[Gasification] [Digestion] composition of pyrolysis gas

Thomas Reed tombreed2010 at gmail.com
Mon Jan 24 11:27:49 CST 2011

Dear Dr Karve

Good question! I hope that someone will come through with an exact answer.  Meanwhile, here are some useful comments.

Gasification produces a gas with well known properties and converts essentially all the biomass to a gas of composition

CO 21; H2 19; CH4 5; N2 52; Misc 3 Volume % dry gas basis.

The air/ fuel ratio for gasification is 6/1.  Most of the air is needed to convert the 20 % charcoal to CO, as in

C + 1/2 (O2 + 3.76 N2) ==> CO + 1.9 N2

A/F = 11.4


For wood pyrolysis, the 20% charcoal does not need to be converted, so 

C H1.4 O0.6 ==> 0.4 C + 0.6 "CH2O" +0.1 H2

MW.  23.             4.8.              18.         0.2

The 0.4 C mostly comes from the lignin.  The "CH2O" is the formula for CarboHydrates, the cellulose and hemicellulose components of biomass, but is broken during pyrolysis.  It would be great if it were broken into CO and H2, but that would be very endothermic, so there will be many compounds making up "tar", and water and CO2.

In an effort to collect the tar, I operated our woodgas stove in a pyrolysis mode by putting a 4" elbow over the secondary air holes and attaching a horizontal 4 foot length of water cooled stovepipe.  I did not see any tar, but I collected about 1/2 weight % of the fuel as a soot which probably absorbed the tar.      

I hope someone will take a sample of the gas and tell us all the components.  


Tom Reed   

Dr Thomas B Reed
President, The Biomass Energy Foundation

On Jan 23, 2011, at 9:24 AM, "Anand Karve" <adkarve at gmail.com> wrote:

> 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)
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