Low-temperature closed-cycle spray drying system

Abstract

The invention discloses a low-temperature closed cycle spray drying system. Comprising a material liquid batching and conveying device, a material liquid drying device, a material-gas separation device, a product collection device, a solvent recovery device, a gas medium dehumidification device, a gas medium heating and filtering device, an induced draft fan, a waste heat recovery device, a second throttling valve, an air feeder, an oxygen content detector, a gulp valve, an isolating valve, an exhaust valve and a regeneration heater. By arranging the induced draft fan and the air feeder, a double-fan closed-loop circulation process is formed, so that the interior of the material liquid drying device is in a negative pressure state, solvent evaporation is facilitated, low-temperature drying is achieved, and the device is suitable for drying heat-sensitive materials; the waste heat recovery device is arranged, and evaporation and condensation circulation of a refrigerant are utilized, so that moisture-containing mixed gas is cooled, and condensation, recovery and cyclic utilization of a solvent are realized; and meanwhile, heat released by condensation of the moisture-containing mixed gas is used for carrying out primary heat regeneration and waste heat recovery on a dry gas medium discharged from the gas medium dehumidification device, so that energy and production cost are saved.

Description

Technical Field

[0001] The invention relates to the technical field of powder material drying systems, and in particular to a low-temperature closed-circuit spray drying system. Background Art

[0002] Spray drying is a method in which liquid materials are atomized and dispersed into very fine mist-like droplets, which come into contact with high-temperature hot air in a drying chamber. Due to the large contact area, the water is quickly vaporized to obtain a dry powder product.

[0003] The drying medium of the closed-loop spray drying system adopts a closed-loop circulation flow mode, and usually uses inert gases such as nitrogen as the heating circulation gas, which can keep the system working in a low-oxygen state. At the same time, the system maintains a slightly positive pressure state to prevent outside air from entering the device.

[0004] The existing spray drying system still has certain shortcomings when in use. The drying process uses heated high-temperature gas for drying, which can easily cause damage to heat-sensitive materials. At the same time, the temperature of the exhaust gas after drying is relatively high. The closed-loop system for dehumidification and solvent recovery requires cooling of the circulating gas, resulting in a large amount of heat loss and low energy utilization. Summary of the invention

[0005] In order to solve the problems that the above-mentioned existing closed-loop circulation spray drying system uses heated high-temperature gas for drying during the drying process, which is easy to cause damage to heat-sensitive materials, and the temperature of the exhaust gas after drying is relatively high, and the closed-loop circulation system dehumidification solvent recovery needs to cool the circulating gas, resulting in a large amount of heat loss and low energy utilization rate, the present invention provides a low-temperature closed-loop circulation spray drying system, which forms a double-fan closed-loop circulation process by arranging an induced draft fan and a supply fan, so that the liquid drying device is in a negative pressure state, which is conducive to solvent evaporation, does not require a very high temperature circulating gas medium for drying, and realizes drying at low temperature, which is suitable for drying heat-sensitive materials; by arranging a waste heat recovery device, the refrigerant evaporation and condensation cycle is used to cool the wet mixed gas, and the solvent condensation recovery and recycling are realized; at the same time, the heat released by the condensation of the wet mixed gas is used to perform preliminary heat recovery on the dry gas medium coming out of the gas medium dehumidification device, and the waste heat is recovered, thereby saving energy and production costs.

[0006] To achieve the above-mentioned purpose, the present invention provides a low-temperature closed-loop spray drying system, comprising a liquid feed batching and conveying device, a liquid feed drying device, a gas separation device, a product collecting device, a solvent recovery device, a gas medium dehumidification device and a gas medium heating and filtering device, wherein the discharge port of the liquid feed batching and conveying device is connected to the feed port of the atomizing device at the top of the liquid feed drying device, a gas medium inlet is arranged at the top of the liquid feed drying device, the gas medium inlet is connected to the gas outlet of the gas medium heating and filtering device, the discharge port at the bottom of the liquid feed drying device is connected to the feed port of the gas separation device, the discharge port at the lower end of the gas separation device is connected to the feed port of the product collecting device, the gas outlet at the upper end of the gas separation device is connected to the inlet of the solvent recovery device, the gas outlet at the upper end of the solvent recovery device is connected to the gas inlet of the gas medium dehumidification device, the gas outlet of the gas medium dehumidification device is connected to the gas inlet of the gas medium heating and filtering device, and the product collecting device and the solvent recovery device are both cyclone separation devices; The liquid material batching and conveying device is used to prepare the material to be dried and the solvent into a liquid material, and then heat and pressurize it and convey it to the liquid material drying device for atomization and drying; the gas medium heating and filtering device is used to heat and filter the gas medium, and convey the heated and filtered gas medium into the liquid material drying device. The gas medium is an inert gas, so that the liquid material drying device is a low-oxygen environment to prevent the material from being denatured, degraded, and oxidized; the liquid material drying device is used to atomize the liquid material first, and then use the dehumidified and heated gas medium to dry the atomized liquid material. During the drying process, the solvent and water in the liquid material evaporate and mix with the gas medium to form a humidified liquid material. The mixed gas and the material droplets in the feed liquid are dried into solid powder products; the dried solid powder products are discharged from the discharge port at the lower end of the feed liquid drying device together with the wet mixed gas and enter the feed gas separation device for solid-gas separation, the separated solid powder products enter the product collection device for collection, the separated wet mixed gas is cooled and enters the solvent recovery device for gas-liquid separation, the separated solvent is recovered by the solvent recovery device for recycling, the separated gas medium enters the gas medium dehumidification device for dehumidification, the dehumidified gas medium enters the gas medium heating and filtering device for heating and filtering, and then enters the feed liquid drying device again for recycling; The invention is characterized in that: it also includes an induced draft fan, a waste heat recovery device, a second throttle valve and a blower; the waste heat recovery device includes a precooler, a supercharger, an evaporator, a compressor, a condenser, and a first throttle valve; the precooler includes a hot air duct and a cold air duct; the evaporator includes a first gas medium duct and a first refrigerant duct; the condenser includes a second gas medium duct and a second refrigerant duct; the air outlet of the feed-liquid separation device is connected to the air inlet of the induced draft fan, the air outlet of the induced draft fan is connected to the inlet of the hot air duct, the outlet of the hot air duct is connected to the inlet of the supercharger, the outlet of the supercharger is connected to the inlet of the first gas medium duct, the outlet of the first gas medium duct is connected to the The inlet of the solvent recovery device is connected, the air outlet at the upper end of the solvent recovery device is connected to the air inlet and outlet at the lower end of the gas medium dehumidification device, the air inlet and outlet at the upper end of the gas medium dehumidification device is connected to the inlet of the second throttle valve, the outlet of the second throttle valve is connected to the inlet of the cold air duct of the precooler, the outlet of the cold air duct is connected to the inlet of the second gas medium duct, the outlet of the second gas medium duct is connected to the inlet of the blower, and the outlet of the blower is connected to the inlet of the gas medium heating and filtering device, forming a double-blower closed-loop circulation drying system, the induced draft fan is set to an exhaust type, so that the drying inner cavity of the liquid drying device forms a low-temperature negative pressure drying environment, and the solvent in the liquid evaporates rapidly under the low-temperature negative pressure drying environment; The outlet of the first refrigerant pipeline is connected to the inlet of the compressor, the outlet of the compressor is connected to the inlet of the second refrigerant pipeline, the outlet of the second refrigerant pipeline is connected to the inlet of the first throttle valve, and the outlet of the first throttle valve is connected to the inlet of the first refrigerant pipeline; the refrigerant is converted from a low-pressure liquid into a low-pressure gas through the evaporator by absorbing heat in the first gas medium pipeline, and is pressurized into a high-pressure gas through the compressor, and then condensed into a high-pressure liquid by the condenser, releasing heat to heat the circulating gas medium in the second gas medium pipeline, and the high-pressure liquid of the refrigerant expands into a low-pressure liquid through the first throttle valve and re-enters the evaporator to absorb heat and vaporize, forming a refrigerant evaporation and condensation cycle; The wet mixed gas separated from the liquid-slurry separation device enters the hot air duct of the precooler through the induced draft fan, is absorbed by the cold air duct, enters the supercharger after preliminary cooling, and enters the first gas medium duct of the evaporator under high pressure, is evaporated by the refrigerant and cooled by heat, the moisture in the wet mixed gas is condensed into liquid and enters the solvent recovery device with the saturated circulating gas medium for gas-liquid separation, the separated solvent is collected and recovered, the separated circulating gas medium enters the gas medium dehumidification device for further dehumidification, the dehumidified gas medium enters the second throttle valve, expands into low-pressure gas through the second throttle valve, enters the cold air duct of the precooler, absorbs heat from the hot air duct, and then enters the condenser, absorbs heat released by condensation of the refrigerant high-pressure gas, and is sent to the gas medium heating and filtering device by the blower after preliminary heat recovery, and enters the liquid-slurry drying device after heating and filtration by the gas medium heating and filtering device, thus forming a low-temperature closed-loop circulation of the gas medium.

