Does liquid water drain from wood (specifically SYP) as it dries in a conventional high-temperature kiln? If so, how can we estimate the amount to properly prepare a drainage system?
(Sawing and Drying Forum)
From Contributor V:
No it doesn't, if there is water in your kiln it does not come from the wood. I've seen this with a steam supply system that was poorly designed. The problem was two-fold: The spray line feed pipe came out the bottom of the main steam line, effectively acting as a condensate return line/drainage line off the steam line. The result was that when humidification was required from the steam spray it would spray all the condensate in the steam line into the kiln first and then steam. This problem was multiplied by the second problem. Steam traps where not placed optimally, resulting in excessive condensate throughout the system.
For example, if a fresh cut board weighs five pounds per board foot, then weighs three pounds per board foot after itís been dried in an oven to 0% moisture content, that means it had two pounds of water in every board foot. Two pounds of water per board foot compared to the lumberís dry weight of three pounds per board foot is a ratio of 2:3óso the lumber has a moisture content of 2/3, or 67%. Thatís similar to oak, for example, which is usually about 68% moisture content when fresh cut. Itís really astounding how much water has to be removed from wood to make it suitable for finished products. Take the example of a truckload of oak. Fresh cut oak weighs about 5.4 pounds per board foot. So a truckload of 8,000 board feet weighs about 43,560 pounds - just under 22 tons. Once you remove enough water to get the oak down to a moisture content of 6%-8%, it weighs about 3.5 pounds per board foot. So that truckload now weighs 28,000 pounds, or about 14 tons. That means that to completely dry a truckload of 8,000 board feet of oak, you have to remove 15,560 pounds of water - almost eight tons, close to 2,000 gallons of water. Some of this water will be vented from you kiln but not nearly all of it. Our plant sits near a breeder stream for trout and we had to plug all of our kiln drains. I definitely notice the water now and I agree with the earlier post that water in a kiln could be related to a poorly designed steam system, but not necessarily. To answer your question yes, liquid water does drain from wood.