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Carbon dioxide removal from biogas

  1. May 21, 2012 #1
    I've been searching the posts here and I think this question may be a little below most of you.
    I've cobbled together a homemade biogas generator and I'm wanting to improve the quality of the biogas by removing some of the CO2 (or all of it if I can) which will leave me with a higher calorific value gas (as the remaining gas is predominantly Methane) and possibly something which I could even burn in my standard gas boiler?

    I know CO2 will dissolve in water, and I also know that if I add heat to the water it will liberate some of the CO2 dissolved (/reacted)

    The questions are

    How much heat do I need to input to liberate the CO2?
    What temperature do I need to achieve, I'll be using waste gas from a condensing boiler so probably about 60 C is my limit?
    What by-products will I produce either with or without releasing the CO2? (so I'll know what materials I can use)
    Is it all worth the effort of should I just constantly replenish the water supply? (again by-products above will tell me if I can re-use the waste water for irrigation, or if I'll cause any problems by dumping it in the sewer, albeit as a constant low flow).
    Would water saturated with CO2 actually be beneficial in the greenhouse (i.e. tomatoes not day after tomorrow)

    I hope this isn't too simple for you guys out there, Chemistry is about twenty five years old for me!
    Regards
    Paul
     
  2. jcsd
  3. May 21, 2012 #2

    uby

    User Avatar

    it sounds like you want to 'getter' the CO2. a 'getter' is any compound which can selectively react with a species and sequester it.

    for CO2, any carbonate-forming oxide would do the trick. for example, barium oxide will react rapidly with CO2 to form barium carbonate. a newly discovered reaction is getting some buzz involving the reaction of lithium nitride (Li3N) with CO2 at elevated temperatures to form lithium oxide, lithium cyanamide and carbon nitride.
     
  4. May 22, 2012 #3
    Thanks uby,
    Are these reactions easily reversible? i.e. can I use nature to regenerate a 'getter'?
    More importantly are the reagents cheap??
    The reactions will be taking place at room temperature, I'm trying to remove CO2 from biogas, before I burn it.
    Thanks again.
     
  5. May 25, 2012 #4
    Search google for "co2 water scrubber for biogas". It is a tank with some parking materials (plastic balls). Compressed biogas at 1000kpa comes from the bottom to mix with compressed water (1200kpa) coming from the top. Co2 dissolve in the water and purified biogas is gotten from the top of the tank. To remove Co2 and recycle the water, you pump the water to a stripping system where you use air to strip out co2 from the water at low pressure.
     
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