[0007] As a further improvement of the present technology, the product collecting device includes a product collecting air delivery pipe, the air outlet of the second throttle valve is provided with two routes, one route is connected to the inlet of the cold air pipe, and the other route is connected to one end of the product collecting air delivery pipe, the other end of the product collecting air delivery pipe is connected to the feed port of the product collecting device, the lower end outlet of the feed-liquid separation device is connected to the product collecting air delivery pipe, the solid powder product separated from the feed-liquid separation device is wind-fed into the product collecting device for collection by using the dehumidified gas medium, the gas medium separated by the cyclone from the product collecting device merges with the humid mixed gas separated by the feed-liquid separation device and flows together.

[0008] As a further improvement of the present technology, the liquid drying device includes a drying tower and an atomizing device installed on the top of the drying tower. The gas medium inlet is arranged at the top of the drying tower. A hot air distribution device with spiral air inlet is provided in the gas medium inlet. The hot air distribution device causes the gas medium to flow into the drying tower body in a spiral shape, thereby prolonging the contact time between the heated gas medium and the liquid droplets.

[0009] As a further improvement of the present technology, the gas medium heating and filtering device includes a heater and a first high-efficiency filter, the outlet of the second gas medium pipeline is connected to the air inlet of the blower, the air outlet of the blower is connected to the inlet of the heater, the outlet of the heater is connected to the inlet of the first high-efficiency filter, and the outlet of the first high-efficiency filter is connected to the gas medium inlet on the liquid drying device; The circulating gas medium preliminarily heated by the waste heat recovery device is transported to the heater through the blower and heated to the inlet air temperature required for liquid drying, and then enters the liquid drying device through the gas medium inlet.

[0010] As a further improvement of the present technology, the drying system further comprises a regeneration heater, the air blower comprises a first air outlet and a second air outlet, the first air outlet is connected to the heater inlet, and the second air outlet is connected to the regeneration heater inlet; The gas medium dehumidification device includes an adsorption tower A and an adsorption tower B. The upper end of the adsorption tower A is provided with a first air inlet and outlet, and the lower end is provided with a second air inlet and outlet. The upper end of the adsorption tower B is provided with a third air inlet and outlet, and the lower end is provided with a fourth air inlet and outlet. The adsorption tower A and the adsorption tower B are in parallel structure. The first air inlet and outlet are connected in parallel with the third air inlet and outlet in three ways. In the first way, the first air inlet and outlet and the third air inlet and outlet are both connected to the pressure balance valve. In the second way, the first air inlet and outlet are connected to the first air inlet valve, and the third air inlet and outlet are connected to the third air inlet valve. After the first air inlet valve and the third air inlet valve are connected in parallel, they are connected to the outlet of the regeneration heater, and the switching states of the first air inlet valve and the third air inlet valve are always opposite. In the third way, the first air inlet and outlet are connected to the first outlet valve, and the third air inlet and outlet are connected to the first outlet valve. The air outlet is connected to the third air outlet valve, and the first air outlet valve and the third air outlet valve are connected in parallel to the inlet of the second throttle valve, and the switching states of the first air outlet valve and the third air outlet valve are always opposite; the second air inlet and outlet are connected in parallel with the fourth air inlet and outlet in two ways, in the first way, the second air inlet and outlet are connected to the second air inlet valve, and the fourth air inlet and outlet are connected to the fourth air inlet valve, and the second air inlet valve and the fourth air inlet valve are connected in parallel to the outlet of the solvent recovery device, and the switching states of the second air inlet valve and the fourth air inlet valve are always opposite, in the second way, the second air inlet and outlet are connected to the second air outlet valve, and the fourth air inlet and outlet are connected to the fourth air outlet valve, and the second air outlet valve and the fourth air outlet valve are connected in parallel to the inlet of the supercharger, and the switching states of the second air outlet valve and the fourth air outlet valve are always opposite; When adsorption tower A is for forward adsorption of solvent, the second air inlet valve and the first air outlet valve are opened, the first air inlet valve and the second air outlet valve are closed, and the gas medium separated from the solvent recovery device enters the adsorption tower A from the second air inlet valve, and after being dehumidified by tower A, it comes out from the first air outlet valve and enters the second throttle valve, and then is divided into two paths, respectively entering the product collection air delivery duct and the cold air duct; at this time, adsorption tower B is for reverse regeneration, the third air inlet valve and the fourth air outlet valve are opened, the fourth air inlet valve and the third air outlet valve are closed, and the part of the circulating gas medium preliminarily heated by the waste heat recovery device is transported to the regeneration heater through the second air outlet of the blower and heated to the regeneration temperature, and then enters the adsorption tower B from the third air inlet valve, and reversely dries the adsorption tower B, so that the solvent in the adsorption tower B evaporates and merges with the regeneration heated gas medium to form a humid mixed gas, which comes out from the fourth air outlet valve and merges with the humid mixed gas coming out of the hot air duct of the precooler, and then enters the supercharger to circulate together; The working status of adsorption tower A and adsorption tower B rotates periodically. When the adsorption solvent of adsorption tower A reaches saturation, the pressure balance valve opens to balance the pressure and temperature of adsorption tower A and adsorption tower B. Then, adsorption tower A will switch to reverse regeneration and adsorption tower B will switch to forward adsorption of solvent. The switch status of each inlet valve and outlet valve rotates accordingly.

