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How to calculate Boiler Efficiency?

 Boiler Efficiency 


Performance Evaluation of Boiler:-

The performance parameter of boiler like evaporation ratio and the efficiency deteriorates with time due poor combustion, heat transfer surface fouling and poor maintenance and operation. Even for a new boiler, reasons such as a deteriorating fuel quality, water quality etc. can result in a poor boiler Performance. Evaporation ratio and boiler efficiency helps to find out the deviation of boiler efficiency.

Boiler Evaporation ratio:-
Boiler Evaporation ratio, is also known as a steam to fuel ratio is a common and simple indicator for boiler Performance trending.

The typical valve of evaporation ratio on a different types of fuel used are as follows:-

  • Biomass fired boiler    :   2.0 to 3.0
  • Oil fired boiler              :   13.5 to 14.5
  • Coal fired boiler           :    4.0 to 5.5
  • Gas fired boiler            :    11.0 to 13.0

Boiler Efficiency:-

The thermal efficiency of boiler is defined as the percentage of heat input is effectively utilized to generate steam. 

Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel.

This is also known as the "input-output method" due to the fact that its only needs the useful output (steam) and the heat input for evaluating the efficiency. This efficiency can be evaluated by the using following formula. 

    Boiler efficiency=(Heat Output÷Heat Input)×100

Parameter to be monitored for the Calculation of the boiler efficiency:

Quantity of steam Generated per hour(Q) in kg/hr.

Quantity of fuel used per hour (q) in kg/hr 

Working pressure in kg/cm2 (g) and superheat temperature in any. 

The temperature of feed water (°C). 

Type of fuel and gross calorific valve of the fuel (GCV) in kcal/kg of fuel.


Boiler efficiency(n)=[{Qx(hg - hf)}÷q×GCV]×100

 

Where,

hg = enthalpy of saturated steam in          kcal/kg of steam.

hf = enthalpy of feed water  in kcal/kg of water

The fuel calorific value may be gross or net or accordingly, the efficiency reported is referred to as efficiency on GCV or NCV basis.

Let's take a example, 

Example:-

Find out the efficiency and evaporation ratio of boiler with the Data given below:-

Type of boiler                            : Coal Fired

Quantity of steam Generated :  8 TPH

Steam Pressure/temp.              :  10 kg/cm2(g)/                                                                          180°c

Quantity of fuel consumed     : 1.8 TPH

Feed Water Temperature        : 85°C

GCV of coal                                 : 3200 kcal/kg

Enthalpy of saturated steam at 10 kg/cm2 pressure                                     : 665 kcal/kg

Enthalpy of feed water           : 85 kcal/kg 


Solution:- 


Boiler Efficiency(n) = [{8×(665-85)}÷1.8×3200]×100

Boiler Efficiency = 80 % 

Evaporation ratio= Quantity of steam Generated kg/hr÷ Quantity of fuel consumed kg/hr

Evaporation ratio = 8000÷1800

Evaporation ratio = 4.44

It should be noted that boiler may not generate 100% saturated bry steam, and there may be some amount of wetness in steam.



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