Nitric acid evaporator heat recovery system in adipic acid production process

Abstract

The utility model discloses a nitric acid evaporator heat recovery system in the adipic acid production process. The nitric acid evaporator heat recovery system comprises a falling film evaporator, a cyclohexanol material heater, a steam condensate storage tank, a material storage tank, an evaporator feeding tank, a feeding heater and the like. Materials in an evaporator feeding tank are preheated and heated through a feeding heater and enter a falling film evaporator; after the material is heated and evaporated by using high-pressure steam as a heat source, the binary acid material enters a material storage tank and then enters a binary acid separation device; a gas-phase substance of the falling-film evaporator enters a nitrous acid recovery system; high-temperature steam condensate enters the cyclohexanol material heater to serve as a heat exchange medium, steam condensate return water subjected to heat exchange of the cyclohexanol material heater is sent to the steam condensate storage tank, and then the steam condensate return water is sent to the feeding heater through the steam condensate conveying pump to preheat materials. Heat is transferred from the falling film evaporator to the cyclohexanol material heater and then to the feeding heater, and is subjected to three times of heat exchange, so that the heat of high-pressure steam is fully utilized, and the consumption of steam in production is reduced.

Description

Technical Field

[0001] This utility model designs an evaporator heat recovery device, specifically relating to a nitric acid evaporator heat recovery system in the adipic acid production process. Background Technology

[0002] Currently, the main adipic acid production process both domestically and internationally is the nitric acid oxidation of cyclohexanol, which has advantages such as high reaction efficiency, good selectivity, and high product yield. In the cyclohexanol oxidation process, nitric acid is used as the oxidant under the action of a catalyst to produce adipic acid. To ensure stable production, ease of control, reduce side reactions, and improve the yield of adipic acid, an excess of nitric acid is usually added. Therefore, the adipic acid waste liquid contains a certain proportion of nitric acid solution. Falling film evaporators are used to recover the nitric acid from the adipic acid waste liquid. However, the nitric acid recovery process in falling film evaporators requires high-pressure steam. However, the condensate of high-pressure steam is very hot, and direct discharge poses safety hazards and wastes heat energy. Therefore, based on the production concepts of safety, reduced consumption, and energy saving, there is still room for optimization in the nitric acid recovery process of nitric acid evaporators. Utility Model Content

[0003] The purpose of this invention is to provide a heat recovery system for a nitric acid evaporator in the adipic acid production process, so as to realize the heat recovery during the nitric acid evaporation process, reduce energy consumption costs, and thus reduce the production cost of adipic acid.

[0004] To solve the aforementioned technical problems in the production process, the technical approach adopted by this utility model is as follows:

[0005] A heat recovery system for a nitric acid evaporator in an adipic acid production process includes a nitric acid evaporator, a cyclohexanol material heater, a steam condensate storage tank, a material storage tank, and a feed heater. The tube-side inlet of the nitric acid evaporator is connected to a high-pressure steam pipeline. The tube-side outlet of the nitric acid evaporator is connected to the tube-side inlet of the cyclohexanol material heater via a pipeline and a steam trap valve assembly installed on the pipeline, thereby heating the cyclohexanol material in the shell side of the cyclohexanol material heater. The tube-side outlet of the cyclohexanol material heater is connected to the inlet of the steam condensate storage tank. The outlet of the steam condensate storage tank is connected to the tube-side inlet of the feed heater. The steam condensate from the tube-side outlet of the feed heater is discharged externally. The shell-side inlet of the feed heater is connected to the evaporator feed tank. The shell-side outlet of the feed heater is connected to the shell-side inlet of the nitric acid evaporator.

[0006] Furthermore, the nitric acid evaporator has a gas phase outlet at the top of the shell side and a liquid phase outlet at the bottom of the shell side. The liquid phase outlet is connected to the material storage tank, and the gas phase outlet is connected to the nitrite absorption system to recover nitric acid. The liquid phase outlet in the material storage tank is connected to the dicarboxylic acid separation process, and the gas phase outlet in the material storage tank is connected to the gas phase system.

[0007] Furthermore, a steam condensate transfer pump is installed on the pipeline between the steam condensate storage tank and the feed heater, and a material transfer pump is installed on the pipeline between the evaporator feed tank and the feed heater. Two pipelines are installed at the outlet of the steam condensate transfer pump, one of which is connected to the feed heater, and the other of which is connected to the feed pipeline of the material transfer pump.

