How to build a DIY timber drying kiln

[elfinwood saws]

We are making our own kiln for drying firewood, We are insulating one end of our shed a 30ftx30ftx20ft high area, powered by a 100kw biomass boiler and 5000 litre heat sink tank and a couple of heater boxes with fans like the ones you see hanging in factories to blow warm air, the doors into the kiln are going to be 2 tautliner artic truck curtains mounted on there sliding tracks so we pull them open to load the kiln. When shut they should flap gently to let the moisture out a bit like a giant flap valve. Also we are going to sell the excess heat to a couple of houses next to our yard, to run their central heating and we,ve signed up the RHI scheme so we will get paid to run our boiler.

[JamesNI]

That's quite the set up you have there! Look forward to seeing it all set up. How long are you hoping a cycle in the kiln will take to dry the wood?

[elfinwood saws]

We have no idea how long a drying cycle will be yet,I would be very very happy at a 7 day cycle as we should get at least 60 cube of wood in the kiln, but i'd still be happy if it takes 14 days.

[Woodworks]

Going to try a run with firewood next week. It will be spruce and poplar going in (just what I have in offcuts at the moment). I've built some boxes at that better fill the space than the ones that I previously had, so will be able to get 10.5 cubic metres of firewood in there with plenty of space for air circulation.

 

One thing that I am going to try that I've not done before is a higher temperature but only extracting for 16hrs a day (spread out evenly over 24hrs). The reason for this is that the energy requirement for increasing the temperature in the kiln goes up incrementally in a linear fashion whereas the moisture carried in the air as the temperature goes up goes up exponentially. For instance, 24hr/day extraction at 35c results in 140ltr a day extracted. 16hr/day extraction at 50c results in 265lts a day extracted. All for the same theoretical power draw.

 

Anyway, I've calculated that to take 10.5 cube from fresh to 15% will take 13.5 days at a cost of about £13 a cubic metre in electricity. Sounds like quite a high cost, but I should be able to sell it at at least a £25 a cube premium over normal firewood without it clogging up my yard for a year whilst it air dries.

 

I'll take some photos on Tuesday when it goes in.

 

Jonathan

 

Any pics yet Jonathan?

[Boy English]

when I first started firewood I ran out of seasoned but had another 15ton of green to go at, in abit of a needs must situation I knocked up a box made from fridge panels (used to make cold stores) 20ft long about 1.5m high and the same wide.. laid some metal crates in there as a fake floor about 6" above the true floor and made a tube up entering in that gap connected to an Andrews hi blow space heater.. the front was separate and used as a door for loading and unloading the wood (just threw it in loose) and when shut left a gap at the top 2" wide the full lengh of the box..

 

used to burn the heater for 4 hours nearly flat out and the wood would be lovely afterwards, this was a few years ago and neither me or the customers had a moisture meters but never had any complaints (all returning custom)

 

from memory I would get 4 burns to a 47kg bottle

 

the wood was split to hell after a burn..seemed nice and dry, even delivered it still warm several times

Edited December 5, 2013 by Boy English

[Big J]

Any pics yet Jonathan?

 

God it was a bugger get the crates in. No pictures as by the time the telehandler showed up it was dark. This is now strictly a test run - if it works in principle, I'll build a most suitable kiln as loading this one is a cow!

 

J

[Woodworks]

God it was a bugger get the crates in. No pictures as by the time the telehandler showed up it was dark. This is now strictly a test run - if it works in principle, I'll build a most suitable kiln as loading this one is a cow!

 

J

 

Sorry to hear that. Hope sorting it is not too big a PITA.

[Big J]

Well, the firewood is out and it's not really worked that well. It's taken nearly 4 weeks to dry the timber, the moisture content isn't consistent across the batch and it's just too expensive on electricity.

 

Worth a go, however the kiln I have is only suitable for drying sawn timber.

[youcallthatbig]

Big J,interesting results,not enough heat or air flow or a combination of the two? I use something similar to your setup(insulated container c/w dehumidifier+ heat),but I cannot imagine how crates of split logs could be dried uniformly without really high temps to effectively bake the logs, but then what about case hardening ?not sure what "log pro" do, to achieve the results they claim in the time scale quoted..... but it sure would not be suitable for boards, so I can empathize with your last comment

[Rob D]

Has anyone started with one of these LogPro's?

 

 

LogPro - Biomass Firewood Kiln Specialists

 

 

It all looks good in principle - ok you have to shell out £5,000-00 as a bond for the equipment - but other than that it is free?

 

 

Only other negative is that you need to be doing a fair bit of firewood to make it worth your while... could you also use this to dry milled timber - although possible could only be useful for softwood as seems far to quick for hardwood....