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Title:
A KILN
Document Type and Number:
WIPO Patent Application WO/2006/053392
Kind Code:
A1
Abstract:
A kiln (10) for drying a charge of lumber (12) using air heated by solar radiation (14) includes a housing (16) having a longitudinal wall (18) extending between end walls (20) and providing opposite sides (24, 26) and a roof (28) to define an enclosed drying chamber (30) within which the charge (12) is able to de dried. The wall (18) is formed by spaced apart first, second and intermediate layers (38, 40, 42), the first layer (38) located inwardly of the second layer (42), and the intermediate layer (40) located between the first and second layers (38, 42). Air is able to be heated between the first and intermediate layers (38, 40) by solar radiation (14) passing through the intermediate and second layers (40, 42) and then fed back into the drying chamber (30), while air in the space between the intermediate and second layers (40, 42) acts to thermally insulate the air between the first and intermediate layers (38, 40).

Inventors:
WEIR GREGORY WARREN (AU)
Application Number:
PCT/AU2005/001756
Publication Date:
May 26, 2006
Filing Date:
November 18, 2005
Export Citation:
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Assignee:
AUSTRALIAN CHOICE TIMBER SUPPL (AU)
WEIR GREGORY WARREN (AU)
International Classes:
F24S10/50; F26B3/28; A23B7/02; A23B7/03; A23B9/08; A23L3/40; B27K5/00; F26B21/02; F26B25/10; F26B25/12
Foreign References:
FR2834334A12003-07-04
US5992048A1999-11-30
Other References:
PATENT ABSTRACTS OF JAPAN
DATABASE WPI Week 199141, Derwent World Patents Index; Class Q76, AN 1991-301778
Attorney, Agent or Firm:
Hind, Raymond (1 Nicholson Street MELBOURNE, Victoria 3000, AU)
Download PDF:
Claims:
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A kiln of the type hereinbefore defined for drying or heattreating a charge of lumber, the kiln further comprising: air feed means for feeding air between the first and intermediate layers to enable solar heating of the air, the air feed means being selectively operable to feed air between the first and intermediate layers in a first direction from the first side of the drying chamber to the second side of the drying chamber or to feed air between the first and intermediate layers in a second direction from the second side of the drying chamber to the first side of the drying chamber; and means for promoting a drying airflow within the drying chamber, the means for promoting a drying airflow being selectively operable to promote a drying airflow from the second side of the drying chamber through the charge of lumber to the first side of the drying chamber when the air feed means is acting in the first direction or to promote a drying airflow from the first side of the drying chamber through the charge of lumber to the second side of the drying chamber when the air feed means is acting in the second direction.
2. A kiln as claimed in claim 1 , wherein the air feed means includes selectively operable first and second air pumps and selectively operable first and second air distribution means, the first air pump having associated inlet and outlet manifolds for feeding air between the first and intermediate layers in the first direction from the first side of the drying chamber to the second side of the drying chamber, the second air pump having associated inlet and outlet manifolds for feeding air between the first and intermediate layers in the second direction from the second side of the drying chamber to the first side of the drying chamber; the first air distribution means having associated inlet and outlet manifolds for feeding the air heated between the first and intermediate layers into the second side of the drying chamber, and the second air distribution means having associated inlet and outlet manifolds for feeding the air heated between the first and intermediate layers into the first side of the drying chamber.
3. A kiln as claimed in claim 1 or claim 2, further comprising a controller for controlling the operation of the air feed means and the means for promoting a drying airflow, wherein the controller is operable to reverse the direction that the air feed means feeds air between the first and intermediate layers and to correspondingly reverse a direction of the drying airflow within the drying chamber.
4. A kiln as claimed in claim 3, wherein the controller includes a timer that is operable to cause the reverse at predetermined times and/or periodically.
5. A kiln as claimed in claim 3, wherein the controller is operable to cause the reverse as a function of the relative humidity of the charge adjacent the first side of the drying chamber and the relative humidity of the charge adjacent the second side of the drying chamber.
6. A kiln as claimed in any one of claims 1 to 5, further comprising airflow sensors for detecting at least one of the temperature and the relative humidity of the drying airflow within the drying chamber at the first and second sides of the drying chamber so that the at least one of the temperature and the relative humidity of the drying airflow is able to be detected upstream of the charge.
7. A kiln as claimed in 6, comprising a first airflow sensor located at the second side of the drying chamber for detecting the at least one of the temperature and relative humidity of the drying airflow upstream of the charge when the air feed means acts to feed air between the first and intermediate layers in the first direction and the means for promoting a drying airflow acts to promote a drying airflow from the second side of the drying chamber through the charge to the first side of the drying chamber.
8. A kiln as claimed in 6 or claim 7, comprising a second airflow sensor located at the first side of the drying chamber for detecting the at least one of the temperature and relative humidity of the drying airflow upstream of the charge when the air feed means acts to feed air between the first and intermediate layers in the second direction and the means for promoting a drying airflow acts to promote a drying airflow from the first side of the drying chamber through the charge to the second side of the drying chamber.
9. A kiln of the type hereinbefore defined for drying or heattreating a charge of lumber, wherein the housing of the kiln further includes an internal frame for supporting the longitudinal wall, the frame being tensioned by one or more cables associated with the frame, the or each cable stiffening the frame by deflecting the frame outwardly.
10. A kiln as claimed in any one of claims 1 to 8, wherein the housing of the kiln includes an internal frame for supporting the longitudinal wall, the frame being tensioned by one or more cables associated with the frame, the or each cable stiffening the frame by deflecting the frame outwardly.
11. A kiln as claimed in claim any one of claim 9 or claim 10, the frame having a series of resiliency flexible generally arcuate structures, the structures extending across the housing and spaced apart from one another along the length of the housing.
12. A kiln as claimed in any one of claims 9 to 11 , wherein the or each cable is coupled to at least a respective one of the structures by pulleys, the or each cable extending substantially a portion of the roof of the longitudinal wall to base portions at the sides of the housing.
13. A kiln as claimed in claim 9 to 12, further comprising one or more tensioning devices disposed adjacent the base portions of the housing, the or each tensioning device being operable to tension at least one of the one or more cables to stiffen the frame.
14. A kiln as claimed in claim 13, wherein the or each tensioning device is anchored to the ground to thereby fasten the or each cable and the kiln relative to the ground.
15. A kiln as claimed in claim 13 or claim 14, wherein the one or more cables are adapted to be selectively coupled and released from the tensioning device(s).
16. A kiln as claimed in any one of claims 9 to 15, wherein the or each cable is selected from the group comprising a monofilament of wire, a mono¬ filament of plastic, a multistrand cable of wires and a multistrand cable of plastics.
17. A kiln of the type hereinbefore defined for drying or heattreating a charge of lumber, wherein the housing of the kiln is mounted for movement along parallel spaced apart rails so that the housing can be moved over an adjacent charge, each rail being adapted to cooperate with the housing to prevent the housing lifting away from the rails as a result of windloading.
18. A kiln as claimed in any one of claims 1 to 16, wherein the housing of the kiln is mounted for movement along parallel spaced apart rails so that the housing can be moved over an adjacent charge, each rail being adapted to cooperate with the housing to prevent the housing lifting away from the rails as a result of windloading.
19. A kiln as claimed in claim 17 or claim 18, wherein the housing includes a plurality of wheels by which the housing is mounted for movement along the rails, the wheels adapted to roll along the rails.
20. A kiln as claimed in claim 17 or claim 18, wherein the housing includes a plurality of skids by which the housing is mounted for movement along the rails, the skids adapted to slide along the rails.
21. A kiln as claimed in any one of claims 17 to 20, wherein each rail includes at least one transversely extending rail flange between which the wheels or skids run, the rail flanges disposed above housing flanges extending transversely from the housing to maintain the housing flanges captive.
22. A kiln of the type hereinbefore defined for drying or heattreating a charge of lumber, the kiln further comprising: a baffle located within the drying chamber above the charge of lumber, the baffle forming part of the means for promoting a drying airflow within the drying chamber from the second side of the drying chamber through the charge of lumber to the first side of the drying chamber; and a plurality of removable side panels that are positioned adjacent sides of the charge within the kiln; the baffle and the panels defining an internal steam chamber about the charge within the kiln.
23. A kiln as claimed in any one of claims 1 to 21 , the kiln further comprising: a baffle located within the drying chamber above the charge of lumber, the baffle forming part of the means for promoting a drying airflow within the drying chamber from the second side of the drying chamber through the charge of lumber to the first side of the drying chamber; and a plurality of removable side panels that are positioned adjacent sides of the charge within the kiln; the baffle and the panels defining an internal steam chamber about the charge within the kiln.
24. A kiln as claimed in claim 22 or claim 23, wherein the panels are adapted to be attached to the baffle to hang down the sides of the charge.
25. A kiln as claimed in claim 22 or claim 23, wherein the panels are defined by walls that are mounted on wheels whereby the walls can be rolled in and out of the kiln and positioned around the sides of the charge to form the steam chamber.
26. A kiln as claimed in any one of claims 22 to 25, wherein each panel includes an insulating material.
27. A method of applying a layer (the "outer layer") of the longitudinal wall over a previously applied layer (the "inner layer") of the longitudinal wall of a kiln of the type hereinbefore defined for drying or heattreating a charge of lumber, the method comprising: applying one or more inflatable spacers against an outwardly facing surface of the inner layer; applying the outer layer over the inner layer by drawing the outer layer over the or each spacer and the inner layer; and securing the applied outer layer relative to the inner layer; whereby, the or each spacer assists in establishing and/or maintaining the inner and outer layers in a spaced apart arrangement during application of the outer layer.
28. A method as claimed in claim 27, further comprising inflating the or each spacer to establish a space between the inner and outer layers after applying the or each against the outwardly facing surface of the inner layer and before applying the outer layer over the inner layer.
29. A method as claimed in claim 27 or claim 28, further comprising deflating and removing the or each deflated spacer from between the inner layer and the secured outer layer.
30. A method as claimed in any one of claims 27 to 29, further comprising: securing the outer layer to the first end wall of the housing before applying the outer layer over the inner layer; applying the outer layer over the inner layer by drawing the outer layer over the or each spacer and the inner layer from the first end wall to the second end wall; and securing the applied outer layer relative to the inner layer by securing the outer layer to the second end wall and the sides of the housing.
31. A method as claimed in any one of claims 27 to 30, further comprising applying at least two inflatable spacers transversely over the inner layer, a first of the inflatable spacers applied over a portion of the longitudinal wall adjacent the first end wall and a second of the inflatable spacers applied over a further portion of the longitudinal wall adjacent the second end wall.
32. A method as claimed in any one of claims 27 to 31 , wherein the or each spacer substantially extends transversely over the inner layer from a lower portion of the one of the sides of the housing to a lower portion of the other of the sides of the housing.
33. A method of operating a kiln of the type hereinbefore defined for drying or heattreating a charge of lumber, the method comprising: repeatedly reversing both a direction air is fed between the first and intermediate layers and a direction of the drying airflow promoted within the drying chamber; wherein, the reversing of the direction air is fed between the first and intermediate layers causes the direction air is fed between the first and intermediate layers to switch between a first direction from the first side of the drying chamber to the second side of the drying chamber and a second direction from the second side of the drying chamber to the first side of the drying chamber, and the reversing of the direction of the drying airflow promoted within the drying chamber causes the direction of the drying airflow promoted within the drying chamber to switch between from the second side of the drying chamber through the charge of lumber to the first side of the drying chamber and from the first side of the drying chamber through the charge of lumber to the second side of the drying chamber.
34. A method as claimed in claim 33, wherein both the direction air is fed between the first and intermediate layers and the direction of the drying airflow promoted within the drying chamber are reversed at predetermined intervals.
35. A method as claimed in claim 34, wherein the predetermined intervals are substantially in the range of 15 minutes to several hours.
Description:
A kiln

