[Stoves] Low-smoke coal

[IPC]

Dear Crispin

The devolatilised coal was made in a char furnace de-rated for the purpose.
In essence, you need to cook the coal in the absence of air to a temperature
of around 300 deg C (you find out just what temperature by conventional TGA
- thermogravimetric analysis - it depends on the coal).  You use the
volatiles coming off as fuel for the heating.  

The feed coal we used was a standard bituminous B-grade coal with a cv of
around 25MJ/kg,15% ash  and 28% volatiles.  We needed to size it before
devolatilisation to suit the customer's needs - -25 +12mm as I recall.  We
generated a bit of duff during devolatilisation, and should have screened it
again before delivery - the fines could always add to the heat.  The plant
wasn't wildly expensive - and much more reliable than a briquetting plant.
(My usual advice to would-be briquettors is "Don't!") We designed a 100
000t/annum plant, and I could probably dig out the costs.

I think an "every encouragement" route towards devolatilised coal rather
than briquettes is better - we certainly found it so.  If you try to buy
briquetting machines, you find that everyone has been in the business (NB,
past tense!). If you go big enough, you have some surplus fuel condensed
from the volatiles, and people in the coke-oven business love you, because
it is the best source of all sorts of things like naphthalene.  

Keep cool!

(Dr)Philip Lloyd
Energy Research Centre
University of Cape Town
Private Bag Rondebosch 7701
South Africa
Tel +27 (0)21 650 3896
Fax +27 (0)21 650 2830




-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: 03 January 2008 05:42
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Water in coal

Dear Philip

Very interesting numbers.  I was talking to Prof Horsfall about this many
years ago at he Wits Rural Facility near Acornhoek.  He was in the Coal
Chair at Wits and make low smoke coal at the power station near the airport.
It was greyish to look at and only viable because of the use of waste heat
at the power station.  It was really hard to light.

Turns out he used to with my Grandfather's 'niece' at the London Coal Board.
Had a yuk about that.

>We produced several hundred tons of the stuff, which was tested in a 
>large-scale test in Qalabotjha.

What was the original coal like?

>Production costs would add about 5%
>to the retail price.

The process was energised by...?

>The merchants are dead against any
>changes.

We call it the coal mafia.  The markup is tremendous.  No one wants to take
them on.

>You would also get a lot of drying during the devolatilisation

I would settle for that.  However failing everything else, we can go very
low with emissions by changing the stoves to work in a downdraft / sidedraft
fashion.

The "every encouragement' angle has been the plan to ban the burning of  raw
coal and force everyone to burn semi-coked briquettes.  How much sense does
it make to burn semi-coked coal briquettes in a badly made copy of a Russian
wood stove?

I have not seen the costing of the briquetting operations.  It seems to me
that the development of new fuels by force available from only a few
suppliers will mean higher costs.  At present high _existing_ costs drive
people to burn _tires_ in their stoves in an attempt to stay warm.  You can
imagine what that is like!  I didn't get around to burning some in the
downdraft unit.  Next time...

The investment for briquetting equipment is millions and will require about
20 plants around town. It is hard to see that being only 5% of the coal
price.  However if it removes the moisture, or most of it, it is a better
deal. Perhaps the treatment can be funded by the water loss, if you get my
drift.

Regards
Crispin


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