What is the function of economizer in steam power plant?

Economizer use the heat of exhaust steam to raise the temperature of incoming water in the boiler.

Economizer increases the efficiency of power plant.

Economizer is the power plant accessory/equipment which use the heat of exhaust steam to raise the temperature of incoming water in the boiler. It increases the efficiency of plant.

Economiser is a heat-exchanger between Air-pre-Heater & Primary-superheater,situated on the2nd pass of the water-tube boiler. After coal combustion  in furnace zone i(n the1st pass then) flue gas pass radiant/2ndary super-heater into De-super-heater enter into the2nd pass, first in2ndary-Superheater then into Economiser to APH, then through ESP(Electrostatic Precipitator) to IDFAN( Induced Draft Fan), goes out to Atmosphere through Stack.

In Economiser Counter Flow occur between Flue-gas & High-pressure water, because of Counter folw maximum heat transfer will occur.Generally40 to60 degree of High-pressure water will increase.To increase the temperature of High pressure water upto40 Degree Celsius we need extra huge amount of coal to burn. So we are using the waste flue gas to heat the water, means we are saving/Economising  extra coal usage.That is why this is called Economiser, at the same same time Boiler Heat loss will be less, Boiler efficiency increases, most important we are reducing Global warming.

ECONOMIZER IS A MOST IMPORTANT PART OF THE STEAM POWER PLANT. WHEN RECYCLED HOT AIR WHICH IS ACTUALLY COLLECTED FROM CHIMNEY IS FURTHER STREAMED TOWARDS THE SET OF PIPES CONTAINING HOT WATER CAN GIVE A EXTRA BOOST TO THE WHOLE HEATING PROCESS

A common application of economizers in steam power plant is to capture the waste heat from boiler stack gases (flue gas) and transfer it to the boiler feedwater. This raises the temperature of the boiler feedwater, lowering the needed energy input, in turn reducing the firing rates needed for the rated boiler output.

Economiser means Saveing in power plant in fual combustion it produced the heat so we can utilized the heat to instal a eco like aph etc.. it is used to coll water to heat and send to  the boiler drum.