[Digestion] Eliminating Sulfides.

Ken Calvert renertech at xtra.co.nz
Tue Oct 5 14:57:44 PDT 2010

Igor,  to my way of thinking, the use of ferric chloride is expensive, because it is difficult to recover out of the system and you have to keep buying more.  I am not sure quite where you intend to use it?  If you are adding it to the input into the digester  it will settle inside and gradually clog your system.   For me, the best filter system is 
a heavy steel, or a plastic drum  filled with bashed up rusty tin cans.  Make sure they are rusty, because new ones are still coated with a varnish that they use instead of the old tin plate.  Place the iron oxide filter between the digester and the flexy gas bag for storage.  This makes for an even rate of flow with enough moisture in the gas to activate the reaction.  The H2S in the gas reacts with the metalic iron or iron oxide and makes iron sulfide.   When nearly all the oxide has gone, and the only way to be really sure is to have two drums in parallel and switch from one to the other at regular intervals,  all that is required to regenerate that drum is to open it to the air.
In the presence of oyygen ferrous sulfide reverts to metalic iron and elemental sulfur, along with the evolution of a lot of heat  With a heavy steel drum that is no problem, you just hook a small blower onto one outlet.   With a plastic drum its a case of just opening the inlet and outlet .and positioning the drum in such a way that the heat will 
cause a convention flow of hot air.  And if the drum gets too hot reduce the air current.  With all the iron back into its metalic state the drum is ready for recycle, until there is so much flowers of sulfur that every thing gets clogged up.    ATB.  Ken C.
  ----- Original Message ----- 
  From: Igor Škrjanec 
  To: For Discussion of Anaerobic Digestion 
  Sent: Wednesday, October 06, 2010 12:55 AM
  Subject: Re: [Digestion] (no subject)

  Na 4.10.2010 20:15, Arturo Ávalos je pisal: 
    Hello all

    Does someone know something about use ferric chloride to reduce the sulfur content in the biogas?

    Thanks for the information


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  Hallo Arturo

  Ferric chloride is normally use for a neutralizations of H2S. Hydrogen sulfide is slightly soluble in water and acts as a weak acid, because of this is harmful for a CHP unit.

  H2S is a product of sulfate-reducing bacteria which are also present in biogas reactor. Sulfate-reducing bacteria use present sulfats from substrates to oxidize the organic matter.

  Hydrogen sulfide reacts with metal ions to form metal sulfides (H2S + FeCl2 ? FeS + 2 HCl). Iron sulfide is not soluble and it is not problematic for a biogas process and CHP unit.

  When biogas plant works normally hydrogen sulfide is not problematic, because of its oxidation with aerobic bacteria to elementary sulphur.




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