[Gasification] Relationship between Gas Composition and FluidizedBed Temperature

[Lim Mook Tzeng]

Dear Doug Williams,

Now I have a clearer picture of what my results meant.
Just to confirm some of your statements, the fluidized bed I am running does
defluidize with bed temperatures exceeding 850C due to clinkering. I have
the lumps of clinker to prove it. H2 production would be limited.

Also have found additional information, and I quote:
'Concentrations of CO2, H2O are expected to increase with increasing air
ratio, while CO, CH4 and H2 would decrease' [X.T. Li et al (2004), Biomass
gasification in a circulating fluidized bed, Biomass and Bioenergy, Vol. 26.
171-193.]. An increase in air ratio normally increases the bed temperature.

This statement is opposite from Rezaiyan and Cheremisinoff. Thus would confirm
the differing gas composition trend between types of gasifiers.

I am still in the midst of collecting more reliable data on the gas
composition. I hope one day I would be able to email you that the results
concur and match with the theoritical explanation.

Thanks

Rgds,
Mook Tzeng Lim

On 10/19/06, doug.williams <Doug.Williams at orcon.net.nz> wrote:
>
> Dear Mook Tzeng,
>
> After discussion with my colleagues in Australia, I am sure that your
> information is not referring to Fluidized bed gasifiers, and applicable to
> high temperature downdraft packed bed gasifiers only.
>
> Fluidized beds increase the CH4 with temperature, and CO2 decreases, but
> H2
> is limited by the restriction of maintaining the bed temperature to a
> maximum of 800C to prevent slagging in the bed. These conditions apply to
> air blown fluidized systems, and probably applies to oxygen and
> steam  blown
> syngas production.
>
> Applicable to all systems that produce CO at high temperature from the
> corresponding  reduction of the CO2, will be the location of the measuring
> sensor, because CO will revert back to CO2 and soot in any after bed
> space,
> so can create confusion if trying to adjust the CO2 reduction with
> temperature alone. In the event that you do increase the temperature, you
> will probably see an increase in CO2. A common sign of this situation, is
> coke forming in the gas outlet ducts, in which case, a redesign of the
> system is in order.
>
> I am sure that there are variations to the above statement applicable to
> specific systems, but there is a degree of commercially sensitive
> information about these systems. Your original conclusions are valid from
> the understanding that I have applied to your question.
>
> Doug Williams,
> Fluidyne Gasification.
>
>
> > Dear All,
> >
> > I quote the following from Rezaiyan J. and Cheremisinoff Nicholas P.
> > (2005, Gasification
> > Technologies. CRC Press, Taylor and Francis Group)
> > "CH4 decreases with increasing temperature; CO and H2 formation
> increases
> > with increasing temperature while CO2 decreases with increasing
> > temperature".
> >
> > Does this apply to all gasifier types? The trend of the composition from
> > experiments I am running showed that the trend is completely the reverse
> > of
> > the statement above.
> >
> > Please comment on any on the above.
> >
> > regards
> > Mook Tzeng Lim
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>
>