firewood kiln - How do you build one? does anyone know

[openspaceman]

 

Do you reckon I'm going to be at risk of spontaneous combustion with an internal temperature of 80-90c?

 

Not likely as your air is only going in at 100C. The risk comes when you are recirculating and most of the water is gone, the temperature rises quite quickly.

 

The key thing to measure will be temperature and RH at the outlet. My guess is you will be wasting a lot of heat which can still do useful work.

[arboriculturist]

Bloody useful again. You imput is much appreciated

 

Realistically, due to the lack of a capacious burn chamber or buffer tank, the kiln will be on in 10 hour blocks. It doesn't take long to get to temperature (about 20 minutes) and would be pumping hot air at around 100c for all that time.

 

There is no heat exchanger - it's a simple case of hot air pumped into one end and vented out the other. Efficiency is not an issue for me as the whole set up only cost a couple of grand, and one day's cutting on the sawmill produces enough offcuts to fuel the biomass boiler for several days.

 

Thank you for the figures on what saturation point would be. Late last night I just couldn't find the tables I needed!

 

Do you reckon I'm going to be at risk of spontaneous combustion with an internal temperature of 80-90c?

 

With an isolated heat exchanger Jon and those temperatures you will have no issues.

 

Lets have an update on your Poland thread ! - i'm a bit bored

[ash_smith123]

Does anyone know a rough price for the farm2000 or dragon boilers? Can't seem to find a price online

[Big J]

With an isolated heat exchanger Jon and those temperatures you will have no issues.

 

Lets have an update on your Poland thread ! - i'm a bit bored

 

Patience man! I'm only just getting started with it! Generally all good, but badly set up bands letting the cutting down a bit at the moment. Will be resetting them next week so should be good to go then.

 

Got everything up and running today and did a test burn for a couple of hours. Still have the door and back to insulate as well as cladding it, which should improve thermal efficiency a bit. Anyway, on a 2hr burn (one partial restoking) I got the internal air temperature up to about 62 celcius - no firewood in it though (empty box).

 

I reckon with the addition of the final insulation and crates of firewood taking up airspace and slowing airflow, we shouldn't have any issues getting up to 80 celcius.

 

Pictures will follow....

[arboriculturist]

Patience man! I'm only just getting started with it! Generally all good, but badly set up bands letting the cutting down a bit at the moment. Will be resetting them next week so should be good to go then.

 

Got everything up and running today and did a test burn for a couple of hours. Still have the door and back to insulate as well as cladding it, which should improve thermal efficiency a bit. Anyway, on a 2hr burn (one partial restoking) I got the internal air temperature up to about 62 celcius - no firewood in it though (empty box).

 

I reckon with the addition of the final insulation and crates of firewood taking up airspace and slowing airflow, we shouldn't have any issues getting up to 80 celcius.

 

Pictures will follow....

 

This is more like it - some action at last.

 

Very much looking forward to hearing how it performs once you have everything calibrated and fully bedded in, having run a few 1000 metres through it. - that is the time when all our questions will be answered.

 

I hope it progresses well:001_smile:

[Duffryn]

Does anyone know a rough price for the farm2000 or dragon boilers? Can't seem to find a price online

 

Ash - Forget Dragon Farm 2000 is your only choice. Flue height might be an issue with Farm 2000 but give them a call. Consider going 200kw and above to to get the 5.5p, they have straw compliant boilers too.

[ash_smith123]

Thanks Iain! Maybe Looking to build one again the start of next year really. We will see how this winter goes. I did see they do straw compliant boilers, that would be handy, Plenty of straw around here!

[Big J]

Second day running the boiler and it seems to be going well. We finished off insulating the bottom 19 inches of the container and cladding it today, which seemed to make a difference. All that is left is to insulate the back of the container and construct an insulated panel to hang over the doors.

 

Boiler was running sweetly today and internal temperature in the kiln at the far end (the doors) from the hot air inflow was around 50-56 celcius for most of the day. This is the coldest part of the kiln, as far as I can tell, and the middle is about 15 celcius warmer.

 

Arriving at the yard this morning (the kiln was off overnight - it's not possible to run it as the longest you can leave it without restoking it is about an hour) there was water pouring out the bottom of the container and much condensation inside. This strikes me as good, as the firewood has had the night to sweat as it cools and then the heat is very quickly restored (it was 18c on arrival to the yard, and 45c within 25 minutes) and the water evaporates.

 

How do these temperatures compare to other kilns used here? I reckon it's averaging 60-65c across the kiln for 9 hours. With reasonably freshly felled softwood, how long would you reckon it would need? This is all quite different to the sawn timber drying!

[briquette_seller]

How long does restoking the boiler take?

[Big J]

2 minutes, max. The firebox is 0.84 cubic metres. Offcuts are cut with the chainsaw to 70 cm, or thereabouts. It just burns quite quickly due to the forced airflow.