Mobile Retorts

[the village idiot]

Many thanks Goaty (my IT guru). Should be a couple more pictures on the way.

[Goaty]

Here they are ©The village idiot.

 

[sandspider]

You need to paint some Thomas the tank engine eyes on that!! Interesting design - for some reason I thought it would be a ring kiln design.looks good. How much wood does the central chamber hold?

[the village idiot]

Central chamber volume is 1.7 cubic mtrs not accounting for air space.

 

I did think about putting faces on the end doors, would look particularly effective for when you get flames shooting out of the 'mouth'!

 

Bizzarely, when the kiln came back from the engineers in Exeter a picture of Mr Greedy had appeared on the side.

[skyhuck]

Would an old Farm 2000 or similar not be way cheaper??

 

In fact one with a rotted out water jacket would only be worth scrap.

[the village idiot]

I think it probably would be possible to make something similar yourself if you were very good at metal work, which I am not.

 

There are several things to take into account. You need to be sure you can seal the inner chamber. You need retorting pipes to channel the wood gasses. You would also need to install chimneys and the whole outer shell including the doors needs to be well insulated.

You would also need to ensure that the temperature was easy to manage. It could get a bit disconcerting if the temperature rockets up and there's nothing you can do about it.

 

All that being said, you could bodge one up but be prepared for weeks of fiddling about to make it work properly. I am not an overly practical person and prefer to get things 'ready to go'. I'd be interested to know if anybody does decide to have a go. A good starting point would be a stainless steel vessel of some description with a flanged door/lid.

[skyhuck]

Stainless steel will not last long, as I understand it the constant expanding and contracting causes cracks, thats why its not used for wood boilers.

 

Its OK if its very thin, such as in flues and heat exchangers, but not once its thick enough to be used for a boiler or stove.

 

I could be wrong, but thats what I was told when I asked why SS was not used for boilers.

[the village idiot]

That's very interesting. I have had a lot of trouble nailing down whether stainless would be a good option or not. Some engineers swear it is the only option for long term durability, others maintain it would be little or no better (or worse) than mild steel, and considerably more expensive.

I imagine you will get metal fatigue with whatever material is used. I have not yet seen a kiln that hasn't warped over time. I guess the trick is to design a machine that is easy to work on and bash back into shape.

Cracking would obviously be a real headache!

[openspaceman]

That's very interesting. I have had a lot of trouble nailing down whether stainless would be a good option or not. Some engineers swear it is the only option for long term durability, others maintain it would be little or no better (or worse) than mild steel, and considerably more expensive.

I imagine you will get metal fatigue with whatever material is used. I have not yet seen a kiln that hasn't warped over time. I guess the trick is to design a machine that is easy to work on and bash back into shape.

Cracking would obviously be a real headache!

 

It's a considerably worse conductor than mild steel but the real reason it's not used in retorts is that it depends on a thin layer of chromium oxide forming, this is refractory in normal use as long as it is in an oxidising atmosphere, otherwise the layer gets attacked by acids and it loses its resistance. The inside of a retort is oxygen free, or the charcoal would burn, and the offgas given off during pyrolysis is pyroligneous acid...

[the village idiot]

It's a considerably worse conductor than mild steel but the real reason it's not used in retorts is that it depends on a thin layer of chromium oxide forming, this is refractory in normal use as long as it is in an oxidising atmosphere, otherwise the layer gets attacked by acids and it loses its resistance. The inside of a retort is oxygen free, or the charcoal would burn, and the offgas given off during pyrolysis is pyroligneous acid...

 

Excellent! A bit of cold hard chemistry. It's taken two years of asking the question to finally have an intelligable scientifically sound answer to the stainless steel retort conundrum.

Thank you openspaceman!