A high-temperature, multi-stage adjustable heat recovery distillation system

Abstract

This invention discloses a high-temperature, multi-stage adjustable heat recovery distillation system, belonging to the technical field of distillation systems. It includes a distillation column, an evaporator assembly, a compressor, a reboiler heat exchanger, an ejector, a gas-liquid separator, a first storage tank, and a second storage tank. The evaporator assembly includes a first evaporator and a second evaporator connected in series. One end of the distillation column is connected to the first evaporator, and the second evaporator is connected to the second storage tank. Both the first and second evaporators are connected to the ejector. One end of the gas-liquid separator is connected to one end of the ejector, and the other end is connected to the first storage tank, the first evaporator, and the second evaporator, respectively. This invention employs compression and ejection, utilizing the flash gas from the liquid supply as power to eject the heat pump working gas from the second evaporator, achieving multi-stage recovery of the condensation heat of the column top gas. This simultaneously increases the evaporation temperature, improves the heat pump distillation efficiency, and reduces operating costs.

Description

Technical Field

[0001] This invention relates to the field of distillation system technology, and more particularly to a high-temperature, multi-stage adjustable heat recovery distillation system. Background Technology

[0002] In the petrochemical and chemical industries, heat pump distillation technology is being widely adopted as a means of energy conservation and consumption reduction. Among them, closed-loop heat pump distillation systems are characterized by high safety, wide applicability, and high system stability.

[0003] For the overhead gas of the column, which is a non-azeotropic medium with a large temperature range, there is a problem of large temperature glide during condensation. The temperature glide is related to the composition and proportion of the multi-component gas.

[0004] When a heat pump distillation system is used in a high-temperature transmedium distillation column, the following problems may occur:

[0005] One approach is to reduce the evaporation temperature of the heat pump distillation system so that the heat from the overhead gas can be fully recovered. However, this method results in a lower evaporation temperature, which can severely impact the overall energy efficiency of the heat pump distillation.

[0006] Another approach involves using a heat pump distillation system for the high-evaporation-temperature section and a water-cooled cooler for the low-evaporation-temperature section, resulting in heat loss into the environment and wasting cooling water and overhead gas heat. If the overhead medium temperature glide requires cooling water below 30°C, the high ambient temperature in summer may prevent the cooling water from meeting the requirements, necessitating the addition of an icing system, which increases costs. Furthermore, the incomplete recovery of some heat also leads to lower overall energy efficiency of the heat pump distillation system.

[0007] Meanwhile, the height difference between the top condenser and the bottom heat exchanger of a distillation column is generally large, which leads to stability issues in the liquid supply of closed-loop heat pump distillation. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a high-temperature, multi-stage adjustable heat recovery distillation system. It utilizes an ejector to harness the working gas from the pressure-reduced flash of the heat pump system's liquid supply pipeline, thereby recovering the condensation heat across the high-temperature medium in a multi-stage manner. This increases the evaporation temperature of the heat pump distillation system and completely recovers the heat from the overhead gas, eliminating the need for cooling water and ice machines. This improves the operating efficiency of the distillation system, reduces equipment operating and investment costs, and solves the stability problem of liquid supply with large height differences. Pressure-reduced flash refers to the phenomenon where high-pressure liquid, when flowing through valves, orifice plates, pressure reducers, or other throttling elements in the pipeline, experiences a sudden pressure drop below its saturated vapor pressure at the current temperature, causing a portion of the liquid to instantly vaporize into steam; this is also known as flash vaporization.

[0009] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0010] A high-temperature, multi-stage adjustable heat recovery distillation system includes a distillation column, an evaporator assembly, a compressor, a reboiler heat exchanger, an ejector, a first liquid storage tank, a second liquid storage tank, and a gas-liquid separator. The evaporator assembly includes a first evaporator and a second evaporator, connected in series in their tube sides. One end of the tube side of the first evaporator is connected to the distillation column, and the other end of the tube side of the first evaporator is connected to one end of the tube side of the second evaporator. The other end of the tube side of the second evaporator is connected to the second liquid storage tank. The tube sides of the first and second evaporators flow with the top medium of the column. The shell sides of the first and second evaporators flow with the heat pump medium. One end of the shell side of the first evaporator is connected to the compressor inlet after converging with the ejector outlet. The shell side outlet of the second evaporator is connected to the ejector's inlet. The shell sides of the first and second evaporators are connected in parallel.

