What are Superheaters, Economisers and Air Preheaters?
A superheater is a vital part of the a boiler system that is used to increase the overall efficiency of a thermal power plant. More specifically, it is a device which converts wet steam (saturated steam) into dry steam as dry steam contains more thermal energy. Dry steam is also less likely to condense within the engine cylinders or the casing of a steam turbine.
Are there more than one type of Super Heater? There certainly is. In all, there are three types of Super Heaters: radiant superheaters, convection superheaters and separately fired superheaters. Depending on the size of the plant, they can vary from a few meters long to a few hundred meters.
Aptly named, an economiser is a mechanical device that reduces energy consumption. It does this by acting as a heat exchanger, preheating the fluids that enter a boiler or recovering residual heat from the combustion products. It is designed to save energy by using the exhaust gases from the boiler to preheat the cold fluid, mainly water, that is used to fill it. An increase in fuel prices means that power plants are having to increase the boiler efficiency and this is made possible with the assistance of Economisers.
As well as a boiler system, economisers cal also be found in heating, refrigeration, ventilation and air conditioning systems.
Air Heaters are an important part of the heat exchange process. Similar to economisers, they are devices that transfer heat from one surface to another – but this time from fluid to air. The main objective is to increase the thermal efficiency of a boiler system by recovering the heat from the flue gas and using it to heat the air.
Air heaters can be classified as tubular, recuperative or regenerative based on their operating principle. The first two are usually found in steam generators in thermal power stations.
In the recuperative type, fluid (such as flue gas) is warmed through energy that is passed through a heat absorbing surface such as a metallic tube or plate. The captured heat is released into the cooler air and directed back into the boiler.
Regenerative air preheaters are usually used for iron or glass manufacture. They capture and recycle about 60% of the heat energy exiting the boiler, which would otherwise be lost.