[Stoves] Help! Are there insulated biogas stoves?

[Andrew Heggie]

On 13 November 2017 at 07:21, Karolina Hagegård
<karolinahagegard at gmail.com> wrote:
 So I asked if he wouldn't be
> interested in developing an insulated biogas stove for me, by the same
> principle as the firewood stove he had, and I'd be selling it together with
> my digesters. To my surprise, he wasn't!... He said that in his experience,
> gas needs lots of air, so you couldn't insulate it... Is it true?

Karolina

It's an interesting question but I suspect the reason you'll have
difficulty finding one is that it is not necessary. Biogas, which I
take to be a mixture of methane and carbon dioxide with perhaps a
trace of hydrogen sulphide, burns directly and cleanly in a flame as
long as the gas and air are correctly premixed. The premixing is
achieved by the biogas under slight pressure (we use around 20
millibars for domestic natural gas) entraining the right amount of air
before the burner.This will give the hottest flame for the pot as long
as the pot is the correct distance from the flame, such that the flame
is not quenched by the pot nor too far away that the flame is
needlessly heating air before it gets to the pot.

The solid fuel stove has a more tortuous route before it produces a
flame, it first has to produce a gas by converting the solid with heat
to evolve the gas,  even then the vapours and gases in the flame are a
more complex mixture of pyrolysis products, nitrogen from the primary
air, CO2, CO , Methane, Hydrogen and other volatile organic compounds.
Also there is less opportunity to premix air with this hot gassy
mixture, so the air often enters from the outside in a diffuse flame.
As a result there is the need to maintain the primary and secondary
(flame) temperature without it either radiating the heat away or being
quenched by the pot in order for the far more complex oxidation
reactions to complete within the flame, hence the need to insulate the
combustion chamber.

Andrew