Kiln Drying Forum
Wood Drying Topics => Moisture Variability => Topic started by: JMS on October 03, 2012, 10:18:43 AM
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Does anyone know the typical variability seen in a steam fired kiln?
Thanks,
JMS
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The variability seen within kiln is highly dependent on a number of factors. Some factors include the incoming distribution of moisture content, the incoming distribution of lumber diet, the inter-package variability of storage yard time (from stickering to kiln), the variability in stickering process, and within-kiln charge environmental variabilities (such as baffling, venting, etc...)
We have performed many within-kiln uniformity of drying characterizations for a number of mills over the years. Previously we developed a methodology for doing this using the inline MC data that was also tracked by package location within the kiln. Since particular charges can have varying input parameters as mentioned above, our process averaged out the input variabilities by looking at 4 or 5 consecutive charges and processing out those variabilities that really have nothing to do with the potential for kiln performance in terms of unifomity of drying.
Given a baseline situation where we knew the kiln was in good working order, we were able to characterize the uniformity of the kiln drying process itself by looking at and analyzing these 4 or 5 continuous charges. With kilns that were considered to be in good working order, we found a uniformity of about +/- 1% MC throughtout the kiln. I should mention we characterized some kilns and easily found "hot" and "cold" spots within a kiln that had a mechanical issue, sometimes resulting in uniformity variances of about 3% or 4% "wet" spots.
I am attaching an image that shows a particular "kiln mapping" we performed where you can see uniformities within about +/- 1%MC. The X=1, X=2 are track 1 and track 2. The Y=1 to Y=4 are the number fo stacks high, the ZZ=1 to ZZ=5 are the number of packages deep into the kiln. The more negative numbers are "drier" indicated by the "browner" colors. If you interpret these maps correctly, you can see that there is a more drier are of the kiln in the left top area (Y=1 is the bottom of the kiln and Y=4 is the top stack)