A technique for reducing contaminants in an osb chip drying apparatus

Abstract

The invention relates to a drying apparatus (100) for drying OSB wood chips, comprising a dryer (20) having a drying chamber (22) designed to dry the OSB wood chips, whereby hot drying gas is introduced into the drying chamber (22), a burner (10) having a combustion chamber (12) for providing the hot drying gas, and a device (80) configured to return at least a portion of the dryer exhaust gas discharged from the drying chamber (22) directly to the burner (10) in order to burn pollutants contained in the portion of the dryer exhaust gas in the burner (10). The device (80) is further configured to maintain the temperature of the portion of the dryer exhaust gas to be returned to the burner (10) at a temperature which is higher than the condensation temperature of the water vapor carried in the portion of the dryer exhaust gas.

Description

Technical Field

[0001] This invention relates to the field of environmental technology. In particular, this invention relates to a technique for reducing emissions of pollutants generated during the drying of OSB wood chips in a drying facility. Background Technology

[0002] Drying equipment configured to dry moist materials (especially sawdust or OSB wood chips) is known. Such drying equipment includes a dryer (e.g., a drum dryer) with a drying chamber into which the material to be dried is fed in a controlled manner. Furthermore, a controlled volumetric flow rate of hot drying gas (e.g., hot air) is introduced into the drying chamber, slowly conveying the material through it. The hot drying gas flows throughout the drying chamber, heating the material and absorbing moisture released during the process. At the outlet of the drying chamber, the dried material is separated from the drying gas (e.g., by a cyclone separator). The drying gas at the outlet of the drying chamber is saturated with water vapor and typically contains contaminants generated during the drying process; this is called dryer exhaust. The dryer exhaust can be purified and released into the environment as waste gas.

[0003] To improve the efficiency of drying equipment, it is also known to return at least a portion of the dryer exhaust gas exiting the drying chamber outlet to a mixing chamber upstream of the drying chamber inlet. The returned dryer exhaust gas (also known as return dryer exhaust) is mixed there with hot drying gas. The gas mixture is then fed back into the drying chamber to dry the damp material. By adding return dryer exhaust, less hot drying gas needs to be supplied by the burner. In particular, the waste heat from the return dryer exhaust can be utilized, meaning the drying equipment can operate more efficiently and energy-savingly overall.

[0004] DE 40 23 518 A1 discloses a drying apparatus in which a portion of the dryer exhaust gas discharged at the outlet of the combustion chamber is returned directly to the combustion chamber of the burner via a return gas line. The returned dryer exhaust gas portion (or the portion of the dryer exhaust gas returning to the combustion chamber) is then passed through a tower-shaped condenser scrubber, which cools the dryer exhaust gas portion below the condensation temperature (dew point temperature), thereby dehumidifying the dryer exhaust gas portion. This condensation process also partially purifies the dryer exhaust gas, as contaminants contained in the dryer exhaust gas are also condensed out. This means that the returned dryer exhaust gas portion, having been cooled below the dew point and at least partially dehumidified and purified, is sent back to the burner or combustion chamber. However, using a condenser scrubber is expensive; furthermore, a significant portion of the condensation heat is lost in the condenser scrubber or can only be recovered with considerable technical effort.

[0005] Furthermore, EP 2 230 477 A1 discloses a wood chip drying apparatus for drying wood chips, which has a return device for returning dryer exhaust gas to the drying cycle. The return device has a dryer exhaust gas heater with a regenerative and / or catalytic heat exchanger configured to heat the dryer exhaust gas to a relatively high temperature in the range of 720°C to 900°C, such that the organic matter or solid particles carried in the dryer exhaust gas are primarily oxidized (combusted). A portion of the heat-regenerated dryer exhaust gas is then fed into the burner as combustion air. Another portion of the heat-regenerated dryer exhaust gas can be fed into a mixing chamber located between the burner and the drying chamber. The use of catalytic heat exchangers is complex and costly.

[0006] Furthermore, US 5,983,521 A discloses a drying apparatus in which dryer exhaust gas supplied at the outlet of the drying chamber is completely returned to the drying cycle. Here, the dryer exhaust gas, or the returned dryer exhaust gas, is split into two branch streams, which are then returned to different regions of the combustion chamber. Each of the two returned dryer exhaust gas branch streams passes through a heat exchanger, where heat from the gas flow originating from the combustion chamber is transferred to the corresponding returned dryer exhaust gas branch stream. One of the two heat exchangers, primarily heated by the burner, is a so-called high-temperature heat exchanger, and the other is a so-called low-temperature heat exchanger. However, no statement is made regarding the temperature of the two returned dryer exhaust gas branch streams. This method of returning dryer exhaust gas is also technically complex because two heat exchangers and corresponding return lines must be provided for the two branch streams. Furthermore, this method involves complex control of the two returned dryer exhaust gas branch streams.

[0007] Furthermore, WO 01 / 59381 A1 discloses a drying apparatus in which a portion of the dryer exhaust is returned both to the combustion chamber and to a mixing chamber between the combustion chamber and the drying chamber. For this purpose, the return line is divided into two branch lines, one leading to the combustion chamber and the other to the mixing chamber. A fan for controlling the return dryer exhaust flow is located in the common section of the return line, i.e., upstream of the two branch lines. However, this makes it difficult to control the return dryer exhaust flow towards the combustion chamber. Additionally, the drying apparatus described in WO 01 / 59381 A1 uses a belt dryer. Such dryers are known to operate at relatively low temperatures (<100°C) on the one hand, but require a large drying gas flow (approximately three times the drying gas flow required by a drum dryer). Because the operating temperature of the drying apparatus is moderate, the temperature of the return dryer exhaust flow is also moderate; this creates a risk that moisture in the return dryer exhaust flow may condense on the combustion chamber walls, thereby damaging the burner.

