Thermal Power Plant

What are the main circuits in the Thermal Power Plant?

Answer:Thermal Power plant consists of four main circuits, they are:

·                     Feed water and steam flow circuit

·                     Coal and ash circuit

·                     Air and gas circuit

·                     Cooling water circuit

Steam power plant works on which cycle?

Answer: Steam power plant works on the principle of Rankine Cycle

Why Thermal Power Plants are always situated by the side of rivers or lakes?

Answer: Thermal Power Plants are situated close to the rivers or lakes because to meet the large quantity of the water requirement. Water is required in the steam power plants

·                     steam in the boiler

·                     for cooling purposes such as in condensers

·                     as carrying medium such as in disposal of ash

·                     for drinking purpose

What is the purpose of deaerator in steam power plant?

Answer: The presence of dissolved gases like oxygen and carbon dioxide in water makes the water corrosive, as they react with metal and forms iron oxide. The solubility of the gases in the water decreases with increase in the temperature and becomes zero at boiling point or saturation point.The purpose of the deaerator is to reduce the dissolved oxygen content in the condensate ( feed water) by increasing its temperature. These gases are removed in the deaerator  by heating the feed water to saturation temperature through the bled steam from the turbine.

Why cooling towers require in the Steam power plant ?

Answer: Cooling towers cool the warm water discharged from the condenser and feed the cooled water back to the condenser. There are two types of cooling methods provided in the cooling towers, they can be either wet type or dry type

Wet type Cooling towers: In wet cooling towers warm water from the condenser are made to spray on slats or horizontal bars and air is passed from bottom, as the water splashes down from one slat to other due to gravity air and water mixes and heat is rejected in to the air

Dry type Cooling tower:

 Dry type towers are employed where the cooling water is not available in plenty. In dry type warm water from condensate is made to flow through the finned tubes over which cooling air is passed. Heat is rejected to air as water is cooled

Why are feed water heaters are used?

Answer:Regenerative Feedwater heaters are employed in steam power plants to improve the cycle efficiency. Also it increases the steam flow rate and reduces the steam flow to the condenser. They raise the temperature of the feed water before it enters the economizer

What is the Thermal efficiency of steam power plant?

Answer: Thermal efficiency of steam power plant is defined as the ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of combustion. Generally Thermal efficiency of the steam power plant will be in the range of 30-35%

What is the overall efficiency of the Thermal Power Plant or Steam Power Plant?

Answer: Overall efficiency of the system is defined as the ratio of heat equivalent of electrical output to the heat of combustion. Generally Overall efficiency of the steam plant will always be less than the thermal efficiency of the steam plant, it will be of the order of 29-33%

Overall efficiency of steam plant is determined by multiplying the thermal efficiency of the plant with efficiency of the generator (electrical efficiency)

Why the Thermal efficiency of the steam power plant is quite low?

Answer: In Steam power station, more than 50% of the total heat of combustion is lost as heat rejected to the condenser and the loss is unavoidable as the heat energy cannot be converted in to mechanical energy with out a drop in temperature. Steam in the condenser is at lowest temperature. This is the reason that the thermal efficiency of the power plant is quite low.

On what factors efficiency (thermal) of the steam plant depends?

Answer: Efficiency of the thermal plant depends on three factors, they are

1.             pressure of steam entering the turbine

2.             temperature of the steam entering the turbine

3.             pressure in the condenser

Thermal efficiency increases with increase in temperature and pressure of the steam entering the turbine. For this reason high temperature and pressure are used. Thermal efficiency is effectively increased by decreasing the pressure in the condenser, so pressure in the condenser is kept as low as possible.Thermal efficiency also increases by reheating the steam between turbine stages