Return air system for fluorine-containing material processing

Abstract

The present application provides a return air system for treating fluorine-containing materials, in which the fluorine-containing gas in the terminal treatment unit is cooled and defluorinated by a defluorination unit, and then the gas is further cooled and dehumidified by an air treatment unit, and then enters the terminal treatment unit for cooling the dried material therein, thereby forming a circulating air path; an auxiliary treatment unit is also provided on the air path to stabilize the airflow and reduce noise, adjust the air volume, and ensure the stability of the system; the return air system realizes the goal of recycling the return air of the dried material, thereby achieving the purpose of energy saving and emission reduction.

Description

Technical Field

[0001] The present application mainly relates to the field of air treatment technology, and in particular to a return air system for treating fluorine-containing materials. Background Art

[0002] Dry gas is required in the process of treating fluorine-containing materials. At present, fresh air is usually introduced into the dehumidifier unit for dehumidification and cooling. The fresh air is filtered and cooled by the dehumidifier unit components and then passes through two-stage dehumidification wheels for dehumidification and drying. The dry gas then enters the material processing unit for corresponding treatment of the material.

[0003] For example, an energy-saving low-dew-point rotary dehumidifier (patent number CN106196346B) disclosed in a patent for invention uses a two-stage dehumidification rotary dehumidifier for dehumidification. The temperature and humidity of the mid-surface evaporator are stable during the process state, and the condensation heat of the mid-surface evaporator is recovered through the mid-surface condensing unit. Through the series energy-saving route and the parallel energy-saving route, the heat energy of the secondary condenser, the primary condenser, and the heating condenser is reduced, reducing the operating power of the unit, meeting the dual goals of low dew-point air outlet and lower regeneration temperature. However, the high enthalpy and latent heat of the fresh air and the excessive refrigeration energy consumption are not conducive to achieving the needs of energy conservation and emission reduction. Therefore, a solution is proposed to recycle the gas after material treatment to form a return air system to achieve the goal of energy conservation and emission reduction.

[0004] However, hydrogen fluoride in the material is highly corrosive and can easily damage equipment. Therefore, if you want to use the return air after dehumidification to process the material, you need to remove the hydrogen fluoride in the return air to avoid damage to the equipment. Summary of the Invention

[0005] In response to the above-mentioned defects of the prior art, the present application provides a return air system for treating fluorine-containing materials. The return air system can remove fluorine from the gas containing fluoride, cool and dehumidify it, and recycle it, thereby achieving the purpose of energy saving by treating the return air.

[0006] The present application provides a return air system for treating fluorine-containing materials, comprising a defluorination unit, an air treatment unit and a terminal treatment unit connected in sequence through a return air duct to form a circulating air duct;

[0007] The terminal treatment unit contains drying materials that need to be cooled. The high-temperature air used to dry the materials contains fluorides, which are discharged to the defluorination unit through the return air duct.

[0008] The defluorination unit is used to defluorinate and cool the high-temperature fluorine-containing air discharged from the terminal treatment unit;

[0009] The air handling unit is used to further cool and dehumidify the return air after defluorination and cooling. The return air after cooling and dehumidification enters the terminal processing unit to cool the drying material in the barrel, forming a circulating air path.

[0010] Preferably, an auxiliary processing unit is further included, which is connected between the air processing unit and the terminal processing unit through a return air duct, and performs flow stabilization and noise reduction on the return air duct and adjusts the stable air volume.

[0011] Further preferably, the auxiliary processing unit includes a static pressure box, a return air duct and a one-way valve;

[0012] The static pressure box is used to stabilize the flow and reduce noise. Its two ends are connected to the return air outlet of the air handling unit and the return air inlet of the terminal processing unit through the return air duct.

[0013] The static pressure box is also provided with a return air duct connected to the return air path at the front end of the air handling unit, so that the air overflowing from the static pressure box can flow back; a one-way valve is provided on the return air duct to ensure that the air flow in the return air duct flows from the static pressure box to the air handling unit.

