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Title:
A TIMBER DRYING KILN
Document Type and Number:
WIPO Patent Application WO/2000/011421
Kind Code:
A1
Abstract:
A timber drying kiln (21) includes heating pipes (2), ventilation openings (4), a water atomizer (6), fans (8), an upper chamber (10), a lower chamber (12), an intermediate ceiling (14), an insulated door (18), a roof (20) and at least one upright panel. The panel includes upper panels (22, 24) located in the upper chamber (10) and a lower panel (26) located in the lower chamber (12) where the timber is placed for drying. The panels are mounted for movement between a first position, in which the panel divides the chamber into two sub-chambers, and a second position, in which the chamber is not divided.

Inventors:
LIM WEE HOU (SG)
Application Number:
PCT/SG1998/000064
Publication Date:
March 02, 2000
Filing Date:
August 20, 1998
Export Citation:
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Assignee:
LIM WEE HOU (SG)
International Classes:
F26B25/12; (IPC1-7): F26B9/06; F26B3/00
Foreign References:
US4753020A1988-06-28
US4176466A1979-12-04
US5325604A1994-07-05
Attorney, Agent or Firm:
Mccallum, Graeme David (Lloyd Wise Tanjong Pagar P.O. Box 636 Singapore 6, SG)
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Claims:
CLAIMS
1. A timber drying kiln comprising a chamber, a movable member mounted for movement between a first position in which the movable member divides the chamber into two subchambers and a second position, in which the chamber is not divided.
2. A timber drying kiln according to claim 1, wherein the second position is adjacent a side wall of the chamber.
3. A timber drying kiln according to claim 1 or claim 2, wherein the chamber comprises an upper chamber and a lower chamber, separated by a substantially planar member.
4. A timber drying kiln according to any of the preceding claims, wherein the movable member comprises at least one upright panel.
5. A timber drying kiln according to claim 4 when dependent on claim 3, wherein the panel comprises an upper panel located in the upper chamber and a lower panel located in the lower chamber.
6. A timber drying kiln according to claim 5, wherein the upper panel comprises a first subpanel and a second subpanel.
7. A timber drying kiln according to claim 6, wherein the first subpanel and the second subpanel may be moved independently of each other.
8. A timber drying kiln according to claim 6, wherein the first subpanel and the second subpanel move together.
9. A timber drying kiln according to any of claims 5 to 8, wherein the upper panel and the lower panel comprise a combination of stationary and movable panels.
10. A timber drying kiln according to claim 9 wherein the stationary panel is fixed in the upper chamber.
11. A timber drying kiln according to claim 9 or claim 10, wherein the movable panel moves in the lower chamber along the length of the kiln.
12. A timber drying kiln according to any of the preceding claims, wherein the movable member is movably mounted on wheels.
13. A timber drying kiln according to any of the preceding claims, wherein the movable member is movably mounted on rollers.
14. A timber drying kiln according to any of the preceding claims, wherein the movable member is movably mounted on rails.
15. A timber drying kiln according to any of the preceding claims, wherein the panel is substantially perpendicular to a plane defined by the fans.
16. A timber drying kiln according to any of the preceding claims, wherein the panel comprises a rigid material adapted to hold shape and dimension.
17. A timber drying kiln according to any of claims 1 to 15, wherein the panel comprises a flexible material adapted to hold shape and dimension.
18. A timber drying kiln according to any of claims 1 to 15, wherein the panel comprises a combination of both rigid and flexible material adapted to hold shape and dimension.
19. A timber drying kiln according to claim 16 or claim 18, wherein the rigid material comprises metal.
20. A timber drying kiln according to any of claims 16,18 or 19, wherein the rigid material comprises wood.
21. A timber drying kiln according to claim 17 or claim 18, wherein the flexible material comprises plastic.
22. A timber drying kiln according to any of claims 17, 18 or 21, wherein the flexible material comprises rubber.
23. A timber drying kiln according to any of the preceding claims, wherein the panel is substantially impenetrable to air.
Description:
A TIMBER DRYING KILN The invention relates to a timber drying kiln.