[0008] Although, as mentioned above, many drying equipment are known to have return devices for recirculating and recovering dryer exhaust gas in order to improve the efficiency of such equipment on the one hand and reduce pollutant emissions on the other, improvements are still needed.

[0009] In particular, this invention aims to provide a technology that further reduces pollutant emissions from drying systems (especially OSB wood chip drying systems) and is also cost-effective and simple to design. Furthermore, the provided technology should be easily adaptable to existing OSB wood chip drying equipment. Summary of the Invention

[0010] To address the aforementioned problems, a first aspect of the present invention provides a drying apparatus for drying OSB wood chips. The drying apparatus includes: a dryer having a drying chamber configured to dry OSB wood chips by introducing hot drying gas into the drying chamber; a burner having a combustion chamber for providing the hot drying gas; and a device configured to return at least a portion of the dryer exhaust gas discharged from the drying chamber to the burner for burning contaminants contained in the dryer exhaust gas in the burner. The device is further configured to maintain the temperature of the returned dryer exhaust gas above the condensation temperature of water vapor carried in the dryer exhaust gas.

[0011] OSB chips are long, thin shavings obtained from debarked round logs and used to manufacture OSB (Oriented Strand Board). OSB chips differ from conventional wood chips in their dimensions. They can have lengths ranging from 100-200 mm, widths ranging from 10-50 mm, and thicknesses ranging from 0.5-1 mm. To manufacture OSB, the OSB chips are dried in a drying apparatus, then bonded together in several layers in an oriented manner (e.g., using a spreading process), and then pressed together.

[0012] The dryer exhaust that is saturated with water vapor generated when moist OSB wood chips are dried and is discharged at the outlet of the drying equipment (more precisely, at the outlet of the drying chamber) is called dryer exhaust. The dryer exhaust returned to the burner, or the dryer exhaust section, is subsequently also referred to as return dryer exhaust or return dryer exhaust section.

[0013] Dryer exhaust released during the drying process of OSB wood chips, or exhaust returned to the dryer, may be contaminated with pollutants. These pollutants can primarily consist of volatile organic compounds (VOCs) and / or particulate matter that pollute the environment. Examples of VOCs are terpenes ((C5H8)n, n≥2), which can be released during the drying process of OSB wood chips. However, these pollutants can also include other compounds, such as nitrogen-based compounds (e.g., nitrous oxide N2O, ammonia NH3, nitrogen oxides NO). xThey have a significant negative impact on the environment.

[0014] The burner of the drying equipment can be configured to produce a burner flame in a combustion chamber, with a flame temperature in the range of 600°C to 1200°C, preferably in the range of 600°C to 800°C. The burner can be, for example, a gaseous fuel burner, an oil-based fuel burner, a solid fuel burner (e.g., a wood chip burner), or a variety of fuel burners configured to produce a flame temperature within the aforementioned temperature range. With the aid of the burner flame, the drying gas supplied to the combustion chamber, or a continuously supplied volumetric flow rate of drying gas, can be heated to a desired temperature in the range of 600°C to 1200°C, preferably in the range of 600°C to 800°C. For example, dry air can be used as the drying gas. In this case, ambient air can be (continuously) supplied to the combustion chamber, where it is heated to the desired temperature with the aid of the burner flame.

[0015] Furthermore, the burner flame can be used to heat and purify the dryer exhaust gas returning to the burner. It has been shown that contaminants released during the drying of OSB wood chips and contained in the dryer exhaust gas (particulate matter, particularly VOCs, nitrous oxide, ammonia, and dust particles) can be effectively combusted (oxidized) at the burner or at flame temperatures in the range of 600°C to 1200°C. The heated / hot dried gas can be (again) supplied to the dryer or a mixing chamber located between the burner and the dryer, along with the returned dryer exhaust gas heated and purified in the burner.

[0016] Therefore, the drying device according to the invention, which returns dryer exhaust to the burner, not only recovers a portion of the dryer exhaust and makes it usable again in subsequent drying processes, but also burns the contaminants carried in the dryer exhaust in the burner flame. This reduces contaminant emissions from the drying device in a structurally simple manner. The additional purification devices known in the prior art for purifying the returned dryer exhaust are not required in the device according to the invention.

[0017] The dryer can be configured as a drum dryer, with a rotating drum serving as the drying chamber. The drying chamber (drum) can be configured to continuously transport OSB wood chips, fed into the drying chamber at the inlet side, to the opposite outlet side of the drying chamber; thus, the OSB wood chips moving towards the outlet side are exposed to the hot drying gas / drying air introduced into the drying chamber and are therefore dried. The hot drying gas, continuously introduced at the inlet side of the drying chamber, flows through the drying chamber, absorbs the moisture released from the OSB wood chips in the drying chamber, and exits the drying chamber at the outlet as dryer exhaust. The temperature of the hot drying gas can depend on the properties of the OSB wood chips and can be adjusted accordingly. The dryer preferably operates with the drying gas at a temperature in the range of 230°C to 500°C, and even more preferably at a temperature in the range of 250°C to 400°C. The volumetric flow rate of the hot drying gas supplied to the drying chamber can be adjusted accordingly based on the amount of OSB wood chips supplied.