[0011] As a further improvement of the present technology, it also includes an oxygen content detector, an air supply valve, an isolation valve and an exhaust valve. The oxygen content detector is arranged at the air outlet of the second throttle valve, and is used to detect the oxygen content in the dehumidified gas medium in real time, and send the detection data to the system controller. The connecting pipe between the heater and the blower is provided with an air supply valve, an isolation valve and an exhaust valve in sequence. The low-temperature closed-loop spray drying system should be maintained in a low-oxygen state. When the oxygen content in the system exceeds the set value, the system controller controls the air supply valve to supplement the circulating gas medium to ensure that the low-oxygen state is maintained and the product is not changed. The exhaust valve is used to open the air supply valve and the exhaust valve at the same time before the system is started, so that the gas medium is input into the liquid drying device while oxygen is discharged, so that a low oxygen environment is formed in the liquid drying device; the exhaust valve is also used to maintain the system pressure. When the pressure in the liquid drying device exceeds the set value, the system controller controls the exhaust valve to exhaust outwards.

[0012] As a further improvement of the present technology, the slurry batching and conveying device includes a liquid batching tank, a feeding pump and a slurry flowmeter. A stirring device is arranged inside the liquid batching tank for dissolving and mixing the raw materials and the solvent into a slurry; a heating jacket is arranged outside the liquid batching tank for heating and keeping the slurry warm; the liquid batching tank is provided with an inert gas protection device for isolating the slurry from contact with the external air to avoid material denaturation, degradation and oxidation; a homogenizing and emulsifying device is arranged inside the liquid batching tank for refining the material so that the material can be more evenly dispersed in the slurry.

[0013] As a further improvement of the present technology, the liquid drying device comprises a drying tower and an atomizing device arranged on the top of the drying tower, the upper part of the drying tower is a cylindrical structure, and the lower part is an inverted cone structure, the taper of the inverted cone structure is ≤60°, and a vibrating hammer that is conducive to discharging is installed on the outer side wall of the inverted cone structure; The atomizing device is an air flow atomizing device, a centrifugal atomizing device or a pressure atomizing device; The outer side surface of the side wall of the drying tower is provided with a heat-insulating jacket or a cooling jacket. The heat-insulating jacket is used for drying non-heat-sensitive materials, and the cooling jacket is used for drying heat-sensitive materials.

[0014] As a further improvement of the present technology, the material-gas separation device includes a cyclone separator, a bag filter and a second high-efficiency filter, the lower end discharge port of the material-liquid drying device is connected to the feed port of the cyclone separator, the air outlet at the top of the cyclone separator is connected to the feed port of the bag filter, the air outlet at the top of the bag filter is connected to the air inlet of the second high-efficiency filter, the air outlet of the second high-efficiency filter is connected to the air inlet of the induced draft fan, and the solid powder product outlets at the bottom of the cyclone separator and the bottom of the bag filter are connected to the product collection air delivery pipeline; A pulse back-flushing unit is arranged on the top of the bag filter, and the back-flushing gas of the pulse back-flushing unit adopts inert gas.

[0015] As a further improvement of the present technology, the cyclone separator includes a primary cyclone separator and a secondary cyclone separator, the feed port of the primary cyclone separator is connected to the discharge port of the liquid drying device, the upper air outlet of the primary cyclone separator is connected to the feed port of the secondary cyclone separator, the upper air outlet of the secondary cyclone separator is connected to the feed port of the bag filter, and the solid powder product outlets at the bottom of the primary cyclone separator and the secondary cyclone separator are both connected to the product collection air delivery pipe.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The present invention forms a double-fan closed-loop circulation process by setting an induced draft fan and a blower, so that the liquid drying device is in a negative pressure state, which is conducive to the evaporation of the solvent. It does not require a very high temperature circulating gas medium for drying, and achieves drying at low temperature, which is suitable for drying heat-sensitive materials; 2. The present invention provides a waste heat recovery device and utilizes the refrigerant evaporation and condensation cycle to cool the wet mixed gas, thereby realizing the solvent condensation recovery and recycling; at the same time, the heat released by the condensation of the wet mixed gas is utilized to perform preliminary heat recovery on the dry gas medium coming out of the gas medium dehumidification device, thereby recovering the waste heat and saving energy and production costs; 3. The present invention ensures that the system is in a low oxygen state by setting up an air supply valve and an oxygen content detector, so that the material will not be denatured, degraded or oxidized; 4. The present invention provides a pressurized gas, an evaporator and a gas medium dehumidification device, so that the circulating gas medium is dehumidified in two stages, namely, the evaporator absorbs heat and then condenses the solvent and the gas medium dehumidification device absorbs the solvent under high pressure, thereby greatly reducing the moisture content and enhancing the drying capacity; by providing a regeneration heater, the adsorption tower A and the adsorption tower B are periodically rotated for adsorption and reverse regeneration, so that the gas medium dehumidification device can continuously dehumidify, ensuring the continuous closed-loop drying operation of the system, and the high-temperature regenerated gas after moisture absorption from the adsorption tower can be returned to the waste heat recovery device, heat recovery, and energy saving; 5. The present invention precools the wet mixed gas by arranging a precooler, recovers part of the heat of the dry tail gas, and at the same time reheats the dehumidified gas medium, thereby improving the heat utilization efficiency; 6. The present invention sets a product recovery air delivery pipeline and uses part of the dehumidified gas medium to pneumatically deliver the solid powder product into the product collection device, so that the dried material is easy to cool and not easy to absorb moisture, thereby improving the product collection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a gas medium dehumidification device according to an embodiment of the present invention; Figure 3 It is a schematic diagram of heat balance symbols of drying tower materials in the embodiment of the present invention and the prior art.

