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6 cylindier compressor

6 cylindier compressor

6 cylindier compressor

On our first stage of our hydrogen compressor..the head end discharge valves stay much hotter than the crank end discharge valves.  We have 2 similar compressors that have this problem.  There is no difference in the suction valves.   the head end discharge valves run about 305 degrees on the head end and 370 on the crank end.  We have changed these valves out a few times and the they keep getting hot.  The other 2 stages are fine. Any suggestions?

RE: 6 cylindier compressor

Ok correction... 305 on the head end and 270 on crank end.  Any help appreciated.

RE: 6 cylindier compressor

You don't mention the discharge valves.  They too can change the internal compresion ratio which changes the discharge temperature if they do not open correctly (to much spring tension or to small or area).  

Since its the internal cylinder pressures that dictate ratios and temperature, there maybe a problem with the head on head end.  Does it have pockets or clearance?  some times the gas entering the cylinder can not fully distribute and the will be lower than suction line pressure in the cylinder which means the ratios on that end will be higher and so will the temperature at the discharge. Not only will it be hotter, but you throughput will be lower than projected.

A beta analyzer will tell you if you are having this type of problem.  Cooper Energy Services presented a paper at the 2007 GPA conference where they discovered a problem with their latest cylinder designs and getting proper inflow performanace.

RE: 6 cylindier compressor

We have a program that calculates the compression ratios.  It reads 3.34 for the CE and 3.30 for the HE for the machine that's running hot.  On the other machine its 3.42 for both HE and CE. It's an older style Cooper Jm-6 compressor.  Do the ratios correlate with the machine running hot?

RE: 6 cylindier compressor

With a 1.2% difference in ratio's I'd expect only a 3 deg F difference.  Your cylinders must have a high water circulation rate to get the temperatures of the gas down below 300F unless the suction temperature is below 60 F, what are your exact suction and discharge  temps and press?  How do you get internal compression ratios? Are you monitoring internal pressures though a Kiney valve?

RE: 6 cylindier compressor

Just curious; what kind of compression ratios are your other stages running?  3.0+ compression ratios are pretty high for Hydrogen service.  These kind of C.R. would make the unit run very hot.  Most of the time Hydrogen compressors have ratios closer to 2 to 2.5.

RE: 6 cylindier compressor

         Before Yesterday

Suction Temp 96  Discharge 302
Suction pres 61  Disch Pres 192  

We remachined the valves yesterday

However the compressor is still running a bit hotter than the other one.  We ran it this morning at full load for a few minutes and we had to cut it to half-load because of temperature.  Compression ratio said 3.14 for the few minutes it ran.

We have 3 stages for the makeup service
2nd stage compression ratio 2.5   3rd stage 2.6

And yes we do have kiene valves and use the program Prognost for our ratios and such.

RE: 6 cylindier compressor

How long have you had this problem? Are they new machines?

An interesting test would be to shutdown the machine and swap the CE valves with the HE valves, and see how it runs. And then shut it down again and swap the valves back to their original locations.

If the problem follows the valves then it may be a valve problem. If not, then it's probably something else.

You might also consider unloading the CE momentarily to see if that has any effect on the HE....ie. some kind of acoustic resonance in the discharge passage.

Compression ratio only tells part of the story. The temperature differential indicates that more work is being performed on however much gas is passing through the HE vs CE. Dcasto asked if you had HE pockets on the troublesome cylinder but we have not received your response. Do you? What is your HE clearance...it should be on the cylinder nameplate. What is the volume of each clearance pockets (if any)? Are you running with HE pockets open or closed?

Are powers absorbed by the HE and CE of this cylinder per predicted values? It would be helpful if you could post up the PV plots for HE and CE.

Best regards,

Tom McGuinness, PE
Turbosystems Engineering

RE: 6 cylindier compressor

"You might also consider unloading the CE momentarily to see if that has any effect on the HE....ie. some kind of acoustic resonance in the discharge passage."

To add:

Your ability to do this depends on your cylinder and process configuration. With parallel machines sharing common interstage equipment and station bypasses between each stage, then unloading the 3rd stg CE is easy to do. However, if each machine is a self-contained train with own intercoolers & KO vessels, then you would need to unload all stages when unloading the 3rd stage CE, otherwise you may pop the 2nd stage PSV.

Recip compressors have a lot of "knobs" to turn. Performance is affected by several variables. If I were confronted with this problem, the first thing I'd do is model compressor performance and then use the model to try to replicate the problem.

Best regards,

Tom McGuinness, PE
Turbosystems Engineering

RE: 6 cylindier compressor

It's the 1st stage cylinder we have trouble with.  We have tried switching the valves and the problem continued.  I'm pretty sure we can only really unload the head end on that machine.  No we do not have HE clearance pockets, sorry forgot to answer that question.  We have pressure transmitters on both the HE and CE.

RE: 6 cylindier compressor

1st stg....okay. If you've swapped valves HE to CE (without installing new valves) and the problem follows the valves back and forth, then it does not sound like a valve problem, per se.

You mention "the other one" is a Cooper JM-6. Are both machines the same? What is the make, model, speed, power and capacity of the problematic machine? How many cylinders per stage? What are the HE and CE clearances of the 1st stg cyls...(it's on the cylinder nameplate)? Is this a new machine?

If the machines are motor driven, you probably have suction valve unloaders on all cylinders. You mention cutting the problematic machine to half load, which I'm guessing involved unloading the HE SV unloaders on all cylinders. If so, you may well be able to unload the 1st stg CE instead of the HE while unloading the HE of all other cylinders. If the machine is 2+2+2 cylinder config then only pick one of the troublesome 1st stg cyls...asuming you're having problems with both 1st stg cyls.

As you may gather, there's a lot of details one needs to know to begin to troubleshoot this problem effectively. A forum such as this probably isn't the right venue. From what's been described so far, this does not sound like a routine problem.

Best regards,

Tom McGuinness, PE
Turbosystems Engineering

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