WO2013158009A1

WO2013158009A1 - Method and arrangement for drying wood by controlled inlet of fresh air

Info

Publication number: WO2013158009A1
Application number: PCT/SE2013/000052
Authority: WO
Inventors: Eric BJÖRKMAN
Original assignee: Alent Drying AB
Current assignee: Alent Drying AB
Priority date: 2012-04-17
Filing date: 2013-04-16
Publication date: 2013-10-24
Anticipated expiration: 2014-10-17
Also published as: SE536331C2; EP2839229A1; EP2839229A4; SE1200230A1

Abstract

The present invention relates to a method and arrangement for drying an existing batch of wood in a drying house, wherein a flow of circulating air (10, 110) is produced in the drying kiln (1, 101), a flow of fresh air (12; 112) is supplied to the drying kiln (1; 101), the flow of fresh air (12; 112) is mixed into the flow of circulating air (10, 110), and part of the circulating air is vented from the drying kiln (1, 101) as an exhaust air flow (11; 111). Significant for the method of the present invention is that the flow of fresh air (12; 112) is carried to a lower, central part of the drying kiln (1, 101) where the flow of fresh air (12; 112) is deflected upwards and mixed with the flow of circulating air (10, 110).

Description

METHOD AND ARRANGEMENT FOR DRYING WOOD BY CONTROLLED INLET OF FRESH AIR

Technical field of the invention

The present invention relates to a method and

arrangement for drying an existing batch of wood in a drying kiln, wherein a flow of circulating air is produced in the drying kiln, a flow of fresh air is delivered into the drying kiln, the flow of fresh air is mixed into the flow of

circulating air, and that some of the circulating air is evacuated from the drying kiln as an exhaust air flow.

Prior art

SE-C-512 988 discloses a method and arrangement for drying wood, wherein condensate forms during drying.

Significant for the invention is that the hot condensate is handled so that its heat content is conserved as far as possible. The condensate is collected in a container and is used for conditioning the batch of wood on hand and also during the heating phase for the subsequent batch of wood.

In a batch kiln it is normal for the fresh air first to pass a heater battery and be heated together with the

circulating air before it meets the wood batch. The edges of the batch are therefore exposed to a particularly high drying power; this is because the effect of the dry fresh air and the heating of the circulating air combine, increasing the risk of cracking in the wood.

Object and features of the invention

One primary object of the present invention is to provide a method and arrangement for drying wood which evens out the drying power so that the entire batch of wood is dried uniformly .

Another object of the present invention is to reduce the drying time for a batch of wood.

Another object of the present invention is to reduce the energy consumption for drying a batch of wood.

At least the primary object of the present invention is achieved by means of the characteristics indicated in the independent patent claims. The preferred embodiments of the invention are defined in the dependent claims.

Brief description of the drawings

Embodiments of the invention will be described below with reference to the accompanying drawings, wherein:

Figure 1 shows a principle drawing of a first embodiment of an arrangement for drying wood according to the present invention;

Figure 2 shows a principle drawing of a second embodiment of an arrangement for drying wood according to the present invention;

Figure 3 shows an end view of the arrangement for drying wood according to Figure 2; and

Figure 4 shows a plan view of part of the arrangement for

drying wood according to Figure 2.

Detailed description of the preferred embodiments of the invention

The schematically illustrated arrangement for drying wood in Figure 1 comprises a drying kiln 1, which takes the batch of wood to be dried, wherein the batch of wood in Figure 1 comprises a number of wood packages VP. The drying kiln 1 is provided with a door 2 for loading and unloading the batch of wood to be dried.

Drying kiln 1 contains a horizontal floor/horizontal slab 3, which carries a heater battery 4 and circulation fans 5. An evacuation chimney 9 is arranged centrally in the drying kiln 1 and extends through the roof of the drying kiln 1. The lower end of the evacuation chimney 9 goes through the floor 3. An evacuation damper 7 and an evacuation fan 6 are arranged in evacuation chimney 9. A first arrow 11 indicates the drying air/circulating air being removed through the evacuation chimney 9.