[0018] In the figure: 1, liquid dispensing tank, 2, feeding pump, 3, drying tower, 4, atomizing device, 5, primary cyclone separator, 6, secondary cyclone separator, 7, bag filter, 8, product collecting device, 81, product collecting air delivery pipeline, 9, second high-efficiency filter, 10, induced draft fan, 11, precooler, 111, hot air pipeline, 112, cold air pipeline, 12, supercharger, 13, evaporator, 131, first gas medium pipeline, 132, first refrigerant pipeline, 14, solvent recovery device, 15, gas medium dehumidification device, 151, adsorption tower A, 5111, first air inlet and outlet, 1512, first air inlet valve, 1513, first air outlet valve, 1514, second air inlet and outlet , 1515, second air outlet valve, 1516, second air inlet valve, 152, adsorption tower B, 1521, third air inlet and outlet, 1522, third air inlet valve, 1523, third air outlet valve, 1524, fourth air inlet and outlet, 1525, fourth air outlet valve, 1526, fourth air inlet valve, 153, pressure balance valve, 16, second throttle valve, 17, first throttle valve, 18, compressor, 19, oxygen content detector, 20, condenser, 201, second gas medium pipeline, 202, second refrigerant pipeline, 21, air blower, 22, regeneration heater, 23, exhaust valve, 24, isolation valve, 25, air supply valve, 26, heater, 27, first high-efficiency filter. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figure 1As shown, the embodiment of the present invention includes a liquid feed batching and conveying device, a liquid feed drying device, a gas-feed separation device, a product collecting device, a solvent recovery device, a gas medium dehumidification device and a gas medium heating and filtering device. The discharge port of the liquid feed batching and conveying device is connected to the feed port of the atomizing device 4 at the top of the liquid feed drying device. A gas medium inlet is provided at the top of the liquid feed drying device. The gas medium inlet is connected to the gas outlet of the gas medium heating and filtering device. The discharge port at the bottom of the liquid feed drying device is connected to the feed port of the gas-feed separation device. The discharge port at the lower end of the gas-feed separation device is connected to the feed port of the product collecting device 8. The gas outlet at the upper end of the gas-feed separation device is connected to the inlet of the solvent recovery device 14. The gas outlet at the upper end of the solvent recovery device 14 is connected to the gas inlet of the gas medium dehumidification device 15. The gas outlet of the gas medium dehumidification device 15 is connected to the gas inlet of the gas medium heating and filtering device. The product collecting device 8 and the solvent recovery device 14 both adopt cyclone separation devices, and the bottoms of the product collecting device 8 and the solvent recovery device 14 are used for product collection and solvent recovery, respectively.

[0021] The liquid batching and conveying device is used to prepare the material to be dried and the solvent into a liquid, and then heat and pressurize it and convey it to the liquid drying device for atomization and drying; in this embodiment, the gas medium is nitrogen, and the gas medium heating and filtering device is used to heat and filter the nitrogen, and send the heated and filtered nitrogen into the liquid drying device, so that the liquid drying device is a low-oxygen environment to prevent the material from being denatured, degraded, and oxidized; the liquid drying device is used to atomize the liquid first, and then use the dehumidified and heated nitrogen to dry the atomized liquid. During the drying process, the solvent and water in the liquid evaporate and mix with the nitrogen to form a humid mixed gas, and the liquid The material droplets in the drying device are dried into solid powder products; the dried solid powder products are discharged from the lower end discharge port of the liquid drying device together with the wet mixed gas and enter the material gas separation device for solid-gas separation; the separated solid powder products enter the product collection device 8 for collection; the separated wet mixed gas is cooled and enters the solvent recovery device 14 for gas-liquid separation; the separated solvent is recovered by the solvent recovery device 14 for recycling; the separated nitrogen enters the gas medium dehumidification device 15 for dehumidification; the dehumidified nitrogen enters the gas medium heating and filtering device for heating and filtering, and then enters the liquid drying device again for recycling; The drying system of this embodiment also includes an induced draft fan 10, a waste heat recovery device, a second throttle valve 16 and a blower 21; the waste heat recovery device includes a precooler 11, a supercharger 12, an evaporator 13, a compressor 18, a condenser 20 and a first throttle valve 17, the precooler 11 includes a hot air duct 111 and a cold air duct 112, the evaporator 13 includes a first gas medium duct 131 and a first refrigerant duct 132, and the condenser 20 includes a second gas medium duct 201 and a second refrigerant duct 202; the air outlet of the feed-liquid separation device is connected to the air inlet of the induced draft fan 10, the air outlet of the induced draft fan 10 is connected to the inlet of the hot air duct 111, the outlet of the hot air duct 111 is connected to the inlet of the supercharger 12, the outlet of the supercharger 12 is connected to the inlet of the first gas medium duct 131, and the first The outlet of the gas medium pipeline 131 is connected to the inlet of the solvent recovery device 14, the air outlet at the upper end of the solvent recovery device 14 is connected to the air inlet and outlet at the lower end of the gas medium dehumidification device 15, the air inlet and outlet at the upper end of the gas medium dehumidification device 15 is connected to the inlet of the second throttle valve 16, the outlet of the second throttle valve 16 is connected to the inlet of the cold air pipeline 112 of the precooler 11, the outlet of the cold air pipeline 112 is connected to the inlet of the second gas medium pipeline 201, the outlet of the second gas medium pipeline 201 is connected to the inlet of the blower 21, the outlet of the blower 21 is connected to the inlet of the gas medium heating and filtering device, forming a double-fan closed-loop circulation drying system, the induced draft fan 10 is set to an exhaust type, so that the drying inner cavity of the feed liquid drying device forms a low-temperature negative pressure drying environment, and the solvent in the feed liquid evaporates rapidly under the low-temperature negative pressure drying environment; The outlet of the first refrigerant pipeline 132 is connected to the inlet of the compressor 18, the outlet of the compressor 18 is connected to the inlet of the second refrigerant pipeline 202, the outlet of the second refrigerant pipeline 202 is connected to the inlet of the first throttle valve 17, and the outlet of the first throttle valve 17 is connected to the inlet of the first refrigerant pipeline 132; the refrigerant is converted from a low-pressure liquid into a low-pressure gas by absorbing heat in the second gas medium pipeline 131 through the evaporator 13, and is pressurized into a high-pressure gas through the compressor 18, and then condensed into a high-pressure liquid by the condenser 20, releasing heat to heat the circulating nitrogen in the second gas medium pipeline 201, and the high-pressure liquid of the refrigerant is expanded into a low-pressure liquid through the first throttle valve 17, and re-enters the evaporator 13 to absorb heat and vaporize, forming a refrigerant evaporation and condensation cycle; The wet mixed gas separated from the liquid-slurry separation device enters the hot air duct 111 of the precooler 11 through the induced draft fan 10, absorbs heat in the cold air duct 112, and enters the supercharger 12 after preliminary cooling. The pressurized wet mixed gas enters the first gas medium pipeline 13 of the evaporator under high pressure, and is cooled by the refrigerant evaporation to take away the heat. The moisture in the wet mixed gas is condensed into liquid and enters the solvent recovery device 14 with the saturated circulating nitrogen for gas-liquid separation. The separated solvent is collected and recovered, and the separated circulating nitrogen enters The gas medium dehumidification device 15 further dehumidifies, and the dehumidified nitrogen enters the second throttle valve 16, expands into low-pressure nitrogen through the second throttle valve 16, and the low-pressure nitrogen enters the cold air duct 112 of the precooler 11, absorbs the heat of the hot air duct 111, and then enters the condenser 20, absorbs the heat released by the condensation of the refrigerant high-pressure gas, and is sent to the gas medium heating and filtering device by the blower 21 after preliminary heat recovery. After being heated and filtered by the gas medium heating and filtering device, it enters the liquid drying device, thus forming a low-temperature closed-loop circulation of the gas medium.

[0022] The existing spray drying system is also equipped with a gas medium dehumidification device, but all of them have only one-stage condensation dehumidification. The condensation dehumidification is limited by the dew point of the solvent under normal pressure, and the dehumidification effect is not good.

