BLOG ON THERMAL POWER PLANT (Part 3- Construction of the plant and parts)

BLOG ON THERMAL POWER PLANT (Part 3- Construction of the plant and parts)

 

THIS BLOG WILL COVER CONSTRUCTION AND WORKING OF PLANT AND PLANT

 

 THE WORKING OF THERMAL POWER PLANT

WATCH THE ABOVE VIDEO FOR CLEAR UNDERSTANDING

 

BELOW I HAVE UPLOADED THE VIDEO FOR UNDERSTANDING THE PARTS OF THERMAL POWER PLANT

 

Boiler :

 It is used to convert the water into steam where coal is burnt. It is a relatively huge structure with a typical boiler of a 500 MW plant would be equivalent to 5 storied building. The boiler material will mostly made of cast iron to with stand high temperature and pressure. The construction of boiler varies depending upon the heat transfer method used. In a traditional boiler, the boiler has holes on the lower bottom for the coil powder to enter. The coal enters in such a way that , it creates a vortex inside the boiler. This is to ensure that coal spends maximum time before settling down and gets burnt completely. The outer surface of the boiler has thousands of pipes in which water runs through. This is the process in which heat is exchanged. The flue gases rising out of burning coal pass through the super heater as shown in the figure.

 

Turbine :

Steam turbines convert the energy acquired by the steam in to the mechanical energy. These turbines are couple with the alternators which produce the electrical energy from the mechanical energy. Two types of turbines are widely prevalent : impulse turbines and reaction turbines.

In the impulse turbines, steam expands at the nozzles and achieved kinetic energy is used to rotate the blades of the turbine. The blades change the direction of steam but not the pressure. Thus change in momentum can be accounted for rotation of the rotor. In the reaction turbines, steam is partially expanded on the nozzles and remaining expansion takes place during the flow over moving blades.

Generally there are two or three sets of turbines at one go. All the enrgy stored in the steam cannot be obtained at one go from a single turbine. So, there are two or three sets of turbines located which are connected by a shaft. Now the high pressure steam enters into the first turbine, lets call it HP turbine. Once the expansion takes place, the pressure falls. Hence we need to use a turbine designed for lower pressure appropriate to the out coming steam. So the second turbine will be a medium pressure turbine (MP turbine).

Further , in some cases a third turbine is also added to make more energy out of steam and this is called a low pressure turbine. The specifications of turbines are calculated during the plant design and later during operations, same ratings of steam pressure and temperature need to be maintained for optimum operation. Given below is a figure illustrating the construction of the three stage turbine.

 

 Pulveriser :

 To generate the massive amount of heat which is required instantaneously , a lot of coal is to be burnt. If chunks of coal is used, very less surface area of coal is exposed and it takes a lot of space to burn enough coal chunks for required power. As a result, to overcome this problem, coal is pulverized into powder which is as smooth as talc. Now this powder is blown into the boiler. Thus, as powder has a very higher surface area compared to chunks of coal, very large amount of coal can reburnt instantaneously in less volume efficiently. This is the underlying interesting fact for using of a pulveriser.

 

Super heater :

The steam is super heated in order to make it hold more energy and transfer it to the turbine. This job is accomplished by the super heater. Super heater is showed in the boiler schematic. The flue gases coming out of the boiler are used to super heat the steam. 

Economizer :

The water entering into the boiler must have a temperature compatible with the boiler temperature. So, the heat left with the flue gases after super heater is used to heat the water in the economizer. The economizer has convoluted tubes in which water flows and the flue gases flow over these tubes in a closed structure.

Air preheater :

The air used for combustion of the coal is also pre heated by the flue gases so as to take maximum heat from the gases before they diffuse in to the atmosphere. It is also to ensure that the un heated air should not interfere with proper combustion inside the boiler.

Condenser :

As discussed earlier, the job of condenser is to turn the steam from the turbine into water and thereby reducing the amount of water required for each cycle. There are many types of condensers. The familiar ones are Jet type and Surface type. In the jet type , the cooling water and the steam are mixed and the resultant steam water mixture is drawn outside. Surface type uses a different circuit for both and the steam is converted into water and cooling water turns hot. The surface type are the widely prevalent ones.

 

 

 

 

Generators :

The generators also called alternators are coupled with turbines which generate electrical energy. The output of the generator at 11KV is stepped up to higher voltage of 220KV and transmitted through the transmission lines. Here , the interesting area of study is to control the output power of the generator. As the load on the system continuously vary and as the energy cannot be stored, the output of generator has to be varied according to load

     from ..ABDUR REHMAN CHHAPRA...