulates in direct or indirect contact with

warmer water (the heat source) and the water is thereby cooled (see illustration). A cooling

tower may serve as the heat sink in a conventional thermodynamic process, such as

refrigeration or steam power generation, and when it is convenient or desirable to make final

heat rejection to atmospheric air. Water, acting as the heat-transfer fluid, gives up heat to

atmospheric air, and thus cooled, is recirculated through the system, affording economical

operation of the process.

Two basic types of cooling towers are commonly used. One transfers the heat from warmer

water to cooler air mainly by an evaporation heat-transfer process and is known as

the evaporative or wet cooling tower.

Evaporative cooling towers are classified according to the means employed for producing

air circulation through them atmospheric, natural draft, and mechanical draft. The other

transfers the heat from warmer water to cooler air by a sensible heat-transfer process and is

known as the non-evaporative or dry cooling tower.

Non-evaporative cooling towers are classified as air-cooled condensers and as air-cooled

heat exchangers, and are further classified by the means used for producing air circulation

through them. These two basic types are sometimes combined, with the two cooling

processes generally used in parallel or separately, and are then known as wet-dry cooling

towers.

Evaluation of cooling tower performance is based on cooling of a specified quantity of water

through a given range and to a specified temperature approach to the wet-bulb or dry-bulb

temperature for which the tower is designed. Because exact design conditions are rarely

experienced in operation, estimated performance curves are frequently prepared for a

specific installation, and provide a means for comparing the measured performance with

design conditions.

Low Pressure Heater: It is a feed water heater used to pre heat water after it releases from

the condenser. Preheating the feed water reduces the irreversibilities 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. LP Feed water Heater’s pressure ratings

range between 400 and 1,500 psig. LP Feed water Heaters are designed as single zone with

a condensing section or two zones with a condensing section and integral sub cooler

section. Drain coolers are employed because of heat consumption improvement in case of

drain introduction into the lower heater through the level control valve.

De-aerator: A deaerator is a device that is widely used for the removal of oxygen 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). Dissolved carbon dioxide combines with water to form carbonic

acid that causes further corrosion. Most deaerators are designed to remove oxygen down to

levels of 7 ppb by weight (0.005 cm³/L) or less as well as essentially eliminating carbon

dioxide.

There are two basic types of deaerators, the tray-type and the spray-type:

The tray-type (also called the cascade-type) includes a vertical domed deaeration

section mounted on top of a horizontal cylindrical vessel which serves as the deaerated

boiler feedwater storage tank.

The spray-type consists only of a horizontal (or vertical) cylindrical vessel which serves

as both the deaeration section and the boiler feedwater storage tank.

Air Ejector: Air Ejectors are based on the ejector-venturi principal and operate by passing motive air or gas through an expanding nozzle. The air ejector draws out the air and vapours which are released from the condensing steam in the condenser. If the air were not removed from the system it could cause corrosion problems in the boiler. Also, air present in the condenser would affect the condensing process and cause a back pressure in the condenser.

It works on the principle of convergent /divergent nozzle as it provides the venture-effect at

the point of diffusion as the tube gets narrows at the throat the velocity of the fluid increases

and because of the venture-effect it pressure decreases, vacuum will occur in the diffuser

throat where the suction line will be provided.

An air ejector which uses the high pressure motive fluid such as air or steam to flow through

the convergent nozzle the function of the convergent nozzle is to convert the pressure

energy of the motive fluid into the velocity energy.

High Pressure Heater: Tube Sheet High-Pressure Heaters are designed as two zones or

three zones with a condensing section, desuperheater and integral sub cooler. The use of a

desuperheater reduces the terminal temperature difference (TTD) of the entire Feed water

Heater. A negative TTD of up to 3°C can be achieved by the use of a desuperheater,

depending on the steam inlet temperature. The tube wall temperature must be over the local

saturation temperature in all operation conditions. The use of a separate cross-connected

desuperheater improves the heat consumption and increases the Feed water temperature at

the boiler inlet. HP Feed water heater’s pressure ratings range from 1,500 to 4,800 psi

Boiler Feed Pump: 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 take suction from a condensate

return system and can be of the centrifugal pump type or positive displacement type.

