Drying system for particulates

Abstract

The present invention addresses the problem of proposing a drying system for particulates that has excellent energy conservation properties and that can easily achieve a good thermal balance in the system as a whole. The present invention is provided with: a continuous conduction heat-transfer type dryer 10 that dries particulates M; a condenser 20 that cools an exhaust gas G; a vacuum pump 30 that puts the interior of the drier into a reduced-pressure state; and a heat pump 40 that raises the temperature of a first heat medium α1, which has decreased as a result of said medium being used to heat the particulates in the dryer, and that cools a first refrigerant β1 the temperature of which has increased as a result of said refrigerant being used to cool the exhaust gas in the condenser. This drying system for particulates is configured so that, using the heat pump, the temperature of the first refrigerant is lowered by 3-15°C and the first refrigerant is circulated and supplied to the condenser at a temperature of 12-35°C, and the temperature of the first heat medium is raised by 3-15°C and the first heat medium is circulated and supplied to the dryer at a temperature of 65-98°C.

Description

Powdery or granular material drying system

[0001] The present invention relates to a drying system for powdery or granular materials. In particular, the present invention relates to a powdery or granular material drying system that efficiently achieves energy saving by using a heat pump.

[0002] Drying operations can be broadly classified by heat transfer methods and contact methods with the processing target. Various modes exist depending on combinations of these, as well as combinations with the conveying method of the processing target and the like. The heat transfer methods include direct heating, indirect heating, heating by electromagnetic waves, and the like. The contact methods with the processing target include stationary type, airflow type, stirring type, fluidized bed type, and the like.

[0003] In drying operations, measures are devised to efficiently apply thermal energy to the processing target in order to promote the evaporation of water and solvents. Here, the solvent refers to moisture remaining in the processing target and all liquids used as solvents or dispersion media in the manufacturing process, and is hereinafter also referred to as "volatile matter". Furthermore, studies such as reducing the pressure have also been conducted to lower the boiling point of the volatile matter.

[0004] For example, as an example of a drying system used for materials of industrial products, there is a fluidized bed drying system. However, general fluidized bed drying systems have the problems that the apparatus becomes large-scaled and a large amount of exhaust gas is generated. The exhaust gas in the drying operation contains volatile organic compounds (hereinafter referred to as "VOC") derived from monomers and the like originating from the raw materials of the processed powdery or granular material, not only in the case of drying organic solvents but also in the case of drying water. Therefore, a regenerative thermal oxidizer (hereinafter referred to as "RTO") capable of removing VOC is introduced in the exhaust process. However, since the exhaust gas flow rate is large in the fluidized bed drying system, there is also a problem that the equipment cost and running cost of this RTO increase.

[0005] High-temperature drying is unsuitable for drying substances with low thermal decomposition points, softening temperatures, or melting points. One example of a drying method for such powders and granules is a vacuum drying system, which dries under vacuum or reduced pressure. In this vacuum drying system, volatile components in the powder or granules can be evaporated and dried without raising the powder or granules to high temperatures. Therefore, it has the advantage of easily reducing residual components such as VOCs. On the other hand, under reduced pressure, it is difficult to efficiently transfer a large amount of heat by heating with hot air alone. For this reason, conductive heat transfer from the dryer casing, etc., is used in combination to raise the temperature to near the boiling point of the volatile components and perform drying. In addition, general vacuum drying systems have the problem that continuous supply and discharge of powders and granules is difficult, making them unsuitable for large-scale processing.

[0006] Therefore, in order to solve the above-mentioned problems, the applicant has previously developed a continuous conduction heat transfer type dryer that continuously supplies powdered or granular raw materials, supplies a heating medium to a stirring means under reduced pressure, and performs drying treatment of powdered or granular raw materials by heating while stirring, and has filed a patent application (Patent Document 1).

[0007] International Publication No. 2023 / 203974

[0008] However, the continuous conduction heat transfer dryer disclosed in Patent Document 1, etc., has problems from an energy-saving standpoint because it uses a large amount of fossil fuels to supply the amount of heat required for drying. In other words, the thermal energy of the heat transfer medium heated by fossil fuels is absorbed as internal energy (sensible heat and latent heat) into the evaporated volatile components and discharged outside the dryer as exhaust gas. This exhaust gas is condensed and discharged in a condenser installed to reduce the load on the vacuum pump. On the other hand, the thermal energy exchanged in the condenser is absorbed into the refrigerant circulating within the condenser and is dissipated as heat without being utilized by a cooling tower or chiller.

