Introduction to CFPP

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INTRODUCTION TO POWER PLANTS

Electricity in bulk quantity is produced in power plants. The types of power plants are:

(1) Thermal

(2) Hydel

(3) Nuclear

(4) Gas turbine power plants

(5) Combined Cycle power Plants

(6) Diesel Engine

(7) Wind power plant

(8) Solar power plant

THERMAL POWER STATION (STEAM POWER STATION)

A generating station which converts heat energy of coal combustion into electrical energy is known as a steam power station

• Steam power station basically works on the Rankine cycle. Steam is produced in the boiler by utilising the heat of coal combustion. The steam is then expanded in the prime mover (i.e steam turbine ) and is condensed in a condenser to be fed in to the boiler again. The steam turbine drives the alternator which converts mechanical energy of the turbine into electrical energy. This type of power station is suitable where coal and water are available in abundance and a large amount of electric power is to be generated.

RANKINE CYCLE

This is the simplest theoretical vapour cycle, which is the basis for operation of a steam plant. Superheated steam from boiler is fed in to the prime mover (Turbine) and is expanded there. After which it enters the condenser emerging as condensate. With the help of a pump this condensate is again fed into the boiler.

• Rankine cycle is a heat engine with vapor power cycle. The common working fluid is water. The cycle consists of four processes.

1. Isentropic expansion (Steam turbine)

2. Isobaric heat rejection (Condenser)

3. Isentropic compression (Pump)

4. Isobaric heat supply (Boiler)

SCHEMATIC ARRANGEMENT OF THERMAL POWER PLANT

MAIN PARTS OF POWER PLANT1. Steam generating Unit (Boiler)

2. Steam turbine Unit

3. Alternator Unit

4. Electro Static Precipitator (ESP)

5. Coal Handling Plant (CHP)

6. Ash handling system (AHP)

7. Air compressor system

8. Circulating Water pump house

9. De mineralized (DM) water plant

10.Make up water pump house

11. Electrical switchgear

12.Electrical Switch yard

MAIN CIRCUITS OF POWER PLANT

1. Fuel and ash circuit2. Air and gas circuit3. Feed water and steam circuit4. Cooling water circuit

FUEL AND ASH CIRCUIT

This circuit deals mainly with feeding the boiler with coal for combustion purposes and taking care of the ash that is generated during the combustion process and includes equipment and paraphernalia that is used to handle the transfer and storage of coal and ash.

AIR AND GAS CIRCUIT

we know that air is one of the main components of the fire triangle and hence necessary for combustion. Since lots of coal is burnt inside the boiler it needs a sufficient quantity of air which is supplied using either forced draught or induced draught fans. The exhaust gases from the combustion are in turn used to heat the ingoing air through a heat exchanger before being let off in the atmosphere. The equipment which handles all these processes fall under this circuit.

FEED WATER AND STEAM CIRCUIT

This section deals with supplying of steam generated from the boiler to the turbines and to handle the outgoing steam from the turbine by cooling it to form water in the condenser so that it can be reused in the boiler plus making good any losses due to evaporation etc.

COOLING WATER CIRCUIT

This part of the thermal power plant deals with handling of the cooling water required in the system. Since the amount of water required to cool the outgoing steam from the boiler is substantial, it is either taken from a nearby water source such as a river, or it is done through evaporation if the quantity of cooling water available is limited.

1. COAL HANDLING SYSTEM:

The coal is transported to the power station by road or rail and is stored in the coal storage plant. Storage of coal is primarily a matter of protection against coal strikes, failure of transportation system and general coal shortages. From the coal storage plant, coal is delivered to the coal handling plant where it is pulverised (i.e., crushed into small pieces) in order to increase its surface exposure, thus promoting rapid combustion without using large quantity of excess air. The pulverised coal is fed to the boiler by belt conveyors. The coal is burnt in the boiler and the ash produced after the complete combustion of coal is removed to the ash handling plant and then delivered to the ash storage plant for disposal. The removal of the ash from the boiler furnace is necessary for proper burning of coal.

2. STEAM GENERATING PANT:

Boiler:

The heat of combustion of coal in the boiler is utilized to convert water into steam at high temperature and pressure. The flue gases from the boiler make their journey through super- heater, economizer, air pre-heater and are finally exhausted to atmosphere through the chimney.

Super heater:

The steam produced in the boiler is wet and is passed through a superheater where it is dried and superheated ( i.e., steam temperature increased above that of boiling point of water) by the flue gases on their way to chimney. Superheating provides two principal benefits. Firstly, the overall efficiency is increased. Secondly, too much condensation in the last stages of turbine (which would cause blade corrosion) is avoided. The superheated steam from the superheater is fed to steam turbine through the main valve.

Economiser:

An economiser is essentially a feed water heater and derives heat from the flue gases for this purpose. The feed water is fed to the economiser before supplying to the boiler. The economiser extracts a part of heat of flue gases to increase the feed water temperature.

