[Stoves] Fire Stump / stump-incuts

[Crispin Pemberton-Pigott]

Dear Roger

 

>Why isn't the secondary combustion process be applied in cooking? or
another angle why could these appliances do both jobs?

 

Secondary and even tertiary combustion is commonly applied in stoves. In
fact even an open fire has secondary combustion of the gaseous products that
evolve from the solid fuel. In some cases, the secondary air enters the
combustion area together with the primary, and sometimes it is brought in
via a separate channel (esp through a number of holes). On occasion the
secondary air is blown in with a fan or a chimney (which is a natural draft
'fan' in that it provides something like forced air).

 

There are combustors that provide most of the secondary air with the primary
air, and add a small amount of secondary (sort of 'supplementary' air) above
the primary combustion area. An example of this the GTZ 7 series stove (now
renamed GIZ 7 because they changed the name of the organisation). It has a
grate setup that allows most of the needed secondary air to pass through a
thin layer of burning coke where it is preheated and partly used. There
follows a small set of holes (about 8) that let in just enough secondary air
to complete the burning. This has the result that the amount of air pissing
into the fire is minimised, but enough. The result is a very high flame
temperature.

 

Stoves that are known for having very restricted primary and lots of
secondary are the gasifiers like the CampStove from Tom Reed. His stove has
a small fan and most of the air, nearly all of it, is secondary. There are
natural draft gasifiers and pyrolysers (that deliberately make char) which
accomplish the same thing using slightly taller stoves that basically have a
short chimney section inside. 

 

They are all built to create gases then burn them at a secondary stage. The
GIZ 7 stoves can arguably be analysed as having three sets of air supplied:
primary air to devolatilise the coal or wood, then secondary air preheated
by passing through a thin layer of nearly burned fuel, then preheated
secondary air that passes through a set of holes about in the middle of the
flaming area (combustion chamber). This last 'air' is tertiary in that it is
one of three supplies, however there are only really two burning areas: the
primary one and the secondary one. Not every stove fits easily into simple
categorisation.

 

I would be interested in hear from you what has been built. Is the primary
or secondary air deliberately pre-heated before entering the fire? Do you
control the amount of secondary air during the burn (for example closing it
off when the fire gets low(er)?

 

Regards

Crispin

 

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