Home > Engineering, Science, Scrap Heap > On Anaerobic Digesters and CO2

On Anaerobic Digesters and CO2

Regular readers will know that we built a prototype digester last year. It was relatively successful, but not very efficient due to the design, which was based around cost rather than gas production.

It was a proof-of-concept model.

Since then, I have designed, but not built models that should work a lot better, and I have also done some reading on the subject, since I can do little else with my wrist in plaster.

One thing that I found out recently – the gas produced is mainly methane [CH4], but there is a lot of carbon dioxide [CO2] in the mix. This could prove a bit of a problem as CO2 is, of course, inert and is even used in fire extinguishers, not the sort of gas one would want in the supply to a burner of some sort.

The answer, of course, is to clean the gas to remove at least most of the CO2

I believe that passing the CH4/CO2 mix through water does clear out the CO2, leaving a much purer gas fuel.

There is also the possibility of the fuel gas containing sulphur and passing the gas through a stainless steel scrubber will remove this.

However, anaerobic digester design, at personal/small community lever, is a very inexact science. Lots of people are building them, some are successful, others less so. There is a plethora of information on the web, some of it contradictory, so it is a very confusing field.

So, is there anyone out there with experience of building digesters who can verify (or otherwise) the necessity/efficiency of CO2 and sulphur removal?

You input would be most helpful and time saving.

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  1. December 27, 2010 at 20:43

    I think I may have the answer. Pleae contact me via linkein.

  2. Zach
    April 24, 2011 at 04:24

    Hey, did you figure out your CO2 removal issue? I too am interested in the straight forward and simple ways to do this. I have used stainless shavings for the H2S, but am looking for some more cost effective ways for the CO2 issue…

  3. June 30, 2011 at 15:39

    The biogas will burn better without it but it isn’t necessary to remove it.

    CO2 becomes bicarbonate in alkaline solutions (e.g. sodium bicarbonate a.k.a. baking soda; or calcium carbonate aka limestone). CO2 goes into alkaline solutions and comes out of acid solutions. It can also be removed with vacuum pressure or increased in solution with higher pressure.

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