CA2818551A1 - Method for drying wood - Google Patents
Method for drying wood Download PDFInfo
- Publication number
- CA2818551A1 CA2818551A1 CA2818551A CA2818551A CA2818551A1 CA 2818551 A1 CA2818551 A1 CA 2818551A1 CA 2818551 A CA2818551 A CA 2818551A CA 2818551 A CA2818551 A CA 2818551A CA 2818551 A1 CA2818551 A1 CA 2818551A1
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- Prior art keywords
- air
- drying chamber
- cross
- heat exchanger
- drying
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/02—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure
- F26B21/04—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure partly outside the drying enclosure
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/06—Controlling, e.g. regulating, parameters of gas supply
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B23/00—Heating arrangements
- F26B23/001—Heating arrangements using waste heat
- F26B23/002—Heating arrangements using waste heat recovered from dryer exhaust gases
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B2210/00—Drying processes and machines for solid objects characterised by the specific requirements of the drying good
- F26B2210/16—Wood, e.g. lumber, timber
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Drying Of Solid Materials (AREA)
Abstract
A description is given of a method for drying wood, wherein the wood is subjected in a pre-drying chamber (1) to heated incoming air (11) sucked in over a cross-flow heat exchanger (8) and is subjected in a main drying chamber (2) to recirculated air (3), passed in circulation (6) over a heating register (5), from which a partial stream is separated as extracted air (7) and is replaced by incoming air, which is preheated with the aid of the extracted air (7) in a cross-flow heat exchanger (8). To allow the waste heat to be used advantageously, it is proposed that a shared cross-flow heat exchanger (8) arranged upstream of the pre-drying chamber (1) and the main drying chamber (2) is subjected to the extracted air (7) separated from the recirculated air (3), and that the incoming air (11) heated in this cross-flow heat exchanger (8) is used on the one hand to pre-dry the wood in the pre-drying chamber (1) and on the other hand to supplement the extracted air (7) extracted from the recirculated air (3) of the main drying chamber (2).
Description
1 , Method for drying wood 1. Field of the Invention The invention relates to a method for drying wood, where the wood in a preliminary drying chamber is subjected to warm air that has been drawn in over a cross-flow heat exchanger and also subjected to circulating air in a main drying chamber, with this air passing over coil heaters and part of the air flow being expelled as exhaust air and replaced with fresh air that is preheated in a cross-flow heat exchanger with the aid of the exhaust air.
2. Description of the Prior Art In order to be able to dry piles of wood with very different initial moisture levels to a predetermined final moisture level within a narrow tolerance range while requiring comparatively low energy consumption, a known solution (AT 504578 B) is to pre-dry the wood in two entry-side drying zones by supplying air to them that is heated be-tween these drying zones such that the wood is dried to be within a moisture range above fibre saturation point, and then to dry it to the final moisture level in at least one additional drying zone with the aid of recycled air circulating past a coil heater.
The perceptible heat of the partial stream of warmed circulating air that is separated from the circulating air flow in the form of exhaust air and replaced by fresh air is used on the one hand to supplement the circulating air flow and on the other to pre-dry the piles of wood in separate cross-flow heat exchangers, in the same way as the perceptible heat of the air supply expelled after flowing through the pre-drying zones is used for preheating the air supply in each case. However, only a comparatively small proportion of the heat energy of the exhaust air from the drying zones can be . 2, used for preheating as the water vapour absorbed during drying can hardly be con-densed under the prevailing temperature conditions. Consequently, the heat of con-densation is not available for preheating.
SUMMARY OF THE INVENTION
Therefore, the object of the invention is to provide a method for drying wood in which the heat content of the exhaust air following the drying process can be used advan-tageously for preheating the air required for drying.
Based on a method of drying wood in the manner described above, the invention ful-fils the object by separating the exhaust air from the circulating air impinging upon a cross-flow heat exchanger arranged ahead of the pre-drying chamber and the main drying chamber. With the aid of the fresh air supply heated in this cross-flow heat ex-changer, the wood in the pre-drying chamber is pre-dried on the one hand and the air expelled from the circulating air in the primary drying chamber is replaced on the oth-er.
The invention is based on the knowledge that the ratio of exhaust air impinging upon each cross-flow heat exchanger corresponds to the ratio of the preheated fresh air supply as a result of the known flow in the area of each cross-flow heat exchanger.
Consequently, given the relatively small differences between the temperatures of the expelled air and the fresh air it cannot be anticipated that a large proportion of the water vapour absorbed by the fresh air during drying and contained in the exhaust air will condense in the region of each cross-current heat exchanger respectively.
