Condensation trap/moisture removal ???

[Mortimer Firewood]

Hotter the better but moving that hot air through the logs is just as important. If you enter a commercial kiln while it's in operation you notice the air movement before the heat.

[farmer rod]

What Ive come up with so far....

 

Home build heat exchanger, 1 sheet 1.2 by 2.4 Aluminium sheet 2mm thick, sandwiched in between two sheets of ply, but spaced off to give a 30mm air gap either side. Mounted vertically.

 

Outward air travelling downwards, condenses moisture on the Ally sheet dripping off at the bottom, inward air rises up gaining temperature and if reintroduced near the fan inlet would probably not require its own fan.

 

Assuming the kiln is running at 40 C, 10 degree differential across the sides will give 2.5 kw of saved heat, in theory this would be equivalent to running 1 kg of water out and a bit of air cooling every 20 minutes.

 

Apart from the 50 quid for parts, this is 2.5 kwh every hour the kiln is running,for free no moving parts . Saving at 3 p per kWh 7.5 pence per hour

 

It would be interesting to know how much water a dehumidifier would extract per kWh of leccie, More energy is retained as the water is vented out cold, but even though the enegy is not lost it is costing 11 p or so buy electric instead of being provided by cheap wood ( and accruing RHI entitlement (and being sustainable))

 

I must get back to work!!

[openspaceman]

Can anyone enlighten me about the optimum operating temp in log drying kilns please

 

Define optimum?

 

Broonie posted the best temperature for speed some months back.

 

Otherwise it depends on heat source and air circulation plus size of log. Wood chip will dry in 40C 40%RH in a few hours but a 2kg log will take several days.

[farmer rod]

Define optimum?

 

Broonie posted the best temperature for speed some months back.

 

Otherwise it depends on heat source and air circulation plus size of log. Wood chip will dry in 40C 40%RH in a few hours but a 2kg log will take several days.

 

:biggrin:I was hoping for any old answer just to calculate from. There must be a temperature around which losses increase and productivity decreases.

 

I havent found Broonies post yet!

[openspaceman]

:biggrin:I was hoping for any old answer just to calculate from. There must be a temperature around which losses increase and productivity decreases.

 

I havent found Broonies post yet!

 

120-125 C because once water approaches boiling it also loses its viscosity, go higher than that and you start giving off volatile organic compounds and above about 230C you are into the early realms of pyrolysis (torrefaction) and high oxygen content organics like acetic acid are given off.

 

The higher than boiling temperature give a differential across the log to get heat into the middle and boil off even the bound water.

[farmer rod]

120-125 C because once water approaches boiling it also loses its viscosity, go higher than that and you start giving off volatile organic compounds and above about 230C you are into the early realms of pyrolysis (torrefaction) and high oxygen content organics like acetic acid are given off.

 

The higher than boiling temperature give a differential across the log to get heat into the middle and boil off even the bound water.

 

Broonies was over 100C as well, I hadnt imagined anyone doing it that hot, although its obviously going to be miles quicker. However it rather takes it out of the realms of an add on to a Log Gassifying boiler with a domestic heritage.

 

Im off for a recalculate !

[openspaceman]

Broonies was over 100C as well, I hadnt imagined anyone doing it that hot, although its obviously going to be miles quicker.

 

One Certainly Would think of going that hot

 

 

However it rather takes it out of the realms of an add on to a Log Gassifying boiler with a domestic heritage.

 

Im off for a recalculate !

 

Which is why I gave the caveat about the heat source!

 

My old boss Gavin ran his chip dryer at 40C as this is what he could recover from the coolant of the large reciprocating engine they were planning to use.

 

If you are circulating water at 90C down to 70C on the return then I reckon you could run a kiln up to about 55 without ridiculously large heat exchangers, Lorry radiators won't last in a pressurised circuit but I have some air conditioning units that need someone handy with soldering joints which must be good for a few kilowatts.

 

Are you wanting to pre dry chip in front of your boiler or venturing into logs? If the latter I can sell you the raw material :-)

Edited December 30, 2014 by openspaceman

[broonie]

http://arbtalk.co.uk/forum/milling-forum/51366-how-build-diy-timber-drying-kiln.html http://www.fpl.fs.fed.us/documnts/fplrn/fplrn254.pdf

[openspaceman]

What Ive come up with so far....

 

Home build heat exchanger, 1 sheet 1.2 by 2.4 Aluminium sheet 2mm thick, sandwiched in between two sheets of ply, but spaced off to give a 30mm air gap either side. Mounted vertically.

 

Nice but cheaper with bacofoil.

 

Outward air travelling downwards, condenses moisture on the Ally sheet dripping off at the bottom, inward air rises up gaining temperature and if reintroduced near the fan inlet would probably not require its own fan.

 

Probably better control with a separate fan and humidistat.

 

 

It would be interesting to know how much water a dehumidifier would extract per kWh of leccie, More energy is retained as the water is vented out cold, but even though the enegy is not lost it is costing 11 p or so buy electric instead of being provided by cheap wood ( and accruing RHI entitlement (and being sustainable))

 

That's right, all the energy the dehumidifier uses gets dumped back in the kiln but the electricity costs several times more than the wood heat. If you have a simple kWh meter I'll stick it on the drying room at work and weigh the water produced. I have done this before but cannot find the figures though I remember it was not as efficient as expected, My guess is they work best around 20C and one that worked at 40C would use different mass and pressure of refrigerant (do car air conditioning systems vary between hot and cold territories?). It's still my preferred method of drying clothes

[FJMatt]

Broonies was over 100C as well, I hadnt imagined anyone doing it that hot, although its obviously going to be miles quicker. However it rather takes it out of the realms of an add on to a Log Gassifying boiler with a domestic heritage.

 

my kiln which recirculates can get up to 75c at the hottest point and 57c at the coolest both are core temp, on a 130kw biomass boiler it leaves the boiler at 86c+, which is also heating two cottages

you can see on the graph [all four probes] where the vents were open ,it slowly drops,

then the doors are opened, dry wood taken out [lowest temp]

[wet wood put it] doors closed temp rises then you can see were it vents

the straight lines are where the lap top goes to sleep,

all the probes are deep inside the stillages to get core temperature