Anti surge design

[wd1980]

Folks;
I need to know if there is a standard that limit the opening the anti surge of a valve for the turndown cases only, i mean short duration for the upset and not considered as a design case for the turndowns?

otherwise what king of risks associated with this design?

rgds

 

[LittleInch]

None I know of.

I can't really understand what you're talking about though. Can you explain in a bit more than one line please.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[wd1980]

Very simple.

can a compressor work with fully open anti-surge valve for turn down cases 24/24h, 7/7 for 20 years dsign lifre?

rgds

 

[LittleInch]

Ah - A compressor anti surge valve - you should have said.

Well yes if there is a cooler involved in the loop or if the A/S flow is a small fraction of the forward flow.

So to fill in your missing gaps, I take it that you have a compressor of size [X], rated for a flow of [Y] at a discharge pressure of [Z].

You now want to run the said compressor beyond the left hand side of its curve, so rather inefficient, and close to or to the left of the surge line. Hence the A/S valve will open to allow [M] percent gas back to the suction via a cooler (Y/N).

So you A/S valve will be getting a lot of wear that it is not designed for and may Fail or erode, but that's your problem, not the writer fo any standard.

If you could fill in x,y,z and M we might get somewhere. Or correct my assumption.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

No problem with the A/S valve running near full open all the time provided the compression unit designer has taken into account all of the following
a) Any noise issues if the velocity d/s the A/S valve exceed 20m/sec
b) The recycle gas temp d/s the A/S valve is not higher than the normal feedgas temp
c) If this is a multicomponent gas, then check if the recycle gas stream will "lean out" and lower the mol wt of the gas

Normally, capacity turndown over the long term is handled by the station capacity recycle valve, but in some plants, the A/S valve doubles up as the capacity recycle also - not a good idea if you ask me, but some designers do this.

Is this a recip or centrifugal compressor, and is this compressor on some kind of VSD?

 

[wd1980]

thx gents,
this is a centrifugal compressor w/o a VSD, the designer has intended to use the recycle mode in turndown condition instead of using a VSD

 

[LittleInch]

Yes, but we're no further forward here.

The valve will not be fully open or else the compressor won't flow any gas any where.

So how much gas is going to be going around the A/s loop in the turndown condition as a percent of the compressor throughput?

The designer clearly doesn't have OPEX in mind when coming up with this scenario.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

No problems with running fixed speed centrifugal at full recycle with A/S valve near full open provided conditions stated earlier are met. A waste of energy, yes.