Feed water pumps range in size up to many horsepower and the electric motor is usually

separated from the pump body by some form of mechanical coupling. Large industrial

condensate pumps may also serve as the feed water pump. In either case, to force the water

into the boiler, the pump must generate sufficient pressure to overcome the steam pressure

developed by the boiler. This is usually accomplished through the use of a centrifugal pump.

Another common form of feed water pumps run constantly and are provided with a minimum

flow device to stop over-pressuring the pump on low flows. The minimum flow usually

returns to the tank or deaerator.

Article IV. Bhushan Power Plant Layout:

In division-2 of Bhushan Power Plant, there are 3 CFBC boilers of 275 TPH.

The boilers are 2 pass, cold cyclone, natural circulation, CFBC (Circulating Fluidised Bed

Combustion).

The 106kg/cm2, 545 ⁰C steam produced goes to the common steam distribution header,

where it is transferred to 3 Turbo-Blower of 65 TPH, 1 Turbo-Generator of 620 TPH,

process steam line and auxiliary steam line.

After steam passes through the turbo blower, the steam is sent to the shell and tube

condenser where it is cooled and gets collected to the hot well. Here the temperature of DM

water reaches from 40-50⁰C.

To produce vacuum (-0.9kg/cm2) in the condenser, air-ejector is added. The feed water

goes to the air ejector through condensate extraction pump.

Now, the feed water goes to the LP Heater for gradual increase of feed water temperature.

Then it goes in the deaerator which is located to the top of the plant where it is mixed with

pure feed water from DM Plant, mechanically deaerated (which increases the temperature of

feed water to approx. 160⁰C) and is dozed with DEHA (di-ethyl hydroxyl amine) which

removes the oxygen from the water and prevent it from corrosion.

After this the feed water goes to the boiler feed pump which is located in the base of the

plant. The pressure in this region is very high since it has to force the water to the HP Heater

which is located high above the ground.

The feed water goes to the HP Heater-1 and then HP Heater-2 and finally reaches to the

feed control system, which has 3 pass: 40%, 100%, and 100% by-pass. From here the

feed water enters the boiler and the cycle repeats.

Boiler

Article I. Introduction:

A boiler is an enclosed vessel that provides a means for combustion heat to be transferred

into water until it becomes heated water or steam. The hot water or steam under pressure is

then usable for transferring the heat to a process. Water is a useful and cheap medium for

transferring heat to a process. When water is boiled into steam its volume increases about

1,600 times, producing a force that is almost as explosive as gunpowder. This causes the

boiler to be extremely dangerous equipment that must be treated with utmost care.

The boiler system comprises of: feed water system, steam system and fuel system. The feed

water system provides water to the boiler and regulates it automatically to meet the steam

demand. Various valves provide access for maintenance and repair. The steam system

collects and controls the steam produced in the boiler. Steam is directed through a piping

system to the point of use. Throughout the system, steam pressure is regulated using valves

and checked with steam pressure gauges. The fuel system includes all equipment used to

provide fuel to generate the necessary heat. The equipment required in the fuel system

depends on the type of fuel used in the system.

The water supplied to the boiler that is converted into steam is called feed water. The two

sources of feed water are: (1) Condensate or condensed steam returned from the processes

and (2) Makeup water (treated raw water) which must come from outside the boiler room

and plant processes. For higher boiler efficiencies, the feed water is preheated by

economizer, using the waste heat in the flue gas.

Article II. Classification:

There are virtually infinite numbers of boiler designs but generally they fit into one of two

categories:

Fire tube or “fire in tube” boilers; contain long steel tubes through which the hot gasses from

a furnace pass and around which the water to be converted to steam circulates. (Refer

Figure 2.2). Fire tube boilers, typically have a lower initial cost, are more fuel efficient and

easier to operate, but they are limited generally to capacities of 25 tons/hr and pressures of

17.5 kg/cm2.

Water tube or “water in tube” boilers in which the conditions are reversed with the water

passing through the tubes and the hot gasses passing outside the tubes (see figure 2.3).

These boilers can be of single- or multiple-drum type. These boilers can be built to any

steam capacities and pressures, and have higher efficiencies than fire tube boilers.

Packaged Boiler: The packaged boiler is so called because it comes as a complete

package. Once delivered to site, it requires only the steam, water pipe work, fuel supply and

electrical connections to be made for it to become operational. Package boilers are generally

of shell type with fire tube design so as to achieve high heat transfer rates by both radiation

and convection.