[0008] Furthermore, the pipeline between the feed heater and the nitric acid evaporator is equipped with a main feed valve, a feed regulating valve, and a feed flow meter in sequence according to the flow direction of the material. The feed regulating valve and the feed flow meter are connected in a single-loop control manner so that the opening degree of the feed regulating valve is controlled by the flow data of the feed flow meter.

[0009] Furthermore, a steam regulating valve is installed on the high-pressure steam pipeline, and a steam pressure gauge is installed on the shell side of the nitric acid evaporator. The steam regulating valve and the steam pressure gauge are connected in a single-loop control manner so that the opening degree of the steam regulating valve is controlled by the pressure data of the steam pressure gauge.

[0010] Furthermore, the steam trap valve assembly includes a steam trap and a steam trap bypass. The steam trap is a dual-valve steam trap, and valves are provided on the front and rear pipes of the steam trap and on the steam trap bypass.

[0011] Furthermore, the nitric acid evaporator is a falling film evaporator, and each tube in the top section of the nitric acid evaporator is equipped with a distributor to ensure that the incoming material is evenly distributed and flows downwards.

[0012] Furthermore, the cyclohexanol material heater is located on the main pipeline, and a bypass pipeline connected in parallel with the cyclohexanol material heater is provided on the main pipeline.

[0013] Furthermore, the nitric acid evaporator, the cyclohexanol material heater, and the feed heater are all shell-and-tube heat exchangers, in which the material flows through the shell side and the heat exchange medium flows through the tube side. The material and heat exchange medium in the nitric acid evaporator and the feed heater exchange heat in a co-current manner, while the material and heat exchange medium in the cyclohexanol material heater exchange heat in a counter-current manner.

[0014] The process of using this utility model is as follows: During the evaporation process of the nitric acid evaporator, nitric acid vapor goes to the nitrite absorption system, and after recovery, nitric acid is reused. The liquid phase in the nitric acid evaporator forms a film under the action of the distributor and the solution's own gravity. After evaporation, the liquid phase flows into the material storage tank and is sent to the dicarboxylic acid separation process. High-pressure steam is condensed in the falling film nitric acid evaporator and discharged as high-temperature steam condensate through the steam trap valve group, sent to the cyclohexanol material heater. After further condensation, the condensate still has high heat energy and is sent to the condensate storage tank. The condensate is pumped by the steam condensate pump to the feed heater to preheat the material in the evaporator feed tank. The preheated and cooled steam condensate is then sent for reuse. Simultaneously, a branch pipe is installed on the main pipe of the steam condensate transfer pump, connected to the inlet of the material transfer pump, used to replace the material transfer pump and pipeline when the unit is stopped or the pump is switched.

[0015] Advantages of this utility model:

[0016] (1) In the process of cyclohexanol production, medium-pressure steam is needed to heat up the cold material. The high-temperature steam condensate of the nitric acid evaporator replaces the medium-pressure steam of the cyclohexanol heater as the heat source, so as to realize the reasonable recovery and utilization of the heat of the steam condensate and reduce the consumption of medium-pressure steam in cyclohexanol production.

[0017] (2) Since the material temperature in the feed tank of the nitric acid evaporator is low, directly supplying it to the nitric acid evaporator will result in more high-pressure steam consumption. A feed heater is installed before the nitric acid evaporator to preheat the material before supplying it to the nitric acid evaporator, thereby reducing the amount of high-pressure steam used.

[0018] (3) The feed heater needs a heat source to heat up. The condensate of the cooled steam is used to heat up the feed heater, which reduces the intervention of other heat sources (such as low-pressure steam) and achieves the goal of making full use of thermal energy. Attached Figure Description

[0019] Appendix Figure 1 The diagram shows the process flow of this utility model, with the following symbols representing the components: 1. Nitric acid evaporator, 2. Cyclohexanol material heater, 3. Steam condensate storage tank, 4. Material storage tank, 5. Feed heater, 6. Steam condensate transfer pump, 7. Material transfer pump, 8. Evaporator feed tank, 9. Feed flow meter, 10. Feed regulating valve, 11. Steam regulating valve, 12. Steam pressure gauge, 13. Steam trap valve assembly, 131. Steam trap, 132. Steam trap bypass, 14. Main feed valve, 15. Feed replacement valve. Detailed Implementation

[0020] The present invention will be further explained and illustrated below with specific examples, but this does not limit the scope of protection of the present invention.

