xxxx
232 posts
TimePosted 31/03/2011 09:53:41
xxxx says

preheater fan power , flow & pressure

my ph fan is desigened to handle 100000 m3/hr @ 370 deg @ 250 kw shaft power @ 0.56 kg/m3 density @ 990 rpm @ 670 mmwg as per fan curve . now after putting WHR boiler in the system my fan inlet temp is 210 deg , now i use only 90% speed for the same production of kiln with WHR boiler . As per calculations volume will be 100000*0.9 m3/hr density will be 0.75 kg/m3 due to lower temp. pressure will be 670*0.75/0.56*0.9*0.9 & power should be 250 *0.9*0.9*0.9*0.75/0.56 kw I think the calculation is correct but in the operation i do not get such high pressure at the fan inlet . please comment about the calculations & reduced speed of fan for the same output ramesh

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Michael Clark
312 posts
TimePosted 04/04/2011 09:51:47

Re: preheater fan power , flow & pressure

The fan laws do state that volume is proportional to fan speed but “at fixed inlet and discharge resistance”. As the fan inlet pressure has changed so the volume drawn by the fan will not be 90% of that before the installation of the waste heat recovery system. There are other constants in the fan pressure equation. Finally there is also a term for fan efficiency in the fan power equation. If the speed of the fan has been reduced to 90% of its previous value then the fan efficiency will have changed.

The volume reduction for the reduction in gas temperature can be calculated from the Ideal Gas Laws. This suggests that the fan speed required should only be about 75% of that required before the installation of the waste heat recovery system. However, the waste heat recovery system will have increased the pressure drop across the system. That will be why the fan speed has only reduced to 90% rather than 75%.

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