These boilers are classified based on the number of passes – the number of times the hot

combustion gases pass through the boiler. The combustion chamber is taken, as the first

pass after which there may be one, two or three sets of fire-tubes. The most common boiler

of this class is a three-pass unit with two sets of fire-tubes and with the exhaust gases

exiting through the rear of the boiler.

Boiler Efficiency

Thermal efficiency of boiler is defined as the percentage of heat input that is effectively

utilised to generate steam. There are two methods of assessing boiler efficiency.

1) The Direct Method: Where the energy gain of the working fluid (water and steam) is

compared with the energy content of the boiler fuel.

2) The Indirect Method: Where the efficiency is the difference between the losses and the

energy input.

Article III. Boiler Components:

There are many parts in the boiler which have their unique role in steam generation. They

are classified as:

Boiler Acessories: These are those devices which are installed with a boiler and

its neighbouring area to increase the efficiency of the boiler. These are not the

essential parts of the boiler and thus without installing these devices, the boiler

components can be accomplished through at a lower efficiency. The following are the

important accessories of the boiler:

1. Feed Pump

2. Injector

3. Super Heater

4. Economiser

5. Air Pre-Heater

6. Steam Separator

Feed Pump:

• The feed pump is a pump which is used to deliver feed water to the boiler.

• Double feed pump is commonly employed for medium size boilers.

• The reciprocating pump are continuously run by steam from the same boiler to

which water is to be fed.

• Rotary feed pumps are of centrifugal type and are commonly run either by a

small steam turbine or by an electric motor.

Injector:

The function of an injector is to feed water into the boiler. It is commonly employed for

vertical and locomotive boilers and does not find its application in large capacity high

pressure boilers. It is also used where the space is not available for the installation of a feed

pump.

In an injector the water is delivered to the boiler by steam pressure; the kinetic energy of

steam is used to increase the pressure and velocity of the feed water.

Super Heater:

• The function of super heater is to increase the temperature of the steam above

its saturation point.

• To superheat the steam generated by boiler.

• Super heaters are heat exchangers in which heat is transferred to the

saturated steam to increase its temperature.

• Superheated steam has the following

advantages :

i) Steam consumption of the engine or turbine is reduced.

ii) Losses due to condensation in the cylinders and the steam pipes are reduced.

iii) Erosion of turbine blade is eliminated.

iv) Efficiency of steam plant is increased.

Economiser:

• Function: It is a device in which the waste heat of the flue gases is utilsed for

heating the feed water.

• To recover some of the heat is being carried over by exhaust gases.

This heat is used to raise the temperature of feed water supplied to the boiler.

• Advantages:

i) The temperature range between various parts of the boiler is reduced which results in

reduction of stresses due to unequal expansion.

ii) If the boiler is fed with cold water it may result in chilling the boiler metal.

iii) Evaporative capacity of the boiler is increased.

iv) Overall efficiency of the plant is increased.

Air Preheater:

• Waste heat recovery device in which the air to on its way to the furnace is

heated utilizing the heat of exhaust gases

• The function of air pre-heater is to increase the temperature of air before

enters the furnace.

• It is generally placed after the economizer; so the flue gases passes through

the economizer and then to the air preheater.

• An air-preheater consists of plates or tubes with hot gases on one side and air

on the other.

• It preheats the to be supplied to the furnace. Preheated air accelerates the

combustion and facilitates the burning of coal.

Degree of Preheating depends on:

(i) Type of fuel, (ii) Type of fuel burning equipment, and (iii) Rating at which the

boiler and furnaces are operated.

There are three types of air preheater :

1. Tubular type 2. Plate type 3. Storage type.

Steam Seperator:

The steam available from a boiler may be either wet , dry; or superheated; but in many cases there will be loss of heat from it during its passage through the steam pipe from the boiler to the Engine tending to produce wetness. The use of wet steam in an engine or turbine is uneconomical besides involving some risk; hence it is usual to endeavor to separate any water that may be present from the steam before the latter enters the engine. This is accomplished by the use of a steam separator. Thus, the function of a steam separator is to remove the entrained water particles from the steam conveyed to the steam engine or turbine. It is installed as close to the steam engine as possible on the main steam pipe from the boiler.

