Circulating evaporation nitric acid recovery system in adipic acid production

Abstract

The invention discloses a circulating evaporation nitric acid recovery system in adipic acid production, which is provided with a gas-liquid separation circulating tank, a heater, a falling film evaporator and a vacuum system connected with the upper part of the gas-liquid separation circulating tank through a pipeline, and a flash plate with flash holes is laid in the gas-liquid separation circulating tank; the heaters comprise the first heater and the second heater which are arranged in parallel, forced circulation is adopted for the heaters and the gas-liquid separation circulation tank, materials are pushed to flow under the action of the circulation pump, the tube pass turbulence degree is improved, scaling is reduced, and the problems that a traditional evaporator is high in energy consumption, prone to scaling and the like are solved. In addition, a falling-film evaporator is adopted, a falling-film distributor, namely an overflow weir, is arranged above a tube bundle, materials uniformly enter a heating tube through the falling-film distributor, and a uniform thin liquid film is formed, so that turbulent flow is remarkably enhanced, a thermal boundary layer is destroyed, and strong shearing and scouring effects are generated.

Description

Technical Field

[0001] This invention belongs to the field of adipic acid production technology, and specifically relates to a circulating evaporation nitric acid recovery system in adipic acid production. Background Technology

[0002] The adipic acid unit uses cyclohexanol as raw material and produces adipic acid via nitric acid oxidation. Excess nitric acid is used in the oxidation reaction to stabilize the reaction, facilitate control, reduce side reactions, and increase the yield of adipic acid. This also reduces the NO produced during the oxidation reaction. X The gas is recovered and the mother liquor acid is recycled, which reduces the consumption of HNO3 and the loss of adipic acid.

[0003] The circulating evaporation system achieves efficient nitric acid recovery through multi-stage evaporation (such as rising film and falling film evaporators) and condensation technology, with a nitric acid recovery rate of over 95%, significantly reducing the consumption of fresh nitric acid and lowering raw material costs. Simultaneously, the latent heat of vapor recovered by the system is used for waste liquid preheating, forming a cascaded energy utilization system and further reducing energy consumption. However, this system requires the configuration of multi-stage evaporators, condensers, crystallization equipment, and an automated control system, resulting in a significant initial investment.

[0004] In adipic acid production, the nitric acid recovery evaporator is a falling film evaporator. Falling film evaporation relies on the formation of a uniform thin film of liquid on the heat exchange tube wall. If the liquid distribution is uneven, some tube walls will be exposed, and easily crystallizing materials will form scale on the tube walls, rapidly reducing heat transfer efficiency and requiring frequent cleaning.

[0005] Therefore, it is necessary to improve the circulating evaporation nitric acid recovery system in adipic acid production to solve the problems of high energy consumption and easy scaling of traditional evaporators. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a circulating evaporation nitric acid recovery system for adipic acid production, which solves the problems of high energy consumption and easy scaling in traditional evaporators.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A circulating evaporation nitric acid recovery system for adipic acid production includes a gas-liquid separation circulating tank, a heater, a falling film evaporator, and a vacuum system connected to the top of the gas-liquid separation circulating tank via pipelines. The gas-liquid separation circulating tank is lined with flash plates having flash holes. The heater includes a first heater and a second heater arranged in parallel. A circulating pump is also installed on the pipeline at the bottom of the gas-liquid separation circulating tank, entering the bottom of the first heater, the bottom of the second heater, and the top of the falling film evaporator from the bottom of the pipe. The material heated by the first heater enters the gas-liquid separation circulating tank through a discharge pipeline connected to the top of the first heater, with the inlet of the discharge pipeline located above the flash plate. The material entering the top of the falling film evaporator via the circulating pump, after acting within the falling film evaporator, flows to the top of the second heater through a top gas phase pipeline. The material heated by the second heater enters the gas-liquid separation circulating tank through a discharge pipeline connected to the top of the second heater, with the inlet of the discharge pipeline also located above the flash plate.

[0008] The top inner side of the falling film evaporator is also provided with an overflow weir, and the overflow weir includes an overflow weir tube seat and an overflow pipe fixed at the front end of the overflow weir. The overflow weir tube seat is fixedly installed on the falling film evaporator, and the overflow pipe has multiple overflow grooves located on the same horizontal plane, and the included angle of the teeth of adjacent overflow grooves is 45°~90°.