How-ever, if the fresh air supplied to the cross-flow heat exchanger is increased dramati-cally in comparison to the amount of exhaust air impinging on the cross-flow heat ex-changer, the heat content can be removed from the exhaust air despite the relatively small differences in temperature. This leads to the condensation of at least a sub-stantial proportion of the absorbed water vapour, resulting in the utilisation of a large part of the heat energy in the exhaust air as a consequence. For this reason, accord-ing to the invention the exhaust air expelled as a partial air flow from the warmed flow of circulating air in the main drying chamber impinges upon a combined cross-flow , 3, . , heat exchanger for the pre-drying and main drying chambers. The air supply required not only for pre-drying, but also for replacing the exhaust air separated from the air circulating in the main drying chamber is drawn into this combined cross-flow heat exchanger. The predominant use of the thermal energy from the exhaust air expelled from the flow of air circulating in the main drying chamber to heat the incoming air for pre-drying generally makes additional warming of the air superfluous. This means that compared to conventional drying systems of this type, significant energy savings are achieved, without adversely affecting the drying outcome.
Although the only important thing is to preheat a high ratio of incoming air using a low exhaust air ratio, something which is readily possible with a specially designed cross flow heat exchanger, particularly simple design scenarios result if the air expelled from the air circulating in the primary drying chamber flows successively through several parallel heat exchanger units of a cross flow heat exchanger for the fresh air supply as this allows the use of conventional heat exchange units.
As mentioned above, good pre-drying of the wood can be achieved with the fresh air supply for the pre-drying chamber warmed by the expelled air from the main drying chamber, with it being possible to match the temperature of the exhaust air from the pre-drying chamber with the air temperature of the incoming air to a large degree, such that external dissipation seems expedient. However, if the exhaust air from the pre-drying chamber has sufficient excess heat in comparison with the incoming air for economical heat recovery, the air expelled from the pre-drying chamber can impinge upon a cross-flow heat exchanger for the incoming air, arranged ahead of the cross-flow heat exchanger being impinged by the exhaust air from the main drying cham-ber, thus facilitating the use of this excess heat.
Although it is advantageous to have at least two drying chambers arranged succes-sively in the direction in which the material to be dried is conveyed to effect continu-ous pre-drying and primary drying according to the invention, this drying method is not limited to the conveyance of the material to be dried from the pre-drying chamber to the main drying chamber. Consequently, the material to be dried could also be successively subjected to preliminary and primary drying in the same drying cham-4' ber. For this purpose, provision is to be made for at least two drying chambers that are to be operated alternately as preliminary drying chamber and main drying cham-ber accordingly. This means that each of these drying chambers must be connected to a closed loop that guides the circulating air over a coil heater. This increases con-struction costs, especially as the drying chambers must be provided with an appro-priate switching facility in order either to convey the main flow of preheated fresh air from the shared cross-flow heat exchanger through the drying chamber for pre-drying or to maintain the flow of circulating air via a heating element, depending on the op-erating mode. A stream of exhaust air from the flow of circulating air is replaced by some of the preheated fresh air, impinging upon the shared cross-flow heat ex-changer.
BRIEF DESCRIPTION OF THE DRAWING
The method in accordance with the invention will be described in more detail with reference to the drawing. In the drawing Fig. 1 shows an apparatus for performing the method of the invention for drying wood in a simplified block diagram, Fig. 2 shows in a schematic longitudinal cross-section a device for drying timber combined into stacks of wood according to the invention, Fig. 3 shows an embodiment of an apparatus for performing the method according to the invention in a simplified block diagram, Fig. 4 shows a drying chamber of the apparatus according to Figure 3 in an operating position for primary drying and Fig. 5 shows the drying chamber according to Figure 4 in the operating position for drying, but with the drying air flow conveyed in the opposite direction.
DESCRIPTION OF THE PREFERRED EMBODIMENT
According to Figure 1, the inventive method is used for drying wood in bulk form. The pieces of wood are initially conveyed into a preliminary drying chamber 1 for pre-drying and then into a main drying chamber 2. In the primary drying chamber 2 drying is effected by means of circulating air 3, which is conducted via a blower 4 and over a . 5 , coil heater 5 in a closed loop 6. Part of this circulating air flow 3 is expelled from the circulating air flow, impinging upon a cross-flow heat exchanger 8 via a blower 9 with the aid of the exhaust air 7 formed by this partial flow. This cross-flow heat ex-changer 8 has a plurality of heat exchanger units 10 arranged in series with respect to the exhaust air 7 from the main drying chamber 2. Fresh air 11 is drawn in by means of a blower 12 at the same time. According to Figure 1, the heated stream of air 13 for the pre-drying chamber 1 is conveyed to an additional cross-flow heat ex-changer 15 after absorbing vaporised wood moisture as exhaust air 14, with said heat exchanger arranged upstream of the cross-flow heat exchanger 8 for the fresh air 11 in order to utilise the remaining heat after the release of vaporisation heat to the timber material in addition to pre-heating the fresh air 11.
