[Stoves] coffee grounds as TLUD fuel?

Mon Mar 17 07:30:47 CDT 2014

David,

I concur with Anh and his recommendation that you use a retort within the TLUD to convert the coffee grounds to charcoal.  I have used the TLUD powered retort approach with wood pellets to show students how a retort works.  I load a one quart paint can with wood pellets.  I put just a few holes in the lid of the can and then use it to seal the quart can tightly.  You can experiment with the number, size and placement of the holes.  In any case, they should not be so numerous or large that they allow air to back flow into the retort can.

With loose, low density, coffee grounds I would keep the retort to a small diameter to facilitate heat transfer across the entire contents.

The retort should then be centered in a one gallon scale TLUD.  I would use wood pellets as the feedstock for the retort. Fill the TLUD such that the retort is buried in pellets fairly near to its top.  Light the pellets.  At first the only syngas will be from the pellets.  Then from both the pellets and the retort.  Lastly the TLUD will self extinguish and the flames from the syngas will only be coming from the retort.  At least this is how it goes when I use wood pellets.  It is important the the bottom portion of the retort be sitting in a good bed of hot TLUD charcoal.  This is what allows it to complete the conversion of the its contents.  Note:  Because you use the hot charcoal to finish the retort, some of the TLUD charcoal will be consumed in the process.  Thus your charcoal harvest from the TLUD portion will be diminished.  You may gain some coffee charcoal, but check to see if NET NET you are ahead of the game.

I  have tried this with light fluffy materials and it is a challenge as the light fluffy materials to not transfer heat well.  This will lead to good charcoal at the edges of the retort, but little or no charcoal in the center.  Much experimentation is likely to be required.

Anh is also correct that it is NOT necessary to have the holes at one end of the retort pointing down.  There MUST be some holes at one end to avoid creating an explosive device that could hurt you.

BTW:  Are you aware of the company in Canada that makes coffee logs for your fireplace?  I  believe they mix the dried grounds with wax as a binder.  They burn very nicely -- at least the few I have tried work well in my wood stove.

Lastly, a better use for the grounds might be to create a grounds, charcoal, compost mix to use in your garden.  Folks in my area love untreated coffee grounds for their tomato plants.

Pls keep us posted on your results.

Cheers.

Jock

Jock Gill
P.O. Box 3
Peacham,  VT 05862

Cell: (617) 449-8111

google.com/+JockGill

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> On Mar 17, 2014, at 2:09 AM, Anh <ntanh at greengenvn.com> wrote:
> 
> David,
> 
> You can try to put the ground into a tall metal box or tube (bottom must be
> sealed) and put the whole thing inside, on the side of the stove. Can fill
> the stove with 2/3 of the boxes, the rest is normal wood/pellets. Heat will
> turn the content inside the boxes to biochar and the gases will burn inside
> the stove. During the process, you will see gas burning on top of the
> box/tube. For better effect, can try a cap on the box/tube with some holes
> to let the gas out. That can handle any other lose biomass too. 
> 
> Anh
> 
> -----Original Message-----
> From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
> David Young
> Sent: Monday, March 17, 2014 10:43 AM
> To: stoves at lists.bioenergylists.org
> Subject: [Stoves] coffee grounds as TLUD fuel?
> 
> Dr. Paul Anderson suggested that I join this list and ask about the use of
> coffee grounds as stove fuel.
> 
> At my house, coffee grounds are an energy-dense household waste that usually
> ends up in the garbage.  I'm interested in turning them to fuel for a
> natural-draft TLUD.
> 
> In order to keep the grounds from sifting out the bottom of the fuel
> canister, or clogging the primary air supply, they have to be bound together
> or encapsulated.  Dr. Anderson and I spoke about this problem at a recent
> biochar meeting at the University of Illinois.  Let me tell you some of the
> ideas that have come up so far.
> 
> Dr. Anderson suggested that I try to make "cigars" of the dried grounds:
> sprinkle a line of grounds on a couple of layers of newspaper, wet an edge
> of the newspaper, wrap it around the grounds and seal.  Then, twist the ends
> closed.  Later, stand the dried cigars up and pack them into the TLUD.  I
> will have to try that out.  I love the simplicity of it, and I like the idea
> of reusing another form of waste to encapsulate the grounds.
> 
> I have already experimented some with encapsulating grounds.  In my first
> experiment, I packed a stainless-steel tea ball about 2-inches in diameter
> with dried grounds, and embedded in that in fragments of twigs 1/4-inch in
> diameter or narrower.  My first experiment yielded a smelly, smoldering
> mess.  In the mean time, I have learned more about how a TLUD is supposed to
> behave, and I have modified my stove, so I will have to try the tea ball
> again with my improved stove.
> 
> In second and third experiments, I created narrow "cups" to hold dried
> grounds by drilling 1/2-inch holes lengthwise into the center of windfall
> tree branches 1-inch in diameter and about 3 inches in length.  I stopped
> drilling just short of the end.  I packed grounds into the cavity that the
> drill left.  The cups went into the TLUD, with commercial wood pellets
> surrounding and on top of the cups.  The cups and the grounds burned to
> charcoal in the stove.  While that showed that some grounds can be burned in
> the stove, there was too much labor involved, and grounds contributed very
> little to the total fuel load.
> 
> I have an idea of how to bind the coffee grounds.  Some people are growing
> mushrooms on coffee grounds---a neat demonstration can be found on YouTube,
> <http://www.youtube.com/watch?v=HnLt0Xkm-Hs>.  Perhaps I can grow mushrooms
> on coffee grounds in order for the mycelium to bind the grounds into a solid
> mass that could be dried and used for TLUD fuel?
> This has the advantage that the fungus would do most of the work.
> 
> Another of the ideas that Dr. Anderson had was to pulp some newspaper and
> use that as a binder.  I hadn't thought of that, and I will have to try it,
> too.
> 
> BTW, I have been following the Jock/Crispin conversation about ND-TLUD
> stoves.  Reading it, I realize that I need to tune-up my stove on all fuels
> before I carry on experimenting with coffee grounds: my stove produces
> red-orange flames that reach past the the top of its chimney, and it's my
> understanding that this is a sign of poor air/fuel mixing or air and fuel in
> the wrong proportion.  I should have some questions about how to tune up my
> stove in the next day or two.
> 
> Dave
> 
> --
> David Young
> dyoung at pobox.com    Urbana, IL    (217) 721-9981
> 
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