[0009] The first heater is also equipped with a temperature control pipeline, and the temperature control pipeline is equipped with an SL regulating valve, and the SL regulating valve is cascaded with a thermometer installed outside the gas-liquid separation circulation tank.

[0010] The bottom of the second heater is also equipped with a cooling pipeline. The recovered liquid enters the bottom of the gas falling film evaporator through the bottom pipeline of the second heater, and a cooler is installed on the cooling pipeline.

[0011] The upper part of the falling film evaporator is also equipped with a high-pressure steam regulating valve, which is connected in series with a thermometer installed at the bottom of the falling film evaporator for control.

[0012] The lower part of the tube side of the falling film evaporator is also provided with a dilution line for introducing diluent.

[0013] The flash pores are evenly distributed on the flash plate, and the pore diameter is 5~20mm.

[0014] A vertically arranged baffle is also provided behind the flash plate.

[0015] The heating temperature of the first heater is 85~95℃.

[0016] The beneficial effects of this invention are: This invention discloses a circulating evaporation nitric acid recovery system for adipic acid production. It comprises a gas-liquid separation circulating tank, heaters, a falling film evaporator, and a vacuum system connected to the gas-liquid separation circulating tank via pipeline. The gas-liquid separation circulating tank is lined with flash plates with flash holes. The heaters include a first heater and a second heater arranged in parallel. Forced circulation is applied between the heaters and the gas-liquid separation circulating tank, and the material flow is propelled by a circulating pump, increasing the turbulence in the tubes and reducing scaling. This solves the problems of high energy consumption and easy scaling associated with traditional evaporators. Furthermore, it employs… The falling film evaporator features a falling film distributor (overflow weir) above the tube bundle. Material enters the heating tubes uniformly through the distributor, forming a uniform thin liquid film (falling film). This significantly enhances turbulence, disrupts the thermal boundary layer, and generates strong shear and scouring effects. This structure substantially improves heat transfer efficiency by 30%-70%, significantly reduces steam consumption, effectively inhibits scaling, and extends the operating cycle. It is suitable for concentrating high-viscosity, easily scaling materials and has advantages such as compact structure and stable operation. This system enables continuous circulation of material between the evaporator and the circulating tank, achieving gradual concentration. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a structural cross-sectional view of the overflow weir; Figure 3 This is a side view of the overflow pipe; Figure 4 This is a side view of the flash plate; Figure 5 This is a top view of the flash plate. Detailed Implementation

[0018] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0019] This invention provides a circulating evaporation nitric acid recovery system for adipic acid production, such as... Figures 1 to 5 As shown.

[0020] A circulating evaporation nitric acid recovery system for adipic acid production includes a gas-liquid separation circulating tank a, a heater b, a falling film evaporator c, and a vacuum system e connected to the top of the gas-liquid separation circulating tank a via a pipeline. The gas-liquid separation circulating tank a is lined with a flash plate 1 having flash holes. The heater includes a first heater b and a second heater d arranged in parallel. A circulating pump a4 is also provided on the feed pipeline at the bottom of the gas-liquid separation circulating tank a, and enters the bottom of the first heater b, the bottom of the second heater d, and the top of the falling film evaporator c from the bottom of the pipe. The material heated by the first heater b enters the gas-liquid separation circulating tank a through the discharge pipeline b3 connected to the top of the first heater, and the inlet of the discharge pipeline b3 is located above the flash plate 1.

[0021] The material that enters the top of the falling film evaporator c via the circulating pump a4 is then transported to the top of the second heater d via the top vapor phase pipeline c4 after being acted upon in the falling film evaporator c. The material heated by the second heater d enters the gas-liquid separation circulation tank a through the discharge pipeline d1 connected to the top of the second heater d. The inlet of the discharge pipeline d1 is also located above the flash plate 1.