The exhaust air 7 separated from the circulating air 3 in the main drying chamber 2 is replaced by a partial flow 16 of the preheated fresh air 11 drawn in via the blower 12.
With the aid of the exhaust air 7 separated from the warm circulating air 3, a quantity of fresh air is preheated in the cross-flow heat exchanger 8, which for example equates to 10 - 20 times the amount of exhaust air 7. As the cross-flow heat ex-changer 8 is subjected to these different ratios of air a substantial part of the water vapour held in the exhaust air 7 from the primary drying chamber 2 condenses so that the heat of condensation is available for pre-heating the fresh air 11.
Due to the extensive utilisation of the heat content of the exhaust air 7 relative to the fresh air 11 it is possible to dispense with a coil heater for preheating the fresh air flow 13 to the pre-drying chamber 1, resulting in particularly advantageous energy conditions for preliminary and primary drying.
According to Fig 2, provision is made for a drying device, where timber combined into piles 17 are sequentially conveyed through a pre-drying chamber 1 and a subse-quent main drying chamber 2. The woodpiles 17 conveyed out of the main drying chamber 2 after drying are stored temporarily in a cooling zone 18 in order to utilise the waste heat of this woodpile 17 to preheat the fresh air 11 before this fresh air is heated with the aid of the exhaust air 7 from the main drying chamber 2 by the cross-flow heat exchanger 8 in the manner described in conjunction with Fig. 1.
However, in contrast to Fig. 1 the main drying chamber 2 has two drying zones, each with a . 6 closed loop of circulating air 3, where the two coil heaters 5 paired with the circulating streams can ensure favourable temperature conditions for the separated counter-rotating circulating air flows 3 for the graduated primary drying process. The fresh air supply 11 heated in the cross-flow heat exchanger 8 is then distributed to the fans 12 where it is separated into a stream of fresh air 13 for the pre-drying chamber 1 and a partial flow 16 for replacing the exhaust air 7 expelled from the circulating air 3 in the main drying chamber 2, in turn ensuring the flow rates favourable for utilising the heat content of the exhaust air 7 in the area of the cross-flow heat exchanger 8.
In the case of the embodiment according to Fig. 2, the temperature of the heated fresh air flow 13 is chosen such that the exhaust air 14 from the pre-drying chamber 1 is only slightly above the ambient temperature, allowing this exhaust air 4 to be blown di-rectly out into the open.
While according to Fig. 1 and 2 the material to be dried is fed successively through the pre-drying chamber 1 and then through the main drying chamber 2, according to the embodiment shown in Fig. 3 to 5, both the pre-drying and primary drying occur in the same drying chamber. According to the functional block diagram in Fig. 3, for this purpose provision is made for two identically structured drying chambers 19 that are operated alternately as a pre-drying chamber 1 and main drying chamber 2. For this reason the two drying chambers 19 are each connected to a closed loop 6 for circu-lating air 3, which comprises a blower 4 and a coil heater 5. However, it must be en-sured that the closed loop 6 for the circulating air can be switched off by means of switching devices 20 and 21. In an analogous manner it must be ensured that the exhaust air 7 is conveyed from the drying chamber 19 operating as the main drying chamber 2 to the cross-flow heat exchanger 8 via a blower 9, while this exhaust air path is blocked for drying chamber 19 serving as the pre-drying chamber 1. In turn, this is achieved by the switching devices 22 in the duct for supplying air to impinge upon the cross flow heat exchanger 8. When the drying chamber 19 is used as the main drying chamber 2, the duct that serves to extract the exhaust air 14 formed by the full flow of fresh air 13 when the drying chamber 19 is used as the pre-drying chamber 1 must be closed via a switching device 23, so that a circulating flow of air can form within the drying chamber 19.
According to the switch positions illustrated in Fig. 3, the drying chamber 19 on the right serves as the pre-drying chamber 1, which receives a supply of heated fresh air 1'1 via the blower 12. The fresh air flow 13 is conveyed via the blower 4 into the dry-ing chamber 19 using the switching device 20, with the coil heater 5 switched off. The flow of fresh air 13 conveyed into the drying chamber 19 is blown outside as exhaust air 14 via the open switching device 23 after the vaporised wood moisture has been absorbed.
