I am almost afraid to post this idea... The culvert kiln!

[crtreedude]

I don't know if I have completely lost my mind (tis a definite possibility I will have you know) or I might just have a decent idea.

I am trying to come up with a way to do inexpensive kilns - the expensive ones come later. It occurred to me that I just need to have a heat source, and enclose to maintain the heat and seal up for water. The top needs to have adjustment for vents to relieve excess heat.

So, after thinking for a while, it occurred to me that I can use concrete tubes, i.e. culverts to hold up the wood AND to gently heat it. Our culverts are very thick and have lots of wire in them. Six inch in diameter are readily available.

So, I am thinking of having them every 32 inches or so, which means the test kiln will be about 4 varas long (about 11 feet). Each one will have its own fire pit and chimney, with control on the fire from restriction of air.

We assembly it, and then inclose it. If we do it right, I am thinking we will have enough draft to pull the smoke after we have a good fire going.

Okay, have at it, why won't it work or am I a genius? 

[crtreedude]

One nice thing about independent fire pits is that the middle could be a bit warmer than the ends, helping to dry more evenly.

Okay folks, have at it!

[beenthere]

No idea what just how you are trying to do the drying.....
I'm too slow, I guess.
 

[Texas Ranger]

Most kilns require a steady, low temp, dual cycle to operate.  Not to mention air flow.  I think you would create a new market for honey comb lumber.

[Gary_C]

I don't know if I have completely lost my mind (tis a definite possibility I will have you know) or I might just have a decent idea.

Okay, have at it, why won't it work or am I a genius? 

It's the first part that is right. 

What a kiln needs to provide is;

1. A uniform air flow so that all the ends, sides, and middle of the boards sees the same conditions.
2. Closely controlled and uniform temperature and humidity in the air.
3. Allow carefully scheduled changes in the temperature and humidity as the wood dries uniformly.

If your culverts can do those three things, it will work. If not, you can probably get wood dry, but not uniformly nor straight.

[crtreedude]

Thanks all. It might work, but then again, it might not. What I was thinking of is supplemental heat to something like a solar kiln. As far as air flow, the devil is in the details of making the stack so that the air can flow through, and since hot air rises, it should move - requires ventilation.

Many of our tropical woods are very easy to dry - since there isn't much here like seasons, the wood doesn't normally shift much, but there are exceptions of course.

The key is not to dry too fast, and seal the ends, after that, most things seem to work okay. Nothing like what you have to deal with in oak, etc.

[olyman]

cr--i read of a man--that took a 6 foot dia steel culvert--like what would go under a driveway--he enclosed the ends--then built the firepit---and that was his dryer--said it worked very well--and the price was right--as it was a good used one--he got it for free!!!!!  also--you could use the body of a used school bus--as thats what im going to use---

[Ironwood]

I thought you were going to say that you were using the big black smooth interior walled plastic pipe. I have a 48" x 20'er that appeared at my buddies place after hurricane Ivan flooded these parts of Western PA.  You would not be  able to just throw some fire under it, however you would have solar gain to some degree.

 Ironwood

[Texas Ranger]

Solar powered kiln would seem to be the more practical method, considering where Fred is, at the moment.

[crtreedude]

Solar powered kiln would seem to be the more practical method, considering where Fred is, at the moment.

Solar kilns are wonderful here for 4 months of the year, and then the rains come... Maintain the same basic design, but supplement heat.

Since it is nearly free to try, I am going to give it a go - and load it up with some junk wood. What is life without experiments, eh?

[SwampDonkey]

Depending on how hot those concrete culverts get you might see them crack or bust open with the heat. And others in here know more about kilns than I do, as I know next to nothing on them. I don't envision a happy ending. 

[Radar67]

CR, are you talking about using the culverts as a stove of sorts? To contain the fire and use ducting to transfer the heat to a solar type kiln?

[crtreedude]

yes, we are using the culverts as chimneys, with a slight pitch. The idea is that the concrete will buffer the heat. And, we know that it will survive, people use them as chimneys all the time here, we might have to line them, but that isn't a problem.

Concrete will give us mass to buffer the changes of temperature, we are talking a slow fire, with control.

At the very least, I will have a ready made place for grilling...

[crtreedude]

Depending on how hot those concrete culverts get you might see them crack or bust open with the heat. And others in here know more about kilns than I do, as I know next to nothing on them. I don't envision a happy ending. 

Sigh, they always laugh at genius.... 