[0009] This invention has been made in view of the problems of the background technology described above. Its purpose is to reuse the thermal energy previously used for the evaporation of volatile components, which was then wasted heat, by using a heat pump to raise the temperature of the heat transfer medium. This provides a drying system for powders and granules that is highly energy-efficient and allows for easy adjustment of the overall thermal balance of the system.

[0010] To achieve the above-mentioned objectives, the present invention provides a drying system for powders and granules as described in [1] to [7] below. [1] A drying system for powders and granules, comprising: a continuous conduction heat transfer dryer that indirectly heats a continuously supplied powder or granules with a first heat transfer medium; a condenser that indirectly cools exhaust gas discharged from the dryer with a first refrigerant to condense volatile components in the exhaust gas; a vacuum pump that creates a reduced pressure inside the dryer by vacuum sucking the exhaust gas through the condenser; and a heat pump that raises the temperature of the first heat transfer medium, which has been used to heat the powder or granules in the dryer and whose temperature has decreased, and cools the first refrigerant, which has been used to cool the exhaust gas in the condenser and whose temperature has increased, wherein the heat pump lowers the temperature of the first refrigerant in the range of 3 to 15°C and circulates it to the condenser as a first refrigerant at a temperature of 12 to 35°C, and raises the temperature of the first heat transfer medium in the range of 3 to 15°C and circulates it to the dryer as a first heat transfer medium at a temperature of 65 to 98°C. [2] The drying system for powders and granules according to [1], characterized in that the first heat transfer medium is water. [3] The drying system for powders and granules according to [1] or [2], characterized in that the dryer has a casing, a supply port for powders and granules provided at the top of one end of the casing, a discharge port for powders and granules provided at the bottom of the other end of the casing, and an exhaust port for exhaust gas provided at the top of the casing, the exhaust port being connected to the vacuum pump which reduces the pressure inside the casing, a hollow shaft being rotatably spanned inside the casing, hollow stirring means being arranged on the hollow shaft at predetermined intervals, and the first heat transfer medium being supplied to the hollow shaft and the hollow stirring means to heat the powders and granules while stirring under reduced pressure.[4] The powder drying system according to any one of [1] to [3] above, characterized in that the heat pump comprises an expansion valve for expanding a heat exchange medium, a first heat exchanger that performs heat exchange between the heat exchange medium expanded by the expansion valve and the first refrigerant used to cool the exhaust gas and whose temperature has risen, a compressor for compressing the heat exchange medium that has undergone heat exchange in the first heat exchanger, and a second heat exchanger that performs heat exchange between the heat exchange medium compressed by the compressor and the first heat medium used to heat the processed powder and granules and whose temperature has dropped. [5] The powder drying system according to any one of [1] to [4] above, further comprising an air heater for heating a carrier gas supplied into the dryer, and a second heat medium for heating the air heater is added to the first heat medium and heat is exchanged with the first refrigerant in the heat pump. [6] A drying system for powders and granules according to any one of [1] to [5] above, characterized in that a second refrigerant for cooling the vacuum pump is added to the first refrigerant and heat is exchanged with the first heat medium in the heat pump. [7] A drying system for powders and granules according to any one of [1] to [6] above, characterized in that the dryer is a continuous conduction heat transfer type dryer that performs constant rate drying and loss rate drying of powders and granules.

[0011] The powder drying system according to the present invention described above includes a heat pump that raises the temperature of the first heat medium used to heat the powder in the dryer, which has decreased in temperature, and cools the first refrigerant used to cool the exhaust gas in the condenser, which has increased in temperature. This configuration results in a powder drying system with excellent energy efficiency. Furthermore, the powder drying system according to the present invention uses the heat pump to lower the temperature of the first refrigerant in the range of 3 to 15°C and circulate it to the condenser as a first refrigerant at a temperature of 12 to 35°C, and raises the temperature of the first heat medium in the range of 3 to 15°C and circulates it to the dryer as a first heat medium at a temperature of 65 to 98°C. Therefore, it is possible to achieve efficient heat exchange without putting a load on the heat pump, and it is a powder drying system that can easily maintain the overall thermal balance of the system.

[0012] A block diagram showing one embodiment of the powder and granular material drying system according to the present invention. A partially cutaway side view showing an example of a dryer used in the powder and granular material drying system according to the present invention. An enlarged cross-sectional view of the portion along the line X-X in Figure 2. A conceptual diagram showing an example of an air lock valve. A diagram showing the powder and granular material feeding process in the air lock valve of Figure 4. A conceptual diagram showing an example of a heat pump used in the powder and granular material drying system according to the present invention.