[0018] To return at least one portion of the dryer exhaust to the burner, the device (hereinafter also referred to as the return device) may include at least one return line. A first end of the return line is connected to the outlet of the dryer chamber, and a second end of the return line is connected to the burner. For example, at least one return line may be connected to the combustion chamber and / or the burner muffle furnace.

[0019] If at least one return line connects to both the combustion chamber and the burner muffle furnace, then at least one return line can split into two branch lines at its second end. The first branch line can lead directly to the combustion chamber; the second branch line can (directly) lead to the burner muffle furnace. The first portion of the dryer exhaust returning to the burner can be supplied to the combustion chamber (the high-temperature zone of the combustion chamber) as combustion air or main air through the first branch line. The second portion of the dryer exhaust returning to the burner can be supplied to the burner muffle furnace as cooling air through the second branch line. After cooling the burner muffle furnace, the second portion can enter the high-temperature zone of the combustion chamber, where it is further heated and purified. This means that both portions of the dryer exhaust returning to the burner are heated to high temperatures in the combustion chamber, and the contaminants they contain are burned off. The dryer exhaust purified in this way can then be supplied to the drying chamber for further drying.

[0020] Alternatively, at least one return line may include two return lines, wherein a first return line is connected to the combustion chamber of the burner, and a second return line is connected to the burner muffle furnace. The first return dryer exhaust portion can return to the combustion chamber via the first return line (as combustion air). The second dryer exhaust portion can return to the burner muffle furnace via the second return line (as cooling air).

[0021] The dryer exhaust leaving the drying chamber has a temperature higher than the condensation temperature (dew point temperature) of the water vapor carried in the dryer exhaust. Preferably, the temperature of the dryer exhaust returning to the burner remains above the condensation temperature (dew point temperature) throughout the return process. In other words, the return device is configured to maintain the temperature of the returning dryer exhaust above the condensation temperature (dew point temperature) during the return process. This can be achieved, for example, by insulating at least one return line. Insulating at least one return line helps ensure that the returned dryer exhaust transported in the return line loses very little heat and thus remains above the condensation temperature.

[0022] Additionally or alternatively, the return unit may also include a preheating device or be coupled to an (external) preheating device. The preheating device may be configured to preheat at least one return line as needed. This may be necessary, for example, when the dryer is started and at least one return line (albeit insulated) is "cooled" due to low ambient temperatures. To prevent the temperature of the dryer exhaust returning to the burner from falling below the condensation temperature, the preheating device can be activated to preheat at least one return line to the desired temperature (preheating temperature). The preheating temperature may be lower than or equal to the temperature of the return dryer exhaust.

[0023] According to the implementation scheme, the preheating device may include a preheating gas source, which can be selectively connected to the return line of the return device to introduce preheated gas into the return line. The flow of preheated gas through the return line can bring the return line to the desired preheating temperature. Specifically, dehumidified preheated air can be used as the preheating gas.

[0024] By consistently maintaining the temperature of the return dryer exhaust section above the condensation temperature, water vapor contained in the return dryer exhaust section is prevented from partially condensing in the return line designed for return, on the combustion chamber walls, or on the burner muffle furnace. This prevents valuable condensation heat from being lost during return; it also prevents moisture from condensing in the return line or on the combustion chamber walls, which could cause long-term damage to the burner.

[0025] The return device may further include a control device for controlling the volumetric flow rate of the dryer exhaust portion to be returned. The control device may include at least one conveying fan disposed on at least one return line. The at least one conveying fan may be configured to move the returned dryer exhaust portion in the direction of the burner. Therefore, the volumetric flow rate of the returned dryer exhaust portion flowing in at least one return line can be regulated or controlled (actively) by at least one conveying fan. The returned dryer exhaust volumetric flow rate can be adjusted based on the burner output or based on the required volumetric flow rate of the drying gas in the drying chamber. If the return device has two branch lines or at least two return lines for returning a first portion of the dryer exhaust to the combustion chamber and a second portion of the dryer exhaust to the burner muffle furnace, at least one conveying fan can be disposed in each of the at least two return lines or two branch lines to actively regulate the volumetric flow rates of the first and second dryer exhaust portions.

[0026] In addition, the control device may include a valve assembly disposed in at least one return line. The valve assembly may be used to further regulate the volumetric flow rate of the dryer exhaust section to be returned, which will be supplied to the muffle furnace of the combustion chamber and / or burner.

[0027] The drying equipment may also have a mixing chamber disposed between the burner and the dryer. This can be configured to mix the hot drying gas supplied by the burner with the dryer exhaust gas returning to the mixing chamber and / or with external drying gas, and then supply it to the drying chamber. By adding the dryer exhaust gas and / or external drying gas to the drying gas supplied by the burner, the resulting drying gas mixture can be brought to a temperature suitable for dryer operation, which can be significantly lower than the temperature of the drying gas supplied by the burner. Preferably, the drying gas (drying gas mixture) supplied to the dryer through the mixing chamber has a temperature in the range of 230°C to 500°C, more preferably in the range of 250°C to 400°C. The volumetric flow rate of the hot drying gas supplied to the drying chamber through the mixing chamber can be adjusted according to the amount of OSB wood chips supplied.

