A cooling system for NMP rectification

Abstract

The application relates to a cooling system for NMP rectification, which comprises a condenser, a cooling tower, a lithium bromide cooling unit and a cooling water storage tank, the lithium bromide cooling unit is internally provided with an evaporation area, a liquefaction area and a throttle valve, rectification tower steam condensate outside the lithium bromide cooling unit passes through the evaporation area and is connected with the cooling tower, a circulating water pool is arranged at the bottom of the cooling tower, the cooling tower and the circulating water pool are both connected with the liquefaction area, a feeding port and a discharging port are arranged on the condenser and used for conveying NMP materials, a liquid inlet and a liquid outlet are arranged on the condenser, the liquid outlet is connected with the throttle valve inside the lithium bromide cooling unit, a liquid inlet pipe is arranged between the liquid inlet and the throttle valve, and the cooling water storage tank is arranged on the liquid inlet pipe. The application can improve the purification effect of NMP recovery.

Description

Technical Field

[0001] This application relates to the field of NMP recovery technology, and in particular to a cooling system for NMP distillation. Background Technology

[0002] NMP is a commonly used organic solvent with wide applications in industry. NMP recovery and NMP distillation are two processes related to NMP treatment. NMP recovery refers to the process of reusing used NMP. In some industrial processes, NMP may be contaminated or diluted, requiring recovery for extraction and purification.

[0003] NMP recovery typically involves both physical and chemical methods. Physical methods include techniques such as distillation, evaporation, rectification, and extraction, used to separate and recover NMP from waste liquids. NMP rectification is a purification process for NMP. Through rectification, impurities and other solvents in NMP can be separated to obtain a high-purity NMP product.

[0004] When recovering NMP, NMP is in a gaseous state and needs to be liquefied by a condenser during cooling to separate impurities from the NMP. Existing circulating water towers are commonly used to supply cooling water to the condenser and provide refrigeration conditions. However, in summer, the ambient temperature of the water inside the circulating water tower is around 30 degrees Celsius. Thus, the NMP material will not be lower than 30 degrees Celsius after cooling, and there is a possibility that the gaseous NMP material will not be completely liquefied, forming a gas-liquid mixture. On the one hand, the unliquefied NMP material will enter the vacuum pump of the distillation column later. The impurities inside the NMP material can easily corrode the vacuum pump components of the distillation column. On the other hand, it reduces the purification effect of NMP recovery. Summary of the Invention

[0005] To improve the purification effect of NMP recovery, this application provides a cooling system for NMP distillation.

[0006] This application provides a cooling system for NMP distillation using the following technical solution:

[0007] A cooling system for NMP distillation includes a condenser, a cooling tower, a lithium bromide cooling unit, and a cooling water storage tank. The lithium bromide cooling unit has an evaporation zone, a liquefaction zone, and a throttling valve inside. The condensate from the distillation tower passes through the evaporation zone and is connected to the cooling tower. A circulating water pool is provided at the bottom of the cooling tower. Both the cooling tower and the circulating water pool are connected to the liquefaction zone. The condenser has a feed inlet, a discharge outlet, a liquid inlet, and a liquid outlet. The feed inlet and the discharge outlet are used to transport NMP material. The liquid outlet is connected to the throttling valve inside the lithium bromide cooling unit. An inlet pipe is installed between the liquid inlet and the throttling valve. The cooling water storage tank is installed on the liquid inlet pipe.

[0008] By adopting the above technical solution, the high-temperature distillation column steam condensate passes through the evaporation zone inside the lithium bromide unit. The lithium bromide aqueous solution inside the lithium bromide cooling unit evaporates into water vapor after passing through the evaporation zone. Subsequently, the water in the circulating water tank passes through the liquefaction zone, and the water vapor liquefies into high-pressure, low-temperature liquid water. The water in the circulating water tank is heated and returns to the cooling tower for cooling. The high-pressure, low-temperature liquid water reaches the throttling valve. At the same time, when the gaseous NMP material passes through the condenser, it is cooled by the cooling water in the cooling water storage tank and forms liquid NMP material. The heated cooling water flows through the throttling valve, and the high-pressure, low-temperature liquid water expands rapidly and vaporizes through the throttling valve. In this process, it absorbs a large amount of heat from the heated cooling water, and the cooling water cools down rapidly and returns to the cooling water storage tank for later use. The cooled distillation column steam condensate is discharged into the cooling tower, achieving the effect of circulating cooling of gaseous NMP material. High-pressure, low-temperature liquid water absorbs heat to become high-pressure, high-temperature liquid water, which is then used for initial cooling. The heated cooling water discharged from the condenser rapidly expands and vaporizes through a throttling valve, absorbing heat from the cooling water again. This two-stage heat absorption process rapidly cools the cooling water to about 10 degrees Celsius. The entire cooling process takes place inside the lithium bromide cooling unit and is unaffected by external environmental factors. In contrast, cooling tower cooling mainly relies on water evaporating and absorbing heat through contact with the surrounding air, which is more susceptible to environmental factors. Therefore, the cooling effect of cooling towers is limited in summer. Compared to the former, the cooling water temperature after two cooling stages is lower. This ensures that all gaseous NMP material can be liquefied, reducing the possibility of corrosion of the vacuum pump components in the subsequent distillation column, and also improves the purification effect of NMP recovery.

