[Digestion] Digestion Digest, Vol 5, Issue 16

[Sumedh Bapat]

Dear Dr. Karve,

Here is a note on Pyrolytically generated gas form wood.

A wood gasifier takes wood chips, sawdust, charcoal, coal, rubber or similar
materials as fuel and burns these incompletely in a fire box, producing
solid ashes and soot (which have to be removed periodically from the
gasifier) and wood gas. The wood gas can then be filtered for tars and
soot/ash particles, cooled and directed to an engine or fuel cell. Most of
these engines have severe purity requirements of the wood gas, so the gas
often has to pass through extensive gas cleaning in order to remove or
convert (i.e. to " <http://en.wikipedia.org/wiki/Cracking_(chemistry)>crack")
tars and particles. The removal of tar is often accomplished by using a
water scrubber. Running wood gas in an unmodified gasoline-burning internal
combustion engine may lead to problematic build-up of unburned compounds.

The quality of the gas from different gasifiers varies a great deal. Staged
gasifiers, where pyrolysis and gasification occur separately (instead of in
the same reaction zone as was the case in e.g. the WWII gasifiers), can be
engineered to produce essentially tar-free gas (less than 1 mg/m³), while
single-reactor fluid-bed gasifiers may exceed 50,000 mg/m³ tar. The fluid
bed reactors have the advantage of being much more compact (more capacity
per volume and price). Depending on the intended use of the gas, tar can be
beneficial as well by increasing the heating value of the gas.

The heat of combustion of producer gas (a term used in the U.S. meaning wood
gas produced for use in a combustion engine) is rather low compared to other
fuels. Producer gas has a lower heating value of 5.7 MJ/kg versus 55.9 MJ/kg
for natural gas and 44.1 MJ/kg for gasoline. The heating value of wood is
typically 15-18 MJ/kg. Presumably, these values can vary somewhat from
sample to sample. The same source reports the following chemical composition
by volume which most likely is also variable:

   - Nitrogen N2: 50.9%
   - Carbon monoxide CO: 27.0%
   - Hydrogen H2: 14.0%
   - Carbon dioxide CO2: 4.5%
   - Methane CH4: 3.0%
   - Oxygen O2: 0.6%

Thank you,
Sumedh Bapat


On Mon, Jan 24, 2011 at 1:30 AM, <digestion-request at lists.bioenergylists.org
> wrote:

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>   1. composition of pyrolysis gas (Anand Karve)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sun, 23 Jan 2011 18:31:39 +0800
> From: Anand Karve <adkarve at gmail.com>
> To: For Discussion of Anaerobic Digestion
>        <digestion at lists.bioenergylists.org>
> Subject: [Digestion] composition of pyrolysis gas
> Message-ID:
>        <AANLkTikc8vq=k6ghLk9+4o47Xi6js1QVYn1czHY6nD8c at mail.gmail.com<k6ghLk9%2B4o47Xi6js1QVYn1czHY6nD8c at mail.gmail.com>
> >
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> I would like to know the composition of pyrolysis gas. This has nothing to
> do with anaerobic digestion but the need for this information arose because
> of the fact that lignocellulosic material, which represents the largest
> bulk
> of biologically produced organic material, cannot generate biogas through
> A.D. Combustible gas, and of course a lot of tar were produced when I
> heated dry agricultural waste under anaerobic conditions, but when
> I consulted konwledgiable persons, and asked them about the composition of
> this gas, all of them, without exception, informed me that this gas
> contained about 55% nitrogen, about 40% carbon monoxide and small
> quantities
> of hydrogen and methane. This is obviously the composition of producer gas,
> which is produced when a substance is gassified by burning it. As the
> process of burning requires air, and since the oxygen is used up in the
> process of burning, one gets the high nitrogen content in the producer
> gas. In my experiment, I just heated the material in a closed vessel, The
> starting material itself has no protein, and no outside air is allowed to
> get into the vessel. So there can be no nitrogen in the gas (or very little
> of it).
> Yours
> A.D.Karve
>
> --
> ***
> Dr. A.D. Karve
> President, Appropriate Rural Technology Institute (ARTI)
>
> *Please change my email address in your records to: adkarve at gmail.com *
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> End of Digestion Digest, Vol 5, Issue 16
> ****************************************
>



-- 
Kind Regards,


*Sumedh Bapat*
*+919881090693 / +919879110924*
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