Boiler Mountings: Boiler mountings are the components generally mounted on the

surface of the boiler to have safety during operations. These are essential parts of

the boiler, without which the boiler operation is not possible. The following are the

important mountings of the boiler:

1. Water Level Indicator

2. Pressure gauge

3. Safety valves

4. Stop valve

5. Blow off cock

6. Feed check valve

7. Fusible Plug

8. Blow Down Valve

(a) Water indicator: It is an important fitting which indicate the water level inside the boiler

to an observer.

(b) Pressure gauge: A pressure gauge is used to measure the pressure of the steam boiler.

It is fixed in front of the steam boiler.

(c) Safety valves: There are the devices attached to the steam chest for preventing

explosions due to excessive internal pressure of steam. There are four types of safety

valves.

i. Lever safety valve

ii. Dead weight safety valve

iii. High steam and low water safety valve

iv. Spring loaded safety valve

(d) Stop valve: It is the largest valve on the steam boiler. It is used to control the flow of

steam from boiler to the main steam pipe.

(e) Blow off cock: It is fitted to the bottom of a boiler drum and consists of a conical plug

fitted to the body or casting. Its function is to empty the boiler whenever required and to

discharge the mud, scale or sediments which are accumulated at the bottom of the boiler.

(f) Feed check valve: It is a non-return valve fitted to a screwed spindle to regulate the lift.

Its function is to regulate the supply water which pumped into the boiler by the feed pump.

(g) Fusible plug: It is fitted to the crown plate of the furnace or the fire. Its object is to put off

the fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit

and thus avoids the implosion which may take place due to overheating of the furnace plate.

(h) Blow down valve: It is fitted to the lower side of the boiler. Its function is to reduce the

impurities of the boiler.

Article IV. Boilers in Power Plant:

AFBC Boilers

It stands for Atmospheric Fluidised Bed Combustion Boiler. It is a FBC boiler which

operates on the atmospheric pressure.

Atmospheric fluidised-bed combustion (AFBC) boilers offer efficient, cost effective and reliable steam generation. AFBC technology promises to provide a viable alternative to conventional coal-fired and other solid fuel-fired boilers. This involves little more than adding a fluidized bed combustor to a conventional shell boiler. Such systems have similarly being installed in conjunction with conventional water tube boiler.

Coal is crushed to a size of 1 – 10 mm depending on the rank of coal, type of fuel fed to the combustion chamber. The atmospheric air, which acts as both the fluidization and combustion air, is delivered at a pressure, after being preheated by the exhaust fuel gases. The in-bed tubes carrying water generally act as the evaporator. The gaseous products of combustion pass over the super heater sections of the boiler flow past the economizer, the dust collectors and the air preheater before being exhausted to atmosphere.

Salient Features:

Low fluidizing velocity for lower wear of bed tubes.

Deep bed operation for better combustion.

High pressure drop bed nozzles which ensures even air distribution even at low loads. No clicker formation in our AFBC boilers.

Optimised stud pattern for long life.

Flexibility to choose from Charcoal start-up, Oil assisted Charcoal start-up or pure Oil start-up.

Flexibility to choose from either Underfeed, Overbed feeding or even a combination of both.

Normally, superheaters are in convection and bed superheaters avoided for improved reliability.

Variety of design to choose from Box type “El-Passo” design to nose type design or to two pass bottom supported design.

Doosan Guidelines on Superheater and circulation which were developed for large boilers are employed even in the smallest of the boilers.

The smallest of the boilers will have proper drum internals and cyclones for effective steam separation.

The ever reliable Babcock spreaders & feeders employed in overbed feeding.

For abrasive fuels, special design considerations and provision of sacrificial shields.

Continuous improvement & refinement ongoing.

CFBC Boilers

It stands for Circulating Fluidised Bed Combustion Boiler. In a circulating system the bed parameters are so maintained as to promote solids elutriation from the bed. They are lifted in a relatively dilute phase in a solids riser, and a down-comer with a cyclone provides a return path for the solids. There are no steam generation tubes immersed in the bed. Generation and super heating of steam takes place in the convection section, water walls, at the exit of the riser.

CFBC boilers are generally more economical than AFBC boilers for industrial application requiring more than 75 – 100 T/hr of steam. For large units, the taller furnace characteristics of CFBC boilers offers better space utilization, greater fuel particle and sorbent residence time for efficient combustion and SO2 capture, and easier application of staged combustion techniques for NOx control than AFBC steam generators.

