A steam power plant as shown in the below schematic, which consists of a Boiler,

Question

A steam power plant as shown in the below schematic, which consists of a Boiler, a Turbine, a condenser and a pump as four components. The turbine has a power output of 220 MW and the pump consumes 10 MW to keep the system to be operated. The plant consumes coal at a rate 36 tons /hour. The coal has its heating value of 30,000 kJ/kg.

Fig. 1 Schematic of a steam power plant

1.      Describe the functions of each component and the entire process of the steam power plant;

2.      Determine the plant efficiency

3.      How much heat is discharged from condenser?

4.      If the water is used for cooling in the condenser and only is allowed to rise 5 degree C in temperature, determine the rate of water in terms of tons/hour.

Explanation / Answer

1)

PUMP

It is used to pump the water into the boiler

BOILER

Here the water to heated to get transformed into steam(by doing so we increase the enthalpy of steam) which has ability to do work

TURBINE

Here the steam energy is exploited and transferred to Mechanical/Electrical energy by using an Impluse or Reaction Turbine

CONDENSER

The steam from the turbine exits is at a higher temperature.Here the steam is cooled by using a coolant (typically water but at very low temperature) and the recoverd steam is again pump with some fresh water into the boiler and the cycle continues

2)

Plant efficiency = Work input/Heat Input

Work output = Turbine output - Pump input = 210 MW

Heat Input = mass of Coal Consumed*Calorific Value

mass of Coal Consumed = 36 tons/hr = 36*907.19/3600 = 9.702 kg/s

Heat Input(Qin) = 9.702*30000 kJ/s

Heat Input = 272157 kW = 272.157 MW

Plant efficiency = 210/272.157 = 0.7716 or 77.16%

3)

Heat Dischared from the condenser (Qout)

Qin = Qout + W

272.157 = Qout + 210

Qout = 62.157 MW

4)

This dischared heat should be observed by coolant water

Qout = m*Cp*dT

m is the mass flow rate of coolant water

Given

dT = 5

Cp = 4.18 kJ/kg

m*4.18*5= 62157

m = 2974.02 kg/s

m = 2974.02*3600/907.19 tons/hr

m = 11801.79 tons/hr

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