[0009] Optionally, the condenser includes a mounting cylinder, end caps, mounting plates, and cooling pipes. One end cap is installed at each end of the mounting cylinder. The feed inlet is located on one of the end caps, and the discharge outlet is located on the other end cap. The mounting plate is detachably connected between the end caps and the mounting cylinder. Several cooling pipes are detachably connected between the two mounting plates. The liquid inlet and the liquid outlet are both installed on the mounting cylinder and communicate with the interior of the mounting cylinder.

[0010] By adopting the above technical solution, when cooling gaseous NMP material, the gaseous NMP material enters the cooling pipe through the feed port. At the same time, the cooling water storage tank delivers cooling water to the installation cylinder through the liquid inlet, where it exchanges heat with the cooling pipe. Then, it flows to the throttle valve through the liquid outlet, where it is vaporized and absorbs heat by the lithium bromide aqueous solution. It then returns to the cooling water storage tank, thus forming a circulating cooling water circuit. When the gaseous NMP material encounters the cooler cooling pipe, it liquefies into liquid NMP material and is discharged from the discharge port, achieving the effect of cooling the gaseous NMP material.

[0011] Optionally, one end of the cooling pipe is provided with a connector, the surface of the connector is wrapped with a sealing strip, a retaining ring is connected to the connector, the cooling pipe is threaded through the connector onto one of the mounting plates, the retaining ring is attached to the mounting plate, a connecting sleeve is connected to another mounting plate, and the other end of the cooling pipe passes between the connecting sleeve and the other mounting plate.

[0012] By adopting the above technical solution, when installing the cooling pipe, the connector is threaded onto one of the mounting plates until the retaining ring abuts against the mounting plate. Then, the other end of the cooling pipe is inserted into the other mounting plate to complete the installation of the cooling pipe. After the cooling pipe comes into contact with gaseous NMP material, it will deform upon heating. The other end of the cooling pipe is inserted into the connecting sleeve, providing an extension condition for the heated side of the cooling pipe and reducing the possibility of deformation and damage to the cooling pipe.

[0013] Optionally, a plurality of heat dissipation plates are connected to the surface of the cooling pipe, and the plurality of heat dissipation plates are evenly distributed around the circumference of the cooling pipe.

[0014] By adopting the above technical solution, the heat dissipation plate is used to increase the contact area between the cooling pipe and the cooling water inside the mounting cylinder, thereby increasing the heat exchange between the cooling pipe and the cooling water per unit time and further improving the cooling effect of NMP materials.

[0015] Optionally, a regenerating pipe is connected between the liquid outlet and the throttling valve. Several heat-conducting rods are threaded through the regenerating pipe, with some of the heat-conducting rods located inside the regenerating pipe and the remaining parts located outside the regenerating pipe.

[0016] By adopting the above technical solution and setting up heat-conducting rods, the heat inside the heat recovery pipe is dissipated to the outside through the heat-conducting rods, which helps to dissipate the heat of the cooling water inside the heat recovery pipe, so that the temperature of the cooling water returning to the cooling water storage tank is lower, and the cooling effect of gaseous NMP material is further improved.

[0017] Optionally, the mounting cylinder is connected to a plurality of connecting plates, the area of ​​which is larger than the area of ​​the semicircle inside the mounting cylinder, and adjacent connecting plates are staggered.

[0018] By adopting the above technical solution, the connecting plate is used to help extend the movement path of the cooling water into the installation cylinder, thereby increasing the contact time between the cooling pipe and the cooling water, so that the cooling pipe and the cooling water can exchange as much heat as possible, and further improving the cooling effect of gaseous NMP materials.