[0014] Preferably, the defluorination unit includes a defluorination device, a cooling device and a defluorination fan; the return air duct is connected to the cooling device, the defluorination device and the defluorination fan in sequence;

[0015] The cooling device is a surface cooler, which cools down the high-temperature fluorine-containing air discharged from the terminal treatment unit;

[0016] The defluorination device is a defluorination tower, which is used to defluorinate the fluorine-containing air after being cooled in the return air duct;

[0017] The defluorination fan is a centrifugal fan, which is used to provide power to the return air so that the return air can overcome the resistance of the defluorination device.

[0018] Further preferably, two defluorination towers are provided in parallel, and the switch of the return air duct is controlled by three-way valves provided at the inlet and outlet of both ends of the defluorination towers, so that the two defluorination towers can be used alternately.

[0019] Preferably, the air handling unit includes a dehumidifier, a cooling unit, a heating unit, a heat exchanger, a filter, a main fan and a regeneration fan;

[0020] The air handling unit includes a return air duct and a regeneration air duct. The return air duct is discharged from the defluorination unit and sequentially connected to the main fan, filter device, cooling unit, dehumidification unit, and then enters the terminal treatment unit. The regeneration air duct is connected to the fresh air, filter device, cooling unit, heat exchanger, dehumidification unit, and then discharged after heat exchange in the heat exchanger, and desorption treatment is performed on the dehumidification unit to ensure its normal operation.

[0021] The regeneration fan is arranged on the regeneration wind path to provide power for the regeneration wind;

[0022] The heating unit heats the regeneration air to improve the desorption efficiency of the regeneration air.

[0023] Further preferably, the dehumidification unit is a dehumidification wheel; the dehumidification wheel includes a treatment area and a regeneration area; the treatment area of ​​the dehumidification wheel dehumidifies the return air duct, and the regeneration area dehydrates the high-temperature fresh air to restore the adsorption capacity of the wheel.

[0024] Preferably, the dehumidification unit includes two dehumidification wheels arranged in series in the air path, namely a first wheel and a second wheel; the heating unit includes a first steam coil and a second steam coil, the first steam coil is used to heat the fresh air entering the first wheel, and the second steam coil is used to heat the fresh air entering the second wheel.

[0025] Preferably, the terminal processing unit includes a terminal barrel and a terminal fan; after the return air is discharged from the air processing unit, it is powered by the terminal fan and sent into the terminal barrel to process the dried material in the barrel.

[0026] Further preferably, the terminal barrel and the terminal fan are both provided in plurality; the plurality of terminal fans correspond one-to-one to the plurality of terminal barrels, forming a plurality of branch air paths of the return air path in parallel.

[0027] The beneficial effects of this application include at least:

[0028] 1. The gas used to treat fluorine-containing materials can be recovered, defluorinated, cooled and dehumidified to become dry gas, and then used again to treat fluorine-containing materials. Compared with the fresh air system, which requires cooling and dehumidifying the fresh air, the return air system involved in this application consumes less energy to process the return air.

[0029] 2. The defluorination tower uses alumina adsorbent for adsorption-based defluorination, which can reduce the hydrogen fluoride concentration to zero. After the hydrogen fluoride gas is defluorinated, it can avoid corrosion to the equipment.

[0030] 3. By setting the main fan, ensure that the air supply of the dehumidifier unit is greater than that of the terminal fan to avoid negative pressure.

[0031] 4. Add a return air duct at the static pressure box. When the terminal fan does not need too much air volume, the overflow air will flow back to the main fan.

[0032] 5. Multiple branches of the terminal processing unit can be opened according to actual needs to achieve energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1A schematic diagram of the main functional units and return air flow direction of the return air system of an embodiment of the present application;

[0034] Figure 2 This is a structural diagram of an embodiment of the return air system;

[0035] Figure 3 This is a schematic diagram of the main functional components of the air handling unit of this return air system and the flow direction of return air and regeneration air;

[0036] In the figure,

[0037] 100. Fluorine removal unit:

[0038] 110. Defluorination device, 111. First defluorination tower, 112. Second defluorination tower;

[0039] 120. Cooling device;

[0040] 130. Fluorine removal fan;

[0041] 200. Air handling unit:

[0042] 210, dehumidification unit, 211, first rotor, 212, second rotor;

[0043] 220, cooling unit, 221, first chiller, 222, second chiller;

[0044] 230, heating unit, 231, first steam coil, 232, second steam coil;

