[Stoves] Insulation and stove life

[Paal Wendelbo]

Stovers
Crispin is right, the best insulation is air, and arranged the right way it 
will give some preheating to the intake off secondary air at the same time 
as it will prevent destroying the metal. By natural draft you will have a 
yellow charcoal with a temperature of about 900˚C and by forced air you will 
have white charcoal of a temperature of about 1000 ˚C, the temperature 
blacksmiths need for forcing and welding steel.
But what is convenient temperature for cooking? It is definitely not 1000 
˚C. On top of charcoal it can sometimes be too hot, on open fire from wood 
sometimes too low. I have found that my horizontal TLUD ND PP stove works 
best with a temperature about 700 ˚C for cooking, about 450 ˚C for simmering 
and around 200 ˚C for baking bread. And to obtain that, I need no insulation 
anywhere in the stove.
Regards Paal W

-----Opprinnelig melding----- 
From: ajheggie at gmail.com
Sent: Sunday, June 09, 2013 2:26 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Insulation and stove life

[Default] On Sat, 8 Jun 2013 14:10:58 -0700,Bob Tingleff
<bob at tingleff.com> wrote:

>Belonio's TLUD design calls for an insulated gasifier reactor, with the
>inner cylinder being 20 gauge stainless, though Paul O's version is not
>insulated. And Rocket stoves are insulated.  So I'm surprised to see the
>comments below pass without any discussion. I wonder if Belonio's rice husk
>gasifier stoves have longevity problems.

Insulation is necessary to reduce heat loss, so we are not saying don
not use insulation. What we are saying is if the insulation is added
to the "cool" side of a metal surface in the stove then it can cause
the metal work to get to a temperature at which it fails, normally by
oxidation.

On our high pressure pyrolysis unit we had blocks of ceramic
insulation inside a steel containment but it was necessary to allow
for cooling of the outer skin because stray hot gas could get past the
insulation joints to heat the steel.

Steel seems to survive the temperature in a TLUD quite well, but this
is only a temperature of around 600C. If the TLUD pyrolysis front
reaches the primary air inlet and the char starts burning in updraught
mode the temperature rapidly reaches over 1100C and steel fails
quickly.

AJH

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