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BFP Discharge from BFP Intermittent Stage

07/21/2016 10:07 PM

I am preparing P&ID for feed water system of a combined cycle power plant. The BFP discharge goes to HP economiser and HP steam attemperator. I have seen in some P&Ids

1. the feed water for HP steam attemperator is shown to be taken out from the pump. 2. the feed water for HP steam attemperator is taken as tap off from the discharge line.
I wish to know whether in the first case the discharge is taken from an intermittent stage of pump (something analogous) to extraction steam from Steam turbine)?

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#1

Re: BFP discharge from BFP intermittent stage

07/22/2016 4:05 AM

You mean "intermediate" stage rather than "intermittent" stage. I suppose it is conceivable that a BFP would have a tap off of an intermediate stage. If so, the P&ID should show the ranges of intended pressure and flow, which should differ noticeably from inlet and outlet values.

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#4
In reply to #1

Re: BFP discharge from BFP intermittent stage

07/22/2016 1:03 PM

Tornado,

Correct me if I am wrong.

The intermediate tap can be provided if, the pressure of the feed water to attemperator matches some intermediate stage pressure value in pump rather than the pump inlet and outlet values.

So, if I am faced with a situation wherein I have to decide whether to go for intermediate stage tap-off or a direct tap-off from discharge line; I need to check the pressure value of feed water required in the attemperator. Based on that, i need to take the decision.. Right?

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#2

Re: BFP Discharge from BFP Intermittent Stage

07/22/2016 11:05 AM
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#5
In reply to #2

Re: BFP Discharge from BFP Intermittent Stage

07/22/2016 1:05 PM

Thanks and lot for suggesting this book SolarEagle. I am going through the book. Still I would request you to give your comments on my question, if possible.

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#6
In reply to #5

Re: BFP Discharge from BFP Intermittent Stage

07/22/2016 3:54 PM

Well you are the one designing this system, the numbers need to work across the board....I can't say what should be done without knowing the entire design....

Here is some reasoning...

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#3

Re: BFP Discharge from BFP Intermittent Stage

07/22/2016 12:28 PM

The answer to your question is no. If the steam header is taking water to regulate steam temperature, this is at high pressure, it typically is not done to tap off the pump before final output, since if something went wrong, you would wipe the final HP stage of the pump, bad idea. If coming with a line to the steam header directly from the pump, you still have to have a flow-regulating valve to control the final steam temperature.

It is generally preferred to take the water injection to steam header from a line tapped off the main boiler feed-water line, usually these things are near each other and it reduces the pipe layout slightly.

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#7

Re: BFP Discharge from BFP Intermittent Stage

07/24/2016 10:24 AM

Dear Mr.dreamz

The Boiler Feed Pump (Pressure at the) Delivery alone should bsould be connected to the HP Heater and same pressure should be used for ATTEMPERATOR to control the Steam Temp. as desired. Of course, there will be a small pressure drop between the Feed Pump Outlet and the Inlet of HP Heater.

Higher pressure of the Feed Water will give a very fine Spray Particles and readily mixes with high tem. steam and the efficiency of De-Super Heating will increase.

We should not take taping from the intermediate stage (even if provision is available). for De-Superheating in the Attemperator.

DHAYANANDHAN.S

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#8
In reply to #7

Re: BFP Discharge from BFP Intermittent Stage

07/24/2016 10:55 AM

Dhayanandhan,

Thank you for your reply . I agree that a higher pressure of feedwater going to the attemperator will result in a finer spray and better desuperheating. However, I have seen past projects where they have taken an intermittent stage tap-off. I will now check the pressure of the feedwater going into the attemperator of those projets. If the pressure is different(lesser) than the BFP discharge pressure then I will try to find out whether their was any specific reason for it?

Even, the cost of such pump with intermittent stage tap-off will also be higher since the BFP vendor in most of the cases will have to manufacture such a pump separately. Only a specific reason pertaining to the project might have resulted in such a provision.

Please, correct me if I am going in the wrong direction about this.

--

Ashutosh Sonawane

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#9
In reply to #8

Re: BFP Discharge from BFP Intermittent Stage

07/24/2016 11:30 AM

Thank you Mr.dreamz, for your quick response.

Pl. post the information after veryfaction so that this Forum Members will come to know the facts.

DHAYANANDHAN.S

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#10
In reply to #9

Re: BFP Discharge from BFP Intermittent Stage

07/24/2016 11:39 AM

Yes. I will post the info as soon as I can.

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#11
In reply to #7

Re: BFP Discharge from BFP Intermittent Stage

07/25/2016 10:51 AM

I basically said the same thing before you stated it, and I gave you a good answer, it is the KISS method - Keep it simple stupid.

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#12
In reply to #11

Re: BFP Discharge from BFP Intermittent Stage

07/25/2016 10:59 PM

James,

Yes. Apologies for not acknowledging you. Yes you meant the same thing.

Thanks for your guidance..

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#13

Re: BFP Discharge from BFP Intermittent Stage

07/27/2016 4:17 AM

I checked the project where the tap-off was being taken from intermittent stage of BFP. The pressure for the attemperator spray is lesser than the pressure of the discharge line of BFP.

Thank you all for your comments. It helped me clear my understanding a lot.

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#14

Re: BFP Discharge from BFP Intermittent Stage

07/31/2016 5:49 PM

Just love all the TLAs!

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#15
In reply to #14

Re: BFP Discharge from BFP Intermittent Stage

07/31/2016 7:21 PM

What's a TLA? Some kind of acronym, no doubt.

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#16
In reply to #15

Re: BFP Discharge from BFP Intermittent Stage

08/01/2016 4:22 PM

Totally Lame Answer = TLA ?

The Last Answer = TLA ?

Total Local Ambiguity = TLA ?

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#17
In reply to #14

Re: BFP Discharge from BFP Intermittent Stage

08/01/2016 10:35 PM

Yeah, What is TLA?

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