Circulating fluidized-bed (CFB) boiler technology offers high reliability and availability coupled with low maintenance costs, and complies with stringent emission regulations. The CFB technology utilised employs a unique, simple U-beam particle separator design. This CFB technology helps you to:

Avoid costly maintenance and outages caused by thick refractory failures as seen in CFB boilers with hot cyclone design

Reduce the erosion potential compared to hot cyclone design Avoid sootblower-induced erosion Reduce maintenance costs compared to mechanical / pneumatic systems

Salient Features:

The solid particles separated from the flue gas are re-circulated back into the furnace through the loop seal.

The range of fuels that can be successfully burned in CFBCs is very broad.

The CFB, with its low combustion temperature is an especially good solution for coals with low ash fusion temperatures,

Preventing the formation of slag.

High Combustion Efficiency

The continuous circulation of solids through the CFBC system keeps the fuel in an ideal combustion environment for a long period of time.

CFBs do not require complicated and expensive downstream flue gas desulphurisation equipment to meet environmental regulations.

Better sulphur capture with less limestone and improved heat transfer.

Operation over a wide range of boiler loads is possible without starting and stopping burners and auxiliary equipment.

The maximum velocity of flue gas across various zones is fixed at an optimum level.

Considering low temperature staged combustion associated with the CFBC, the ash particle shape and structure do not reach the level of creating adverse implications in this velocity range.

Elimination of hundreds of opening for the arrangement of heating surfaces and in turn the access and inspection openings

CFB boiler requires less manpower to operate and maintain.

The parameters to be monitored in CFBC are less.

PF Boilers

It stands for Pulverized Fuel Boilers. Most coal-fired power station boilers use pulverized coal, and many of the larger industrial water-tube boilers also use this pulverized fuel. This technology is well developed, and there are thousands of units around the world, accounting for well over 90% of coal-fired capacity.

The coal is ground (pulverized) to a fine powder, so that less than 2% is +300 micro meter (μm) and 70-75% is below 75 microns, for a bituminous coal. It should be noted that too fine a powder is wasteful of grinding mill power. On the other hand, too coarse a powder does not burn completely in the combustion chamber and results in higher unburnt losses.

The pulverized coal is blown with part of the combustion air into the boiler plant through a series of burner nozzles. Secondary and tertiary air may also be added. Combustion takes place at temperatures from 1300-1700°C, depending largely on coal grade. Particle residence time in the boiler is typically 2 to 5 seconds, and the particles must be small enough for complete combustion to have taken place during this time.

This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc.

One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the centre of the furnace.

Salient Features:

Front or opposed wall firing for catering different fuels & boiler size.

Down shot firing for very low VM coals

Reheat control by either Gas recirculation or by divided gas pass boiler.

Super heater & re-heater of all boilers, specially treated for boiler & furnace upset conditions.

Standard or Low NOx burners.

Flexibility to choose either Doosan E-mills or any other pulveriser as per customer choice.

Extremely conservative design for pressure parts & non pressure parts.

Conservative design of Hot structures to cater for accidental heavy structural loads due to ash accumulation etc.

For abrasive coals, special design considerations and provision of erosion protection shields, baffles and flow streamliners.

Article V. Boiler Maintenance

Boiler maintenance is key to ensuring that your boiler is safe. While rare, gas leaks can be

very dangerous and are often difficult to detect in your home. Having professional work

carried out on your boiler is the best way to protect yourself against such disaster. The first

thing you can do to make sure that you’re getting the most from your boiler is to put it

through annual servicing. The cost of doing so is likely to pale into insignificance when

compared to the amount you could otherwise be spending on unforeseen repairs. A boiler

which isn’t cared for regularly is also likely to be inefficient, costing more than it needs to in

running costs.

The basic maintenance procedures are:

Functionality testing of all components. Inspection and cleaning of all pipes and components. Replacement of any parts which are no longer functioning. Regular use and checking of boilers mountings.

Turbines

Article I. Introduction

Steam turbine is one of the most important prime-mover for generating electricity. This falls

under the category of power producing turbo-machines. In the turbine, the energy level of

the working fluid goes on decreasing along the flow stream. The purpose of turbine

technology is to extract the maximum quantity of energy from the working fluid, to convert it

into useful work with maximum efficiency, by means of a plant having maximum reliability,

minimum cost, minimum supervision and minimum starting time. This chapter deals with the

types and working of various types of steam turbine.

