questions about steam and kiln drying wood

[Jerome B]

Okay I am a little confused about how steam is involved in the kiln drying of wood.
I am doing research on a cabinet shop that was active in the late 1840's. I know that they were kiln drying wood. Does this mean that they needed a source of large volumes of steam, perhaps a steam engine?

Do you have to use steam when kiln drying wood? And if you don't what happens?

Thanks,

Jerome B

p.s. I hope that I put this on the right sectionof the forum

 

[JackLeg]

Scott Smith is our resident "kiln expert" and hopefully he'll weigh in here.

There are several methods of drying wood and the DH or dehumidification kilns are probably the most popular for small to medium sized operations. Basically, if I understand it correctly, it's a "heat pump/air conditioner" system that removes mositure from the wood at a very controlled rate. Control is the key word here.

I have a small solar kiln (800 bf) which serves my needs nicely, but I'm not drying for production runs and have time to let "ol Sol" do its work.

 

[DaveO]

Do you have to use steam when kiln drying wood? And if you don't what happens?

Thanks,

Jerome B

Jerome, steam is generally not condusive to drying wood. You want to remove moisture so dry air is best. Steam is often used to add a little moisture back to the outer surface of the wood in kiln drying, as it dries the fastest. That is known as conditioning the charge. It can help to prevent "case-hardening". Most likely steam is used to blend the colors of heartwood and sapwood, especially in Walnut, and to enhance the working properties of Beech.

MTCW,
Dave

 

[jeff...]

Not that I know much about this subject but I have done extensive research.

Steam in Kiln drying is used in three different circumstances.

1) First step in a Kiln schedule to equalize the initial moisture content of a large charge of lumber.

2) Again during the first step in a dying schedule to bleed the heartwood into the sap wood. Mainly used for walnut and cherry.

3) At the end of a schedule to reduce case hardening and increase workability in some species like beech.

Thanks

 

[scsmith42]

Jerome,

Steam has long been the most widely used heating medium for kiln drying of lumber in large commercial "conventional" kilns. Steam is moved from the boiler into the kiln by pipes, and the heat is then transferred to the circulating air in the kiln. Historically, many lumber processing operations required steam for a variety of applications, and it was therefore natural to include sufficient boiler capacity for kiln-drying operations.

In recent years dehumidification kilns have been rapidly increasing, and many new kiln installations are DH rather than steam.

Jeff and Dave are correct in that Steam is not injected directly into the kiln chamber for drying purposes, but rather for the conditioning, equilization, etc purposes that they stated.

Steam is generated by a boiler, rather than a steam engine, and no - you don't have to use steam in order to dry. For smaller operations, DH kilns are becoming the system of choice. Solar kilns are also used for low volume systems.

Scott​

 

[JimD]

When you steam walnut, I guess it makes the sapwood darker but I hate what it does to the heartwood. Walnut air dried has a redish color sometimes with purpleish streaks. If you steam it, it is almost grey. Oil helps it when you are finishing but it is never as nice as air dried.

I've also read that steaming will not darken the sapwood of cherry but I am not sure.

Jim