[Stoves] Inquiry re blue flame from rice husk gasifier

Wed Jan 16 18:14:33 CST 2019

Dear Paul and Everyone

While the tales of Olde are forthcoming, something should be added about the roots of close-coupled gasifier combustion at small scale.  Here is some grist for the mill.

IN 1998 Vince Court<https://www.eco-blaze.com/index.php> in Nova Scotia patented his small scale gasifier/burner. This was investigated by a group who tested it at NRCAN in 2000.

http://www.reap-canada.com/online_library/feedstock_biomass/15%20Assessment%20of.PDF<https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.reap-canada.com%2Fonline_library%2Ffeedstock_biomass%2F15%2520Assessment%2520of.PDF&data=02%7C01%7C%7C21f28ff197e1482afc9f08d67c09c2f5%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636832778694718877&sdata=iJnAp6%2FUVVjef2kMpgvOZzGjXOSOWwWFqG%2F6gvGOkK0%3D&reserved=0>

See Table 6. They took the prototype from Vince and he never got a cent from the invention.

By late 2000 Roger Samson, looking for a way to create demand for switchgrass pellets, something he was promoting as a biofuel since the 80’s, had been working on making a small gasifier.

https://ep.probeinternational.org/2000/12/18/biomass-breakthrough-cuts-heating-costs-and-greenhouse-gas-emissions/<https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fep.probeinternational.org%2F2000%2F12%2F18%2Fbiomass-breakthrough-cuts-heating-costs-and-greenhouse-gas-emissions%2F&data=02%7C01%7C%7C21f28ff197e1482afc9f08d67c09c2f5%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636832778694718877&sdata=kU3L0osfWqRZOIUgJ6LIcK87sX2srVgvDRKZSL7DiAs%3D&reserved=0>

Roger was also working in Mayon, Philippines, with another granular fuel: rice hull.  Roger, now experienced with the Dellpoint Stove as inspiration (in terms of the flame’s appearance), introduced to an early MTS version more turbulence with a pair of air inlets from below.  He demonstrated it to Alexis in Panay, who at that time had a commercial scale gasifier that was not very clean, and did not have blue flame.

Alexis went on to make a number of tall, thin gasifiers with, variously, fans and char-dumping capability.  I saw one first at the GACC Roadmap conference in Bangkok.

Roger first saw the blue flame and vortex mixing while looking at the Dellpoint Stove and credits everything to that inspiration.  He was able to get the same result with the turbulent mixing in the Mayon Turbo Stove (2001). BTW, it uses waste heat coming from the side of the combustion chamber to dry the (gravity-feeding) rice hull before it reaches the pyrolysation zone.  (That refers to the earlier message about drying rice hull fuel.)

The Mayon Turbo Stove was tested for emissions not long after that and shown to have remarkably low PM2.5 emissions (being a gasifier and all). In 2008 it was tested again and included in a paper on 6 stoves and their GHG emissions.  The MTS had obviously been mis-operated and clearly its GHG emissions mis-calculated (specifically, the CO2).  The authors agreed at least to the latter and withdrew the paper, re-issuing it not with corrections, but with the MTS removed, leaving the Rocket Stove as the top performer. So it became a 5-stove review<MacCarty%20N,%20Ogle%20D,%20Still%20D,%20Bond%20T,%20Roden%20C.%20A%20laboratory%20comparison%20of%20the%20global%20warming%20impact%20of%20five%20major%20types%20of%20biomass%20cooking%20stoves.%20Energy%20Sustainable%20Development,%202008>. For the record, the earlier test showed the MTS was much cleaner-burning than the tests of those 5.

Reaching an agreement with Roger, I worked in Waterloo with two of his interns on improving the efficiency.  I replaced the two tubes at the bottom centre with one, adding a flat metal cap to drive the incoming air to the side. This gasified more of the char, improving the completeness of pyrolysation and reducing fuel consumption. This arrangement also maintained the needed turbulence while greatly limiting the excess air, which had always been too high. The consequence of that excess air has been unnecessarily high CO. Adding a cooking plate on top with small pot stands completed the changes, and the cooking efficiency was doubled. The final version had higher power, lower emissions of everything, less requirement for attention to the fuel feeding and by management of the air entry, good control of the cooking power.

The output at the bottom of the updated MTS is a higher ash char with no volatiles because by the end of the vertical drop, the pyrolysis is more complete.

I maintain that the blueness of the flame is caused by combustion conditions in which the hydrogen can be combusted first followed by CO combustion in a relatively high concentration.  When there is strong mixing the colour is more pink and pale yellow as they are burning together.

Burn ‘em clean!
Crispin
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