Field of the Invention

This present invention relates to a kiln, a method of constructing a kiln and a method of operating a kiln for drying or heat-treating a material. More particularly the present invention relates to a kiln, a method of constructing a kiln and a method of operating a kiln for drying or heat-treating a material that uses solar radiation to provide part or all of the heat for drying or heat-treating the material.

While the present invention will be described hereinafter with reference to the preferred material of timber or lumber, it will be understood that the present invention may have broader application to drying other materials, such as fruit and vegetables, for example.

Background to the Invention

Cut or sawn "green" timber or lumber usually has a relatively high moisture or water content. Prior to practical application, green lumber is typically dried to a moisture content of less than 20%, depending on what the lumber is to be used for. Drying lumber inhibits shrinking or swelling of the lumber in use, improves the strength of the lumber, and significantly reduces the weight of the lumber making it both easier to work with and cheaper to transport.

While lumber may be dried in ambient air, typically drying kilns that provide drying environments in which the temperature, relative humidity and drying airflow are all able to be controlled are used to both accelerate the drying process and improve the quality of the dried lumber. The costs associated with the construction and operation of conventional lumber drying kilns, including the cost associated with providing heat energy for drying the lumber, usually contribute significantly to the cost of the dried lumber.

Summary of the Invention

The present applicant has developed a kiln that uses air heated by solar radiation for drying one or more stacks of timber or lumber (hereinafter referred to as a "charge of lumber"). More particularly, the kiln includes: a housing having a longitudinal wall extending between first and second end walls and providing opposite sides and a roof to define an enclosed chamber for drying a charge of lumber, the longitudinal wall being formed by first, second and intermediate spaced apart layers, the first layer being located inwardly of the second layer, the intermediate layer being located between the first and second layers, the arrangement being such that air between the first and intermediate layers can be heated by solar radiation passing through the intermediate and second layers, and air between the intermediate and second layers can act to thermally insulate the air between the first and intermediate layers; wherein, in operation, air drawn from a first side of the chamber adjacent one of the sides of the housing is fed between the first and intermediate layers to a second side of the chamber adjacent the other of the sides of the housing to enable solar heating of the air which is fed into the second side the chamber to be entrained within a drying airflow which circulates within the chamber by passage through the charge of lumber from the second to the first side.

Such a kiln will be hereinafter referred to as "a kiln of the type hereinbefore defined".

Preferably, the first layer is generally opaque and has a black or at least darkly coloured outwardly facing surface that acts to absorb solar radiation passing between the generally transparent second and intermediate layers. A first air inflation system may be used to maintain an insulating outer zone or barrier defined between the second and intermediate layers to effectively form an insulating static air cell, the outer zone enveloping an inner zone defined between the first and intermediate layers to inhibit the loss of heat from air passing through the inner zone to the external environment.

The first, intermediate and second layers may be formed from one or more suitable materials, such as plastic sheeting or cladding, for example. The first layer may be formed from thermally insulating plastic sheeting having a plurality of regularly distributed air-filled cells, like that sold under the trade mark "Bubble Wrap", and the intermediate and second layers may be formed from regular flat plastic sheeting, for example.