[0013] Hereinafter, one embodiment of the powder drying system according to the present invention will be described in detail with reference to the drawings.

[0014] As shown in Figure 1, the powder drying system 100 according to the present invention comprises at least the following components: a continuous conduction heat transfer dryer 10 that indirectly heats a continuously supplied powder M with a first heat transfer medium α1; a condenser 20 that indirectly cools the exhaust gas G discharged from the dryer 10 with a first refrigerant β1 to condense the volatile components in the exhaust gas G; a vacuum pump 30 that creates a reduced pressure inside the dryer 10 by vacuum sucking the exhaust gas G through the condenser 20; and a heat pump 40 that raises the temperature of the first heat transfer medium α1, which has decreased in temperature after being used to heat the powder M in the dryer 10, and cools the first refrigerant β1, which has increased in temperature after being used to cool the exhaust gas G in the condenser 20.

[0015] The dryer 10 used in the powder drying system 100 according to the present invention can have the configuration shown in Figures 2 and 3. Specifically, it has a horizontally elongated casing 11, a supply port 12 for powder (raw material) M provided at the upper part of one end of the casing 11, a discharge port 13 for dried powder (product) M provided at the lower part of the other end of the casing 11, and an exhaust port 14 for exhaust gas G provided at the upper part of the casing 11. The exhaust port 14 is connected to the vacuum pump 30 which reduces the pressure inside the casing 11 (see Figure 1). A hollow shaft 15 is rotatably spanned inside the casing 11, and a plurality of hollow stirring means 16 are arranged on the hollow shaft 15 at predetermined intervals. Furthermore, by supplying the first heat transfer medium α1 to the hollow shaft 15 and the hollow stirring means 16, a continuous conduction heat transfer type dryer can be constructed that indirectly heats the powder M while stirring it under reduced pressure.

[0016] The supply port 12 and discharge port 13 for the granular material M provided in the casing 11 may each be equipped with an airlock valve 17 for continuously supplying and discharging the granular material M in an airtight state. The airlock valve 17 can be configured as follows, conceptually shown in Figure 4: a valve casing 18 having an inlet 18A opening upwards and an outlet 18B opening downwards, and a valve 19 rotatably provided within the valve casing 18 to either close the inlet 18A or close the outlet 18B. The granular material M is then introduced into the valve casing 18 from the inlet 18A with the valve 19 closed only at the outlet 18B (Figure 5(a)). Next, the valve 19 is rotated to close both the outlet 18B and the inlet 18A (Figure 5(b)), and then to close only the inlet 18A (Figure 5(c)). This causes the granular material M inside the valve casing 18 to be discharged from the outlet 18B and airtightly introduced into the casing 11 via the supply port 12 (or discharged outside the casing 11 via the discharge port 13).

[0017] In addition to the hollow shaft 15 and hollow stirring means 16 described above, the heating means for the powdered material M may also be configured such that the casing 11 has a double-layer structure (jacket structure), as shown in Figure 3, and the first heat transfer medium α1 is supplied to this double-layer casing 11 as well. This allows the powdered material M to be indirectly heated from the casing 11. The hollow stirring means 16 can be disc-shaped, paddle-shaped, or screw-shaped. However, a disc shape is preferred because it can secure a large heat transfer area in contact with the material to be processed. Furthermore, the hollow stirring means 16 may be provided with scraping members or pins as needed.

[0018] The dryer 10 described above maintains a reduced pressure state of 30 kPa or less absolute pressure inside the casing 11 by the vacuum pump 30. Furthermore, it is preferable to use an embodiment in which a first heat transfer medium α1 at a temperature of 65 to 98°C is supplied to the heating means, such as the hollow shaft 15 and the hollow stirring means 16, and the heat for drying is released to the powder M, causing the first heat transfer medium α1 to drop to a temperature in the range of 3 to 15°C before being discharged from the heating means, such as the hollow shaft 15 and the hollow stirring means 16. This is preferable because, by creating a reduced pressure state using the vacuum pump 30 and a heated state using the first heat transfer medium α1 in the dryer 10, even powders and granules such as organic matter and chemicals that are sensitive to heat can be dried without causing thermal degradation by lowering the boiling point of volatile components, and efficient heat exchange can be achieved without placing a load on the heat pump 40, which will be described in detail later. From this viewpoint, it is particularly preferable to use this embodiment in which the vacuum pump 30 reduces the pressure inside the casing 11 to an absolute pressure of 5 to 20 kPa, a first heat transfer medium α1 at a temperature of 70 to 98°C is supplied to heating means 15, 16, etc., and the first heat transfer medium α1 that has cooled to a temperature in the range of 5 to 10°C is discharged from the heating means 15, 16, etc.

