[Gasification] Gasification Operational Principles

[Kevin Chisholm]

Dear Fredric

Thanks very much for your comments and the URL. I went there and had no 
problem with opening the drawings and figures. Do you have a translation 
of the Finnish text you could send along?

Thanks!

Kevin


Fredrik Ek wrote:
> Doug and list,
>
> Now I have modified my gasifier in accordance with your advice. As I use a
> system for preheating the air, I decreased the size of the nozzle bore from 12
> mm to 10 mm instead of 8 mm. The inner diameter of the reduction tube is 110 mm
> as I had a stainless pipe of that size. This is a little less than the 130 mm
> restriction I had before. The height between the nozzle level and the upper
> edge of the reduction tube is your suggested 125 mm, a little more than the 110
> mm I had before. The grate is set to a distance 75 mm below the upper edge of
> the reduction tube. The nozzle tip ring diameter is the same 250 mm as before
> and so is the fire tube diameter of 350 mm.
>
> Yesterday I lit the gasifier the first time after I made the changes; I had to
> drive some 50 km to an occasion where I was giving a presentation about biogas.
> At start up it took very long before the smoke shifted from cream colour to the
> greyish blue colour that I use as an indicator of reasonably low tar for
> leading the gas to the filters. The fresh and smashed BBQ charcoal I had filled
> the gasifier with at start was giving tar off. Also the lack of a strong coked
> tar/char/ash slope between the nozzle tips and the throat likely had some
> influence on the amounts of tar. The flare flame was also getting very small
> during start up indicating a plugged reduction zone. As I was eager to test the
> thing a little more I anyway started the car and went off. After not more than 5
> km the pressure drop over the entire system had risen to 3,5 m WC, and I had to
> switch to gasoline to get to my destination.
>
> After the biogas occasion I made an attempt to ignite the gasifier to slowly
> burn it empty for easier service, but for the first time ever during my 18600
> km driving on wood gas with this car this was not possible. The thing was
> simply so plugged that my start up fan was unable to cause any flow of gas
> through the gasifier. So next I will lift the grate some distance and hope for
> better performance. How much should I lift the grate? Yet I have not installed
> meters for following up the pressure drop over different components of the
> system.
>
> You asked for drawings of gasifiers, under the link below the VAKOLA drawings
> can be found. Click the blue “täältä” and open the zipped files. Most of the
> mobile gasifiers built in Finland today are of about this design. Tar is not
> any problem with a correctly sized VAKOLA gasifier when coarse chips, wood
> blocks or peat briquettes are used for fuel. The inner air pre-heating space
> surrounding the “fire tube” is separated from the heat of the hearth by an
> internal layer of ash/coked tar/charcoal. Not much heat exchange takes place
> there, at least not on the oxidation side. This kind of air cooling of the
> heart is useful for avoiding serious damage to the unit when the gasifier
> sometimes is driven all empty. Vesa, another Finnish wood gas driver, once
> tried dry charcoal as the only fuel in his gasifier built for peat and wood
> blocks. The result was that all components of the hearth that were not air
> cooled melted. Vesa dug them out together with the ash in the size of peas. As
> the hearth tube had this emergency cooling only the constriction and the grate
> had to be replaced. 
>
> A link with drawings:
>
> http://gamma.nic.fi/~otaina/puukaasu.htm
>
> I do not agree on the statement that the space under the flat restriction is
> empty of char with the VAKOLA design. All the content of the “fire tube” has
> been filled with char each time I have opened my mobile gasifier, the gasifier
> has never had a grate scraper. What I agree on is that the char close to the
> walls has been less packed than the char in the middle, so this does the same
> thing for leading the gases away from the centre.
>
> By the way, is there some reason for why the reduction tube in the Pioneer class
> gasifier not is char/ash insulated all the way down to the grate?
>
> Best regards,
>
> Fredrik Ek
>
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