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Regenerative Air Pregeaters in ACFB boilers

Regenerative Air Pregeaters in ACFB boilers

Regenerative Air Pregeaters in ACFB boilers


We are selecting a contractor for a new 300 MW coal fired utility in South America, the boiler will use ACFB (Atmospheric Circulating Fluidized Bed) technology. In the same place we are already erecting a 150 MWe unit with ACFB boiler and one regenerative Ljungstrom air preheater.

For the new unit we requested two flue gas trains (Air preheater, bag filter, ID fan) each one 60% capacity (we have used this configuration in some 150 MWe PC boilers we opperate), but one of the possible bidder argumented that two Ljungstrom air preheaters shall not be used in ACFB boilers so they will supply only one.

Is there any limitation about the number of air preheater for a ACFB boilers or it may be decied freely by customer? I've seen many units in many sizes with two air preheaters but all were PC technology.

By the way, we allowed bidders to propose either tubular or regenerative air preheater.

Thanks all for your help.

Javier Guevara E.
Projects, Mechanical Engineer

RE: Regenerative Air Pregeaters in ACFB boilers

The configuration that you propose makes sense to me, but I do not have any experience with ACFB's. I would question the supplier's reasoning. They should be able to provide justification based on experience. There may be a sound reason behind their recommendation.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

RE: Regenerative Air Pregeaters in ACFB boilers

I have seen economic optimizatons by european manufacturers that show the optimum size in large plants is toward single large air heaters and fans, ducting, etc. rationalized by high demonstrated availablity.

Having said that , the use of a Ljungstrom style APH on a CFB can lead to other issues, mainly excess air leakage and higher than guaranteed SA fan power consumption. The trend in most CFB's is to use multiple tubular or heat pipe style APH's in series with an intermediate water cooled economizer- this limits the air leakage to almost Nil.

RE: Regenerative Air Pregeaters in ACFB boilers

A Ljunstrom APH has a guaranteed 8% leakage rate brand new in the box and it only gets worse over its life and can approach 25% when it gets some age on it.


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