When drying lumber within a kiln, usually one or more drying schedules prescribing a progressive sequence of increasing operating temperatures and decreasing relative humidity levels within the chamber are followed. The prescribed changes to the operating temperature and relative humidity may be triggered to occur at predetermined times or when the moisture content of the lumber reaches predetermined levels, for example. The schedules may also include details of other kiln operating parameters and are advantageously tailored for different kilns, lumber qualities and/or types, and operating climates.

When drying a charge of lumber in a kiln of the type hereinbefore defined, the duration of the drying cycle has been found to be anywhere in the order of 3 to 20 days for a charge of soft wood, and anywhere in the order of 4 to 12 weeks for a charge of hard wood, for example. It will be understood that the prescribed drying cycle duration and operating conditions within the kiln may be dependent on a range of factors, including the characteristics of the charge, desired moisture content of the dried charge, the operating characteristics of the kiln and the climate in which the kiln operates.

Alternatively, a kiln of the type hereinbefore defined may be used to heat-treat a charge of lumber to kill insects and pathogens so as meet quarantine export regulations in many jurisdictions, for example. Heat-treating a charge of lumber for that purpose normally involves heating the charge at a predetermined

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temperature for a predetermined time, which may be as little as 8 hours, for example.

Advantageously, a kiln of the type hereinbefore defined includes a control unit or system having software for automatically monitoring and controlling the operation of the kiln when drying a charge of lumber. The control system may be located locally (or "on-site"), or it may be located and adapted to control operation of the kiln remotely. Alternatively, the operation of the kiln may be effected by an operator manually following a predetermined drying schedule, or by an operator in combination with a control unit or system.

The kiln may include a supplementary heating system, such as a gas or steam heating system, that is able to be selectively employed in addition to the solar heating when ambient conditions are such that solar heating is either inadequate or not available, such as at night, on excessively cold days and at times of dense cloud cover. Alternatively, heating systems incorporating heated water, electric coils or perhaps even heated oil, for example, may be used to provide supplementary heat.

The kiln may also include internal air circulation fans for promoting the drying airflow within the chamber, with the fans housed in a plenum wall suspended from an upper portion of the housing of the kiln above the charge. A baffle may extend from the plenum wall and over the top of the charge of lumber to create a division between either side of the plenum wall containing the air circulation fans. This arrangement creates a pressure differential between the sides of the chamber to cause the drying airflow within the chamber to pass through the charge of lumber below the baffle from the second side of the chamber to the first side of the chamber and then to return to the second side by passage through the circulation fans and plenum wall over the baffle and the charge of lumber.

The baffle may be formed from plastic sheeting hanging down from the plenum wall and lowered over the top of the charge of lumber. Alternatively, the baffle may be formed from other suitable materials, such as metal sheeting for example.

The kiln may be adapted for movement over a charge of lumber such that a charge of lumber to be dried is able to be stacked external of the kiln, and the kiln is able to moved into a drying position whereby the kiln encloses the stacked charge. The housing may include wheels or skids by which the housing may be mounted on parallel rails or tracks to provide for the movement of the housing over the charge, for example. Alternatively, the kiln may be fixedly mounted to the ground, for example, and trolleys or forklifts used to stack and unstack lumber in the kiln.

When drying lumber, if the drying airflow within the chamber were to only pass through the charge in the same direction during drying of the charge, the dried charge may exhibit excessive variation in moisture content, with a first side of the charge through which the drying airflow first passes drying quicker than a second side of the charge downstream of the first side. To expose the charge to more uniform drying conditions, the direction of the drying airflow within the kiln may be repeatedly reversed, such that the drying airflow is repeatedly switched between first passing through the first side of the charge and first passing through the second side of the charge.

It will be understood that the most effective exchange of heat to air being fed between the first and intermediate layers of the kiln during normal operation occurs when the coolest air from within the drying chamber is fed between the first and intermediate layers. When the fans within the chamber are reversed to reverse the direction of the drying airflow within the chamber to expose the charge to more uniform drying conditions however, if air is continued to be fed into between the first and second layers from the same side of the chamber, heated air that has not passed through the charge of lumber may be fed into between the first

and intermediate layers there by negating the heat exchange effect. It will be understood that this can lead to significant reductions in the operating efficiency of the kiln.

According to one aspect of the present invention, there is provided a kiln of the type hereinbefore defined for drying or heat-treating a charge of lumber, the kiln further comprising: air feed means for feeding air between the first and intermediate layers to enable solar heating of the air, the air feed means being selectively operable to feed air between the first and intermediate layers in a first direction from the first side of the drying chamber to the second side of the drying chamber or to feed air between the first and intermediate layers in a second direction from the second side of the drying chamber to the first side of the drying chamber; and means for promoting a drying airflow within the drying chamber, the means for promoting a drying airflow being selectively operable to promote a drying airflow from the second side of the drying chamber through the charge of lumber to the first side of the drying, chamber when the air feed means is acting in the first direction or to promote a drying airflow from the first side of the drying chamber through the charge of lumber to the second side of the drying chamber when the air feed means is acting in the second direction.

According to a further aspect of the present invention, there is provided a method of operating a kiln of the type hereinbefore defined for drying or heat-treating a charge of lumber, the method comprising: repeatedly reversing both a direction air is fed between the first and intermediate layers and a direction of the drying airflow promoted within the drying chamber; wherein, the reversing of the direction air is fed between the first and intermediate layers causes the direction air is fed between the first and intermediate layers to switch between a first direction from the first side of the drying chamber to the

second side of the drying chamber and a second direction from the second side of the drying chamber to the first side of the drying chamber, and the reversing of the direction of the drying airflow promoted within the drying chamber causes the direction of the drying airflow promoted within the drying chamber to switch between from the second side of the drying chamber through the charge of lumber to the first side of the drying chamber and from the first side of the drying chamber through the charge of lumber to the second side of the drying chamber.

By periodically reversing at the same time both the direction of the drying airflow and the direction air is fed between the first and second layers during a drying cycle, it has been found to be possible to achieve a more uniform moisture content throughout the drying charge while maintaining the normal operating efficiency of the kiln.

Further, larger kilns, due to economies of scale, can normally be operated more cost effectively than smaller kilns. A problem with larger kilns though, particularly when they are used in excessively windy climates, is that they are generally more susceptible wind-loading which, if sufficiently strong, can permanently damage the kiln. This problem of wind-loading often constrains the size and capacity of kilns built in practice.

One proposal for addressing this problem is to use pre-fabricated rigid trusses to strengthen the housing of a kiln, particularly the housing of a larger kiln. Such trusses are able to be designed and pre-fabricated to provide sufficient structural integrity to the housing for the housing to be able withstand considerable wind- loading in practice. However, the costs and labour associated with the initial construction, installation and ongoing maintenance of such trusses often make their use prohibitive to lumber drying operators.

According to a further aspect of the present invention, there is provided a kiln of the type hereinbefore defined for drying or heat-treating a charge of lumber,

wherein the housing of the kiln further includes an internal frame for supporting the longitudinal wall, the frame being tensioned by one or more cables associated with the frame, the or each cable stiffening the frame by deflecting the frame outwardly.

By using one or more cables to tension and stiffen the frame, the frame is advantageously able to be constructed from lightweight materials that are relatively easy to handle, but which would otherwise have insufficient stability.

Further, in the instance of a kiln in which the housing is mounted on parallel rails to provide for the movement of the housing over an adjacent charge, wind-loading has been found to be sufficient on occasions to lift away and displace the kiln from the rails. Smaller kilns, if they are not wrecked by such displacement, generally may be straightforwardly lifted back on to the rails. With displaced larger kilns however, lifting them back onto the rails may be either impractical or not possible.