Timber in its natural state always contains a large amount of moisture. This type of timber is commonly referred to as "unseasoned"or"green"timber. The high water content of the timber influences the properties of the timber to such an extent that the timber is not in a condition to enable it to be used to manufacture quality wood products. Furthermore, wet timber is dimensionally unstable and does not maintain its original size regardless of how accurately it is machined. In addition, it cannot be worked effectively due to the high water content. Also green timber weighs more than dried timber and therefore green timber is more expensive to transport. Unseasoned timber is also susceptible to fungal and insect attack and is structurally relatively weak.

Therefore, it is desirable to dry timber before using the timber. However, if the timber is dried out too quickly, it will crack and distort. Therefore, it is necessary to dry the timber under controlled conditions and to control in particular, the heat and humidity in the drying environment.

Hence, timber is normally dried in an enclosed environment in a timber drying kiln where the drying out process can be accurately controlled. A timber drying kiln is basically an enclosure used to dry unseasoned timber by reducing its moisture content. The kiln has four basic functions, namely, heating, ventilation, humidification and air circulation.

However, different types of timber have different cellular structures, sizes, etc. Therefore different types of timber have different drying properties. Generally, timber is categorized into three groups - hardwood, medium hardwood and softwood. The hardwood group is the most difficult to dry and must be processed at a low temperature. Generally, this group has the longest drying time. The medium hardwood group has medium to good drying properties. The softwood group is more easily dried and can be processed at a higher temperature.

Generally, this softwood group has the shortest drying time.

The thickness of the timber also affects its drying schedule as a thicker piece of timber takes longer to dry.

The whole capacity of the timber drying kiln is preferably loaded with timber of the same type and of the same thickness.

However, this is usually not possible to achieve and, in practice, a user will normally mix one type of timber with another type. Under such circumstances, the drying schedule for the timber load within the kiln will have to be based on the hardest and/or thickest type of timber in the kiln.

The arrangement of the timber in the kiln is also important to the drying process. Timber to be placed in the kiln is first "stacked"and then the stacked timber is"loaded"into the kiln. The timber is"stacked"means that the pieces of timber are placed on top of each other with a gap (spacer) between each piece. The gap provides an air path between each piece of timber. The stacked timber is"loaded"means that the stacked timber is placed into the kiln and arranged in such a manner that all other air paths, except for the gaps through the timber pieces, are sufficiently blocked off. If the stacked timber is loaded poorly into the kiln, most of the air flow would be diverted away from the gaps between the stacked timber pieces.

There are two different types of kiln. One type of kiln has a door at the front of the kiln, permitting pieces of timber to be placed into the kiln through the front with the help of a forklift. This type of kiln is known as a front loading kiln.

The second type of kiln has a door at one end of the kiln such that pieces of timber can be placed into the kiln through that end of the kiln with the help of a transfer truck. This type of kiln is thus known as an end loading kiln.

When investing in a kiln, the user will have to consider the following factors : (1) the operating concept ; (2) the loading method ; and (3) the capacity.

One problem with both types of currently available timber drying kilns is that they have a fixed capacity. This is commonly to accomodate loads of either 50 tons of timber, 75 tons of timber or 100 tons of timber load. Therefore, the user will have to consider purchasing a number of kilns of different capacities to provide for flexibility to deal with problems such as delays in timber delivery, meeting clients' delivery requirements and economical kiln operation. As the kiln involves a high-capital expenditure, the user has to be careful to purchase a kiln that is of an appropriate size for his requirements as the capacity of the kiln cannot be increased or decreased at a later date. For example, if a kiln with a fixed capacity of 50 tons of timber is purchased, it cannot be modified to accomodate 75 tons of timber.

Similarly, if a kiln with a capacity of 100 tons of timber is purchased and it is too big for the purchaser's requirements, the capacity of the kiln cannot be reduced.

The following are examples of situations which a user may encounter with currently available fixed capacity kilns.

Example A A user has two timber drying kilns of capacities 50 tons and 100 tons. The 50 tons kiln is already being used to dry 50 tons of timber while the 100 tons kiln is waiting to be used for a 100 tons timber load which is due to be delivered.

However, only 50 tons of the 100 tons of timber is delivered.