In the area of the left-hand drying chamber 19 serving as a main drying chamber 2, the switching device 20 is switched such that the closed loop 6 for the circulating air 3 is connected 3 to the drying chamber 19 so that the circulating air 3 is conveyed in the closed loop via the blower 4 and the activated coil heater 5. As the switching de-vice 23 is closed and the switching device 22 for the exhaust air 7 is open, some of the circulating air flow is separated from the stream of circulating air as exhaust air 7 in order to subject the cross-flow heat exchanger 8 to flow of exhaust air 7.
As the switching device 21 is open a partial air flow 16 can be channelled off from the heat-ed fresh air 11 drawn through the blower 12 and added to the closed loop 6 to re-place the expelled exhaust air 7.
If the main drying process in the left drying chamber 19 serving as the main drying chamber 2 and the pre-drying process in the right drying chamber 19 serving as the pre- drying chamber 1 are completed, the stack of wood 17 can be discharged from the left drying chamber 19 and replaced with a damp wood pile to be dried in order to operate the right drying chamber 19 as main drying chamber 2 and the left drying chamber 19 as the pre-drying chamber 1 after switching the switching devices and/or the switching devices 21, 22 and 23 accordingly.
Figure 4 shows one of the two drying chambers 19 according to Figure 3 in use as a primary drying chamber 2. Some of the circulating air 3 being conveyed with the aid of the blower 4 in the closed loop via the coil heater 5 is expelled as waste air 7 from the circulating air flow and conveyed by a blower 9 through the open switching device 22 to the cross-flow heat exchanger 8, such that the fresh air supply 11 is heated with the aid of the expelled exhaust air 7, with a part of the air flow 16 from said fresh . 8, air supply being conveyed via switching device 21 to the circulating air flow 3 as a replacement for the extracted exhaust air 7.
The main flow of the heated fresh air is fed via the switching device 20 to the other drying chamber 19 operating as the pre-drying chamber 1, with the blower 4 being used to draw in this fresh air stream 13 into the drying chamber 19. After flowing through the woodpile 17, the stream of fresh air 13 is blown outside as exhaust air 14 via the switching device 23. The direction the blower 4 conveys the air is the opposite to that in Figure 4, but this is not mandatory. The switching device 20 is duplicated according to the embodiment in Fig. 4 and 5, as are the switching devices 21 and 23, with each of the switching devices not in use being labelled as 20' and 21' or 23'. In this way, the direction the circulating air 3 flows or the fresh air 13 flows through the woodpiles 17 can be reversed as required by selecting the switching devices accord-ingly, not only when using the drying chamber 19 as the pre-drying chamber 1 but al-so as the main drying chamber 2.
The perceptible heat of the partial stream of warmed circulating air that is separated from the circulating air flow in the form of exhaust air and replaced by fresh air is used on the one hand to supplement the circulating air flow and on the other to pre-dry the piles of wood in separate cross-flow heat exchangers, in the same way as the perceptible heat of the air supply expelled after flowing through the pre-drying zones is used for preheating the air supply in each case. However, only a comparatively small proportion of the heat energy of the exhaust air from the drying zones can be . 2, used for preheating as the water vapour absorbed during drying can hardly be con-densed under the prevailing temperature conditions. Consequently, the heat of con-densation is not available for preheating.
SUMMARY OF THE INVENTION
Therefore, the object of the invention is to provide a method for drying wood in which the heat content of the exhaust air following the drying process can be used advan-tageously for preheating the air required for drying.
Based on a method of drying wood in the manner described above, the invention ful-fils the object by separating the exhaust air from the circulating air impinging upon a cross-flow heat exchanger arranged ahead of the pre-drying chamber and the main drying chamber. With the aid of the fresh air supply heated in this cross-flow heat ex-changer, the wood in the pre-drying chamber is pre-dried on the one hand and the air expelled from the circulating air in the primary drying chamber is replaced on the oth-er.
The invention is based on the knowledge that the ratio of exhaust air impinging upon each cross-flow heat exchanger corresponds to the ratio of the preheated fresh air supply as a result of the known flow in the area of each cross-flow heat exchanger.
Consequently, given the relatively small differences between the temperatures of the expelled air and the fresh air it cannot be anticipated that a large proportion of the water vapour absorbed by the fresh air during drying and contained in the exhaust air will condense in the region of each cross-current heat exchanger respectively.
How-ever, if the fresh air supplied to the cross-flow heat exchanger is increased dramati-cally in comparison to the amount of exhaust air impinging on the cross-flow heat ex-changer, the heat content can be removed from the exhaust air despite the relatively small differences in temperature. This leads to the condensation of at least a sub-stantial proportion of the absorbed water vapour, resulting in the utilisation of a large part of the heat energy in the exhaust air as a consequence. For this reason, accord-ing to the invention the exhaust air expelled as a partial air flow from the warmed flow of circulating air in the main drying chamber impinges upon a combined cross-flow , 3, . , heat exchanger for the pre-drying and main drying chambers. The air supply required not only for pre-drying, but also for replacing the exhaust air separated from the air circulating in the main drying chamber is drawn into this combined cross-flow heat exchanger. The predominant use of the thermal energy from the exhaust air expelled from the flow of air circulating in the main drying chamber to heat the incoming air for pre-drying generally makes additional warming of the air superfluous. This means that compared to conventional drying systems of this type, significant energy savings are achieved, without adversely affecting the drying outcome.