[0028] To allow at least a portion of the dryer exhaust to return to the mixing chamber, a return device can be further connected to the mixing chamber. According to one variant, at least one return line can be additionally connected to the mixing chamber at its second end. This can be achieved by dividing the return line into at least two branch lines at its second end, wherein the first branch line leads to the burner and the second branch line leads to the mixing chamber. According to another variant, the return line can have at least three branch lines at its second end, wherein the first branch line leads to the combustion chamber, the second branch line leads to the burner muffle furnace, and the third branch line leads to the mixing chamber. The volumetric flow rate in the return line, particularly the proportion of the volumetric flow rate in each branch line, can be actively controlled by a valve assembly of at least one of the aforementioned conveying fans and / or control devices.

[0029] The drying equipment may also include a separation device located at the outlet of the drying chamber and configured to separate OSB wood chips from the dryer exhaust. For example, the separation device may include one or more cyclone separators configured to separate OSB wood chips.

[0030] The drying equipment may also include a filtration device configured to filter out contaminants from the dryer exhaust section, which are released into the environment and therefore do not return to the burner through the aforementioned device, allowing the dryer exhaust section to be reused in the drying process.

[0031] According to a second aspect of the invention, an apparatus for producing OSB is provided, wherein the apparatus comprises: a device for producing OSB wood chips; a drying device according to a first aspect of the invention for drying OSB wood chips; a device for bonding the dried OSB wood chips; a device for orienting and layering the bonded OSB wood chips into a plurality of layers; and a pressing device for pressing the layers into OSB (Oriented Strand Board).

[0032] According to a third aspect of the invention, a method is provided for reducing contaminants generated during the drying of OSB wood chips in an OSB wood chip drying apparatus. The method includes the steps of: returning at least a portion of the dryer exhaust generated during the drying of OSB wood chips to a burner of the dryer apparatus; maintaining the temperature of the portion of the dryer exhaust to be returned to the burner at a temperature higher than the condensation temperature of the water vapor contained in the dryer exhaust; and burning the contaminants contained in the returned dryer exhaust in the burner.

[0033] Preferably, the temperature of the returned dryer exhaust section is maintained above the condensation temperature (dew point temperature) throughout the return process. In other words, the method according to the invention operates in such a way that the temperature of the returned dryer exhaust section does not fall below the condensation temperature throughout the return process. For example, the method operates in such a way that the temperature of the dryer exhaust section to be returned (the returned dryer exhaust section) is maintained at at least 100°C. Preferably, the temperature of the returned dryer exhaust section is maintained in the temperature range of 105°C to 135°C, and even more preferably in the temperature range of 115°C to 135°C.

[0034] In a particularly simple embodiment of this method, the returned dryer exhaust can be maintained at a temperature above the condensation temperature, but not above the temperature of the dryer exhaust leaving the drying chamber. The typical temperature of the dryer exhaust leaving the drying chamber is in the range of 115°C to 135°C; therefore, the returned dryer exhaust can be maintained within the temperature range of 115°C to 135°C (e.g., 125°C) or at a slightly lower temperature. This makes the method particularly easy to implement because no additional heat exchanger and / or heating device is required to raise the temperature of the returned dryer exhaust.

[0035] By consistently maintaining the temperature of the return dryer exhaust section above the condensation temperature, partial condensation of water vapor contained in the return dryer exhaust section is prevented within the return line designed for return or in the burner. This prevents valuable condensation heat loss during return and also prevents moisture from condensing in the return line or on the combustion chamber walls, which could cause long-term damage to the burner.

[0036] To ensure that the return dryer exhaust is always kept above the condensation temperature of water vapor, the return line used to return the dryer exhaust, or at least partially used for this purpose, can be preheated as needed. This preheating step is optional and is performed as needed, for example, if the return line has already "cooled down" due to the colder external temperature when starting the dryer, or if there is a risk that the return dryer exhaust will be below the condensation temperature when returning to the burner.

[0037] For preheating, preheating gas (e.g., dehumidified preheated air) can be introduced into at least one return line, or introduced before returning to the dryer exhaust section. The temperature of the preheating gas can be lower than or equal to the temperature of the returned dryer exhaust. Preferably, the preheating gas can have a temperature in the range of 70°C to 110°C, more preferably in the range of 80°C to 100°C. This allows the return line to reach the desired preheating temperature. This enables the returned dryer exhaust or the returned dryer exhaust section to have a predetermined holding temperature higher than the condensation temperature over the entire return path.

[0038] The return step may include returning the first dryer exhaust portion to the burner and returning the second dryer exhaust portion to the mixing chamber. The dryer exhaust portion returned to the mixing chamber can be mixed there with the dryer gas / dryer air supplied by the burner before being supplied to the dryer.

[0039] The dryer exhaust returned to the burner can be directly returned to the combustion chamber. In an alternative variation, the dryer exhaust returned to the burner can first be supplied to the burner muffle furnace for cooling before being sent into the combustion chamber. In another alternative variation, a portion of the dryer exhaust returned to the burner can be directly supplied to the combustion chamber (as combustion air), and another portion (the remaining portion) can be supplied to the burner muffle furnace. In all variations, the dryer exhaust returned to the burner is passed through the high-temperature zone of the combustion chamber, thereby heating the dryer exhaust to a temperature in the range of 600°C to 1200°C, preferably in the range of 600°C to 800°C, and thus purifying it. Within this temperature range, contaminants contained in the returned dryer exhaust, such as VOCs, nitrogen-based contaminants such as ammonia or nitrous oxide, and solid particles (such as dust particles), are combusted.

