Boiler Efficiency (Steam Power Plant)

 

 Boiler Efficiency (Steam Power Plant)

There are three types of electrical power stations namely:

a) Hydro electricity

b) Thermal Power Plant

c) Nuclear Power Plant

Hydro electricity is the generation of electricity based on the potential energy of the water in a dam driving or turning the water turbines. 

Thermal Power Plant or Steam Power Plant is the generation of electricity based on the rotation of a steam turbine by the steam that impinges on the blades on the turbine.

The generation of electrical power in the nuclear power plant  is based on energy that is derived or obtained from  radioactive substances.

The generation of   power in b above is the main focus of  Power Machines N5 and Power Machines N6.

The steam that drives the steam turbines is generated from a storage component of the power plant referred to as the boiler.

A boiler is a water storage device. The continuous addition of heat from the burning of fuels such as coal or gas increases the temperature of the water from room temperature to 100 degrees centigrade. 

This is the boiling point of water. Steam emanates from the surface of the boiling water.  

Classification of Steam Power Plant

There are two main types of Steam Power Plants.

a) Basic or Standard Steam Power Plant

b) Improved Steam Power Plant

An Improved  Steam Power Plant is a plant that has:

a) an economiser only

b) economiser and a superheater

c) economiser, a superheater and an air heater

An Imroved Steam  Power Plant utilizes the heat from the flue or products of combustion of the fuel (coal or gas) such that there is a savings in fuel in the everyday operation of the plant.

Usually in the standard or basic power plant, the heat in the flue is allowed to dissipate into the air or environment.

The heat is utilized in each of the components as stated above.

The economiser is a component in which the water is preheated by the flue or products of combustion above room temperature before it is fed into the boiler.

The superheater is a component in the plant in which the heat in the flue is utilized such that the steam produced from the boiler is improved or the temperature of the steam  increased.

The airheater is a component in which the air required for combustion is heated or preheated above room temperature. This heated air contains the oxygen that burns the coal or the gas.

Formula for Boiler Efficiency.

The formula for boiler efficiency depends on the type of Steam Power Plant.

There

a) Standard Steam Power Plant

b) Improved Steam Power Plant

a) Standard Steam Power Plant

The formula for Boiler Efficiency is 

Boiler Efficiency = [(Heat absorbed by the Water)/ (heat supplied by the fuel)] X100%

Heat absorbed by the Water= h2 -h1

h2= enthalpy of steam when steam is released at the surface  of the boiling water

h1= enthalpy of steam at the instant that heat energy is added to the water in the boiler.

heat supplied by the fuel= CVXm

CV=calorific value of the fuel in terms of the heat energy released when 1kg of fuel is completely burnt

m= mass of the fuel that undergoes complete combustion.

The formulas for Standard Steam Power Plant is based on the information given in the Power Machines problem.

a) h2 is based on a constant pressure  formula (Cp) 

b) h2 is based on the formula of dryness fraction.

c) h2 is based on a superheat temperature. (superheat tables)

b) Improved Steam Power Plant

Economiser only

Efficiency= {(Heat absorbed in the economiser)+(Heat absorbed by water in the boiler)}/{Heat supplied by the fuel} X 100%

Economiser and Superheater

Efficiency= {(Heat absorbed in the economiser)+(Heat absorbed by water in the boiler) +(Heat absorded by steam in the superheater}/{Heat supplied by the fuel} X 100%

Economiser, Superheater and Air Preheater

Efficiency= {(Heat absorbed in the economiser)+(Heat absorbed by water in the boiler) +(Heat absorded by steam in the superheater)+(Heat supplied in the Air Preheater)}/{Heat supplied by the fuel} X 100%