Advise wanted on home made retort

[Woodworks]

My first one has worked well but the old water tank that is used as the firebox is starting to suffer and I quite fancy getting something made up as long as it does not cost the earth. Not quite sure what way to go at the moment but looking to continue to use barrels for the charcoal and brash to cook them just wondering how best to make a firebox cheaply, strongly and preferably insulated.

 

 

This is the current one as was but it's not so pretty now

Edited May 21, 2016 by Woodworks

[SteveA]

Is that a galvanised tank? If so, according to what I've read on rocket stoves the galvanised coating can let off some pretty bad toxic substances.... best to be avoided.

 

Apparently stainless steel would last far, far longer than the usual more common mild steel barrels.

 

I've been considering making a brick retort as I figured it would be long lasting and relatively cheap if using reclaimed bricks. Trouble is.... finding plans for one ain't so easy.

 

cheers, Steve

[Woodworks]

Thanks Steve

 

Had considered a brick retort but from what I can make out regular bricks aren't up to it and I need the ones known as smooth cream's due to their heat resistance. Snag is they cost nearly a pound a piece and it still needs building. The galvanising did behave a bit oddly in the first few burns but I kept out the way of the fumes. Its all various shades of rust now. Not had any problems with the barrels to date it's only the clamps for the lids that are looking worse for wear.

[openspaceman]

Is that a galvanised tank? If so, according to what I've read on rocket stoves the galvanised coating can let off some pretty bad toxic substances.... best to be avoided.

 

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.

 

Apparently stainless steel would last far, far longer than the usual more common mild steel barrels.

 

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've been considering making a brick retort as I figured it would be long lasting and relatively cheap if using reclaimed bricks. Trouble is.... finding plans for one ain't so easy.

 

cheers, Steve

 

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.

[SteveA]

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

[SteveA]

If I dig a hole on our farm it'll fill with water pretty quick but we could do an above ground version of this (we've already got quite a few mounds of subsoil to build it with).... Earth Pit Biochar - Simple, Easy, Cheap - Complete How-to

 

cheers, Steve

[Woodworks]

Steve I tried earth mounded up around my retort but when it gets cooked it runs like sand making it impossible to have nice clean square edges like in the link. It may be something to do with our type of soil but bare it mind.

 

Edit. just looked more closely at the link and realise the nice clean edges are to show charcoal in the soil.

[agg221]

If I dig a hole on our farm it'll fill with water pretty quick but we could do an above ground version of this (we've already got quite a few mounds of subsoil to build it with).... Earth Pit Biochar - Simple, Easy, Cheap - Complete How-to

 

cheers, Steve

 

I copied this - [ame]

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It's a good shape for getting the branches in and packing down evenly.

 

Alec

[openspaceman]

Steve I tried earth mounded up around my retort but when it gets cooked it runs like sand making it impossible to have nice clean square edges like in the link. It may be something to do with our type of soil but bare it mind.

.

 

 

Yes the soil will need to be a clay type.

 

I originally saw this done in a report from Africa, probably early 60s, before pollution, AGW or biochar were even dreamt of, where a drott had dug the pit so it had a slope in and out and was probably 8' deep in the middle. Once burned the charcoal was covered with old corrugated sheets and then the soil pushed back on with the drott.

 

Nowadays I'd probably ask on freegle for an old 250 gallon oil tank, insulate the sides with rockwool and cut the top off. I'd also load and unload mechanically.

 

I did change the burn parameters on a kob pyrot wood chip stoker and this produced char and the ash system unloaded it to a sealed wheely bin. Alex English went one step further and dumped the char with an auger past a water seal which quenched it and maintained the induced draught in the boiler.

[SteveA]

I copied this -

 

It's a good shape for getting the branches in and packing down evenly.

 

Alec

 

Nice, good plan.

Does the slope of the sides make much difference?.... 70degrees has been mentioned but would it make much difference if it was 45degrees (or thereabouts)?

cheers, Steve

 

Yes the soil will need to be a clay type.

 

I originally saw this done in a report from Africa, probably early 60s, before pollution, AGW or biochar were even dreamt of, where a drott had dug the pit so it had a slope in and out and was probably 8' deep in the middle. Once burned the charcoal was covered with old corrugated sheets and then the soil pushed back on with the drott.

 

Nowadays I'd probably ask on freegle for an old 250 gallon oil tank, insulate the sides with rockwool and cut the top off. I'd also load and unload mechanically.

 

I did change the burn parameters on a kob pyrot wood chip stoker and this produced char and the ash system unloaded it to a sealed wheely bin. Alex English went one step further and dumped the char with an auger past a water seal which quenched it and maintained the induced draught in the boiler.

 

We've got clay soil so no problems there.

Not sure what a drott or a kob pyrot wood chip stoker is? Kind of lost me there!

cheers, steve