[0019] Optionally, a plurality of connecting posts are connected between two adjacent connecting plates.

[0020] By adopting the above technical solution, cooling water enters the mounting cylinder and is blocked by the connecting plate. The connecting plate will be subjected to a certain degree of impact, and after prolonged use, the connecting plate is prone to deformation and damage. By setting the connecting column, the structural strength of the connecting plate is improved, and the possibility of damage to the connecting plate is reduced.

[0021] Optionally, the cooling pipe is made of stainless steel.

[0022] By adopting the above technical solution, the cooling pipe made of stainless steel can meet the heat exchange requirements, have high hardness to reduce the degree of deformation of the cooling pipe, and have high corrosion resistance, which can withstand the internal corrosion from NMP materials and the corrosion from impurities in water, thus extending the service life of the cooling pipe.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] 1. The high-temperature distillation column steam condensate passes through the evaporation zone inside the lithium bromide unit. The lithium bromide aqueous solution inside the lithium bromide cooling unit evaporates into water vapor after passing through the evaporation zone. Subsequently, the water in the circulating water tank passes through the liquefaction zone, where the water vapor liquefies into high-pressure, low-temperature liquid water. The water in the circulating water tank is heated and returns to the cooling tower for cooling. The high-pressure, low-temperature liquid water reaches the throttling valve. At the same time, when the gaseous NMP material passes through the condenser, it is cooled by the cooling water in the cooling water storage tank and forms liquid NMP material. The heated cooling water flows through the throttling valve, where the high-pressure, low-temperature liquid water rapidly expands and vaporizes. In this process, it absorbs a large amount of heat from the heated cooling water, which rapidly cools down and returns to the cooling water storage tank for later use. The cooled distillation column steam condensate is discharged into the cooling tower, achieving the effect of circulating cooling of gaseous NMP material. High-pressure, low-temperature liquid water absorbs heat to become high-pressure, high-temperature liquid water, which is then used for initial cooling. The heated cooling water discharged from the condenser rapidly expands and vaporizes through a throttling valve, absorbing heat from the cooling water again. This two-stage heat absorption process rapidly cools the cooling water to about 10 degrees Celsius. The entire cooling process takes place inside the lithium bromide cooling unit and is unaffected by external environmental factors. In contrast, cooling tower cooling mainly relies on water evaporating and absorbing heat through contact with the surrounding air, which is more susceptible to environmental factors. Therefore, the cooling effect of cooling towers is limited in summer. Compared to the former, the cooling water temperature after two cooling stages is lower. This ensures that all gaseous NMP material can be liquefied, reducing the possibility of corrosion of the vacuum pump components in the subsequent distillation column, and also improves the purification effect of NMP recovery. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall principle of the cooling system in the embodiments of this application.

[0026] Figure 2 This is a schematic diagram of the condenser in an embodiment of this application.

[0027] Figure 3 This is a cross-sectional view used in the embodiments of this application to illustrate the internal structure of the condenser.

[0028] Figure 4 This is an exploded view used in the embodiments of this application to illustrate the structure of the cooling pipe and connecting plate.

[0029] Figure 5 This is an exploded view used to illustrate the cooling pipe structure in the embodiments of this application.

[0030] Explanation of reference numerals in the attached drawings: 1. Condenser; 11. Mounting cylinder; 111. Liquid inlet; 112. Liquid outlet; 113. Heat recovery pipe; 1131. Heat conduction rod; 114. Connecting plate; 1141. Connecting column; 12. End cap; 121. Feed inlet; 122. Discharge outlet; 13. Mounting plate; 14. Cooling pipe; 141. Connector; 1411. Retaining ring; 142. Connecting sleeve; 143. Heat dissipation plate; 2. Cooling tower; 21. Circulating water tank; 3. Lithium bromide cooling unit; 31. Lithium bromide aqueous solution; 32. Evaporation zone; 33. Liquefaction zone; 34. Throttling valve; 4. Cooling water storage tank. Detailed Implementation

[0031] The following is in conjunction with the appendix Figures 1-5 This application will be described in further detail.

[0032] This application discloses a cooling system for NMP distillation. (Refer to...) Figure 1 The cooling system for NMP distillation includes a condenser 1, a cooling tower 2, a lithium bromide cooling unit 3, and a cooling water storage tank 4. The lithium bromide cooling unit 3 internally houses a lithium bromide aqueous solution 31, an evaporation zone 32, a liquefaction zone 33, and a throttling valve 34. A circulating water tank 21 is located below the cooling tower 2, and both the circulating water tank 21 and the cooling tower 2 are connected to the liquefaction zone 33. A condensate pipe for conveying condensate from the distillation tower is installed on the evaporation zone 32. The lithium bromide aqueous solution 31 passes sequentially through the evaporation zone 32, the liquefaction zone 33, and the throttling valve 34.