Air preheater:

An air preheater increases the temperature of the air supplied for coal burning by deriving heat from flue gases. Air is drawn from the atmosphere by a forced draught fan and is passed through air preheater before supplying to the boiler furnace. The air preheater extracts heat from flue gases and increases the temperature of air used for coal combustion. The principal benefits of preheating the air are : increased thermal efficiency and increased steam capacity per square metre of boiler surface.

3. STEAM TURBINE:

The dry and superheated steam from the superheater is fed to the steam turbine through main valve. The heat energy of steam when passing over the blades of turbine is converted into mechanical energy. After giving heat energy to the turbine, the steam is exhausted tothe condenser which condenses the exhausted steam by means of cold water circulation.

4. CONDENSER:

A condenser is a device which condenses the steam at the exhaust of turbine. It serves two important functions. Firstly, it creates a very low pressure at the exhaust of turbine, thus permitting expansion of the steam in the prime mover to a very low pressure. This helps in converting heat energy of steam into mechanical energy in the prime mover. Secondly, the condensed steam can be used as feed water to the boiler.

5. ALTERNATOR:

The steam turbine is coupled to an alternator. The alternator converts mechanical energy of turbine into electrical energy. The electrical output from the alternator is delivered to the bus bars through transformer, circuit breakers and isolators.

6. STEP UP TRANSFORMER:

A step-up transformer which step-up the generation voltage for transmission of power to grid.7. SWITCHGEAR EQUIPMENT:

It houses such equipment which locates the fault on the system and isolate the faulty part from the healthy section. It contains circuit breakers, relays, switches and other control devices.

8. FEED WATER:

The condensate from the condenser is used as feed water to the boiler. Some water may be lost in the cycle which is suitably made up from external source. The feed water on its way to the boiler is heated by water heaters and economiser. This helps in raising the overall efficiency of the plant.

9. COOLING ARRANGEMENT:In order to improve the efficiency of the plant, the steam exhausted from the turbine is condensed by means of a condenser. Water is drawn from a natural source of supply such as a river, canal or lake and is circulated through the condenser. The circulating water takes up the heat of the exhausted steam and itself becomes hot. This hot water coming out from the condenser is discharged at a suitable location down the river. In case the availability of water from the source of supply is not assured throughout the year, cooling towers are used. During the scarcity of water in the river, hot water from the condenser is passed on to the cooling towers where it is cooled. The cold water from the cooling tower is reused in the condenser.

10. WATER TREATMENT PLANT:Boilers require clean and soft water for longer life and better efficiency. However, the source of boiler feed water is generally a river or lake which may contain suspended and dissolved impurities, dissolved gases etc. Therefore, it is very important that water is first purified and softened by chemical treatment and then delivered to the boiler. The water from the source of supply is stored in storage tanks. The suspended impurities are removed through sedimentation, coagulation and filtration. Dissolved gases are removed by aeration and degasification. The water is then ‘softened’ by removing temporary and permanent hardness through different chemical processes. The pure and soft water thus available is fed to the boiler for steam generation.

11. ASH HANDLING SYSTEM:

Fly ash collection:

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan. The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent transport by trucks or railroad cars .

Bottom ash collection and disposal:

At the bottom of the furnace, there is a hopper for collection of bottom ash. This hopper is always filled with water to quench the ash and clinkers falling down from the furnace. Some arrangement is included to crush the clinkers and for conveying the crushed clinkers and bottom ash to a storage site . Ash extractor is used to discharge ash from Municipal solid waste fired boilers.

BOILER

• Types of fluidized bed combustion boilers1. Atmospheric fluidized abed combustion

(AFBC / Bubbling bed)2. Circulating fluidized bed combustion (CFBC)

BOILER1. Economizer2. Water walls3. Riser tubes4. Drum5. Super heater6. Re-heaters7. De-super heaters8. Air heaters9. Coal feeding system10. Coal handling system11. Ash handling system12. Secondary air (SA) fan13. Primary air (PA) fan14. Induced air (ID) fan

TURBINE1. Condenser 2. De-aerator3. Condensate extraction pump (CEP)4. Boiler feed pump (BFP)5. Ejectors6. Lubrication oil system7. LP heaters8. HP heaters9. Auxiliary cooling water system

ELECTRICAL

1. Generator2. Excitation system3. Generator Transformer4. Unit Auxiliary Transformer5. Station Transformer6. Auxiliary Distribution Transformers7. Various levels of switchgears8. Variable frequency drives 9. Motors10. Protective Relays11. Battery system (Direct current (DC))

INSTRUMENTATION

1. Distributed Control System (DCS)– SYSTEMS (HMI)– Uninterruptible power supply (UPS)– Controllers– A-D converters– D-A converters– Comparators– Transducers

TYPES OF VALVES1. Gate valves2. Globe valves3. Ball valves4. Plug valves5. Butterfly valves6. Diaphragm valves7. Check valves8. Safety valves9. Knife valves

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