[Stoves] Stove terminology

Wed Aug 31 15:54:35 CDT 2011

Dear Steve and Andrew and Martin

>>http://www.wallnoefer.it/cgi/sdcgi.exe?USERID=25760132DDEF731103E0347DD&SID=E&action=mtemplate&ebene=005002&mkrecno=23&iklasse=1&REPLTPL=TPLSPARTE,TPLEMPTY

>Martin and Steve these are interesting looking heaters, does it mention whether they forced air, the >downdraught section certainly looks like it has a high velocity. I'm familiar with the batch loaded Kunzel and >Kob gasifier boilers but these are orced air and in the case of the kunzel the primary compartment is >presurrised and so cannot be opened in use.

Yes Steve, that is the one. It is a German stove that start off Up-Draft with a grate below and quite a big space under it. There is a pipe connecting the top to the chimney as well as another connecting the space under the grate to the same chimney. You can see it has approximately the same volume of space above and below the grate. It is not very clean burning unless the fire is a) large and b) exactly right for the size of stove. The principle was patented in 1895 in the USA. The stove may have a patent on it, but if it is on that lighting method, it is an invalid patent (there are lots of them – don’t be impressed by a patent’s existence) Also check that is still in force.

Once the fire is started, the top exit it closed and the fire is forced into a DownDraft mode by the draft from the chimney.  One of the researchers in Ulaanbaatar tried to build a small version (smaller) and it did not perform very well. The main reason has to do with what a clean burning downdraft stove looks like. The two glass windows cost twice as much as a traditional stove (each).

A huge fire can easily be made to burn cleanly, and if the fire power stays constant, it will continue to be clean. However when starting, and after most of the fuel has burned, it is no longer in a balanced relationship with the combustion volume. The solution is a combustion chamber of limited portions so that the clean burning environment can be maintained with a much smaller fire, especially in the beginning if the purpose is to limit smoke production.

It is especially smoky when switching from TLUD to TLDD/BLDD. 

There is a Top-Lit Up-draft/Cross-Draft stove in Ulaanbaatar made by a local artisan. It is extremely clean burning with wood and coal, though better with coal. I think it is almost two 9’s cleaner than the baseline stove (1 x 9 = 90%, 2 x 9 = 99%, 3 x 9 = 99.9% cleaner.)

A second TLCD stove will be introduced this year as well, based on the CD stove from GIZ (ex-GTZ). I repeat my estimation that this type of burner is at least as clean as a TLUD and it can be refuelled continuously, something that should appeal to a number of customers and stovers on this list. I presented a Workshop (paper) at the Domestic Use of Energy conference in Cape Town in April on why I think it burns so cleanly, supported by some ‘probables’ and ‘likelys’ because I am not sure anyone knows why it is so clean. The main point is, we can consistently reproduce the effect in different products.

I noticed, Paul, that the TLCD is not on the list of stove types. A crossdraft stove has a hopper with a pyrolysing environment at its bottom terminated with an angled grate. The grate, unlike an angled-feed stove to a grate under the combustion chamber, has the grate extended under the whole hopper. This allows some air to get into the fuel to pyrolyse it long before it gets to the combustion chamber. 

The fuel falls by gravity under the combustion chamber as burned fuel turns to ash and drops down through the grate. The flaming combustion takes place in the combustion chamber above the grate, immediately next to the hopper. There is some nominal insulation between them.

The fire is lit by putting wood (small) into the combustion chamber and top-lighting it. This gives immediate cooking heat while the fire works its way down to the fuel underneath (coal, wood pellets etc). It is very easy to light. The hopper can be refilled whenever you like.  The idea was thought of by Prof Lodoysamba from the National University of Mongolia. He is a nuclear physicist and works as the Head of the Electronics Dept. and measures air particles on the side.

Regards

Crispin

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