Axial Control Valve Sizing

[neroverdi41]

Hello

I need to make Axial Control Valve sizing for a line with a size of 16”.
Parameters:
P1=82-36 bar
P2=82-36 bar
Q=10000-100000 sm3/h
T=15 C

How can I size it? Also, why are two different pressure values given for inlet and outlet?
Can you help me urgently?

 

[neroverdi41]

It's flow velocity, not flow rate, but I just did a very simple calculation.

100000scmh (highest flow) is 27.7 smc/sec

Allowing for ideal gas, that turns into 0.77 actaul m3/sec (acms) at 36 bar
16" pipe internal area is approx 0.118 m2, so 1m is 0.118m3/m.

So velocity is 0.77 / 0.118 = 6.5m/sec. MAX. That's really very low for a gas flow velocity.

Min veleocity is going to be about 20 times less (10,000 scmh @ 82 bar, which is very very low.

Normally flow velocity inside a control valve is a lot higher than in the main pipe, so in your case my guess is you need something like a 10" or 8" control valve in order to get the range of CV you need.

at first I chose 10“ but due to the deadline we had a 12” valve ready. that's why I chose it. they want the speed especially low. then I thought I would lower the cv value with the cage design. that's why I asked about CFD in another topic.

 

[georgeverghese]

The turndown case will also have to be accommodated, which I guess is : P1 = 82barg,P2=36bar, Q=10e3sm3/hr. The resulting Cv must be higher than the min permissible Cv as recommended by the control valve vendor. From this table, say for 12inch valve, the min Cv for the case of equal %, multipath cage type, for example, is 11(where max Cv at 100% open is 1875).

What Cv do you get for min flow / turndown ?

https://www.emerson.com/documents/automation/data-sheets-type-flv-axial-control-valve-tartarini-en-en-6634658.pdf

 

[LittleInch]

I agree.

A 10:1 turndown with similar inlet / outlet pressures would be bad enough and probably difficult to get int he normal 20-80% open range you want, but add in the 36 to 82 bar inlet / outlet range and its more like 25:1.

You really need two different sized valves once you go over abut 5:1 total rangeability. You can't expect miracles from one valve.

Probably one 4" or 6" for the low flows up to maybe 30 or 40,000 scmh and then a 10 or 12" for the larger flows.

 

[neroverdi41]

The turndown case will also have to be accommodated, which I guess is : P1 = 82barg,P2=36bar, Q=10e3sm3/hr. The resulting Cv must be higher than the min permissible Cv as recommended by the control valve vendor. From this table, say for 12inch valve, the min Cv for the case of equal %, multipath cage type, for example, is 11(where max Cv at 100% open is 1875).

What Cv do you get for min flow / turndown ?

https://www.emerson.com/documents/automation/data-sheets-type-flv-axial-control-valve-tartarini-en-en-6634658.pdf

I have never analyzed under minimum conditions. normally maximum conditions:
37-36 bar and 100000 sm3/h flow
but when I define the inlet-outlet pressure in the program, it automatically calculates the flow rate and calculates 10000 sm3/h. for your information.

 

[neroverdi41]

The turndown case will also have to be accommodated, which I guess is : P1 = 82barg,P2=36bar, Q=10e3sm3/hr. The resulting Cv must be higher than the min permissible Cv as recommended by the control valve vendor. From this table, say for 12inch valve, the min Cv for the case of equal %, multipath cage type, for example, is 11(where max Cv at 100% open is 1875).

What Cv do you get for min flow / turndown ?

https://www.emerson.com/documents/automation/data-sheets-type-flv-axial-control-valve-tartarini-en-en-6634658.pdf

Unfortunately, the customer wants one size valve.

 

[LittleInch]

Customer sounds line he doesn't know what he wants.....

It's up to you to tell them that his process requirements can't be accomplished in one valve to any level of reliability or control.

 

[georgeverghese]

Sizing control valves for the min flow case is an integral part of control valve selection, and often overlooked by process and instrumentation engineers. The end result is not good if ignored - poor controllability at low flow resulting in frequent shutdowns / unsafe operating conditions / operators resorting to unusual measures in a futile attempt to correct for this oversight.

There is no choice but to get it done right at the selection phase. You will most likely have to kick up a fuss now about this small matter with the plant owner's process / facilities engineer and sort this out.

 

[LittleInch]

If you want an analogy think of your valve like a petrol engined car with only one gear.

