[Gasification] Blue water gas...... Why bother?

[drew]

I do like to think that my awareness evolves, thanks ;-)

doug.williams wrote:

> Hi Drew, and Colleagues,
>
> Drew, there is nothing like the evolution of awareness, and you are 
> right on when you suggest that you introduce steam via a riser tube in 
> the reduction zone. However, you cannot put it through the centre, 
> because as Tom R, say's, it is endothermic, and you will cool the 
> reduction char. If however, you had your steam coil or similar device 
> located in the exit gas stream, you should be able to put steam in at 
> least 800C to the top of the throat tube.

If you introduce steam heated to the same temperature (or as much as 70C 
higher via hilsch tube based heat exchanger) as the gas that is leaving 
the gassifier (which it seems to me in a properly insulated system 
should be the same temp as the bottom of the char bed?), would that cool 
the process?     I am sure that the difference in total heat capacity of 
the inflowing steam, and outgoing produced gas would have to be balanced 
(a fixed amount of heat is available in the outgoing gas, that is all 
the heat available to superheat the steam, therefore the steam 
introduced would need to be limited relative to the output gas)   (If an 
IC engine is used a hilsch tube could be used on it's exhaust as well to 
generate a low mass flow higher temp gas stream to run the primary steam 
generator).   If you generate your steam via two heat exchangers  (the 
superheater/heat exchanger could be run off the outgoing gasses split 
via routed via a  hilch tube, to give a smaller mass flow, at + 70 C 
temp boost, coupled to the exhaust gas then you would be adding steam to 
the incandesant char zone, with enough energy to decompose to the H2 and 
O, needing only the incandesant char C to strip the oxygen from the H2O, 
resulting in a gass flow of CO, and H2, surrounding the riser tube, if 
the riser tube is surrounded by a larger diameter riser tube that ends 
at a lower point (similar to the bayonet used in Kalle gassifier but 
inverted).   If a vaccum is applied to this lower pipe, and the diameter 
and relative heights of the two riser tubes are correct the gasses drawn 
into the lower tube should be very clean H2 and CO perhaps of high 
enough purity to be suitable for compressing? while the normal producer 
gas continues to be drawn through the normal system.

>
> Now, if you do this, it requires the highest possible throat 
> temperature (12-1500C), because you are adding water over that found 
> in the fuel. So the question remains, can you add more water than the 
> driest biomass (20% oven dry, chemically bound), and make more H2? 
> Water by the way will thermally crack once you start getting over 
> 850C. This answers your first question,
>
>> The water shift reaction can happen at 500C ?
>
>
> No it cannot.

Can we find a consensus on this temp?    We seem to have two different 
opinions, are they based on differing circumstances?

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