[crtreedude]

I don't know if I have completely lost my mind (tis a definite possibility I will have you know) or I might just have a decent idea.

Okay, have at it, why won't it work or am I a genius? 

It's the first part that is right. 

What a kiln needs to provide is;

1. A uniform air flow so that all the ends, sides, and middle of the boards sees the same conditions.
2. Closely controlled and uniform temperature and humidity in the air.
3. Allow carefully scheduled changes in the temperature and humidity as the wood dries uniformly.

If your culverts can do those three things, it will work. If not, you can probably get wood dry, but not uniformly nor straight.

By the way, I was going to say, I can do all these things and I greatly appreciate you listing them.  The key is going to be not to rush it. For optimal speed, you need to have a lot more control, but do it slower, and things go better. We also air dry for a while before putting anything in a kiln. It helps a lot. Rarely do we have problems in the kiln, because whatever was bad, shows up before.

[beenthere]

I'm anxious to see some pics. Maybe then I will comprehend your game plan.

I can't say it won't work. Hope it does. 

Pics...asap   

[crtreedude]

Pics will be - yesterday we ran a test and amazing enough, the overall idea tested out just fine.

An interesting thing, while researching kilns, etc. I found out this is not a new idea. DanG, I thought I could patent it or something.  Using flues instead of steam heat is done by some systems. I was amazed in truth.

One thing, after lots of ready, has occurred to me: don't try to be too fast. What I am going to do is try to simulate a solar kiln, which means heat it up during the day, and let it cool down at night. This means that the wood has a chance to rest and equalize moisture between the inside of the wood and the outside. This is why (from my reading) the quality from solar kilns tend to be so good, so if I do the same, life should be very good, and I personally don't want to tend the fire at night.

Now, for something totally wacko, I am planning on one of the stoves that drives the flue to be something I can cook a pizza in at the end of the day, or roast meat or potatoes... Every see an Adobe oven?

[Cedarman]

Fred, the restauranteur!

[timberfaller390]

Had a chance to get somepics yet?

[crtreedude]

Okay folks, just to force me to take pictures. The kiln LIVES. And, amazingly, shows every sign of being a success. Nice, gentle heat too. By Jove, I do think it is going to work wonderfully.

We are loading up the first test. So far, it appears the temperature goes up to about 120 F and stays there - we let it stop during the night to equalize the moisture between inside and outside in the wood.

So, pictures hopefully tomorrow.

[SwampDonkey]

Need to go another 60 ° don't ya? That's if your exporting....bugs eh?

[WH_Conley]

We want pics of the pizza too.

[crtreedude]

Need to go another 60 ° don't ya? That's if your exporting....bugs eh?

Could do it for sure, just need to seal it up a bit more. But, not necessary. I don't have much of an export - and besides, you can't export without spraying - which kills the bugs.

[crtreedude]

We want pics of the pizza too.

  already we are moving to the important stuff.

[Ironwood]

Fred,
 

 I just modified my "PIG", which is a 12' long, 36" and 30" diameter, double walled steel pipe . I was designed to be a wood oven, steam chamber, and someday maybe a vac kiln. There is a 3" gap between the 1/4" thick tubes. These were "drops" from a freind's structural steel shop when they were making HUGE cantilevered outdoor advertising signs. The air gap between was designed to be used for a water jacket running off my shops boiler, which has never been hooked up, SOOOO I have thrown a wood burner under it and used the 3" gap as a flue. There is a blanket of R-20 insulation over it, and covered with recycled rubber roofing (hence PIG, or "PIG in a BLANKET"). I have had some serious "point heats" where the stove flame licks the inner pipe, mostly when my internal fan kicks off at 225-230 degrees. I finally decided that it was still going to be years before a boiler is anywhere near ready to heat this thing, so I built some internal baffles and mounted a double squirrel cage fan externally on the door, the air is briefly cooled when hitting the outdoor "plumbing" and some aluminum drops act as condensors to condensate the humidity (acting as a crude dehumidifier). I don't have any pics on 'puter but will get them off the camera. My 6 year old has now dubbed the PIG, the WALRUS as the  blower and aluminum condensation drop tubes look like a walrus face and the mass of the thing is well,... walrus like. Sometimes I wonder what memeories of me they will carry with them

 I say all this to give you some backround on my IMHO. I think your thermal mass my be too great to let it cool down too much at night. You may find to get the day time heats you want, that you may need to not let up too much at night. I do know you dont want the excessive heats that I do, I am sterilizing specialty products, but you will still need to get it higher to force that inner moisture out.

