Counter flow kilns revisited

[Aaron]

Would appreciate some feedback regarding the success of their counter-flow kiln to produce better moisture standard deviations.  Thanks.

[GeorgeCulp]

I have seen a few of these in action in southern yellow pine, however I am no expert yet I will share my impressions.

I believe that one of he benefits is that as the dry lumber exits the kiln on one track fans force air through the layers removing the residual heat and transfer it to the ingoing green lumber on the opposite track. This could definitely be grounds for energy savings.

Too, as that residual heat is transferred to the green lumber some moisture will be removed. Some of that moisture will condense and run off yet some "may" go toward conditioning of the the dry track lumber. (It may help moisture deviation but I don't think it will be enough to counteract any warpage due to overdrying)

I think most of the kilns in the south that dry with this method are direct fired. A common problem that can be experienced with direct fired kilns is an imbalance in heat distribution.  With standard kilns this can cause variances in drying in different places in the kiln. With the continous kiln all the lumber will experience the same heat distribution conditions. This is a good thing.

[GeorgeCulp]

Since my post above I have spent some time investigating the Continuous Dry Kiln.

One experiment we did was to dry a charge of 2" dimension SYP, pull out one of the dry tracks and replace it with a green track and then run with fans only for 6 hours. A 2x10x16 from the "dry" track had lost 7,660 lbs of water. A stack of 2x10x16 from the green track had lost 1220 lbs of water. Not bad for just 6 hours and the heat from the other track.

Yet, in the CDK I feel that heat that is recaptured in the "conditioning chambers" is coming from the hot moist air from the main kiln chamber that migrates into the conditioning champers consequeintly being circulated through the lumber, heat transferred to the lumber, and the moisture condensed out on to the floor.

In our experiment above we witnessed no liquid moisture in the kiln. Yet, reports are given of a "rain forest" effect going on in the conditioning chamber.

I feel that liquid moisture in the conditioning chamber is a result of the hot moist air in the kiln migrating over to the con. ch.  Its a good thing, there's a lot heat there to be captured.