FI74137C - Method for arranging the circulation of drying air in timber dryers - Google Patents

Description

741 37 1 Method for arranging the circulation of drying air in wood-based kilns Förfarande for att arrangera circulating in the open air 5

The invention relates to a method for arranging a circulation of drying air in timber dryers, in which the packages of timber to be dried are circulated in a drying channel in which a circulating air flow is arranged through the packages of timber to be dried. and in connection with which the circulating air duct is provided with blowing devices for providing a recirculating air flow opposite to the direction of rotation of the timber packages and a supply air flow and exhaust air flow to this recirculating air flow.

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Timber dryers with a drying channel are already known. In this transverse position, wood-stacked drying package packages assembled by means of spacers are recycled through this channel. The circulation of the dryer packages in the drying duct is arranged to be opposite to the circulation of the drying air. Fresh sawn package packages are brought to one end of the drying channel and the pre-dried packages are taken out of the opposite end of the drying channel.

It is also known that the so-called chamber dryers in which a certain amount of 30 batch dryer packages are placed, which are removed after drying and a new product batch is placed in place. However, recycled timber dryers are cheaper to use and energy efficient than chamber dryers.

It is an object of the present invention to further develop the above-mentioned timber dryers in which the dryer packages are recycled in a transverse position.

2 74137 1 With regard to the state of the art related to the present invention, reference is made to FI patent No. 34574 (AB Evemaskiner), which discloses a timber dryer with a drying channel open at both ends, divided into drying zones with partitions between them. However, this known solution has the disadvantage that in adjacent zones the drying air flows will be in opposite directions, i.e. in every other drying zone the drying air flow will be parallel to the direction of rotation of the timber packages. This arrangement is not advantageous in terms of drying efficiency. A disadvantage of the above-mentioned dryer is also that it has two separate air circulations and thus a double number of fans. It is an object of the present invention to avoid this drawback.

With regard to the state of the art related to the invention, reference is also made to FI patents 37485 and 40702 (A.S. Mörch, Sundsvall, Sweden). From said patents, a timber drying plant is known which uses ducts in the air duct above the drying duct, through which air is blown between one or more circulating timber packages. According to FI patent 37485, said air intake is provided by its own fan and a special air duct, from which air is blown at a high speed between said timber packages. Nevertheless, no mention was made of the air to be blown and the air passing through the timber packages at this point, which have different drying capacity, not mixed so well that a uniform drying result would be guaranteed. The method according to the invention also presents an effective solution to these problems.

The division of the drying duct into several zones is advantageous, because when using a single-zone drying duct, its length becomes limited due to the small pressure difference of the pot-blowers. Convection air is also needed the less drier the timber is. The air velocity at the end of the duct must thus be considerably lower than at the beginning.

In order to achieve the above and later objects, the invention is characterized in that said drying air flow is provided by different fan machines for different drying zones, and that the drying capacity of the drying air flow to the latter or latter zones is arranged to be adjustable so that the drying capacity of the drying air flow will be substantially equal to the drying capacity of the drying air taken from the recirculation air duct in the intermediate space.

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The invention will now be described in detail with reference to an embodiment of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

The dryer shown schematically in the figures comprises a dryer building with walls 13 and a partition wall 14 in the middle thereof, two parallel dryer ducts 10 are formed on both sides. Convection air ducts 16 bound between the roof of the dryer building 15 and the intermediate level 17 are connected by drying air supply and exhaust arrangements. The recirculating air ducts 15 have fans 20 and circulating air flow heating coils 21 and 22. The timber packages to be brought for drying are brought through the doors 33 by carriages moving on rails or roller tracks 11 to the beginning of the drying ducts 10.

20 The first drying packages in the drying ducts 10 are marked

with reference P ^. In the drying ducts 10, the packages P move transversely on the roller tracks or rails 11. The last drying package at the end 34 of the drying ducts 10 is denoted by the reference P1. Dryer packages P

propagate in the drying ducts 10 in the opposite direction to the drying air flow F. As the packets at the end of the drying channels 10 have dried to a sufficiently low moisture level, the packets are taken out of the end of the channels 10 through the doors 32.

30 dry replacement air (arrow F,) is introduced into the duct of the drying air into the duct 16 on the suction side of the fans 20. At the same point, polishing is taken out of the recirculation air flow F1 (arrow F sucked in by the fan 24. Between the supply air flow F1 and the exhaust air flow F, heat recovery is arranged in the duct 25 in a manner known per se. In connection with the supply air flow F1 there is a control flap 26 dryer control system.

The above is a wood drying technique known per se and has been described only as a background of the present invention.

^ 74137

According to the invention, the continuous timber dryer is arranged in two or more zones by dividing the drying channel or channels 10 into two or more drying zones 10Λ and 10B, in which the drying air flow F1 is parallel, i.e. There is no partition between the drying zones 10A and 10B, only the intermediate space 23 and the conveyor 30. Above the intermediate space 23 the intermediate plane 17 has an air intake 18 with a control damper 19 connected to the control system. A drying air outlet flow F is supplied to the intermediate space 23. After the opening 18, the recirculating air ducts 16 have dry supply air intake ducts 27 with a fan 28 and a damper 29 connected to the control system. The fan 28 provides a supply air flow after the intake, which is mixed with the recirculation air flow through the heating coil 22.

