« 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.