Firewood kiln- anyone made one?

[ecotreecare]

I've just about sold out of dry wood- very annoying as its not even winter yet!

 

I'm wanting to build a kiln out of a 20ft container. Was thinking of using a diesel air forced heater blowing in one end and a electric fan sucking the air through into some heat resistant ducting out around the side of the container back into the heater. Hopefully this way I'll get plenty of warm air flow through the container drying the wood out.

 

I would split the wood into custom made narrow metal crates and load them in with the fork lift. Even if we can do 40cube a week I would be happy.

 

What do you guys think? Would it work? Has anyone built one?

[b101uk]

Rather than burn diesel would it not be better to burn some wood to provide some heat via an old stove with a back boiler then put some radiators as well as the stove in the container then just have some small fans to move the air within while the natural draw of the stove along with vent holes in the container expel damp air.

 

After all its hardly “green” to burn diesel to dry wood

[treequip]

Last one I looked at was an insulated van body with an electic heater and a de humidifier. That's a lower energy profile than a diesel heater and fan, probably cheaper to set up as well.

[18 stoner]

Here's mine, its cheeper to set up, free to run, greener, and much bigger!

 

 

 

[ThrustSSC]

18 stoner, out of interest, what dimensions have you gone for there, and how do you find it for vehicular access? Forklift, tractor or telehandler?

[18 stoner]

They are 27foot hoops, spaced at 8 feet, 12 bays long. I think its around 12 feet high.

 

We usually split outside(unless its raining) straight into bags on pallets and put in the tunnel with a small tractor with forks on the rear. When it comes to delivery we pick them up with front end loader tractor straight into truck/trailer. The hoops/doorway is high enough for access with a medium sized tractor with a cab on.

 

Although its nearly 100foot long, circulation is good with no doors on, and acheives 16% M.C. in one summer on hardwoods.

[Big J]

Solar kilns are the way forward for drying firewood if you need it in a hurry. Using electricity to heat the kiln just seems daft given the tiny profit margins.

 

Perhaps some sort of hybrid system where you use solar water heating panels to collect the heat, pump it into radiators inside and then circulate the air is possible.

[ecotreecare]

Whilst I like the idea of burning wood to dry more wood we are not insured for fires at our yard. it’s a pain in the bum but we cant do anything about it. Burning diesel isn’t very green however I’m wanting we can turn on and leave on whilst were away working.

 

Was hoping for a one week turn around, I like the idea of a tunnel house but I don’t think it will be quick enough.

[renewablejohn]

Your just to impatient. During the summer our solar kilns dry to less than 20%MC in 3 months during the winter it is more like 6 months.

 

Our kilns similar to 18 stoner but with concrete bog mat floors to allow forklift to stack either 1x2x1 or 2x2x2 in tunnel depending on tunnel shape. Processor in front of tunnel to allow processing in Manchester sunshine.

[Big J]

One week turnaround is going to be tricky without huge heat imput and huge airflow. Force dry timber too quickly and you can case harden it (outside dries rapidly, causing a barrier preventing effective moisture removal from inside) resulting in timber that is dry on the outside, but wet inside. Additionally, there is such a monstrous volume of water in a cubic metre of timber that again, a week is ambitious.

 

Assume you have a kiln with a nominal 40 cube capacity. That's about 20 cubic metres solid volume once air space has been accounted for. Assume a rough average moisture content of 60-70% (allows for a mix of various hardwoods at various MC) and you have timber that is about 33% water and 67% wood. Now assuming you want to take you timber down to 15% MC, you need want to remove 80% of the water. That equates to 5280 litres of water.

 

Now, put that on a 7 day cycle and you have to extract 754 litres a day, or 31.4 litres an hour.

 

Assuming you have a fairly industrial extractor fan, you could extract 500 cubic metres an hour. Assuming an average outside temperature of 15 celcius and 70% relative humidity, your cubic metre of air will come in with 8.75ml of water in it. You need it to leave with 63ml (more at the start really) on average over the cycle to acheive you stated aim within your target time. This means you basically need a constant 45-50 celcius (closer to 50 is better as 45 might not be enough).

 

Maintaining that kind of heat is going to be expensive. My kiln for drying furniture grade timber consumes almost 3kw in heating to maintain 28-29 celcius (at current ambient 10 celcius outside) on 200 cubic metres an hour extraction. You are going to need many times that to maintain close to 50 celcius. The only way to reduce the heating cost is with a heat recovery unit, but I've not found one that is rated over 35 celcius.

 

Best just to get a poly tunnel me thinks!