A PRESENTATION ON STEAM POWER PLANT

Mister KhanM. Tech

SLIET, Snagrur

Introduction Layout of Steam Power Plant Essential Requirement of SPP Selection of Site Layout and units of modern SPP Coal and Ash handling System Air and gas circuit Boilers Accessories used in SPP Steam Turbine and Steam Turbine Generator Steam Condensers Cooling ponds and cooling towers History of Steam Power plant Existing and Upcoming thermal power plants in India Advantages and Disadvantages of SPP Conclusion

Contents

A Steam Power Station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electric 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.

Some thermal power plants also deliver heat energy for industrial purposes, for district heating, or for desalination of water as well as delivering electrical power.

A large part of human CO2 emissions comes from fossil fuelled thermal power plants; efforts to reduce these outputs are various and widespread.

INTRODUCTION

Rankine Cycle

Reliability Minimum capital cost Minimum operation and maintenance cost Capacity to meet peak load effectively Minimum loss of energy in transmission Low cost of energy supplied to the consumers Reserve capacity to meet future demands

Requirements of SPP Design

Availability of raw material Nature of land Cost of land Availability of water Transport facilities Ash disposal facilities Availability of labour Size of plant Load center Public problems Future Extensions

Selection of Site

Layout of Modern Steam Power Plant

Coal and ash handling circuit- Coal arrives at the storage yard and after necessary handling, passes on to the furnaces through the fuel feeding device. Ash resulting from combustion of coal collects at the back of the boiler removed through ash handling system.

Air and gas circuit- Air taken from atmosphere by forced induced draught fan and passes on to the furnace through the air preheater heated by flue gases which passes to the chimney via the preheater. Flue gases are then passes through Precipitator, Economizer and air preheater before being exhausted to the atmosphere.

Feed water and steam flow circuit- Condensate leaving the condenser is first heated in a closed feed water heater through extracted steam from the lowest pressure extraction point of the turbine. It then passes through the deaerator and a few more water heaters before going in to the boiler through economizer.

Cooling water circuit- To keep maintain the low pressure in condenser. It may be taken from natural gas, lake or sea of may be some water circulate over again.

Units Modern SPP

Coal Handling Circuit

Coal Delivery :- From the supply points the coal may be delivered to power station through rail, road, river or sea.

Unloading:- Coal delivered by truck directly may dump the coal to outdoor storage. If transported by sea unloading equipment like portable conveyors, coal accelerators etc. are used.

Preparation:- if coal delivered in form of lumps the coal preparation carried by:

1. breakers 4. dryers

2. crushers 5. magnetic separators

3. sizers Transfer:- Transfer means handling of coal between the unloading point and the

final storage point from where it discharge to the firing equipment. Belt Conveyor is very suitable means of transporting large quantities of coal over large distance.

1.Inclination at which coal can be elevated- 20˚

2. Average Speed of Belt Conveyor – 60 – 100 meter per minute

3.Load carrying capacity – 50 –100 tonnes/hour and it can easily transfer

through 400m. It is used in medium and large power plants.

Stages in Coal Handling Circuit

Diagram of Belt Conveyor

Storage of coal :- Storage of coal gives protection against the in interruption of coal supplies when there is delay in transportation of coal. There should be no standing water in storage area, Fire fighting equipment should be available, it should be protected against wind erosion.

Inplant Handling:- it refer to coal handling between final storage and the firing equipment . It includes the equipment such as belt conveyors, screw conveyors, Bucket elevators to transfer the coal. Weigh lorries, hoopers and automatic scales used to record the quantity of coal delivered to furnace.

Weighing and Measuring:- To weigh the quantity of coal following equipment are used –

1. Weigh Bridge 2. Belt Scale

3. Weigh Lorry 4. Automatic Scale Furnace Firing:- Since the source of heat is the combustion of fuel, a working

unit must have equipment necessary to receive the fuel and air in proportion as per the boiler steam demand, mix, ignite, and perform other combustion duties such as distillation of volatile from coal prior to ignition.

* Method of furnace firing depends upon the type of fuels and in SPP mainly the

Bituminous Coal is used as fuel because it is one of the best coal type contains

no moisture, easy to crack and ash contents are very low. Volatile matter on dry

ash free basis range from between 10% and 14% to 40% and over. Calorific

Value of Bituminous coal is 6000 kcal/kg.