[0023] In this embodiment, a supercharger 12, an evaporator 13 and a gas medium dehumidification device 15 are provided, so that the circulating gas medium is dehumidified in two stages by passing through the evaporator 13 to absorb heat and then condense the solvent under high pressure and then passing through the gas medium dehumidification device 15 to adsorb the solvent. The dew point of the solvent under high pressure is higher than that under normal pressure, and the solvent is more easily condensed into liquid. Increasing adsorption dehumidification can also accelerate the liquefaction of the solvent, thereby greatly reducing the moisture content of the gas medium and greatly improving the dehumidification effect. The dry nitrogen after dehumidification in this embodiment greatly improves the drying effect of the material; like Figure 3 The figure shows the material heat balance parameters of the dry nitrogen after the boosted two-stage dehumidification in this embodiment and the dry nitrogen after the atmospheric pressure condensation dehumidification in the prior art respectively entering the drying tower to atomize and dry the atomized droplets. The balance symbol on the line where t0, t1, and t2 are located in the figure represents the dry nitrogen after dehumidification in this embodiment, and the balance symbol on the line where t0', t1', and t2' are located represents the dry nitrogen after dehumidification in the prior art. According to the law of conservation of material energy, the material heat balance formula can be obtained as follows: G2C M t M1 / W+ C1t M1 +LI0+L(I1-I0)= G2C M t M2 / W+ LI2+Q L (1) Where: G2 is the flow rate of the material out of the dryer, Kg / h; CM is the specific heat of the product, kJ / kg.℃; t M1 is the raw material temperature, ℃; W is the evaporation rate, kg / h; C1 is the specific heat of the solvent, kJ / kg.℃; L is the dry gas consumption, kg dry gas / h; I0 is the fresh air enthalpy, kJ / kg dry gas; I1 is the hot air enthalpy, kJ / kg dry gas; t M2 is the product temperature, °C; I2 is the wet air enthalpy, kJ / kg dry gas; Q L is the system heat loss, kJ / kg water.

[0024] By using the material heat balance formula (1) to calculate, the calculation results are as follows: After dehumidification in this embodiment, the dry nitrogen with a dry bulb temperature of 20°C and a relative humidity of 10% is heated to 35°C and a relative humidity of 4%. After 1 kg of water is evaporated in the drying tower 3, the exhaust air temperature at the bottom discharge port of the drying tower is 25°C, and the exhaust air relative humidity is 26%; To achieve the same hot air relative humidity and exhaust air relative humidity for dry nitrogen with a dry bulb temperature of 20°C and a relative humidity of 30% after dehumidification using existing technology, the hot air temperature must be increased to 56°C and the exhaust air temperature must be increased to 38°C.

[0025] It can be seen from this that compared with the prior art one-stage condensation dehumidification, under the same conditions, the low-temperature negative pressure drying technology of the present invention has a better drying effect and can achieve low-temperature drying at 35 degrees.

[0026] The product collecting device 8 includes a product collecting air delivery pipe 81. The air outlet of the second throttle valve 16 is provided with two routes, one route is connected to the inlet of the cold air pipe 112, and the other route is connected to one end of the product collecting air delivery pipe 81. The other end of the product collecting air delivery pipe 81 is connected to the feed port of the product collecting device 8. The discharge port at the lower end of the liquid-feed separation device is connected to the product collecting air delivery pipe 81. The solid powder product separated from the liquid-feed separation device is sent to the product collecting device 8 by the dehumidified nitrogen wind for collection. The nitrogen separated by the cyclone from the product collecting device 8 and the humid mixed gas separated by the liquid-feed separation device are combined into the induced draft fan and flow together.

[0027] The liquid drying device comprises a drying tower 3 and an atomizing device 4 installed on the top of the drying tower 3. The gas medium inlet is arranged at the top of the drying tower 3. A hot air distribution device with spiral air inlet is arranged in the gas medium inlet. The hot air distribution device makes the nitrogen gas flow into the drying tower 3 in a spiral shape, thereby prolonging the contact time between the heated nitrogen and the liquid droplets, and improving the drying effect and drying quality.

[0028] The drying system of this embodiment further includes an oxygen content detector 19, an air supply valve 25, an isolation valve 24 and an exhaust valve 23. The oxygen content detector 19 is arranged at the air outlet of the second throttle valve 16, and is used to detect the oxygen content in the dehumidified nitrogen in real time, and send the detection data to the system controller. The connecting pipe between the heater 26 and the blower 21 is provided with an air supply valve 25, an isolation valve 24 and an exhaust valve 23 in sequence. The low-temperature closed-loop spray drying system should be maintained in a low-oxygen state. When the oxygen content detector 19 detects that the oxygen content in the system exceeds the set value, the system controller controls the air supply valve 25 to supplement the circulating nitrogen to ensure that the system maintains a low-oxygen state and ensures the invariance of the product. The exhaust valve 23 is used to open the air supply valve 25 and the exhaust valve 23 at the same time before the system is started, so that nitrogen is input into the liquid drying device while oxygen is discharged, so that a low oxygen environment is formed in the liquid drying device; the exhaust valve 23 is also used to maintain the system pressure. When the pressure in the liquid drying device exceeds the set value, the system controller controls the exhaust valve 23 to exhaust to the outside.

[0029] The gas medium heating and filtering device comprises a heater 26 and a first high efficiency filter 27, the outlet of the second gas medium pipeline 201 is connected to the air inlet of the blower 21, the air outlet of the blower 21 is connected to the inlet of the heater 26, the outlet of the heater 26 is connected to the inlet of the first high efficiency filter 27, and the outlet of the first high efficiency filter 27 is connected to the gas medium inlet on the drying tower 3; The circulating nitrogen after preliminary heat recovery by the waste heat recovery device is transported to the heater 26 through the blower 21 and heated to the inlet temperature required for liquid drying, and then enters the liquid drying device through the gas medium inlet.