[0040] The volumetric flow rate of the first dryer exhaust section supplied to the burner and / or the volumetric flow rate of the second dryer exhaust section supplied to the mixing chamber can preferably be controlled based on the required volumetric flow rate in the burner output and / or the drying chamber. The volumetric flow rate of the first dryer exhaust section returning to the burner can be controlled based on whether the dryer exhaust will be supplied to the combustion chamber, the burner muffle furnace, or both. In particular, the first returning dryer exhaust section can be proportionally divided between the combustion chamber and the burner muffle furnace.

[0041] The combustion step may include burning contaminants contained in the returned dryer exhaust at temperatures ranging from 750°C to 1200°C. Combustion is carried out by a burner flame in the high-temperature zone of the burner. This purifies the dryer exhaust returning to the burner, which significantly improves the overall contaminant balance of the drying equipment. Returning at least a portion of the dryer exhaust to the combustion chamber also saves energy, as the returned dryer exhaust already has a temperature exceeding 100°C. This means that the burner must consume considerably less thermal energy compared to if only cooler drying gas (dry air) is supplied to the burner and then it must be heated to the required operating temperature. Attached Figure Description

[0042] Further details and advantages of the invention are described below with reference to the non-limiting embodiments shown in the accompanying drawings.

[0043] Figure 1A schematic diagram of a drying apparatus including OSB wood chips according to the present invention is shown; and Figure 2 A flowchart illustrating a method according to the invention for reducing contaminants in a drying apparatus for OSB wood chips is shown. Detailed Implementation

[0044] Figure 1 A schematic diagram of equipment 1 for producing OSB (oriented strand board) is shown.

[0045] The equipment 1 includes apparatus 2a and 2b for producing OSB wood chips, a drying apparatus 100 for drying the produced OSB wood chips, apparatus 4a and 4b for bonding the dried OSB wood chips, apparatus 5 for orienting and layering the bonded OSB wood chips into several layers, and a pressing apparatus 6 for pressing the layers into OSB boards. The equipment 1 may also include a separator 3 for separating OSB wood chips of different sizes.

[0046] The components of apparatus 1 are described in more detail below. The devices 2a and 2b for producing OSB wood chips may include a debarker 2a configured to debark round logs (with a relatively high moisture content). The apparatus may also include a cutter 2b configured to cut the debarked round logs. A disc, roller, or blade ring cutter may be used as the cutter 2b. With the aid of the cutter 2b, wood chips (long, thin shavings) are produced from the debarked round logs, with a length ranging from 100 to 200 mm and a width ranging from 10 to 50 mm. The thickness can range from 0.5 to 1 mm.

[0047] The produced (damp) wood chips are supplied to drying equipment 100 for drying. More precisely, the wood chips are supplied to drying chamber 22 of dryer 20, where they are dried by means of introduced drying gas or dry air. Embodiments of the drying equipment 100 according to the invention are described in more detail below.

[0048] The dried wood chips are fed into a classifier. Classifier 3 is configured to sort the wood chips or separate them according to different sizes. Smaller wood chips can be used to make the middle layer of OSB, while larger wood chips can be used to make the top layer. The wood chips sorted by size are fed into devices 4a and 4b for bonding. Larger wood chips are fed into bonding device 4a and bonded there, while thinner wood chips are fed into bonding device 4b and bonded there.

[0049] The bonded wood chips are then fed into device 5 to orient and layer the bonded OSB wood chips into several layers. Device 5 is configured to orient the larger bonded wood chips into one or more intermediate layers (intermediate veneers) and the thinner wood chips into one or more top layers (top veneers).

[0050] The aligned layers of OSB wood chips produced in this way are then fed into pressing device 6. Pressing device 6 is configured to press the layers into OSB. This is accomplished under the influence of pressure and temperature, where the glue hardens and the layers are pressed into a board of a specified thickness. A roller press can be used as the pressing device.

[0051] The drying equipment 100 is described in more detail below.

[0052] The drying apparatus 100 includes a burner 10 having a combustion chamber 12, a dryer 20 having a drying chamber 22, and a mixing chamber 30 disposed between the combustion chamber 12 and the drying chamber 22. The drying apparatus 100 may also include a separation device (not shown) disposed at the outlet of the drying chamber 22 for separating dryer exhaust and OSB wood chips. Furthermore, the drying apparatus 100 may include a dryer exhaust discharge device 50 (or separation device) coupled to the mixing chamber 30, a device 80 for returning at least a portion of the dryer exhaust to the burner 10 (and optionally returning another portion to the mixing chamber 30), and a filter device 62 for filtering contaminants from the dryer exhaust portion (contaminants being released into the environment). The device 80 for returning at least a portion of the dryer exhaust is also referred to hereinafter as a return device 80.

[0053] Burner 10 is configured to supply hot, dry gas to mixing chamber 30. For this purpose, burner 10 has a combustion chamber 12 and a muffle furnace zone 11, the muffle furnace zone 11 having a fuel supply device 14 (e.g., gas, oil, or wood chips) and a supply device 15 for combustion gas / air and / or dry gas / air. The combustion gas / air and / or dry gas / air is fed into combustion chamber 12 and there is heated to the desired temperature by the burner flame. The burner can be a gas burner, an oil burner, a chip burner (e.g., a wood chip burner), or a variety of fuel burners configured to produce a flame temperature in the combustion chamber in the range of 600°C to 1200°C (preferably in the range of 600°C to 800°C). Therefore, the heated, dry gas / air exiting combustion chamber 12 can also have a temperature in the range of 600°C to 1200°C, preferably in the range of 600°C to 800°C. The term "dry gas" or "combustion gas" will be used consistently throughout this document, but it should be clear that the term can also refer to dry air or combustion air.

