Mobile Retorts

[the village idiot]

Is that Fuelwood in Warwick?

 

I presumed he meant four seasons fuel as Nick's yard is littered with burnt out retorts, but maybe Fuelwood are developing one? That would be cool.

[timbernut]

Surprising fuelwood haven't come up with something before as they are an innovative company, think they originally designed the trekkasaw before selling it to Loglogic, can't believe they've never investigated it

[MartinN]

Probably because no one has been able to crack the cost benefit ratio in the design. I think the Exeter retort is more expensive now than at the original launch price. I think it started out at £12,000.

 

If you get 300 burns before significant corrosion of the inner chamber, reducing wall thickness, then that would be about £40 a burn before big remedial work like replacing the inner chamber. I.e. About 30 pence per kg which is quite high.

 

The Exeter does seem to benefit from being easy to replace this part. Maybe there is an argument for ordering in this part, easier to ship, and sending the this old bit back for remedial work. That way it does not need to be out of action for any length of time. And rig up for doing this replacement on site.

 

Say at £165 per burn then that would be about £50,000 say £12,500 per annum if 300 completed over 4 years. Is that realistic? In other words adding about £9,000 to the bottom line, once the cost of the retort is taken into account. For a self contained unit it is attractive. I guess anyone working doing firewood etc is likely to have 40 tons of wood not suitable for firewood that is just waste, ideal for the Exeter.

 

Having mobility and easy to service (do remedial work) is the goal for the one man business. If treble the volume at half the capital outlay could be achieved it would boost wholesale sales after capital cost to £34,000 per annum for the same number of burns. I think this is achievable, and may be more. Getting the volume of raw material then is the problem 150 tons plus per annum. I'm not sure how much is physically possible in terms of what coppicers move in a day.

 

Somewhat back of the envelope calculations, I know. I'm not sure what it would cost to buy in 150 tons in other words what would be top price of material feedstock.

[the village idiot]

Probably because no one has been able to crack the cost benefit ratio in the design. I think the Exeter retort is more expensive now than at the original launch price. I think it started out at £12,000.

 

If you get 300 burns before significant corrosion of the inner chamber, reducing wall thickness, then that would be about £40 a burn before big remedial work like replacing the inner chamber. I.e. About 30 pence per kg which is quite high.

 

The Exeter does seem to benefit from being easy to replace this part. Maybe there is an argument for ordering in this part, easier to ship, and sending the this old bit back for remedial work. That way it does not need to be out of action for any length of time. And rig up for doing this replacement on site.

 

Say at £165 per burn then that would be about £50,000 say £12,500 per annum if 300 completed over 4 years. Is that realistic? In other words adding about £9,000 to the bottom line, once the cost of the retort is taken into account. For a self contained unit it is attractive. I guess anyone working doing firewood etc is likely to have 40 tons of wood not suitable for firewood that is just waste, ideal for the Exeter.

 

Having mobility and easy to service (do remedial work) is the goal for the one man business. If treble the volume at half the capital outlay could be achieved it would boost wholesale sales after capital cost to £34,000 per annum for the same number of burns. I think this is achievable, and may be more. Getting the volume of raw material then is the problem 150 tons plus per annum. I'm not sure how much is physically possible in terms of what coppicers move in a day.

 

Somewhat back of the envelope calculations, I know. I'm not sure what it would cost to buy in 150 tons in other words what would be top price of material feedstock.

 

Others may disagree but I don't believe the economics stack up with the Exeter unless you can secure a grant to help with the purchase cost. Charcoal is not worth enough and the Exeter is in my view not strong enough to get a guaranteed decent return if shelling out the full whack.

You might well get 300 burns out before the steel of the retort chamber gets too thin, but it will buckle to the point of needing attention long before this, potentially after only 100 burns or so. What I don't know at present is what the remedial work would cost to get the kiln to 300 burns.

I still think the Exeter is the best option out there for the woodsman producers wanting a retort kiln. All affordable charcoal kilns buckle so it is well worth having a metalworking friend who owes you a favour or two. Better still, use blackmail- steal the omnipresent nudie girl calendar out of his workshop and replace it with soppy kittens 2015. Once the kiln work has been completed you can return his diary of dirty desire.

 

I think your figures are good for the potential of the Exeter. 300 burns over 4 years is very doable. I would slightly lower the yield per burn to 150kg unless you exclusively use beech or hornbeam, and with a conversation ratio of 4:1 (dry wood:Charcoal you would need more like 45 to 50 tons of wood per annum.

 

If you can produce a kiln capable of three times the yield at half the capital outlay, producing consistently good product you would bring a smile to the blackened whiskered lips of many a humble Wood Collier!

My suspicion is that as you suggested earlier you would really need to use heat resistant stainless to produce a non warping retort, but that would necessitate pricing it out of the reach of the people who want it.

