Ok, bit of a weird one.
I am thinking of building a eco friendly drying kiln for timber.(low temp).
Ingredients are 1 knackered freezer truck/Artic trailer. (the kiln).
Reclaimed radiators, thermostat, circulating fans, roof vents, and a couple of industrial dehumidifiers.
Heat scource I have come up with is a large wood burner boiler, to heat a large heat store/exchanger. What I have is a 4x1x2m well insulated Tank.
Heres your puzzle, what do I fill it with that will hold the heat best. 8000l water, or 8 Cubic metres of sand, or something else. Est Tank temp 80-100 degrees C at peak.
Must retain a good temp for no shorter than say 15hrs after heat scource removed, without dropping below 30.

System work as follows.
2 sets of pipes running evenly through the tank. 1 to the wood boiler, and 1 to radiators in the kiln. (heat exchanger)
Kiln pumps run 24 hrs a day keeping the kiln at a constant temp of about 30-40 degrees.
Wood burner fired up for 8-12 hrs to reheat the heat store.

Yes a carbon emmision is made (the smoke), but very low energy costs.

What I need your help with is the heat store.

The floor is yours.

 

have you considered a sand and metal shaving mix? you can get metal shavings from most places that use sheet metal (id expect it would need to be very fine shavings but Id expect it to hold enough heat within the sand to do the trick. not sure if it would work but it makes sense that it would.

George

 

I can certainly help, but a few points to think about:

Consider it as an energy balance - ie an adiabatic (constant heat) system with energy in = energy out.

Consider mass of wood, moisture content in wood, required level of dryness, flow of dehumidifiers, flow through vents, energy lost through kiln walls, energy input from burner (include efficiency for fuel used).

Consider pump flow to control temperature on recycle back to heat store. Best to use a heavy, refined oil with a high specific heat capacity. This also reduces the risk of producing steam / pressure with water - don't use sand as there will be thermal gradients across the heat store.

Sounds like a good project for a local University Chemical Engineering dept.


Nik

 

Haha - I'm puzzled to see how it's ecofriendly in the slightest but sounds like a good recycling project!

 

The dehumidifiers will chuck out quite a bit of heat on their own. If the "kiln" is well insulted they may bring the temp up to 30 Degrees alone.

It depends how quickly you want the wood to dry, and how much you do at once I guess.

Seems like a lot of trouble unless it's a commercial venture. Otherwise leave it outside in a well ventilated, dry sunny spot over summer.

 

"Consider mass of wood, moisture content in wood, required level of dryness, flow of dehumidifiers, flow through vents, energy lost through kiln walls, energy input from burner (include efficiency for fuel used)."

I have experience in commecial wood kilns. The wood is installed fresh felled 75% moisture, and comes out 6-8 weeks later at 12-15%, ready for use.
Has to be slow or it "shakes" and looses its internal structure.

"Consider pump flow to control temperature on recycle back to heat store. Best to use a heavy, refined oil with a high specific heat capacity. This also reduces the risk of producing steam / pressure with water - don't use sand as there will be thermal gradients across the heat store."

Standard buy of the shelf kilns (about £20000) use hot air or oilburning boilers, and have an operating cost of about £600/week. Using water and radiators means I will only need a good central heating pump (about 200watts). Standard pressure relief valve built in, in case of steam in system.

Thanks for your help.

 

As you can guess from the size, it would be commercial about 30 tonnes a load. Air drying takes about 6 to 15 years depending on thickness of planks.
Humidifiers are mounted externally and use vents to remove moisture.

 

Total power load on a purchased kiln is about 8000 watts.
On this set up it should be no more than 1500 watts.
Beauty of it is, the waste/failed wood from the drying provides the heat.
And as you pointed out every part of the system will be recycled.

 

Blimey - I never cease to be amazed by what one finds on SN from dead pixels at Currys to eco-kilns and even, occasionally, some chat about Scoobies. ASTONISHING!!

 

Ha Ha, stay out of NSR if all you are interested in is Cars. I had enough trouble at first on here because I own an SVX!!!.

 

I fail to see how swearing at the kiln will attain a temp of 30° C !!

 

Sorry - I lost interest after reading "Eco Friendly"

 

Quality typo that one