[Gasification] Fwd: RE: Whole log pyrolysis for char production was Re: W...

[Ken Boak]

Jason,

Thanks for the interesting comments. I suppose that firebricks are a simple
capacitive thermal mass, to prevent the outer casing of the traditional
cast iron stove from seeing the worst effects of thermal cycling, and to
prevent excessive surface temperature.

Taking this capacitive idea to the max, I guess is the masonry stove, which
is all thermal mass intended to absorb and slowly release the heat from a
brief but intense fire.

I have magnetite bricks left over from an electric storage heater (common
in the UK). My intention was to experiment with these for heat retention.

What is the problem with pyrolysis occurring too early?  Is it simply
because fuel is pyrolysing in the wrong place, and there is no means to
transfer the pyrolysis gases to the combustion chamber, or is the problem
tar generation in the fuel magazine?

My motivation for design is a more efficient woodstove, which radiates more
heat into the room in which it's located - say the living room, plus
provides adequate hot water via a heat exchanger to provide heating for
some additional rooms and hot water.

The nominal 8kW stove I have at the moment fails to produce much radiant
heat, and I am sure that the simple heat-exchanger tank at the back of the
combustion chamber seriously effects the combustion temperatures resulting
in more emissions and poor, inefficient combustion. For this reason I
believe that the only way to control emissions and combustion temperatures,
is to first gasify the wood fuel and then burn the wood gas at high
temperature with preheated secondary air.

Traditional stoves generally lose a lot of heat straight up the chimney.
Whilst this generates draft, it is a major cause of inefficiency. Some heat
could be recuperated for secondary air pre-heating, using a simple
concentric heat exchanger made from twin-wall fluepipe.

A good stove should be easy to light, be easy to load, easy to clean out
ash. Additionally it should have a convenient batch burn time, and the
ability to control the heat (turn down), without too much loss of
efficiency.  The stove should be capable of handling the predominant fuel
type (say split logs) without additional fuel preparation.

There may be good reason to have the stove non-reliant on electrical power,
relying on natural draft and thermosyphoning for it's normal operation.

These are the features that I consider necessary to meet customer
expectations.

Having intensively run my existing stove for around 14 hours per day for
the last 16 days, as the primary source of heat over the festive holiday
period, I am tolerating its less than ideal performance, but am now certain
that there must be a better design.


regards


Ken
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