Although the only important thing is to preheat a high ratio of incoming air using a low exhaust air ratio, something which is readily possible with a specially designed cross flow heat exchanger, particularly simple design scenarios result if the air expelled from the air circulating in the primary drying chamber flows successively through several parallel heat exchanger units of a cross flow heat exchanger for the fresh air supply as this allows the use of conventional heat exchange units.
As mentioned above, good pre-drying of the wood can be achieved with the fresh air supply for the pre-drying chamber warmed by the expelled air from the main drying chamber, with it being possible to match the temperature of the exhaust air from the pre-drying chamber with the air temperature of the incoming air to a large degree, such that external dissipation seems expedient. However, if the exhaust air from the pre-drying chamber has sufficient excess heat in comparison with the incoming air for economical heat recovery, the air expelled from the pre-drying chamber can impinge upon a cross-flow heat exchanger for the incoming air, arranged ahead of the cross-flow heat exchanger being impinged by the exhaust air from the main drying cham-ber, thus facilitating the use of this excess heat.
Although it is advantageous to have at least two drying chambers arranged succes-sively in the direction in which the material to be dried is conveyed to effect continu-ous pre-drying and primary drying according to the invention, this drying method is not limited to the conveyance of the material to be dried from the pre-drying chamber to the main drying chamber. Consequently, the material to be dried could also be successively subjected to preliminary and primary drying in the same drying cham-4' ber. For this purpose, provision is to be made for at least two drying chambers that are to be operated alternately as preliminary drying chamber and main drying cham-ber accordingly. This means that each of these drying chambers must be connected to a closed loop that guides the circulating air over a coil heater. This increases con-struction costs, especially as the drying chambers must be provided with an appro-priate switching facility in order either to convey the main flow of preheated fresh air from the shared cross-flow heat exchanger through the drying chamber for pre-drying or to maintain the flow of circulating air via a heating element, depending on the op-erating mode. A stream of exhaust air from the flow of circulating air is replaced by some of the preheated fresh air, impinging upon the shared cross-flow heat ex-changer.
BRIEF DESCRIPTION OF THE DRAWING
The method in accordance with the invention will be described in more detail with reference to the drawing. In the drawing Fig. 1 shows an apparatus for performing the method of the invention for drying wood in a simplified block diagram, Fig. 2 shows in a schematic longitudinal cross-section a device for drying timber combined into stacks of wood according to the invention, Fig. 3 shows an embodiment of an apparatus for performing the method according to the invention in a simplified block diagram, Fig. 4 shows a drying chamber of the apparatus according to Figure 3 in an operating position for primary drying and Fig. 5 shows the drying chamber according to Figure 4 in the operating position for drying, but with the drying air flow conveyed in the opposite direction.
DESCRIPTION OF THE PREFERRED EMBODIMENT
According to Figure 1, the inventive method is used for drying wood in bulk form. The pieces of wood are initially conveyed into a preliminary drying chamber 1 for pre-drying and then into a main drying chamber 2. In the primary drying chamber 2 drying is effected by means of circulating air 3, which is conducted via a blower 4 and over a . 5 , coil heater 5 in a closed loop 6. Part of this circulating air flow 3 is expelled from the circulating air flow, impinging upon a cross-flow heat exchanger 8 via a blower 9 with the aid of the exhaust air 7 formed by this partial flow. This cross-flow heat ex-changer 8 has a plurality of heat exchanger units 10 arranged in series with respect to the exhaust air 7 from the main drying chamber 2. Fresh air 11 is drawn in by means of a blower 12 at the same time. According to Figure 1, the heated stream of air 13 for the pre-drying chamber 1 is conveyed to an additional cross-flow heat ex-changer 15 after absorbing vaporised wood moisture as exhaust air 14, with said heat exchanger arranged upstream of the cross-flow heat exchanger 8 for the fresh air 11 in order to utilise the remaining heat after the release of vaporisation heat to the timber material in addition to pre-heating the fresh air 11.
The exhaust air 7 separated from the circulating air 3 in the main drying chamber 2 is replaced by a partial flow 16 of the preheated fresh air 11 drawn in via the blower 12.