According to a further aspect of the present invention, there is provided a kiln of the type hereinbefore defined for drying or heat-treating a charge of lumber, wherein the housing of the kiln is mounted for movement along parallel spaced apart rails so that the housing can be moved over an adjacent charge, each rail being adapted to cooperate with the housing to prevent the housing lifting away from the rails as a result of wind-loading.

Further, when lumber dries below about 30% moisture content, it normally shrinks. Shrinking generally takes place progressively from the outwardly facing surface(s) of each piece of lumber inwardly, and can result in drying stresses developing within the lumber. In the instance of hardwoods, these stresses can causes cells to collapse. Collapse can manifest in severe and non-uniform malformation of the cross-section of each piece of drying lumber to the extent that it is often rendered unusable in that form.

One method of relieving drying stresses building up in drying lumber for the purposes of collapse recovery is to periodically apply steam to the drying charge of lumber (commonly known as "steam reconditioning"), in which steam that may have a temperature in excess of 90 degrees Celsius, for example, may be periodically applied to the drying charge. Steam reconditioning advantageously re-constitutes the original shape and form of the fibres in the lumber so as to recover the original, usually rectangular, shape of each piece of lumber. However, many of the parts of the kiln, including motors to drive pumps associated with airflow within the kiln, or the wall of the housing which may be formed from plastic sheeting, for example, may not be able to withstand the excessively high temperatures associated with steam reconditioning.

According to a further aspect of the present invention, there is provided a kiln of the type hereinbefore defined for drying or heat-treating a charge of lumber, the kiln further comprising: a baffle located within the drying chamber above the charge of lumber, the baffle forming part of the means for promoting a drying airflow within the drying chamber from the second side of the drying chamber through the charge of lumber to the first side of the drying chamber; and a plurality of removable side panels that are positioned adjacent sides of the charge within the kiln; the baffle and the panels defining an internal steam chamber about the charge within the kiln.

The internal steam chamber defined by the baffle and the panels advantageously is able to be used to temporarily thermally shield parts of the kiln outside of the steam chamber that would be otherwise exposed to the high temperature steam during steam reconditioning within the kiln. The internal steam chamber advantageously facilitates the regular steam reconditioning of a drying charge of lumber within the kiln without the need to move the charge to and from a separate steam reconditioning chamber external of the kiln.

Further, when constructing a kiln of the type hereinbefore defined, in practice it has been found to be difficult to establish and maintain an insulating space between the intermediate and second layers when applying the second layer over the intermediate layer during manufacture of the kiln, or in certain circumstances to establish and maintain a space between the first and the intermediate layers. This problem has been found to be particularly prevalent when the layers are formed from a relatively flexible material like plastic sheeting.

According to a still further aspect of the present invention, there is provided a method of applying a layer (the "outer layer") of the longitudinal wall over a previously applied layer (the "inner layer") of the longitudinal wall of a kiln of the type hereinbefore defined for drying or heat-treating a charge of lumber, the method comprising: applying one or more inflatable spacers against an outwardly facing surface of the inner layer; applying the outer layer over the inner layer by drawing the outer layer over the or each spacer and the inner layer; and securing the applied outer layer relative to the inner layer; whereby, the or each spacer assists in establishing and/or maintaining the inner and outer layers in a spaced apart arrangement during application of the outer layer.

Brief Description of the Drawings The present invention will be now described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a kiln mounted on rails;

Figure 2 is an enlarged cross-section of detail A of Figure 1 showing the spaced apart layers of the longitudinal wall of the kiln;

Figure 3 is a schematic view of a cross-section of the kiln of Figure 1 showing the normal circulation of air within the kiln during the drying of a charge of lumber;

Figure 4 is a schematic view of the air feed unit of the kiln of Figure 1 having first pumping and distribution units;

Figure 5 is a schematic cross-section of the kiln of Figure 1 adapted for the repeated reversing of the direction of the circulation of air within the kiln during the drying of a charge of lumber;

Figure 6 is a schematic cross-section of the kiln of Figure 5 showing the circulation of the air within the kiln in a first direction;

Figure 7 is a schematic cross-section of the kiln of Figure 5 showing the circulation of air within the kiln in an alternate second direction;

Figure 8 is a schematic cross-section of an internal frame for supporting the kiln shown in Figure 1 showing the use of cables to stiffen the frame; Figure 9 is a cross-section of one of the wheels of the kiln of Figure 1 shown mounted on a rail, the rail being adapted to cooperate with the housing of the kiln to prevent the housing lifting or moving away from the rail;

Figure 10 is a section view of the wheel and rail of Figure 10 taken along the line B-B; Figure 11 is a schematic cross-section of the kiln of Figure 1 showing a temporary internal steam chamber that may be constructed within the kiln;

Figure 12 is a side view of the kiln of Figure 1 showing inflatable spacers applied across an outwardly facing surface of the intermediate layer to assist in establishing and/or maintaining an insulating space during the application of the second layer when constructing the kiln; and

Figure 13 is a cross-section of the kiln of Figure 13 showing the second layer applied across the inflatable spacers and the intermediate layer.

Detailed Description It will be understood that for the purposes of clarity, not all of the described parts have been shown in all of the drawings.

A kiln 10 developed by the applicant for drying or heat-treating a charge of lumber 12 using air heated by solar radiation (generally indicated by the reference numeral 14), which is an example of a kiln 10 of the type hereinbefore defined, and which is sometimes referred to as a "slip kiln", is shown in Figures 1 to 4. The kiln 10 includes a housing 16 having a longitudinal wall 18 extending between first and second end walls 20 (only the first or front end wall 20 being able to be seen in Figure 1) and providing opposite sides 24, 26 and a roof 28 to define an enclosed drying chamber 30 within which the charge 12 is able to de dried.

The housing 16 of the kiln 10 is mounted for movement along parallel spaced apart rails 32 so that the housing 16 can be moved over an adjacent charge 12. A base of the housing 16 includes a plurality of wheels 34 (shown in detail in Figures

9 and 10) that are adapted to roll along the rails 32 so that the entire housing 16 can be moved along the rails 32 in either of the directions indicated by the arrows

36. The housing 16 is open at an underside and the end walls 20 may to be opened or temporarily removed so that the housing 16 can be moved along the rails 32 from a drying position over a first dried charge 12 to a drying position over an adjacent second charge 12 to be dried that may be stacked externally of the kiln 10 while the first charge 12 is drying. The end walls 20 may then be closed or replaced to reform the enclosed drying chamber 30. Moving the housing 16 from over one charge 12 to over an adjacent charge 12 avoids the need to build the kiln

10 large enough to accommodate a forklift or trolley to stack and unstack lumber within the drying chamber 30, and also minimises downtime of the kiln 10 between drying operations. A winch (not shown), for example, particularly in the instance of larger kilns 10, may be used to move the housing 16 along the rails 32.

Alternatively, instead of a plurality of wheels 34, the base of the housing 16 may include a plurality of skids (not shown) by which the housing 16 is mounted for movement along the rails 32, with the skids adapted to slide along the rails 32, for example. The skids may be formed from a high density plastic, for example.

Further alternatively, it will be understood that the housing 16 may not be mounted for movement along rails 32 and may instead be fixedly mounted to the ground, for example, such that the charge 12 would need to be stacked and unstacked within the drying chamber 30.

With reference to Figure 2, the longitudinal wall 18 is formed by spaced apart first, second and intermediate layers 38, 40, 42 that may be applied over and supported by an internal frame 136 (an example of which is shown in Figure 8) of the housing 16. The first layer 38 is located inwardly of the second layer 42, and the intermediate layer 40 is located between the first and second layers 38, 42. Air is able to be heated between the first and intermediate layers 38, 40 by solar radiation 14 passing through the intermediate and second layers 40, 42, while air in the space between the intermediate and second layers 40, 42 acts to thermally insulate the air between the first and intermediate layers 38, 40.