[0022] The material circulates between the forced circulation pump a4, the heating tube, and the gas-liquid separation circulation tank a. Inside the heating tube, the material is heated to boiling and generates steam. This steam then transfers heat between the various stages of evaporators in the heater, causing the moisture and nitric acid vapor in the material to be continuously evaporated. At the same time, the forced circulation system ensures that the material maintains a high-speed flow in the evaporation chamber, effectively preventing scaling and precipitation, and improving evaporation efficiency and heat transfer effect.

[0023] The inner top of the falling film evaporator c is also provided with an overflow weir. The overflow weir structure helps the liquid to be distributed more evenly, so that the liquid can better form a uniform liquid film when flowing down. The overflow weir includes an overflow weir tube seat 21 and an overflow pipe 22 fixed at the front end of the overflow weir. The two are fixed by a locking nut 23. The overflow weir tube seat 21 is fixedly installed on the falling film evaporator. The overflow weir tube seat 21 is provided with corresponding fixing screw holes 24. The opening of the overflow pipe 22 is arranged downward. Multiple overflow grooves are opened on the overflow pipe at the same horizontal plane, and the included angle of the teeth of adjacent overflow grooves is 45°~90°, which can make the liquid evenly distributed along the circumferential wall, ensuring that the liquid can flow evenly into the falling film evaporator tubes, improving the evaporation efficiency and heat exchange effect. The height of the overflow groove is usually 1-10mm, which can be determined according to the design requirements of the falling film evaporator and the characteristics of the material.

[0024] Overflow weirs require high precision in machining and installation. They have low flow resistance, which can prevent blockages and facilitate later use, disassembly, replacement and cleaning.

[0025] The gas-liquid separation circulation tank is connected to a vacuum system via pipeline at the top, and a pressure gauge maintains a slight negative pressure in the tank. The vacuum system includes a two-stage jet pump, a condenser, an air purifier, and a recovery tank. The first-stage jet pump compresses air and ejects it at high speed through the first-stage nozzle, which is then drawn in and mixed. The air is then decelerated and pressurized in the diffuser. The outlet gas from the first stage is usually sent to the condenser, which condenses the condensable working vapor and some gas into liquid and discharges it, greatly reducing the volume and load of gas entering the second-stage pump. The condenser receives the non-condensable gas after condensation and compresses it again using the working medium to a higher outlet pressure or a lower inlet pressure (i.e., a higher vacuum). Finally, the mixed fluid enters the condensation recovery tank.

[0026] The jet pump abandons traditional steam and uses high-pressure compressed air. The high-pressure working fluid, compressed air, is accelerated to a very high speed through a converging jet pump nozzle. When the high-speed jet leaves the nozzle, its static pressure drops sharply, creating a vacuum zone at the nozzle outlet and the mixing chamber inlet. Nitric acid gas in the pumped container is drawn into the low-pressure zone and enters the mixing chamber. In the mixing chamber, the high-speed compressed air and the low-speed pumped nitric acid gas undergo intense turbulent mixing and momentum exchange. Some of the kinetic energy of the compressed air is transferred to the pumped nitric acid gas, and the mixed fluid enters the diffuser. The cross-section of the diffuser gradually expands, and the flow velocity decreases. According to Bernoulli's principle, the kinetic energy of the fluid is converted back into static pressure, increasing the pressure of the mixed fluid to a level sufficient to overcome the back pressure (usually atmospheric pressure or the inlet pressure of the next stage pump), and finally discharged from the system into the nitric acid recovery tank.

[0027] The first heater b is also equipped with a temperature control pipeline, and the temperature control pipeline is equipped with an SL regulating valve b1. The SL regulating valve b1 and the thermometer b2 installed outside the gas-liquid separation circulation tank a are controlled in series to maintain the temperature between 85 and 95°C.

[0028] The bottom of the second heater is also provided with a cooling pipe d2. The recovered liquid enters the bottom of the gas falling film evaporator c through the bottom pipe of the second heater d, and a cooler is provided on the cooling pipe d2.

[0029] The gas-liquid separation circulating tank A has a material feed line at the bottom of its body. A start-up regulating valve A2 is installed on the material feed line and is connected to a level gauge A1 installed on the tank body to control and maintain the tank's liquid level. High-speed circulation is achieved through a centrifugal pump to prevent gas trapping. Inside the heating tubes, the material is heated to boiling and generates steam. This steam then transfers heat between the various evaporators, continuously evaporating moisture and nitric acid vapor from the material. Simultaneously, the circulating pump ensures high-speed flow of the material within the evaporation chamber, effectively preventing scaling and sedimentation, and improving evaporation efficiency and heat transfer.

