(Okay, this time in English.)
Dear Islander
I've read this paper few months ago and - to be honest - I did not understand anything. It applies to all other explanations of how gasification works. Even after watching Gasification 101 from APL I knew all the processes that are happening in the gasifier, yet still didn't know how to build one. Common practice of describing gasification as 'combustion in limited amount of air' is so totally misleading! It's combustion in limited amount of
oxygen. Limited not by restricting air access but by burning part of the fuel in as high temperature as possible. For a long time I did not encounter the idea of gasification explained that way. I did not see it explained sufficiently in any place. Looks like people who are doing this either do not understand it or can't explain it, because the way it works is too obvious for them.
Luk did not only show me how it goes but explained the idea in two plain sentences!
Now I understand what superficial velocity is. But it's an engineering term which does not explain things. You have to know how things work prior to understand it. One has to get over the 'limited amount of air' curse. Once I know that it's not about limiting air access, but on the contrary: pushing even more air through the fuel bed to consume oxygen by burning tars, SV is pretty self-explanatory. The higher air flow rate is, the hotter combustion zone gets, more tars are burned and more cleaner gas is produced.
Regarding my crossdraft prototype, I tried to ignite charcoal bed starting from gas exit, leaving air flow as it was. Once it lit up fully, I added some pellets, but again it gave me lots of tarry gas and worked only few minutes. After that smoke was not burnable anymore. Looks like it's broken by design. Without enough char in fuel tube at the top it hardly works, so it seems that it is the fuel tube part that is doing almost all the job.
I put this prototype aside for a while and switch to more classic downdraft. As an interlude I took this old L-shaped thing made of refractory concrete I used previously.
WP_20150424_12_53_52_Pro.jpg
Insulated with rock wool, this time fed with fine-grained coal, was producing gas like this:
WP_20150911_17_42_00_Pro.jpg
Now I plan to build something similar to
Spacepeter's gasifier but using refractory concrete instead of steel pipe for fire tube, making hearth diameter extending a bit downwardly for easier fuel flow.
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