[0021] A device for recovering heat from the evaporation of adipic acid and nitric acid, such as Figure 1As shown, the system includes a nitric acid evaporator 1, a cyclohexanol material heater 2, a steam condensate storage tank 3, a material storage tank 4, and a feed heater 5. The tube-side inlet of the nitric acid evaporator 1 is connected to a high-pressure steam pipeline. The tube-side outlet of the nitric acid evaporator 1 is connected to the tube-side inlet of the cyclohexanol material heater 2 via a pipeline and a steam trap valve group 13 installed on the pipeline, thereby heating the cyclohexanol material in the shell side of the cyclohexanol material heater 2. The tube-side outlet of the cyclohexanol material heater 2 is connected to the inlet of the steam condensate storage tank 3. The outlet of the steam condensate storage tank 3 is connected to the tube-side inlet of the feed heater 5 via a pipeline and a steam condensate transfer pump 6 installed on the pipeline. The steam condensate from the tube-side outlet of the feed heater 5 is sent out. The shell-side inlet of the feed heater 5 is connected to the evaporator feed tank 8, and the shell-side outlet of the feed heater 5 is connected to the shell-side inlet of the nitric acid evaporator 1.

[0022] The nitric acid evaporator 1 has a gas phase outlet at the top of the shell side and a liquid phase outlet at the bottom of the shell side. The liquid phase outlet is connected to the material storage tank 4, and the gas phase outlet is connected to the nitrite absorption system to recover nitric acid. The liquid phase outlet in the material storage tank 4 is connected to the dicarboxylic acid separation process, and the gas phase outlet in the material storage tank 4 is connected to the gas phase system.

[0023] The pipeline between the evaporator feed tank 8 and the feed heater 5 is equipped with a material conveying pump 7. The outlet of the steam condensate conveying pump 6 is equipped with two pipelines, one of which is connected to the feed heater 5 and the other of which is connected to the feed pipeline of the material conveying pump 7.

[0024] The pipeline between the feed heater 5 and the nitric acid evaporator 1 is equipped with a feed main valve 14, a feed regulating valve 10 and a feed flow meter 9 in sequence according to the flow direction of the material. The feed regulating valve 10 and the feed flow meter 9 are connected in a single-loop control manner so that the opening degree of the feed regulating valve 10 is controlled by the flow data of the feed flow meter 9.

[0025] The high-pressure steam pipeline is equipped with a steam regulating valve 11, and the shell side of the nitric acid evaporator is equipped with a steam pressure gauge 12. The steam regulating valve 11 and the steam pressure gauge 12 are connected in a single-loop control manner so that the opening degree of the steam regulating valve 11 is controlled by the pressure data of the steam pressure gauge 12.

[0026] The steam trap valve group 13 includes a steam trap 131 and a steam trap bypass 132. The steam trap 131 is a double valve group steam trap, and valves are provided on the front and rear pipes of the steam trap 131 and on the steam trap bypass 132.

[0027] The nitric acid evaporator 1 is a falling film evaporator, and each tube in the top section of the nitric acid evaporator 1 is equipped with a distributor to ensure that the incoming material is evenly distributed and flows downwards.

[0028] The cyclohexanol material heater 2 is located on the main pipeline, and a bypass pipeline connected in parallel with the cyclohexanol material heater 2 is provided on the main pipeline. A bypass valve is provided on the bypass pipeline. Both the cyclohexanol material heater 2 and the feed heater 5 are shell-and-tube heat exchangers, in which the material flows through the shell side and the heat exchange medium flows through the tube side.