A number of seal flaps 8 are arranged on the underside of the floor 3. These extend down towards the upper wood packages VP in the batch of wood in the drying kiln 1. The purpose of the seal flaps 8 is to screen the space above the batch of wood, i.e. air is prevented from circulating in this area, and instead is forced to circulate through the wood packages VP. In this context it should be noted that the volume of the batch of wood decreases during drying. This means that the height of the batch of wood decreases, a height reduction of up to half a metre may occur.

The circulation fans 5 generate an air circulation flowing around inside the drying kiln 1. This circulation flow is symbolised by the arrows 10. Where the direction of

circulation is that shown in Figure 1, the circulation fans 5 bring about a flow to the left in the upper part of the drying kiln 1. The circulating air then flows downwards past the left end of the floor 3, and to the right through the batch of wood, after which the circulating air turns upwards and then to the left through the heater battery 4. By changing the direction of rotation of circulation fans 5 circulating air is made to flow in the opposite direction to the direction shown in Figure 1.

An air inlet 14 with a fresh air damper 13 is arranged on the right wall in Figure 1, wherein a flow of fresh air 12 can pass in through fresh air damper 13. A condensing panel 15, that condenses part of the circulating air when it passes condensing panel 15, is arranged in the immediate vicinity of the fresh air damper 13. The condensate 17 formed in this way is collected in a collection vessel 16 that is arranged inside the drying kiln 1 adjacent to the lower part of condensing panel 15.

The space between the condensing panel 15 and the adjacent wall of the drying kiln 1 defines a fresh air channel 25 that branches out into a number of sub-channels 31

extending along the bottom of the drying kiln 1 to a central area in the drying kiln 1. In the central area of the drying kiln 1 the flow of fresh air 12 is deflected upwards in the centre of the batch of wood. This takes place by means of the deflectors 34 extending across the sub-channels 31. The heated and dry fresh air mixes with the circulating air 10 flowing horizontally. The fresh air has a very low vapour content that quickly, through dilution, lowers the vapour content of the circulating air which thus regains a higher drying power in a position in the drying kiln 1 where this increased drying power is most needed. When fresh air is supplied to the middle of the drying kiln 1 according to the present invention, this increase in drying power takes place in two stages,

safeguarding the edge packages at the same time as the middle packages are dried better.

In the embodiment shown, the deflectors are made up of baffles 34 extending upward from the bottom of the channels 31.

A condensate line 18 runs from the collection vessel 16. This line is connected to a filter 19 and a pipeline 21 runs from filter 19. A pump 20 is connected to pipeline 21.

Downstream of pump 20 pipeline 21 divides into two branches 21A and 21B that extend into the drying kiln 1, wherein the branches 21A, 21B are provided with spray nozzles 22 at their free ends. By means of pump 20, condensate 17 can be pumped from the collection vessel 16 and delivered to the drying kiln 1 as pressurised condensate.

The alternative embodiment shown in Figure 2 of an arrangement for drying wood comprises a drying kiln 101, which takes the batch of wood to be dried, wherein the batch of wood in Figure 2 similarly comprises a number of wood packages VP. The drying kiln 101 is provided with a door 102 for loading and unloading the batch of wood to be dried.

Drying kiln 101 is provided a horizontal floor 103 that supports both a heater battery 104 and circulation fans 105. An evacuation chimney 109 is arranged centrally in the drying kiln and extends through the roof of the drying kiln 101. The lower end of the evacuation chimney 109 goes through the floor 103. An evacuation damper 107 and an evacuation fan 106 are arranged in evacuation chimney 109. A first arrow 111

indicates the drying air/circulating air being removed through the evacuation chimney 109.

A number of seal flaps 108 are arranged on the underside of the floor/plate 103. These extend down towards the upper wood package VP in the batch of wood in the drying kiln 101.