You're concentrating on getting the design right to do 100mph.
Your customer also wants it to be able to travel at 5mph. But you only have one fixed gear. The car will jump, stall and won't work very well at anything less than 20mph

Neither will your valve.

Hence why we've all been saying that the process information you have is not sufficient to size your valve correctly or even figure out if one valve will actually work.

 

[neroverdi41]

The turndown case will also have to be accommodated, which I guess is : P1 = 82barg,P2=36bar, Q=10e3sm3/hr. The resulting Cv must be higher than the min permissible Cv as recommended by the control valve vendor. From this table, say for 12inch valve, the min Cv for the case of equal %, multipath cage type, for example, is 11(where max Cv at 100% open is 1875).

What Cv do you get for min flow / turndown ?

https://www.emerson.com/documents/automation/data-sheets-type-flv-axial-control-valve-tartarini-en-en-6634658.pdf

I did an analysis under minimum conditions. I gave 82 bar to the inlet and 36 bar to the outlet and opened the valve to 20%. Cv 11 and automatically calculated the flow rate as 2600 m3/h. When I gave 82 bar to the inlet and 10,000 sm3/h flow rate to the outlet, the Cv value I obtained was 36.5. The outlet pressure dropped to 8.8 bar. Now, according to what you say, is the pressure-pressure I should base on correct?

 

[neroverdi41]

If you want an analogy think of your valve like a petrol engined car with only one gear.

You're concentrating on getting the design right to do 100mph.
Your customer also wants it to be able to travel at 5mph. But you only have one fixed gear. The car will jump, stall and won't work very well at anything less than 20mph

Neither will your valve.

Hence why we've all been saying that the process information you have is not sufficient to size your valve correctly or even figure out if one valve will actually work.

Thank you for your opinion and help. I am lucky to be able to consult people like you.

 

[neroverdi41]

I agree.

A 10:1 turndown with similar inlet / outlet pressures would be bad enough and probably difficult to get int he normal 20-80% open range you want, but add in the 36 to 82 bar inlet / outlet range and its more like 25:1.

You really need two different sized valves once you go over abut 5:1 total rangeability. You can't expect miracles from one valve.

Probably one 4" or 6" for the low flows up to maybe 30 or 40,000 scmh and then a 10 or 12" for the larger flows.

What about a multipath cage design and a shrinking cage design?

 

[neroverdi41]

Sizing control valves for the min flow case is an integral part of control valve selection, and often overlooked by process and instrumentation engineers. The end result is not good if ignored - poor controllability at low flow resulting in frequent shutdowns / unsafe operating conditions / operators resorting to unusual measures in a futile attempt to correct for this oversight.

There is no choice but to get it done right at the selection phase. You will most likely have to kick up a fuss now about this small matter with the plant owner's process / facilities engineer and sort this out.

Thank you for your opinion and help. I am lucky to be able to consult people like you.

 

[LittleInch]

What about a multipath cage design and a shrinking cage design?

I don't know. What I do know is that in my experience it's very difficult to find a valve trim that will do that sort of flow range. The internal valve design I leave to the vendor having given them whatI think are the min, normal, max flow cases and see what they can do.

 

[LittleInch]

A few documents which might help.

 

[neroverdi41]

A few documents which might help.

Thank you very much.

 

[georgeverghese]

The quoted "min Cv" in that table of 11 for the 12inch valve implies a rangeability which far exceeds the typical value of 30, since 1875/11 = 170. Hence I would interpret the min Cv of 11 as being that for mechanical integrity and not for controllability - see footnote to those tables.

Hence, the min Cv I would limit it to, for controllability purposes for a 12inch valve, would be 1875/30 = 63, not 11.

Control Rangeability is typically 25-30 ( max Cv / min operable Cv). For special designs, it can be as high as 50 - see Perry in the chapter on process controls / subsection on control valves.

 

[neroverdi41]

The quoted "min Cv" in that table of 11 for the 12inch valve implies a rangeability which far exceeds the typical value of 30, since 1875/11 = 170. Hence I would interpret the min Cv of 11 as being that for mechanical integrity and not for controllability - see footnote to those tables.

Hence, the min Cv I would limit it to, for controllability purposes for a 12inch valve, would be 1875/30 = 63, not 11.

Control Rangeability is typically 25-30 ( max Cv / min operable Cv). For special designs, it can be as high as 50 - see Perry in the chapter on process controls / subsection on control valves.

Thank you for your information. I will definitely take this into consideration.