Hydraulic Compressors

[ngvfleet]

I am interested in the CNG compressor technology utilizing hydraulic compression. i currently build cng stations in the midwest utilizing atlas copco, arial compressors xebec gas dryers ect. I am a GC not an engineer! i have been reading about hydraulic compressors like these

http://www.sicom-compressori.com

but can not find anyone in the states that have one. I am looking into it for the operational benefits ie..oil free, lower operations and maintenance cost. I will be looking for a consultant to design a compressor for a specialty application that will meet these specs

Natural Gas compression
oil free
inlet 15 to 30 psi
outlet pressure 500 to 700 psi
flow rate 350 scfm

I like the thought of hydraulic compression from a maintenance stand point, but would be interested in a centrifuge or rotary screw compressor as well. Of course what i am wanting is to get to a price point..I would have the ability to assemble the compressor...at cost price point of 55 to 75K
Am I going in the right direction? or am I approaching this from the wrong angle?

 

[unclesyd]

Here is the Haskel site who's equipment I've used for several years with very good results.
I definately would give them a call with your requirements as normally the websites don't tell the whole tale.

http://www.haskel.com/corp/details/0,10294,CLI1_DIV139_ETI9788,00.html

You might also search on net for gas intensifiers. I think you will find several as there is a big push for both CNG and H2 filling stations.

 

[ngvfleet]

Thanks for the tip. I have sent them a request for info. from your experience is the price point that I am trying to get to reasonable? with the specs i have is this going to be the best type of compression?

 

[zdas04]

(I'm going to assume that your "psi" means "psig") Your application is somewhere between 11.5 and 24.0 ratios. Looking at the worst case (15 psig to 700 psig) you are looking at around 235 hp/MMCF/d. Your flow rate works out to about 0.5 MMCF/d so you need around 120 hp.

The 24 ratio case would be 4.9 ratios/stage for a two stage machine. That is a touch too high for an air-cooled cylinder, but a water cooled cylinder would be fine.

So a 120 hp, water cooled, two stage hydraulic compressor is what you're looking for. That sounds like it is probably a custom application. I worked on a machine like this last year, but the company kind of refocused itself and the compressor fell through the cracks. Getting the cylinders right (both size, clearance, and stresses) was pretty easy, but the valves were kicking my butt when they dropped funding.

The Engineering work on the first compressor will eat up every bit of your $55-75k before the first lathe touches the first chunk of steel. The first compressor will be pretty expensive because you won't have any jigs or fixtures to facilitate fabrication. After the Engineering, and the first compressor, I would expect to be able to build machines like this for around $500/hp. For a 150 hp machine you would be looking at numbers in the neighborhood of $75k. I would guess that you are looking at around a year to get the first machine on the ground if you are clear of patent violations (or can license existing patents).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[CH5OH]

an oil free hydraulic driven compressor sounds a bit like a contradiction in terms.I can see the advantage of a simple recip design but then again, you still need a hydraulic power pack (good flexibility, not so good an efficiency)

 

[zdas04]

Oil-free refers to the compressor end. The compressor is moving slowly enough that you can lubricate the piston movement through material-selection of the compressor-end rings and seals. The hydraulic end does have oil in it.

David

 

[ngvfleet]

CH5OH.. Are you suggesting that in terms of cost and reliability a recip compressor is a better option? i am needing my gas to be free of contaminants. so my thinking on hydraulic compression is no possibility of contaminants from lubrication.

 

[CH5OH]

what I mean is :you use the same cylinder for gas and oil.although it will keep the gas part more free of oil than use of cylinder lubricators,it is not oil free,what about when sealing between gas and oil starts to wear?

 

[zdas04]

For this application, I would design it with the two hydraulic cylinders being enough larger than the "crank end" compressor chamber so that the hydraulic pressure is less than the second-stage discharge pressure so a leaking shaft seal would let gas go into the oil instead of oil into the gas. It is just Engineering.

David

 

[CH5OH]

what about a multistage centrifugal?
most of the time one concept will be in favour compared to another concept,when looking at the operating cost and out of favour looking at installation cost.

i would think the benefit of hydraulic compressor lies in installation cost, not in operation/maintenance cost.(low
relyability pace setter of a recip are the valves, this you still have with a hydraulic compressor.

 

[ngvfleet]

CH5OH,
Do you have any recommendations on suppliers for multistage centrifugal compressors or approximate price range for the outlined specs?

 

[CH5OH]

probably not, the outlined specs include the hydraulic power pack needed or would that be on a rental bases?
since it's your project, asking a budget quote doesn' hurt
atlas copco, manturbo,...
as your mind and motivation is set on a hydraulic compressor, i'll keep my mouth shut

 

[zdas04]

Good luck finding a 150 hp 4 stage centrifugal to move 0.5 MMCF/d

David

 

[CH5OH]

zdas04,
if you insist:

http://www.sundyne.com/cda/ind/pr/viewimage/1,10526,CLI1_DIV92_ETI7223_IMD2_MDI41,00.html

 

[zdas04]

I don't insist. That graph didn't tell me anything. But I'm not in this market. Just trying to help. I have had a great deal of difficulty buying a small hp multi-stage centrifigal compressr. Several people say they sell them, but their priority seems to be focused on big frames.

David

 

[zdas04]

Oh yeah, the stated conditions are 350 SCFM. At 30 psig suction, that is 100 acfm. That puts you off your curve at 5 compression ratios and the application needs at least 11.

David

 

[unclesyd]

You could also take a look at a Sundyne Compressor for your operation. We use these to recirculate H2 in one of our processes. At one time we also used these to Butane.

http://www.sundyne.com/ind/details/0,10494,CLI1_DIV92_ETI7605,00.html

 

[CH5OH]

zdas04,
I am not used to work with non metric units
i thought 350 SCFM meant suction cubic feet/minute
and atmospheric cubic feet/minute
a wikki search later:
standard cubic and actual cubic
...
same here, just want to help
wouldn't hurt to contact sundyne and see if they can stretch the curve a bit