Direct steam injection into cooling water line at pump suction

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Discussion Overview

The discussion revolves around the operational challenges of injecting steam into a cooling water line at pump suction to generate hot water, specifically addressing the resulting cavitation issues that damage pumps and seals. Participants explore alternative methods for achieving the desired hot water temperature without resorting to a heat exchanger.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes the current method of steam injection leading to cavitation and seeks alternatives to installing a heat exchanger.
  • Another participant suggests injecting steam after the pump or using a closed loop heat exchanger as potential solutions.
  • A participant mentions a nearby condensate tank and questions whether using condensate instead of steam at the pump suction would eliminate steam bubbles and solve the cavitation issue, or if relocating the injection point to the pump discharge is necessary.
  • Another participant emphasizes the importance of checking the Net Positive Suction Head (NPSH) when pumping hot water or liquids with high vapor pressure, noting that steam must be fully condensed and mixed before entering the pump to avoid cavitation.
  • This participant also argues that it is preferable to send condensate back to the boiler rather than using it elsewhere, but acknowledges that using it as hot water is better than sending it down the drain.

Areas of Agreement / Disagreement

Participants express differing views on the best approach to avoid cavitation, with some advocating for the use of condensate while others suggest alternative injection methods. The discussion remains unresolved regarding the optimal solution.

Contextual Notes

Participants highlight the need for careful consideration of NPSH and the conditions under which steam or condensate is used, indicating that assumptions about the effectiveness of these methods may vary based on specific operational parameters.

tinakaran26
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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.
 
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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.
 
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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?
 
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.
 
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