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By means of the arrangement described above, the temperature and humidity level of the drying air flow F1 directed to the end 34 of the drying channels 10 can be adjusted separately by adjusting the damper 29 and the radiator 22. Thus, the drying operation in the latter drying zones 10B can be controlled.

In addition, the control damper 19 can be used to control the distribution of the circulating air in the different zones 10A and 10B.

According to a particularly preferred embodiment of the invention, the state of the circulating air flow F1 at the intermediate space of zones 10A and 10B is adjusted to its drying capacity to the same level as the drying capacity (temperature, humidity) of the inlet flow F1. This provides the practical advantage that, even if the circulating air flow F1 and the tap flow F1 are not completely mixed with each other, which is in practice a fact, the circulating air flow 30 F1 in the latter zone 10A is obtained with a uniform drying capacity. This ensures even drying for zone 10A.

According to Fig. 1, at the gap 23 between zones 10A and 10B, there is a conveyor 30 by which the dryer packets P1 are transferred from the end-35 of the first zone 10Λ to the beginning of the second zone 10B (packet 1 ').

The dryer according to the invention can also be used in such a way that the dryer packages are taken out of the dryer at the end of the first JO: zone I: 5 74137, e.g. by means of a side transfer trolley, via a special intermediate outlet (not shown). With regard to this arrangement, reference is made to the applicant's earlier Finnish patent application No. 831000 (filed on March 24, 1983). This intermediate outlet 5 is advantageous, e.g. in the case where there is a demand for timber with a moisture level of 12%. In this case, for example, the timber to be dried to a moisture level of 18% is taken out of the intermediate space 23, i.e. out of the intermediate outlet after the first zone 10A, while the packages to be dried to a lower moisture content of 12% are led through both the second zone 10B and taken out of the dryer. through.

Another important advantage of the invention is that when used with propeller blowers, sufficiently large pressure differences are not always achieved, which adversely limits the length of the drying channels. In this case, when using the zone division according to the invention and the drying air intake F 1, the drying channels 10 can be dimensioned to be sufficiently long.

If necessary, two or more drying air intakes 18,23 can be arranged in succession 20, i.e. more than two zones ΙΟΛ, ΙΟΒ. Most preferably, the system is adapted and adjusted so that the drying capacity of each tap flow is equal to the drying capacity of the circulating air flow F 1, whereby a complete drying result is obtained despite the incomplete mixing of these drying air flows.

The following are claims within the scope of which the various details of the invention may vary within the scope of the inventive idea.

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Claims (3)

A method of arranging the circulation of the drying air in wood dryers, in which method the wood package (P) to be dried is circulated in a drying duct (10), in which duct (10) a circulating air stream (F directed through the wood package (P) to be dried and in connection with which drying duct (10), most preferably above it, is a circulating air duct (16), the opposite ends of which are connected with the end (34,35) of the drying duct (10). and in connection with which circulating air duct (16) has been provided fan means (20,24,28), which provide a circulating air flow (F 2) opposite to the direction of circulation (P) and a circulating air flow in this direction. (F ^) inlet air flow (F ^) and an outlet air stream (F ^), and which drying channel (10) has been divided into two or more drying zones (10A, 10B), in each of which zones (10A) .10B) the drying air stream (F ^) is pa rallell and opposite in relation to the direction of circulation of the wood package (P), characterized in that said dry-air stream (F ^) is provided on the various drying zones (10A.10B) with a common blowing machine (20), and that the drying capacity of drying air stream (20) F ^) arriving at the latter zone or zones (10B) has been arranged to be adjustable in such a way that the drying capacity of the drying air stream (Fj ^) coming out of the latter drying zone or drying zones (10A, 10B) will be substantially at the same level as the drying capacity of the drying air (F F) taken to the intermediate space from the circulation air duct (16). 1 Patent claim 1 A. Jonkin patent tivaatimuksen 1-3 mukainen menetelmä, tunnettu siitä, eti in kuivatusvöhykkeiden (10A.10B) wellin (23) kohdalle on järjestetty puutavarapakettien (P) veliulosotto site, et korkeampaan kostuspitoisuuteen kuivat kyseisen veliulosoton tai -ottojen kautta ja että mata-limpaan kostustasoon kuivattavat puutavarapaketit (P ^) otetaan kuivaamosta ulos sen jälkeen only ne ovat kulkeneet kaikkien kuivatusvyöhykkeiden (ΙΟΑ, ΙΟΒ) kautta. 10 15 20 25 30 35 8 74137 2. A method according to claim 1, characterized in that one or more intermediate air outlets (F)) are provided in the space (23) or the mail spaces of the various drying zones (10A, 10B), which are provided / provided with control devices (19). ) for the amount of air, with which at least a part can be regulated to the amount of circulating air (F 35 Method according to any one of claims 1-2, characterized in that in the direction of the circulating air flow (F