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Molecular Sieve: CO2 from off-spec fuel

Molecular Sieve: CO2 from off-spec fuel

Molecular Sieve: CO2 from off-spec fuel

With a small stream of off-spec fuel (35 to 45% Ch4, with N2 and CO2) would like to extract Clean useable CO2 while boosting the heating value of the fuel stream.

Energy required will be about 1.6 MMBTU/h, or about 5000 scfh.  Will need to compress to approx. 75 psig - either before or after the sieve stage.

Is a Molecular Sieve the right approach?  Who makes em?  Where do I go to get more details?


R Adamson
VP Engineering
Mariah Energy Corp.

RE: Molecular Sieve: CO2 from off-spec fuel

The correct method for removing CO2 is dependant on CO2 concentration.  At low CO2 concentrations mole sieves from UOP, ZeoChem, and Grace are good places to start.  At CO2 concentrations over 1%, then amines or other solvet/reaction based systems are best.  If concentrations are over 20%, then UOP and others have membranes.

You mentioned N2, this will also have an impact on which process you use as will H2O.

RE: Molecular Sieve: CO2 from off-spec fuel

Thanks for input.

The CO2 concentration is about 30%, so very high.  Two aims are to harvest clean CO2 and increase BTU rating of fuel.


R Adamson
VP Engineering
Mariah Energy Corp.

RE: Molecular Sieve: CO2 from off-spec fuel

This high CO2 would be a good candidate for a membrane but you won't get a "clean" CO2.  The best way to get clean CO2 is an amine.  The membrane will leave about 5% methane in the vent gas. I see your signed up in the membrane section, so you are familar with this.  I looked a combination membrane amine and there is a fit where one of the recycled membrane steams become fuel.  After the membrane gets the gas down to about 8% to 15%, the amine can be used to polish.

Here is a thought. Propylene Carbonate.  You won't find a lot on it as there only a dozen plants in existance. Kinder-Morgan has one in Utah and Dynergy has on near Ft. Stockton. It does not use heat to "regenerate" the solution, instead the solution is flashed at 5 psia to get the CO2 out of solution. Actually, it is staged down in steps with the first stage flash at 200 psig becomes a recycle to the inlet and the next two stages are vented.

RE: Molecular Sieve: CO2 from off-spec fuel

Thanks for your help.  Will keep looking into this in the background because similar challenges come up with off-spec fuel sources from time to time.  Unfortunately, the customer has decided on another approach so the project is off (for now).

R Adamson
VP Engineering
Mariah Energy Corp.

RE: Molecular Sieve: CO2 from off-spec fuel

A number of issues have to be taken into account, which would ultimately dictate what process route you go.

1. Small gas volumes, hence keep away from HP sweetening/membranes/molecular sieves etc. 1st criteria is to consider a process that will have revenue generation to pay back for the cost of the plant.
2. As part of the Guideline 60 Flare Reduction Program in Alberta, we have put together a low cost process for treating sour or sweet gas. Prime market is solution gas and casing gas. Process can accomplish any combination of A. Gas Sweetening B. Dehydration C. Hydrocarbon Dew Point Control. Will produce gas at LHV > 950 Btu/SCF + meet sales gas CO2/H2S specs. 75 psig pressure achieved at IBL without reciprocating or screw compressors. Brand new skidded plant in building would cost about Can$220,000 +/- 5 %. Hence, you can do your calculations for payback.
3. You can not have the best of both worlds. The first objective is to recover the methane and forget about CO2. Our processs will treat the off gas so that you have zero emission of hydrocarbons.
4. This technology will compete against micro-turbines. It will clean up the gas for gas turbines, reciprocating engines, furnaces etc. You do not put a flame to the gas and get 20 % efficincy with a single cycle micro-turbine. You make clean natural gas (LHV and Wobbe number exceed turbine vendor requirements) which is suitable for fired equipment and if the need be, you can compress it and sell it to Novagas, Atco etc.

If you respond, we can continue the discussions. I am currently out of Canada in Belgium and will be on the move to the UK on business next week. Use contact EMail: courtneydehn@canada.com

Courtney Dehn
Process Manager
TG Engineering Inc,

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