[0011] The two ends of the column bottom heat exchanger are respectively connected to the distillation column. The top gas of the distillation column passes through the first evaporator and the second evaporator in sequence and is condensed in stages. The other end of the compressor is connected to the column bottom heat exchanger. One end of the first liquid storage tank is connected to the column bottom heat exchanger, and the other end of the first liquid storage tank is connected to the gas-liquid separator. The gas phase outlet of the gas-liquid separator is connected to the gas inlet of the ejector. The gas phase of the gas-liquid separator serves as the power source for the ejector. The gas-liquid separator is also connected to the first liquid storage tank, the first evaporator, and the second evaporator.

[0012] By adopting the above technical solution, the overhead gas of the distillation column passes through the first evaporator and the second evaporator, respectively, and undergoes staged condensation in the evaporators. The heat pump working fluid in the evaporators recovers heat from the overhead gas, causing the heat pump working fluid to vaporize. After being heated and pressurized by the compressor, it enters the reboiler heat exchanger to provide energy for the reboiler heat exchanger. The overhead gas typically undergoes heat exchange in the tube side, while the heat pump working fluid typically undergoes heat exchange in the shell side. The high-temperature, high-pressure heat pump working fluid releases heat and condenses into a liquid in the reboiler heat exchanger before entering the first storage tank. Due to gravitational potential energy and pipeline pressure loss or regulating valve factors, the condensed liquid heat pump working fluid... During the liquid supply process, isenthalpic pressure reduction refers to the thermodynamic process in which the enthalpy (h) of a fluid, usually a gas or vapor, remains constant as its pressure decreases. This process will release a portion of gas, i.e., medium-pressure gas, whose pressure is higher than the evaporation pressure. The medium-pressure gas separated in the gas-liquid separator enters the ejector and serves as the driving force to recover the condensation heat of the high-temperature cross-medium, thereby increasing the evaporation temperature of the heat pump distillation system and completely recovering the heat of the overhead gas. This eliminates the need for cooling water and ice machines, improving the operating efficiency of the distillation system, reducing equipment operating costs and investment costs, and simultaneously solving the stability problem of liquid supply with large height differences.

[0013] Furthermore, a second regulating valve is provided between the gas-liquid separator and the first evaporator; a third regulating valve is provided between the gas-liquid separator and the second evaporator.

[0014] Furthermore, a first regulating valve is provided between the first liquid storage tank and the gas-liquid separator.

[0015] Furthermore, a fourth regulating valve is provided between the gas-liquid separator and the injector.

[0016] Furthermore, a fifth regulating valve is provided between the injector and the second liquid storage tank.

[0017] Furthermore, the first evaporator is a shell-and-tube evaporator.

[0018] Furthermore, the second evaporator is a shell-and-tube evaporator or a plate evaporator.

[0019] In summary, compared with the prior art, the beneficial effects of the above technical solution are:

[0020] (1) The present invention provides a high-temperature cross-stage adjustable heat recovery distillation system, which adopts compression and injection, uses the liquid flash gas as power to eject the heat pump working gas of the second evaporator, realizes the staged recovery of the condensation heat of the top gas, and at the same time improves the evaporation temperature, improves the heat pump distillation efficiency, and reduces the operating cost.

[0021] (2) The present invention provides a high-temperature cross-stage adjustable heat recovery distillation system that does not use an ice machine or cooling water to completely recover or subcool the high-temperature cross-medium condensation heat, thereby reducing cooling water and power consumption and lowering investment and operating costs.

[0022] (3) This invention provides a high-temperature cross-stage adjustable heat recovery distillation system, which solves the problem of poor liquid supply stability in distillation columns with large height differences and avoids the influence of flash gas on the liquid supply regulating valve during the climbing process;

[0023] (4) The present invention provides a high-temperature cross-stage adjustable heat recovery distillation system. When the distillation system fluctuates slightly, the fourth regulating valve and the fifth regulating valve can be used to fine-tune the system, so that the system can operate stably without adjusting the load of the compressor. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of Example 1;

[0025] Figure 2 This is a schematic diagram of the overall structure of Example 2.

[0026] Explanation of reference numerals in the attached drawings: 1. Distillation column; 2. Compressor; 3. Ejector; 4. First evaporator; 5. Bottom heat exchanger; 6. First liquid storage tank; 7. Gas-liquid separator; 8. Second evaporator; 9. Second liquid storage tank; 10. First regulating valve; 11. Second regulating valve; 12. Third regulating valve; 13. Fourth regulating valve; 14. Fifth regulating valve. Detailed Implementation

[0027] The principles and features of the present invention are described below with reference to all the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] This invention discloses a high-temperature, multi-stage adjustable heat recovery distillation system.

