Screw compressor for CO2

[chemtechnical]

I would like to find a screw compressor suitable for compression of 625kg/hr of CO2 gas from 0 barg & 35degC to 18barg.

Will appreciate any comments.

 

[Montemayor]

chemtechnical:

The type and make of screw compressor is easy to identify:
use a Mycom screw with oil spray sealing the screw lobes. I've used these machines on a variety of CO2 compression packages. The potential problem may be the capacity. I've applied screws on much larger CO2 streams and can only guess at this moment if Mycom has a small screw for your application. But a quick call or inquiry with them will give you the answer. There are other screw machines, but I'm more familiar with Mycom's.

The main problem you will face is the post-compression oil separation efficiency and oil return. This has always been the main obstacle to a successful screw application in services such as this one. This problem can be overcome and controlled, but you need a designer who has succeeded in the past and has the experience to prove it. It isn't a complicated science, but it does require "know-how".

The original screw compressor that was developed and marketed for many years proved a failure at process compression applications while operating "dry" - the way it was originally envisioned. It wasn't until developers realized that a dry machine was never going to be able to compete successfully that they turned to a "wet" machine - one sealed with recirculated lube oil. Today the screw is successfully fullfilling a niche in the refrigeration compression business thanks to that decision. The application has been applied to CO2 compression and subsequent liquefaction as well.

Good luck with finding a screw machine small enough.

Art Montemayor
Spring, TX

 

[Montemayor]

chemtechnical:

Please excuse my oversight in not furnishing the Mycom website where you can start to get assistance and help in this application:

http://www.chemicals-technology.com/contractors/compressors/mayekawa/index.html#mayekawa1

Regards

Art Montemayor
Spring, TX

 

[chemtechnical]

Montemayor:

Many thanks for your reply. You mentioned you have used screw machines on a variety of CO2 compression packages. Are they foodgrade CO2? What are the capacities? Similar operating conditions as mine?

I have in fact corresponded with Mycom Australia. They recommend model 1612LSC-LBM which is very expensive. It was also a bit vague if it is suitable for foodgrade CO2. Do you know which and who would be the best Mycom office and person to contact?

I would also like to explore other screw machines. Can you please advise the other brands?

Thank you very much for your help.

 

[Montemayor]

chemtechnical:

Most all of the bulk CO2 that I've ever compressed has been slated for the food industry - either as liquid CO2 or Dry Ice. As I said, the major challenge is getting the oil out of the CO2 gaseous product - that's not part of the screw machine's know-how, but is the property of the engineering company who puts the compressor package together. I've witnessed and visited other screw machine applications and they seemed to be operating well - except that you don't know all the dirty little secrets in the background unless you're the operator: how good does their oil removal system work? No one in the industry likes to talk about contaminated food grade CO2 - it's too serious a subject to even joke about.

Today, major purchase contracts (like Coca-Cola's) like to impose a sophisticated CO2 purity analysis on each shipment. I wouldn't mind that because I know I can produce food grade quality consistantly - albeit with added costs for downstream activated carbon adsorption prior to liquefaction. These costs, I would pass on to customers like Coca-Cola who insist on belt-and-suspenders type of guarantees. It's a different market now than what it was 40 years ago, but the basic business rules still apply.

I compressed to 220 psig and went on to mechanical oil separation, some oil adsorption, adsorptive drying, and liquefaction with an NH3 refrigeration cycle. I always used a flooded NH3 evaporator in the form of a BKU reboiler. If push came to shove in guaranteeing a max. oil content in fractions of a ppm, then I would simply put a guard bed on my activated alumina dryers and demand on-line stream analysis on an hourly basis.

You mention that Mycom is expensive; I wouldn't doubt it from your perspective. But bear in mind that you're going to rely heavily on compressor reliability and mechanical integrity for 24-hr/day, 7-day/wk performance all year. I would not rely on pricing to decide on the compressor make. I would rely on experience, history, and mechanical integrity as more important for the kind of product you are thinking of producing.

Hopes this helps.

Art Montemayor
Spring, TX

 

[PSucher]

There are MANY diferent brands of process oil flooded screw compressors: Howden, Mycom, Aerzen, GHH, Kobelco, Tamrotor to name a few. Only a couple have a "compound" machine (Mycom & Kobelco). Kobelco & Mycom offer factory direct packaging of their unit (noting that packaing costs are 80% to 90% of the system purchase cost).

Mycom allows others to package their compressor, Kobelco does not (currently).

We can supply (build and engineer) quote all screw compressor mentioned above, except Kobelco. We have extensive experience with CO2 compression processing.

Please e-mail me at PSucher@ToromontProcess.com if you wish for us to work with your company your application.

Pat

 

[usjbh]

It's been over 25 years since I've done any system engineering using screw compressors for clean air, but I always used Balston coalescing filters to remove the oil. They are now part of Parker and you can contact them for your post filtration requirements.

http://www.parker.com/balston/cat/english/lf9a.pdf

 

[jpak]

Mycom U.S.A. will be happy to submit a budget quote to you. Please contact me at jpak@mycomcpc.com. Please note that for many of our compressors in food application, we utilize food grade oil (i.e., for soft drink and cereal companies)

Best regards,
J. Pak

 

[wms]

Mycom is the way to go. However, unless you can sell your product for $ 10/Ton or more you will not be able to justify the expense of so small a plant. What is the purity of the CO2 stream, and source?

 

[chemtechnical]

wms,
Thanks for your reply. The final product CO2 can easily be sold for more than $10/ton. The CO2 stream entering the CO2 compressor is water saturated and is 99.9% CO2 (dry basis). The CO2 is generated from combustion of light diesel.