* Furnace Firing with coal as fuel is done by three methods:

1. Stroker firing- A Stroker is a power operated fuel feeding mechanism.

2. Pulverized Fuel Firing- In this coal is reduced into fine powder with the

help of grinding mill and then projected into combustion chamber with the

help of hot air current .

Ash Handling

Boilers burning pulverized coal generates approx. 80% fly ash and 20% bottom ash. Bottom ash particles are collected under the furnace in a water-filled ash hooper. Fly ash is collected in dust collector with either electrostatic precipitator or a baghouse.

Handling of ash includes:-

1. its removal from the furnace.

2. loading on the conveyors and delivery to the fill or dump where it can b disposed

of by sale or otherwise. Three major factors should be considered for ash disposal as it is very dangerous

for living organism as well as environment :-

1. Plant Site

2. Fuel Source

3. Environmental Regulation

Mechanical handling system- This system is generally employed for low capacity coal fired power plant. Hot ash from boiler furnace is made to fall over belt conveyor after cooling through water then transported to an ash bunker through the belt conveyor.

Hydraulic System- In this system ash is carried with the flow of water with high velocity through a channel and finally dumped in the sump.

Pneumatic System- This system can handle abrasive ash as well as fine dusty material such as fly ash and soot. The exhauster at the discharge creates a high velocity stream which picks up ash and dust and then these are carried in the conveyor pipe.

Steam Jet System- In this case steam at sufficiently high velocity is passed through a pipe carrying dry solid materials of considerable size. A jet of high Pressure steam is passed in the direction of ash travel through a conveying pipe in which the ash from the boiler ash Hooper is fed. The ash is disposed into the ash Hooper

Ash Handling Systems

The constituents of fly ash are- SiO2(30-60%), Al2O3(15-30%), unburnt carbon upto 30%, CaO(1-7%), MgO & SO3 in small amounts. In fly ash the carbon content should be small & silicon content should be high as possible.

Disposal :- It is disposed in two ways

1. Dry System- Fly ash is transferred into a bunker pneumatically.

2. Wet System- Fly ash is mixed with water and sluiced to the settling ponds or

dumping area near the plant. Applications:-

1. It is used in concrete as an add mixture or in-part replacement of cement, fine

aggregate.

2. Fly ash and binder in the form of lime are mixed by auto claving and blocks

are form which are light in weight. These blocks have low thermal

conductivity and stable against temperature.

Fly Ash – Its Composition, Disposal & Application

Air is taken in from atmosphere through the action of a forced or induced draught fan and passes on the furnace through the air preheater, where it has been heated by the heat of flue gases which pass to the chimney via the pre heater

It consist mainly of chimney draught & steam jet draught Chimney draught:-

The small pressure difference which causes flow of gases to take place is termed as draught

Draught may be classified as

1.Natural or chimney draught:-

The chimney is a boiler installation that produces a draught where by the air & gas are forced through the fuel bed. It carries the products of combustion to such a hide before discharging them that they will not injurious to surroundings

2.Artificial draught:-

Artificial draughts are used to produced total static draught varrying from 30-350 mm of water column. It may be a mechanical or steam jet draught

Air and Gas Circuit

3.Forced draught:-

A blower or a fan is installed near the base of boiler to forced the air through the cool bed & other passages through the furnace, economiser etc. It is a possitive pressure draught

4.Induced draught:-

This draught is usually used when the economiser and air preheater are incorporated in the system. It is similar to natural draught

5.Balanced draught:-

It is a combination of forced & induced draught system. The forced draught overcomes the resistance in the air preheater & chain grate stoker while the induced draught fan overcome draught losses through boiler economiser

6.Steam jet draught:-

Steam jet is directed into the smoke box near the stack, the air is induced through the fuels, the grate & ash pit to the smoke box

A boiler is defined as the closed vessel in which steam is produced from water by combustion of fuel

