HRSG blowdown heat recovery

HRSG blowdown heat recovery6A4Horizontal boiler

HRSG6A4Horizontal boiler

Recently, I browse some useful information about HRSG blow down heat recovery, and some people have the questions about it- Is it possible to use HRSG blow-down heat for condensate water preheating purpose?if yes,how that will affect HRSG performance? Today, I sum up some answers as follow:6A4Horizontal boiler

Answer 1: Technically, yes, but it may not be economical for a small system. In a well-tuned (multi-pressure) HRSG with a 0.50% continuous blow-down rate, the steam flow-rate would need to be very high to make the capital cost of the extra heat ex-changer economical. In such a case, you would generate only slightly more steam. Note that you must also prevent oxygen from leaking into the water (which happens all the time with condensers), as you would then need stainless steel rather than carbon steel materials in the heat ex-changer.6A4Horizontal boiler
6A4Horizontal boiler
Answer 2: Yes, it can be accomplished with a plate and frame HX if both stream are low pressure and there is a considerable blow-down flow. It also avoids causing chemistry upsets as would occur if the blow-down was cascaded .An opposite effect can be had if one cooled the condensate that feeds the BFP, and this would cause greatly increased NPSH while not requiring a physically large gravity head above the BFP. At most plants, though, such a compact design is not required.6A4Horizontal boiler
6A4Horizontal boiler
Answer 3: I agree with above mentions, a gasket-ed PHE can be used with low pressure steam systems. However, this is not typical of an HRSG where the HP steam pressure and the feed-water pressure are typically much higher than a gasket-ed PHE can accommodate. A PHE can be used with the LP (or integral decorator) portion of an HRSG and would be much more economical than the equivalent conventional shell-and-tube heat ex-changer would be, but the blow-down rate must be relatively high. One advantage of a PHE is the materials of construction are already stainless steel (not carbon steel).6A4Horizontal boiler
6A4Horizontal boiler
Answer 4: The answer depends on the amount of blow-down. Modern combined cycle plants have small make up water requirements and consequently low blow down rates. If HRSH contains multiple pressure levels, it is possible to cascade blow-down or flash steam from the blow-down tank into the lower pressure steam drum, to slightly increase steam production and minimize water losses to blow-down. You need to review TDS levels in your feed water to determine required blow-down and feasibility of any recovery.6A4Horizontal boiler

Answer 5: This normally done with an inexpensive flash vessel to recover the heat of blow-down water in format of flashing steam. The Flash steam is then used to pre-heat the condensate.6A4Horizontal boiler
6A4Horizontal boiler
After reading this article, I think everybody will have well understand about HRSG blow-down heat recovery issues. More information about HRSG you can learn more from here: boiler

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