[Terrapreta] Let's talk retort materials for a little bit

[Greg and April]

I'm willing to put up with a little cost to gain some efficiency and life. 
I don't want to use more than 1/4" of material, since thinner walls improve 
thermal efficiency.    I figure that some warping is fine, and not really 
going to change the overall efficiency.

Temperature will be fairly uncontrolled, unless/until a thermocouple and 
damper is installed.

I am planning on a layer of castable refractory on the inside of the outer 
shell, so it will have a layer of protection and so it can be of lesser ( 
cheaper ) material.

I am thinking about improving thermal efficiency by routing the chimney so 
that it dips below the level of the retort, before going up as it normally 
would - in this way the heat builds up around the inner shell, before 
exiting.


Greg H.


----- Original Message ----- 
From: "Kevin Chisholm" <kchisholm at ca.inter.net>
To: "Greg and April" <gregandapril at earthlink.net>
Cc: "Terra Preta" <terrapreta at bioenergylists.org>
Sent: Wednesday, May 14, 2008 15:07
Subject: Re: [Terrapreta] Let's talk retort materials for a little bit


> Dear Greg
>
> Greg and April wrote:
>> What kind of materials make a good retort?
>>  Titanium?
>> Carbon Steel?
>> Stainless Steel?
>>  What?
>
> There are several answers...
>
> 1: If you want low cost... then carbon steel
> 2: If you want longer life, then use thicker carbon steel
> 3: If you want longer life still:
>    lower the temperature of the metal to hold it to about 700 F
> 4: If you want longer life still, use SS, and limit shell temperature to 
> aprox. 900 F
>
> Enclose the heated surfaces so that they only "see" products of 
> combustion, with minimum possible excess air.
>
> Titanium is very expensive, but would probably be good to a higher 
> temperature. However, it has a significant tenancy to form Nitrides and 
> Carbides.
>
> Hope this is helpful.
>
> Best wishes,
>
> Kevin
>>  Greg H.
>>  ------------------------------------------------------------------------
>
>