Classification of boilers:-

1.Horizontal, vertical or inclined

2.Fire tube & water tube

3.Externally fired & internally fired

4.Forced circulation & natural circulation

5.High pressure & low pressure boiler

6.Stationary & portable

BOILERS

1.The working pressure & quality of steam required

2.Steam generation rate

3.Floor area available

4.Accessibility for repair and inspection

5.Comparative initial cost

6.Erection facility

7.The fuel & water available

8.Operating & maintainance cost

Selection of boiler

They are the auxiliary plants required for steam boilers for their proper operation and further increase of their efficiency

Feed Pumps It is a pump which is used to deliver feed water to the boiler. They are of two types :

1. Reciprocating pumps

2. Rotary pumps

It is desirable that the quantity of water supplied should be atleast equal to that evaporated and supplied to the engine.

Accessories

It has a function to feed water into the boiler . It is commonly employed for large capacity high pressure boiler . It is 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 feed water.

Injector

It is a device in which the waste heat of the flue gases is utilized for heating the feed water. They are of two types

1. Independent type:-

It is installed in chamber apart from the boiler setting. The chamber is

situated at the passage of the flow of the flue gases from the boiler .

2. Integral type :-

It is the part of boiler heating surface and is installed within the boiler

setting.

Economiser

Its function is to increase the temperature of air before it enters the furnace. It is generally placed after the economizer so the flue gases pass through the economizer and then to the air pre heater . Pre heated air accelerates the combustion and facilitate burning of coal. There are three types of air preheater :

Tubular types Plate type Storage type

Air Preheater

The function is to increase the temperature of the steam above its saturation point. Superheated steam has following advantages: Steam consumption is reduced Losses due to condensation are reduced Erosion of turbine blade is eliminated Efficiency of SPP is increased

They are of two types:- Convective Superheater Radiant Superheater

Superheater

Feed water heating with steam at low pressure then boiler pressure usually raises overall plant efficiency.

Feed water heater may be classified as follows :-

1. Open or Contact heaters-

- Tray Type

- Jet Type

2. Closed or surface heater

Feed Water Heater

They are used to give a supply of pure water as a make up feed for the boilers. Raw water is evaporated by using extracted steam and the condensed to give distilled and pure feed water. They are of two types:

1. Film type evaporator

2. Submerged type evaporator

Evaporator

The steam turbine is a prime mover in which the potential energy of the steam is transformed into kinetic energy and latter in its turn is transformed into the mechanical energy of rotation of the turbine shaft.

Classification of steam turbines:- According to action of steam –

1. Impulse

2. Reaction

3. Combination of impulse and reaction According to no. of pressure stages –

1. Single stage turbine

2. Multistage impulse and reaction turbines According to direction of steam flow-

1. Axial turbine

2. Radial turbine

Steam Turbines

According to no. of cylinder –

1. Single cylinder turbine

2. Double cylinder turbine

3. Three cylinder turbine

4. Four cylinder turbine According to the method of governing-

1. Turbine with throttle governing

2. Turbine with nozzle governing

3. Turbine with bypass governing According to heat drop process-

1. Condensing turbine with generator

2. Back pressure turbine

3. Low pressure turbines

4. Topping turbines

According to steam condition at inlet to turbine –

1. Low pressure turbine (1.2 – 2 ata)

2. Medium pressure (upto 40 ata)

3. High Pressure (above 40ata)

4. Turbines of supercritical pressure (above 225 ata) According to their usage in industry –

1. Stationary turbines with constant speed of rotation

2. Stationary steam turbine

3. Non Stationary turbines with variable speed

The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure turbine at one end, followed by an intermediate pressure turbine, two low pressure turbines, and the generator.

As steam moves through the system and loses pressure and thermal energy it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy.

Superheated steam from the boiler is delivered through 14–16-inch (360–410 mm) diameter piping to the high pressure turbine where it falls in pressure to 600 psi (4.1 MPa) and to 600 °F (320 °C) in temperature through the stage. It exits via 24–26-inch (610–660 mm) diameter cold reheat lines and passes back into the boiler where the steam is reheated in special reheat pendant tubes back to 1,000 °F (500 °C).

The hot reheat steam is conducted to the intermediate pressure turbine where it falls in both temperature and pressure and exits directly to the long-bladed low pressure turbines and finally exits to the condenser.