[0019] As shown in Figure 1, the dryer 10 may be configured to include an air heater 50. The air heater 50 may be configured to indirectly heat outside air drawn in through an air filter 51 using a second heat transfer medium α2. By supplying the air heated by this air heater 50 as a carrier gas a into the casing 11 of the dryer 10 by the suction force of the vacuum pump 30, condensation of evaporated volatile components contained in the exhaust gas G inside the dryer 10 and the bag filter 60 (described later) can be prevented, and fine powder can be prevented from adhering to the inner walls of the dryer 10 and the bag filter 60.

[0020] Furthermore, a bag filter 60 for collecting fine particles contained in the exhaust gas G can be provided between the dryer 10 and the condenser 20 which cools the exhaust gas (including the carrier gas a if the configuration is such that air heated by the air heater 50 is supplied to the casing 11 of the dryer 10 as carrier gas a). This bag filter 60 can be configured to include a backwasher 61 and a knocker 62, with the backwasher 61 removing fine particles adhering to the bag inside the bag filter 60, and the knocker 62 preventing fine particles from accumulating in the conical part at the bottom of the bag filter 60. The fine particles m collected by the bag filter 60 are returned to the dryer 10 through a fine particle discharge valve 63 attached to the bottom of the bag filter 60, as shown in Figure 1.

[0021] The exhaust gas G, from which fine particles have been removed by the bag filter 60, has its volatile components condensed in the condenser 20. Further, the volatile mist is collected in the demister 21 located downstream of the condenser. The gaseous components are sucked in as exhaust gas G by the vacuum pump 30 and discharged after passing through the separator 31 located downstream of the vacuum pump 30. Meanwhile, the condensate generated in the condenser 20 and the mist collected in the demister 21 are temporarily stored in the condensate tank 22, as shown in Figure 1, and discharged by the condensate drain pump 23.

[0022] The condenser 20 is configured to indirectly cool the exhaust gas G with a first refrigerant β1. From the viewpoint of achieving efficient heat exchange without placing a load on the heat pump 40, which will be described in detail later, and from the viewpoint of easily balancing the overall thermal state of the system, the first refrigerant β1 is preferably used in an embodiment in which it is supplied to the condenser 20 at a temperature of 12 to 35°C, absorbs heat from the exhaust gas G and is heated to a temperature of 3 to 15°C before being discharged from the condenser 20. Furthermore, from the same viewpoint, it is particularly preferable to use in an embodiment in which it is supplied to the condenser 20 at a temperature of 15 to 30°C, absorbs heat from the exhaust gas G and is heated to a temperature of 5 to 10°C before being discharged from the condenser 20.

[0023] The vacuum pump 30 that sucks exhaust gas G from the dryer 10 via the bag filter 60 and the condenser 20 can be a water-sealed pump or a dry pump cooled by a second refrigerant β2.

[0024] The heat pump 40, which raises the temperature of the first heat transfer medium α1 used to heat the powder M in the dryer 10 and cools the first refrigerant β1 used to cool the exhaust gas G in the condenser 20 and has increased in temperature, can be as shown in the conceptual configuration diagram of Figure 6. That is, it can be a heat pump comprising an expansion valve 41 for expanding the heat exchange medium γ, a first heat exchanger 42 for performing heat exchange between the heat exchange medium γ expanded by the expansion valve 41 and the first refrigerant β1 used to cool the exhaust gas G in the condenser 20 and has increased in temperature, a compressor 43 for compressing the heat exchange medium γ that has been heat-exchanged in the first heat exchanger 42, and a second heat exchanger 44 for performing heat exchange between the heat exchange medium γ compressed by the compressor 43 and the first heat transfer medium α1 used to heat the powder M in the dryer 10 and has decreased in temperature.

[0025] As the heat exchange medium γ used in the heat pump 40, various known heat exchange mediums such as fluorocarbon-based mediums (HFC-245fa, etc.), non-fluorocarbon-based mediums (R-1234ze(E), etc.), ammonia, carbon dioxide, and air can be used. Among these, non-fluorocarbon-based mediums (R-1234ze(E), etc.) and carbon dioxide, which have a low environmental impact, can be preferably used. Furthermore, it is preferable to use water as the first heat transfer medium α1. The first refrigerant β1 can be appropriately changed depending on the type of volatile components in the exhaust gas G condensed in the condenser 20, but water may be used if there are no problems.