The first, second and intermediate layers 38, 40, 42 are all formed from regular sheeting, although it will be understood that they may be formed from a range of other suitable materials. For example, the first layer 38 may alternatively be formed from thermally insulating plastic sheeting having a plurality of regularly distributed air-filled cells. The first layer 38 is generally opaque, and has a black outwardly facing surface 44 to promote absorption of solar radiation 14 passing through the intermediate and second layers 40, 42, and preferably a white inwardly facing surface 46 to reflect any light within the drying chamber 30. The intermediate and second layers 40, 42 are transparent.

A first air inflation system (not shown) may be used to maintain an insulating outer zone or barrier 48 defined between the intermediate and second layers 40, 42 to effectively form an insulating static air cell, the first air inflation system pumping air from the external environment into the outer zone 48. The insulating outer zone 48 envelopes an inner zone 50 defined between the first and intermediate layers

38, 40 to inhibit the loss of heat from air passing through the inner zone 50 to the external environment.

With reference to Figure 3, the kiln 10 includes air feed means in the form of an air feed system 52 (shown schematically in Figure 4) for feeding air between the first and intermediate layers 38, 40. The air feed system 52 includes a selectively operable first pumping unit 54 and selectively operable first air distribution means in the form a first distribution unit 56.

The first pumping unit 54 is located adjacent a first side 58 of the chamber 30, and is selectively operable to feed air under pressure between the first and intermediate layers 38, 40 (as indicated by the arrow 60) in a first direction (as indicated by the arrows 62) from the first side 58 of the chamber 30 to a second side 64 of the chamber 30 to enable solar heating of the air. The first distribution unit 56 is located adjacent the second side 64 of the chamber 30, and is selectively operable to feed the air heated between the first and intermediate layers 38, 40 into the second side 64 of the drying chamber 30 (as indicated by the arrow 66).

An example of a pumping unit 54 shown schematically in Figure 4 includes an air pump 68 having associated inlet and outlet manifolds 70, 72. The inlet manifold 70 includes a chamber inlet 74 through which air is able to be selectively drawn from the first side 58 of the chamber 30 into the pump 68 and an external inlet 76 through which air is able to be selectively drawn from the external environment into the pump 68. The outlet manifold 72 includes a series of outlets 78 through which the pump 68 is able to selectively feed under pressure the air drawn in through the inlets 72, 74 between the first and intermediate layers 38, 40.

In one form of the pump 68, for example, the inlet manifold 70 may have a single larger inlet in connection with a section of tubular duct, with a first end of the duct extending into the chamber 30 and a second end of the duct extending out to the

external environment. The chamber inlet 74 (through which air is drawn from the first side 58 of the chamber 30) and the external inlet 76 (through which air is drawn from the external environment) may be in the form of openings at the first and second ends of the duct, respectively, with flaps associated with each of the openings able to be selectively opened and shut as required to control whether air is drawn into the pump 68 from within the chamber 30 or from the external environment.

An example of a distribution unit 56 shown schematically in Figure 4 includes an air pump 80 having associated inlet and outlet manifolds 82, 84. The inlet manifold 82 includes a series of inlets 86 through which heated air is able to be selectively drawn from between the first and intermediate layers 38, 40 into the pump 80. The outlet manifold 84 includes a chamber outlet 88 through which the pump 80 is able to selectively feed the heated air drawn in through the inlets 86 under pressure into the second side 64 of the chamber 30 during normal operation, and an external outlet 90 through which the pump 80 is able to selectively feed the heated air drawn in through the inlets 86 to the external environment under certain circumstances, such as when the temperature of the air within the kiln 10 is too hot as and it would be undesirable to feed further solar heated into the chamber 30. Alternatively, the distribution unit 56 may not include a pump, and instead operate to feed heated air through the outlets 88, 90 by utilising the pressure generated by the pumping unit 54, with actuated damper motors determining through which outlet 88, 90 the air is fed.

It will be understood that the number and configuration of the pumping and distribution units 54, 56 of the kiln 10, and similarly the number and configuration of the associated inlet and outlet manifolds and inlets and outlets, is not limited to the described number or form, and may be scaled or adapted as the size of the kiln 10 requires. For example, the distribution unit 56 may include multiple chamber outlets 88 for feeding the air heated between the first and intermediate layers 38, 40 into the chamber 30. While only one chamber outlet 88 is shown

schematically in Figure 4, it will be understood that the outlet manifold 84 preferably has multiple chamber outlets 88 for discharging the heated air back into the drying chamber 30 in a well-dispersed manner so as to avoid the formation of a hot spot which can lead to non-uniform drying. For example, the outlet manifold 84 may be provided by a plastic duct that runs the full length of the kiln 10, with multiple chamber outlets 88 formed along the length of the duct.

The kiln 10 further includes means for promoting a drying airflow within the chamber 30 in a first direction (as indicated by the arrows 92) from the second side 64 through the charge 12 to the first side in the form of internal air circulation fans 94 housed in a plenum wall 96 suspended from an upper portion of the housing 16 of the kiln 10 above the charge 12. A baffle 98 extends from the plenum wall 96 and over a top of the charge 12 to create a division between either side of the plenum wall 96 housing the air circulation fans 94. The baffle 98 may be formed from plastic sheeting hanging down from the plenum wall 96 and lowered over the top of the charge 12. Alternatively, the baffle 98 may be formed from other suitable materials, such as metal sheeting, for example.

The fans 94 are able to propel air within the chamber 30 in the upper region between the baffle 98 and the roof 28 in a direction from the first side 58 of the chamber 30 to the second side 64. This induces a negative pressure within the chamber 30 at the first side 58 and similarly a positive pressure at the second side

64. This pressure differential promotes a drying airflow (as indicated by the arrows

92) through the charge 12 below the baffle 98 from the second side 64 to the first side 58. The air subsequently returns to the second side by passage between the baffle 98 and the roof 28.

The kiln 10 further includes first sensors 100 for detecting the temperature and relative humidity of the drying airflow within the chamber 30. The sensors 100 are located at the second side 64 of the chamber 30 adjacent the first distribution unit

56 so as to detect the temperature and relative humidity of the drying airflow

upstream of the charge 12.

The kiln 10 further includes a controller 102 having software for automatically monitoring and controlling the operation of the kiln 10, including the sensors 100, the pumping and distribution units 54, 56 and the fans 94, during a drying cycle. The controller 102 is adapted for wired communication, as generally indicated by the communication cable 104 schematically extending between the controller 102 and the other parts of the kiln 10 in Figure 3, and is located near the housing 16 such the controller 102 controls the operation of the kiln 10 generally on-site. Alternatively, the controller 102 may be located and adapted to control the operation of the kiln 10 remotely, for example. Further, to facilitate the control of the operation of the kiln 10 from a remote location, the controller 102 may alternatively be adapted for wireless communication with the sensors 100, the pumping and distribution units 54, 56 and fans 94, for example.

The circulation of air within the kiln 10 when the kiln 10 is in normal operation to dry a charge is shown schematically in Figure 3. Air is drawn from the first side 58 of the chamber 30 through the chamber inlet 74 of the pump 68 of the pumping unit 54 (as indicated by the arrow 106), and fed by the pump 68 under pressure through the outlets 78 into the space between the first and intermediate layers 38, 40 (as indicated by the arrow 60). As the air passes between the first and intermediate layers 38, 40 from the first side 58 of the chamber 30 to the second side 64 (as indicated by the arrows 62), the air is heated by solar radiation 14 passing through the intermediate and second layers 40, 42.