[0030] Preferably, the drying system of this embodiment further includes a regeneration heater 22, and the air blower 21 includes a first air outlet and a second air outlet, the first air outlet is connected to the inlet of the heater 26, and the second air outlet is connected to the inlet of the regeneration heater 22; The gas medium dehumidification device 15 includes an adsorption tower A151 and an adsorption tower B152. The adsorption tower A151 is provided with a first air inlet and outlet 1511 at the upper end and a second air inlet and outlet 1514 at the lower end. The adsorption tower B152 is provided with a third air inlet and outlet 1521 at the upper end and a fourth air inlet and outlet 1524 at the lower end. The adsorption tower A151 and the adsorption tower B152 are parallel structures. The first air inlet and outlet 1511 and the third air inlet and outlet 1521 are connected in parallel in three ways. The first way connects the first air inlet and outlet 1511 with the third air inlet and outlet 1521. The third air inlet and outlet 1521 are both connected to the pressure balance valve 153. In the second way, the first air inlet and outlet 1511 are connected to the first air inlet valve 1512, and the third air inlet and outlet 1521 are connected to the third air inlet valve 1522. The first air inlet valve 1512 and the third air inlet valve 1522 are connected in parallel to the outlet of the regeneration heater 22, and the switching states of the first air inlet valve 1512 and the third air inlet valve 1522 are always opposite. In the third way, the first air inlet and outlet 1511 are connected to the first outlet valve 1513, and the third air inlet and outlet 1521 are connected to the third air inlet valve 1522. The air port 1521 is connected to the third air outlet valve 1523, the first air outlet valve 1513 and the third air outlet valve 1523 are connected in parallel and then connected to the second throttle valve, and the switch states of the first air outlet valve 1513 and the third air outlet valve 1523 are always opposite; the second air inlet and outlet 1514 and the fourth air inlet and outlet 1524 are connected in parallel in two ways, in the first way, the second air inlet and outlet 1514 is connected to the second air inlet valve 1516, the fourth air inlet and outlet 1524 is connected to the fourth air inlet valve 1526, the second air inlet valve 1516 and the fourth air inlet and outlet 1524 are connected to the fourth air inlet valve 1526, and the second air inlet valve 1516 and the fourth air inlet and outlet 1524 are connected in parallel. After the air inlet valve 1526 is connected in parallel, it is connected to the outlet of the solvent recovery device 14, and the switch states of the second air inlet valve 1516 and the fourth air inlet valve 1526 are always opposite. In the second path, the second air inlet and outlet 1514 is connected to the second air outlet valve 1515, and the fourth air inlet and outlet 1524 is connected to the fourth air outlet valve 1525. After the second air outlet valve 1515 and the fourth air outlet valve 1525 are connected in parallel, they are connected to the inlet of the supercharger 12, and the switch states of the second air outlet valve 1515 and the fourth air outlet valve 1525 are always opposite. When the adsorption tower A151 is in the forward adsorption of solvent, the second air inlet valve 1516 and the first air outlet valve 1513 are opened, the first air inlet valve 1512 and the second air outlet valve 1515 are closed, and the nitrogen separated from the solvent recovery device 14 enters the adsorption tower A151 from the second air inlet valve 1516, and after being dehumidified by the adsorption tower A151, it comes out from the first air outlet valve 1513 and enters the second throttle valve 16, and then is divided into two paths, entering the product collection air delivery pipe 81 and the cold air pipe 112 respectively; at this time, the adsorption tower B152 is in the reverse regeneration, the third air inlet valve 1522 and the fourth air outlet valve 1525 are opened, and the fourth air inlet valve 152 6 and the third air outlet valve 1523 are closed, and part of the circulating nitrogen after preliminary heat recovery by the waste heat recovery device is transported to the regeneration heater 22 through the second air outlet of the blower 21 and heated to the regeneration temperature (the regeneration temperature is usually greater than 170°C), and then enters the adsorption tower B152 from the third air inlet valve 1522, and reversely dries the adsorption tower B152, so that the solvent in the adsorption tower B152 evaporates and merges with the regenerated heated nitrogen to form a wet mixed gas, and the wet mixed gas comes out of the fourth air outlet valve 1525 and merges with the wet mixed gas coming out of the hot air duct 111 of the precooler 11, and then enters the supercharger 12, and circulates together; The working states of adsorption tower A151 and adsorption tower B152 rotate periodically. When the adsorption solvent of adsorption tower A151 reaches saturation, the pressure balance valve 153 opens to balance the pressure and temperature of adsorption tower A151 and adsorption tower B152. Then, adsorption tower A151 switches to reverse regeneration and adsorption tower B152 switches to forward adsorption of solvent. The switch states of each inlet valve and outlet valve rotate accordingly.

[0031] In this embodiment, a regeneration heater 22 is provided to enable the adsorption tower A151 and the adsorption tower B152 to periodically alternate between adsorption and reverse regeneration, so that the gas medium dehumidification device 15 can continuously dehumidify, ensuring the continuous closed-loop drying operation of the system. The high-temperature regenerated gas after absorbing moisture from the adsorption tower can be returned to the waste heat recovery device to recover heat and save energy.

[0032] Preferably, the liquid material batching and conveying device includes a liquid preparation tank 1, a feeding pump 2 and a liquid material flowmeter. The liquid preparation tank 1 is provided with a stirring device inside, which is used to dissolve the raw material and the solvent into a liquid material; the liquid preparation tank 1 is provided with a heating jacket outside, which is used to heat and keep the liquid material warm. The heat source of the heating jacket can be an additional heat source, or the refrigerant in the waste heat recovery device can be used to provide heat to heat the liquid material to about 60°C, reduce the viscosity of the liquid material, and facilitate transportation and atomization; the liquid preparation tank 1 is provided with an inert gas protection device, which is used to isolate the liquid material from contact with the outside air to avoid material denaturation, degradation and oxidation; the liquid preparation tank 1 is provided with a homogenizing and emulsifying device, which is used to refine the material so that the material can be more evenly dispersed in the liquid material.

[0033] Preferably, the upper part of the drying tower 3 is a cylindrical structure, and the lower part is an inverted cone structure, the taper of the inverted cone structure is ≤60°, and a vibrating hammer that is conducive to discharging is installed on the outer wall of the inverted cone structure; The atomizing device 4 adopts an air flow atomizing device, a centrifugal atomizing device or a pressure atomizing device; The outer side surface of the side wall of the drying tower 3 is provided with a heat-insulating jacket or a cooling jacket. The heat-insulating jacket is used for drying non-heat-sensitive materials, and the cooling jacket is used for drying heat-sensitive materials.

[0034] Preferably, the material-gas separation device comprises a primary cyclone separator 5, a secondary cyclone separator 6, a bag filter 7 and a second high-efficiency filter 9, the lower end discharge port of the material-liquid drying device is connected to the feed port of the primary cyclone separator 5, the upper end air outlet of the primary cyclone separator 5 is connected to the feed port of the secondary cyclone separator 6, the upper end air outlet of the secondary cyclone separator 6 is connected to the feed port of the bag filter 7, the air outlet at the top of the bag filter 7 is connected to the air inlet of the second high-efficiency filter 9, the air outlet of the second high-efficiency filter 9 is connected to the air inlet of the induced draft fan 10, and the solid powder product outlets at the bottom of the primary cyclone separator 5, the secondary cyclone separator 6 and the bag filter 7 are all connected to the product collection air delivery pipeline 81; A pulse back-flushing unit is provided on the top of the bag filter 7, and the back-flushing gas of the pulse back-flushing unit adopts inert gas.