[0026] In the above-described drying system for granular materials, the following configuration is preferable from the viewpoint of further improving the effective use (reuse) of thermal energy. Specifically, it is preferable to have a configuration in which a second heat transfer medium α2, which heats the air heater 50 used to heat the carrier gas a supplied to the dryer 10, is added to the first heat transfer medium α1 and heat-exchanged with the first refrigerant β1 in the heat pump 40. It is also preferable to have a configuration in which a second refrigerant β2, which cools the vacuum pump 30 that sucks in exhaust gas G, is added to the first refrigerant β1 and heat-exchanged with the first heat transfer medium α1 in the heat pump 40. Furthermore, as shown in Figure 1, a configuration in which heat exchange is performed in the heat pump 40 with both the first heat transfer medium α1 and the second heat transfer medium α2, and with both the first refrigerant β1 and the second refrigerant β2. In this case, water can be used as the second heat transfer medium α2 that heats the air heater 50, just as with the first heat transfer medium α1. Furthermore, as shown in Figure 1, a heat medium tank 45 for storing the first heat medium α1 and the second heat medium α2 can be provided upstream of the heat pump 40, and a heat medium pump 46 can be provided to suck the heat mediums α1 and α2 from the heat medium tank 45 and send them to the heat pump 40. Also, water can be used as the second refrigerant β2 for cooling the vacuum pump 30, similar to the first refrigerant β1, and a refrigerant tank 47 for storing the first refrigerant β1 and the second refrigerant β2 can be provided upstream of the heat pump 40, and a refrigerant pump 48 can be provided to suck the refrigerants β1 and β2 from the refrigerant tank 47 and send them to the heat pump 40.

[0027] The powder drying system 100 according to the present invention is configured such that, through heat exchange between the first heat medium α1 and the first refrigerant β1 in the heat pump 40 described above, the temperature of the first refrigerant β1 is lowered to a range of 3 to 15°C and circulated to the condenser 20 as the first refrigerant β1 at a temperature of 12 to 35°C, and the temperature of the first heat medium α1 is raised to a range of 3 to 15°C and circulated to the dryer 10 as the first heat medium α1 at a temperature of 65 to 98°C. By performing heat exchange between the refrigerant side and the heat medium side in the heat pump 40 within this temperature range, efficient heat exchange can be achieved without placing a load on the heat pump 40. This is because if the temperature difference between the supply temperature of the heat medium side (65 to 98°C) and the supply temperature of the refrigerant side (12 to 35°C) is too large, the workload of the compressor 43 of the heat pump 40 increases, and the efficiency (COP) of the heat pump decreases. Furthermore, if the temperature difference between the heat transfer medium inlet and outlet (3 to 15°C) and the temperature difference between the refrigerant inlet and outlet (3 to 15°C) is too small, the required flow rate of the medium for heat exchange will become enormous, which will put a load on the heat exchangers 42 and 44 of the heat pump 40. From this viewpoint, it is more preferable that the heat pump 40 lowers the temperature of the first refrigerant β1 in the range of 5 to 10°C and circulates it to the condenser 20 as the first refrigerant β1 at a temperature of 15 to 30°C, and raises the temperature of the first heat transfer medium α1 in the range of 5 to 10°C and circulates it to the dryer 10 as the first heat transfer medium α1 at a temperature of 70 to 98°C. Furthermore, it is particularly preferable that the heat pump 40 exchanges heat between both the first heat transfer medium α1 and the second heat transfer medium α2, and between both the first refrigerant β1 and the second refrigerant β2, and circulates and supplies the heat transfer mediums α1 and α2, or the refrigerants β1 and β2, within the above temperature range to the equipment, respectively.

[0028] In this invention, as described above, a heat pump 40 is used to perform heat exchange between the heat medium and the refrigerant circulating within the system, thereby effectively utilizing (reusing) thermal energy. For this reason, it is less susceptible to instability and disturbances on the heat source side, unlike heat pumps that utilize other heat sources, such as the atmosphere or geothermal energy. That is, since both the heat medium and the refrigerant are thermal energy within the same continuous process, stable heat exchange is maintained. Furthermore, when the thermal energy on both the heat medium and refrigerant sides is utilized without excess, the output heat on the heat medium side may increase due to the driving power of the heat pump 40, potentially disrupting the overall thermal balance of the system. In this case, as shown in Figure 1, by providing a chiller (cooling device) 70 in the refrigerant circulation line, the overall thermal balance of the system can be easily adjusted, enabling stable continuous drying.