[0054] The heated dry gas in combustion chamber 12 is fed into mixing chamber 30, where it is mixed with dryer exhaust gas originating from drying chamber 22 and returned via return device 80 (returned dryer exhaust gas section). By recirculating and reusing at least a portion of the dryer exhaust gas exiting from drying chamber 22, the energy efficiency of drying system 100 can be significantly improved. Optionally, another gas stream (air stream) containing preheated gas (air) can be fed into mixing chamber 30 (…). Figure 1 (Not shown in the image), the gas flow is released, for example, in an external device (e.g., a wood processing device) operating outside the drying device 100. This further improves the energy balance of the drying device 100.

[0055] By mixing the heated dry gas supplied from combustion chamber 12 with the returning dryer exhaust (and optionally an additional supply airflow), the temperature of the dry gas (dry gas mixture) generated in mixing chamber 30 and supplied to drying chamber 22 is reduced. However, by properly mixing and adjusting the gas supply from combustion chamber 12, the temperature is regulated so that the dry gas generated in mixing chamber 30 has a desired temperature value approximately 20°C to 40°C higher than the temperature at the dryer inlet. This excessively high temperature in mixing chamber 30 may be necessary to compensate for heat losses due to convection and radiation.

[0056] The dryer 20 is preferably a drum dryer, which operates in a temperature range of 230°C to 500°C, and more preferably in a temperature range of 250°C to 400°C (e.g., 350°C), depending on the quantity and properties of the OSB wood chips (size, moisture content, wood type). Therefore, the temperature of the drying gas supplied in the mixing chamber 30 is 20°C to 40°C higher. Such a temperature is sufficient to dry the OSB wood chips.

[0057] The OSB wood chips to be dried are continuously fed into drying chamber 22 at the entrance of the drying chamber and continuously conveyed within drying chamber 22 until they reach the drying chamber exit. The process of supplying and conveying OSB wood chips within drying chamber 22 is described in detail below. Figure 1 The schematic diagram is not shown. Furthermore, depending on the quantity and properties of the OSB wood chips to be dried, the mixing chamber 30 provides the required volumetric flow rate of drying gas to the drying chamber 22. The hot drying gas supplied to the drying chamber 22 flows throughout and heats the OSB wood chips, absorbing the moisture released in the process, thereby drying the OSB wood chips.

[0058] The aforementioned operating temperature is in the range of 230°C to 500°C, preferably in the range of 250°C to 400°C, and is substantially controlled by the burner 10 (e.g., by controlling the fuel supply and thus the burner output). In any case, the temperature inside the drying chamber 22 is always set so that the moisture and contaminants released during the drying process cannot be re-condensed inside the drying chamber 22.

[0059] Therefore, the dryer exhaust gas flowing out of the outlet of drying chamber 22 has a relatively high temperature, which is higher than the condensation temperature of water vapor. The typical temperature value of the dryer exhaust gas at the outlet of drying chamber 22 is above 100°C, preferably in the temperature range of 115°C to 135°C (e.g., about 125°C).

[0060] The separation device provided at the outlet of the separation drying chamber 22 (in Figure 1 After the OSB wood chips carried in the dryer exhaust (not shown), at least a portion of the dryer exhaust can be returned to the burner 10 via the return device 80. The remaining portion can be sent to the filter device 62 via the dryer exhaust discharge device 50, where the remaining portion is purified / filtered and released into the environment.

[0061] exist Figure 1 In the drying apparatus 100 shown, the return device 80 includes at least one return line 82. A first end of this line is connected to the dryer exhaust discharge device 50. Alternatively, it is conceivable to connect at least one return line 82, with its first end (directly) connected to the outlet of the drying chamber 22 or to a separation device provided at the outlet for separating the dryer exhaust and OSB wood chips. Furthermore, a second end of the return line 82 is connected to the burner 10 so that a first portion of the returned dryer exhaust returns to the burner 10. The return line 82 may also be connected to the mixing chamber 30 so that a second portion of the returned dryer exhaust returns to the mixing chamber.

[0062] exist Figure 1 In the embodiment shown, at least one return line 82 has three branch lines at its second end, wherein the first branch line 82a (directly) leads to the burner chamber 12, the second branch line 82b leads to the burner muffle furnace 11, and the third branch line 82c leads to the mixing chamber 30.

[0063] A portion of the first dryer exhaust gas returning to the burner 10 can be introduced directly into the combustion chamber 12 of the burner 10 as combustion gas via the first branch line 82, where it is heated to a temperature greater than or equal to 600°C by the burner flame, for example, to a temperature in the range of 600°C to 1200°C, preferably to a temperature in the range of 600°C to 800°C. Another portion of the first return dryer exhaust gas returning to the burner 10 can also be fed into the burner muffle furnace 11 as cooling gas / air via the second branch line 82b. This return dryer exhaust gas is then also fed into the combustion chamber 12, where it is further heated to a temperature of 600°C to 1200°C, preferably to a temperature of 600°C to 800°C, and purified.

