10 replies to this topic

[CHEMSTRONG]

I have centrifugal compressor. For which i want to know whether compresdor will go in surge even if surge valve is open in following cinditions during discharge valve closure or compressor trip or compressor trip or compressor countdown or compressor suction valve closure ?

[fallah]

I have centrifugal compressor. For which i want to know whether compresdor will go in surge even if surge valve is open in following cinditions during discharge valve closure or compressor trip or compressor trip or compressor countdown or compressor suction valve closure ?

 

The query isn't so clear...

 

Anyway, if antisurge valve is open, compressor won't go in surge following to above mentioned conditions provided that the valve had been properly sized...

Edited by fallah, 14 December 2018 - 01:48 PM.

[CHEMSTRONG]

I wish to know under which conditions compressor will go into surge ? As for most of the conditions antisurge valve will take care

[fallah]

I wish to know under which conditions compressor will go into surge ? As for most of the conditions antisurge valve will take care

 

When the ASV, in any reason, won't be open while needed to be open and also when it's undersized...

[CHEMSTRONG]

Dear Sir,

I want to know whether compressor will go in surge even if surge valve is sized properly and it is opened in 1 sec when operating point reaches backup line on flow vs head curve. Also i wish to know whether compressor will go in surge if emergency shutdown is done or normal stop of compressor or compressor trip or compressor countdown or suction valve is closed. Request your advice?

[CHEMSTRONG]

Sorry i meant compressor countdown instead of countdown in above post.

[Bobby Strain]

??

[MF003]

Dear

 

It is posssible if your anti surge valve or antisurge line size (i. e the flow at anitisurge condition is higher than choke flow in the anti surge line) is inadequatly sized. 

[CHEMSTRONG]

Bobby Sir,

 

I meant compressor coastdown.

[Bitan729]

If the sizing of anti-surge valve and corresponding pipe lines are proper, then it should not go in surge, provided :

1.Inlet guide vane starts to malfunction, suction filter is heavily choked (flow through compressor at particular pressure boost ratio is in surge zone of that compressor ,i.e,  gas flow through the system is lower than stable operating zone at particular head).

2.Sometime some compressor vendor design their compressor anti-surge control system based on only current or power it is taking, so if there is any error on reading or sensing current or power then the anti-surge system can not work properly.

3.Change in gas density, molecular weight of inlet gas can have effect in surging of compressor but generally it's effect is negligible. You can also check if there is any drastic change in cooling water temperature, inter-coolers performance etc.

4. Some vendor install differential pressure transmitter at the inlet of compressor to measure the flow through machine and design anti-surge system based on that. If the transmitter starts to malfunction, then the compressor can surge unexpectedly.

5. You can also check if the anti-surge valve is working properly or not. 

6.The tuning parameter (PID controller's adjustable value) can also be changed according to your system requirement.

7. Check the NRV (if any) at the discharge of compressor for any passing problem.

 

a. After compressor stop or trip the anti-surge valve generally gets full open command from surge control system. So it should not get inter stage or overall surge just after trip or stop in loaded condition.Generally the anti-surge valves are of failed open type. 

b.System will surge drastically if you suddenly stop inlet or outlet of compressor. Machine will always surge drastically if you close inlet valve ,i.e,cut the inlet flow of compressor.

c.During coast down time the IGV stays in a minimum opening with anti-surge valve at 100% open condition to maintain some flow through compressor till it stops rotating. So chances of surge in cost down condition is negligible.

After coast down time the IGV may gets fully closed based of your compressor vendor's control philosophy.

d. Even in fully close condition of IGV there remains some opening in IGV body ,i.e, some gas can always flow through 100% close IGV (Inlet guide vane).  

 

Generally vendors do two type of surge test: Throttle surge (the minimum flow to maintain at particular pressure ratio to prevent surge. They do it for different pressure ration and accordingly configure ASC) and natural surge (the maximum head a compressor can produce before surge). 

 

From surge curve you can check that centrifugal compressor can be operated at lower flow in case of lower pressure ratio than higher pressure ratio ( or discharge pressure) before touching the surge line/curve. So sometimes vendors do throttle surge test at operating pressure and at it's above pressure only ,i.e, they ignore or omit surge test in lower pressure ratios, and use the surge point as set point  in ASC,determined in operating pressure ratio or discharge pressure. 

 

Some centrifugal compressor may have VFD (Variable frequency drive, to operate at different rotational speed to match require flow at require heads etc) for which surge control strategy shall be more complicated. 

 

Regards,

Bitan729

 

Edited by Bitan729, 06 April 2019 - 10:55 PM.

[breizh]

Hi ,

You may find some interest reading the documents attached .

Hope this is helping you.

Good luck.

Breizh