Starting of RAPH is also one of the starting permissive for starting the ID fan.during boiler startup only air is present in the furnace.why cant we start RAPH after running the ID fan?
RAPH means rotary air pre-heater..its normally used in modern thermal power plants to improve boiler efficiency.it comes under heat recovery systems in boilers.
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Main reason is to reduce cold end corrosion in the heater unit. You want the boiler flue gas temperature to be above a certain value, or you risk sulphur attack on cold surfaces of the heater unit.
could you please elabourate a bit more on this. As i am training for a boilermans licence.
The boilers that we have are only just ticking over. we realy need to turn one boiler off, But the building manager will not let us as we would need a cold start.
The Boiler that would be left in service will still be running at a quarter of it's capacity, So yes the boilers are vastly oversised for there application.
When ever you start up any boiler system, ( especially firing fuels with high sulphur content such as bunker oil or lignite coal) you need to ensure that all hot surfaces coming in contact with the flue gas of combustion are below a certain temperature ( call the acid dew point temperature ). This problem is especially true in heat exchangers ( such as your rotary air heater).
Therefore, you want to start your boiler ID fan without passing the flue gas thru the rotary air heater. Instead you bypass the gas for a certain time, till the flue gas temperture rises sufficiently for the phenomemon of acid condensation in the cold surfaces of the air heater not to happen.
You can read more about this for websites on the net
thanks for your answer.actually the cold end corrosion takes place after light up the boiler. but before we start the oil gun we must purge out the explosive gases from the furnace.it is done by operating the fans at lower load(FD at 30%).at first we will start the Id fan then FD finally we light up the boiler.cold end corrosion is possible after light up.but we are starting the RAPH before starting the ID fan.why?
Thank you for your reply.But it seems that you are referring to older boilers that were run on coal and oil that needed to be heated for it to be used.
The boilers that we are using are only 5 years old and are due for their first ultrasonic testing next week. These boilers are running on gas only, so they have a blower that dose a test run before they fire up. This test run is presumable for the dew point that you mentioned. As far as i am aware there is no sulphur in the gas. And as such a cold start should be possible. Is this correct.
Power Plant Operation
Re: Power Plant Operation