Steam Turbine Generator

The generator, 30 feet (9 m) long and 12 feet (3.7 m) in diameter, contains a stationary stator and a spinning rotor, each containing miles of heavy copper conductor—no permanent magnets here. In operation it generates up to 21,000 amperes at 24,000 volts AC (504 MWe) as it spins at either 3,000 or 3,600 rpm, synchronized to the power grid. The rotor spins in a sealed chamber cooled with hydrogen gas, selected because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses.

This system requires special handling during start up, with air in the chamber first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly explosive hydrogen–oxygen environment is not created.

The power grid frequency is 60 Hz across North America and 50 Hz in Europe, Oceania, Asia (Korea and parts of Japan are notable exceptions) and parts of Africa.

The electricity flows to a distribution yard where transformers step the voltage up to 115, 230, 500 or 765 kV AC as needed for transmission to its destination.

It is a device in which steam condenses and heat released by steam is absorbed by water. It serves the following purposes: It maintains a very low back pressure on the exhaust side of the piston of the

steam engine or turbine. The steam expands to a greater extend resulting in increase in available heat energy.

It supplies to the boiler pure and hot feed water.

Steam Condenser

Jet Condensers :- The exhaust steam and water come in direct contact with each other and temperature of the condensate is same as that of cooling water leaving the condenser. These condensers are of three types:

1. Parallel Flow Type

2. Counter Flow Type

3. Ejector Type. Surface Condensers:- The exhaust steam and water do not come in to direct

contact. The steam passes over the outer surface of tubes through which a supply of cooling water is maintained. They may b single pass or double pass. Surface condensers are classified on the direction of flow of condensate .

1. Down Flow Type2. Central Flow Type3. Inverted Flow Type4. Regenerative Type5. Evaporative Type

Classifications of Condensers

The condenser transfer the latent heat of the exhaust steam to water exposed to the atmosphere. This water is called circulating or cooling water . The requirement of cooling water is large as 5-8kg/kWh. This means a 1000 MW station will require about 100 thousand tonnes of circulating water per day even with the use og cooling tower

The cooling water supply is made by following types:

1.River or sea

2.Cooling ponds

3.Spray ponds

4.Cooling towers

Cooling Ponds

In SPP the hot water from condenser is cooled in cooling tower so that it can be reused in condenser for condensation of steam. In cooling tower water is made to trickle down drop by drop so that it comes in contact with the air moving in the opposite direction. As a result of this some water is evaporated and is taken away with air. In evaporation the heat is taken away from the bulk of water, which is thus cooled.

Classification of cooling tower Natural Draught Cooling Tower :- The hot water from the condensers is

pumped to the nozzle situated near the bottom. The air enters the Cooling Tower from the air openings provided near the base, rises upward and takes up the heat of the falling water.

Mechanical Draught Cooling Tower :- In these towers the draught of air for cooling the tower is produced mechanically by means of propeller fans. They are of two types-

1. Forced Draught

2. Induced Draught

Cooling Towers

Reciprocating steam engines have been used for mechanical power sources since the 18th Century, with notable improvements being made by James Watt.

The very first commercial central electrical generating stations in the Pearl Street Station, New York and the Holborn Viaduct power station, London, in 1882, also used reciprocating steam engines. The development of the steam turbine allowed larger and more efficient central generating stations to be built.

By 1892 it was considered as an alternative to reciprocating engines. Turbines offered higher speeds, more compact machinery, and stable speed regulation allowing for parallel synchronous operation of generators on a common bus.

Turbines entirely replaced reciprocating engines in large central stations after about 1905. The largest reciprocating engine-generator sets ever built were completed in 1901 for the Manhattan Elevated Railway. Each of seventeen units weighed about 500 tons and was rated 6000 kilowatts; a contemporary turbine-set of similar rating would have weighed about 20% as much.

