STEAM POWER PLANT

SARDAR PATEL COLLEGE OF ENGINEERING

ELECTRICAL DEPARTMENT

Topic : Steam Power Plant Subject: Electrical Power Generation

A steam power plant converts the chemical energy of the fossil fuel (Coal) into mechanical energy/electrical energy.This is done by raising the steam in the boilers, expanding it through the turbines and coupling the turbines to the generators which converts mechanical energy to electrical energy.Purposes of Steam Power Plant 1. to produce electric power 2. to produce steam for industrial processes like textile, food manufacturers, paper mills etc.

Introduction

LAW OF CONSERVATION OF ENERGYChemical energy of fuelHeat energy in furnaceHeat energy of medium waterKinetic energy of turbine rotorElectromotive force Electricity generation

Division of a Steam power plantCoal Handling Plant Water Treatment Plant Fuel and Ash Plant Feed Water and Steam PlantCooling Water Plant

Coal and Ash handling plant:Coal arrives at the storage yard and after necessary handling passes to the furnace through fuel feeding device. Ash after combustion collects at the back of the boiler and is removed to the ash storage yard.Air and Gas handling plant:Air is taken in from the atmosphere through the action of a forced or induced draught fan and passes on to the furnace through the air preheater, where it has been preheated by the flue gases which pass to the chimney via preheater. Feed water and Steam flow plant:Condensate leaving the condenser is first heated in a closed feed water heater through extracted steam from the lowest pressure extraction point of turbine. -deaerator- economiser -boiler.

Coal Handling System

Wagon Tippler

ASH HANDLING PLANT

The Ash from the boiler is collected in two forms:Bottom Ash(Slurry) Its a waste which is dumped into a Ash PondFly ash: Fly ash is separated from Flue Gases in ESP(Electro static Precipitator).

Fly Ash & Flue GasesEconomizer

ESP

Bottom ash(wet ash)Ash Pond Boiler

Cylo

ChimneyFly ashFlue GasesCement Factory

In Boiler the water circulates due to difference in density of water in the lower temp. and higher temperatures of boilerWet steam from boiler is heated up in Superheater----Prime mover---HP turbine---Superheater----LP turbine-----condenser ---hot well.Cooling water circuit: The cooling water supply to the condenser helps in maintaining a low pressure in it. Water may be taken from a natural source.

Components of Steam Power PlantBoiler 7. Boiler feed pumpSuperheater 8. Wagon TipplerReheater9. Crusher houseEconomiser10. Coal MillAir-heater11. Induced draught fan2. Steam Turbine12. Ash Precipitators3. Generator13. Boiler Chimney4. Condenser14. Forced draught fan5. Cooling Tower15. Water treatment plant6. Circulating Water Pump 16. Control room 17. Switch yard

Steam generating plantThe steam generating plant consists of a boiler for the production of steam and other auxiliary equipment for the utilization of flue gases1) Boiler: The heat of combustion in the boiler is utilized to convert water into steam at high temperature and pressure

Boiler at Warnakbori Thermal Power Station

Steam generating plant2) Super heater: The steam produced in boiler is wet and is passed through a super heater where it is dried and superheated. Hence Increases efficiency

Steam generating plant3) Economizer: Its essentially a feed water heater and derives heat from the flue gases

Steam generating plant4) 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 drought fan and is passed through air preheater before supplying to the boiler furnace.

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

Turbo Machine is defined as a device that extracts energy from a continuously flowing fluid by the dynamic action of one or more rotating elements .The prefix turbo is a Latin word meaning spin or whirl implying that turbo machines rotate in some way.

Turbine Full View

A steam turbine is mainly used as an ideal prime mover in which heat energy is transformed into mechanical energy in the form of rotary motion.

A steam turbine is used in Electric power generation in thermal power plants. Steam power plants.To propel the ships, submarines.

In steam turbines, the heat energy of the steam is first converted into kinetic (velocity) energy which in turn is transformed into mechanical energy of rotation and then drives the generator for the power generation.

