Role of APH and Economiser in boiler operation and performance.
1. Both APH and Economiser are used as heat recovery units to recover heat from flue gases thereby reducing the temperature of flue gases thus reducing heat loss going into atmosphere.
2, APH air preheater is used to recover the heat from flue gas and transfer the same to cool atmospheric air before going into furnace.
3. heated primary and secondary air is always advantage for good combustion of fuel in the furnace. a reduction of 22 degree in flue gas reduces the fuel by 1%.
thereby increasing the boiler efficiency.
4.Apart from heat recovery unit this APH also act as pollution control unit to lesser extent. The present norms of 50 ppm of suspended particulate matter (SPM) Prescribed by POLLUTION CONTROL BOARDS plays an important role in selecting suitable design of APH.
5. Heat transfer in APH is mainly by convextion process. The design of passing air through the tubes and flue gases from out side is always desirable for better maintenance and easy cleaning.
6. Presently designers of APH are prefering carton stell tubes for cold end and carbon steel for hot end to minimize cold end corrosion of tunes. but my recommendation is to go with carton steel tubes only for both cold and hot sides as it gives longer life and replacement will be less.
7.Economiser is another important heat recovery unit in boiler design. It unimaginable to have boiler with out economiser. feed water is heated in the economiser before feeding it into the boiler drum. Feed water temperature nearer to the saturation temperature of steam is always recommended before feeding into boiler drum.As the flue gas temperature is higher after leaving bank tubes Economiser is placed first and APH after it. also heat transfer from gas to water always more efficient than transfer of heat from gas to air. therefore Economiser's efficiency is always more than that of APH. more over Economiser is considered as pressure part integral with boiler pressure parts and needs IBR Approval. whereas APH is non pressure part and IBR approval is not necessary. as as a rule every 6 degree rise in feed water temperature 1% fuel is saved. thus Economiser saves alot of fuel and increases boiler efficiency considerably.
7. Another important equipment in boiler system is deareter where the dissoved oxygen and other gases are removed from from feed water by heating the water minimum 105 degree and more depending upon boiler working pressure and temperature of super heated steam . this removal of oxygen and other gases is necessary to protect the tubes from pitting and erosion. but this areator is not a heat recovery unit.
For further information one can always reach me by email or phone given below
K GOPALAN.
Kgopalan1956@gmail.com
9420663740/9108956202.