[0035] The above are only preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A low-temperature closed-loop spray drying system, comprising a liquid feed batching and conveying device, a liquid feed drying device, a gas separation device, a product collecting device, a solvent recovery device, a gas medium dehumidification device and a gas medium heating and filtering device, wherein the discharge port of the liquid feed batching and conveying device is connected to the feed port of the atomizing device at the top of the liquid feed drying device, a gas medium inlet is arranged at the top of the liquid feed drying device, the gas medium inlet is connected to the gas outlet of the gas medium heating and filtering device, the discharge port at the bottom of the liquid feed drying device is connected to the feed port of the gas separation device, the discharge port at the lower end of the gas separation device is connected to the feed port of the product collecting device, the gas outlet at the upper end of the gas separation device is connected to the inlet of the solvent recovery device, the gas outlet at the upper end of the solvent recovery device is connected to the gas inlet of the gas medium dehumidification device, the gas outlet of the gas medium dehumidification device is connected to the gas inlet of the gas medium heating and filtering device, and the product collecting device and the solvent recovery device are both cyclone separation devices; The liquid material batching and conveying device is used to prepare the material to be dried and the solvent into a liquid material, and then heat and pressurize it and convey it to the liquid material drying device for atomization and drying; the gas medium heating and filtering device is used to heat and filter the gas medium, and convey the heated and filtered gas medium into the liquid material drying device. The gas medium is an inert gas, so that the liquid material drying device is a low-oxygen environment to prevent the material from being denatured, degraded, and oxidized; the liquid material drying device is used to atomize the liquid material first, and then use the dehumidified and heated gas medium to dry the atomized liquid material. During the drying process, the solvent and water in the liquid material evaporate and mix with the gas medium to form a humidified liquid material. The mixed gas and the material droplets in the feed liquid are dried into solid powder products; the dried solid powder products are discharged from the discharge port at the lower end of the feed liquid drying device together with the wet mixed gas and enter the feed gas separation device for solid-gas separation, the separated solid powder products enter the product collection device for collection, the separated wet mixed gas is cooled and enters the solvent recovery device for gas-liquid separation, the separated solvent is recovered by the solvent recovery device for recycling, the separated gas medium enters the gas medium dehumidification device for dehumidification, the dehumidified gas medium enters the gas medium heating and filtering device for heating and filtering, and then enters the feed liquid drying device again for recycling; Features: The condenser also includes an induced draft fan, a waste heat recovery device, a second throttle valve and an air supply fan; the waste heat recovery device includes a precooler, a supercharger, an evaporator, a compressor, a condenser, and a first throttle valve; the precooler includes a hot air duct and a cold air duct; the evaporator includes a first gas medium duct and a first refrigerant duct; the condenser includes a second gas medium duct and a second refrigerant duct; the gas outlet of the feed-liquid separation device is connected to the gas inlet of the induced draft fan, the gas outlet of the induced draft fan is connected to the inlet of the hot air duct, the outlet of the hot air duct is connected to the inlet of the supercharger, the outlet of the supercharger is connected to the inlet of the first gas medium duct, the outlet of the first gas medium duct is connected to the solvent recovery device; The inlet of the solvent recovery device is connected, the air outlet at the upper end of the solvent recovery device is connected to the air inlet and outlet at the lower end of the gas medium dehumidification device, the air inlet and outlet at the upper end of the gas medium dehumidification device is connected to the inlet of the second throttle valve, the outlet of the second throttle valve is connected to the inlet of the cold air duct of the precooler, the outlet of the cold air duct is connected to the inlet of the second gas medium duct, the outlet of the second gas medium duct is connected to the inlet of the blower, the outlet of the blower is connected to the inlet of the gas medium heating and filtering device, forming a double-fan closed-loop circulation drying system, the induced draft fan is set to an exhaust type, so that the drying inner cavity of the liquid drying device forms a low-temperature negative pressure drying environment, and the solvent in the liquid evaporates rapidly under the low-temperature negative pressure drying environment; The outlet of the first refrigerant pipeline is connected to the inlet of the compressor, the outlet of the compressor is connected to the inlet of the second refrigerant pipeline, the outlet of the second refrigerant pipeline is connected to the inlet of the first throttle valve, and the outlet of the first throttle valve is connected to the inlet of the first refrigerant pipeline; the refrigerant is converted from a low-pressure liquid into a low-pressure gas through the evaporator by absorbing heat in the first gas medium pipeline, and is pressurized into a high-pressure gas through the compressor, and then condensed into a high-pressure liquid by the condenser, releasing heat to heat the circulating gas medium in the second gas medium pipeline, and the high-pressure liquid of the refrigerant expands into a low-pressure liquid through the first throttle valve and re-enters the evaporator to absorb heat and vaporize, forming a refrigerant evaporation and condensation cycle; The wet mixed gas separated from the liquid-slurry separation device enters the hot air duct of the precooler through the induced draft fan, is absorbed by the cold air duct, enters the supercharger after preliminary cooling, and enters the first gas medium duct of the evaporator under high pressure, is evaporated by the refrigerant and cooled by heat, the moisture in the wet mixed gas is condensed into liquid and enters the solvent recovery device with the saturated circulating gas medium for gas-liquid separation, the separated solvent is collected and recovered, the separated circulating gas medium enters the gas medium dehumidification device for further dehumidification, the dehumidified gas medium enters the second throttle valve, expands into low-pressure gas through the second throttle valve, enters the cold air duct of the precooler, absorbs heat from the hot air duct, and then enters the condenser, absorbs heat released by condensation of the refrigerant high-pressure gas, and is sent to the gas medium heating and filtering device by the blower after preliminary heat recovery, and enters the liquid-slurry drying device after heating and filtration by the gas medium heating and filtering device, thus forming a low-temperature closed-loop circulation of the gas medium.

2. A low-temperature closed-circuit spray drying system according to claim 1, characterized in that: The product collecting device includes a product collecting air delivery pipeline, the air outlet of the second throttle valve is provided with two routes, one route is connected to the inlet of the cold air pipeline, and the other route is connected to one end of the product collecting air delivery pipeline, the other end of the product collecting air delivery pipeline is connected to the feed port of the product collecting device, the lower end outlet of the feed-liquid separation device is connected to the product collecting air delivery pipeline, the solid powder product separated from the feed-liquid separation device is wind-fed into the product collecting device for collection by utilizing the dehumidified gas medium, the gas medium separated by the cyclone from the product collecting device merges with the humid mixed gas separated by the feed-liquid separation device and flows together.

3. A low-temperature closed-circuit spray drying system according to claim 1, characterized in that: The liquid material drying device comprises a drying tower and an atomizing device installed on the top of the drying tower. The gas medium inlet is arranged at the top of the drying tower. A hot air distribution device with spiral air inlet is arranged in the gas medium inlet. The hot air distribution device causes the gas medium to flow into the drying tower body in a spiral shape, thereby prolonging the contact time between the heated gas medium and the liquid material droplets.

4. A low-temperature closed-circuit spray drying system according to claim 1, characterized in that: The gas medium heating and filtering device comprises a heater and a first high efficiency filter, the outlet of the second gas medium pipeline is connected to the air inlet of the blower, the air outlet of the blower is connected to the inlet of the heater, the outlet of the heater is connected to the inlet of the first high efficiency filter, and the outlet of the first high efficiency filter is connected to the gas medium inlet of the liquid drying device; The circulating gas medium preliminarily heated by the waste heat recovery device is transported to the heater through the blower and heated to the inlet air temperature required for liquid drying, and then enters the liquid drying device through the gas medium inlet.

