Methds of screw compressor liquid injection

[RANGER1]

Can anyone advise on different methods of liquid injection on NH3 screw compressors.

liquid injection usually derates compressor capacity , but what about if its injected into
discharge line of compressor.

Usually compressors have a specific port to inject high pressure liquid into machine.
Amount of liquid is controlled so to maintain oil/discharge temp.

For example a booster compressor you could inject into discharge line.

What about second stage machines is there any proven method .


Thanks RANGER

[mbc]

in two stage system or in screw compressors with economizer system ( in low temp.) to reduce discharge temperature (for a lot of reason ) and increase capacity of compressors we use injection liquid to discharge line of first stage.(By DX system)
or we send low stage discharge to intermediate (or high stage separator) and our suction line in 2end stage took gas from there (cooled gas) and discharge it to condenser.( mainly control by level control or by float valves)

[Josip]

Hi, RANGER1

Can anyone advise on different methods of liquid injection on NH3 screw compressors.

liquid injection usually derates compressor capacity , but what about if its injected into
discharge line of compressor.

Usually compressors have a specific port to inject high pressure liquid into machine.
Amount of liquid is controlled so to maintain oil/discharge temp.

For example a booster compressor you could inject into discharge line.

What about second stage machines is there any proven method .


Thanks RANGER

To second stage compressors we can inject liquid into ECO port (some compressors are equipped with additional ports for liquid injection ... if we inject liquid into discharge pipe we need to use liquid refrigerant pump to raise the liquid pressure above discharge/condensing pressure, but with higher running cost for installation ... with possible problems if all injected liquid not evaporate when passing separator ...

Personally, I do not like any liquid injection for oil cooling ... IMHO it is good and cheap solution, but sometimes cause too much headache

... the best (also the most expensive) for both, the first and for the second stage is external oil cooler ... with air or water or even better with thermo-syphon oil cooler...

Best regards, Josip

[RANGER1]

Thanks
I vaguely remember something like thermopump system similar to Saroe SMC recip set up.

Because it derates compressor injecting into liquid injection port or economizer I thought there might be somethng out there but have never seen it.

[josef]

Sorry, only experience as Josip wrote, and I do not like liquid injection. I work a lot on Frick-York, where the liquid injection, many compressors suffer. I say liquid no. You say thermopump, Sabroe SMC uses reciprocating compressor, otherwise I met no up with the screw.
Sorry Ranger

[Josip]

Hi, RANGER1

Thanks
I vaguely remember something like thermopump system similar to Saroe SMC recip set up.

Because it derates compressor injecting into liquid injection port or economizer I thought there might be somethng out there but have never seen it.

Thermo-pump system is possible on Sabroe reciprocating compressors with ammonia, only. Quite complicated with solenoids, thermo probes, orifices etc .... it is good because it is going into discharge gas, without influence on capacity ...

Best regards, Josip

[CanadianIce]

Hi Guys

Vilter has a small liquid pump unit for liquid injection called V-Plus. The pump uses a frequency drive controlled by discharge gas temperature. The liquid is pushed through a TXV and into the compressor discharge. The few I work with seem to work fine.

C Ice

[Segei]

I saw one plant that use liquid pump to inject liquid NH3 into discharge lines. However, it was old plant that has oil separators 3-5 meters away from the compressors. This implementation gives time for NH3 liquid to evaporate. I'm not sure that this approach can be done for modern compressor packages, unless you have very precise control of liquid injection. Booster compressors require very little of oil cooling and can have liquid oversupply.

[sterl]

Why cool the discharge gas from a compressor with injected liquid? The only thing you are net accomplishing is cooling oil before it hits the coalescers which makes them more effective...So the arrangement Segei references makes some sense. For a high stage machine: That liquid turns into discharge gas and therefore gets condensed at the condenser iimmediately thereafter.... If you had brought the gas up hot, the condenser would have had a lower mass flow and been a higher performing heat exchanger due to the large temperature difference....\

For a booster: The vapor from the evaporated injected liquid gets compressed twice...and still did not produce a temperature anywhere near its saturated pressure of injection or absorb any heat associated with a refrigeration effect.

Liquid injecting into booster discharge is very much the same as evaporating liquid from an intercooler..though you can gain considerably by de-superheating the booster discharge with high pressure liquid only, this short circuits the heat of compression of the low stage directly to the condenser without gnerating vapor for the high stage to handle....In fact this can be done "directly" by overcooling and subsequently using the discharge gas to reheat the oil...not as strange as it sounds, if you reduce the booster discharge by 30-deg the high stage machines have less mass flow and lower demand.

Liquid injection with side port loads is an interesting combination with a lot of possibilites; though it does rely on moving part control devices and in the later versions, considerable electronics and software...I believe it all suits a fairly slow excitation type of load best and that when it starts to give issues too many are fiddle with rather than repaired or reworked properly...

[HallsEngineer]

The best methos i have found is the danfos EKC319 and an AKV as it only injects the right amout required when set up correctly.