CA2203066A1 - Wood drying kiln - Google Patents

Abstract

A wood conditioning kiln is operated using air circulation as the heating medium. The kiln has a kiln chamber containing a large diameter air propeller. The propeller is mounted adjacent one wall of the chamber and is surrounded by a short duct when operated, the propeller drives air against and through a stack of wood in the chamber and draws air from its backside, creating an air circulation through the wood. This continual cycle of the air increases its temperature and drives the wood. The chamber has an air inlet and an air outlet that are controlled according to the temperature and humidity conditions inside the kiln.

Description

WOOD DRYING KILN
FIELD OF THE INVENTION
The present invention relates to a kiln for the conditioning of wood.
BACKGROUND
In conventional wood conditioning kilns, air is circulated through the wood in a closed chamber. The temperature and humidity of the air are controlled to reduce the moisture content of the wood and, in some cases, to raise the temperature of the wood for pasteurization.
10 Conventionally, the kilns are large, permanent installations. The heat required for the wood conditioning is supplied using steam or electricity.
The present invention is concerned with an apparatus that does not use steam, electric or other heaters and can be mechanically driven.
This allows the kiln to be manufactured as a portable unit, usable in 15 locations without auxiliary power supplies or boilers.
SUMMARY
According to the present invention there is provided a wood conditioning kiln comprising:
a chamber for containing wood to be conditioned;
an air propeller;
means mounting the air propeller in the chamber, adjacent one side of the chamber for rotation on a propeller axis substantially normal to said one side of the chamber;
an annular duct surrounding the propeller, the duct having an 25 inlet end adjacent but spaced from said one side of the chamber; and drive means for rotating the propeller for drawing air into the duct from adjacent said one side of the chamber and propelling air from the duct across the chamber.
The propeller and duct function as a ducted fan to produce a recycling air flow through a stack of wood in the chamber, around the walls of the chamber and back through the duct. The frictional resistance to this flow is high and the air temperature rises rapidly without the use of auxiliary heaters.
For temperature and humidity control, an inlet may be provided in the chamber wall adjacent the propeller and an outlet on the opposite wall. Opening these will draw in fresh air from outside and discharge hot, 10 humid air to the outside, moderating the temperature and humidity.
The inlet and outlet may be controlled by an automatic controller according to temperature or humidity levels monitored within the chamber.
Where desired, the propeller may have a variable pitch to 15 control the air circulation in the kiln. The pitch may be varied using the temperature and humidity controls.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:
Figure 1 is a side view of the kiln, in section;
Figure 2 is a plan view of the kiln, along line 2-2 of Figure 1;
and Figure 3 is a view of the propeller and duct taken along line 3-3 of Figure 2.

Referring to the accompanying drawings, there is illustrated a kiln 10 that is based on a rectangular chamber 12. The walls of this chamber incorporate thermal insulation 14. A door 16 is fitted in one end of the chamber. Two rails 18 extend into the chamber for supporting a wheeled trolley 19 Adjacent one side wall 20 of the chamber is a large diameter 5 propeller 22. This is an air propeller of the type used for propeller driven aircraft. It has blades 24 radiating from a hub 26. The hub is mounted on a shaft 28 that extends through the wall 20 of the chamber for connection to the output of a motor 30.
Surrounding the propeller 22 is an annular duct 32. This is a 10 relatively short duct with an inlet end 33 facing the side wall 20 of the chamber .
An air inlet 34 is formed in the side wall 20 of the chamber to one side of the propeller and duct and near the top. The inlet is controlled with a flap valve 36 operated by an actuator 38. An air outlet 40 is formed 15 in the side wall 42 of the chamber opposite the side wall 20. This outlet is near the bottom of the side wall 42. The inlet and outlet are offset towards opposite ends of the chamber. A flap valve 44 controls flow through the air outlet 40 under the control of an actuator 46.
A controller 48 is connected to the actuators 38 and 46 to 20 control their operation. The controller is also coupled to two thermal probes50 and 52 in the chamber and a wet and dry bulb hygrometer 54 inside the chamber.
In use, a stack of wood 56 is placed on the trolley 19 and is loaded into the chamber. The thermal probe 50 is located in the center of 25 the stack of wood, while the probe 52 is located on its surface. When the door 16 is closed, the motor 30 is actuated to drive the propeller 22. This produces a flow through the duct 32, from the inlet 34, and discharges it against the stack of wood 56. The air flowing through and around the wood travels to the opposite side of the chamber and, on reaching side wall 42 travels along the walls, around the wood, and back to the inlet 34 of duct 32. This cycling of the air produces considerable heat and raises the 5 temperature within the kiln, drying the wood. When temperature and humidity conditions in the kiln are too high as detected by the thermal and humidity monitors, the controller 48 opens the air inlet 34 and the outlet 40 to allow fresh air to enter the chamber and humid air to leave.
This unit is self-contained. It requires only a mechanical power 10 source, which can be an internal combustion engine, an electric motor or any other source of mechanical power. The modest amount of electricity used by the controller is readily provided by a small generator driven by the motor where no other power source is available.
The unit can be produced in the size of a transport container 15 for delivery by any known mode of transport to remote sites.
While one particular embodiment of the invention has been described in the foregoing, it is to be understood that other embodiments are possible and are intended to be included within the scope of this application. Thus, as discussed above, the propeller may have a variable 20 pitch with pitch control being effected according to the temperature and humidity conditions in the chamber, as monitored by the controller.

Claims (6)

1. A wood conditioning kiln comprising:
a chamber for containing wood to be conditioned;
an air propeller;
means mounting the air propeller in the chamber, adjacent one side of the chamber for rotation on a propeller axis substantially normal to said one side of the chamber;
an annular duct surrounding the propeller, the duct having an inlet end adjacent but spaced from said one side of the chamber; and drive means for rotating the propeller for drawing air into the duct from adjacent said one side of the chamber and propelling air from the duct across the chamber.

2. A kiln according to Claim 1 including an air inlet in said one side of the chamber and an air outlet in a side of the chamber opposite said one side.

3. A kiln according to Claim 2 including thermostatic means for monitoring temperatures in the chamber and venting control means responsive to said thermostatic means for opening and closing the air inlet and air outlet to maintain desired temperature conditions in the chamber.

4. A kiln according to Claim 2 or 3 including humidity monitoring means for monitoring the humidity of air within the chamber, the venting control means comprising means responsive to a humidity level above a preset level for opening said air inlet and air outlet.

5. A kiln according to any preceding Claim wherein the propeller has a variable pitch.

6. A kiln according to Claim 5 including pitch control means for varying the propeller pitch.