Best location of Anti-Surge Valve 2

[Midan]

Hi All,

what is the best practice in Anti Suge Valve location in Centrifugal Compressor package?
I had seen some applications where the Anti Surge valve is upstream the Dischage cooler, while my Company common practice is downstream the Dischage Cooler.
Do you think there is any advantage for any of them.

Thanks for Your replies

 

[pmover]

not knowing the layout (actual or otherwise), think about the compressor outlet gas temperature. recycling discharge (warmer) gas back to compressor suction will result in a higher compressor outlet gas temp. there is most likely an upper temperature limit that must not be exceeded.
typically, anti-surge valves are located as close the the compressor outlet to reduce system resistance; thus allow minimal compressor flow conditions to be met. for an installation with gas coolers, the anti-surge valve should be installed downstream of the gas cooler to allow for anti-surge protection under all operating modes. the anti-surge valve should be located as close to the gas cooler outlet piping as practical. again, the objective is to reduce the system resistance across the centrifugal compressor to maintain a minimal flow through the compressor.
if the distance from the compressor outlet to gas cooler outlet is lengthy, then consideration may be given for a dedicated gas cooler downstream of anti-surge valve. the gas cooler need only be sized for a flow required to meet process &/or minimal compressor flow conditions. this additional gas cooler has an economical impact on the project and needs careful consideration. there are some processes in which these coolers installed. each application/process will need to be evaluated.

hope this helps.
-pmover

 

[Midan]

Dear pmover,

Thanks for your advice, but throttling through the anti surge valve has a cooling effect.
shouldn't be considered?

Regards

 

[Longinthetooth]

The cooling through the antisurge valve will be inconsequential compared to the temperature rise through the compressor.

 

[pmover]

the cooling or JT effect depends upon the gas. like geordie87 states, it may be "inconsequential". suggest using reliable process simulator data or using the NIST website to obtain the resulting outlet temperature based on conditions before and after the anti-surge valve. NIST website is located at:

http://webbook.nist.gov/chemistry/fluid/

good luck!
-pmover

 

[knapee]

Dear Sir

There is much more risk for this anti-surge problem in multistage compressor than that in single stage compressor. Therefore, it is difficult to control only one recycle (or bypass) line with one anti-surge valve (from compressor discharge back to compressor inlet) for this anti-surge compressor.
Because each stage compressor unit has very different operation pressure and temperature, it is very hard and expensive to use only one recycle line with one anti-surge valve to control many units at the same time in the multi-stage compressor.

The most expectable solution is to install recycle line with one anti-surge valve in each unit(from discharge to inlet) in multi-stage compressor.

Hope this help.

Thanks.

 

[tgmcg]

Throttling across a control valve is an isenthalpic process. If on 100% recycle, the enthalpy rise from compression will accumulate around the recycle loop if no cooler is provided to remove that heat. This can result in excessive compressor discharge temperatures. For most applications, it is necessary to have a cooler in the recycle loop...it can be the main cooler in the compressor discharge, a main cooler in the compressor suction line, or a dedicated cooler in the recycle line itself. However, occasionally for start-up and shutdown purposes a hot-gas bypass type recycle line will suffice for these short operational transients, in addition to the recycle loop including the cooler. You want to try to limit the amount of pipe volume between the compressor discharge, the nearest downstream discharge check valve and the HP side of the surge control valve. The purpose of the surge valve is to both recycle more flow and reduce the differential pressure across the compressor.