[0029] The powders and granules M to be processed by the drying system 100 according to the present invention, as described above, are not particularly limited. They can be widely used for drying synthetic resins, foods, chemical products, etc. While the particle size and moisture content are not particularly limited, considering the fluidity within the dryer, the median diameter (D50) is preferably 1 μm to 1000 μm. The moisture content is preferably 10 to 70% WB. The moisture content in the processed powders and granules consists of residual moisture in the material being processed and any liquids used as solvents or dispersion media in the manufacturing process; any commonly used solvent is acceptable.

[0030] Next, an embodiment of a method for drying powders and granules using the powder drying system 100 according to the present invention described above will be specifically explained.

[0031] A vacuum pump (water-sealed pump) 30 reduces the pressure inside the dryer 10 to an absolute pressure of 9.3 kPa. Inside the dryer 10, the hollow shaft 15 and the hollow stirring means 16 are heated and rotated by a first heat transfer medium (water, temperature 87°C, supply rate 389802 kg / h) α1. Powdered material (polyvinyl chloride (PVC), median diameter 170 μm, moisture content 22% WB) M is continuously supplied to this dryer 10 (manufactured by Nara Machine Works Co., Ltd., model NVD-28, stirring means diameter 2800 mm) from the supply port 12 via an air lock valve 17 at a rate of 12500 kg (DB) / h. In addition, air heated by an air heater 50 (carrier gas a) is supplied into the dryer 10 by the suction force of the vacuum pump 30. The air heater 50 is heated by a second heat transfer medium (water, temperature 87°C, supply rate 1824 kg / h) α2.

[0032] The granular material M supplied into the dryer 10 is heated by conductive heat transfer from heating means 15, 16, etc., which are heated by the first heat transfer medium α1, and is dried through a constant-rate drying region and a decrease-rate drying region. The granular material M, dried to a moisture content of 0.2% WB, is continuously discharged from the discharge port 13 located at the other end of the lower part by activating the air lock valve 17. Meanwhile, the first heat transfer medium α1, which is supplied to the heating means 15, 16, etc. of the dryer 10 and whose temperature has dropped from 87°C to 82°C for heating the granular material M, is sent to the heat transfer medium tank 45 via piping. In addition, the second heat transfer medium α2, which is supplied to the air heater 50 for heating the carrier gas a and whose temperature has dropped from 87°C to 82°C, is also sent to the heat transfer medium tank 45 via piping.

[0033] The exhaust gas (including carrier gas a) G, which contains volatile components evaporated from the granular material M, is sucked out of the dryer 10 by the vacuum pump 30, fine particles are removed by the bag filter 60, and the exhaust gas flows into the condenser 20. The fine particles m collected in the bag filter 60 are returned to the dryer 10 via the fine particle discharge valve 63. The condenser 20 is cooled by the first refrigerant (water temperature: 20°C, supply rate: 191031 kg / h) β1, which absorbs heat from the exhaust gas G flowing into the condenser 20, condenses and removes volatile components in the exhaust gas G, is sucked into the vacuum pump 30, and exhausted via the separator 31. The condensate produced by the condenser 20 is temporarily stored in the condensate tank 22 and drained by the condensate drainage pump 23. The vacuum pump 30 is cooled by the supply of the second refrigerant (water temperature: 20°C, supply rate: 30000 kg / h) β2 as a sealant.

[0034] The first refrigerant β1, supplied to the condenser 20 and whose temperature rises from 20°C to 30°C due to the condensation of volatile components in the exhaust gas G, is sent to the refrigerant tank 47 via piping. Similarly, the second refrigerant β2, supplied to cool the vacuum pump 20 and whose temperature rises from 20°C to 30°C, is also sent to the refrigerant tank 47 via piping.

[0035] The first heat transfer medium α1 and the second heat transfer medium α2 sent to the heat transfer medium tank 45 are sent to the heat pump 40 by the heat transfer medium pump 46, and the first refrigerant β1 and the second refrigerant β2 sent to the refrigerant tank 47 are sent to the heat pump 40 by the refrigerant pump 48. Then, in the heat pump 40, heat exchange takes place between the heat transfer mediums α1 and α2 and the refrigerants β1 and β2. The temperature of the refrigerants β1 and β2 is lowered by 10°C to 20°C and circulated to the condenser 20 and the vacuum pump 30, and the temperature of the heat transfer mediums α1 and α2 is raised by 5°C to 87°C and circulated to the dryer 10 and the air heater 50.

