cold start up of boiler

[pradeep4u]

Dear All
I want to know that whether 50-55 degree celcius temperature increase is thumb rule for cold start up of boilers. What Happens when we increase temp to about 70-75 degree per hour? On what factors does temperature incrrease depends on?

Regards
Pradeep

 

[TGS4]

Thermal transients generate thermal stresses, which decrease fatigue life. Higher ramp rates could lead to premature cracking down the road.

 

[EdStainless]

There are plants built for higher ramp rates, but if not designed for it 50C is about the limit.
If it is new plant and you exceed the recommended rate you will shorten its life, if it is an older plant you will probably never reach operation as you will break things first.
The stresses from non-uniform heating can be very high. And the faster that you go the less uniform it will be.

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P.E. Metallurgy, Plymouth Tube

 

[davefitz]

The allowable temperature ramp rate is inversely proportional to the square of the wall thickness. A 2" thick drum can ramp 9 times faster than a 6" thick drum and develop the same amount of fatigue damage due to thermal stress. A rational method of determining the allowable ramp rate ( based on limiting fatigue damage) is presented in the EU code EN 12952-3 annex C. There are additional limits , such as allowable top-to-bottom drum metal temperature differential, that may limit the startup rate.

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