|Fig. 1: Construction of Stack in Steam Boiler System|
Stack is a equipment to take out the product of combustion at a sufficiently high elevation to prevent disturbance caused by ash, low flying smoke, and soot and to disperse the combustion gases. To perform flue gas flow through steam boiler room such as furnace, superheater, steam boiler bank, economizer, air heater, dust collector until be discharged to atmosphere, requires a certain amount of draft. Amount of draft can be generated by fan either force draft fan or induced draft fan to overcome the pressure drop (draft loss) that are developed in the steam boiler. Beside that, height and difference between the outside air and inside flue gas temperature of the stack can produce the draft.
Excessive heat temperature of stack is something should be avoided because it show that there are heat loss and efficiency reduction of steam boiler. The following formula may be used to calculate draft generated by a stack:
Stacks are designed in the worldwide steam boiler system are commonly completed with caged ladder, walk way, and instrument nozzle to measure the concentration of either excess O2 and CO2 to determine the operating excess air level. CO or carbon monoxide is also measured to determination of incomplete combustion in flue gas of steam boiler.