[Stoves] Coal dust briquetting

Tue Mar 5 21:50:02 CST 2019

I agree it is interesting.

In Bishkek the duff is sold to the power station which grinds it to powder anyway and blows it into the fire. The combustion is completed within 3 or 4 metres of the entrance. It never hits the floor.

It is during that time that silica xenospheres are formed.

The fan only has to be able to Loft the particles. Peanuts.

If sub-bituminous coal has hydrocarbons that melt under the auto-ignition point (400, say) then it can be bonded with its own juices, so to speak. That is how wood pellets are held together. Melted lignin.

As I said, I didn't look into this very deeply. Philip told me it could be done.

Obviously we need to research this immediately because a whole industry could rise from these mountains of duff, presently and naturally oxidizing as fast as they are able. Check out the Witbank-Middleburg mine dump fires that burned for thirty years, as I recall smelling them. That was auto-ignition. It was a reeking hellscape for years.

Regards
Crispin
From: pienergy2008 at gmail.com
Sent: March 5, 2019 10:20 PM
To: crispinpigott at outlook.com
Reply to: ndesai at alum.mit.edu
Cc: psanders at ilstu.edu; stoves at lists.bioenergylists.org
Subject: Coal dust briquetting

Crispin:

Very interesting. I wonder if this is specific to South African context - if I remember correctly, relatively softer coal, and your duff coal coming from large grinders at coal-fired plants or mines and factories.

So how do you get air, at what speed? Electric or diesel-powered fans?

Isn't there a vibrant market in Nairobi for briquettes from charcoal dust?

Alibaba.com has charcoal dust slurry and briquetting machines. Can you use them?

I once worked on coal ash, but I wonder how much coal dust is available around US, Canadian, or Chinese, Indian mines and what it is used for. Any idea?

Nikhil

------------------------------------------------------------------------
Nikhil Desai
(US +1) 202 568 5831
Skype: nikhildesai888

On Tue, Mar 5, 2019 at 9:59 PM Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
I have long given up on the EPA taking AA scientific path to anything. I don't know what they are up to, but it is not what I thought.

Duff coal (under 6mm) is easily separated into +2mm and dust. The problem with the dust is not that it is unburnable but that it is wet and very expensive to dry. It holds the moisture rather efficiently.

So how to create a usable product? First Gerrie of the "rock" which is to say, powdered rock which is ash. Because it has been ground to a powdered state by handling and crushing, the ash, or a lot of it, can in theory be removed by flotation in a dense media, but that makes it wet. Big problem.

So by blasting air over it or under it, a fluoridation takes place AND water evaporates so it is possibly to get three fractions rather inexpensively: the light fraction (density 1.4) which would have floated on the dense media, then the ash which is rock at the bottom (density >2.5) and "middlings" which in a normal is wasted as well because few want it.

Neither do we.

So the light fraction is pretty clean coal. Being powder and if it is South Africa, it has enough bitumen to be pressed hard and it will stock together without any binder.

Thus we can get say 60m tons of high quality high energy coal pellets of just the right size and shape, while stopping the auto-ignition of the stockpiles (followed by a decade of terrible combustion).

The use of air to separate gold dust from dirt was extensively used in the gold rush days in southern Australia. Water was extremely expensive and had to be brought by ox cart some huge distance. So the gold was pre-concentrated by fan a couple of times and then the precious water did the final washing.

Philip Lloyd did a lot of work on trying to find viable ways to use this wasted resource. Before him Prof Horsfal at Wit's Univ worked on semi-coking on the basis that smoke could be removed from the coal, rather than that a good stove wouldn't make any.

Stay well
Crispin
From: pienergy2008 at gmail.com<mailto:pienergy2008 at gmail.com>
Sent: March 5, 2019 8:02 PM
To: crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>
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Cc: d.michael.shafer at gmail.com<mailto:d.michael.shafer at gmail.com>; schmidt at ithaka-institut.org<mailto:schmidt at ithaka-institut.org>; psanders at ilstu.edu<mailto:psanders at ilstu.edu>; stoves at lists.bioenergylists.org<mailto:stoves at lists.bioenergylists.org>
Subject: Re: Off-topic: Biomass power and charmaking

Crispin:

Density of demand makes the portability of densified fuel relevant. In and of itself, fuel density is no matter. "Marketable radius" implicitly refers to demand density; Washington, DC gets wood from within 30 miles if that, but charcoal briquettes from hundreds of miles, and much of northern and coastal part of US is in the same fortunate situation because it has the money  to go with its preferences. Biomass fuel logistics are relatively easy. Otherwise transport, storage and retailing costs do not necessarily favor denser fuels.

Think or uranium.

My favorite anecdote is from around 1980 when petroleum products were FLOWN to an African country. (Rwanda or Burundi or CAR.) Dense fuels, once adopted, should be stockpiled. (I once worked on storage tanks and railway or pipeline alternatives in central Africa. I don't think densified solid fuels other than charcoal or briquettes have a prayer in Africa yet.)

I wish I could go back 60 years and compute the economics of chunk charcoal, charcoal briquettes, kerosene, and stoves in my home and hometown.

I wonder how you would "wash" coal with air. (I spent close to a year on litigation involving water-washing of Pennsylvania bituminous coal to drive out sulfur to meet the EPA standard for SO2 emissions. That is when I went to see the washing plant to understand how elemental sulfur could be washed off but organic sulfur couldn't, and that coal seams are not of uniform quality to satisfy EPA fancies. That is also when I confirmed that EPA can be capricious and political, despite all its purported competence in science.)

Nikhil Desai
Skype: nikhildesai888

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