7 replies to this topic

[manojkaila]

Dear Sir,

 

We are using Propylene liquid for flash in three stage from 21 Kg/cm2 to 7 Kg/cm2 to 2.2 Kg/cm2 to 0.091 Kg/cm2. We are facing problem during the flashing hydrates formed in control valve & we are forced to open the bypass. Our moisture spec is 1 PPM wt%. Our control valve is anti cavitation type with cage inside. 

 

How we can solve this problem ?

 

Regards,

[manojkaila]

Do we need anti cavity valve. If same I will replace with ordinary valve what is the draw back

[Zauberberg]

How do you know that hydrates are the cause? Why don't they form in the bypass line, after flashing across the bypass valve? Process conditions upstream and downstream are essentially the same as for the control valve.

 

In order to find the best solution for the problem, you should be 100% sure about what is the true cause.

[ankur2061]

manojkalia,

 

Provide a heat tracing (electric / steam / hot water) on the valve body. This has worked for me in the past in troubleshooting freezing and ice crystal formation in the control valve.

 

Regards,

Ankur.

[manojkaila]

Dear Dejan,

 

We opened the control valve & found full of hydrates. After cleaning few hours it is running fine & then again same problem. On bypass it is running fine. Mr Ankur given some good solution. But again my try to remove the root cause which may be double cage anti cavity control valve. Our flow is also very high 50 MT/hr from one line such we have three train. 

[Bobby Strain]

Your problem is moisture and oil in the propylene. Remove the moisture and the problem will disappear. Or, the deposits you found may be congealed oil, not hydrate. In this case you may need to use a different control valve. Let us know the outcome.

 

Bobby

[Zauberberg]

If Hydrates are proven and the bypass is working fine, I'd think of two options:

 

1) Use the same type of control valve such as the one installed in the bypass line - obviously it has been working without any issues and there are no adverse effects arising from the conventional valve design?

2) Eliminate the cause of hydrate formation (or whatever it is that you are finding stuck in the control valve)

 

The option mentioned by Ankur may also work fine - it all depends how effective this trace heating will be and are there any adverse effects on the process downstream of the valve.

[manojkaila]

Dear All,

 

I am very sorry for delay conclusion. I would like to conclude the topic and share the lesson learned with all of you.

First of all let me commit that this is not fully hydrate problem but improper design for this use. The root cause confirm by valve vendor is the design of the control valve retainer. Original design is Channel stream retainer which is highly susceptible for blockage due to fine particles which are very usual in big system. Vendor suggested new Cav control retainer and we changed with new control valve with new type of retainers. Now our problem is solved. So my learning is that during detail engineering we have to take care if we are using channel stream retainer then we need to add strainer in up stream of this control valve with very fine mesh.

 

Attached is the details will help to understand the difference between two type of design.

 

I hope this will help some value addition. Feel free for any further information.

 

Regards,

 

Manoj

 

 

 

Attached Files

•  Control Valve Retainer.docx   191.48KB   30 downloads