The purpose of the seal flaps 108 is to screen the space above the batch of wood, i.e. air is prevented from circulating in this area, and instead is forced to circulate through the wood packages VP. The circulation fans 105 generate an air circulation flowing around inside the drying kiln 101. This circulation flow is symbolised by the arrows 110. Where the direction of circulation is that shown in Figure 2, the circulation fans 105 bring about a flow to the left in the upper part of the drying kiln 1. The circulating air then flows downwards past the left end of the floor 103, and to the right through the batch of wood, after which the circulating air turns upwards and then to the left through the heater battery 104. By changing the direction of rotation of circulation fans 105 circulating air is made to flow in the opposite direction to the direction shown in Figure 2.

An air intake 114 with a fresh air damper 113 is arranged in the right section of the upper part of the drying kiln in Figure 2, wherein a fresh air flow 112 can pass in through fresh air damper 113. Below fresh air damper 113 an insulated partition wall 135 is arranged that directs the flow of fresh air 112 behind a condensing panel 115 which condenses part of the circulating air 110 when this passes the

condensing panel 115. Before condensate 117 reaches the collection vessel 116 it passes through a filter 119.

The space between the condensing panel 115 and the adjacent wall of the drying kiln 101 defines a fresh air channel 125 that branches out into a number of sub-channels 131 extending along the bottom of the drying kiln 101 to a central area in the drying kiln 101. In the central area of the drying kiln 101 the flow of fresh air 112 is deflected upwards in the centre of the batch of wood. The heated and dry fresh air is mixed with the horizontal flow of circulating air 110 and, similarly to that described in connection with Figure 1, the drying of the batch of wood is improved.

A pipeline 121 runs from the collection vessel 116. A pump 120 is connected to pipeline 121. Downstream of pump 120 pipeline 121 divides into two branches 121A and 121B that extend into the drying kiln 1, wherein the branches 121A, 121B are provided with spray nozzles 122 at their free ends. By means of pump 120, condensate 117 can be pumped from the collection vessel 116 and delivered to the drying kiln 101 as pressurised condensate. Figures 3 and 4 show more in detail an example of how the means for the supply of fresh air can be configured in the embodiment of the arrangement for drying wood shown in Figure 2. Figure 3 is a view through the opening covered by the door 102.

As shown in Figures 3 and 4, a number of spacers 130 are arranged on the bottom of drying kiln 101, wherein according to the embodiment shown, eight spacers 130 are arranged on the bottom of the drying kiln 101. By way of example and not of limitation an appropriate cross sectional dimension of the spacers 130 of 150x150 mm is indicated. The spacers 130 extend across the plane of the paper in Figure 3. A wood package VP is positioned above the spacers 130, wherein the length of the wood package VP is across the length of the spacers 130. A cover 132 is lowered between certain adjacent spacers 130 so as to form a space with a height of about 2 cm between the cover 132 and underside of the wood package (VP) . This forms sub-channels 131 between the bottom of the drying kiln, two adjacent spacers 130 and cover 132. Spacers 130 have a length corresponding to the length of the batch of wood, which consists of a number of wood packages (VP) . The spacers extend along the plane of the paper in Figure 2. The channels 131 extend to the middle of the batch of wood where the channels 131 terminate with the deflectors 134 across the channels 131 so that the flow of fresh air 112 is angled upward and mixed into the flow of circulating air 110. In the embodiment shown, the deflectors are made up of baffles 134 extending upward from the bottom of the channels 131.

With regard to that part of the bottom of the drying kiln 101 that is situated to the right of the wood package VP on the lower far right, a panel 136 or the like is arranged at a certain distance to the bottom of the drying kiln 101 and parallel to the bottom. This forms a broad transition channel 133 for the flow of fresh air 112 to channels 131. The panel 136 connects to the cover 132 in the area where the ends of the spacers 130 are.