[0064] By intensely heating the returned dryer exhaust to a temperature ranging from 600°C to 1200°C, in both cases (direct return to combustion chamber 12 or return via burner muffle furnace 11), contaminants carried in the returned dryer exhaust (particularly VOCs (e.g., volatile terpenes), nitrogen-based contaminants (e.g., nitrous oxide, ammonia), and / or particulate matter, which increases in quantity during the drying of OSB wood chips), can be oxidized / burned. This allows for effective purification of the returned dryer exhaust by directly burning contaminants in burner 10, which improves the contaminant balance of the drying equipment 100.

[0065] The second return dryer exhaust can be fed into the mixing chamber 30 via the third branch line 82c. Due to the significantly lower temperature in the mixing chamber (temperatures in the range of 250°C to 400°C), the returned dryer exhaust is not significantly purified. However, mixing the second return dryer exhaust with the dry gas supplied from the combustion chamber 12 can improve the energy balance of the drying equipment 100. This is because, as described in more detail below, the return device 80 is configured to maintain the returned dryer exhaust at a temperature above 100°C; therefore, the returned dryer exhaust has a high heat content; in particular, no additional evaporative heat is required.

[0066] To improve or optimize the energy balance, particularly the contaminant balance, of the drying equipment 100, it is desirable to return as much of the dryer exhaust gas from the outlet of the drying chamber 22 as possible to the burner 10. The amount (volume flow rate) of the returned dryer exhaust gas to the burner 10 depends particularly on the operating load of the burner 10, which in turn depends on the nature and quantity of the OSB wood chips to be dried. Furthermore, care must be taken to ensure that the relatively oxygen-deficient portion of the dryer exhaust gas returning to the combustion chamber 12 does not cause the oxygen content of the combustion gases in the combustion chamber to drop below 13 vol.%, as a drop below 13 vol.% would no longer guarantee stable combustion. To avoid this, a volume flow rate of external combustion gas / air with a significantly higher oxygen content (approximately 20-21 vol.%) can be continuously supplied to the combustion chamber 12 via the supply device 15, and then mixed with the volume flow rate of the returned dryer exhaust gas in the combustion chamber 12.

[0067] The return device 80 according to the invention is configured to control the volumetric flow rate of the first and second dryer exhaust sections returning to the burner 10 or mixing chamber based on the operating load (and particularly, also based on the oxygen content in the combustion chamber 12). For this purpose, the return device 80 has a control device having at least one conveying fan 84 disposed in at least one return line 82. The conveying fan 84 can be used to actively regulate the volumetric flow rate of the dryer exhaust delivered through at least one return line 82.

[0068] The control device may also include valve devices configured to distribute the volumetric flow rate of the return dryer exhaust gas returned via at least one return line 82 to branch lines 82a, 82b, 82c leading to the mixing chamber 30 and to the burner 10 or the burner muffle furnace 11 and to the combustion chamber 12. The valve devices are in... Figure 1 Not shown in the diagram. According to a simplified embodiment, the valve device may include at least one flap valve configured to divide the returned volumetric flow rate into corresponding branch volumetric flow rates for branch lines 82a, 82b, 82c.

[0069] It should be understood that, Figure 1 The return device 80 shown is an exemplary embodiment. Another return device 80 is also conceivable, in which at least one return line 82 leads solely to the combustion chamber 12 of the burner 10. In this case, the valve device for dividing the returned volumetric flow rate into branch volumetric flow rates can also be omitted.

[0070] As described above, the return device 80 is further configured to maintain the returned dryer exhaust (volume flow rate) at a temperature higher than the condensation temperature of the water vapor carried in the dryer exhaust section. To achieve this, the return device 80, and in particular at least one return line 82, may be thermally insulated.

[0071] In addition, the return device 80 may include a preheating device (in Figure 1 (Not shown in the image). The preheating device can be configured to maintain at least one return line 82 at a desired temperature level. For example, the preheating device may include a preheating gas source or be connected to an external preheating gas source. The (external) preheating gas source may optionally be connected to at least one return line 82. The preheating gas source can be configured to supply warm gas or warm air to at least one return line 82 for preheating at least one return line 82. Although at least one return line 82 is insulated, a situation may occur where the return line 82 "cools down" at colder ambient temperatures, particularly when the drying equipment 100 is started. In this case, the preheating gas source can be activated as needed to supply preheated gas to the return line 82.

[0072] Generally, it is sufficient if the temperature of the preheated gas supplied by the preheating gas source is not significantly lower than the temperature of the return dryer exhaust, preferably in the range of 70°C to 110°C, and more preferably in the range of 80°C to 100°C. This temperature is usually sufficient to adequately preheat at least one return line 82, so that the return dryer exhaust can be prevented from cooling below the condensation temperature.

[0073] Therefore, the insulation and optional preheating devices described herein ensure that the return dryer exhaust remains above the condensation temperature throughout its return process. This prevents water vapor or contaminants carried in the return dryer exhaust section from condensing uncontrollably along at least one return line 82 or in the combustion chamber 12 or the burner muffle furnace 11.

[0074] Combination Figure 2 The method for reducing contaminants in OSB wood chip drying equipment according to the present invention is further discussed. This method can be achieved by means of combining... Figure 1 The described drying apparatus 100 is implemented, in particular, by means of the return device 80 described therein.

[0075] According to the first step S20, at least a portion of the dryer exhaust generated during the drying of OSB wood chips is returned to the burner 10 via the return device 80, specifically via at least one return line 82.

