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General Discussion / Re: Continuous Kilns and Minimum Board Feet Question
« Last post by M Gallahar on May 05, 2015, 09:44:35 AM »
Thanks, George.

Do you use a continuous kiln? Anything I should be aware of? Any advice?
General Discussion / Re: Continuous Kilns and Minimum Board Feet Question
« Last post by GeorgeCulp on April 28, 2015, 01:40:07 PM »
Mostly depends on the length of the CDK. If your lumber we'll say requires 30 hours to dry then if you have a 60 foot kiln then your push rate would be 2 feet per hour. If you have a 30 foot kiln then the push rate would be 1 foot per hour.

Those are extreme examples yet should serve to show you how "how much board footage is required" is a question you can answer yourself.
General Discussion / Re: Other Benefits to Continuous Kilns
« Last post by GeorgeCulp on April 28, 2015, 01:36:08 PM »
Almost all the continuous kilns in the south are direct fired. A direct fired kiln can have considerable varying dry bulb temps within the kiln due to the difficulty of balancing.

In a CDK all the lumber will see the same drying conditions down the length of the kiln even if they are varied which will make a large difference in resulting quality. Any top to bottom variances down the length of the kiln will still be there.

Direct fired burners normally have to operate from a high rate of heat output to a low rate of heat output. As Mike pointed out the heat demand will be steady. The direct fired heat plant can then be diesigned for this "sweet spot" of continuous operation which will helps its operation greatly.

In a CDK moisture migrates from the main drying chamber to the conditioning chamber on each end where the moisture laden air can be circulated through the green track, then heat will be removed by the green lumber and you get liquid runoff. The air then goes through the dry lumber on the other track and is reheated slightly and back around. Here is where the energy savings are as well as a heat plant running steady state.

Since a CDK rarely ever shuts down no time is lost switching out charges which over a week could possibly cost close to a charge depending on your charge time.

You don't necessarily have to have HIGH volume items to run in a CDK, you can just have a shorter kiln which will lengthen the pushrate time therefore causing the lumber to be in the kiln longer. I do agree that it is not good to be changing sizes. In fact, it is optimal to run the same size on each track, as to run different thicknesses on each track will cause some different air flow measurements.

If increased volume is not the primary desire, but increased quality and energy saving are, then a shorter CDK could be the answer.
General Discussion / Re: Kiln supply duct temp
« Last post by GeorgeCulp on April 28, 2015, 01:14:45 PM »
What kind of direct  fired kiln do you have? Shavings fired, vortex style burner, or a saw dust, slope grate burner?

I assume you have operated at 500 degrees before, am I correct? And now you can't get above 400? Correct?

Barring a massive leak of heat there are only two things can affect your supply duct temperature as you have described....1. you are not burning fuel at a rate you previously did (could also mean wet fuel if you have a vortex burner), 2. you are moving more air now than before with your recirculation blower.

Is your kiln taking longer to get to temperature? If so, then you most likely are not combusting the same amount of fuel. If your kiln is getting to temperature in the same amount of time at 400 as you were at 500 then you most likely are moving more air with your recir blower.

Knowing if you are  shavings fired or green sawdust would help a lot.

George Culp
Dry Kiln Maintenance / Re: kiln coils & steam traps
« Last post by Grady on April 26, 2015, 10:59:13 PM »

. Remember, a water logged steam heating coil, becomes a "cooling" coil when water logged!!

I have heard this before. I do wonder though, if that zone in a kiln was experiencing a Cooling effect due to water logging, would the DB temperatures in that zone drop and the modulating steam control valve open more to compensate? once the steam valve opens more that should eventually create enough pressure to flush the trap empty.  I only ask this because i have been told the same thing with my kiln setup by a bloke who was trying to sell me bucket traps to replace the float traps we currently use.
General Discussion / ISPM 15 Heat Treatment
« Last post by HencoV on April 18, 2015, 11:24:08 PM »
We recently did an installation on a kiln to do heat treatment of pallets to comply with ISPM15 heat treatment regulations. The client runs a small pine sawmill and dips all timber in anti fungal dip. He then manufactures the pallets, followed by the Heat treatment of 56 Deg C core temp on the thick bearer part of the pallet for 30 minutes. DB temp goes up to 80 Deg C.  After this the kiln goes over into a drying cycle. (more to prevent the hot water boiler from boiling over than actual drying!, though it does get rid of free surface water)

Despite all the above the pallets started growing fungus at a client's storage facility (in a shed) during a particularly humid period, less than a week after manufacturing and treatment.

During HT the humidity in the kiln goes very high and water start accumulating on the timber surface and on the kiln floor. We suspect that this "washed" off the anti fungal dip, or the 80 Deg C temp may have de-activated the active ingredient of the anti fungal dip. Further the MC of the pallets were not reduced significantly enough to prevent fungal growth to re-appear under perfect fungal growth conditions in a shed that was probably saturated with spores anyway.

This leads to 2 questions:

How effective is ISPM15? Is this not just to "stop the buck" at the manufactures gate, meaning...the timber was OK when it left his facility?
Is there a different regulation stating that timber needs to be HT treated AND below 20%MC to prevent fungal growth at time of leaving the manufacturing facility?
Industry Articles / Re: Investigation of Historic Equilibrium Moisture Content Data
« Last post by HencoV on April 18, 2015, 10:48:44 PM »
Interesting reading. Unfortunately (fortunately ;)), I don't think any of the information will ever be used in training drying operators or managers, or in real life production facilities....Not that I am trying to bring science and research down. Research like this is important in understanding the big picture.
General Discussion / Re: Other Benefits to Continuous Kilns
« Last post by M Gallahar on April 16, 2015, 10:30:13 AM »
Thanks for the response, Michael. Focusing on high volume products makes a lot of sense.
General Discussion / Continuous Kilns and Minimum Board Feet Question
« Last post by M Gallahar on April 16, 2015, 10:25:37 AM »
What is the minimum board feet of drying per month required to make a continuous kilns feasible?
General Discussion / Re: Other Benefits to Continuous Kilns
« Last post by HencoV on April 14, 2015, 07:43:12 AM »
I would like to see a list of all benefits and negatives on these kilns? Apparently what sells it is the steady energy supply as Mike pointed out. From a control and optimizing point of view I wonder about a few issues:

As seen on the pic, the timber coming out such a kiln looks servery over dried judging by the colour? Is this normal? Overdrying is normally associated with down grade? ...hoping it will be sorted out in the conditioning chamber?

What happens if you need to re-dry boards that comes out wet?...need another kiln?

Are these kilns really so energy efficient?  "lb steam per board ft dried" and "kW hours per board ft dried" ratios versus the same ratios of similar capacity standard batch kiln (volume per month) would be interesting to see?

 Not sure about the control of these kilns. If you get excessive down grade, can you change any conditions, except taking it out sooner or changing energy input/ DB set point..which increase drying time?

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