Lumber conditioning kiln

Abstract

A lumber conditioning kiln comprising an enclosure defining a closed chamber for receiving a stack of lumber so positioned as to provide space at the top and at the ends, a dehumidifier in said chamber containing an evaporator, said dehumidifier defining a flow path through the evaporator and a bypass passage around the evaporator, a blower for inducing air flow into the flow path of the dehumidifier for dehumidifying air and discharging dry air therefrom, fans for effecting a circulation of air within the chamber in a direction such that dry air from the dehumidifier is conducted across the top of the stack to the far end and from there reversely through the stack to the one end where the moisture-laden air from the stack is induced into the flow path of the dehumidifier and wherein there are dampers for reducing the air flow over the evaporator and increasing the air flow through the bypass.

Description

BACKGROUND OF INVENTION

This invention relates to a process for kiln drying wood. In known processes, air is circulated through the stacked wood in a kiln chamber. The temperature and humidity of the air in the kiln are controlled in accordance with established kiln schedules which have been developed for various sizes, conditions and types of wood. A typical schedule, taken from the U.S. Department of Agriculture Handbook #circulated circuited so that the refrigerant leaving the evaporation coil is approximately the same as the air temperature. This provides refrigerant from the evaporation coil cool enough to cool the compressor motor and a constant pressure in the evaporator which prevents the compressor from being overloaded and overheated.

The controls that position the dampers can be proportioning, electric, pneumatic or electronic.

A controller 46 is provided for starting and stopping the compressor motor 28 and responds to sensor means 48 connected thereto by a line 50 which senses the condition of the air entering the passage above the stack which is comprised of dry air from the dehumidifying unit and the untreated air which bypasses the dehumidifying unit. The sensor means 48 comprises wet and dry bulb sensors. When the wet bulb indicates an excess of moisture in the air, it starts the dehumidifying cycle by starting the compressor motor. When the moisture is reduced to an acceptable level, the dehumidifying cycle is stopped by stopping the compressor motor. When the dry bulb sensor indicates an excess of temperature, it starts the exhaust fan 49. However, when the temperature decreases to an acceptable level, it stops the exhaust fan and starts the supplemental heater 36. A humidistat may be used in place of a wet bulb.

Optionally, the damper 40a may be omitted and the air flow controlled solely by the damper 38a. When so constructed, closing the damper 38a will divert the air through the bypass passage 40 so as to increase the flow through the bypass passage and simultaneously reduce or stop the flow through the flow passage 38. Alternately, the damper 38a may be omitted and the damper 40a in the bypass passage employed to control the flow, when open to promote an increased flow through the bypass passage to thus reduce flow through the flow path 38. In either instance, the damper or dampers may be automatically or manually operated.

In conjunction with the dehumidifying unit, there is provided a system to recover the water that is condensed from the air on the evaporator coil and using it to restore some moisture to the stack when conditions require it. This system is shown in FIG. 2 wherein a drainpipe 52 conducts water from the drain pan 32 of the dehumidifier into a condensate pump 54 which, in turn, pumps the condensate through a conductor 56 to a storage tank 58. Water from the storage tank is delivered by way of a conductor 60 and adjustable valve V1 to a trough 62 within which are situated a dry bulb and the wick of a wet bulb 64 and 66, respectively. A fan 68 maintains a circulation of air over the wick 66. In order to alleviate a too dry condition in the kiln, a conductor 70 connected to the bottom of the storage tank by way of a float valve 72 will supply water from the tank to an evaporator-type humidifier 74 located within the base of the dehumidifier through a float valve 72 and is heated there by an electric heater 76 whenever the humidity in the kiln is too low.

The system thus comprises circulating air through a stack of lumber so as to remove excess moisture therefrom, dehumidifying the moisture-laden air and recyling it. This provides certain advantages over the prior art in that it enables operating over wide ranges of temperature, increases the rate of drying, thereby reducing the damage from mold and stain, allows existing kiln schedules to be employed, and enables operating in such a way as to prevent the dehumidifying unit from being overloaded and/or overheated. Additionally, the system enables recovery of the water from the drying operation and using it in an evaporator-type humidifier to restore some of the moisture to the lumber following the drying operation to relieve stresses that are developed during the drying operation.

It should be understood that the present disclosure is for the purpose of illustration only and includes all modifications or improvements which fall within the scope of the appended claims.

Claims

1. In a kiln for drying lumber, means defining an enclosed chamber for receiving a stack of lumber with a space above and at the ends of the stack, dehumidifying means in the chamber including a condenser, an evaporator and a compressor, means defining an enclosure in the chamber within which the condenser and evaporator are contained, said enclosure being provided with intake and outlet openings through which moist air from the stack enters the enclosure and dehumidified air leaves the enclosure, said evaporator preceding the condenser in the flow path of the air passing through the enclosure, said condenser being so positioned in the enclosure that all of the air entering the enclosure must pass through the condenser, means situated in the enclosure beyond the condenser in the direction of flow for inducing flow through the enclosure, damper means situated in the enclosure preceding the evaporator, the position of which may be controlled to control the flow of air entering the enclosure through the evaporator to maintain the temperature of the evaporator at a predetermined level and, hence, the load on the compressor and means for automatically changing the position of the damper means in response to temperature sensing means positioned in the path of the air leaving the evaporator.

2. A kiln for drying lumber according to claim 1 wherein there are fans arranged at one end of the stack for inducing circulation of air from the one end across the top of the stack to the other end and from thence through the stack to the one end.