[0029] After passing through the steam regulating valve 11, the high-pressure steam from the nitric acid evaporator 1 exchanges heat with the adipic acid material from the feed heater 5 in a co-current manner. Then, it passes through the steam trap valve group 13 and is sent to the cyclohexanol material heater 2 by a differential flow. The cyclohexanol material and the steam condensate are in a counter-current manner, with the cyclohexanol material flowing through the shell side and the steam condensate flowing through the tube side. After one heat exchange, the steam condensate is sent to the steam condensate storage tank 3, which has a pipeline at the bottom connected to the steam condensate transfer pump 6. The steam condensate with heat energy is sent to the feed heater 5. The liquid kinetic energy in the feed heater 5 comes from the material transfer pump 7. The steam condensate heats the material in the feed heater 5. The steam condensate after heat exchange is sent out for recycling. The material in the feed heater 5 is sent to the nitric acid evaporator 1 for evaporation after passing through the feed main valve 14, the feed regulating valve 10, and the feed flow meter 9. The outlet of the steam condensate transfer pump 6 has a branch line leading to the inlet of the material transfer pump 7. This branch line is used to replace the outlet pipeline when the unit is stopped or the material transfer pump 7 is switched.

[0030] This utility model also includes a steam trap valve assembly 13, which is connected to the tube outlet at the bottom of the nitric acid evaporator 1 to remove non-condensable gases from the steam condensate.

[0031] In this embodiment, each tube in the top section of the nitric acid evaporator 1 is equipped with an overflow distributor with a height of 10 cm.

[0032] In this embodiment, the steam regulating valve 11 and the steam pressure gauge 12 form a simple control system, and a root valve is provided at the steam pressure gauge 12; the feed regulating valve 10 and the feed flow meter 9 form a simple control system.

[0033] In this embodiment, the nitric acid evaporator 1, the cyclohexanol material heater 2, and the feed heater 5 are all shell-and-tube heat exchangers. The nitric acid evaporator 1 and the feed heater 5 exchange heat in a co-current manner, while the cyclohexanol material heater 2 exchanges heat in a counter-current manner.

[0034] In daily production, the material in nitric acid evaporator 1 comes from adipic acid mother liquor transported by material conveying pump 7. After preheating by feed heater 5, it is fed into nitric acid evaporator 1 to evaporate nitric acid, controlled by feed regulating valve 10 and feed flow meter 9. The evaporated nitric acid gas is distilled off at the top and supplied to the nitrite absorption system for absorption and reuse. The liquid phase of nitric acid evaporator 1 is evenly distributed by distributor, and then flows along the wall into material storage tank 4 under the action of elevation difference. From material storage tank 4, it is sent to the dicarboxylic acid separation process for separation. The top of material storage tank 4 is equipped with a gas phase pipeline to the gas phase collection system, where it is chemically absorbed and reused. Nitric acid evaporator 1 is heated by high-pressure steam. The high-pressure steam is controlled by a simple control system consisting of steam regulating valve 11 and steam pressure gauge 12 to ensure the pressure and temperature requirements of nitric acid evaporator 1 when the load changes. The steam condensate in nitric acid evaporator 1 passes through steam trap valve group 13 and then enters cyclohexanol material heater 2. Steam trap valve group 13 has a bypass branch for maintenance and replacement of the steam trap. The cyclohexanol material heater 2 is a counter-current shell-and-tube heat exchanger. Through counter-current heat exchange, the cold cyclohexanol material is heated, while the temperature of the steam condensate decreases, and it is collected in the steam condensate storage tank 3. The condensate is then pumped by the steam condensate transfer pump 6 to the feed heater 5 for further heating. The outlet of the steam condensate transfer pump 6 has two branches, leading to the feed heater 5 and the inlet of the material transfer pump 7, respectively. After passing through the main feed valve 14, the feed regulating valve 10, and the feed flow meter 9, the condensate from the feed heater 5 enters the nitric acid evaporator 1, realizing the recycling of the steam condensate from the nitric acid evaporator 1.

[0035] According to the process design, the heat source for nitric acid evaporator 1 is high-pressure steam, and the pressure control system is set to 1.5 MPa (gauge pressure). Its feed composition consists of succinic acid, glutaric acid, adipic acid, water, nitric acid, metal catalyst ions, and monobasic acids. The cold-end feed temperature of cyclohexanol material heater 2 is designed to be 93℃, and the hot-end discharge temperature is designed to be 122℃. The bottom condensate temperature of nitric acid evaporator 1 is approximately 195℃, with a temperature deviation of ±5℃ depending on the load of nitric acid evaporator 1. After heat exchange, the steam condensate temperature is still 113℃. The cold-end feed temperature of feed heater 5 is approximately 65℃, and the hot-end discharge temperature is required to be approximately 90℃. The steam condensate feed temperature is approximately 118℃ (after deducting heat loss during transportation), and the discharge temperature is approximately 57℃. With this process addition, the daily consumption of low-pressure steam during nitric acid evaporation is reduced by approximately 31.3%, the daily consumption of medium-pressure steam is reduced by approximately 34.6%, and the daily consumption of high-pressure steam is reduced by approximately 19.7%, further saving on adipic acid production costs.