With the aid of the exhaust air 7 separated from the warm circulating air 3, a quantity of fresh air is preheated in the cross-flow heat exchanger 8, which for example equates to 10 - 20 times the amount of exhaust air 7. As the cross-flow heat ex-changer 8 is subjected to these different ratios of air a substantial part of the water vapour held in the exhaust air 7 from the primary drying chamber 2 condenses so that the heat of condensation is available for pre-heating the fresh air 11.
Due to the extensive utilisation of the heat content of the exhaust air 7 relative to the fresh air 11 it is possible to dispense with a coil heater for preheating the fresh air flow 13 to the pre-drying chamber 1, resulting in particularly advantageous energy conditions for preliminary and primary drying.
According to Fig 2, provision is made for a drying device, where timber combined into piles 17 are sequentially conveyed through a pre-drying chamber 1 and a subse-quent main drying chamber 2. The woodpiles 17 conveyed out of the main drying chamber 2 after drying are stored temporarily in a cooling zone 18 in order to utilise the waste heat of this woodpile 17 to preheat the fresh air 11 before this fresh air is heated with the aid of the exhaust air 7 from the main drying chamber 2 by the cross-flow heat exchanger 8 in the manner described in conjunction with Fig. 1.
However, in contrast to Fig. 1 the main drying chamber 2 has two drying zones, each with a . 6 closed loop of circulating air 3, where the two coil heaters 5 paired with the circulating streams can ensure favourable temperature conditions for the separated counter-rotating circulating air flows 3 for the graduated primary drying process. The fresh air supply 11 heated in the cross-flow heat exchanger 8 is then distributed to the fans 12 where it is separated into a stream of fresh air 13 for the pre-drying chamber 1 and a partial flow 16 for replacing the exhaust air 7 expelled from the circulating air 3 in the main drying chamber 2, in turn ensuring the flow rates favourable for utilising the heat content of the exhaust air 7 in the area of the cross-flow heat exchanger 8.
In the case of the embodiment according to Fig. 2, the temperature of the heated fresh air flow 13 is chosen such that the exhaust air 14 from the pre-drying chamber 1 is only slightly above the ambient temperature, allowing this exhaust air 4 to be blown di-rectly out into the open.
While according to Fig. 1 and 2 the material to be dried is fed successively through the pre-drying chamber 1 and then through the main drying chamber 2, according to the embodiment shown in Fig. 3 to 5, both the pre-drying and primary drying occur in the same drying chamber. According to the functional block diagram in Fig. 3, for this purpose provision is made for two identically structured drying chambers 19 that are operated alternately as a pre-drying chamber 1 and main drying chamber 2. For this reason the two drying chambers 19 are each connected to a closed loop 6 for circu-lating air 3, which comprises a blower 4 and a coil heater 5. However, it must be en-sured that the closed loop 6 for the circulating air can be switched off by means of switching devices 20 and 21. In an analogous manner it must be ensured that the exhaust air 7 is conveyed from the drying chamber 19 operating as the main drying chamber 2 to the cross-flow heat exchanger 8 via a blower 9, while this exhaust air path is blocked for drying chamber 19 serving as the pre-drying chamber 1. In turn, this is achieved by the switching devices 22 in the duct for supplying air to impinge upon the cross flow heat exchanger 8. When the drying chamber 19 is used as the main drying chamber 2, the duct that serves to extract the exhaust air 14 formed by the full flow of fresh air 13 when the drying chamber 19 is used as the pre-drying chamber 1 must be closed via a switching device 23, so that a circulating flow of air can form within the drying chamber 19.
According to the switch positions illustrated in Fig. 3, the drying chamber 19 on the right serves as the pre-drying chamber 1, which receives a supply of heated fresh air 1'1 via the blower 12. The fresh air flow 13 is conveyed via the blower 4 into the dry-ing chamber 19 using the switching device 20, with the coil heater 5 switched off. The flow of fresh air 13 conveyed into the drying chamber 19 is blown outside as exhaust air 14 via the open switching device 23 after the vaporised wood moisture has been absorbed.
In the area of the left-hand drying chamber 19 serving as a main drying chamber 2, the switching device 20 is switched such that the closed loop 6 for the circulating air 3 is connected 3 to the drying chamber 19 so that the circulating air 3 is conveyed in the closed loop via the blower 4 and the activated coil heater 5. As the switching de-vice 23 is closed and the switching device 22 for the exhaust air 7 is open, some of the circulating air flow is separated from the stream of circulating air as exhaust air 7 in order to subject the cross-flow heat exchanger 8 to flow of exhaust air 7.
As the switching device 21 is open a partial air flow 16 can be channelled off from the heat-ed fresh air 11 drawn through the blower 12 and added to the closed loop 6 to re-place the expelled exhaust air 7.