[0029] Example 1

[0030] Reference Figure 1 A high-temperature, multi-stage adjustable heat recovery distillation system includes a distillation column 1, an evaporator assembly, a compressor 2, a column bottom heat exchanger 5, an ejector 3, a gas-liquid separator 7, a first liquid storage tank 6, and a second liquid storage tank 9. The evaporator assembly includes a first evaporator 4 and a second evaporator 8. Both ends of the column bottom heat exchanger 5 are connected to the distillation column 1, and one end of the distillation column 1 is connected to the first evaporator 4. The gas from the top of the distillation column 1 passes sequentially through the first evaporator 4 and the second evaporator 8, and is condensed in stages within the evaporators. One end of the compressor 2 is connected to the first evaporator 4 and the ejector 3, and the other end of the compressor 2 is connected to the column bottom heat exchanger 5. The heat pump working fluid vaporized in the evaporator is heated and pressurized by the compressor 2 before entering the column bottom heat exchanger 5. One end of the first liquid storage tank 6 is connected to the column bottom heat exchanger 5, and the other end of the first liquid storage tank 6 is connected to the gas-liquid separator 7. One end of the second liquid storage tank 9 is connected to the second evaporator 8. In this configuration, one end of the first evaporator 4 is connected to the distillation column 1 and the ejector 3, and the other end of the first evaporator 4 is connected to one end of the second evaporator 8. The other end of the second evaporator 8 is connected to the second storage tank 9 and the ejector 3. The tube side of the first evaporator 4 and the second evaporator 8 is circulated with the top medium of the column; the shell side of the first evaporator 4 and the second evaporator 8 is circulated with the heat pump medium. One end of the shell side of the first evaporator 4 is connected to the outlet of the ejector 3 and then to the inlet of the compressor 2. The shell side outlet of the second evaporator 8 is connected to the ejector port of the ejector 3. The shell sides of the first evaporator 4 and the second evaporator 8 are connected in parallel.

[0031] Specifically, distillation column 1 is connected to a first evaporator 4, which in turn is connected to a second evaporator 8, i.e., the first evaporator 4 and the second evaporator 8 are connected in series. The overhead gas from distillation column 1 passes through the first evaporator 4 and the second evaporator 8 sequentially, where it undergoes staged condensation. The heat pump working fluid in the first evaporator 4 and the second evaporator 8 recovers heat from the overhead gas medium. The liquid phase heat pump working fluid vaporizes and, after being heated and pressurized by compressor 2, enters the reboiler heat exchanger 5 to provide heat for it. The overhead gas undergoes heat exchange in the tube side of the first evaporator 4 and the second evaporator 8, while the heat pump working fluid undergoes heat exchange in the shell side. The high-temperature, high-pressure heat pump working fluid releases heat and condenses into a liquid in the reboiler heat exchanger 5, entering the first storage tank 6. The first storage tank 6 is placed on the ground, and a first regulating valve 10 is added between the first storage tank 6 and the gas-liquid separator 7 to control the liquid level in the first storage tank 6.

[0032] The gas-liquid separator 7 is positioned at the same height as the first evaporator 4 and the second evaporator 8, typically at the top of the tower. Due to gravitational potential energy and pipeline pressure loss, the liquid heat pump working fluid undergoes isenthalpic pressure drop during the liquid supply process, resulting in the flashing of a portion of gas, i.e., medium-pressure gas. The pressure of this gas is higher than the evaporation pressure. The separated medium-pressure gas enters the ejector 3 as a power source. The outlet of the ejector 3 is connected to the suction line of the compressor 2, and the ejector port of the ejector 3 is connected to the outlet of the second evaporator 8.

[0033] A second regulating valve 11 is installed between the first evaporator 4 and the gas-liquid separator 7, and a third regulating valve 12 is installed between the second evaporator 8 and the gas-liquid separator 7. The second regulating valve 11 regulates the liquid level in the first evaporator 4, which is typically a shell-and-tube evaporator. The third regulating valve 12 controls the liquid level or outlet superheat in the second evaporator 8, which is typically a shell-and-tube evaporator or a plate evaporator.

[0034] A fourth regulating valve 13 is provided between the gas-liquid separator 7 and the ejector 3. The fourth regulating valve 13 controls the pressure of the gas-liquid separator 7, thereby controlling the air intake of the ejector 3, and thus controlling the heat exchange of the second evaporator 8.

[0035] Based on the operating principle of injector 3, the air intake of the ejector port is mainly related to the inlet pressure of injector 3, the inlet flow rate of injector 3, the outlet pressure of injector 3, and the ejector port pressure.

