Pressure Control Vale

[Kaabi313]

Greetings,

This is my first post here and I would greatly appreciate it if I can get some assistance from the experts here.

I'm working on a project to design pressure control valves for natural gas service that is going to feed an H2 plant in a refinery. The H2 plant will require about 4 MMSCFD of NG but the plant want to have the option of pulling between 5 - 25 MMSCFD of NG from the supplier, the maximum flow rate will be used in case they want to supply the entire refinery from that line. I don't believe there is a one PCV that can handle that range of flow but I could be wrong. From your experience, is there a PCV that can have this range of flow, if yes could you please point me to the right direction? I did some research on Fisher control valves but I had no luck. Right now I'm thinking if there is no PCV that can handle this flow range, then I should go with a stages control valves in parallel, one will handle the range between 3-10 MMSCFD and the other one from 10-25 MMSCFD. If I can get some guidance on best way to design this and do the sizing for this scenario I would greatly appreciate it.

The line we are connecting to is a 6" line.
Maximum inlet pressure is 1200 psig
Normal inlet pressure 800 psig
Required Operating pressure downstream the PCV 600 - 550 psig
Temp: 85 F

Thanks again

 

[LittleInch]

I hope that what you are working on is actually a pressure control system and not trying to design the valve itself...

4 to 25 is a fair range, but should be able to be found by one of the valve suppliers ni a single valve. Much more than 10:1 turndown becomes a big issue, but your 5-6:1 is not so bad.

What you need to do is write up a data sheet and supply as many operating conditions in steady state as you can think of, but the minimum and key data to supply is max DP at min SS flow and min dp at max SS flow. Also make sure you get from your gas supplier what his minimum guaranteed pressure is so that you can account for this for the worst case situation (max flow)

You can't possibly find out all the different valve trims these control valve vendors have so don't try and second guess them, just talk to a technical sales rep and send them the data sheet.

If your max flow is only occasional, you could advise the vendors that you can live with a higher % open for the max flow case (normally you don't want higher than about 70%).

If you go for two streams, the issue will be does it need to be a "bumpless" transfer when you hand over control from one valve to the other? This is harder to achieve in reality than you think and needs some fancy control system.

Also look at how much volume you have between the CV and the end user. My experience is that you want to maximise this as much as possible, preferably with over sized pipe, so that you can smooth out the flow irregularities. Whatever happens, when you turn it on it won't work first time and you will spend some hairy moments in the control room fiddling with the PID controller loop to get a smooth response that keeps pace with the change in flow rate.

Hope this helps

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Kaabi313]

LittleInch,

Thank you for your kind response and your feedback. I will take all your comments into considiration.

Appreciated again

 

[LittleInch]

No problem. If you like a post there's a button for that...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way