Gas Compressor Flowrate and Re-Cycle flow 1

[Morph711]

Folks,

Am I correct in thinking that a significant drop in gas temperature upstream of a Compressor will result in gas being denser? Resulting in increased mass flowrate throughput. With the recycle flow around the Compressor being set in manual. The Compressor discharge tripped on high temperature because the re-cycle valve was not closed in fast enough.

 

[compguy22]

What type of compressor is a primary info and you did not provide it.
We do not know the train arrangement neither. Is not clear the link between the various elements described.

If this is centrifugal, a lower inlet temperature means lower actual volume flow, unless mass flow is increased. This means higher pressure ratio and operation near surge which would trigger operation of anti-surge valve (see picture "lowtemp" OP case).

If at constant volume flow, because mass flow was increased, lower temperature means lower head required to achieve a certain pressure ratio.

Either you lower speed (see map), if such regulation is available, if not then there will be higher pressure thus high temperature and potential risk of trip on HH. If speed regulation is not available, recycle can be used to operate at higher flows so to maintain discharge pressure as required (case OP "low temp high flow").

The map is Q-H type and ignore effect of efficiency accros map (i.e. assumes constant efficiency for simplification of head calc.).

 

[Morph711]

Hi thanks for the reply. Yes centrifugal. We were doing deluge testing and the cooling on the pipes and compressor started to increase the mass flow upstream for a bit. The compressor was maxed out on speed, so yes should of slowed the revs down significantly. As we weren't watching the compressor during the deluge testing, too late to react.

 

[georgeverghese]

You mean the compressor gas turbine driver tripped out on high exhaust temp due to compressor mass flow overload ?

 

[Morph711]

Tripped on the export cooler d/s of compressor. Another contributing factor was the slight fouling on one of the cooler exchangers. Higher sea water temps and lack of hypo dosing does not help. Going to close one of the coolers and start another sea water lift pump. Might help who knows?

 

[georgeverghese]

There is previous talk (2-3months ago??) on this website about problems associated with hypo dosing of open loop sea water meant for cooling - see if those help.