[0036] Furthermore, the flash gas volume is related to the operating conditions of the heat pump system and the pressure of the gas-liquid separator 7. According to theoretical calculations and the performance of the ejector 3, the mass flow rate of the ejector port is generally about 0.4-0.5 times the flow rate of the ejector power source. According to the theoretical calculation of isenthalpic throttling, the gas flow rate in the gas-liquid separator 7 is about 30% of the total flow rate, that is, the liquid flow rate accounts for 70%. Furthermore, the load of the second evaporator 8 is about 17%-21% of the load of the first evaporator 4.

[0037] A fifth regulating valve 14 is installed between the ejector port of the ejector 3 and the heat pump working fluid side outlet of the second evaporator 8. The fifth regulating valve 14 is used to regulate the outlet flow rate of the medium side at the top of the second evaporator 8. Specifically, when the outlet temperature of the medium side at the top of the second evaporator 8 is higher than the target temperature, the opening of the fifth regulating valve 14 is increased; when the outlet temperature of the medium side at the top of the second evaporator 8 is lower than the target temperature, the opening of the fifth regulating valve 14 is decreased.

[0038] According to the ejector principle of ejector 3, the pressure at the outlet of ejector 3 is higher than the pressure at the ejector port of ejector 3, that is, the evaporation pressure of the second evaporator 8 can be lower than the evaporation pressure of the first evaporator 4.

[0039] Furthermore, the most suitable scenario for this invention is when the medium at the top of the tower is a non-azeotropic mixture with a large temperature range. During the condensation process, the gas exhibits a large temperature glide, and the condensation temperature gradually decreases as the gas mixture at the top of the tower condenses, resulting in a lower evaporation temperature required on the heat pump working fluid side. Using the system of this invention, the condensation heat of the gas at the top of the tower can be recovered in stages. The higher temperature range uses the first evaporator 4 at the top of the tower, and the lower temperature range uses the second evaporator 8 at the top of the tower, which can improve the evaporation temperature.

[0040] Furthermore, the present invention is also applicable to the following scenarios: the overhead medium is a single-component or azeotropic mixture of gases, and the overhead medium is completely condensed in the first evaporator 4 at the top of the column, thus fully recovering the latent heat of the gas. In the second evaporator 8 at the top of the column, the overhead medium is subcooled, which allows for better extraction and reflux.

[0041] The specific example calculation is as follows:

[0042] The top of distillation column 1 in a certain project is a non-azeotropic mixed gas with a condensation temperature glide from 45-30℃; the bottom boiling point is 65℃. The condensation load of the top gas is completely recovered, with a heat of about 2000kw, and the bottom heat requirement is 2850kw.

[0043] Electricity price for users: 0.7 yuan / kWh; Price of purchased steam: 250 yuan / ton.

[0044] The following table compares the parameters of several schemes for introducing a closed-loop heat pump distillation system, as shown in Table 1.

[0045] Table 1 Comparison of Scheme Parameters

[0046]

[0047] By adopting the technical solution of the present invention, the evaporation temperature can be increased by 3°C, the power consumption per hour can be reduced by 69kW, and the operating cost can be saved by 390,000 yuan per year, which is about 10% of the operating cost.

[0048] The working principle of this invention is as follows:

[0049] The overhead gas from distillation column 1 passes through a first evaporator 4 and a second evaporator 8, where it undergoes staged condensation. The heat pump working fluid in the first evaporator 4 and the second evaporator 8 recovers heat from the overhead gas, causing it to vaporize. After being heated and pressurized by compressor 2, it enters the reboiler heat exchanger 5 to provide energy. Generally, the overhead gas undergoes heat exchange in the tube side, while the heat pump working fluid undergoes heat exchange in the shell side. The high-temperature, high-pressure heat pump working fluid releases heat and condenses into a liquid in the reboiler heat exchanger 5 before entering the first liquid storage tank 6. Due to gravitational potential energy and pipeline pressure loss, the heat pump working fluid undergoes isenthalpic pressure drop during the liquid supply process, resulting in the release of a portion of gas, namely medium-pressure gas. The pressure of this gas is higher than the evaporation pressure. The separated medium-pressure gas enters ejector 3 and serves as the driving force to recover the condensation heat of the high-temperature cross-medium in stages, thereby increasing the evaporation temperature of the heat pump distillation system and completely recovering the heat of the overhead gas. This eliminates the need for cooling water and ice machines, improving the operating efficiency of the distillation system, reducing equipment operating costs and investment costs, and simultaneously solving the stability problem of liquid supply with large height differences.

