CENTRIFUGAL PUMPS AND VFD pumps

[IYYAPPA]

Hi friends I am working in oil -chemical industry. Actually we r using 2 centrifugal pumps of 500 m3/ hr capacity each. Its discharge pressure goes up to 8 bar before the filter. Due to 8 bar we often have problem of leak in filter cover gasket.pressure releif valve lifting. So we throttle t discharge valves to reduce pressure to 4 bar and run 2 pumps. I THINK if i change this centrifugal to VFD pumps its possible to use one pump only also is it efficiency in terms of capacity and electrical consumption. Thanks

 

[georgeverghese]

So check the pump performance curves to see if there is a reduced speed at which you can get 900-1000m3/hr at 4barg discharge..

A better solution would be fix this gasket leakage / PSV lifting problem at the filter. That would be easier than to fit VFD to these 2 pumps.

 

[LittleInch]

IYYAPPA,

Your post doesn't make sense. If you throttle the pump to 4 bar then your flow also falls to ??. Adding a second pump also presumably throttled to 4 bar won't add any flow.

First off work out what pressure does your downstream system need to flow at whatever flow you want.

Only then can you start fiddling with the pumps, but it sounds like something isn't right if your filter leaks and the pressure relief valve lifts (!)

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

 

[mk3223]

It seems that the VFD pumps could be an alternative to improve your existing pump with pressure control valve system. Other alternatives can be: upgrading filter with better gasket and PSV, replacing pumps with low head and high flow rate, etc. The final solution can be based on what's the availability of the operation budget.

 

[SandCounter]

Depending on the NPSHA, you might consider moving the filter to the suction side of the pump.

I used to count sand. Now I don't count at all.

 

[FACS]

VFD isn't for the pump, it's for the motor.

A centrifugal pump can have a VFD motor on it so I'm confused what you are asking.

Charlie

http://www.facsco.com

 

[John2025]

Sounds like you need a bigger filter that has less resistance at the flow rate you want to use. Check the specs on the filter.

 

[DrClassic]

Begin with simple solutions coz the problem may be very simple.Do u have vent on top points? If not install . Air bubbles can increase pressure and cause pressure fluctuations among your system. Eccentric reducers for horizontal lines , unneeded fittings may cause the same problem.

 

[MortenA]

As stated many times on these pages VFD is not suited for that many applications. If you PERMANENTLY throttle (that is no controlling) you dont need VFD then you can just replace the impeller of your pumps. This will also reduce the energy consumption of your motor and is less complicated.. You pump data sheet often will give you pump curves with various size impellers, or try contacting you pump manufacturer to get this info.

Best regards, Morten

 

[rotw]

Think what the OP is saying is that because of the throttling, the flow decreased, thus they needed to run two pumps in parallel both discharging at 4 bar after the discharge valve, so doubling the reduced flow get them to match the original demand.

Then the OP is saying that by just reducing the speed, instead of discharge throttling, the system curve will remain basically unchanged, so they would deliver 4 bar at pump discharge at higher flow.

Still the flow is going to decrease in that case too, not the same extent as when throttling at the discharge - bit it would decrease. This needs to be verified. In addition, if the pump + motor were originally fixed speed design, feasibility study needs to be done. Is the motor capable to be adapted to VFD drive and is it also acceptable for the pump (example, distance to critical speed).

Not sure if I got the point of the OP right, but that OP post need to be deciphered really...

 

[bimr]

IYYAPPA,

Agree that the post is not thought through. If you throttle the pump to 4 bar, then your flow throughput will fall since the filter will have less differential pressure across it. This is also a pumped system issue.

What pressure and flow is required downstream of the filter?

 

[LittleInch]

I wouldn't waste any more time. The OP has started 7 posts and replied once to say "thanks" and nothing more...

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