         Ironwood  

[SwampDonkey]

What is interesting is pallets have to been cooked - but not a load of teak. Heck, you can ship it wet if you want!

Maybe it is assumed our tropical pest could never survive up there? I know I would freeze to death... 

[pineywoods]

CT I'm afraid you are going to run into the same thing we did with the solar kilns. A big stack of wood will store a amazing amount of heat, enough that things won't cool off enough at nite to condense out moisture and stabilize things.  That's why we wound up sticking a cheap room de-humidifier in there to wring out the moisture. In any case, keep on tinkering, looks to me like you have a basicly good idea.

[crtreedude]

More update. Surprise, surprise - it works (I feel like a mad scientist on a cheesy movie "it lives! it lives!")

The first load of teak is coming out of the kiln now after about a month, dry as a bone, with no appreciatable defects. In fact, very very good looking. Amazingly so.

Our schedule was 6am to 2 pm, keep the fires burning. During the night, let it cool down. On the weekends, do nothing (too lazy and no one around to watch it besides me).

Highest recorded temperature, 53 C  (that would be about 127 F).

Now, a disclaimer. If you don't know it, teak is about the easiest wood there is to dry. Very stable. And, we put it in after air drying a couple of months.

Still, we are thrilled - and it did a great job of using up scrap wood too.

By the way, yes, our mechanic has been using the fireboxes for cooking in the evening, he says they are great. 

[jim king]

Fred:
I have seen various versions of used container kilns used with good results.  This link will give you some ideas.  The ones I have seen used a simple wood furnace --Two 55 gal drums as the heat source and the used containers are usually very low priced but you would need to but in a cement floor.  The fans and thermostat are the most critical parts.

http://www.palletdrykiln.com/drykiln/Photos.html

[crtreedude]

Hi Jim,

Yes, I have seen those. I wanted to have something that I could build away from electrical sources. For example, as I am sure you are well aware, wet wood is very heavy. Dry it out first, and there is a big savings.

This was built from scrap pretty much, so the cost was perhaps 500 dollars for something that would dry nearly 10,000 BF.

A old container would have cost me 2,000 to 4,000 dollars and another 800 dollars to get it here.

Granted, that isn't much, but I like my solution - and it eats more wood... (sawmills have scrap issues...)

[Paul_H]

Pics will be - yesterday we ran a test and amazing enough, the overall idea tested out just fine.

Okay folks, just to force me to take pictures. We are loading up the first test. So far, it appears the temperature goes up to about 120 F and stays there - we let it stop during the night to equalize the moisture between inside and outside in the wood.

So, pictures hopefully tomorrow.

Here is a link that will help you to post your pics.




http://www.forestryforum.com/board/index.php/topic,23851.0.html

[SwampDonkey]

 

[crtreedude]

Pics will be - yesterday we ran a test and amazing enough, the overall idea tested out just fine.

Okay folks, just to force me to take pictures. We are loading up the first test. So far, it appears the temperature goes up to about 120 F and stays there - we let it stop during the night to equalize the moisture between inside and outside in the wood.

So, pictures hopefully tomorrow.

Here is a link that will help you to post your pics.




http://www.forestryforum.com/board/index.php/topic,23851.0.html

Sorry, I think that is just way too technical for me...   

[Banjo picker]

Fred:
I have seen various versions of used container kilns used with good results.  This link will give you some ideas.  The ones I have seen used a simple wood furnace --Two 55 gal drums as the heat source and the used containers are usually very low priced but you would need to but in a cement floor.  The fans and thermostat are the most critical parts.

http://www.palletdrykiln.com/drykiln/Photos.html

Why would you need a cement floor?  Tim

[crtreedude]

I think the need for a concrete floor is because a lot of the water that comes out of the wood is corrosive. I might be wrong though. I know for example Corteza is very corrosive to tools.

[Banjo picker]

I think the need for a concrete floor is because a lot of the water that comes out of the wood is corrosive. I might be wrong though. I know for example Corteza is very corrosive to tools.

Thanks for the reply.  I have two containers, both still have the axles under them.  One is still road worthy (thinking about making a chip trailer out of it someday) the other I was thinking about turning into a kiln eventually.  One of my favorite words.  They both have wood floors in them now-  Tim

[jim king]

Fred is right, it is the acidity of the water coming out of the wood that eats steel.