Advise wanted on home made retort

[Breezeblock]

Thanks Openspaceman.... excellent answers & even more food for thought!

 

Sorry, I may need to retract my galvanised tank dangerous toxic substances comment.... from my hazy memory I think it was tin cans that were the problem, ie, using large dog food tins for the rocket stove chimney.

 

A fire in a hole in the ground sounds like a simpler option.... I'm warming to just doing that now. Already got a mini digger so digging holes is easy. hmmmm

But maybe that ain't so good for pollution??

 

cheers, steve

 

no you are correct galvanising when heated gives off zinc and you can get metal poisoning from it ask any welder about galvi flu

[the village idiot]

I know it isn't wise to inhale it as an aerosol, particlarly when welding, but it's only zinc oxide so fairly harmless as a powder.

 

 

 

I've mentioned this before but ss depends on a layer of chromium oxide to prevent the iron being exposed to oxidation, this layer is acid soluble and can be reduced in anaerobic conditions, by definition the inside of a retort will become anaerobic.

 

A father and daughter in india copied an idea promulgated by Yury Yudkevitch in Russia for multiple containers inside a combustion chamber such that their off gas contributed to the fire, the original idea being the retorts were cycled to maintain a serial stream of batches. They used ss retorts but whilst they did last longer than tin cans they had a limited duty cycle. Cast iron would be better as the graphite particles resist oxidation.

 

Ordinary mild steel is generally good up to 700c on one side as long as the other is cooled to ambient but with a retort the outside is at or above this whilst thie inside is over 400C so they do burn out eventually. The thing to do is control the temperature outside the retort but this requires increased dwell time, which is why Yury had up to a dozen retorts in his devices.

 

These steel cylinder retorts have heat exchange area limited to the walls of the retort and there is nothing to drive circulation in the retort. A the surface area ratio decreases as the retort size increases there is a size limitation. If the wood has any moisture this not only dilutes the offgas with steam but also increases the time the charge of wood takes to get to pyrolysis temperature.

 

 

 

 

I suspect they need to be fire bricks, this is how the original town gas retorts were built and later modified by Lurgi, the manufacturers to make the crematoria used by Nazis. If you look at the pictures you will see they had cast iron doors.

 

It should be possible to make a hybrid downdraught device similar to the simcoa charcoal plants used to make charcoal for smelting silicon but unless it could be inclined it would need to be quite tall and there would need to be dry feedstock to keep the throughput up. At least there would be plenty of spare drying heat.

 

this charcoal making business goes in cycles like beef cattle systems, you start off with a dog and stick and some grass and then invest in buildings and zero grazing and expensive feeding and mechanised cleaning system, the kit gets old and the market drops so you abandon the buildings get a stick and a dog...

 

Much the same with charcoal, you start with a fire in a hole in the the ground, then invest in a kiln and then a retort but you canno0t afford the wages so you revert to a hole in the ground.

 

Excuse my ignorance, but what are the constraints on making an Exeter style retort from cast iron?

Would it be too difficult/too expensive? Presumably it would have to be non-mobile due to the weight?

[agg221]

Excuse my ignorance, but what are the constraints on making an Exeter style retort from cast iron?

Would it be too difficult/too expensive? Presumably it would have to be non-mobile due to the weight?

 

Several issues. Firstly it would be an awkward shape to cast - very big and thin walled so the tooling would be extremely expensive and failure rates would be high. Secondly it would be virtually impossible to repair if it cracked. Cast iron is typically brittle compared with steel.

 

You could use cast plates and bolt them together over a ring frame. Correctly designed and sealed this would weigh a bit more but not too much and should be very durable. The best option Andy (the other one of the two 'men in suits') came up with was to use a low chromium ferritic stainless steel. I have subsequently found a few suppliers for these and they are not too expensive (it's basically the same stuff that exhausts on diesel vehicles are made from). They are also formable so it would look and act like a standard Exeter but would be a lot more durable.

 

Alec

[Goaty]

A forty is a track laying machine with a loader instead of a bulldozer blade.

[the village idiot]

Several issues. Firstly it would be an awkward shape to cast - very big and thin walled so the tooling would be extremely expensive and failure rates would be high. Secondly it would be virtually impossible to repair if it cracked. Cast iron is typically brittle compared with steel.

 

You could use cast plates and bolt them together over a ring frame. Correctly designed and sealed this would weigh a bit more but not too much and should be very durable. The best option Andy (the other one of the two 'men in suits') came up with was to use a low chromium ferritic stainless steel. I have subsequently found a few suppliers for these and they are not too expensive (it's basically the same stuff that exhausts on diesel vehicles are made from). They are also formable so it would look and act like a standard Exeter but would be a lot more durable.

 

Alec

 

Hmm, interesting.

 

Would the ferretic stainless steel be immune to the anaerobic surface stripping that Openspaceman spoke about?

 

Are there engineers about who are used to working with it?

[donnk]

could you not build one out of clay like a big kiln ?

[Woodworks]

could you not build one out of clay like a big kiln ?

 

Maybe. Snag is I have no idea where to start with building in clay where as I can get my head around steel or building with bricks. Think I should look into it more though