[0076] The return dryer exhaust portion returned to the burner 10 is maintained at a temperature above the condensation temperature of the water vapor contained in the dryer exhaust by the return device 80 (second step S22). This can be achieved, on the one hand, by properly insulating at least one return line 82. However, if necessary, at least one return line 82 can also be preheated to the required temperature using a preheating device.

[0077] In the third step S24, the recirculated return dryer exhaust is then heated to a high temperature in the burner 10. Specifically, the return dryer exhaust is passed through the high-temperature zone of the combustion chamber 12 (a zone with a temperature between 600°C and 1200°C), whereby the contaminants carried therein are effectively oxidized / burned.

[0078] The technology for reducing pollutants described herein has several advantages over existing technologies. The technology is simple, space-saving, and cost-effective because it requires no additional purification equipment. Instead, at least a portion of the returned dryer exhaust is directly returned to the existing burner of the dryer and purified there. This purification can significantly reduce pollutant emissions from the dryer. However, the technology described here also overcomes a long-standing bias that dryer exhaust saturated with water vapor cannot be directly returned to the burner or combustion chamber, as this would hinder the stable operation of the dryer.

Claims

1. A drying apparatus (100) for drying OSB wood chips, comprising: The dryer (20) has a drying chamber (22) configured to dry OSB wood chips by introducing hot drying gas into the drying chamber (22); The burner (10) has a combustion chamber (12) for providing hot dry gas; as well as The device (80) is configured to return at least a portion of the dryer exhaust gas discharged from the drying chamber (22) to the burner (10) so as to burn the contaminants contained in the dryer exhaust gas portion in the burner (10); The device (80) is also configured to maintain the temperature of the dryer exhaust section to be returned at a temperature higher than the condensation temperature of the water vapor carried in the dryer exhaust section.

2. The drying apparatus (100) according to claim 1, wherein the device (80) includes at least one return line (82), a first end of which is connected to the outlet of the drying chamber (22), and a second end of which is connected to the burner (10), preferably to the muffle furnace (11) of the combustion chamber (12) and / or the burner (10).

3. The drying apparatus (100) according to claim 2, wherein at least one return line (82) is insulated, and / or The device (80) further includes a preheating device or the device (80) may be connected to the preheating device, the preheating device being configured to preheat the at least one return line (82) as needed.

4. The drying apparatus (100) according to claim 3, wherein the preheating device includes a preheating source selectively connected to the at least one return line (82) to introduce preheated gas into the return line (82).

5. The drying apparatus (100) according to any one of claims 1 to 4, wherein the device (80) further comprises a control device for controlling the volumetric flow rate of the exhaust gas section of the dryer to be returned.

6. The drying apparatus (100) according to claim 5, wherein the control device comprises: At least one conveying fan (84) is provided in the at least one return line (82) for regulating the volumetric flow rate of the dryer exhaust section to be returned; and / or At least one valve assembly, provided in the at least one return line (82), is used to regulate the volumetric flow rate of the dryer exhaust portion to be returned, which will be supplied to the combustion chamber (12) and / or the muffle furnace (11) of the burner (10).

7. The drying apparatus (100) according to any one of claims 1 to 6, wherein the device (80) is further configured to return a first dryer exhaust portion to the burner (10) and a second dryer exhaust portion to a mixing chamber (30), wherein the mixing chamber (30) is configured to mix the drying gas supplied by the burner (10) with the dryer exhaust portion returned by the device (80) and supply it to the drying chamber (22).

8. An apparatus (1) for producing OSB, comprising: Apparatus for producing OSB wood chips (2a, 2b); Drying apparatus (100) according to any one of claims 1 to 7 for drying the OSB wood chips. Apparatus for bonding dried OSB wood chips (4a, 4b). A device (5) for orienting and layering bonded OSB wood chips into several layers; and A pressing device (6) for pressing the layers into OSB.

9. A method for reducing contaminants generated during the drying of OSB wood chips in an OSB wood chip drying apparatus (100), wherein the method comprises: At least a portion of the dryer exhaust generated during the drying of OSB wood chips is returned to the burner (10) of the drying equipment (100). The temperature of the dryer exhaust portion to be returned to the burner (10) is maintained above the condensation temperature of the water vapor contained in the dryer exhaust portion; and The contaminants contained in the dryer exhaust returned in the burner (10) are burned.

10. The method of claim 9, wherein the temperature of the returned dryer exhaust portion remains above the condensation temperature throughout the return process.

11. The method according to claim 9 or 10, wherein the temperature of the water vapor portion to be returned is maintained at at least 100°C, preferably in the temperature range of 100°C to 135°C, more preferably in the temperature range of 115°C to 125°C.

12. The method according to any one of claims 9 to 11, wherein the step of maintaining the temperature above the condensation temperature comprises selectively preheating a return line (82) configured for returning the dryer exhaust gas, and optionally, wherein preheating comprises introducing preheated air into at least one return line (82).

13. The method according to any one of claims 9 to 12, wherein the return step comprises returning a first dryer exhaust portion to the burner (10), particularly to the combustion chamber (12) and / or to the burner muffle furnace (11), and returning a second dryer exhaust portion to the mixing chamber (30).

14. The method of claim 13, wherein the return step comprises controlling the volumetric flow rates of the first dryer exhaust portion returning to the burner (10) and the second dryer exhaust portion returning to the mixing chamber (30).

15. The method according to any one of claims 9 to 14, wherein the combustion step comprises burning contaminants contained in the returned dryer exhaust at a temperature in the range of 750°C to 1200°C.

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