The heated air is drawn in from between the first and intermediate layers 38, 40 through the inlets 86 of the distribution unit 56 (as indicated by the arrow 108), and fed under pressure through the chamber outlet 88 into the second side 64 of the chamber 30 (as indicated by the arrow 66). The heated air fed into the second side 64 of the chamber 30 is entrained within the drying airflow (as indicated by arrows 92) which circulates from the second side 64 of the chamber 30 through

the charge 12 to the first side to thereby dry the charge 12.

During the drying operation, the insulating outer zone 48 defined between the intermediate and second layers 40, 42 acts to thermally insulate the air being heated as it passes between the first and intermediate layers 38, 40. The insulating outer zone 48 also assists in the removal of moisture or water content that is evaporated from the charge 12 by the drying airflow air within the chamber 30. Cooler air in the outer zone 48 promotes the condensation of moisture contained in the warmer air from within the chamber 30 as it passes between the first and intermediate layers 38, 40 on an inwardly facing surface 110 (shown in Figure 2) of the intermediate layer 40. The condensed water falls down the surface 110 between the first and intermediate layers 38, 40 to the base of the housing 16 under the action of gravity where it is able to be collected and removed from the kiln 10.

In practice, if the insulating outer zone 48 between the intermediate and second layers 40, 42 is either not satisfactorily established during manufacture and/or effectively maintained during the drying of a charge 12, instead of the condensation occurring on the surface 110, the condensation of air within the chamber may occur instead on the inwardly facing surface 46 of the first layer 38, and the condensed moisture may fall down the surface 46 and back onto the ground or floor inside the chamber 30. This can detract significantly from the operational efficiency of the kiln 10 with additional heat energy required to again evaporate this moisture within the kiln 10. Further, evaporated moisture content within the kiln 10 will need to be otherwise removed from the chamber 30, such as by venting air from within the chamber 30 to the external environment, for example, which generally results in considerable drying heat energy being lost from within the chamber 30.

During the drying of the charge 12, the temperature and relative humidity of the drying airflow upstream of the charge 12 are closely monitored by the first sensors

100. Normally, the temperature may be maintained somewhere within the range of 25 to 60 degrees Celsius and the relative humidity somewhere within the range of 40 to 90%, for example. It will be appreciated that these ranges have been provided for example only, and as such may vary between different kiln 10 configurations, and that they may be adapted to suit particular requirements and climates.

If the temperature of the drying airflow within the chamber 30 is too hot, the charge 12 may dry too quickly resulting in excessive drying stresses developing in the charge of lumber 12. Accordingly, to reduce the temperature of the drying airflow should it rise above a first predetermined maximum operating temperature, air heated by solar radiation 14 between the layers 38, 40, instead of being fed into the chamber 30, may be discharged by the distribution unit 56 through the external outlet 90 to the external environment (as indicated by arrow 112). Purging the air heated between the layers 38, 40 substantially allows the relative humidity within the chamber 30 to be maintained at normal operating levels while the temperature of the drying airflow is reduced. Replenishing cooler air that reduces the operating temperature within the chamber is able to be drawn in through the external inlet 76 of the pump 68 of the pumping unit 54 (as indicated by the arrow 114) as required.

The kiln 10 may also include vents (not shown) to complement the function of external outlet 90 of the distribution unit 56, the vents being able to vent air directly from the chamber 30 if the temperature of the drying airflow exceeds a second predetermined maximum operating temperature that may be equal to or higher than the first predetermined maximum operating temperature. Advantageously, an operator may be able manually operate the vents to discharge air from within the chamber 30 when the temperature of the drying airflow is below the second predetermined maximum operating temperature. This allows the operator to pre¬ emptively dump heat from within the chamber 30 as may be desired during a prolonged period of excessively hot weather.

In the instance of excessively cold weather, prolonged periods of low operating temperatures within the chamber 30 have been found to cause casehardening of the charge 12 wherein moisture differentials between the outer "case" and the "core" of the lumber can adversely affect the quality of the dried charge 12. To address these periods of low operating temperatures, the kiln 10 may also include a supplementary heating system (not shown) that are able to be selectively employed to complement the solar heating when solar activity is such that solar heating is either inadequate or not available. Such a supplementary heating system may be employed on excessively cold days and/or at times of dense cloud cover, or even to maintain the air within the chamber 30 above a predetermined minimum temperature at night, for example. The supplementary heating system may include steam heating whereby heated steam is fed into the chamber 30, or gas or mains electricity powered heating whereby heated air is fed into the chamber 30. Alternatively, the supplementary heating system may feed air heated by burning wood residue into the chamber 30.

The relative humidity of the drying airflow within the chamber 30 may be monitored and controlled similarly to the temperature.

According to one development to the example of a kiln 10 of the type hereinbefore defined that is shown in Figures 1 to 4, the kiln 10 may be adapted to provide for the repeated reversing of the direction of the circulation of the air within the kiln 10 when drying a charge 12 so as to avoid the excessive variation in the moisture content of the lumber of the dried charge 12 that can occur if the circulation of air within the kiln 10 is always in the same direction. This may be achieved by repeatedly reversing both the direction air is fed between the first and intermediate layers 38, 40 and the direction of the drying airflow within the chamber 30 during operation of the kiln 10.

With reference to Figure 5, to facilitate the repeated reversing of the direction air is fed between the first and intermediate layers 38, 40, the air feed system 52 of the

kiln 10 further includes a selectively operable second pumping unit 116 and a selectively operable second distribution means in the form a second distribution unit 118. The second pumping and distribution units 116, 118 have substantially the same configuration as the first pumping and distributions units 54, 56, examples of which are shown schematically as part of the air feed system 52 shown in Figure 4.

A first circulation of air within the kiln 10 in a first direction that is achieved by the operation the first pumping and distribution units 54, 56 is shown schematically in Figure 6. For clarity, the second pumping and distribution units 116, 118 of the air feed system 52 of the kiln 10 shown in Figures 5 to 7 are not shown in Figure 6. It will be understood that the circulation in the first direction shown in Figure 6 is the same as the circulation of the example of a kiln 10 of the type hereinbefore defined having only first pumping and distribution units 54, 56 that is shown in Figure 3.

Circulation of air within the kiln 10 in a second or reverse direction that is achieved by the operation the second pumping and distribution units 116, 118 is shown schematically in Figure 7. Again, for clarity, the first pumping and distribution units 54, 56 of the air feed system 52 of the kiln 10 shown in Figures 5 to 7 are not shown in Figure 7. With reference to both Figures 5 and 7, the second pumping unit 116 is located adjacent the second side of the chamber 30, and is selectively operable to draw air in from the second side 64 (as indicated by the arrow 120) and to feed the air under pressure between the first and intermediate layers 38, 40 (as indicated by the arrow 122) in a second direction (as indicated by the arrows 124) from the second side 64 to the first side 58 to enable solar heating of the air. The second distribution unit 118 is located adjacent the first side 58 of the chamber 30, and is selectively operable to draw heated air in from between the first and intermediate layers 38, 40 (as indicated by the arrow 126) and to feed the heated air into the first side 58 of the drying chamber 30 (as indicated by the arrow 128).

To facilitate the repeated reversing of the direction the drying airflow within the chamber 30, the internal air circulation fans 94 are selectively operable to promote a drying airflow in the first direction from the second side 64 through the charge 12 to the first side 58 (as indicated by arrows 92 in Figure 6) when the air feed unit is acting in the first direction (as indicated by the arrows 62 in Figure 6), or to promote a drying airflow in an alternate second direction from the first side 58 through the charge 12 to the second side 64 (as indicated by arrows 130 in Figure 7) when the air feed means is acting in the second direction (as indicated by the arrows 124 in Figure 7).

