Recip Compressor Selection
Recip Compressor Selection
(OP)
Like most Oil & Gas Facilities Engineers I know, I've always left frame and cylinder selection to the packagers (within reason). I'm currently working of a feasibility study and didn't want to ask too much of packagers on a project that may never turn into a sale so I did the preliminary sizing myself.
The application was 9.8 MMCF/d of 98% CO2 2% CH4 going from 93 psia to 861 psia (elevation is 7,300 ft, suction temp 90F) which works out to about 1,380 hp.
It looked to me like the JGK/4 was a good fit for the task (Ariel Performance calculated 312 hp/throw in the first stage, 504 hp in the second, and 242 hp in the third running at 900 rpm).
I asked a packager for lead time on a JGK/4 matched with a CAT 3608 GLD and he came back saying that the application would be a lot better with a JGC/4 (without any clear definition of "better"). To match the machine to the flow, I either needed to reduce the first stage cylinders from 12.5 to 10.5 (which increased the hp requirement to 1586) or slow the driver to 725 rpm.
The JGK is 5.5 inch stroke rated at 635 hp/throw (max for a 4 throw is 2,540 hp). The JGC is 6.5 inch stroke rated at 1,035 hp/throw (max for 4 throw is 4,140 hp).
Do any of you have a feeling of why the packager would prefer the JGC/4 in this application (especially when they have packaged more JGK/4 frames than anyone else, yeah, it is that packager)?
David
The application was 9.8 MMCF/d of 98% CO2 2% CH4 going from 93 psia to 861 psia (elevation is 7,300 ft, suction temp 90F) which works out to about 1,380 hp.
It looked to me like the JGK/4 was a good fit for the task (Ariel Performance calculated 312 hp/throw in the first stage, 504 hp in the second, and 242 hp in the third running at 900 rpm).
I asked a packager for lead time on a JGK/4 matched with a CAT 3608 GLD and he came back saying that the application would be a lot better with a JGC/4 (without any clear definition of "better"). To match the machine to the flow, I either needed to reduce the first stage cylinders from 12.5 to 10.5 (which increased the hp requirement to 1586) or slow the driver to 725 rpm.
The JGK is 5.5 inch stroke rated at 635 hp/throw (max for a 4 throw is 2,540 hp). The JGC is 6.5 inch stroke rated at 1,035 hp/throw (max for 4 throw is 4,140 hp).
Do any of you have a feeling of why the packager would prefer the JGC/4 in this application (especially when they have packaged more JGK/4 frames than anyone else, yeah, it is that packager)?
David





RE: Recip Compressor Selection
a longer stroke means lower piston speeds, which the JGC model does possess. other than the differences in rods loads, it does appear the JGC is more $.
like yourself, i'd be more inquisitive about the matter.
good luck!
-pmover
RE: Recip Compressor Selection
I'm told that the k-frame is more typically matched with a 1200rpm engine, and the c- and d-frames are more typically matched with 1000rpm engines, such as the 3608 and 3612.
RE: Recip Compressor Selection
The JDC WILL NOT WORK WELL. They have normally match the C frame to the 3608 due to an RPM rateing of engine.
pmover, longer stroke is faster piston speed, because the engine speed is fixed. The K frame is also required due to the gas molecules being bigger, CO2 is a big molecule and valve losses and volumetric efficencies are a problem.
Why not a 3606, it'll do 10.1 MMSCFD at 1000 RPM (site rated 1680) If you want a tad more, a lot of people use electric drive coolers which frees up another 90 HP so you can get 10.1 MMSCFD at 900 RPM
RE: Recip Compressor Selection
I contacted Ariel about the application and they said that they like to limit the pseudo-q to under 13 for CO2 and they like to run the compressor as slow as possible. This was before I had the packager suggest the JGC/4 instead of the JGK/4.