As production requires the timber at a prescribed time, the user cannot be able to afford to wait for the additional 50 tons of timber which is still to be delivered. Therefore, the user has to load the 50 tons of timber into the 100 tons kiln.

As the amount of the timber is insufficient to fill up the whole capacity of the kiln, there may be a problem of spaces in the kiln which causes most of the air flow to be diverted away from the gaps between the timber pieces. This results in a longer drying time and poorer drying quality. In addition, the electricity cost per ton of dried timber will be doubled because a 100 tons kiln, instead of a 50 tons kiln, is operating.

Example B An operator has two kilns, each having a capacity of 75 tons.

There is a production requirement for 50 tons of hardwood timber and 50 tons of softwood timber. The operator may combine the two types of timber such that 50 tons of hardwood timber is combined with 25 tons of softwood timber to fill up one of the 75 tons kilns, while the remaining 25 tons of softwood timber is placed in the second 75 tons kiln. This is undesirable as in the first 75 tons kiln, the drying schedule adopted will be that for the hardwood and so the drying time will be longer than necessary for the 25 tons of softwood in that kiln. In addition, the second 75 tons kiln will be under-utilized to dry only 25 tons of timber. Alternatively, each of the 75 tons kilns may be operated as a 50 tons kiln.

In either case, electricity is wasted.

Example C An operator only has a kiln with a capacity of 100 tons.

There are 75 tons of softwood timber and 25 tons of hardwood timber waiting to be dried. There is a sudden requirement for 75 tons of softwood timber. If he mixes the timber to fully load the 100 tons capacity of the kiln, the drying time will be longer, because the drying schedule adopted will be that for the hardwood timber. Alternatively, he may operate the 100 ton kiln as a 75 ton kiln. Either option results in an increase in the drying cost per ton of timber for the softwood timber.

In accordance with the present invention, a timber drying kiln comprising a chamber, a movable member mounted for movement between a first position in which the movable member divides the chamber into two sub-chambers and a second position, in which the chamber is not divided.

Typically, the chamber comprises an upper chamber and a lower chamber, separated by a substantially planar member.

Preferably, the second position is adjacent a side wall of the chamber.

Preferably, the movable member comprises at least one upright panel.

Preferably, the panel comprises an upper and a lower panel ; the upper panel being located in the upper chamber and the lower panel being located in the lower chamber.

Typically, the upper panel comprises a first sub-panel and a second sub-panel.

Preferably, the first sub-panel and the second sub-panel moves separately or together.

Typically, the upper and lower panels comprise a combination of movable and stationary panels ; the upper panel being fixed and the lower panel being movable.

To facilitate the movement along the length of the kiln, preferably the panels may be mounted on wheels or rollers.

The wheels or rollers may in turn be mounted on rails.

Typically, the panel is substantially perpendicular to a plane defined by the fans.

Typically, the panel is fabricated with flexible or rigid material or a combination of both rigid and flexible material adapted to hold shape and dimension. The rigid material can be metal or wood. The flexible material can be plastic or rubber.

Preferably, the panel is non-corrosive and impenetrable to air.

In an alternative example of the invention, the panels are arranged and constructed in a way such that they can roll up or gather up like a curtain or a blind or even fold up against the wall or the ceiling.

Preferably, the movable members can be retrofitted to existing kilns.

An example of a timber drying kiln in accordance with the invention will now be described with reference to the accompanying drawings, in which : Figure 1 is a perspective view of a conventional front- loading timber drying kiln ; Figure 2 is a perspective view of a first example of a front loading timber drying according to the invention ; Figure 3 is a perspective view of the timber drying kiln of Figure 2 with the panels at a standby position ; Figure 4 is a perspective view of the timber drying kiln of Figure 2 with the panels at a 75-ton position ; Figure 5 is a perspective view of the timber drying kiln of Figure 2 with the panels at a 50-ton position ; Figure 6 is a perspective view of a second example of a front loading timber drying kiln according to the invention ; Figure 7 is a perspective view of a conventional end loading timber drying kiln ; Figure 8 is a perspective view of a first example of an end loading timber drying kiln according to the invention ; and Figure 9 is a perspective view of a second example of an end loading timber drying kiln according to the invention.