[0030] The upper part of the falling film evaporator c is also equipped with a high-pressure steam regulating valve c3, which is connected in series with a thermometer c5 installed at the bottom of the falling film evaporator for control. The lower part of the tube side of the falling film evaporator c is also equipped with a dilution pipeline c1 for introducing diluent to reduce the material concentration and prevent scaling.

[0031] The flash evaporation holes 11 are evenly arranged on the flash plate 1, and the hole diameter is 5~20mm. When the liquid passes through the small holes, the pressure drops sharply, which increases the flash evaporation effect. In addition, a vertically arranged baffle 12 is provided behind the flash plate to further break up the droplets and prolong the residence time, thereby enhancing the flash evaporation effect.

[0032] In this embodiment, the first heater b is a vertical tube heater, and the material enters the tube side from the bottom through a centrifugal pump. A guide bar is installed in the tube side. The liquid forms a high-speed flowing film in the tube side through the guide bar, which improves the evaporation effect, and enters the gas-liquid separation circulation tank through the top of the first heater. The shell side of the first heater is heated by low-pressure steam, and the condensate is discharged through the bottom discharge system.

[0033] The second heater d also adopts a vertical tube heater, and the material enters the tube side from the bottom through a centrifugal pump. A guide bar is installed in the tube side; the liquid forms a high-speed flowing film in the tube side through the guide bar, which improves the evaporation effect. It enters the gas-liquid separation circulation tank through the top of the second heater. The shell side of the second heater is heated by high-pressure steam. The condensate enters the cooler on the cooling pipeline through the bottom to reduce the temperature of nitric acid vapor when it enters the bottom of the falling film evaporator.

[0034] The following description, in conjunction with specific embodiments, will provide further details: The adipic acid production circulating evaporation nitric acid recovery system includes a gas-liquid separation circulating tank a connected to a vacuum system e in the gas phase. The gas-liquid separation circulating tank a is regulated to a negative pressure state by a pressure gauge a3, with the negative pressure controlled at 140 mmHg. The gas-liquid separation circulating tank a is connected to the bottom of the gas-liquid separation circulating tank via a circulating pump pipeline (feeding at approximately 10 t / h, with a nitric acid concentration of approximately 30%). The pipeline is connected in series with a feed control regulating valve a2 and a level gauge a1 on the gas-liquid separation circulating tank a, with the flow rate controlled at 20 t / h. The bottom pipeline of the gas-liquid separation circulation tank a enters the first heater from the bottom of the tube side via circulation pump a4, with the temperature controlled at approximately 90°C. The gas-liquid separation circulation tank a then returns from the upper part of the tube side of the first heater b to the upper part of the gas-liquid separation circulation tank a. The shell side temperature is controlled at 90°C via SL regulating valve b1 and thermometer b2 on the gas-liquid separation circulation tank a. The bottom pipeline of the gas-liquid separation circulation tank a enters the second heater d from the bottom of the tube side via circulation pump a4. The discharge d1 enters the upper part of the gas-liquid separation circulation tank a from the top of the tube side of the second heater d. The shell side of the second heater d uses the top pipeline c4 of the falling film evaporator c as a heat source, with a temperature of approximately 130°C. The recovered liquid enters the bottom of the falling film evaporator c via the bottom pipeline d2 of the shell side of the second heater 2, with a cooler d3 installed on the pipeline. When feeding into the falling film evaporator c, the material enters the upper part of the tube side via circulation pump a4. When discharging, the material is discharged via discharge pump c2 (approximately 5t / h, nitric acid concentration approximately 5%).

[0035] The lower part of the tube side of the falling film evaporator c is also equipped with a diluent line c1, while the bottom of the shell side of the second heater d is equipped with a cooling line d2. The upper part of the shell side of the falling film evaporator c is equipped with a high-pressure steam regulating valve c3, which is cascaded with the thermometer at the bottom of the falling film evaporator c.

