[Digestion] Eliminating Sulfides.

[Igor Škrjanec]

  Na 5.10.2010 23:57, Ken Calvert je pisal:
> 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 <mailto:igor.skrjanec at gmail.com>
>     *To:* For Discussion of Anaerobic Digestion
>     <mailto:digestion at lists.bioenergylists.org>
>     *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
>>
>>     //
>>
>>     Arturo
>>
>>
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>
>     Hallo Arturo
>
>
>     Ferric chloride is normally use for a neutralizations of H_2 S.
>     Hydrogen sulfide is slightly soluble in water and acts as a weak
>     acid <http://en.wikipedia.org/wiki/Weak_acid>, because of this is
>     harmful for a CHP unit.
>
>     H_2 S is a product of sulfate-reducing bacteria
>     <http://en.wikipedia.org/wiki/Sulfate-reducing_bacteria> which are
>     also present in biogas reactor. Sulfate-reducing bacteria
>     <http://en.wikipedia.org/wiki/Sulfate-reducing_bacteria> use
>     present sulfats from substrates to oxidize the organic matter.
>
>     Hydrogen sulfide reacts with metal ions to form metal sulfides
>     <http://en.wikipedia.org/wiki/Sulfide> (H_2 S + FeCl_2 ? 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.
>
>
>     Bye
>
>     Igor
>
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Hello Ken,

In Europe we use ferric chloride only in start-up. After month or two 
you don’t need FeCL_2 anymore, because we blowing into reactor small 
quantity of air. This is obligatory for aerobic bacteria which convert 
H_2 S in to elemental sulfur. This method is also efficient, cheap and 
easy to handle.

Normally you need for 1 MW biogas plant around 0,5 m^3 FeCl_2. Because 
of low quantity of FeCL_2 we don’t haw any problems with sediment FeS 
and also this low concentracion of FeS are welcom as a fertilizer.

Igor

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