History of SPP

Name Location Units Capacity (MW)

Vindhyachal Super Thermal Power Station

Madhya Pradesh 6X210, 4X500 3260

Talcher Super Thermal Power Station

Orissa 6 X 500 3000

Amravati Thermal Power Plant

Maharashtra 10 X 270 2700

NTPC Ramagundam

Andhra Pradesh 3X200, 4X500 2600

Chandrapur Super Thermal Power Station

Maharashtra 4 X 210, 3X500 2340

Major Thermal Power Plants In India

Sr. No. Name of Plant Location Capacity (MW)

1. Sangam power Generation Power Ltd.

Allahabad, U.P 2 X 660

2. M.P Power Generation Co Ltd

Satpura, M.P 2 X 250

3. V. S Lignite Power Ltd. Bikaner, Rajasthan

1 X 35

4. Hindalco Industries Ltd. U.P 999.7

5. Durgapur Projects Ltd. West Bengal 2 X 250

Upcoming Thermal Plants in India

NTPC Limited (formerly National Thermal Power Corporation) is the largest state-owned power generating company in India. Forbes Global 2000 for 2010 ranked it 341th in the world.

It is an Indian public sector company listed on the Bombay Stock Exchange although at present the Government of India holds 84.5% (after divestment the stake by Indian government on 19th October, 2009) of its equity. With a current generating capacity of 34894 MW, NTPC has embarked on plans to become a 75,000 MW company by 2017.

It was founded on November 7, 1975. The total installed capacity of the company is 34894 MW (including JVs) with

15 coal based and 7 gas based stations, located across the country. Although the company has 18.79% of the total national capacity it contributes

28.60% of total power generation due to its focus on high efficiency.

National Thermal Power Corporation

S.No City State Capacity (MW)

1. Singrauli Uttar Pradesh 2,000

2. Korba Chhattisgarh 2,600

3. Ramagundam Andhra Pradesh 2,600

4. Farakka West Bengal 2,100

5. Vindhyachal Madhya Pradesh 3,260

6. Rihand Uttar Pradesh 2,000

7. Kahalgaon Bihar 2,340

8. Dadri Uttar Pradesh 2,310

9. Talcher Orissa 3,000

10. Unchahar Uttar Pradesh 1,050

11. Talcher Thermal Orissa 460

12. Simhadri Andhra Pradesh 1,500

13. Tanda Uttar Pradesh 440

14. Badarpur Delhi 705

15. Sipat Chhattisgarh 1660

Total 25,815

NTPC Coal Based Power Plants

Rapid response to changing load. A portion of steam generated can be used as a process steam in different

industries. Can be located conveniently near the load center, hence transmission cost are

reduced . Steam engines and turbines can work under 25% of overload continuously. Fuel used is cheaper and easily available. Less space required in comparison to HPP. Cheap Production and cheap initial cost as compare to diesel power station.

Advantages of SPP

Maintenance and operating costs are high. The cost of plant increases with increase in temperature and pressure. Long time required for erection and putting into action. A large quantity of water is required. Great difficulty experienced in coal handling. The plant efficiency decreases rapidly below 75% load. Presence of troubles due to smoke and heat in the plant. Pollution problems.

Disadvantages

Sector Hydro Thermal Nuclear Total

Central 3455 7574 880 4909

State 5814.7 4933 - 10747.7

Private 550 17038.5 - 17588.5

Total 9819.7 29545.5 880 40245.2

Sector-wise / type-wise capacity addition programme during ninth plan (Figures in MW)

Continuous deterioration in performance of thermal power stations had been observed during early 80's. Therefore, Renovation and Modernisation Schemes(R&M Schemes) were drawn and executed for improving the performance of existing thermal power stations.

Pollution control measures in these power stations being a capital-intensive activity, it accounted for major portion-around 40% of Rs. 12 Billion kept for R&M schemes under phase-I.

During phase-I, 163 units of 34 thermal power stations were covered. As a result of R&M schemes these achieved 10,000 million units of additional generation per annum against the target of 7000 million units.

Encouraged by the results achieved, R&M phase-II programme is presently under progress. Total estimated cost of these works is Rs. 24 Billion.

Conclusion

Most of the Electricity Boards or other generating agencies are facing financial constraints to carry out R&M activities. Therefore, this area has to be taken on priority to arrange financial assistance.

Several organizations have carried out Energy audits of thermal power plants with a view to suggest measures to improve their operational efficiency and to identify areas having wasteful use of energy.

Steps have been suggested to reduce energy losses and their implementation is being monitored vigorously.