[0036] The first heat transfer medium α1, heated to 87°C and circulated to the dryer 10, is used to heat the powder M as a heat source for the hollow shaft 15 and hollow stirring means 16, which are heating means of the dryer 10, as described above. The second heat transfer medium α2, heated to 87°C and circulated to the air heater 50, is used to heat the air as a heat source for the air heater 50, as described above. On the other hand, the first refrigerant β1, cooled to 20°C and circulated to the condenser 20, is used to cool the condenser 20 and condense the volatile components in the exhaust gas G, as described above. The second refrigerant β2, cooled to 20°C and circulated to the vacuum pump 30, is used to cool the vacuum pump 30, as described above.

[0037] As the above cycle is repeated, the drying operation can be performed continuously using only the power of the operating pump and other equipment, without supplying new thermal energy as a heat source. This enables efficient drying of powders and granules. If the supply of power to the operating pump and other equipment disrupts the balance of heat in the entire system, a chiller 70 installed in the line through which the refrigerant circulates will appropriately absorb thermal energy from the passing refrigerant.

[0038] Table 1 shows the inlet temperature, outlet temperature, input rate, thermal energy at the inlet, thermal energy at the outlet, and heat exchange rate ΔQ for the first heat transfer medium α1 of the dryer 10, the second heat transfer medium α2 of the air heater 50, the first refrigerant β1 of the condenser 20, and the second refrigerant β2 of the vacuum pump 30 in the specific powder drying operation described above. The specific heat of water was assumed to be 1 kcal / kg°C, and the conversion was performed using 860 kcal / h = 1 kW.

[0039]

[0040] Table 1 shows that the absolute values ​​of the heat exchange amounts on the heat transfer fluid α1, α2 side and the refrigerant β1, β2 side are approximately equal. Therefore, it can be seen that heat exchange can be carried out smoothly and continuously using the heat pump 40 without any excess thermal energy on either the heat transfer fluid side or the refrigerant side.

[0041] Table 2 shows the energy consumption (electricity usage) of various devices in the above-described specific drying operation of powder and granular material. Table 3 shows the energy consumption (electricity usage and steam usage) of various devices in a conventional system in which the heat medium is heated and circulated by a heater without using a heat pump, and the refrigerant is cooled and circulated by a chiller.

[0042]

[0043] When the electricity usage (1774.34 kW) of the drying system according to the present invention in Table 2 is converted to the electricity usage per 1 t of processed powder and granular material (PVC), it becomes 1774.34 (kW) / 12500 (kg / h) × 0.001 (t / kg) = 141.95 (kWh / tPVC), and when converted at 1 kWh = 3.6 MJ, it becomes 141.95 (kWh / tPVC) × 3.6 (MJ / kWh) = 511.02 (MJ / tPVC).

[0044] The electricity usage (1358.31 kW) of the conventional system without a heat pump in Table 3, by performing the same conversion as above, becomes 1358.31 (kW) / 12500 (kg / h) × 0.001 (t / kg) = 108.66 (kWh / tPVC), and 108.66 (kWh / tPVC) × 3.6 (MJ / kWh) = 391.18 (MJ / tPVC). For the steam usage (2994.09 kg / h) in Table 3, when converted using the value of 503.2 (kcal / kg) of steam latent heat (determined by the temperature and pressure of steam), which indicates the amount of heat of the saturated steam used per hour, it becomes 2994.09 (kg / h) × 503.2 (kcal / kg) = 1506626.09 (kcal / h), and 1 kcal = 4186 × 10 -6 When converted in MJ, 1506626.09 (kcal / h) × 4186 × 10 -6(MJ / kcal) = 6306.74 (MJ / h), and subsequently, when converted per 1 t of treated powder and granular material (PVC), it is 6306.74 (MJ / h) / 12500 (kg / h) × 0.001 (t / kg) = 504.53 (MJ / tPVC). From the above, the energy consumption in the conventional system of Table 3 is 391.18 (MJ / tPVC) + 504.53 (MJ / tPVC) = 895.71 (MJ / tPVC).

[0045] From the above, the energy consumption of the drying system according to the present invention is 511.02 MJ / tPVC, and the energy consumption of the conventional drying system is 895.71 MJ / tPVC. Accordingly, it is found that the drying system of the present invention can effectively utilize (reuse) thermal energy, and can reduce the energy consumption by about 43%.