[0045] 240. Heat exchanger;

[0046] 250, filtering device, 251, adsorption end filtering device, 252, desorption end filtering device;

[0047] 260, main fan;

[0048] 270, regeneration fan, 271, first regeneration fan, 272, second regeneration fan;

[0049] 300. Terminal processing unit:

[0050] 310, end barrel,

[0051] 320, terminal fan;

[0052] 400. Auxiliary processing unit:

[0053] 410, static pressure box;

[0054] 420, return air duct;

[0055] 430. One-way valve. DETAILED DESCRIPTION

[0056] The present invention is described in detail below with reference to the accompanying drawings. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of this application.

[0057] The present application provides a return air system for treating fluorine-containing materials, comprising a defluorination unit 100, an air treatment unit 200, a terminal treatment unit 300 and an auxiliary treatment unit 400. The defluorination unit 100, the air treatment unit 200 and the terminal treatment unit 300 are sequentially connected through a return air duct to form a circulating air duct. Figure 1 As shown, it is a schematic diagram of the return air flow involved in this application. There is a fluorine-containing material that needs to be treated with dry gas in the terminal treatment unit 400. The gas after treating the fluorine-containing material contains fluorine and needs to be discharged to the defluorination unit 100 for defluorination treatment. The discharged fluorine-containing gas (i.e. the return air involved in this return air system) is defluorinated and cooled in the defluorination unit 100, and then further cooled and dehumidified by the air treatment unit 200, and then enters the terminal treatment unit 300 to treat the fluorine-containing material in the terminal barrel 310, forming a circulating air path. Among them, the defluorination unit 100 includes a defluorination fan 130 for providing power to the return air so that the return air overcomes resistance. Because the defluorination device 110 in the defluorination unit 100 is tower-shaped (and upright), and enters from the bottom to the top, the internal return air resistance is very large, so it is necessary to add a defluorination fan 130 to provide power to the return air to overcome the resistance. The air handling unit 200 includes a dehumidifier unit 210. The pressure required by the dehumidifier unit 210 is not too high. It is only necessary to add a main fan 260 in front of the dehumidifier unit 210 to meet the power demand of the return air duct. An auxiliary processing unit 400 is also provided between the terminal processing unit 300 and the air handling unit 200. The auxiliary processing unit 400 includes a static pressure box 410, which is used to stabilize the airflow of the entire system, reduce airflow vibration, reduce negative pressure, and reduce noise. The two ends are respectively connected to the return air outlet of the air handling unit and the return air inlet of the terminal processing unit through the return air duct. A terminal fan 320 is also provided at the air inlet of the terminal processing unit 300 for air supply. Since the air volume demand of the terminal processing unit 300 will be adjusted according to actual conditions, its air volume demand is unstable. If the pressure of the terminal fan 320 is too high, it is easy to cause the negative pressure of the dehumidifier unit 210 to be too high, which is not conducive to the stable operation of the system. After passing through the air handling unit 200, the return air passes through the static pressure box 410 and then enters the terminal treatment unit 300. Therefore, a return air duct 420 is connected to the static pressure box 410 and connected to the return air path at the front end of the air handling unit 200. Specifically, the return air duct 420 connects the static pressure box 410 with the air inlet of the main fan 260, allowing the air overflowing from the static pressure box 410 to flow back. A one-way valve 430 is added to the return air duct 320, so that the air flow is limited to the static pressure box 410 and the air handling unit 200.

[0058] like Figure 2 This is an embodiment of the present application, in which the defluorination unit 100 includes a defluorination device 110, a cooling device 120 and a defluorination fan 130. The return air duct is connected to the cooling device 120, the defluorination device 110 and the defluorination fan 130 in sequence. Specifically, the cooling device 120 adopts a surface cooler to perform preliminary cooling treatment on the return air discharged from the terminal treatment unit 300, and the return air temperature is reduced to 30°C. The return air after cooling needs to enter the defluorination device 110 for defluorination treatment to remove hydrogen fluoride in the air. It is then sent to the air treatment unit 200 through the defluorination fan 130 for further cooling and dehumidification treatment. It should be noted that the above-mentioned defluorination fan 130 is a centrifugal fan, which is functionally the same as the fans involved in other units, and is not a fan with defluorination function.

