sequence open/close valve question

[hswang2]

Dear all Professional engineer
I have a simple question about the on-off valve open sequence question. (drawing is attached)
There are four valves(Tag no is XV-A,B,C,D)located on the inlet pipe of the reactor.
The supply pressure is 12 barg, and the reactor operation pressure is 7 barg.
The operation tech told me that open the valve D first then , B,C, A in order to avoid the water hammer.

Could you please explain to me
how we can tell the kind of the process valve open/close sequence step when we encounter simlar problem?
I wlll really appreciate that any other paper or website you can suggest to me

Thank you very much

 

[MortenA]

Without know why there is four valves upstream the vessel its a bit difficult. Is it because of vere long pipe runs? Are all the valves on/off or are there also control valve?

Best regards

Morten

 

[ash9144]

I assume your supply is steam since you refer to water hammer. The key is opening valve D first and valve A last. I don't think it matters between B,C. The reason is your steam line is filled with condensate. Opening valve D first allows the condensate to flow to the reactor without being heated by the supply steam.

 

[hswang2]

Thank your brillent suggestion.
The process fluid is EO(ethylene oxide), and its boiling point is 11 C @ 1 atm. The process condtion is op=12 barg, and oT=-25 C. and the pipe layout before entering the reactor should not have U shape type to avoid vapor accumulation. The PSV outlet pipe will be put in the pipe line between the EO supply and reactor to avoid EO vapor accumulation.

I am not sure my poit is right or not. Please make a comment if I am wrong.
Thank you very much.

 

[dcasto]

it would be interesting to look at the pressure chnages by calculating the volumes between the valves to see what happens. This sequence you use might be to prevent the pressure from getting below -29C, the limit for normal CS piping.

But, I'm also going to suggest that, because the fluid is EO, you must have a triconics interlock system with at least 2 - double block and bleed valves to assure isolation of the EO. If you don't use double block and bleeds, you'll need 4 valves. Do you monitor the pressures between the valves to assure there is no leaking?

 

[FrancisL]

dcasco - you are right that there may be a need for a high integrity safety interlock system, but it does not have to be Triconex, there are plenty of alternatives.

Francis

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