[Gasification] reducing temp. of gasification

[Anand Karve]

Dear Mr. Shah,
your explanation on the issue of gasification temperature was highly
enlightening. Thanks. I realise, that as a biologist, I should
restrict myself to biogas, an area of research, in which I am getting
very encouraging results.
Yours
A.D.Karve

On Mon, Sep 12, 2011 at 11:26 PM, Shah, Naresh <naresh.shah at uky.edu> wrote:
> What you are describing are two different processes.
>
>  When you heat biomass in absence of oxygen, you are in a purely pyrolysis
> zone and all the gases produced – CO, CO2, H2, H2O, CH4, C2H6, etc. are
> results of breaking of bonds in the biomass.  As the temperature increases,
> there is more energy available to break more bonds and you get more gas.  A
> closed vessel pyrolysis will produce large amount of char as it is very
> difficult to break C-C bonds.
>
>
>
> When you blow oxidant (air) in the reactor, it can react with the biomass.
> This reaction has two effects: (1) Since oxidation is exothermic reaction,
> temperature of the charge increases, and (2) oxidant (air) also chemically
> reacts reaction with  biomass and it is quite effective in breaking C-C
> bonds to produce additional CO and CO2 gases at high enough temperatures
> (>700 C) CO2 can also react with biomass to produce additional CO.  This is
> the main reason for increasing the temperature of gasification. Low
> temperature gasification, even with the use of catalysts, cannot overcome
> this thermodynamic limitation.
>
>
>
> To minimize nitrogen dilution in the product gas stream, the easiest
> solution is to feed oxygen instead of air.  This solution can be a big
> challenge and impractical in small scale gasifiers.  To control the process
> temperature of a closed vessel and to supply heat from outside, one can use
> either externally heated pyrolyzer like coke oven or externally/internally
> heated fluidized bed reactors.
>
>
>
> Use of catalysts in chemical reactions is only to reduce activation energy
> barriers.
>
>
>
> -Naresh Shah
>
>
>
>
>
>
>
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-- 
***
Dr. A.D. Karve
Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)