3. A kiln according to claim 1 comprising means defining a bypass for bypassing part of the air entering the inlet opening around the evaporator.

4. A kiln according to claim 3 wherein the means for bypassing part of the air comprises a bypass passage and a damper positioned in the flow path of the bypass passage.

5. A kiln according to claim 1 comprising means for bypassing the air comprising a bypass passage, a bypass damper positioned in the bypass passage and means for effecting actuation of the bypass damper which simultaneously closes said damper means and opens the bypass damper.

6. A kiln according to claim 1 wherein the space above the stack defines a flow path across the top and wherein the dehumidifier is spaced from the end of the stack adjacent thereto sufficiently so that some of the moisture-laden air leaving the stack at that end re-enters the flow path of the air from the dehumidifier without passing through the dehumidifier.

7. A kiln for drying lumber according to claim 6 comprising sensors in the flow passage across the top of the stack.

8. A kiln for drying lumber according to claim 7 comprising a controller connected to the sensors and to the compressor to effect operation of the latter in response to said sensors.

9. A kiln for drying lumber according to claim 6 comprising dry and wet bulb sensors in the flow passage across the top of the stack.

10. A kiln for drying lumber according to claim 6 comprising relative humidity and dry bulb sensors in the flow passage across the top of the stack.

11. A kiln according to claim 1 wherein there is an exhaust fan in the chamber and a supplemental heater in the dehumidifier for heating the dehumidified air before it is discharged and the means for circulating the air comprises fans positioned above the stack at the one end and/or humidistat and dry bulb sensors positioned in the path of the air flowing across the top of the stack, said sensors operating in response to the temperature and moisture content of the air flowing across the top of the stack to, on the one hand, when there is insufficient moisture, stop the dehumidifier unit and, on the other hand, when there is more than enough moisture, to start the dehumidifier unit, and when the temperature is excessive, to start an exhaust fan and when the temperature is deficient, to stop the exhaust fan and start the supplemental heater.

12. A kiln for drying lumber according to claim 1 comprising a baffle at the top of the enclosure above the stack parallel to and spaced from the top which defines a flow passage across the top of the stack from one end of the stack to the other end thereof.

13. A kiln according to claim 1 wherein the means for controlling the damper means comprises a motor and kinematic means connecting the motor to the damper means.

14. A kiln according to claim 1 comprising a controller connected to the sensor and to the compressor operable in response to the sensor to start and stop the compressor.

15. The method of conditioning lumber comprising within a closed chamber within which is a stack of lumber, circulating air in a predetermined path which commences at one end of the chamber, passes across the top of the stack to the other end and returns through the stack to the one end, at the one end inducing a portion of the air returning through the stack into a dehumidifier in a flow path over the evaporator coil and controlling the flow of air entering the dehumidifier in the event that the refrigerant flowing from the evaporator to the compressor exceeds a predetermined level to bypass the air and around the evaporator.

16. In a system for dehumidifying moisture-laden air which has been circulated through a material to be dried, a dehumidifier including a condenser, an evaporator, and a compressor, means defining an enclosure within which the condensor and evaporator are contained, said enclosure being provided with intake and outlet openings through which the moisture-laden air enters the enclosure and dehumidified air leaves the enclosure, said evaporator preceding the condenser in the flow path of air passing through the enclosure, said condenser being so positioned in the enclosure that all of the air entering the enclosure must pass through the condenser, means situated in the enclosure beyond the condenser in the direction of flow inducing flow through the enclosure, damper means situated in the enclosure preceding the evaporator, the position of which can be controlled to control the flow of air entering the enclosure through the evaporator to maintain the temperature of the evaporator at a predetermined level and, hence, the load on the compressor and means for automatically changing the position of the damper means in response to the condition of the cooling medium flowing from the evaporator to the compressor.

17. A system according to claim 16 wherein said last-named means is a temperature-sensing device located in the flow path of the air through the evaporator.

18. A system according to claim 16 wherein there is conductor means interconnecting the condensor, evaporator and compressor and said last-named means is a temperature-sensing device located in the conductor means through which cooling medium flows from the evaporator to the compressor.

19. A system for removing the moisture content of materials comprising means defining a closed chamber within which the material to be treated is positioned, a dehumidifier positioned in the chamber including a condenser, an evaporator, and a compressor, means defining an enclosure in the chamber within which the condenser and evaporator are contained, said enclosure being provided with intake and outlet openings, means for inducing a flow of air from the outlet opening of the enclosure through the material to be treated and back into the enclosure through the intake opening, said evaporator preceding the condenser in the flow path of the air passing through the enclosure, said condenser being so positioned in the enclosure that all of the air entering the enclosure must pass through the condenser, damper means situated in the enclosure preceding the evaporator, the position of which can be controlled to control the flow of air entering the enclosure through the evaporator to maintain the temperature of the evaporator at a predetermined level and, hence, the load on the compressor, and means for automatically controlling the position of the damper means in response to the condition of the cooling medium flowing from the evaporator to the compressor.

20. A system according to claim 19 wherein said last-named means is a temperature-sensing device located in the flow path of the air through the evaporator.

21. A system according to claim 19 wherein there is conductor means interconnecting the condenser, evaporator and compressor said last-named means is a temperature-sensing device located in the conductor means through which the cooling medium flows from the evaporator to the compressor.