Classification of Steam TurbinesBased on action of steam or type of expansion:Impulse or velocity or De Laval turbineReaction or pressure or Parsons turbine Combination turbineBased on number of stages:Single stage turbine 2. Multi-stage turbineBased on type of steam flow:Axial flow turbine 2. Radial flow turbine

Steam Turbines

Impulse turbine (De Laval Turbine)

Working Principle of Impulse TurbineThe steam is made to fall in its pressure by expanding in a nozzle. Due to this fall in pressure, a certain amount of heat energy is converted into kinetic energy, which sets the steam to flow with a greater velocity. The rapidly moving particles of the steam enter the rotating part of the turbine, where it undergoes a change in the direction of motion, which gives rise to a change of momentum and therefore a force. This constitutes the driving force of the turbine.

Impulse Turbines (De Laval Turbine)

In this type of turbine, steam is initially expanded in a nozzle from high pressure to low pressure. High velocity jet of steam coming out of the nozzle is made to glide over a curved vane, called Blade.

The jet of steam gliding over the blade gets deflected very closely to surface. This causes the particles of steam to suffer a change in the direction of motion, which gives rise to a change of momentum and therefore a force, which will be centrifugal in nature.

Resultant of all these centrifugal forces acting on the entire curved surface of the blade causes it to move.

Reaction steam TurbinePrinciple of working -In this type of turbine, the high pressure steam does not initially expand in the nozzle as in the case of impulse turbine, but instead directly passes onto the moving blades.Blade shapes of reaction turbines are designed in such a way that the steam flowing between the blades will be subjected to the nozzle effect. Hence, the pressure of the steam drops continuously as it flows over the blades causing, simultaneous increase in the velocity of the steam.

Impulse TurbineReaction TurbineThe steam expands (pressure drops) completely in nozzles or in the fixed bladesThe steam expands both in the fixed and moving blades continuously as it flows over them The blades have symmetrical profile of uniform sectionThe blades have converging (aerofoil) profileThe steam pressure while passing over the blades remains constantThe steam pressure while passing over the blades gradually drops Because of large initial pressure drop, the steam and turbine speeds are very high Because of gradual pressure drop, the steam and turbine speeds are lowThe nozzles are fitted to the diaphragm (the partition disc between the stages of the turbine)The fixed blades attached to the casing serve as nozzles

Difference between Impulse & Reaction Turbines

Impulse TurbineReaction TurbinePower is obtained only due to the impulsive force of the incoming steamPower is obtained due to impulsive force of incoming steam as well as reaction of exit steamSuitable for small capacity of power generation & occupies less space per unit powerSuitable for medium & high capacity power generation and occupies more space per unit powerEfficiency is lesserEfficiency is higherCompounding is necessary to reduce speedCompounding is not necessary

Compounding of Impulse Turbines

As the complete expansion of steam takes in one stage (i.e., the entire pressure drop from high pressure to low pressure takes place in only one set of nozzles), the turbine rotor rotates at very high speed of about 30,000 rpm (K.E. is fully absorbed).

High speed poses number of technical difficulties like destruction of machine by the large centrifugal forces developed, increase in vibrations, quick overheating of blades, impossibility of direct coupling to other machines, etc.

To overcome the above difficulties, the expansion of steam is performed in several stages.

Utilization of the high pressure energy of the steam by expanding it in successive stages is called Compounding.

Methods of Compounding: Velocity compounding (Curtis Impulse Turbine) Pressure compounding Pressure-velocity compounding

Velocity compounding

Comprise of nozzles and two or more rows of moving blades arranged in series. In between two rows of moving blades, one set of guide (fixed) blades are suitably arranged.Guide (fixed) blades are fixed to casing and are stationary.

Pressure Compounding

Pressure-Velocity Compounding(Combined Impulse Turbine)Total pressure drop is divided into two stages & the total velocity obtained in each stage is also compounded

Steam turbine governing systemTo control the speed of turbineThrottle GoverningNozzle GoverningBy-Pass Governing

Throttle governing

Nozzle Governing

By-pass Governing

AlternatorSteam turbine is coupled to an alternator which converts the mechanical energy to electrical energy

The electrical output of the alternator is delivered to the bus bars through transformer, circuit breakers and isolators.

Feed WaterThe condensate from the condenser is used as feed water to the boiler.The water that may be lost in the cycle is made up from the external sourceThe feed water on its way to boiler gets heated up by water heaters and economiser.This helps to improve the overall efficiency of the plant

Selection of Site Availability of raw material.Nature of land.Cost of land.Availability of water.Transport facilitiesAsh disposal facilitiesAvailability of labourSize of plantLoad centre Public ProblemsFuture Extension

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