The repeated reversing of the circulation of air within the kiln 10 between the first direction (shown Figure 6) and the second direction (shown in Figure 7) that may be effected by reversing at the same time both the direction of air passing between the first and intermediate layers 38, 40 (as indicated by arrows 62 and 124 in Figures 6 and 7, respectively) and the direction of the drying airflow within the chamber 30 (as indicated by arrows 92 and 130 in Figures 6 and 7, respectively) advantageously promotes a uniform moisture content throughout the lumber of a drying charge 12 without detracting from the overall efficiency of the kiln 10. As discussed above, if only the direction of the drying airflow is reversed, it will be understood that the coolest and wettest air within the chamber 30 may be passed through the charge 12 while the air heated by solar radiation 14 between the first and intermediate layers 38, 40 may be entrained in the drying airflow downstream of the charge 12. This can result in the heated air circulating between the baffle 98 and the roof 28 and subsequently being fed under pressure between the first and intermediate layers 38, 40 without first having substantially passed through the charge 12.

To avoid the temperature and relative humidity of the drying airflow being detected downstream of the charge 12 when the direction of the circulation of air within the kiln 10 is reversed, the kiln 10 further includes second sensors 132 located at the first side 58 of the chamber 30 adjacent the second distribution unit 118. The first

sensors 100 can be used to detect the temperature and the relative humidity upstream of the charge 12 when air within the kiln 10 circulates in the first direction (shown in Figure 6), and the second sensors 132 can be used to detect the temperature and the relative humidity upstream of the charge 12 when the air within the kiln 10 circulates in the second direction (shown in Figure 7).

Both the direction air is fed between the first and intermediate layers 38, 40 (as indicated by arrows 62 and 124) and the direction of the drying airflow promoted within the drying chamber 30 (as indicated by arrows 92 and 130) may be reversed at predetermined intervals that may be in the range of 15 minutes to several hours, for example. The controller 102 may include a timer 134 (shown in Figure 5) that is operable to cause the reverse at predetermined times and/or periodically, for example. It will be understood that alternatively the reversal of the directions may be controlled by other means. For example, the controller 102 may determine the reversal of the directions based on the difference in the relative humidity across the charge 12 as determined by the sensors 100, 132 located at either side 58, 64 of the drying chamber 30.

With reference to Figure 8, according to a further development to the example of a kiln 10 of the type hereinbefore defined that is shown in Figures 1 to 4, the housing

16 of the kiln 10 may include an internal frame 136 (shown in cross-section) for supporting the longitudinal wall 18 that is tensioned by tensioning cables 138. The tensioning of the cables 138 stiffens the frame 136 by deflecting the frame 136 outwardly (as indicated by the arrows 140). Such a frame 136 stiffening system is particularly, but not exclusively, applicable to enhancing the structural integrity of larger kilns 10 that may be subject to excessive wind loading. This allows the supporting internal frame 136 of a larger kiln 10 to be constructed from resiliently flexible lightweight materials that inherently have some resiliency, but would normally lack the sufficient stability to support the kiln 10.

The internal frame 136 may include resiliently flexible, generally arcuate structures

142, one of which is shown in cross-section in Figure 8, that are spaced longitudinally along the wall 18 to support the layers 38, 40, 42 (not shown in Figure 8) away from the charge 12. Each structure includes a plurality of supporting struts 144. Two cables 138 are attached to an upper portion 146 of each structure 142 and pass downwardly either side of the structure 142 through pulleys 148, 150 attached to the structure 142 that guide the cables 138. At least some of the pulleys 150 are supported by the struts 144 to be generally located inwardly relative to the arcuate outer perimeter of the structure 142 so that the tensioning of cables urges the pulleys 150 (and associated struts 144) outwardly (as indicated by the arrows 140) to thereby tension and stiffen the frame 136.

The cables 138 may be mono-filaments of wire, mono-filaments of plastic, multi- strand cables of wires or multi-strand cables of plastics, or any suitable equivalent, for example.

The cables 138 may be tensioned by tensioning devices in the form of cooperating ratchets and pinions 152 disposed adjacent the base portions of the housing 16, although it will be understood that any suitable tensioning devices may be used. Advantageously, the ratchets and pinions 152 may be anchored to the ground to thereby fasten or anchor the cables 138 and the kiln 10 relative to the ground.

When constructing the kiln 10, the cables 138 may initially be slack to facilitate the locating and erection frame 136. Once the frame 136 is in location, the cables 138 may be tensioned to deflect the frame 136 outwardly to stiffen the frame 136.

When the kiln 10 is to be moved along rails 32 (not shown in Figure 8) to a drying position over an adjacent charge 12, the cables 138 are able to be loosened and released from the ratchets and pinions 152. After the kiln 10 has been moved into a drying position over the adjacent charge 12, the cables 138 may be re-tensioned using the same relocated ratchets and pinions 152, or alternatively different ratchets and pinions 152, for example, to re-stiffen the frame 136.

With reference to Figures 9 and 10, according to a further development to the example of a kiln 10 of the type hereinbefore defined that is shown in Figures 1 to 4, when the housing 16 of the kiln 10 is mounted for movement along parallel spaced apart rails 32 so that the housing 16 can be moved over an adjacent charge 12, each rail 32 is adapted to cooperate with the housing 16 to prevent the housing 16 lifting or moving away from the rails 32 in response to excessive wind- loading.

Figures 9 and 10 show one of the wheels 34 of the housing 16 of the kiln 10, in cross-section and side-on respectively, mounted in a corresponding one of the rails 32 that the wheel 34 is adapted to roll along. Each wheel 34 is mounted by an axle 154 located in a recess 156 of a downwardly extending leg 158 of the housing 16 and includes a circumferential recess 160 for engaging a correspondingly shaped axially extending guide 162 associated with the rail 32. The guide 162 runs the length of the rail 32 so as to locate the wheel 34 relative to the rail 32. A housing flange 164 extends transversely from each leg 158. While only one housing flange 164 extending from one side of the leg 158 is shown, it will be understood that two opposed housing flanges 164 extending from opposed sides of the leg 158 may be provided.

Each rail 32 includes a channel portion 166 for receiving the wheels 34 and two rail flanges in the form of opposed plates 168 extending transversely partially across the top of the channel portion 166. The axially extending guide 162 is formed along a base of the channel portion 166. The channel portion 166 and the plates 168 may be formed from steel, for example. In one practical form, the channel portions 166 are located or embedded in a groove formed in a concrete foundation (generally indicated by the reference numeral 170) and securely anchored to the concrete 170 using bolts 172. The plates 168 may then be securely anchored to the concrete 170 using bolts 172 so that they extend transversely partially across the top of the channel portion 166 to overly and

maintain the housing flanges 164 captive. As such, the plates 168 anchor the housing 16 to the rails 32, and to thereby the ground, so as to prevent the kiln 10 being blown off the rails 32 in heavy wind.

It will be understood that various other structures of the rails 32 that cooperate with the housing 16 to prevent the housing 16 lifting away from the rails 32 will similarly fall within the scope of the present invention.