[0033] Reference Figure 1 , Figure 2 and Figure 3The condenser 1 includes a mounting cylinder 11, end caps 12, a mounting plate 13, and cooling pipes 14. The mounting cylinder 11 has openings at both ends. One end cap 12 is connected to each end of the mounting cylinder 11 via a flange. One end cap 12 has a feed inlet 121, and the other end cap 12 has a discharge outlet 122. A liquid inlet 111 and a liquid outlet 112 are fixedly connected to the mounting cylinder 11, with the liquid outlet 112 located above the liquid inlet 111. Both the liquid inlet 111 and the liquid outlet 112 communicate with the interior of the mounting cylinder 11. An inlet pipe is installed between the liquid inlet 111 and the throttle valve 34, and a cooling water storage tank 4 is installed on the inlet pipe. A heat recovery pipe 113 is connected between the liquid outlet 112 and the throttle valve 34. Several heat conduction rods 1131 are installed on the heat recovery pipe 113. Some of the heat conduction rods 1131 are located inside the heat recovery pipe 113, and the remaining part is located outside the heat recovery pipe 113. The heat conduction rods 1131 are used to help dissipate the heat inside the heat recovery pipe 113.

[0034] Reference Figure 3 , Figure 4 and Figure 5 Mounting plates 13 are provided at both ends of the mounting cylinder 11, and are installed between the end cap 12 and the mounting cylinder 11. Cooling pipes 14 are made of 304 stainless steel and several are arranged between the two mounting plates 13. One end of each cooling pipe 14 is fixedly connected to a connector 141, with a sealing strip wound around it to improve the seal between the connector 141 and the mounting plate 13. A retaining ring 1411 is also fixedly connected to the connector 141. The cooling pipe 14 is threaded onto one of the mounting plates 13 via the connector 141. A connecting sleeve 142 is fixedly connected to the other mounting plate 13, and the other end of the cooling pipe 14 is inserted between the connecting sleeve 142 and the other mounting plate 13. The engagement of the connector 141 and the retaining ring 1411 allows for quick installation of the cooling pipe 14, while the engagement of the connecting sleeve 142 and the cooling plate allows for the deformation and extension of the cooling pipe 14.

[0035] Reference Figure 5 In order to improve the heat exchange between the cooling pipe 14 and the cooling water, several heat dissipation plates 143 are fixedly connected to the surface of the cooling pipe 14. In this embodiment, four plates are used as an example.

[0036] Reference Figure 3 and Figure 4 Several connecting plates 114 are fixedly connected inside the mounting cylinder 11. The area of ​​the connecting plates 114 is larger than the area of ​​the semicircle inside the mounting cylinder 11, and adjacent connecting plates 114 are staggered. A connecting post 1141 is fixedly connected between adjacent connecting plates 114. The connecting post 1141 is used to improve the structural strength of the connecting plates 114.

[0037] The implementation principle of a cooling system for NMP distillation according to an embodiment of this application is as follows: During purification, the condensate from the distillation column, which has a higher external temperature, enters the evaporation zone 32 through the condensate pipe to heat the evaporation zone 32. The water in the circulating water tank 21 enters the liquefaction zone 33 to cool the liquefaction zone 33. The lithium bromide aqueous solution 31 inside the lithium bromide cooling unit 3 evaporates into water vapor after passing through the evaporation zone 32, and then liquefies into high-pressure, low-temperature liquid water after passing through the liquefaction zone 33. Subsequently, it flows to the throttle valve 34. At the same time, gaseous NMP material enters through the feed inlet 1. 21 enters the cooling pipe 14 and exchanges heat with the cooling water output from the cooling water storage tank 4 through the cooling pipe 14, causing the gaseous NMP material to be cooled and liquefied. The heated cooling water returns to the throttle valve 34 through the heat return pipe 113. Some of the heat is dissipated through the heat conduction rod 1131. The high-pressure low-temperature liquid water expands and vaporizes (flash evaporation) under the influence of the throttle valve 34. During this process, it absorbs the heat of the heated cooling water twice. After the cooling water is cooled down, it returns to the cooling water storage tank 4. The condensate of the distillation column steam after heat absorption is discharged into the cooling tower 2 to dissipate heat, thereby achieving the effect of continuously cooling the gaseous NMP material.