[0036] This invention solves the problems of high energy consumption and easy scaling in traditional evaporators. By implementing forced circulation between the heater and the separator, and driving material flow under the action of a circulation pump, the turbulence in the tube side is increased, reducing scaling. In addition, a falling film evaporator is used, with a falling film distributor installed above the tube bundle. The material enters the heating tubes evenly through the falling film distributor, forming a uniform thin liquid film (falling film), which significantly enhances turbulence, disrupts the thermal boundary layer, and generates a strong shear scouring effect. This structure greatly improves heat transfer efficiency by 30%-70%, significantly reduces steam consumption, effectively inhibits scaling, and extends the operating cycle. It is suitable for the concentration of high-viscosity, easily scaling materials and has the advantages of compact structure and stable operation. The system enables the material to continuously circulate between the evaporator and the circulation tank, achieving gradual concentration.

[0037] If this patent uses terms such as "first" and "second" to define components, those skilled in the art should know that the use of "first" and "second" is merely for the convenience of describing the invention and simplifying the description, and the above terms have no special meaning.

[0038] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this invention is defined by the appended claims and their equivalents.

[0039] In the description of this invention, it should be understood that the terms "front", "rear", "left", "right", "center", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of this invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

Claims

1. A system for recycling evaporated nitric acid in adipic acid production, characterized by: The gas-liquid separation circulating tank is connected with a vacuum system through a pipeline at the top, and a flash plate with flash holes is arranged in the gas-liquid separation circulating tank; the heater comprises first and second heaters arranged side by side; a circulating pump is arranged on the pipeline at the bottom of the gas-liquid separation circulating tank and enters the bottom of the first and second heaters and the top of the falling film evaporator; the material heated by the first heater enters the gas-liquid separation circulating tank through a discharge pipeline connected to the top of the first heater, and the inlet of the discharge pipeline is arranged above the flash plate; the material entering the top of the falling film evaporator through the circulating pump is connected to the top of the second heater through a gas phase pipeline; the material heated by the second heater enters the gas-liquid separation circulating tank through a discharge pipeline connected to the top of the second heater, and the inlet of the discharge pipeline is also arranged above the flash plate.

2. The system for recycling evaporated nitric acid in adipic acid production according to claim 1, characterized in that: The falling film evaporator is provided with an overflow weir at the top, and the overflow weir comprises an overflow weir pipe seat and an overflow pipe fixed at the front end of the overflow weir; the overflow weir pipe seat is fixedly installed on the falling film evaporator, and the overflow pipe is provided with a plurality of overflow grooves at the same horizontal plane; the included angle of adjacent overflow grooves is 45°-90°.

3. The system for recycling evaporated nitric acid in adipic acid production according to claim 1, characterized in that: The first heater is provided with a temperature control pipeline, and the temperature control pipeline is provided with an SL adjusting valve; the SL adjusting valve and a thermometer arranged outside the gas-liquid separation circulating tank are connected in series.

4. The system for recycling evaporated nitric acid in adipic acid production according to claim 1, characterized in that: The second heater is provided with a cooling pipeline, and the recovered liquid enters the bottom of the falling film evaporator through the bottom pipeline of the second heater; the cooling pipeline is provided with a cooler.

5. The system for recycling evaporated nitric acid in adipic acid production according to claim 1, characterized in that: The upper part of the falling film evaporator is provided with a high-pressure steam adjusting valve connected in series with a thermometer arranged at the bottom of the falling film evaporator.

6. The system for recycling evaporated nitric acid in adipic acid production according to claim 1, characterized in that: The lower part of the falling film evaporator is provided with a dilution pipeline for introducing dilution liquid.

7. The system for recycling evaporated nitric acid in adipic acid production according to any one of claims 1 to 6, characterized in that: The flash holes are uniformly arranged on the flash plate, and the hole diameter is 5-20 mm.

8. The system for recycling evaporated nitric acid in adipic acid production according to claim 7, characterized in that: The flash plate is provided with a vertically arranged baffle behind it.

9. The system for recycling evaporated nitric acid in adipic acid production according to claim 7, characterized in that: The heating temperature of the first heater is 85-95℃.

Images