Boiler efficiency calculation by direct method with examples

In this article we know about boiler efficiency meaning and formula for direct method of calculation. Also we practice with an example.

What is a boiler efficiency

Boiler Efficiency involves the ratio between energy output to energy input. It is a fraction of energy input that actually goes into raising steam.

The formula is as follows:

$Boiler \ Efficiency (%)= \frac{ Energy \ Output \ }{ Energy \ Input } \time 100$

Here

Energy output means heat exported or gained by the fluid of water, steam (Heat of the steam output in Kcal)

Energy input means which is heat provided by the fuel (Heat in fuel input in Kcal)

The efficiency of a boiler is mainly calculated based on the following inputs

Amount of fuel fed to the boiler furnace in Kgs/hour and its gross calorific value in Kcal/kg.

Amount of water being fed by a pump to the boiler in kgs/hr or by keeping track of Steam output from the boiler every hour in kgs/hr which can be measured using steam flow meters.

$Boiler Efficiency involves the ratio between energy output to energy input. It is a fraction of energy input that actually goes into raising steam.$

Generally, the efficiency of the boiler can be tested by the two methods which are direct method and indirect method

The Direct method means, compares how much energy one gains from the working fluid of water and steam is with the total amount of energy contained within the fuel.

The direct method means, measure the efficiency at which energy is input and energy is output

The Indirect Method means measure the efficiency is that the difference between the losses and the energy input

The Direct Method:

The direct method of the boiler efficiency is also known as “input-output method” because for this evaluation considering only the useful heat output i.e steam and the heat input (i.e. fuel).

$Efficiency \ of \ Boiler (%)= \frac{ Energy \ of Heat \ adding \ to \ the \ steam }{ Gross \ Heat \ Energy \ in \ fuel } \time 100$

Formula for Direct method of Boiler efficiency

$Efficiency \ of \ Boiler (%)= \frac{ Steam \ Flow \ Rate \ \time \ (Steam \ Enthalpy - Feed \ Water \ Enthalpy) } {Fuel \ Firing \ Rate \ \time \ Gross \ Calorific \ Value } \time 100$

Example:1

Water consumption and fuel consumption were measured in a boiler at hourly intervals. Weighed quantities of fuel were fed to the boiler during the period of operation. Simultaneously note down the steam generation during the that period. Blow down is to be avoided during the that period. By taking the measured data and calculated the efficiency of boiler as per the below examples.

Boiler Efficiency ( Considering Bagasse as a fuel)

S.No	Description	Values	UOM
	Heat output data
1	Quantity of steam generation	64	TPH
2	Steam Pressure	42	Kg/cm²
3	Steam temperature	410	^oC
4	Enthalpy of the steam (dry & saturated)	773	Kcal/kg
5	Feed water temperature	110	^oC
6	Enthalpy of feed water	110	Kcal/kg

	Heat input data
1	Quantity of fuel consumed	30	TPH
2	Gross Calorific Value of fuel	2100	Kcal/kg

	Boiler Efficiency	67.36	%

	Steam to Fuel ratio	2.13	Ton of steam/Ton of fuel

Example:2

Boiler Efficiency ( Considering Coal as a fuel)

S.No	Description	Values	UOM
	Heat output data
1	Quantity of steam generation	64	TPH
2	Steam Pressure	42	Kg/cm²
3	Steam temperature	410	^oC
4	Enthalpy of the steam (dry & saturated)	773	Kcal/kg
5	Feed water temperature	110	^oC
6	Enthalpy of feed water	110	Kcal/kg

	Heat input data
1	Quantity of fuel consumed	15	TPH
2	Gross Calorific Value of fuel	4000	Kcal/kg

	Boiler Efficiency	70.73	%

	Steam to Fuel ratio	4.27	Ton of steam/Ton of fuel

Example:3

Boiler Efficiency ( Considering Concentrated Spent wash as a fuel)

S.No	Description	Values	UOM
	Heat output data
1	Quantity of steam generation	17	TPH
2	Steam Pressure	43	Kg/cm²
3	Steam temperature	380	^oC
4	Enthalpy of the steam (dry & saturated)	758	Kcal/kg
5	Feed water temperature	110	^oC
6	Enthalpy of feed water	110	Kcal/kg

	Heat input data
1	Quantity of fuel consumed	8.8	TPH
2	Gross Calorific Value of fuel	1900	Kcal/kg

	Boiler Efficiency	65.92	%

	Steam to Fuel ratio	1.9	Ton of steam/Ton of fuel

The Indirect Method:

The efficiency of the boiler can be measured in the indirect method is also easily by measuring all the losses occurring in the boilers using the principles to be described.

We use indirect method to overcome the disadvantages of the direct method. In this method we have to calculate the various heat losses associated with boiler.

The efficiency of boiler can be arrived at, by subtracting the heat loss in-terms of enthalpy from the total input fuel enthalpy.

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