Direct steam injection into cooling water line at pump suction

[tinakaran26]

TL;DR

Direct steam injection into cooling water line at pump suction

Currently there is an operation scenario at one of our plant which directly injecting steam into cooling water line at pump suction in order to generate hot water at 60 deg C for circulation, by doing this its generate vapor at pump suction and lead to cavitation which ultimately damage pump and mechanical seals. Please advise better solution to this rather than installing a heat exchanger.

 

[russ_watters]

Setting aside why you would want to heat up cooling water, you could inject the steam after the pump or use a closed loop heat exchanger.

 

[tinakaran26]

DearRuss

Thank you for the reply. There is another latest update, i have find out there is condensate tank nearby which most of condensate being send to drain. If i replace the steam injection with this condensate from condensate tank at pump suction to get hot water at 60 deg c, is that it will solve the problem since there will be no steam bubble? or still need to relocate the injection point to pump discharge?

 

[jrmichler]

Whenever pumping hot water, or any liquid with high vapor pressure, you need to check the NPSH (Net Positive Suction Head) of the pump. Good search terms to learn about NPSH are pump npsh. Also, study the manufacturer's website and pump catalog for your pump. There will be information about NPSH in there.

NPSH is easy to deal with when pumping condensate because it is only necessary to make sure the pump suction is a sufficient distance below the liquid level. It's more difficult when using steam injection at the pump inlet because the steam must be both fully condensed and fully mixed before entering the pump suction in order to prevent cavitation.

It is better to send condensate back to the boiler than to use it as hot water elsewhere. It is better to use condensate as hot water elsewhere than to send it down the drain. Almost anything is better than sending condensate down the drain.