[0038] High-pressure, low-temperature liquid water absorbs heat to become high-pressure, high-temperature liquid water, which initially cools the heated cooling water discharged from condenser 1. The heated water then rapidly expands and vaporizes through throttling valve 34, absorbing heat from the cooling water again. This two-stage heat absorption process rapidly cools the cooling water to about 10 degrees Celsius. The entire cooling process takes place inside the lithium bromide cooling unit 3 and is unaffected by external environmental factors. In contrast, cooling tower 2 relies mainly on the evaporation and heat absorption of water in contact with the surrounding air, making it more susceptible to environmental factors. Therefore, the cooling effect of cooling tower 2 is limited in summer. In comparison, the cooling water temperature after two cooling stages is lower, which ensures that all gaseous NMP material can be liquefied, reducing the possibility of corrosion of the vacuum pump components in the subsequent distillation tower, and improving the purification effect of NMP recovery.

[0039] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A cooling system for NMP distillation, characterized in that: The system includes a condenser (1), a cooling tower (2), a lithium bromide cooling unit (3), and a cooling water storage tank (4). The lithium bromide cooling unit (3) is equipped with an evaporation zone (32), a liquefaction zone (33), and a throttling valve (34). The condensate from the external distillation tower passes through the evaporation zone (32) and is connected to the cooling tower (2). A circulating water pool (21) is provided at the bottom of the cooling tower (2). Both the cooling tower (2) and the circulating water pool (21) are connected to the liquefaction zone (33). The condenser (1) is provided with a feed inlet (121), a discharge outlet (122), a liquid inlet (111) and a liquid outlet (112). The feed inlet (121) and the discharge outlet (122) are used to transport NMP material. The liquid outlet (112) is connected to the throttle valve (34) inside the lithium bromide cooling unit (3). A liquid inlet pipe is installed between the liquid inlet (111) and the throttle valve (34). The cooling water storage tank (4) is installed on the liquid inlet pipe.

2. The cooling system for NMP distillation according to claim 1, characterized in that: The condenser (1) includes a mounting cylinder (11), an end cap (12), a mounting plate (13), and a cooling pipe (14). One end cap (12) is installed at each end of the mounting cylinder (11). The feed inlet (121) is located on one of the end caps (12), and the discharge outlet (122) is located on the other end cap (12). The mounting plate (13) is detachably connected between the end cap (12) and the mounting cylinder (11). Several cooling pipes (14) are detachably connected between the two mounting plates (13). The liquid inlet (111) and the liquid outlet (112) are both installed on the mounting cylinder (11) and communicate with the interior of the mounting cylinder (11).

3. The cooling system for NMP distillation according to claim 2, characterized in that: One end of the cooling pipe (14) is provided with a connector (141), the surface of the connector (141) is wrapped with a sealing strip, and a retaining ring (1411) is connected to the connector (141). The cooling pipe (14) is threadedly connected to one of the mounting plates (13) through the connector (141), and the retaining ring (1411) fits against the mounting plate (13). A connecting sleeve (142) is connected to the other mounting plate (13), and the other end of the cooling pipe (14) passes between the connecting sleeve (142) and the other mounting plate (13).

4. The cooling system for NMP distillation according to claim 2, characterized in that: The surface of the cooling pipe (14) is connected to a plurality of heat dissipation plates (143), and the plurality of heat dissipation plates (143) are evenly distributed around the cooling pipe (14).

5. The cooling system for NMP distillation according to claim 1, characterized in that: A heat recovery pipe (113) is connected between the liquid outlet (112) and the throttle valve (34). Several heat-conducting rods (1131) are threaded through the heat recovery pipe (113). Some of the heat-conducting rods (1131) are located inside the heat recovery pipe (113), and the remaining part is located outside the heat recovery pipe (113).

6. The cooling system for NMP distillation according to claim 2, characterized in that: The mounting cylinder (11) is connected to a plurality of connecting plates (114). The area of ​​the connecting plates (114) is larger than the area of ​​the semicircle inside the mounting cylinder (11), and adjacent connecting plates (114) are staggered.

7. The cooling system for NMP distillation according to claim 6, characterized in that: A plurality of connecting posts (1141) are connected between two adjacent connecting plates (114).

8. The cooling system for NMP distillation according to claim 2, characterized in that: The cooling pipe (14) is made of stainless steel.

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