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Chomot
Participant

Join Date: Jul 2011
Posts: 3

Boiler Feedwater Pump Water Hammer/Surge Issue

07/07/2011 10:23 PM

I have an issue with two in service boiler feedwater pumps that experience water hammer on start up.

I see that I cannot attach docs to this forum so that makes it difficult for me to show the meat and potato's info about this issue like the drawings and photos of our IP/LP boiler feed water pump system. If anyone wants to do any direct email I am good with that just PM me your address or ask for mine.

Anyway this is the issue, the pumps take condensate water from the deaerator tank and pump it back to the HRSGs. These pumps have bypass recirculation valves on them that returns some water back to the deaerator tank. These recirculation valves are 3" Yaway 9200 ARC valve with a 3" Yarway 9160 Back Pressure Regulator mounted on the inlet of the deaerator tank line from the pump.

The issue we are having is that during pump start up the outlet and bypass lines start vibrating and shaking violently with a lot of hammer noise. This will last until action is taken and the action is to close the pump outlet valve and then slowly open it up. We are unable to just turn the pump on and run it without this hammering occurring. Actions taken to fix this were that the recirculation valves were changed to a different manufacturer and they have been rebuilt a couple of times and additional piping supports were added to stiffen up the system.

The motor driving these Bingham BFW pumps is 150 HP. The pipe between the pump skids and the two HRSGs is 4" and 450 ft long 70% horizontal and 30% vertical in various spots. The DA tank return line is about 40ft primarily vertical.

I have looked into devices like the ones in these links but I have no idea how to size them and believe it or not the venders blew me off saying all I wanted was "free engineering" work, so I am stuck figuring this out on my own and am out of my league for crunching the numbers on something like this.

http://www.shock-guard.com/index-b.htm

http://www.flexicraft.com/Hydropad_Accumulator/Surge/

Anyway if anyone wants to give up some "free engineering" and loves the challenge of solving real world problems I have the opportunity to do so.

Thanks for the help
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Tornado
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Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
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#1

Re: Boiler Feedwater pump water hammer/surge issue

07/08/2011 2:36 AM

This sounds like a cavitation problem, though I'm not sure. What type are your BFW (boiler feed water) pumps? A BPR (back pressure regulator, basically a relief valve) would match up with positive displacement pumps, but centrifugal or turbine pumps would match better with a "Q-min" (minimum flow) bypass valve.

(I'm not a steam guy, but refrigerant pumps face similar NPSH issues.)

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SARANSTAR
Participant

Join Date: Jun 2015
Location: CHENNAI, INDIA
Posts: 2
#5
In reply to #1

Re: Boiler Feedwater pump water hammer/surge issue

06/21/2016 12:30 AM

It might be happened due to temp variation of suction and disch end. Pl do warm up of the pump ensuring entire parts got warmed up then start the pump.

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Holzfeller
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#2

Re: Boiler Feedwater Pump Water Hammer/Surge Issue

07/08/2011 7:59 PM

Not a lot of time now to look into this, but I think Tornado could be right about cavitation. Just the mention of condensate and aeration implies low/high vapour pressure. And the solution of throttling back to reduce flowrate would seem to confirm this.
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MJCronin
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Join Date: Oct 2009
Location: Central Midwest
Posts: 455
Good Answers: 38
#3

Re: Boiler Feedwater Pump Water Hammer/Surge Issue

07/10/2011 9:13 AM

As with most centrifugal pumps, 75% of the problems are on the suction side

This is not a cavitation issue, but an issue of mass-momentum......peculiar to feedwater pumps.

This is an issue that has been the subject of ASME papers since at least the 1940s. This issue is briefly mentioned in the "Pump Handbook" (Igor Karrsik).

Is the suction piping size at least two pipe sizes larger than the boiler feed pump inlet nozzle ?

Have you checked the NPSHr vs. NPSHa calculation.....crucial for boiler feedwater pumps ? Have you talked with your pump vendor rep ?.... Oh, wait your boss told you that you couldn't do this ?

The 450+ feet of suction piping is your problem....the current moron crop of so-called "Combined Cycle Plant Designers" along with their low-cost butt-h*ole MBA managers are guilty of the sins leading to your problem.

You should understand that most pumps are supposed to start against a partly closed discharge valve. It is extra important for your particular situation.

Want to correct the problem and do things the right way ? Evaluate the mass-momentum of the suction side fluid stream, compare it against industry standards and modify the suction side piping.

Boiler pumps cannot operate with tiny suction side piping a long distance away from the liquid source.

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Chomot
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Join Date: Jul 2011
Posts: 3
#4

Re: Boiler Feedwater Pump Water Hammer/Surge Issue

07/17/2011 9:25 PM

You guys are great, based on the advise of this thread this weekend we inspected the witch hat inlet strainers on both pumps and found an old rag in one. I am sure this was causing a cavitation issue.

I will let you know if we still have an issue or not.

Thanks for the help
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Chomot (1); Holzfeller (1); MJCronin (1); SARANSTAR (1); Tornado (1)

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