[timbernut]

Out of interest would heat resistant stainless be resistant enough? I only ask as a few years ago I was considering using twin walled ring kiln with stainless inner (so burns were less affected by inclement weather) and my wife's late uncle,a highly experienced engineer/fabricator (who had made a half dozen or so ring kilns), said stainless would warp too much.

 

Is the inner chamber of the Exeter made of corton steel?

 

Am attempting to build retort and don't have much financial to allow experimentation and I am at a bit of a loss as to what to use for insulation of the outer chamber, thought a vermiculite and cement mix could be possible, any thoughts appreciated!

[Aicchalmers]

Am attempting to build retort and don't have much financial to allow experimentation and I am at a bit of a loss as to what to use for insulation of the outer chamber, thought a vermiculite and cement mix could be possible, any thoughts appreciated!

 

I've been thinking of trying this out for rocket stoves with either vermiculite and cement or clay with fine sawdust, but with the inner metal lining 'sacrificial'; i.e it is a former for the outer insulation and burns away over time leaving the lining in place. Durability would be an issue but if you managed to fire it evenly and end up with a big ceramic kiln then it could work for non-movable applications? Any ideas on physically durable refractory cements? Breezeblock retort kiln?

[steve collins]

Sorry to confuse everyone i meant to say four seasons,

 

back to an earlier question if you cut your 150 tons of timber it would take iro 20 days and if you bought quality wood in at @£45 metre would cost £6750.

so you to keep cost down your will have to source timber and cut/ extract to ride side to make it cheaper and burn from your stack there rather than hauling it around the wood? that's how i would do it

 

As ive only really dealt with container kilns which work extremely well i think the exeter is a little on the small side to make it economically viable if you bought one outright.

 

I also have a plan for a mobile kiln but only at drawing phase at moment might have some figures soon!!

[timbernut]

There's no way I could make it pay if I had to buy wood in at current prices😀

[MartinN]

Out of interest would heat resistant stainless be resistant enough? I only ask as a few years ago I was considering using twin walled ring kiln with stainless inner (so burns were less affected by inclement weather) and my wife's late uncle,a highly experienced engineer/fabricator (who had made a half dozen or so ring kilns), said stainless would warp too much.

 

Is the inner chamber of the Exeter made of corton steel?

 

Am attempting to build retort and don't have much financial to allow experimentation and I am at a bit of a loss as to what to use for insulation of the outer chamber, thought a vermiculite and cement mix could be possible, any thoughts appreciated!

 

NRI kiln specify corton steel due to a protective coating slowing corrosion. I'm not sure ring kilns are made with it here. With regard to the true heat resisting stainless steels they are not practical as these are no longer made in the

UK I've just been quoted minimum order 16 tons to get closer to decent price which is still at a premium.

 

It is not so much warping but as the steel softens, loads distort the metal easier so thick plate with frequent supports would be required, this all adds to weight and cost. When stainless steel operates at high temperature the weld is critical and to get them done properly is expensive and not that easy to find people with those skills.

 

All this adds to weight. To keep more mobile, size has to be reduced killing the economics. Increase in size means fixed position and the costs of bringing wood to the retort. Taking the retort to the wood is optimal especially as the V.I. suggests, going in as a clean up operation after felling.

 

I'm toying with the idea of building a prototype and trying it in my garden, when the neighbour who does not like bonfires is away. Budget is about £1,000 and should do half of the exeter but I should be able to move it easily without lifting gear or power equipment. If it works it could be scaled up to 3 times that of the Exeter with the same spec on weight. There is some complicated metal forming which I may try to do in house unless I can find a local fabricator.

[openspaceman]

Out of interest would heat resistant stainless be resistant enough? I only ask as a few years ago I was considering using twin walled ring kiln with stainless inner (so burns were less affected by inclement weather) and my wife's late uncle,a highly experienced engineer/fabricator (who had made a half dozen or so ring kilns), said stainless would warp too much.

 

Is the inner chamber of the Exeter made of corton steel?

 

Am attempting to build retort and don't have much financial to allow experimentation and I am at a bit of a loss as to what to use for insulation of the outer chamber, thought a vermiculite and cement mix could be possible, any thoughts appreciated!

 

The confusion between fuelwood and 4 seasons has been cleared up but the trekkasaw was developed by the late Paul Elson. The company that developed it closed and their salesman formed fuelwood.

 

The 4seasons kiln looks like it spawned from the webster retort which itself was a copy of a south african one.

 

Back to the main subject:

 

stainless resists corrosion by forming a layer of chrome oxide which then protects the iron. In the absence of air the oxide layer degrades and thus ss isn't much use in the reducing atmosphere of a retort.

 

Corten steel has a rust coating that doesn't flake off and expose a fresh iron which is why it is more weather resistant.

 

I have used vermiculite glued together with high alumina cement but it didn't seem to be very strong and is pobably only good for 600C, I had more success with kaowool fixed with waterglass even that was no where as good as the cast refractory used in the high pressure kiln but we didn't get enough runs to see how that worked long term.