Co-firing coal with uniform wood chips

I have read a fair amount of research regarding co-firing uniform wood particles with coal and have gained enough courage to present the possiblity of co-firing coal and something like cherry pits here on the forum to determine if anyone has tried something like this.

I've read other posts regarding the question of burning wood pellets or corn with coal in the s-130 and understand the responses. If I can summarize the responses: never try burning anything but coal in a stoaker like the AHS s-130.

The research I have read was done at the industrial level where coal was mixed with varying percentages of uniform dry wood chips. The research presents data on mixtures of 10%, 15% and 20% wood chips and reports no loss in efficiency, nor in problems with fuel delivery. They do report a decrease in the consumption of coal.

I spoke with Jeff at AHS about using cherry pits and he said it has never been done before. His concern was the possibility of a bin fire. I have doubts that a 15% - 20% mixture of cherry pits and coal will work, but I'm willing to try it. I will attempt it in the fall and be sure to report back to the forum with my results.

Why cherry pits? They are basically the same size as pea or buck coal, insects don't like them, and they dry fairly quickly. Also, I have access to cherry pits being that my father, using an outdoor multi-fuel boiler, is using them to heat his 3500 sq ft house (radiant) plus 1500 sq ft basement. He gets them for the price of hauling. I believe he gets them from southern pa or Maryland. Not too many places around that process cherries.

Any thoughts??

Thanks

Pret

Might work, but if so I would think poorly. The reason is the stokers are really designed for coal. I have serious doubts that a cherry pit would have the heat output a similar sized piece of anthracite would. That is one problem. The other would be what is left after the burn. Coal just has a dry ash, corn will leave a sticky substance when burnt and would interfere with most stokers operations. I have no idea what a cherry pit would leave behind. They make corn burning stoves, it may work perfectly in those as they would be a similar fuel.

A pound of coal has about 14,000 BTUs. If a pound of pits has about 3,000 BTUs you can see where this is going right away.

I do think that possibly some could be modified for the purpose depending on the characteristics of said fuel in how it burns and the residue left behind. If you want to pursue it, I would start burning it in a hand fired or something similar to see what kind of heat it can make and what is left. The rest would be an engineering exercise.

Industrial boilers typically use a traveling bed, so they are much different than a residential unit and could run dry manure if they want.

I could see pits or wood chips working pretty good in an under feed stoker like an EFM or my IronFireman. The gravity feed nature of the AHS 130 and the 'shearing grate' design may cause some issues, not the least of which could be a bin or hopper fire like Jeff mentioned.

I like Ian's [coaledsweat] suggestion. Better yet, take a look at the ash and residue in your dad's burner.

One comment about the 'uses less coal'. This I don't doubt, since you are diluting the coal by whatever percentage you add wood or pits. Only 80% coal, and 20% pits, well you will use 20% less coal. Overall BTU consumption will be the same unless you somehow change the heat exchanger efficiency in the boiler.

Another concern: the creosote created by the residual moisture in the pits and wood could make a real mess inside a sophisticated boiler like an AHS. Coal can idle down to a low heat with no creosote or smoke created, this is not so for wood, or I suspect for pits. Too much residual moisture.

Check to see the amount of combustion chamber deposits in your father's boiler or stove. Coal will leave only dry fly ash.

I have mixed wood and coal in a hand load fire, but I don't see any increase efficiency or heat output. Just a lot faster burn.

food for thought. Greg L.
.

The ash from burning cherry pits is a very fine white/grayish ash. I do not know the BTU output of a pound of cherry pits, just what my father has shared with me. I am heading there this weekend and will get better data from him regarding what he burned a season using corn, and what he burned this last season using pits. That will give us some type of general idea the BTU output of cherry pits.

It is true that the industrial coal burning units are of a different design, and this idea (co-firing) may be a puff of smoke in the wind. I truly appreciate your ideas and your suggestions. I will report back after the weekend with info on residue, etc.

I did not consider the possible creosote buildup in the AHS, and would NOT want to coat the inside of that boiler with a nice lining of creosote. I'm certain my dad's boiler is black on the inside... I believe his unit is made by WoodMaster and is designed to burn any grain. He has it auger fed from a mobile grain bin.

I do know that he has been depositing all the ash from the pits into a 55 gallon drum that is only 3/4 full - from the entire season. I was impressed by that. My dad lives in Juniata county South of Port Royal on the way to State College from Harrisburg.

Again, I will report back. Thanks fellas.

Pret

I have burned dried cherry pits in my old pellet stove they actually burned better than the pellets did and much hotter. Dried cherry pits I believe have an output of about 13,000 btu's per pound. I agree with cherry pits only burn right being fed from underneath like a harman pellet stove. Per 40 lb. bag only get about 3% ash and with coal you get 10% or more. With your type boiler I don't think they will feed right plus a hopper fire is quite possible. Also if the pits aren't dried properly they will also create an oily residue on your grate and in the exhaust system.

jpen1 wrote:I have burned dried cherry pits in my old pellet stove they actually burned better than the pellets did and much hotter. Dried cherry pits I believe have an output of about 13,000 btu's per pound. I agree with cherry pits only burn right being fed from underneath like a harman pellet stove. Per 40 lb. bag only get about 3% ash and with coal you get 10% or more. With your type boiler I don't think they will feed right plus a hopper fire is quite possible. Also if the pits aren't dried properly they will also create an oily residue on your grate and in the exhaust system.

This is interesting. Im surprised by the amount of btu's per pound you get from the pits. Having a good dry pit mixed with coal at a 20/80 mixture might be something to try.

I googled BTU per pound of cherry pits and found this site. You many be interested in it.

http://listserv.repp.org/pipermail/stov ... 02305.html

This site reports a BTU value between 9 and 10 thousand. Although not as high as coal, it is higher than wood, and any other grain including corn.

I won't be able to test the 20% mixture coal/cherry pits until this coming season, but I'll be sure to report my findings.

If one were to have a good supply of cherry pits, AHS has a wood boiler called the wood gun that can be retrofitted with an air lock delivery system that would be perfect for burning pits.

Fellas, I truly appreciate these discussions. I have read more in the past two weeks than the time I spent in college - both times!

Pret

Pret I checked my info on the cherry pits and your Btu value is very close to the 10,500btu per pound on my literature. I got the value mixed up with some waxed cardboard pellets that I had tried which come in at the 13,000 btu's per pound. I liked burning the cherry pits but I found that even in an underfeed pellet stove I still didn;t feel comfortable burning straight pits beacuse the fire always crept towards the auger. Atleast where I am at it is more expensive to burn the cherry or olive pits.

I have doubts myself, as time progresses and I read more literature on burning pits that co-firing pits with coal will most likely not work. I will still attempt it though.

For anyone who is interested, my brother has been burning straight cherry pits in his Harman corn burning stove and he is very pleased! Works wonderfully he said.

Pret,
I just PM'ed you as well but has anyone else worked with cherry pits or peach pits in an EFM?

Thanks,
Glenn