[0046] While the embodiments of the drying system for powder and granular material according to the present invention have been described above, it goes without saying that the technical scope of the present invention is not limited to the scope described in the above embodiments. It is apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. In addition, it is apparent from the description of the claims that modes with such modifications or improvements can also be included in the technical scope of the present invention.

[0047] The drying system for powder and granular material according to the present invention can be widely used for drying and producing powder and granular materials in a wide range of fields such as synthetic resins, foods, and chemical products.

[0048] 100: Powder drying system, 10: Dryer, 11: Casing, 12: Powder supply port, 13: Powder discharge port, 14: Exhaust gas outlet, 15: Hollow shaft, 16: Hollow stirring means, 17: Air lock valve, 18: Valve casing, 18A: Inlet, 18B: Outlet, 19: Valve, 20: Condenser, 21: Demister, 22: Condenser tank, 23: Condenser drainage pump, 30: Vacuum pump, 31: Separator, 40: Heat pump, 41 : Expansion valve, 42: First heat exchanger, 43: Compressor, 44: Second heat exchanger, 45: Heat transfer fluid tank, 46: Heat transfer fluid pump, 47: Refrigerant tank, 48: Refrigerant pump, 50: Air heater, 51: Air filter, 60: Bag filter, 61: Backwasher, 62: Knocker, 63: Fine particle discharge valve, 70: Chiller, M: Powder / granules, G: Exhaust gas, a: Carrier gas, m: Fine particles, α1: First heat transfer fluid, α2: Second heat transfer fluid, β1: First refrigerant, β2: Second refrigerant, γ: Heat exchange medium

Claims

1. A drying system for powders and granules comprising: a continuous conduction heat transfer dryer that indirectly heats a continuously supplied powder or granules with a first heat transfer medium; a condenser that indirectly cools the exhaust gas discharged from the dryer with a first refrigerant to condense the volatile components in the exhaust gas; a vacuum pump that creates a reduced pressure inside the dryer by vacuum sucking the exhaust gas through the condenser; and a heat pump that raises the temperature of the first heat transfer medium, which has been used to heat the powder or granules in the dryer and whose temperature has decreased, and cools the first refrigerant, which has been used to cool the exhaust gas in the condenser and whose temperature has increased, wherein the heat pump lowers the temperature of the first refrigerant in the range of 3 to 15°C and circulates it to the condenser as a first refrigerant at a temperature of 12 to 35°C, and raises the temperature of the first heat transfer medium in the range of 3 to 15°C and circulates it to the dryer as a first heat transfer medium at a temperature of 65 to 98°C.

2. The drying system for powders and granules according to claim 1, characterized in that the first heat transfer medium is water.

3. The drying system for powders and granules according to claim 1 or 2, characterized in that the dryer has a casing, a supply port for powders and granules provided at the top of one end of the casing, a discharge port for powders and granules provided at the bottom of the other end of the casing, and an exhaust port for exhaust gas provided at the top of the casing, the exhaust port being connected to the vacuum pump that reduces the pressure inside the casing, a hollow shaft being rotatably spanned inside the casing, hollow stirring means being arranged on the hollow shaft at predetermined intervals, and the first heat transfer medium being supplied to the hollow shaft and the hollow stirring means to heat the powders and granules while stirring under reduced pressure.

4. The drying system for powders and granules according to claim 1 or 2, characterized in that the heat pump comprises an expansion valve for expanding a heat exchange medium, a first heat exchanger for performing heat exchange between the heat exchange medium expanded by the expansion valve and the first refrigerant used for cooling the exhaust gas and whose temperature has risen, a compressor for compressing the heat exchange medium that has undergone heat exchange in the first heat exchanger, and a second heat exchanger for performing heat exchange between the heat exchange medium compressed by the compressor and the first heat medium used for heating the processed powders and granules and whose temperature has dropped.

5. A drying system for powders and granules according to claim 1 or 2, further comprising an air heater for heating the carrier gas supplied into the dryer, and characterized in that a second heat transfer medium for heating the air heater is added to the first heat transfer medium and heat is exchanged with the first refrigerant in the heat pump.

6. A drying system for powders and granules according to claim 1 or 2, characterized in that a second refrigerant for cooling the vacuum pump is added to the first refrigerant and heat is exchanged with the first heat transfer medium in the heat pump.

7. The drying system for powders and granules according to claim 1 or 2, characterized in that the dryer is a continuous conduction heat transfer type dryer that performs constant rate drying and loss rate drying of powders and granules.

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