How do you calculate the efficiency of Economiser in Boiler??


What is the Economiser in power plants?

It’s the heat exchanger used in Boilers to recover the heat from exhaust flue gases.

What are the functions of economisers in Boilers?

Functions of economisers:

It recovers the heat from flue gas leaving the boiler, there by reduces the losses

It helps in raising the feed water temperature, there by reduces the fuel consumption

It increases the Boiler efficiency

It lowers the power plant operation cost

What are the different types of economisers?

Types of economisers

Pressurized economisers

Non pressurized economisers

Steaming type

Non steaming pipe

What do you mean by steaming type economisers?

Economisers where only sensible heat is added to feed water

What do you mean by non-steaming type economisers?

Economisers where sensible heat and part of latent is added to feed water

Efficiency Calculations:

ηEco. = (Economiser outlet feed water temperature Two-Economiser inlet feed water temperature Twi)  X 100 / (Economiser inlet flue gas temperature Tfi- Economiser inlet feed water temperature Twi)


 Read APH efficiency calculation


Calculate the economiser effectiveness, whose feed water inlet & outlet temperatures are 160 Deg C & 240 Deg C respectively & flue gas inlet & outlet temperatures 390 deg C & 220 deg c respectively.




Twi = 160 deg C

Two = 240 deg C

Tfi = 390 deg C

Tfo = 220 deg C

ηEco = (Two-Twi) X 100 / (Tfi-Twi)

ηEco = (240-160 ) X 100 / (390-160)

ηEco= 34%


In an non steaming economiser of efficiency 51%, feed water inlet and outlet temperatures are 105 deg c & 160 deg C respectively, calculate the flue gas temperature entering the economiser



Twi = 105 deg C

Two = 160 deg C

Tfi = 370 deg C

Tfo = ? deg C

ηEco= 51%


ηEco = (Two-Twi) X 100 / (Tfi-Twi)

51= (160-105 ) X 100 / (Tfi-105)

Tfi X 51-105 X51 = 5500

Tfi = 212.8 deg C


A economiser inlet feed water & flue gas temperature are 125 deg C and 405 deg C respectively, calculate the feed water leaving the economiser, consider efficiency of economiser 43%



Twi = 125 deg C

Two = ? deg C

Tfi = 405 deg C

ηEco= 43%


ηEco = (Two-Twi) X 100 / (Tfi-Twi)

43= (Two-125 ) X 100 / (405-125)

12040 = 100 X Two-12500

Two = 245.4 deg C


For more calculations related to power plant read Powerplant & Calculations

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