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

[Greg and April]

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----- Original Message ----- 
From: MFH 
To: 'Greg and April' ; 'Terra Preta' 
Sent: Wednesday, May 14, 2008 15:10
Subject: RE: [Terrapreta] Let's talk retort materials for a little bit


If by "retort" you mean the drum used to contain the material to be pyrolised, then the decision about material is between cost and longevity.
 
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That is exactly what I'm talking about.

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Normal steel will last for years and won't heat-distort if the retort is heated and cooled reasonably evenly.
 
A retort made from "boiler plate" will last longer and be more resistant to distortion.

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LOL - I tried looking up the definention of "Boilerplate", and very little of it had to do with metal.

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Cast iron is better still. I've been hunting for scrap cast iron pipes.
 
My experience in this area is from using various materials in various shapes as fireboxes under drying beds for produce like cocoa beans or copra. We once fluked some cast iron pipes left behind by the Japs from WWII, which proved to have very long lives when used as fireboxes. Also had some made using normal steel plate and also boiler plate, with the latter having a longer life.

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How does one make a firebox from pipe?

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Shape was important. Flat surfaces as in a box-shaped firebox distorted in a matter of weeks. Cylindrical shapes were best, particularly if the sides were supported by concrete walls thus preventing a gradual change from cylindrical to oval. Best of all was to line the inside of the cylinder with 2" of cast refractory cement, giving a life despite 24/365 use of many years. This is not suitable for char production as the cement has a considerable insulating effect.

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I was thinking of something a long the lines of having an octagional cross section.    

Now before you start wearing groves in your head, scratching it, trying to figure that out, let me explain.

It's easier to obtain flat plates at lower cost and weld them into shape, than to try and get a single piece of round stock of the same thickness and volume.    As for the possability of warping, a number of brackets can be installed that will resist warping, again these brackets can be made from easy to obtain flat stock.   

I also decieded that I wanted to be able to unload the retort with a shovel and a flat bottom makes it easy for a square point shovel can slide along it. 

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316 or other stainless steels may be okay but at a serious cost escalation. I'd suggest that its more cost-effective to use the cheapest steel and toss it out in a couple of years.
 
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That is some thing to consider, althow there is also the cost of rebuilding it to consider as well. 
 

Greg H.
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