As shown in Figure 4 some adjacent spacers 130 are not connected to a deflector 134 in the area where the centre of the batch of wood is. The reason for this is that forklift truck wheels roll into the space between these adjacent spacers 130. As shown in Figure 4 these spaces are enclosed by means of an air barrier arrangement 137 that prevents the flow of fresh air 112 into these spaces.

With regards to the channel arrangement described above the embodiment shown in Figure 1 is also suitable.

Possible modifications of the invention

The embodiments of the arrangement of the present invention described above are provided with an arrangement for collecting condensate and recycling condensate by spraying it over the batch of wood. However, there are a number of

arrangements for drying wood which are not provided with a condensing panel, i.e. no active collection of condensate takes place. Nonetheless, the principle of the present

invention, i.e. supplying fresh air to a central area of the batch of wood, can also be applied to arrangements for drying wood where the collection of condensate does not take place.

In the embodiments of the arrangement of the present invention described above the deflectors are made up of baffles 34; 134. Within the framework of the present invention other means of deflection are conceivable, wherein, by way of example and not of limitation, these can include fan devices. Fan devices suck the flow of fresh air 12; 112 in sub-channels 31; 131 and blow it out upwards into the centre of the batch of wood.

Claims

1. Method for drying an existing batch of wood in a drying kiln (1, 101), wherein a flow of circulating air (10, 110) is produced in the drying kiln (1, 101), a flow of fresh air (12; 112) is supplied to the drying kiln (1, 101) , the flow of fresh air (12; 112) is mixed with the flow of circulating air (10, 110) , and part of the circulating air is vented from the drying kiln (1, 101) as an exhaust air flow (11; 111),

c h a r a c t e r i s e d in that the flow of fresh air (12; 112) is carried to a lower, central part of the drying kiln (1, 101) where the flow of fresh air (12; 112) is deflected upwards and at the same time mixed with that part of the flow of circulating air (10, 110) passing through the batch of wood.

2. The method according to claim 1, c h a r a c t e r i s e d in that the flow of fresh air (12; 112) is carried to the lower, central part of the drying kiln (1; 101) through channels (131) .

3. The method according to claims 1 or 2,

c h a r a c t e r i s e d in that the flow of fresh air (12; 112) passes a condensing panel (15; 115) as it is carried into the drying kiln (1; 101) .

4. The method according to claim 3, c h a r a c t e r i s e d in that the flow of fresh air (12; 112) is heated as it passes the condensing panel (15; 115) .

5. Arrangement for drying an existing batch of wood in a drying kiln (1, 101), wherein the drying kiln (1, 101)

comprises a door (2, 102) for loading and unloading the batch of wood to be dried, means (5, 105) for generating a flow of circulating air (10, 110), means (4, 104) for supplying heat to the flow of circulating air (10, 110), means (14; 114) for supplying a flow of fresh air (12; 112) to the drying kiln (1; 101) and means (6, 9; 106, 109) for venting part of the circulating air from the drying kiln (1; 101), c h a r a c t e r i s e d in that the arrangement comprises means (25; 125) for carrying the supplied flow of fresh air (12; 112) to a lower, central part of the drying kiln (1;

101), and separate means (34; 134) for deflecting the flow of fresh air (12; 112) upwards in the centre of the batch of wood.

6. Arrangement according to claim 5, c h a r a c t e r i s e d in that the means for carrying the supplied flow of fresh air (12; 112) comprises in part channels (31; 131) that runs along the bottom of the drying kiln (1; 101) .

7. Arrangement according to claim 6, c h a r a c t e r i s e d in that the channels (131) defined in part by spacers (130) located on the bottom of the drying kiln (1, 101) .

8. Arrangement according to one of claims 5-7, wherein it comprises a condensing panel (15; 115) in the drying kiln (1; 101), c h a r a c t e r i s e d in that the means for carrying the supply of the flow of fresh air (12; 112) in part

comprises the space between the condensing panel (15; 115) and an adjacent wall of the drying kiln (1; 101) .