Article II. Principle of Operation

The principle of operation of steam turbine is entirely different from the steam engine. In

reciprocating steam engine, the pressure energy of steam is used to overcome external

resistance and the dynamic action of steam is negligibly small. But the steam turbine

depends completely upon the dynamic action of the steam. According to Newton’s Second

Law of Motion, the force is proportional to the rate of change of momentum (mass ×

velocity). If the rate of change of momentum is caused in the steam by allowing a high

velocity jet of steam to pass over curved blade, the steam will impart a force to the blade. If

the blade is free, it will move off (rotate) in the direction of force. In other words, the motive

power in a steam turbine is obtained by the rate of change in moment of momentum of a

high velocity jet of steam impinging on a curved blade which is free to rotate. The steam

from the boiler is expanded in a passage or nozzle where due to fall in pressure of steam,

thermal energy of steam is converted into kinetic energy of steam, resulting in the emission

of a high velocity jet of steam which, Principle of working impinges on the moving vanes or

blades of turbine.

Attached on a rotor which is mounted on a shaft supported on bearings, and here steam

undergoes a change in direction of motion due to curvature of blades which gives rise to a

change in momentum and therefore a force. This constitutes the driving force of the turbine.

This arrangement is shown. It should be realized that the blade obtains no motive force from

the static pressure of the steam or from any impact of the jet, because the blade in designed

such that the steam jet will glide on and off the blade without any tendency to strike it.

When the blade is locked the jet enters and leaves with equal velocity, and thus develops

maximum force if we neglect friction in the blades. Since the blade velocity is zero, no

mechanical work is done. As the blade is allowed to speed up, the leaving velocity of jet from

the blade reduces, which reduces the force. Due to blade velocity the work will be done and

maximum work is done when the blade speed is just half of the steam speed. In this case,

the steam velocity from the blade is near about zero i.e. it is trail of inert steam since all the

kinetic energy of steam is converted into work. The force and work done become zero when

the blade speed is equal to the steam speed. From the above discussion, it follows that a

steam turbine should have a row of nozzles, a row of moving blades fixed to the rotor, and

the casing (cylinder). A row of nozzles and a raw of moving blades constitutes a stage of

turbine.

Article III. Classification

On the basis of principle of operation, turbines are divided as:

1. Impulse Turbine

2. Impulse-Reaction Turbine

3. Reaction Turbine

Impulse Turbine

If the flow of steam through the nozzles and moving blades of a turbine takes place in such a

manner that the steam is expanded only in nozzles and pressure at the outlet sides of the

blades is equal to that at inlet side; such a turbine is termed as impulse turbine because it

works on the principle of impulse. In other words, in impulse turbine, the drop in pressure of

steam takes place only in nozzles and not in moving blades. This is obtained by making the

blade passage of constant cross- section area

As a general statement it may be stated that energy transformation takes place only in

nozzles and moving blades (rotor) only cause energy transfer. Since the rotor blade

passages do not cause any acceleration of fluid, hence chances of flow separation are

greater which results in lower stage efficiency.

Impulse turbines change the direction of flow of a high velocity fluid or gas jet. The resulting

impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is

no pressure change of the fluid or gas in the turbine blades (the moving blades), as in the

case of a steam or gas turbine all the pressure drop takes place in the stationary blades (the

nozzles). Before reaching the turbine, the fluid's pressure head is changed to velocity

head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this

process exclusively. Impulse turbines do not require a pressure casement around the rotor

since the fluid jet is created by the nozzle prior to reaching the blades on the rotor. Newton's

second law describes the transfer of energy for impulse turbines.

Reaction Turbine

Reaction turbines develop torque by reacting to the gas or fluid's pressure or mass. The

pressure of the gas or fluid changes as it passes through the turbine rotor blades. A

pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or

the turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing

contains and directs the working fluid and, for water turbines, maintains the suction imparted

by the draft tube. Francis turbines and most steam turbines use this concept. For

compressible working fluids, multiple turbine stages are usually used to harness the

expanding gas efficiently. Newton's third law describes the transfer of energy for reaction

turbines.

