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)?Forged Steel Valves

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.

With the altitude derate and the speed hit, I get the 3608 GLD (with engine-driven cooler) has about 1,667 hp at 795 rpm.  The JGC/4 will move 9.8 MMCF/d at this speed (the compressor run called for 1,408 hp).  I don't have a problem with the driver running at 84% of site hp.  120% with a 3606 GLD would give me pause (derated hp at 1,000 rpm is 1,731 hp, slow it down to 795 rpm and the site hp is 1369 hp, the compression load with auxiliaries is 1,614 hp).  I know that I can probably come up with a mix of cylinders that will move 9.8 MMCF/d at 1,000 rpm, but the hp (and fuel) would increase markedly, and the "pseudo-q" value would be out of range (that is where I started).

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.

MORE NEWS