Successful drying cannot be accomplished without ample
and free circulation of air at all times.

If the above instructions are fully carried out, and good judgment
used in the handling and operation of the blower kiln, no difficulties
should be encountered in successfully drying the materials at hand.

The "Pipe" or "Moist-air" Dry Kiln

While in the blower class of dry kiln, the circulation is obtained by
forced draft with the aid of fans or blowers, in the Moist-air kilns
(see Fig. 31); the circulation is obtained by natural draft only,
aided by the manipulation of dampers installed at the receiving end of
the drying room, which lead to vertical flues through a stack to the
outside atmosphere.

The heat in these kilns is obtained by condensing steam in coils of
pipe, which are placed underneath the material to be dried. As the
degree of heat required, and steam pressure govern the amount of
radiation, there are several types of radiating coils. In Fig. 32 will
be seen the Single Row Heating Coils for live or high pressure steam,
which are used when the low temperature is required. Figure 33 shows
the Double (or 2) Row Heating Coils for live or high pressure steam.
This apparatus is used when a medium temperature is required. In Fig.
34 will be seen the Vertical Type Heating Coils which is recommended
where exhaust or low-pressure steam is to be used, or may be used with
live or high-pressure steam when high temperatures are desired.

[Illustration: Fig. 31. Section through a typical Moist-air
Dry Kiln.]

These heating coils are usually installed in sections, which permit
any degree of heat from the minimum to the maximum to be maintained by
the elimination of, or the addition of, any number of heating
sections. This gives a dry kiln for the drying of green softwoods, or
by shutting off a portion of the radiating coils--thus reducing the
temperature--a dry kiln for drying hardwoods, that will not stand the
maximum degree of heat.

[Illustration: Fig. 32. Single Pipe Heating Apparatus for Dry
Kilns, arranged for the Use of Live Steam. For Low
Temperatures.]

[Illustration: Fig. 33. Double Pipe Heating Apparatus for Dry
Kilns, arranged for the Use of Live Steam. For Medium
Temperatures.]

In the Moist-air or Natural Draft type of dry kiln, any degree of
humidity, from clear and dry to a dense fog may be obtained; this is
in fact, the main and most impo