[0036] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art should understand that modifications and equivalent substitutions can be made to the technical solutions of this patent without departing from the spirit and scope of this patent, and all such modifications and substitutions should be covered within the scope of the claims of this patent.

Claims

1. A heat recovery system for a nitric acid evaporator in an adipic acid production process, characterized in that, The system includes a nitric acid evaporator, a cyclohexanol material heater, a steam condensate storage tank, a material storage tank, and a feed heater. The tube-side inlet of the nitric acid evaporator is connected to a high-pressure steam pipeline. The tube-side outlet of the nitric acid evaporator is connected to the tube-side inlet of the cyclohexanol material heater via a pipeline and a steam trap valve assembly installed on the pipeline, thereby heating the cyclohexanol material in the shell side of the cyclohexanol material heater. The tube-side outlet of the cyclohexanol material heater is connected to the inlet of the steam condensate storage tank. The outlet of the steam condensate storage tank is connected to the tube-side inlet of the feed heater. The steam condensate from the tube-side outlet of the feed heater is discharged externally. The shell-side inlet of the feed heater is connected to the evaporator feed tank. The shell-side outlet of the feed heater is connected to the shell-side inlet of the nitric acid evaporator.

2. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, The nitric acid evaporator has a gas phase outlet at the top of the shell side and a liquid phase outlet at the bottom of the shell side. The liquid phase outlet is connected to the material storage tank, and the gas phase outlet is connected to the nitrite absorption system to recover nitric acid. The liquid phase outlet in the material storage tank is connected to the dicarboxylic acid separation process, and the gas phase outlet in the material storage tank is connected to the gas phase system.

3. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, A steam condensate transfer pump is installed on the pipeline between the steam condensate storage tank and the feed heater, and a material transfer pump is installed on the pipeline between the evaporator feed tank and the feed heater. Two pipelines are installed at the outlet of the steam condensate transfer pump, one of which is connected to the feed heater and the other of which is connected to the feed pipeline of the material transfer pump.

4. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, The pipeline between the feed heater and the nitric acid evaporator is equipped with a main feed valve, a feed regulating valve, and a feed flow meter in sequence according to the flow direction of the material. The feed regulating valve and the feed flow meter are connected in a single-loop control manner so that the opening degree of the feed regulating valve is controlled by the flow data of the feed flow meter.

5. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, A steam regulating valve is installed on the high-pressure steam pipeline, and a steam pressure gauge is installed on the shell side of the nitric acid evaporator. The steam regulating valve and the steam pressure gauge are connected in a single-loop control manner so that the opening degree of the steam regulating valve is controlled by the pressure data of the steam pressure gauge.

6. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, The steam trap valve group includes a steam trap and a steam trap bypass. The steam trap is a double valve group steam trap. Valves are provided on the front and rear pipes of the steam trap and on the steam trap bypass.

7. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, 2, 4 or 5, characterized in that, The nitric acid evaporator is a falling film evaporator, and each tube in the top section of the nitric acid evaporator is equipped with a distributor to ensure that the incoming material is evenly distributed and flows downwards.

8. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, The cyclohexanol material heater is located on the main pipeline, and a bypass pipeline connected in parallel with the cyclohexanol material heater is provided on the main pipeline.

9. The nitric acid evaporator heat recovery system in the adipic acid production process according to claim 1, characterized in that, The nitric acid evaporator, cyclohexanol material heater, and feed heater are all shell-and-tube heat exchangers, in which the material flows through the shell side and the heat exchange medium flows through the tube side. In the nitric acid evaporator and the feed heater, the material and the heat exchange medium exchange heat in a co-current manner, while in the cyclohexanol material heater, the material and the heat exchange medium exchange heat in a counter-current manner.

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