David
RE: Recip Compressor Selection
Cylinder Data: Throw 1 Throw 3 Throw 2 Throw 4
Cyl Model 14-1/8T 14-1/8T 12-1/2T 9-5/8T
Cyl Bore, in 14.125 14.125 12.500 9.125
9.85 MMSCFD @ 950 RPM at 1399 HP, it'll fit a 3606
RE: Recip Compressor Selection
But, the question was - why would someone pick a 1035 hp/throw machine when a cheeper 635/650 hp/throw machine would work much better?
David
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
The harder I work, the luckier I seem
RE: Recip Compressor Selection
He didn't spend half a second thinking about it before he gave that answer... so perhaps your packager didn't either?
He also told me who THAT packager probably was... 'cause I didn't have a clue.
RE: Recip Compressor Selection
David
RE: Recip Compressor Selection
The vendor doesn't know that, he just knows the rate frame RPM and the driver RPM, so the C frame goes with 3600 seies CAT's.
You need a 300 RPM, 14" stroke machine, alas, the closest thing is an AJAX.
RE: Recip Compressor Selection
You can probably guess who my client is (biggest producer into your company's processing plants), and I'm simply not going to encourage them by even mentioning an AJAX (they love the things).
btw, I changed my report to use your JGT/4 Cat 3606 LE and the projected cost of the project went down over $1MM.
David
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
The harder I work, the luckier I seem
RE: Recip Compressor Selection
RE: Recip Compressor Selection
I looked at compressing part way and then chilling to liquid and pumping to pressure. Funny thing is that with pure CO2, you get adequate sub-cooling at -20F and 250 psig. With 98% CO2/2% methane you have to go to -30F and 350 psig to get the same sub cooling. The shape of the saturation curve makes a J-T valve (constant enthalpy) and Turbo-Expander (constant entropy) way less useful than I had expected. Pumping from 350 psig to 900 psig only takes 60 hp or so, but chilling from 24F to -30F takes something like 2,800 hp. This option cost 73% more than just compressing it.
If you ever need to deal with Thermodynamic properties of mixtures I highly recommend the NIST REFPROP database. It cost $200 and probably saved me a month's work. I was able to generate p-h diagrams for the mixture and then overlay the pressure/enthalpy traverse on the diagram to get a really quick view to see when I was approaching a phase change. I got the suction/discharge conditions for each stage of compression from Ariel Performance and then went to NIST and got enthalpy. It was really cool to see a five stage compressor follow the constant entropy line in the compressor cylinders and the constant density line in the coolers--this stuff really works. I calculated compressor hp using the NIST enthalpy's and got values within 2-5% of Ariel Performance. Thermodynamics can be really fun with high quality data.
I need to stop bubbling and go back to studying my Rookie 101 course.
David
RE: Recip Compressor Selection
RE: Recip Compressor Selection
I2I
RE: Recip Compressor Selection
RE: Recip Compressor Selection
This is the first job I've done in 10 years that 2% give or take made any measurable difference in a design. I mostly work in blood-guts-and-feathers upstream operations where you are pretty much expecting to get it wrong since no one has ever figured out a reliable way to predict well response to changing line pressure at low pressures. You over-design everything to the point that a 30% error won't be a catastrophe. I haven't run a process simulator since I got trained in an early version of HYSYS (I think) in 1984 on Amoco's mainframe. REFPROP was a revelation for me.
I2I,
As much fun as this project has been, I'm unlikely to need REFPROP again for a few years. Doing the Visual Basic stuff a month ago would have saved me some time, but the cut-and-paste capability in the program was amazingly powerful (and quite intuitive).
David
RE: Recip Compressor Selection
·Yes, the JGK frame is still made.
· You can't run a 3608LE at 750 rpm. It stumbles along at that speed. The 3606LE is a better choice at 900 rpm.
· There are plenty of 3606LE engines available. 3608LEs are scarce.
· The shorter the stroke the better for CO2 with lower piston speeds.
· The JGT frame would be good and if you still have VE problems then add a stage to your pressure range.
RE: Recip Compressor Selection
Thanks for your help.
David
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
The harder I work, the luckier I seem
RE: Recip Compressor Selection
RE: Recip Compressor Selection
David