With reference to Figure 11 , according to a further development to the example of a kiln 10 of the type hereinbefore defined that is shown in Figures 1 to 4, the kiln 10 may include a plurality of removable side panels 174 that are positioned adjacent sides of the charge 12 within the kiln 10, which in combination with the baffle 98 are able to form an internal steam chamber 176 about the charge 12 to facilitate the regular "in-kiln" (that is, within the drying chamber 30 of the kiln 10) steam reconditioning of the charge 12. Advantageously, the steam chamber 176 may be temporarily assembled and disassembled within the drying chamber 30, steam applied inside the steam chamber 176 to relieve drying stresses that may build-up in the charge 12 being dried in the chamber 30, and the steam chamber 176 subsequently disassembled. During steam reconditioning, the steam chamber 176 acts to shield and protect other parts of the kiln 10 outside the steam chamber 176, such as the plastic sheeting from which the layers 38, 40, 42 of the longitudinal wall 18 may be formed as well as other parts of the kiln 10 external the steam chamber 176, from the steam that may be in excess of 90 degrees Celsius, for example.

The removable side panels 174 are adapted be attached to the baffle 98 so as to hang down each side of the charge 12. While only panels 174 hanging down the sides of the charge 12 are shown in cross-section in Figure 11 , it will be understood that the panels 174 will also be attached to the baffle 98 to hang down the front and rear sides of the charge 12 (when viewed front-on in Figure 11) to form a generally enclosed steam chamber 176.

While the baffle 98 may be a unitary part, it will be understood alternatively the baffle 98 may be defined by several baffle panels 178 extending from the plenum wall 96, for example, as shown in Figure 11. The baffle panels 178 and the removable side panels 174 may be formed from any suitable material. The baffle panels 178 and the removable side panels 174 may be formed metal sheeting, such as aluminium sheeting for example. Alternatively, the baffle panels 178 and removable side panels 174 may be formed from a composite of materials, including an insulating layer, such as polystyrene, for example.

An upper end of each removable panel 174 includes an engaging formation, such as a lip portion formed along an upper edge 180 of the removable panel 174, for example, for engaging and disengaging the baffle panels 178 so that the steam chamber 176 may be assembled and disassembled within the kiln 10. The lip portions are able to hook over peripheral edges 182 of the baffle panels 178 to provide for the expeditious assembly and disassembly of the steam chamber 176 about the charge 12 within the drying chamber 30 of the kiln 10. Alternatively, clips may be used to temporarily attach the removable side panels 174 to the baffle panels 178, for example.

Guides 184 extending from the wall 18 or an associated internal frame (not shown) may be used to support the baffle panels 178, or to temporarily support the removable side panels 174.

In an alternative form, the removable side panels 174 may be defined by walls mounted on wheels, for example. The walls may be selectively rolled in and out of the kiln 10 and positioned adjacent the sides of the charge 12 to form in combination with the baffle 98 the temporary steam chamber 176, for example.

Advantageously, the temporary in-kiln internal steam chamber 176 facilitates regular steam reconditioning of the charge 12 without the requirement to either

form the kiln 10 large enough to be able to move a separately formed steam chamber into the drying chamber 30 of the kiln 10 and over the charge 12, or the requirement to transfer the charge 12 to a separate steam chamber 176 external of the kiln 10 each time steam reconditioning is desired.

In practice, it is expected that there will be at least some transmission of the heat from within the steam chamber 176 to a region 186 of the drying chamber 30 external of the steam chamber 176 during steam reconditioning of the charge 12. To prevent any heat that leaks or escapes from the steam chamber 176 damaging parts of the kiln 10 outside the steam chamber 176, the controller 102 and associated sensors within the kiln 10, such as the sensor 100, may be used to maintain the temperature of the region 186 at or below a predetermined maximum safe kiln 10 temperature during steam reconditioning that is lower than the temperature inside the steam chamber 30. For example, the temperature of the region 186 may be maintained at or below 60 degrees Celsius, for example. When the temperature of air in the region 186 exceeds the maximum safe kiln temperature, the controller 102 may operate to release some of the air from the region 186 to the external environment to lower the temperature of the region 186. Air may be released from the region 186 directly through vents (not shown), for example.

With reference to Figures 12 and 13, according to a further development to the example of a kiln 10 of the type hereinbefore defined that is shown in Figures 1 to 4, a method of applying one of the layers 40, 42 of the longitudinal wall 18 over a previously applied one of the layers 38, 40 when constructing the kiln 2 includes the use of one or more inflatable spacers 192 to assist in establishing and/or maintaining a space between these layers 38, 40, 42 when constructing the kiln 10. One form of the method will be described below with reference to a preferred application of the method of applying the second layer 42, that may be of plastic sheeting for example, over the previously applied intermediate (or inner) layer 40. It will be understood however, that in certain circumstances the method may have

application to applying the intermediate layer 40 over the previously applied first layer 38.

The inflatable spacers 192 are applied transversely across an outwardly facing surface of the previously applied intermediate layer 40 of the longitudinal wall 18 such that they lie flat against the outwardly facing surface 194 (also indicated in Figure 2) and they extend over the surface 194 from a base of one side of the housing 16 to a base of the other side of the housing 16 (one side of the housing 16 being shown in Figure 12). A first of the inflatable spacers 192 may be applied over a portion of the intermediate layer 40 adjacent the first end wall 20 (indicated by reference numeral 196) and a second of the inflatable spacers 192 applied over a further portion of the intermediate layer 40 adjacent the second end wall 20 (indicated by reference numeral 198), for example. A further spacer 192 may be applied over a further portion of the intermediate layer 40 intermediate the first and second spacers 192, for example. While three longitudinally spaced apart spacers 192 are shown applied over the intermediate layer 40 in Figure 12, it will be understood that the number of spacers 192 used will depend on both the size of the kiln 10 and the size of the spacers 192 used. The applied spacers 192 may then be secured relative to the intermediate layer 40.

The second layer 42 is then able to be secured to a first of the end walls 20, 22, and the second layer 42 tautly applied by drawing it from the first to the second end walls 20 over both the intermediate layer 40 and the spacers 192. Advantageously, the roof 28 of the longitudinal wall 18 is generally arcuate in cross-section to facilitate the application of the second layer 42.

The spacers 192 are then inflated to establish the insulating space between the intermediate and second layers 40, 42. The second layer 42 is shown in cross- section applied over the spacers 192 and the intermediate layer 40 and the spacers 192 inflated in Figure 13. While it will be understood that alternatively the spacers 192 may be inflated prior to the application of the second layer 42, the

inflation of the spacers 192 prior to application of the second layer 42 has been found to make it difficult to draw the layer 42 across both the intermediate layer 40 and the spacers 192 from the first end wall 20 to the second end wall 20.

The second layer 42 may then be secured tautly to the second end wall 22 to maintain the established insulating inner zone 48 between the intermediate and second layers 40, 42. The spacers 192 can then be deflated and removed from the space between the layers 40, 42. The sides of the second layer 42 can then be secured to the sides 22, 24 of the housing 16 along the base.

While it will be understood that alternatively the spacers 192 could be left between the intermediate and second layers 40, 42, advantageously the spacers 192 are removed to minimise the number of layers through which solar or ultraviolet radiation 14 heating the air between the first and intermediate layers 38, 40 is required to pass. The inflatable spacers 192 may be formed from inflatable enclosed or sealed compartments having an outer skin formed from regular plastic sheeting, with the compartments formed by welding together adjacent portions of the plastic sheeting, for example. In that instance, each layer of plastic has been found to absorb up to 5 to 6% of the solar or ultraviolet radiation 14 passing through the layer, for example.

It will be understood that modifications to the described forms of the present invention can be made without departing from the spirit or scope of the invention. In that regard, it is contemplated that the described configurations and methods of constructing and operating a kiln 10 may be employed in combination even though they may not have been specifically described or shown in such a combination.