Thermal power station

INTRODUCTION AND STEAM POWER STATION

Definition :- "A generating station which converts heat energy of coal combustion into electrical energy is known as a steam power station."

1) Site selection:

➢ The site should be nearest to the coal mines to reduce transmission cost.
➢ Large quantity of cooling water should be available.
➢ Land should not be rocky and marshy.
➢ Chimney of the plant should not obstruct the flying aeroplanes.
➢ The site should not be surrounding by residential building.
➢ If the station is located near the load centre. The distribution cost reduces.
➢ Facility for disposal of ash.

2) Schematic arrangement of steam power station.

3) The main and auxiliary equipment in T.P.P. are

(a) Coal and ash handling plant:

➢ Incoming coal is stored in the coal storage plant. The coal is delivered to the coal handing plant, where it is pulverized in order to increase it’s surface exposure. Thus promoting rapid combustion using large quantity of air.
➢ The pulverized coal is fed to the boiler by belt convenors.

Advantages of pulverization:

1) Gives more surface area for a given more of coal.

2) Fast combustion or more area is exposed to heat and oxygen.

3) Boiler can be stored quickly.

4) Fast response to load changes.

➢ The coal is burnt in the boiler and the ash produced after the completed combustion of
coal is removed to the ash handing plant and delivered to the ash storage plant for
disposal.
➢ Indian coal has ash content of 20 to 40%.
➢ In thermal power plant bituminous coal is used because of low ash content.

(b) Steam generator or boiler:

           Boiler is a device, where in water is converted into steam by utilizing the heat of combustion.
(1) Water tube boiler
➢ The water flows through the tubes and hot combustion gases flow over there tubes.
➢ There boilers are used universally for such plants.
• Features of water tube boiler:
I. Method of water circulation.
II. Improve method of heating.
III. Easy removal of ash from inside the tube.
(2) Fire tube boiler:
➢ The hot combustion gas flow through the tube water is surrounded by the fire tube.

(c) Super heater:

A super heater is a device which raises the temperature of the steam much above
the boiling point of water. In super heater heat is taken from flue gases normal radiant type of heat transfer method is used. It is placed between and turbine. It improves efficiency of plant.
• The use of super heater :
 a) Reduces the steam consumption per given output.
 b) Reduce the condensation loss.
 c) Eliminates the erosion of steam turbine blades due to absence of moisture.
 d) Improve overall efficiency.

(d) Economizer :

Economizer mainly consist of closely spaced parallel tubes through which feed
water on it’s way to boiler flows and the flue gases flow outside the tubes. Some of the heat energy of the flue gases is recovered by heating the feed water to saturation but, not raising boiler efficiency.

(e) Air preheater:

An air preheater increases the temp. 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 preheated before supplying to the boiler furnace. Air pre heaters are placed in between economizer and chimney. The efficiency of boiler is increased.

 (f) Steam turbine:

Definition:- A “steam turbine” may be defined as a rotating m/c , which converts the energy contained in steam in to mechanical energy or rotary energy.

(i) Impulse turbine
➢ The steam expands completely in stationary (fixed) nozzle, the pressure over the moving blades remains constant. So, the steam attains a high velocity and impinges against the moving blades. This result in impulsive force on the moving blades which sets the rotor rotating.
(ii) Reaction turbine
➢ Here, the nozzle is taken moving, as the steam flows from nozzle it wander with the fixed blades and reaction force is produced. So, it sets rotor in motion.

(g) condenser:

➢ A condenser is a device which condenses. The steam at the exhaust of turbine. It serves two important functions.
1) It create 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 prime mover.
2) Condensed steam can be used as feed water in the boiler. It improves power plant
efficiency.

(h) Cooling towers:

➢ A condenser is a device in which exhaust steam from steam turbine is condensed and The heat energy given by the steam during condensation is taken up by the cooling tower.
• Types of cooling tower
➢ Natural draught
➢ Forced draught
➢ Induced draught

(i) Feed water heater:

The steam coming out of the turbine is condensed and the condensate is fed back to the boiler as feed water.
➢ It is necessary to heat the feed water before feeding it to the boiler for the following
reasons:
 1) Feed water heating improver the overall plant efficiency.
 2) The dissolved oxygen and carbon dioxide are removed in the feed water heater.
 3) The quantity of steam produced by the boiler is increased.
 4) Thermal stresses due to cold water entering the boiler are eliminated. 

(j) Generator :

➢ Each alternator is coupled to a steam turbine and converts mechanical energy mechanical energy of the turbine into electrical energy.
➢ Alternator used in thermal power plants are of usually z- pole (or) pole running at 3000 rpm (or) 1500 rpm for 50Hz operation.

(k) Exciter :

➢ Exciter are nothing else but the D.C. generator used to supply field system (rotor).
➢ They are mounted on the same shaft of the alternator.
➢ The capacity of the same exciter is about 0.5% to 3% of the main alternator capacity.

(l) Electrostatic precipitator :

➢ The use of electrostatic precipitator is to remove fine, dust particles from flue gas. It is
connected to high D.C. voltage of about 30 kv . It is placed between combustion chamber and
chimney.

Advantages of steam power plants 

➢ Power station can be located near the load centers.
➢ It requires less space as compared to hydro electric power station.
➢ Requires less transmission and distribution.
➢ Long seasons will not affect the power generation as hydel.

Disadvantages of steam power plants

➢ It pollutes the atmosphere due to production of large amount of smoke and fumes.
➢ It is costlier in running cost as compared to hydro electric plant.

Efficiency of steam power station

The overall efficiency of a steam power station is quite low (about 29%) due to two main
reasons.
a) Huge amount of heat is lost in the condenser.
b) Heat losses occur at various stages of the plant.

➢ Thermal efficiency :

The ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of combustion of coal is known as “ thermal efficiency ” of steam power plant.

 

➢ Overall efficiency:  

The ratio of heat equivalent of electric output to the heat of combustion of coal is   known as overall efficiency of steam power station. 

 

To understand it full in hindi just click here

Hydro power plant click here

Thank You For Watching, to get updated through this type of posts pls. Follow our blogs.