[Gasification] [Stoves] Burning coal in cookstoves

[Thomas Reed]

Dear Kev, John and all:

I have been surprised when burning coal in our WoodGas Cookstove that I 
didn't smell sulfur, but hadn't focussed on the reason.  I think the 
suggestion that starting with wood has created ash that absorbs the S is 
a good one...

TOM REED

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Kevin Chisholm wrote:
> Dear John
>
> John Davies wrote:
>   
>> Crispin,
>>
>> A little clarity on my thoughts.  I use the term wood ash very loosely. My
>> thoughts go in the direction that any wood would burn to ash before the coal
>> was giving off sulphur compounds. In my TLUD coal stove. the ignition is
>> started by burning about 100g of wood kindling above a layer of fine coal.
>> The ash from this wood forms a layer above the coal which can be clearly
>> seen once the wood has been burned. after a while it cannot be clearly seen.
>> Has it dropped into the coal bed below , or has it left the bed as particles
>> in the flue gas ???. I do not know.!
>>   
>>     
>
> Wood ash captures sulphur because it reacts with it and forms a solid 
> compound containing sulphur. In pyrometallurgy, lime is commonly added 
> to combine with sulphur so that it can be "slagged off" and be removed 
> from the metallic phase. Similarily, in the treatment of flue gases from 
> a coal burning power plant, the sulphurous flue gases are reacted with 
> lime to form CaS, or CaSO4. In such a "flue gas desulphurizing 
> operation", the efficiency of lime utilization can be poor... instead on 
> only one mole of Ca being required to capture one mole of S, the molar 
> ratio may be excessive... perhaps the ratio of Ca/S could be 1.2, 1.5 or 
> perhaps as high as 2, in very inefficient cases.
>
> The potassium in the wood ash seems to act as a catalyst, giving an 
> overall reaction along the lines of
>      S + K + Ca ----> KS + Ca ----> CaS + K
>
> The reaction can be thwarted by conditions which lead to the K being 
> consumed by other species. For example, the K can react with SiO2 in the 
> ash to yield a K20-SiO2 glassy phase. Along these lines, too much wood 
> ash could be very bad, in that it could react with the high silica coal 
> ash to make a liquid slag phase at operating temperatures, that could 
> lead to serious clinkering.
>
> The next time you run your TLUD, you might consider checking the 
> resulting coal ash for evidence of glassiness or different appearance. 
> My guess is that your wood ash disappeared by reacting with the coal ash.
>
> Best wishes to all for a Happy and Prosperous 2008
>
> Kevin
>
>
>   
>> With anything up to  5 Kg of coal to be burned, I doubt that there is enough
>> ash to capture all the sulphur. I also doubt that a user would be prepared
>> to add sufficient wood chips into the coal bed to achieve removal.
>>
>> It has to be borne in mind, that those using coal do so because it is much
>> cheaper than firewood in their location. So while the idea is interesting to
>> us, it is unlikely to be utilized by the end user, unless they are forced to
>> do so.
>>
>> At this stage I believe that our aim should be to improve the combustion
>> efficiency, make all the usable heat available, and remove the toxic gasses
>> from the inside of the dwelling. This alone would reduce coal consumption by
>> up to 50 %. And eliminate many deaths due to CO poisoning. That would be a 
>> huge step forward.
>>
>> Wishing all a prosperous and happy 2008.
>>
>> John Davies.
>>
>>   
>>     
>
>
>
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