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l.xie May 8, 2001 13:09


I am designing a circulating fluidized bed(CFB) at laboratory scale. I found many large CFBs use two gas inlets: a vertical primary gas inlet, where gas is blown from the bottom of the bed(air distributor),and a horizotal secondary gas inlet, which is very near the gas distributor.

Is there anyone who can tell me what is the use of the secondary gas inlet?


Murat Koksal May 8, 2001 14:07

Re: HELP! About CFB
The secondary gas injection or the so-called secondary air (SA) injection is mostly used in CFB combustors. With SA, you tend to decrease the total air flow through the bottom of the riser, you create an oxygen lean (fuel rich) region and this helps to control the fuel based NOx formation. NOx is one of the leading pollutants emitted from fossil fuel combustion systems. However, the application of secondary gas injection is not limited to combustion systems. Im fluid catalytic cracking reactors (FCC) (I am talking about CFB reactors, of course) where you produce gasoline, kerosine etc from crude oil, the feed is mostly injected laterally above the main gas inlet. This helps to increase the mixing of the feed with the bed material.

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