[0059] In this embodiment, the defluorination device 110 is preferably a defluorination tower, which is used to defluorinate the fluorine-containing air after cooling in the return air duct. Specifically, the defluorination tower is vertically arranged, 3 meters or 4 meters high and about 1 meter in diameter. The return air enters from the bottom of the defluorination tower and is discharged from the top, which has a large resistance. Therefore, a defluorination fan 130 is provided to provide power to overcome the resistance. Figure 2 As shown in one embodiment, two defluorination towers are installed in parallel: a first defluorination tower 111 and a second defluorination tower 112. First defluorination tower 111 and second defluorination tower 112 are connected by a parallel return air duct. Three-way valves at the inlets and outlets of first and second defluorination towers 111 and 112 control the return air duct, enabling alternating use of the two defluorination towers, one for backup and one for active use. Once one defluorination tower is fully adsorbed, the other can be switched to ensure continuous operation of the entire return air system. The defluorination towers are adsorption-type defluorination towers with built-in alumina adsorbent.

[0060] In some embodiments, the air handling unit 200 includes a dehumidifier 210, a cooling unit 220, a heating unit 230, a heat exchanger 240, a filter 250, a main fan 260, and a regeneration fan 270. The air handling unit 200 includes two air paths, one for return air (indicated by a solid arrow) connected to other units, and the other for regeneration air (indicated by a hollow arrow) for desorption treatment of the dehumidifier 210. Figure 3 As shown, the return air path is the path indicated by the solid arrow, and the regeneration air path is the path indicated by the hollow arrow. The return air path is connected to the defluorination fan 130 and the main fan 260, and then connected to the filter device 250, the cooling unit 220, and the dehumidification unit 210 in sequence before entering the terminal treatment unit 300. Figure 2 In the embodiment shown, the return air duct is discharged from the air handling unit 200 and enters the auxiliary processing unit 400, specifically, the static pressure box 410. Figure 3As shown, the regeneration air path is connected to the fresh air, the filter device 250, the cooling unit 220, the heat exchanger 240, and the dehumidification unit 210, and then discharged after heat exchange through the heat exchanger 240. The regeneration air path mainly performs desorption treatment on the dehumidification unit 210 to ensure its normal operation. Preferably, a heating unit 230 is also provided on the regeneration air path to heat the regeneration air and improve its desorption efficiency. Specifically, the heating unit 230 is preferably a steam coil heating. Preferably, a regeneration fan 270 is also provided on the regeneration air path to provide power for the regeneration air path. It should be noted that the regeneration fan is specifically a centrifugal fan, and its function is no different from other centrifugal fans. It is not a fan with regeneration function.

[0061] Among them, Figure 2 In the illustrated embodiment, the filter device 250 is an air filter comprising an adsorption filter 251 and a desorption filter 252. The adsorption filter 251 is located on the return air path and filters the return air from the main blower 260; the desorption filter 252 is located on the regeneration air path and filters the fresh air.

[0062] The cooling unit 220 is preferably a water chiller, which further cools the return air or regenerated air after being filtered by the filter device 250 in the air path through the cold water coil, and controls the temperature to a temperature range that can enter the dehumidification wheel. Figure 2 In the illustrated embodiment, the cooling unit 220 includes a first chiller 221 and a second chiller 222. The first chiller 221 is disposed on the return air path to cool the return air within the return air path; the second chiller 222 is disposed on the regeneration air path to cool the regeneration air within the regeneration air path.

[0063] Among them, the dehumidification unit 210 is preferably a dehumidification wheel. There are two dehumidification wheels arranged in series on the air path, namely the first wheel 211 and the second wheel 212. The two dehumidification wheels can improve the dehumidification effect on the return air in the return air path. The dehumidification wheel is divided into a processing area (i.e., a dehumidification area) and a regeneration area. The wheel rotates slowly during operation, and the processing area and the regeneration area alternate. The processing area absorbs moisture from the return air, and the regeneration area dehydrates the return air through high-temperature fresh air to restore the adsorption capacity of the wheel. The return air path is connected in series with the processing area of ​​the dehumidification wheel, and the processing area of ​​the wheel dehumidifies and dries the return air; the regeneration air path is connected in series with the regeneration area of ​​the dehumidification wheel, and desorbs the adsorbed wheel area (such as Figure 2 The dehumidification wheel shown in the figure has a small fan-shaped area on the upper right that is the regeneration area). Preferably, a heating unit is used in the regeneration air path to heat the fresh air to improve the desorption efficiency. Figure 2In the specific embodiment shown, the heating unit is preferably a steam coil, including a first steam coil 231 and a second steam coil 232. Specifically, the two steam coils cooperate with two dehumidification wheels, respectively, to heat the fresh air entering the regeneration zone of the wheel, forming high-temperature dry air and improving the desorption efficiency of the wheel.