In the case of steam turbines, such as would be used for marine applications or for land-

based electricity generation, a Parsons type reaction turbine would require approximately

double the number of blade rows as a de Laval type impulse turbine, for the same degree of

thermal energy conversion. Whilst this makes the Parsons turbine much longer and heavier,

the overall efficiency of a reaction turbine is slightly higher than the equivalent impulse

turbine for the same thermal energy conversion.

Impulse-Reaction Turbine

In this turbine, the drop in pressure of steam takes place in fixed (nozzles) as well as

moving blades. The pressure drop suffered by steam while passing through the moving

blades causes a further generation of kinetic energy within the moving blades, giving rise to

reaction and adds to the propelling force which is applied through the rotor to the turbine

shaft. Since this turbine works on the principle of impulse and reaction both, so it is called

impulse-reaction turbine. This is achieved by making the blade passage of varying cross-

sectional area (converging type).

In practice, modern turbine designs use both reaction and impulse concepts to varying

degrees whenever possible. Wind turbines use an air-foil to generate a reaction lift from the

moving fluid and impart it to the rotor. Wind turbines also gain some energy from the impulse

of the wind, by deflecting it at an angle. Turbines with multiple stages may utilize either

reaction or impulse blading at high pressure. Steam turbines were traditionally more impulse

but continue to move towards reaction designs similar to those used in gas turbines. At low

pressure the operating fluid medium expands in volume for small reductions in pressure.

Under these conditions, blading becomes strictly a reaction type design with the base of the

blade solely impulse. The reason is due to the effect of the rotation speed for each blade. As

the volume increases, the blade height increases, and the base of the blade spins at a

slower speed relative to the tip. This change in speed forces a designer to change from

impulse at the base, to a high reaction style tip.

Article IV. Turbines in Bhushan Power Plant

There are four impulse-reaction turbine of Siemens. Three of them are attached to a turbo

blower producing 23 MW of power and the compressed air generated by the blower are

sent to the cold blast furnace, while the tubo-generator produces 165 MW of power.

There are 19 stages in turbine and all of them are impulse stages. The criteria of turbine

includes:

Inlet

Pressure= 106kg/cm2

Silica= 0.02

Temperature= 545⁰C

Outlet

Pressure= -0.92kg/cm2

Temperature= 45⁰C

Condenser

Article I. Introduction

In systems involving heat transfer, a condenser is a device or unit used to condense a

substance from its gaseous to its liquid state, typically by cooling it. In so doing, the latent

heat is given up by the substance, and will transfer to the condenser coolant. Condensers

are typically heat exchangers which have various designs and come in many sizes ranging

from rather small (hand-held) to very large industrial-scale units used in plant processes. For

example, a refrigerator uses a condenser to get rid of heat extracted from the interior of the

unit to the outside air. Condensers are used in air conditioning, industrial chemical

processes such as distillation, steam power plant-sand other heat-exchange systems. Use of

cooling water or surrounding air as the coolant is common in many condensers.

Article II. Types

There are two broad classes of condensers:

1. Direct Contact Type Condenser, where the condensate and the cooling water directly

mix together and come out as a single stream.

2. Surface Condenser, where are shell and tube heat exchangers where the two fluids

do not come in direct contact and the heat released by the condensation of the steam

is transferred by the walls of the tubes into the cooling water continuously circulating

inside them.

Direct Contact Type Condenser

In this type of condenser, vapours are poured into the liquid directly. The vapours lose

their latent heat of vaporization; hence, vapours transfer their heat into liquid and the liquid

becomes hot. In this type of condensation, the vapour and liquid are of same type of

substance. In another type of direct contact condenser, cold water is sprayed into the vapour

to be condensed.

These can be of three types:

1. Spray condenser

2. Barometric condenser

3. Jet condenser.

Surface Condenser

It is a shell and tube heat exchanger installed at the outlet of every steam turbine in thermal

power stations. Commonly, the cooling water flows through the tube side and the steam

enters the shell side where the condensation occurs on the outside of the heat transfer

tubes. The condensate drips down and collects at the bottom, often in a built-in pan called

a hot-well. The shell side often operates at a vacuum or partial vacuum, often produced by

attached air-ejectors. Conversely, the vapour can be fed through the tubes with the coolant

water or air flowing around the outside.

They are mostly popular in Power Plants. These condensers are heat exchangers which

convert steam from its gaseous to its liquid state at a pressure below atmospheric pressure.

