Boiler Priming Problem

[uwm]

We have a 250 hp low pressure boiler rated at 8500lbs/hr.
we modulate between 12 and 14 psi. We have equipment that operates once a day that has a steam demand of 4000 lbs/hr. When the equipment turns on the high steam demand lowers the pressure( to about 5 psi) in the entire system and the condensate tank over flows the feed water tank starts droping and the boiler starts cycling on the low water cutoff. This lasts for about 45 min. I am guessing that the low pressure in the system creates a vacuum that sucks the water out of the boiler which is ending up in the condensate tank and the pumps can't keep up so it overflows. Is there any fix for this situtation.

 

[GenB]

you may have to install a reducer in the steam outlet.
you may have contaminated water now you will have tyo flush the boiler, then you will treat with anti-foaming chemicals.
ER

 

[TBP]

This sounds like a little food plant system, with problems that show up during wash time. I'd suspect mechanical issues such as a condensate tank/pumpset undersized for this big load spike, and/or the start-up load at the 4,000 #/hr point of use is somewhat larger than was anticipated. Otherwise, the steam system pressure should stay in the normal operating range. The feedtank level will drop because water is being pulled out for the boiler faster than the condensate can be pumped back. In any event, the condensate pump will likely start on a float switch in the condensate tank, and won't have any way to sense the level in the feed tank. (It shouldn't need to, anyway.)

I've seen some systems with problems like this where the feedpumps had been selected with the same discharge head as the boiler operating pressure. (This mistake happens a LOT, in little plants.) The pump can just manage at low loads, but once the peak hits, it's all over. Boilers trip, tanks overflow out in the plant, run out of water back in the boiler room, etc.

This has the aroma of a mechanical systems problem, rather than a chemical issue.