After producing steam, the flue gas comes out from the system. Some heat energy remains in the flue gas when it goes out. If we cannot utilise this heat energy, it gets lost. Boiler economiser is a device which uses a portion this remained energy of the flue gas to heat up inlet water (feed water) to the boiler. Since the heat energy is given to the water before it gets fed to the boiler, the requirement of fuel for producing steam is optimised. Because of that, we call this device as economiser.
Basic Construction and Working Principle of Economizer
The construction and working principle of boiler economiser are simple. At the bottom part, it has a horizontal inlet pipe through which we feed water with normal temperature to the economizer. There is another horizontal pipe fitted at the top of the economiser. These two horizontal pipes, which are bottom and top pipes connected through a group of vertical pipes. There is an outlet valve fitted on the top horizontal pipe to supply hot water to the boiler. The flue gases from the boiler furnace flow through the vertical pipes of the economizer. Here, the flue gases transfer remain heat to the water through the surface of the vertical pipe when the water goes up through the vertical pipes to top horizontal pipe. In this way heat of the flue gases gets utilised through the economizer for heating up the water before entering into the boiler for producing steam.
The flue gas will have ash particles mixed with it which will get deposited on vertical pipe surfaces. If a special care is not taken there will be a thick layer of soot on the surfaces which insulate the heat to enter the water.
To remove this soot, the scraper is attached to each vertical pipe which continuously moves up and down by means of a chain pulley system. By scraping the soot fall down to the soot chamber placed at the bottom of the economizer. Then we collect the soot from the soot chamber. This is how a boiler economiser works. This is very simple form of boiler economiser.