[Stoves] Modified traditional Mongolian stove - pictures

[Crispin Pemberton-Pigott]

Dear Ronald

>Dear Jeff,
>I'm wondering a bit what you mean-- if you turn the stove 90° on an axis
you'd have a side load >horizontal draft-- I'm not just playing semantic
tricks here: the chief gain in the TLUD is the even >distribution of natural
airflow optimized for the whole of the pyrolysis plane. 

Ah...but not quite so fast. What the end-lit cross draft (hereinafter ELCD)
burners do is to create an angled plane that accomplishes what the TLUD does
vertically. There is actually nothing involving gravity with the TLUD,
almost. A TLUD can be run upside down (BLDD) so why not on its side?

The essential provision is that it be done in a box, preferably a non-leaky
one. Apart from the low ignition emissions, the major advantage is that it
can be refuelled.

It works because the air control is maintained, though with quite different
materials and flow paths from a regular sheet metal TLUD.

The Mongolian requirement is for a stove that will last 10 years with user
maintenance. It should be in the 7-13 kW range. It must be refuellable and
burn wet lignite (a form of young, brown coal).

We are reproducing the TLUD effectiveness without going to the extreme of
trying to leave the char unburned. It surprises me that there seems to be
general acceptance that the cleanliness of a TLUD is to do with the fact
they are char producing. This is simply no so. It is clean because the
combustion conditions are right for the portion of the fuel that is burning
burned (the volatiles). As Dean has pointed out, changing the air supply at
the end can burn the char if you want.

John Davies does exactly the same thing burning coal in a packed bed
gasifier: first devolatilisation  then coke burning, but he is also burning
it vertically. What the ELCD stove does is to create a set of burning
conditions that modify themselves, so to speak, creating the right
conditions for TLUD wood ignition followed by the different conditions for
continuous and complete burning of the coal. 

Once the wood is lit, the small chips of coal around it fall over the wood
and are quickly lit. This also opens a hole in the 'floor' of the fire
meaning an air entrance near the outlet of the combustion chamber which is
the entrance of the pipe in which the smoke is burned by the flames. The
hole provides enough air to change the ratio of primary to secondary and
maintain a pretty clean burn.

It is not a classic TLUD vertical profile, obviously, but as the air drafts
sideways from the loading door through the coal to the pipe at the opposite
end, it creates the same result: evaporated volatiles, evaporated moisture,
and CO. As there is a bowl-shaped fire burning near the pipe, the
combustibles are dealt with immediately or in the pipe.

Again, please make no assumptions, everyone, that the low PM from TLUD's is
the result of not burning the carbon. The ELCD probably has lower PM than
anything tested so far (based on the numbers we have heard from Aprovecho
tests) and it definitely burns the carbon. If you think of 1500 mg of PM 2.5
being considered as an emissions standard for about 15 MJ of heating power,
that is 100 mg/MJ. The GTZ 7.5 has been run twice in the past few days with
quite casual ignition, with a total of less than 0.5 mg/MJ over a 5 hour
run.  Merely reversing the ignition position to the fuel door end increases
emissions to about 300 mg/MJ. (By the way the GTZ 7.5 is not an ELCD stove.
It has a hopper.)

So I conclude that it is quite possible to run a TLUD on its side and thus
overcome the primary problem of not being able to refuel one.

>regards,
>Ronald von derbesinnlichenweihnachtsstimmung

Materialistisch Weihnachtsgrüße ...
Crispin