Oh, and regarding your last question whether it is fully open or throttling, I think it is at the very crux of the issue. If the valve is throttling at the rated point, as I would expect, there is an energy penalty in the compressor. If it is fully open, I would expect the controllability to...
@georgeverghese:
I am not at my desk now and I cant draft a sketch, but for the sake of simplicity think of the default one stage, fixed speed, centrifugal compressor, with suction throttling and the pressure upstream of the STV being controlled by the compressor performance controller...
Dear gents,
What is the most common sizing criterion to design a centrifugal compressor suction throttling valve? On one hand, I can allow in the STV a DP equivalent to some percentage of the system dynamic pressure drop of the suction side (some 20-25%). On the other hand, some people...
Dear colleagues,
A colleague and I have been tasked with coming up with a procedure to drain some 500 m of a 10 inch pipe initially totally full of LNG. We must empty the line into a vessel which is elevated by some 8 m, and the line is on the ground. Unfortunately there are a couple of...
Hello,
Annex E "Guidelines for Anti-surge Control Systems" in the latest revision of API 617 9th Ed includes some recommendations (i.e. the annex is marked as "informative) on the design of anti-surge control systems for axial and centrifugal compressors. Section E.2.5 "Trapped Volumes"...
Gents:
When starting up a centrifugal compressor, do you normally allow the discharge isolation valve to open before or after the discharge pressure of the compressor matches the discharge header pressure?
For instance, consider a single stage centrifugal compressor driven by a fixed...
Gents,
What are the requirements of the suction line of a centrifugal/reciprocating compressor? I have been having a discussion with a colleague about this and we would appreciate if someone could shed some light on the issue.
From his point of view, no pockets + free draining towards...
Gents:
I am currently involved in the analysis of the results/findings of a dynamic simulation of the ESD of a gas compressor. This is a fairly large unit compressing some 300 MMSCFD of natural gas between 350 and 1000 psig. The results provided by the third party in charge of this...
Gents:
Apologies for not coming back to you until today. For some reason I never got any notifications and I failed to come back...
Thanks for your replies. Please be aware that my background is Chem Eng so I am not really well versed in stress analysis etc. Yes, the 200,000 Pa I was...
Gents,
I am wondering if based on your experience the ESD trip of a centrifugal compressor needs to be investigated by the Stress analysis engineers.
I am a Process Engineer who is working on the dynamic analysis of a compressor. One of the scenarios we are studying is the ESD trip of...
Dear all,
When compressor Vendors state the moment of inertia of their machines/drivers they normally state the MOI and a reference speed. I have never fully understood why: I assumed that the moment of inertia of a rotating element is constant irrespective of its speed.
Aspentech...
Dear all,
I am currently working on a NGL recovery plant with a patented Ortloff's RSV process. The overhead of the Demethanizer (99% C1 i.e. very lean gas) is routed to the suction of a recompressor (of course coupled to a turboexpander) and then it is compressed to around 1000 psig by a...
Gents,
Disclaimer: Process Eng background here with only superficial knowledge of intimate details of valve design: be gentle! ;)
It seems to be common practice amongst my Process Eng colleagues that a full bore, ball on/off valve shall not be open before ensuring that the differential...
Many thanks for your replies, @georgeverghese and @rotw.
I understand your scenario, but is it realistic to consider that, even assuming that the antisurge controller fails to react (control loop failure), the full closure of the suction PCV may lead to vacuum conditions at the compressor...
Gents,
I have seen a few gas compressors driven by a fixed speed electric motor controlled by suction throttling where the inlet throttling valve has a mechanical stop, or some other means to prevent the valve from fully closing. I've enquired a couple senior process engineers at my company...
Dear colleagues,
I am currently working on a natural gas compression plant, and the dynamic simulation study carried out by a third party contractor concluded that most of the compressors shall be furnished with a Cold Gas Bypass loop (i.e. an additional on/off valve bypassing the antisurge...
Dear colleagues,
I am currently working on a natural gas compression plant, and the dynamic simulation study carried out by a third party contractor concluded that most of the compressors shall be furnished with a Cold Gas Bypass loop (i.e. an additional on/off valve bypassing the antisurge...
Gents,
It seems to be common practice amongst my colleagues that a full bore, ball on/off valve shall not be open before ensuring that the differential pressure between the upstream and downstream side is lower than 15-30 psi. Some colleagues argue that this holds for liquid, but some of...
