PSV vs HIPPS on fuel gas supply line of Centrifugal Compressor 1

[dungprocess]

Dear all

I have a centrifugal compressor driven by a Gas Turbine. Due to limited flare system capacity, we want to install a HIPPS on fuel gas supply line acrivated by PZHH (may be putting some voting mechanism) rather than a common PSV on the compressor discharge line.
Please advise your objection to this concept.
Thank you and regards
Dung

 

[georgeverghese]

This is an unusual way to set up a HIPS for compressor discharge PSV limitations, but that is somewhat irrelevant now.

To justify HIPS, you will have to demonstrate to higher Operations and Engineering management that (a) all reasonable methods to debottle neck the compressor discharge PSV / flare system to handle the higher rate have been studied and found to be not possible (b)that the risk involved in operating the HIPS for the remaining life of this facility are lower than project construction risks for the modifications that could be made to avoid a HIPS.

 

[georgeverghese]

You must be suggesting a PZHH (perhaps a 2oo3 voting) on compressor discharge (not on FG supply) to cut out the FG supply to the GT with dual SDVs' set up in series - one of the problems I can see is the reduced integrity of the signal transmissions and activation from main panel compressor USD to the local turbine panel to close these valves. There should also be sufficent gap between PZHH and the PSV setpoint to allow response time for these valves to close / antisurge recycle valve to pop open. The worst case for this would be when the cause for this would be a spurious closure of the compressor exit trip valve while the compressor is running flat out. It could take several seconds for the turbine compressor assembly to slow down even after the FG is isolated - an intermediate gearbox will slow down the deceleration even more. Presume you intend to run this on a dynamic simulator on high resolution to see what may happen ?

 

[LittleInch]

It depends on why you think you need a full flow PSV on the compressor discharge. We can only assume you have an adequate anti surge system to prevent compressor surge during no flow. Can the PSV cope with the compressor minimum flow?

Also how much above design pressure can your system see. If less than 33%, you might be OK as a short term spike to B 31.3.

Your HIPPS would need to be a dedicated system linking your 2003 PTs direct tot he logic board then onto your dual in line fail closed valves.

Certainly a bit novel, but not clear to me what scenario you are trying to resolve with this system.

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

 

[MortenA]

Im not certain of your system - the flow to the flare will come from the FG line, but you are afraid of overpressuring the FG system and thus would like a full flow PSV on the compressor discharge (assuming the line where the FG is taken from?).

Could you limit flow using a restriction orifice in the FG line e.g. upstream the control valve that i assume lets down the pressure from whatever to GT FG pressure or maybe replace the Cv with a smaller size so that the PSV would not have to be so big?

 

[dungprocess]

Dear

Sorry for late response, I am a bit busy last few days.

georgeverghese:
Sorry but I don; get your point, if HIPPS is installed on compressor discharge, it can operate independently to Compressor UCP, eg if blocked outlet says two PZHH on compressor discharge will demand HIPPS installed on Fuel Gas supply line to close and therefore compressor ultimately stop (at least to raise a higher pressure than normal discharge pressure). I do agree that as per API 521, application of HIPPS can only be implemented if the common PSV is not practical.

LittleInch:
As said above, I am trying to avoid blocked outlet case of export SDV. Thanks for your reminder on the link between no flow case on surge protection system.

MortenA:

I am trying to protect my compressor during blocked outlet event by cut off the fuel gas line with highly reliable instrumented protection system not protect my fuel gas system, the reason is simple fuel gas system operates at lower pressure hence PSV protection can be easily accommodated but for process side the flow and pressure is much higher.

Cheers
Dung

 

[don1980]

I think this is a perfectly acceptable application for HIPPS. A HIPPS can protect the compressor outlet from overpressure, while not adding any load to the flare. The main concern when using HIPPS is that it's critically important for the owner to have a strong integrity management program - one that safely manages the risk of the HIPPS becoming nonfunctional due to neglect or inadvertant change. The safety-integrity of the HIPPS is obviously no greater than the integrity of the management system. If that management system is strong, then HIPPS is a good solution for this speciifc case.

A HIPPS design that shuts off the fuel gas flow will obviously have the desired effect - shutting off the compressor - however, I think you can also design the HIPPS to directly trip the compressor motor.

 

[tickle]

If a HIPPS is put in place to shut down FG to the compressor, ensure that you are not going to bypass the system during commissioning and other non-standard operation (either using bypass valves or manual control operation).

 

[georgeverghese]

To enable dynamic simulation of the deceleration of the entire rotating assembly ( GT power turbine + gearbox + compressor bundle) during the shutdown sequence, you've got to work out the rotating moment of inertia of this assembly - ask your rot machinery specialist or the compressor vendor to help with this. To be conservative, think carefully how much credit you would give to the antisurge recycle valve in this simulation - my opinion is not take any credit.

 

[dungprocess]

Many thanks for the reminder, I just think this is just like the case of inadvertent closure of suction SDV where the only protection is ASV, additionally the speed reduction will bring the operating point out of surge limit but anyway dynamic simulation will tell many things.

 

[Kottam]

Hi,
I want to design vaccum breakers/Air releave valves at high elevation points of the offshore platform fire water system. I would like to know is there any guide lines to design these breakers to avoid column seperation. I am looking for the following details.
1.how many number of breakers are required?
2. how can we design the location of the one breaker to the other
3. What are the critical parameters to be taken into account to design these breakers.
I really appreciate your reply.


Thanks

Regards,
RK