Can I scrubb CO2 out of biogas in normal athmosphere pressure? Or is it waste of time...?

Hello Sakari
Well, all depend on the flow of biogas that you will have for treatment and the percentage of co2, but if it is a significant quantity of biogas, and co2, I am sure you will prefer to use some pressure, maybe a lot.

Other thing is the liquid you wish to use for the treatment, and of course the final use of the biogas.

Flow of biogas is only about 120 liters per minute (small farm size digester)and CO2 content is less than 40% (60 to 65% methane). We are using the purified methane gas as vehicle fuel and it means it should be 97% pure methane!
Liquid used for scrubbing is pure water or water with lime stone (or some other suitable stuff).

 

You've answered your own question- it's a waste of time.  Even large landfill gas energy recovery systems operating with internal combustion engines are using the biogas without attempting to remove the CO2 from the methane.  The additional efficiency derived from operating on purified methane doesn't pay the capital and operating costs of CO2 removal even on such a large scale, so on your scale it's hopeless.

Use the methane to fire a heater or something else which doesn't care so much about the CO2 that comes along for the ride.

i believe you   only have to use pure water to scrub the  gas . we use it to fire our  dual burner boilers   and its doing great. i will also agree with moltenmetal  that its useless to  to try scrubbing out the CO2  gas.  thanks

i agree with my friend molten metal that its useless to scrub out co2  since  we  are using methane gas  to fire our dual burner  boilers  after scrubbing through  process water.

It is essential to scrubb out CO2 because of limited fuel storage in bi-fuel car. In burners it is not needed I agree. But how to make it cost effective??

Do you need to scrubb?
For small production of biogas the most economical option will be membranes. You can go to a 98% CH4 (Nm3) and you will have a low percentage of water.

I do not mind what the method is...main thing is to get calorific value of biogas up. Where I can get the mambranes you mentioned? Is it expensive?

Hi Sakari

1. moltenmetal told you the economical option. To use biogas for cogeneration.

2. You said that it is for the production of vehicle-quality biogas, so I suppose that you need, more or less, CO2<2%, H2S<50ppm and H2O dew point<0ºC

3. If you are with the CH4/CO2 separation, I suppose that the H2S and H2O are not a problem at this point.

4. Here http://www.uop.com/gasprocessing/6010.html you can find an option for this separation with membranes.

5. Expensive? I really don't know. Sorry. But I am sure it is less expensive that a distillation or a scrubber in fixed capital and in operation.

6. If you want to see more options, you can see the Michelle Aresta book Carbon dioxide recovery and utilization

I hope you will find this information useful