[0050] Example 2

[0051] Reference Figure 2 The main difference between Embodiment 2 and Embodiment 1 is that the technical solution of Embodiment 2 eliminates the gas-liquid separator 7, and a second regulating valve 11 is provided between the injector 3 and the first liquid storage tank 6; a third regulating valve 12 is provided between the first liquid storage tank 6 and the second evaporator 8.

[0052] High-pressure working fluid liquid is used as the ejector power source, eliminating the gas-liquid separator 7. The second regulating valve 11 controls the liquid level of the first evaporator 4, and the third regulating valve 12 controls the liquid level of the second evaporator 8 or the superheat of the heat pump working fluid outlet.

[0053] The fifth regulating valve 14 regulates the outlet temperature of the medium side at the top of the second evaporator 8.

[0054] Since Embodiment 2 of the present invention does not solve the stability problem of liquid supply with large height difference, it is more suitable for occasions where the height of the distillation column 1 is not high or the height of the first evaporator 4 and the second evaporator 8 is not high.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature, multi-stage adjustable heat recovery distillation system, comprising a distillation column (1), characterized in that, It also includes an evaporator assembly, a compressor (2), a column bottom heat exchanger (5), an ejector (3), a first liquid storage tank (6), a second liquid storage tank (9), and a gas-liquid separator (7); the evaporator assembly includes a first evaporator (4) and a second evaporator (8), the first evaporator (4) and the second evaporator (8) are connected in series in their tube sides, one end of the tube side of the first evaporator (4) is connected to the distillation column (1), and the other end of the tube side of the first evaporator (4) is connected to one end of the tube side of the second evaporator (8). The other end of the tube side of the second evaporator (8) is connected to the second liquid storage tank (9); the tube side of the first evaporator (4) and the second evaporator (8) flows with the top medium of the tower; the shell side of the first evaporator (4) and the second evaporator (8) flows with the heat pump medium; one end of the shell side of the first evaporator (4) is connected to the outlet of the ejector (3) and then connected to the inlet of the compressor (2); the outlet of the shell side of the second evaporator (8) is connected to the ejector port of the ejector (3); the shell side of the first evaporator (4) and the shell side of the second evaporator (8) are arranged in parallel; The two ends of the reboiler heat exchanger (5) are respectively connected to the distillation column (1). The gas at the top of the distillation column (1) passes through the first evaporator (4) and the second evaporator (8) in sequence, and is condensed in stages therein. The other end of the compressor (2) is connected to the reboiler heat exchanger (5). One end of the first liquid storage tank (6) is connected to the reboiler heat exchanger (5), and the other end of the first liquid storage tank (6) is connected to the gas-liquid separator (7). The gas phase outlet of the gas-liquid separator (7) is connected to the jet. The gas phase of the gas-liquid separator (7) is connected to the inlet of the gas-liquid separator (3). The gas phase of the gas-liquid separator (7) is used as the power source of the ejector (3). The liquid flash gas is used as the power source to eject the heat pump working gas of the second evaporator to realize the cascade recovery of the condensation heat of the gas at the top of the tower. The gas-liquid separator (7) is also connected to the first liquid storage tank (6), the first evaporator (4) and the second evaporator (8) respectively. The gas-liquid separator is located at the top of the tower, and the installation position of the gas-liquid separator is at the same height as the installation position of the first evaporator and the second evaporator.

2. The high-temperature, multi-stage adjustable heat recovery distillation system according to claim 1, characterized in that: A second regulating valve (11) is provided between the gas-liquid separator (7) and the first evaporator (4); a third regulating valve (12) is provided between the gas-liquid separator (7) and the second evaporator (8).

3. The high-temperature, multi-stage adjustable heat recovery distillation system according to claim 1, characterized in that: A first regulating valve (10) is provided between the first liquid storage tank (6) and the gas-liquid separator (7).

4. The high-temperature, multi-stage adjustable heat recovery distillation system according to claim 1, characterized in that: A fourth regulating valve (13) is provided between the gas-liquid separator (7) and the injector (3).

5. The high-temperature, multi-stage adjustable heat recovery distillation system according to claim 1, characterized in that: A fifth regulating valve (14) is provided between the injector (3) and the second liquid storage tank (9).

6. A high-temperature, multi-stage adjustable heat recovery distillation system according to any one of claims 1 to 5, characterized in that: The first evaporator (4) is a shell-and-tube evaporator.

7. A high-temperature, multi-stage adjustable heat recovery distillation system according to any one of claims 1 to 5, characterized in that: The second evaporator (8) is a shell-and-tube evaporator or a plate evaporator.

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