Key Note: "Earlier high super heater temperature was observed only during start up of boiler"
My approach to a solution: As the superheater tube bank is in radiation zone, it is subject to higher temperature than convection zone. During cold startup, as the boiler surfaces are cooler, part of the heat generated is utilised for heating the furnace and boiler. As a result lower steam generates from convection zone. Lower generated saturated steam from the convection zone absorbs all the radiant energy in superheater, leading to higher superheat during startup. The degrees of superheat lowers once steady state is reached.
Key Note: "last one year it's constant at 490 deg. C"
My approach to a solution:
- Probably boiler system has been improved. An increased recovery of heat by preheating the air in an air preheater increases air preheat temperature, resulting in higher theoretical flame temperature, radiation heat transfer & higher degrees of superheat. or
- Lower excess air than designed can result in Higher flame temperature & higher radiation heat transfer in superheater.
One of the following reasons can increase the wall temperature of superheater tubes
- Scaling of the superheater tubes reduces heat transfer, thereby increasing wall temperature of superheater tubes
- Due to improper burner and flame control local hot spots on superheater tubes may arise, this may result in higher temperature in particular coil
regards
Edited by K RAVI VARMA, 29 February 2016 - 09:39 PM.