Coal in a Keith Gassifier?

I had an opportunity drop in my lap the other day. A friend of mine had 75 tonnes of good anthracite coal taking up space that he needed for something else. He told me he would give it to me if I would get it out of his way. I wasn’t really sure what I was going to do with it, but I was not about to look a gift horse in the mouth. I hired some trucks and had it hauled out and heaped it up on my farm.

I was wondering how it would work out trying to burn this stuff in the gassifier?

Hi Kyle. Ya gotta like it when people give you things, WOW, 75 tons! The short answer is NO. The long answer can be found by entering coal in the search box, upper left. Historically, it has been done, but is tricky, and dirty.

Oh well. Guess I will just have to use it for my hydronic heating system.

Anthracite is good stuff but when you burn it, it leaves a big rock behind. Jonathan S made the mistake of starting one of his gasifiers the first time using coal thinking it would be like charcoal and it wiped out his lower section. It is a fossil fuel and has a piled of stored energy but you would have to build a “special” unit to use it. Probably a cross draft with a water drip or the such … I have probably 500 pounds of it in my trailer to play with. ML

I believe I would just have to mix a little in and see what happens. If it does work out to mix a little in 75 tons should put you down the road some distance.

Hi Kyle, Anthricite coal is mostly pure carbon. It does not contain hydrogen like wood does, so putting this in your gasifier will only create carbon monoxide. As Wayne says, try some. Maybe a half a gallon per hopper full. This fuel will not make charcoal. It is so necessary for it to be burned up as it enters the charcoal bed of your gasifier.
IFyou were asking about bituminous coal, the answer is completly different. Do not use bituminus coal in a WK gasifier. This stuff fluffs up, gives off sulfur, is corrosive and makes lots of clinker.
Gary in PA who is sitting on top of a bituminous coal seam

Gary - I am no chemistry whiz, but I was thinking that coal was a commonly used source for making syngas back in the day (hydrogen and carbon monoxide) via coal gassification. Since this is the main product of wood gassification, it made me think that maybe the coal would work in the same way. But, as others have pointed out, you are going to have an issue with clinker, and a coal gassifier would probably be better designed for that specific purpose. I might try mixing a little in, just to see what happens.

My eighth edition of Mark’s Engineering Handbook had 11 pages of information about coal. Personally, I think it’s a very interesting read, but I do some blacksmithing, so my view is probably somewhat biased that way.
We used anthracite coal when I was a kid and the grates needed were very thick CAST iron and HAD to be such to survive for very long. Like 20 years or so living in northern Illinois winters.
As previously mentioned, clinkers as large a 3 or 4 pounds would form on the grates. We’d pull those out with a pair of long-handled tongs. The grates were trianbular in cross section and were geared together just outside the firepot itself. We’ attach a crank to one of the grates and rotate it several times. All grate bars turned in opposite directions and ground up the clinkers into, I think, pieces no larger than about 1/2 inch cubed. Everybody had 5 gallon pails of clinker to use on the driveyway and the road close to the house in the days before they plowed after a snow. Those clinkers were almost as sharp as razor blades, IIRC.
Coking: There is a difference between “making coke” and “coking up” to us blacksmiths. I think that any coal can be managed to produce coke, but only a few ranks (different kinds)of coal actually “coke up” which means that as the coal is heated and volatiles are burned off, the resultant carbon grains stick together. With most ranks of coal this does not occur. You would not want “coking coal” in a gasifier. Think of the worst possible bridging scenario and there you are.
Surprisingly, anthracite coal is NOT the highest heat value-per-pound coal. The highest couple of ranks of bituminous coal actually have a slightly higher BTU/pound heating value. These, by the way, are the ranks of coal the we usually use for blacksmithing.
Sulphur: Not all coal has a high suiphur content. In fact, blacksmith coal is usually chosen for its LOW sulphur content and the bitumious coals that I describe above sometimes fit that bill. As I am sure most of you know, sulphur is bad for steel, making it brittle and otherwise damaging structural properties.
In summary: for anthracite coal, I don’t think you will have much of a “coking up” problem, but it you use a high enough Proportion of it in your fule mix, that is, enough so the buring particles can stick together, you will have very hard clinkers. Even IF the burning particles don’t stick together, you will probably have tiny very abrasive glassy particles flying around in your filter system. I’m not sure I’d want risk ANY of them getting to the engine.

Pete Stanaitis

Gas from Coal:
As I thuimbed forward a few pages in the Mark’s Handbook mentioned in my earlier post, I ran across a 12 page section in the same chapter about making gas from coal. You have to look closely at the several system diagrams to make sure you aren’t looking at the very same gasifiers discussed on this website.
Summary: Coal in general was and is definitley used to make combustible gases.
And, in this section, the physics and some chemistry of the coking process and why certain kinds of coal do or don’t work well are further defined.

Pete Stanaitis