Baby BFP

[sakaran51]

Hi
I am not a pump engineer but basically an electrical engineer.I had come across a pump vendor who insists for a baby boiler feed water pump with a speed of 3350 RPM.It is used to maintain the water level in the boiler, during power failure when main BFPs could not be run due to DG capacity limitation.The higher RPM is required, which is more than the synchronous RPM of. 50HZ motor,to achieve higher efficiency,it is claimed.
My question is,for this kind of application,do we need to go for a VFD driven motor set up,necessarily, to achieve this higher speed?Is there any other options available?

 

[Artisi]

Power failure, pump operating???

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[sakaran51]

Artisi
Pump has not yet been installed.It is a proposal for the project coming up.Will share more details shortly.

 

[Artisi]

You did say, used to maintain water level ...... during power failure, how do you run the pump?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[itsmoked]

Is it a belt driven pump or a direct drive pump. If it's direct drive then you may need a VFD though the usual solution is not to state some pump speed but rather a flow/pressure requirement. With that in hand you then find a pump that runs at your frequency and delivers the flow at the needed head the boiler needs. That allows standard local motors and pumps.

If you try to speed up a pump then you have to also raise the voltage which starts to get complicated quickly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LittleInch]

Find another pump vendor as your current one is, from the information you've given, talking rubbish.

For a fixed duty point you should be able to find a pump to meet your duty at a fixed standard frequency.

If you can post the pump curve we might be able to see what he means but I think someone has an existing pump and needs to make it run faster for your duty. Plenty of pump vendors out there...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TenPenny]

Does your pump vendor realize that you're running 50Hz? Sounds like the vendor doesn't understand your installation.

I used to deal with a mill where they had both 50Hz and 60Hz units in operation, due to legacy installations. It was something I learned to ask about first before going any further.

 

[KoachCSR]

I share in some of the confusion of the previous posts - can you tell us a little more about the purpose of this pump? Are you working with a fired boiler - what is the purpose of introducing feedwater to the boiler during a power outage? Do you not plan to trip the boiler? I don't see how you could possibly have enough auxiliary power to run the FD fan (and ID fan, depending on type of boiler) if you can't run the Boiler Feedwater pump(s). Typically for a fired boiler, you would ensure it tripped with the power outage and "bottle it up" to keep it warm for a relatively quick restart when power is restored...it may be dangerous to introduce relatively "cool" feedwater to the drum if you trip it off at 100% load (depending on the normal operating parameters).

Without more background, a pump to introduce feedwater during a power outage seems like a terrible idea to me.

 

[sakaran51]

Hi
Kindly excuse me for the delay in responding to the various comments,since I could not get the details readily.

First and foremost,this small Boiler Feed Water pump will run not only during the power outage but during normal operation of the boilers along with Main feed water pumps of higher capacity.All the BFPs are connected to common suction & discharge headers.

There is a combination of Waste Heat Recovery Boilers (WHRB)and Circulating Fluidised Bed Boiler connected to a common steam header.A steam turbine generator catering to the captive power consumption of steel plant.
The starting of the plant will be with WHRB & as soon as the turbine starts CFBC will be started
Depending upon the steel plant operation scenarios,the power demand will vary.
In order to have flexibility in boiler operation, in line with plant power demand,a combination of BFPs of higher & smaller capacities will be running.
One of the scenario is power failure(turbine trip & grid not available).During that period the the smaller BFP will be run with an emergency DG,ensuring safety of WHRB.The baby BFP motor is LV and the rating is relatively less compared to Main BFP motor which is 11kV.
The rated flow of baby pump and main pump is 50 cu.m and 90 cu.m;rated speed 3350RPM and 2980RPM respectively.All other parameters like head,design &operating temp.NPSHa are identical.
Now,if you go to my question in OP, you may wish to throw some light with respect to the speed of Baby BFP.

 

[LittleInch]

If you go to my previous answer then you'll have some info.

Basically I can't see why this pump needs to run at any other speed than 2980.

The only reason I can think is that your pump vendor doesn't have a pump that matches your precise duty conditions ( 50 cu m/ hr?) @ xx mhead at 2980 and therefore is using the best pump he has available but that pump needs an increase in speed.

If design head is the same as the bigger pump, there isn't that much difference in power ( 5/9). I thought you were talking one was 10% of the big one, but in terms of your OP all this is irrelevant.

Makes no sense from what you've told us.

Can you post the pump curve?

Or ask another vendor. There are lots of options.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[sakaran51]

Littlech:
Probably you maybe right.Instead of going for a customised design,to meet this particular duty, the pump vendor was offering his standard pump which calls for an increased speed.
Thanks.

 

[LittleInch]

I don't know.

There is no such thing as a "standard pump" for pumps of this sort of size - each pump model has a range of min to max impellor sizes which are machined to suit. Normally most pump vendors have overlapping sets of pump curves so a model 10 would go up to say 150m head and a model 20 starts at 130m and goes to say 250m.

This almost looks like he has a spare pump already machined and wants to get rid of it - but that's pure guesswork.

bottom line though - Do you need a VFD for this duty - In my opinion, no.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TenPenny]

More likely the pump vendor doesn't realize you're working with 50Hz.

Simply reply to the vendor, and say, 'we need a pump selected for 50hz speeds'. Should take about 90 seconds to resolve.