Heat transfer in a coal boiler? 1

[Kutra]

Could any tell me what the heat transfer rate (W/cm2) is in a typical modern coal boiler?
Thanks

 

[pgh]

The heat transfer rate depends on many factors but I would suggest that boiler design is the main one.

But, if your looking for a ballpark type of figure, I would say that 21 W/cm2 is in the range of typical industrial boilers (about 66,000 BTU/h*ft2).

Paul

 

[davefitz]

in what particular part of the boiler? Furnace, radiant superheater, convective pass ? Is it a pulverized coal fired boiler or other type?

 

[Kutra]

I am looking for a ballpark number for the furnace, so your number looks good, Paul. Thanks.
If there are specific technologies (CFB or supercritical?) that provide a greater transfer rate I would be interested in that information as well.

 

[davefitz]

The max peak heat transfer rate would be in a an oil fired furnce at 10% excess air, with a max heat flux of about 110,000 BTU/hr-ft2. For a pulverized coal fired unit, Paul is correct for a typical max of 70,000 btu/hr ft2 and spot upset ( when slag falls off the tube) of about 87,000 btu/hr ft2.

In a furnace the governing phenomena for imposed heat flux is the combustion side process. Due to the high fluxes in a radiant furnace, tube failures due to DNB or psuedo DNB are possible.


For a CFB operating at 1600 F , a max imposed flux of about 31,000 btu/hr ft2 on a bare tube is feasible, but usually the tubes are coated with refractory so the net flux to the tube is lower. These lower CFB furnace heat fluxes make it difficult to fail a tube due to DNB, but failure due to overheat due to dryout or thermal stresses associated with dryout can occur, so it remains important to design the furnace circuit's thermal hydraulic characteristic such that such dryout event occur in a controlled manner.