[0064] Preferably, there are two regeneration fans 270, namely a first regeneration fan 271 and a second regeneration fan 272. Figure 2 In a specific embodiment shown, the first regeneration fan 271 is disposed in the regeneration air path behind the first rotor 211 , and the second regeneration fan 272 is disposed between the second rotor 212 and the second steam coil 232 .

[0065] like Figure 2 In a specific embodiment shown, when the air handling unit 200 is working, the working process of its regeneration air path is as follows: the fresh air is filtered by the desorption end filter 252 and then cooled by the second chiller 222. After heat exchange through the heat exchanger 240, it is heated and dried by the second steam coil 232, and then enters the regeneration area of ​​the second rotor 212 to desorb the second rotor 212. After that, it is heated by the second regeneration fan 272 through the first steam coil 231 and sent to the regeneration area of ​​the first rotor 211 to desorb the first rotor 211. After that, it is sent to the heat exchanger 240 by the first regeneration fan 271 for heat exchange and then discharged.

[0066] like Figure 2 In the illustrated embodiment, the auxiliary processing unit 400 includes a static pressure box 410, a return air duct 420, and a one-way valve 430. Return air from the return air path, after being discharged from the air handling unit 200, enters the static pressure box 410 and then enters the terminal processing unit 300. The static pressure box 410 is also provided with a return air duct 420 that is connected to the return air path in front of the main fan 260, which can return overflow air and ensure stable operation of the entire return air system. Preferably, the return air duct 420 is also provided with a one-way valve 430 to ensure that overflow air flows only in one direction, toward the air handling unit 200.

[0067] In some real-time methods, specifically, the terminal processing unit 300 includes a terminal barrel 310 and a terminal fan 320. It should be noted that the terminal fan 320 is a centrifugal fan. Because it is used in the terminal processing unit 300, it is called a terminal fan for the convenience of understanding the technical solution. Its function is the same as other centrifugal fans, and it only provides power for the return air duct. Figure 2As shown in one embodiment shown, the return air is discharged from the static pressure box 410 and sent to the terminal barrel 310 through the terminal fan 320. After being discharged from the terminal barrel 310, it enters the cooling device 120 of the defluorination unit 100 to complete the return air cycle. Preferably, there are multiple terminal barrels 310 and multiple terminal fans 320. The multiple terminal fans 320 correspond one to one with the multiple terminal barrels 310, that is, each terminal barrel 310 is equipped with a terminal fan 320, forming multiple parallel return air duct branches, which are opened or closed according to actual needs. Figure 2 In a specific embodiment shown, there are three terminal barrels 310 and three terminal fans 320, and they correspond one to one, that is, there are three parallel branch air paths of the return air path, which are then aggregated to the main path of the return air path.

[0068] When the return air system is working, first of all, it is necessary to ensure that the air volume sent by the air handling unit 200 to the static pressure box 410 is greater than the air volume extracted from the static pressure box 410, so as to avoid excessive negative pressure in the air handling unit 200, and the excess air volume flows back to the air handling unit 200 through the return air duct 420. Secondly, the multiple return air branches of the terminal processing unit 300 are not necessarily fully open. For energy-saving reasons, the main fan 260 of the air handling unit 200 is frequency-controlled. When the one-way valve 430 of the return air duct 420 is opened too large, the feedback signal is given to the main fan 260 to reduce the frequency to generate an appropriate air volume. Furthermore, when the terminal processing unit 300 wants to increase the number of openings, it is necessary to feedback a signal to the main fan 260 in advance to increase the frequency and increase the air supply volume to ensure that the air supply volume is still greater than the exhaust volume after the terminal processing unit 300 is turned on.