5. A low-temperature closed-circuit spray drying system according to claim 4, characterized in that: It also includes a regenerative heater, the blower includes a first air outlet and a second air outlet, the first air outlet is connected to the heater inlet, and the second air outlet is connected to the regenerative heater inlet; The gas medium dehumidification device includes an adsorption tower A and an adsorption tower B. The upper end of the adsorption tower A is provided with a first air inlet and outlet, and the lower end is provided with a second air inlet and outlet. The upper end of the adsorption tower B is provided with a third air inlet and outlet, and the lower end is provided with a fourth air inlet and outlet. The adsorption tower A and the adsorption tower B are in parallel structure. The first air inlet and outlet are connected in parallel with the third air inlet and outlet in three ways. In the first way, the first air inlet and outlet and the third air inlet and outlet are both connected to the pressure balance valve. In the second way, the first air inlet and outlet are connected to the first air inlet valve, and the third air inlet and outlet are connected to the third air inlet valve. After the first air inlet valve and the third air inlet valve are connected in parallel, they are connected to the outlet of the regeneration heater, and the switching states of the first air inlet valve and the third air inlet valve are always opposite. In the third way, the first air inlet and outlet are connected to the first outlet valve, and the third air inlet and outlet are connected to the first outlet valve. The air outlet is connected to the third air outlet valve, and the first air outlet valve and the third air outlet valve are connected in parallel to the inlet of the second throttle valve, and the switching states of the first air outlet valve and the third air outlet valve are always opposite; the second air inlet and outlet are connected in parallel with the fourth air inlet and outlet in two ways, in the first way, the second air inlet and outlet are connected to the second air inlet valve, and the fourth air inlet and outlet are connected to the fourth air inlet valve, and the second air inlet valve and the fourth air inlet valve are connected in parallel to the outlet of the solvent recovery device, and the switching states of the second air inlet valve and the fourth air inlet valve are always opposite, in the second way, the second air inlet and outlet are connected to the second air outlet valve, and the fourth air inlet and outlet are connected to the fourth air outlet valve, and the second air outlet valve and the fourth air outlet valve are connected in parallel to the inlet of the supercharger, and the switching states of the second air outlet valve and the fourth air outlet valve are always opposite; When adsorption tower A is for forward adsorption of solvent, the second air inlet valve and the first air outlet valve are opened, the first air inlet valve and the second air outlet valve are closed, and the gas medium separated from the solvent recovery device enters the adsorption tower A from the second air inlet valve, and after being dehumidified by tower A, it comes out from the first air outlet valve and enters the second throttle valve, and then is divided into two paths, respectively entering the product collection air delivery duct and the cold air duct; at this time, adsorption tower B is for reverse regeneration, the third air inlet valve and the fourth air outlet valve are opened, the fourth air inlet valve and the third air outlet valve are closed, and the part of the circulating gas medium preliminarily heated by the waste heat recovery device is transported to the regeneration heater through the second air outlet of the blower and heated to the regeneration temperature, and then enters the adsorption tower B from the third air inlet valve, and reversely dries the adsorption tower B, so that the solvent in the adsorption tower B evaporates and merges with the regeneration heated gas medium to form a humid mixed gas, which comes out from the fourth air outlet valve and merges with the humid mixed gas coming out of the hot air duct of the precooler, and then enters the supercharger to circulate together; The working status of adsorption tower A and adsorption tower B rotates periodically. When the adsorption solvent of adsorption tower A reaches saturation, the pressure balance valve opens to balance the pressure and temperature of adsorption tower A and adsorption tower B. Then, adsorption tower A will switch to reverse regeneration and adsorption tower B will switch to forward adsorption of solvent. The switch status of each inlet valve and outlet valve rotates accordingly.

6. A low-temperature closed-circuit spray drying system according to claim 1, characterized in that: It also includes an oxygen content detector, an air supply valve, an isolation valve and an exhaust valve. The oxygen content detector is arranged at the air outlet of the second throttle valve, and is used to detect the oxygen content in the dehumidified gas medium in real time, and send the detection data to the system controller. The connecting pipe between the heater and the blower is provided with an air supply valve, an isolation valve and an exhaust valve in sequence. The low-temperature closed-loop spray drying system should be maintained in a low-oxygen state. When the oxygen content in the system exceeds the set value, the system controller controls the air supply valve to supplement the circulating gas medium to ensure that the low-oxygen state is maintained and the product is not changed. The exhaust valve is used to open the air supply valve and the exhaust valve at the same time before the system is started, so that the gas medium is input into the liquid drying device while oxygen is discharged, so that a low oxygen environment is formed in the liquid drying device; the exhaust valve is also used to maintain the system pressure. When the pressure in the liquid drying device exceeds the set value, the system controller controls the exhaust valve to exhaust outwards.

7. A low-temperature closed-circuit spray drying system according to claim 1, characterized in that: The liquid material batching and conveying device includes a liquid preparation tank, a feeding pump and a liquid material flow meter. The liquid preparation tank is provided with a stirring device inside for dissolving the raw material and the solvent into a liquid material; the liquid preparation tank is provided with a heating jacket outside for heating and keeping the liquid material warm; the liquid preparation tank is provided with an inert gas protection device for isolating the liquid material from contact with the external air to avoid material denaturation, degradation and oxidation; the liquid preparation tank is provided with a homogenizing and emulsifying device for refining the material so that the material can be more evenly dispersed in the liquid material.

8. A low-temperature closed-circuit spray drying system according to claim 1, characterized in that: The liquid drying device comprises a drying tower and an atomizing device arranged on the top of the drying tower. The upper part of the drying tower is a cylindrical structure, and the lower part is an inverted cone structure. The taper of the inverted cone structure is ≤60°. A vibrating hammer that is conducive to discharging is installed on the outer side wall of the inverted cone structure. The atomizing device is an air flow atomizing device, a centrifugal atomizing device or a pressure atomizing device; The outer side surface of the side wall of the drying tower is provided with a heat-insulating jacket or a cooling jacket. The heat-insulating jacket is used for drying non-heat-sensitive materials, and the cooling jacket is used for drying heat-sensitive materials.

9. A low-temperature closed-circuit spray drying system according to claim 2, characterized in that: The material-gas separation device comprises a cyclone separator, a bag filter and a second high-efficiency filter, the material outlet at the lower end of the material-liquid drying device is connected to the material inlet of the cyclone separator, the air outlet at the top of the cyclone separator is connected to the material inlet of the bag filter, the air outlet at the top of the bag filter is connected to the air inlet of the second high-efficiency filter, the air outlet of the second high-efficiency filter is connected to the air inlet of the induced draft fan, and the solid powder product outlets at the bottom of the cyclone separator and the bottom of the bag filter are both connected to the product collection air delivery pipeline; A pulse back-flushing unit is arranged on the top of the bag filter, and the back-flushing gas of the pulse back-flushing unit adopts inert gas.

10. A low-temperature closed-circuit spray drying system according to claim 9, characterized in that: The cyclone separator comprises a primary cyclone separator and a secondary cyclone separator, the feed port of the primary cyclone separator is connected to the discharge port of the liquid drying device, the upper air outlet of the primary cyclone separator is connected to the feed port of the secondary cyclone separator, the upper air outlet of the secondary cyclone separator is connected to the feed port of the bag filter, and the solid powder product outlets at the bottom of the primary cyclone separator and the secondary cyclone separator are both connected to the product collection air delivery pipeline.

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