Boiler Operation Engineer ( BOE ) Interview Question - 31
Q.What is RAPH & SCAPH and their functions ?
Ans.
Regenerative Air Preheater ( RAPH ) :
Regenerative air pre heater (RAPH) is mainly used for preheating the FD fan outlet air by utilising the outgoing flue gas temperature for making the combustion a rapid and efficient one.
Steam Coil Air Preheater :
Steam coil air pre heater (SCAPH) is employed mainly during start up. As during start up, the flue gas temperature at the inlet of RAPH will be less. If the air extracts more heat from the flue gas, the flue gas temperature falls below 140°C and it leads to cold end corrosion. So to avoid this air is preheated by SCAPH to that steam supplied from the AST header. So that heat transfer rate in RAPH can be reduced without allowing flue gas temperature to fall below 140C. The SCAPH is located after FD fan outlet and before RAPH.
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