Figure 1 is a perspective view of a conventional front loading 100 tons timber drying kiln 1. The basic features of the timber drying kiln 1 include heating pipes 2, ventilation openings 4, a water atomizer 6, eight fans 8, an upper chamber 10, a lower chamber 12, an intermediate ceiling 14, an insulated door 18 and a roof 20. The lower chamber 12 is the main drying area of the kiln in which the timber 16 is placed.

Only six fans are shown in Figure 1 as the other two fans are obscured by the roof 20.

Temperature and humidity conditions in the lower chamber 12 where the timber is placed are closely controlled. Heating maintains the kiln air at a desired temperature, typically between 35°C and 100°C. This is effected by valves (not shown) incorporated into the heating pipes 2 which are in the form of a coil or a radiator and are located at the rear of the timber drying kiln 1 in the upper chamber 10. It should be noted that the heating pipes 2 may also be located at the front of the timber drying kiln 1 or at both the rear and the front of the timber drying kiln 1, extending around the side walls of the timber drying kiln 1. The heating system may use steam or hot water heated in the boilers using a suitable fuel such as wood waste, gas or mineral oil (not shown). Alternatively, the heating system may be run by electricity. The heat in the kiln is prevented from escaping by the insulated door 18.

Ventilation openings 4 are located on the flat roof 20. The openings 4 are adjustable and disposed with regular intervals between them. As the timber 16 gets heated up, a large quantity of moisture is rapidly evaporated from the timber 16.

To keep humidity level in the kiln high, more of the ventilation openings 4 are closed so that the moisture from the timber are prevented from escaping. To keep the humidity level in the kiln low, more of the ventilation openings 4 are opened so that more of the moisture from the timber is carried away and out through the ventilation openings 4. The ventilation openings 4 therefore facilitate air circulation in the kiln to keep the relative humidity to a required level.

Humidification is achieved by admitting steam or hot water through the water atomizer 6. Humidification keeps the humidity within the kiln at a required level when moisture from the timber 16 is insufficient to do this. This is particularly relevant towards the end of a drying run when the moisture levels in the timber are low and so the moisture from the timber is not sufficient to maintain the necessary humidity level in the kiln.

Air circulation is provided by fans 8 located in the upper chamber 10. The fans 8 are flush with one another forming a plane perpendicular to an intermediate ceiling 14 that separates the upper chamber 10 from the lower chamber 12. The plane defined by the fans 8 is substantially parallel to the rear wall of the timber drying kiln 1. The fans 8 provide the air circulation between the upper chamber 10 and the lower chamber 12 to ensure proper air circulation through the gaps between the timber pieces 16 so that heat and humidity are circulated throughout the chamber 12 and in particular to all parts of the timber 16. In addition, the air circulation helps to convey excess moisture away from the timber. This helps to ensure that the timber 16 is evenly dried. The direction of the air flow is shown by the arrows in Figure 1.

Figure 1 also shows the insulated door 18 situated in front of the kiln 1 and the timber 16 being loaded through the front of the kiln 1 by a forklift 100.

Figure 2 is a perspective view of a first example of a front loading timber drying kiln 21 in accordance with the invention. For the purposes for clarity, the heating pipes 2, the ventilation openings 4, the water atomizer 6, the timber 16, the insulated door 18 and the roof 20 are not shown.. The kiln 21 has a capacity available for 100 tons of timber and is installed with a front upper panel 24, a rear upper panel 22 and a lower panel 26. Both the front upper panel 24 and the rear upper panel 22 are located in the upper chamber 10 while the lower panel 26 is located in the lower chamber 12. The panels 22,24 and 26 are substantially perpendicular to the plane defined by the fans 8 which are aligned in a sequence 8A to 8H as shown in Figure 2. The lower panel 26 is disposed between fans 8D and 8E, dividing the chamber 12 into sub- chambers 9 and 11, each with equal volumes of 50 tons. The lower panel 26 is said to be in a 50-ton position. The rear upper panel 22 and the front upper panel 24 are shown moving separately along the length of the kiln in the direction indicated by the arrows 27 and 29 respectively to the 50-ton position between the fans 8D and 8E where the panels 22,24, 26 will then be aligned with one another. To facilitate movement along the length of the kiln, the panels are preferably on wheels, rollers or rails (not shown).

