Butterfly Valves in Slug Flow

[NeilatNEL]

I am looking into the implications of using triple offset 20 inch butterfly valves as alternatives to chokes in a hydrocarbon production system.

Two particular issues we are interested in -

1. Is slug flow more damaging to butterfly valves than multi-orifice control valves? Do butterfly valves suppress slugs or do they help to generate them?

2. Fast closure is important in this application. How good are triple offset butterfly valves in this respect?

Thanks for your help.

Neil

 

[Scotsinst]

Choke valves are used to create pressure drop to control flow.
Butterfly valves are normally used as low-pressure drop valves for on-off service.
The two are not normally considered alternatives. I have never heard of using a butterfly valve to throttle at high pressure drops. If it is two-phase flow, the butterfly valve will not last long.

1. Temperature, pressure and piping layout affects slug flow, not equipment.
2. You can close choke or butterfly valves quickly.

 

[NeilatNEL]

Thanks for that.

We are dealing with a well at the end of its life with low flow rates. If we can reduce the pressure drop in the system then we should be able to increase production enough to justify the expense. In this respect the valve application will probably be closer to that of a control valve than a traditional choke.

There are certainly butterfly valves out there with graduated opening positions (not just on-off).

You may well be right about slug flow being unaffected by valve type. I can envisage how some types of valve could possiblyt act to diffuse a slug and how some designs could help to generate slugs, but maybe this doesn't happen in reality, or maybe any disruption to the slug isn't sustained for any significant distance?

Any multiphase experts out there?

Cheers,

Neil

 

[Scotsinst]

Neil,
I would consider a vee-ball valve rather than a butterfly because it controls better.
You can pick a line size vee-ball (with a solid metal seal) which will control well at reasonable pressure drops and give high capacity when the inlet pressure has dropped more.
There are limitations on flange class (max CL600) which may force you to use a butterfly. If so, I have had not bad luck with Keystone Vanessa 30000 series. Include a digital positioner which will at least help with the control aspect.

 

[NGiLuzzu]

Neil,
for a list of triple-offset butterfly valves Manufacturers' web-sites, including Vanessa (now belonging to "Tyco Valves and Controls Italia Srl" Group), take a look at my post of Aug. 4, 2003 on Thread408-64692.
Hope this helps, 'NGL