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Author Topic: Conventional kiln?  (Read 1757 times)

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Offline DanG

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Conventional kiln?
« on: October 31, 2003, 12:53:46 PM »
I read lots of writing about DH, Solar, and Vacuum kilns, and I've heard mention of the conventional kiln. Can anyone enlighten me as to the principle and operation of this type? I need something to "quick-dry" pine lumber before sending out to the pressure treating plant, and wonder if this would be the answer. :P
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Offline woodhaven

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Re: Conventional kiln?
« Reply #1 on: October 31, 2003, 03:31:13 PM »
Not Sure but they might be refering to steam. Most conventional kilns are steam.
Richard

Offline Den Socling

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Re: Conventional kiln?
« Reply #2 on: October 31, 2003, 04:34:16 PM »
Conventional kilns use steam to heat the air in the kiln through heat exchangers. The heat (drybulb) is raised as fast as possible without damaging the wood. If the chamber is sealed well, a controller keeps the RH down by venting moisture. If the chamber is not well sealed, steam is sprayed to keep humidity up. At the end of drying hardwoods, the wood is stressed because the shell is dryer than the core. Steam is sprayed to raise RH high enough to put some moisture back into the shell and relieve the stress.

SYP is another story. You heat it fast and vent like mad to get the MC (moisture content) down but not "dry".

Offline DanG

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Re: Conventional kiln?
« Reply #3 on: October 31, 2003, 08:47:07 PM »
SYP is the other story I'm after. I need something that can get the MC down to 25% as fast as possible, so I don't have to wait for months before I can have it treated. I'm thinking of a chamber  heated by direct heat from a furnace inside the chamber. There would be a lot of circulation in the appropriate directions and places, and venting would be via an exhaust fan on one side, which would pull in outside air from the other side. The exhaust vent would be located well below the lumber stack, perhaps in a pit, so the moisture would tend to settle there, and the air circulating through the stack would recycle until it became heavy enough to settle into the exhaust pit. The air intake would be a simple opening near the furnace, so the incoming air would be heated as it enters.

I want to try this because my research indicates that: 1. People around here like board fences. 2. Nobody around here is producing high quality, rough cut, full size lumber for this purpose. 3. I can produce 6.5 ft 4x4 posts from small logs purchased at pulpwood prices, and compete favorably with Lowe's and Home Depot for their 8ft "4x4's", and my 10ft 5/4x6 fence boards will look better and be just about as sturdy as their 6/4x5 1/2 dressed boards.  My PT plant will accept the stock on stickers, so I will have better penetration, and can re-dry under a shelter, for a vastly superior product, without a lot of extra handling.
If I can pull this off, I can cut my inventory in half, as far as the drying time is concerned, and still deliver a top quality product at a reasonable price.

Now, I've stated my case, so y'all see if you can shoot me down. I'd prefer to be shot down here and now, than to put all my money and time into the venture and still be embarrased by my own misguided thinking. :) :D
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
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Online Ron Wenrich

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Re: Conventional kiln?
« Reply #4 on: November 01, 2003, 04:21:06 AM »
I won't shoot down your idea.  I'm just wondering about the treating process.  Do they need 25% MC wood?  I always thought that the treating process helped to drive off some of that excess moisture.  Usually they put that stuff under about 35 PSI, unless you're getting some kind of dip treat.

The only thing you're going to have to watch is your cost for heating.  You can use wood scraps, but then, you need some sort of delivery system that can control the heat, and you don't want to be around tending fire all day.

I've always like the DH kilns for their simplicity  You might be able to pull off a solar kiln or do you get too much cloud cover?
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Offline solidwoods

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Re: Conventional kiln?
« Reply #5 on: November 01, 2003, 05:30:30 AM »
Quick dry pine, Kiln chamber out side, painted black, Propane direct fire (Lowes 50-85kbtu ) used furnace fans (220vac), schedule is not picky at all about as fast as you can dry it.  I would pre dry fan/vent 2 day (not night) if you can get a little solar heat.
Or
I copied BBTom's design of Water stove heats house/shop/kiln $9000 new complete (I found a used Taylor 165000btu for $50 + $3500 pipe/fittings/pump/stuff.
So far I wish I would have done it Years ago.
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Oh yea.  I checked Pressure treat in Ga.  They require 20%mc or less. Rough lumber costs a little more.  They put it on a vaccume for 24hr then pump in the CCA and pressurize 200psi+  concentration of CCA determins the exposure rating like .6 .8
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Offline DanG

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Re: Conventional kiln?
« Reply #6 on: November 01, 2003, 09:32:47 AM »
The guy that runs the plant told me, "We like to see it below 25%."  I think the scenario Jim described is similar to what they do here, but I doubt if they hold a vacuum for 2 days. My brother used to operate a plant, years ago, and he said they only hold the vacuum for about an hour, then flood with the chemical and run pressure up to 100 lbs+. He also agrees that treating on stickers would give superior penetration, and redrying on stickers would be good, also.  I read the USFS bulletin on PT lumber, and they reccomend KD before treating, but not after. The heat does something to the absorption process.
My whole project would hinge on being able to sticker right off the mill, and leave it like that until delivery. If I can't do that, labor would eat me up.
Ron, you're probably right about spending a lot of time stoking the fire. :-/  I think I can set up a furnace on the cheap, then make modifications later. That may entail switching to gas, but I'd rather do it with wood. I figger keeping it simple and cheap to start with will prevent me from losing my butt if it don't work out.  I'll only run the kiln on weekends at first, then see what happens with the marketing, once I have a salable inventory.  I think a day and a half at 200 degrees oughta do the trick, but I'll stay flexible on this, too.  Den, you got any input on this?
Thanks for the responses, guys :)
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Offline Den Socling

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Re: Conventional kiln?
« Reply #7 on: November 01, 2003, 10:40:26 AM »
I see a couple problems. First is the direct heat with a furnace in the chamber. That would be very dangerous. To dry wood, you need to force air through the kiln charge. For hardwoods, you're talking 200 to 600 CFM. If you don't keep the air moving, there's nothing to carry the moisture. With SYP, you are trying to move a much larger amount of water so you would need high CFM. So that makes the idea of a furnace in the kiln look especially dangerous. Can you imagine blowing 600 CFM across the surfaces of a wood waste burner? surrounded by nearly dry SYP?  :o  And the wind means that moisture is not going to accumulate at low areas. Most kilns have the vents in the roof. Some have powered vents in the side but high in the chamber.

My guess is this: the cheapest set-up would use an outside furnace. Pump water through a home-made heat exchanger. Make that heat exchanger out of fin pipe used in home heating. Hang the heat exchanger in front of a bank of fans. Baffle a stickered bundle and blow hot air through the kiln charge. Get two thermometers. Drape a wet cloth over one to check the humidity on occasion. Adjust vents manually to keep humidity down without dumping all of the heat.


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