[0069] It should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0070] The above-described embodiments of the present application do not limit the scope of protection of the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the claims of the present application.

Claims

1. A return air system for treating fluorine-containing materials, characterized in that: It includes a defluorination unit, an air treatment unit and a terminal treatment unit which are connected in sequence through a return air duct to form a circulating air duct; The terminal treatment unit contains fluorine-containing materials that need to be treated with dry gas. The gas after treating the fluorine-containing materials contains fluorine and needs to be discharged to the defluorination unit for defluorination treatment; The defluorination unit is used to defluorinate and cool the fluorine-containing gas discharged from the terminal treatment unit; the defluorination unit includes a defluorination device, a cooling device and a defluorination fan; the return air duct is connected to the cooling device, the defluorination device and the defluorination fan in sequence; The air handling unit is used to further cool and dehumidify the return air after defluorination. The return air after cooling and dehumidification enters the terminal processing unit to process the fluorine-containing material in the barrel, forming a circulating air path; The air handling unit includes a dehumidifier, a cooling unit, a heating unit, a heat exchanger, a filter, a main fan and a regeneration fan; The air handling unit includes a return air duct and a regeneration air duct; the return air duct is discharged from the defluorination unit and sequentially connected to the main fan, filter device, cooling unit, dehumidification unit, and then enters the terminal treatment unit; the regeneration air duct is connected to the fresh air, filter device, cooling unit, heat exchanger, dehumidification unit, and then discharged after heat exchange in the heat exchanger, and desorption treatment is performed on the dehumidification unit; The regeneration fan is arranged on the regeneration air path; The heating unit heats the regeneration air; An auxiliary processing unit, which is connected between the air handling unit and the terminal processing unit through a return air duct, stabilizes the flow and reduces noise in the return air duct, and adjusts the stable air volume; The auxiliary processing unit includes a static pressure box, a return air duct and a one-way valve; The static pressure box is used to stabilize the flow and reduce noise. Its two ends are connected to the return air outlet of the air handling unit and the return air inlet of the terminal processing unit through the return air duct. The static pressure box is also provided with a return air duct, which is connected to the return air path at the front end of the air handling unit to allow the air overflowing from the static pressure box to flow back; a one-way valve is provided on the return air duct to allow the air flow in the return air duct to flow from the static pressure box to the air handling unit.

2. The return air system according to claim 1, characterized in that: The cooling device is a surface cooler, which cools down the high-temperature fluorine-containing air discharged from the terminal treatment unit; The defluorination device is a defluorination tower, which is used to defluorinate the fluorine-containing air after being cooled in the return air duct; The defluorination fan is a centrifugal fan, which is used to provide power to the return air so that the return air can overcome the resistance of the defluorination device.

3. The return air system according to claim 2, characterized in that: Two defluorination towers are arranged in parallel, and the switch of the return air path is controlled by three-way valves arranged at the inlets and outlets at both ends of the defluorination towers, so that the two defluorination towers can be used alternately.

4. The return air system according to claim 1, characterized in that: The dehumidification unit is a dehumidification wheel; the dehumidification wheel includes a treatment area and a regeneration area; the treatment area of ​​the dehumidification wheel dehumidifies the return air duct, and the regeneration area dehydrates the high-temperature fresh air to restore the adsorption capacity of the wheel.

5. The return air system according to claim 4, characterized in that: The dehumidification unit includes two dehumidification wheels arranged in series on the air path, namely a first wheel and a second wheel; the heating unit includes a first steam coil and a second steam coil, the first steam coil is used to heat the fresh air entering the first wheel, and the second steam coil is used to heat the fresh air entering the second wheel.

6. The return air system according to claim 1, characterized in that: The terminal processing unit includes a terminal barrel and a terminal fan; after the return air is discharged from the air processing unit, it is powered by the terminal fan and sent into the terminal barrel to process the dried material in the barrel.

7. The return air system according to claim 6, characterized in that: The terminal barrels and terminal fans are both provided in plurality; the plurality of terminal fans correspond one-to-one to the plurality of terminal barrels, forming a plurality of branch air paths of the return air path in parallel.

Images