If the main drying process in the left drying chamber 19 serving as the main drying chamber 2 and the pre-drying process in the right drying chamber 19 serving as the pre- drying chamber 1 are completed, the stack of wood 17 can be discharged from the left drying chamber 19 and replaced with a damp wood pile to be dried in order to operate the right drying chamber 19 as main drying chamber 2 and the left drying chamber 19 as the pre-drying chamber 1 after switching the switching devices and/or the switching devices 21, 22 and 23 accordingly.
Figure 4 shows one of the two drying chambers 19 according to Figure 3 in use as a primary drying chamber 2. Some of the circulating air 3 being conveyed with the aid of the blower 4 in the closed loop via the coil heater 5 is expelled as waste air 7 from the circulating air flow and conveyed by a blower 9 through the open switching device 22 to the cross-flow heat exchanger 8, such that the fresh air supply 11 is heated with the aid of the expelled exhaust air 7, with a part of the air flow 16 from said fresh . 8, air supply being conveyed via switching device 21 to the circulating air flow 3 as a replacement for the extracted exhaust air 7.
The main flow of the heated fresh air is fed via the switching device 20 to the other drying chamber 19 operating as the pre-drying chamber 1, with the blower 4 being used to draw in this fresh air stream 13 into the drying chamber 19. After flowing through the woodpile 17, the stream of fresh air 13 is blown outside as exhaust air 14 via the switching device 23. The direction the blower 4 conveys the air is the opposite to that in Figure 4, but this is not mandatory. The switching device 20 is duplicated according to the embodiment in Fig. 4 and 5, as are the switching devices 21 and 23, with each of the switching devices not in use being labelled as 20' and 21' or 23'. In this way, the direction the circulating air 3 flows or the fresh air 13 flows through the woodpiles 17 can be reversed as required by selecting the switching devices accord-ingly, not only when using the drying chamber 19 as the pre-drying chamber 1 but al-so as the main drying chamber 2.
Claims (4)
1. A method for drying wood, with the wood in a pre-drying chamber (1) subjected to heated fresh air (11) drawn in over a cross-flow heat exchanger (8) and in a main drying chamber (2) subjected to circulating air (3), conveyed in a closed loop (6) over a coil heater (5), with a partial stream separated from said circulating air as extracted air (7) and being replaced by fresh air, which is preheated with the aid of the ex-tracted air (7) in a cross-flow heat exchanger (8), wherein the extracted air (7) separated from the circulated air (3) impinges upon a shared cross-flow heat exchanger (8) arranged ahead of the pre-drying chamber (1) and the main drying chamber (2), and the timber in the pre-drying chamber (1) is pre-dried on the one hand and the extracted air (7) separated from the circulated air (3) in the main drying chamber (2) is supplemented on the other with the aid of the fresh air supply (11) heated in this cross-flow heat exchanger (8) .
2. Method according to Claim 1, wherein the extracted air (7) separated from the cir-culated air (3) in the main drying chamber (2) flows through several heat exchange units (10) in succession arranged in parallel to provide the fresh air supply (11) for the cross-flow heat exchanger (8).
3. Method according to either Claim 1 or 2, wherein the exhaust air (14) from the pre-drying chamber (1) impinges upon a cross-flow heat exchanger (15) for the fresh air supply (11) arranged upstream of the cross-flow heat exchanger (8) impinged upon by the exhaust air (7) from the main drying chamber (2).
