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HRSG Economiser
Can small pump in economiser circuit of a boiler to maintain pressure inside economiser during shutdown conditions?

Hai all,

In our plant we will be doing cyclic shutdown of the GTs during this shutdown period of about 12 hours. Is it feasible to fix a small pump in economiser circuit to retain pressure inside economiser?

Hameed,

this is an interesting question. On this board, most folks seem to be controls experts and not necessarily process experts. However I will give my 2 cents on this question.

I am not sure what you would pressurize the Economiser with. If you pump water into the economizer, you are just adding more water into the drum. You will only be able to do that for so long until you overflow the drum. And that wouldn't really work to keep the system pressurized. Also, that doesn't get you to your end goal which is shorter startup time.

A lot of plants do have recirculation pumps installed on the LP economizer so as to heat up the incoming condensate water to just below boiler temperature. Then once it enters the boiler, it evaporates pretty quickly. However, this only works when GT is fired.

Max

Max,

Thanks for the reply. We have drum level control valve at outlet of economiser, so the drum will not fill. I feel that venting of economiser will not be required in subsequent startup if we retain pressure inside the economiser by using a small reciprocating pump. So that startup time is reduced and feed water pump power consumption will be reduced during startup. Is this feasible? sorry for my poor English.

Regards
Hameed.

Hameed,

Seem to recall that the valving setup in some processes will bypass and valve off the economizer as it cools down. This allows the fired steam generator to keep working.

if you need a overview of a typical HRSG systems, check

http://www.angelfire.com/md3/vganapathy/hrsgcep.pdf

what ever you do, process safety, first and foremost.