Preferably, the panels are locked to the walls of the kiln by a latch mechanism or locked into the ground by a drop bolt.

In one example of the kiln, the panels may be moved manually.

In an alternative example, an activation means may be provided. The activation means (not shown) for the panels may be a hand-operated mechanism, for example a wire rope pulley system operated by a manual hand winch. Alternatively, the activation means may be an electrically-operated mechanism to move the panels along the length of the kiln.

Figure 3 shows the upper and lower panels 22, 24, 26 parallel to and adjacent the side wall 25. When the panels are in this position, the full capacity of the kiln is available for 100 tons of timber and all eight fans 8 are in operation.

In Figure 4, the panels 22,24, 26 are located between the fans 8F and 8G and divide the kiln 21 into two sub-chambers 31 and 33 of capacity 75 tons and 25 tons respectively. If the sub-chamber 31 is loaded, only six fans 8A to 8F will need to be in operation, leaving the two fans 8G and 8H non- operational. The 100 tons kiln 21 thus operates as a kiln with a capacity of 75 tons. Power consumption is reduced by not having to operate fans 8G and 8H.

In Figure 5, the panels 22,24, 26 are located between the fans 8D and 8E and divide the kiln 21 into two equal sub- chambers of capacity 50 tons each. If one of the sub-chambers is loaded with timber, then only four of the eight fans 8 need to be in operation. Therefore, the 100 tons kiln 21 operates as a kiln with a capacity of 50 tons and power consumption is reduced by not operating four of the fans 8.

The timber drying kiln 51 in Figure 6 is a second example of a front loading timber drying timber. It has two sets of upper panels 34, 36 and 44, 46 stationary and a lower panel 38 movable. The panels 44 and 46 are inserted between fans 8F and 8G (at the 75-ton position) while the panels 34 and 36 are inserted between fans 8D and 8E (at the 50-ton position).

Figure 6 shows the lower panel 38 adjacent and parallel to the side wall 25, making available a full capacity for 100 tons of timber. The lower panel 38 is movable to the 75-ton position or the 50-ton position. The panels 34,36, 44, 46,38 form a combination of stationary and movable panels.

Figure 7 is a perspective view of a conventional end loading timber drying kiln 28. In contrast to the front loading kiln 1 of Figure 1, Figure 7 shows an insulated door 30 at one end of the kiln 28. The loading is performed using a conventional transfer truck which is a well known loading system for end loading kilns.

Figures 8 and 9 are perspective views of a first and second examples of end loading timber drying kilns 32,52 in accordance with the invention respectively. The timber drying kilns 32,52 are similar to the timber drying kiln 21 shown in Figures 2 to 6 and identical components have the same reference numerals. In each of the kilns 32,52 a door 30 (not shown) is located at one end of the kiln. The arrows in each of the Figures 8 and 9 indicate the entry points of the kilns 32,52.

The end loading timber drying kiln 32 in Figure 8 is installed with movable upper and lower panels 22,24 and 26.

The end loading timber drying kiln 52 of Figure 9 is installed with fixed upper panels 34,36 44, 46 and a movable lower panel 38.

The panels may be retrofitted into an existing kiln.

Alternatively, the panels may be incorporated into a new kiln during fabrication of the kiln.

An advantage of the invention is that it is of variable capacity. By adding a system of panels into a fixed 100 tons kiln, the 100 tons capacity of the kiln can be divided into sub-chambers. Previously, an operator may have to under- utilize a 100 tons kiln to dry for example 50 tons of timber resulting in a longer drying time, poorer drying quality and increased electricity cost per ton of dried timber. With the variable capacity kiln, the operator simply divides the chamber of the 100 tons kiln into sub-chambers of 50 tons each. One sub-chamber can be loaded with the 50 tons of timber with the fans operating as usual. The fans in the other sub-chamber that contains no timber need not be in operation. This adds more flexibility to the kiln operation and makes kiln operation more economical.