4. Method according to any one of Claims 1 to 3, wherein provision is made for at least two drying chambers (19), which are operated alternately as pre-drying cham-ber (1) and a main drying chamber (2).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ATA2029/2010 | 2010-12-07 | ||
| AT0202910A AT510007B1 (en) | 2010-12-07 | 2010-12-07 | PROCESS FOR WOOD DRYING |
| PCT/AT2011/050035 WO2012075518A1 (en) | 2010-12-07 | 2011-12-01 | Method for drying wood |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2818551A1 true CA2818551A1 (en) | 2012-06-14 |
Family
ID=45463013
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2818551A Abandoned CA2818551A1 (en) | 2010-12-07 | 2011-12-01 | Method for drying wood |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP2649393B1 (en) |
| AT (1) | AT510007B1 (en) |
| CA (1) | CA2818551A1 (en) |
| LT (1) | LT2649393T (en) |
| RS (1) | RS57317B1 (en) |
| RU (1) | RU2569395C2 (en) |
| WO (1) | WO2012075518A1 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103575083A (en) * | 2013-10-10 | 2014-02-12 | 安徽华印机电股份有限公司 | Improved oven waste heat recycling device |
| AT515466B1 (en) * | 2014-02-26 | 2016-05-15 | Mühlböck Kurt | Process for drying bulk material |
| DE102014112525A1 (en) | 2014-09-01 | 2016-03-03 | Pn Power Plants Ag | Process and apparatus for drying biogenic solid fuel |
| DE102015012848A1 (en) * | 2015-10-06 | 2017-04-06 | Eisenmann Se | Device for controlling the temperature of objects and method for controlling a device for controlling the temperature of objects |
| US20190041134A1 (en) * | 2016-02-01 | 2019-02-07 | Stela Laxhuber Gmbh | Continuous flow dryer having at least two sections |
| CN105841464A (en) * | 2016-05-31 | 2016-08-10 | 浙江力泰炉窑科技有限公司 | Heated air circulation drying kiln for non-dismantling heat insulation formworks |
| DE102016014643B4 (en) * | 2016-12-11 | 2021-05-27 | Stela Laxhuber Gmbh | Continuous dryer for drying goods using warm air with at least two sections |
| DE102017108697A1 (en) * | 2017-04-24 | 2018-10-25 | Stela Laxhuber Gmbh | Continuous dryer with an exhaust air return device |
| DE102017108699B4 (en) * | 2017-04-24 | 2024-09-26 | Stela Laxhuber Gmbh | Continuous dryer with a heat exchanger |
| DE102021105614A1 (en) | 2021-03-09 | 2022-09-15 | Herbert Hauptkorn | Device and method for drying objects and/or materials, in particular wood |
| CN113532047B (en) * | 2021-07-26 | 2023-01-17 | 北京林业大学 | Method for drying wood and recycling heat energy |
| CN115585648B (en) * | 2022-10-09 | 2023-11-24 | 岷县耕获农业发展有限责任公司 | Multi-heat-source controllable drying device applied to agricultural and forest products and application method thereof |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2722752A (en) | 1953-05-04 | 1955-11-08 | Morch Arne Soren | Drying plants for wooden sheet material |
| SE429785B (en) * | 1978-10-13 | 1983-09-26 | Svenska Traeforskningsinst | METHOD OF DRYING WITH HOT AIR |
| SU1010422A1 (en) * | 1982-01-08 | 1983-04-07 | Государственный Институт По Проектированию Лесопильных И Деревообрабатывающих Предприятий | Continuous action drier for loose materials |
| WO1990001664A1 (en) * | 1987-02-03 | 1990-02-22 | Drytec Ab | A method of drying wood |
| FI98092B (en) * | 1988-09-27 | 1996-12-31 | Valmet Paper Machinery Inc | Method for drying timber |
| RU7185U1 (en) * | 1997-07-15 | 1998-07-16 | Перевозчиков Дмитрий Петрович | FOREST DRESSING CAMERA |
| RU2157489C2 (en) * | 1997-08-11 | 2000-10-10 | Иосилевич Валерий Викторович | Wood-drying plant |
| DE19825597A1 (en) | 1998-06-09 | 1999-12-16 | Alb Klein Umwelttechnik Gmbh | Sludge drying plant operating in two stages and recycling waste heat |
| US6988545B2 (en) * | 2003-01-27 | 2006-01-24 | Harold Max Good | Heat exchanger systems |
| CA2495959A1 (en) * | 2005-01-31 | 2006-07-31 | Michael M. Sprague | Heat recovery and ventilation system for dryers |
| AT504578B1 (en) * | 2006-11-21 | 2009-11-15 | Muehlboeck Kurt | METHOD FOR DRYING WOOD MATCHED IN STACKS |
-
2010
- 2010-12-07 AT AT0202910A patent/AT510007B1/en active
-
2011
- 2011-12-01 LT LTEP11810548.5T patent/LT2649393T/en unknown
- 2011-12-01 CA CA2818551A patent/CA2818551A1/en not_active Abandoned
- 2011-12-01 RS RS20180561A patent/RS57317B1/en unknown
- 2011-12-01 EP EP11810548.5A patent/EP2649393B1/en active Active
- 2011-12-01 WO PCT/AT2011/050035 patent/WO2012075518A1/en active Application Filing
- 2011-12-01 RU RU2013131100/06A patent/RU2569395C2/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| EP2649393B1 (en) | 2018-02-21 |
| RS57317B1 (en) | 2018-08-31 |
| EP2649393A1 (en) | 2013-10-16 |
| AT510007A4 (en) | 2012-01-15 |
| RU2569395C2 (en) | 2015-11-27 |
| LT2649393T (en) | 2018-07-10 |
| AT510007B1 (en) | 2012-01-15 |
| RU2013131100A (en) | 2015-01-20 |
| WO2012075518A1 (en) | 2012-06-14 |
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