Where cooling water is in short supply, an air-cooled condenser is often used. An air-cooled

condenser is however, significantly more expensive and cannot achieve as low a steam

turbine exhaust pressure (and temperature) as a water-cooled surface condenser.

Article III. Condenser in Bhushan Plant

In division-2 of Bhushan Power Plant, 2-pass counter flow Shell and tube Condenser is

used. There are overall four condenser of Siemens are used below each turbo-blower and

turbo-generator.

There is indirect heat transfer between the cooling water and the condensate. The

condensate (steam) comes from the turbo-blower or turbo-generator to the shell where pipes

are horizontally placed in 2 pass. The cooling water enters the tube, cools the steam and

returns to the cooling tower through condenser outlet. The condensed steam settles to the

hot well where it is sucked to the air ejector which helps in creating vacuum in the condenser

so that there is proper flow of steam in the condenser.

Pressure -0.92 kg/cm2

Temperature 40-45 ⁰C

Surface Area

Deaerator

Article I. Introduction

Deaerators work on the principle that oxygen is decreasingly soluble as the temperature is

raised. In a deaerator, oxygen is separated from the water by creating a head space and

passing steam through the feedwater. The non-condensable gases and a slight excess of

steam are then vented from the system. The two basic types of deaerator are

the spray and tray types

.

Deaerators are designed to be able to achieve 7 ppb of oxygen. Actual performance is in

the range of 5 to 25 ppb for tray type and 20 to 40 ppb for spray type deaerators.

The steam required for deaeration is about 1% of the feedwater flow for every ten degrees

of temperature rise in the deaerator:

Steam required (lb/hr) = (Tout – Tin) * 0.01 / 10°F

This is only an approximation because the heat content of the steam and water will vary

somewhat with actual operating temperature. The deaerator storage tank serves several

purposes:

• Since the pump head is broken in the deaerator because of the head space, the deaerator

water must collected and repumped to the boiler.

• The tank servers as a “battery” of water to prevent starvation of the boiler feedwater pump

and the boilers. Typically, a ten minute supply of water is maintained in the storage tank.

• Oxygen scavenger chemicals are usually added in the deaerator storage tank to further

reduce the dissolved oxygen content (5 ppb or less). The tank provides a residence time for

reaction of the oxygen scavengers with the oxygen.

Article II. Deaerator in Bhushan Power Plant

In division-2 of Bhushan power plant, Mechanical Spray Type deaerator is used.

It is situated 25m above the boiled feed pump. Here the feed water enters the deaerator

dome. Baffle plates are installed in this part where the feed water gets sprayed. Since the air

is lighter than the water, the air rises up while the heavier water particles settles down. By

this way the air is separated from the feed water.

The main working of deaerator is to remove oxygen from the feed water and prevents boiler

from corrosion. This is done by adding hydragene in the LP Dozing chamber.

The deaerator specifications are:-

Type Spray type

Pressure 4.5 kg/cm2

Temperature approx. 160 ⁰C

Valves and Actuators

Article I. Valves A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids,

fluidized solids, or slurries) by opening, closing, or partially obstructing various

passageways.

Valves may be operated manually, either by a handle, lever, pedal or wheel. Valves may

also be automatic, driven by changes in pressure, temperature, or flow. These changes may

act upon a diaphragm or a piston which in turn activates the valve, examples of this type of

valve found commonly are safety valves fitted to hot water systems or boilers.

Article II. Actuators

An actuator is a type of motor that is responsible for moving or controlling a mechanism or

system.

It is operated by a source of energy, typically electric current, hydraulic fluid pressure,

or pneumatic pressure, and converts that energy into motion. An actuator is the mechanism

by which a control system acts upon an environment. The control system can be simple (a

fixed mechanical or electronic system), software-based (e.g. a printer driver, robot control

system), a human, or any other input.

Article III. Types

Valves are quite diverse and may be classified into a number of basic types. Valves may

also be classified by how they are actuated:

Hydraulic

Pneumatic

Manual

Solenoid valve

Motor

Article IV. Valves used in Bhushan Plant

There are three spring loaded motorized valve present in the division-2 of Bhushan Power

Plant. Two of them are in Boiler Drum while the remaining is in Main steam line.

Pressure (boiler drum valve) 127 kg/cm2 -for opening & 129 kg/cm2 -for closing.