Which valves on suction and discharge of high pressure PD pump?

[chemks2012]

Dear all,

I need your help please.

Currently we have high pressure boiler (to generate saturated steam at 60barg, 2000kg/hr) feed pumps with the below stated configuration.

The boiler feed water pumps are high pressure PD pumps (duty and standby) on inverters with the operation pressure of 70barg and 2400kg/hr (max pressure of 80barg, 3000kg/hr at max speed).

The suction side of these PD pumps are connected with a centrifugal booster pump with differential head of 30m, 3m3/hr.

We have a manual block and bleed globe valve arrangement at the suction and discharge of PD pumps.

Currently we cannot achieve required pressure (70barg) and flowrate (2400kg/hr) at the discharge of PD pump and we want to replace those globe valves with full bore (straight through) valves to reduce the pressure drop and hence possible cavitation.

My queries:

1) we are planning to replace suction side globe valves with the ball valves. Do you think ball valves should be ok as the suction side pressure pressure is very low (30m head = 3barg)? Please suggest.

2) we are planning to replace discharge side globe valves with the gate valves? Can we use gate valves for the high pressure lines as high as 70barg? Please comment.

Thanks for your help in advance.

KS

 

[LittleInch]

I can't see a problem with either of those valves. If you want to minimise pressure drop make sure your ball valves are full bore and not reduced bore.

If you are not getting pressure I would check on any pressure recirculating valves, either internal to the pump or external. These often pass and need regular maintenance.

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

 

[chemks2012]

LittleInch

Thanks for your reply.

Yes, we intend to use full bore ball valves at the suction.

I have asked those questions as not sure what was considered during original design that globe valves have been used? E.g. Would there be any scenario that would cause reverse flow from PD pump and hence ball valves may not be suitable?

Also, one of my colleagues was bit reluctant to use gate valves at the discharge of PD pump but I believe as far as gate valves are rated suitably, there should not be any issues.

Sorry, what do you mean by pressure circulating valve? Do you mean pressure relief valve?

There is a pressure relief valve external to pump and it was slightly passing but after changing seat, they are ok.

Regards,
KS

 

[LittleInch]

In that scenario I can't immediately see why globe valves would be used.

Ball valves can seal in both direction so long as you include two sets of seats. I don't really understand your issue.

It seems neither you out your colleagues really understand piping systems and high pressure steam systems don't really seem a good place to learn?

What I meant was that there might be a pressure relief valve within the pump itself as well as an external one .

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

 

[chemks2012]

Thanks LittleInk

With regards to using gate valves at discharge of PD pumps, my colleague's argument was that gate valves doesn't give good sealing/control (just like globe valve) especially due to high pressure of 70barg but I don't agree!

Thanks for your clarification of internal PSV's. Pumps don't have internal PSV's.

Regards,
KS

 

[LittleInch]

Lets be clear here about what you want these valves to do.

Valves that control pressure/flow are different from isolation valves. Ball valves and gate valves are great at isolation and not good at anything else.

Vice versa for control type valves (globe, plug and cage, needle).

To be honest, I'm finding it difficult to believe changing valves will change too much. If your pressure or flow i isn't matching design I think there's something else not right in your system, but only you can see it.

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

 

[chemks2012]

Thanks LittleInk.

At pump suction, along with changing valves, we intend to increase suction pipe size, reduce number off bends etc as well.

Yes, I confirm they are manual isolation valves.

Thanks
KS