An energy-saving and carbon-reducing system and separation process for multi-component alkane separation

Abstract

The present invention belongs to the technical field of multi-component alkane separation and relates to an energy-saving and carbon reduction system and separation process for multi-component alkane separation. The energy-saving and carbon reduction system comprises a separation system, a side-line heat exchanger, and a heat pump system. The separation system comprises a separation tower for separating multi-component alkanes, a first condenser, a second condenser, and a steam heat exchanger. The first condenser and the second condenser are arranged in parallel, with the side-line heat exchanger located at the waist of the separation tower and the steam heat exchanger at the bottom of the separation tower. The side-line heat exchanger and the second condenser are connected by a heat pump system for recovering condensation heat generated by the second condenser and supplying this recovered heat to the side-line heat exchanger. Using the system of the present invention to separate multi-component alkanes allows for liquid phase extraction of the side-line material, increasing the amount of heat recovered from the overhead gas, improving the system's thermal utilization rate, and reducing the system's energy consumption. Furthermore, the heat pump system uses a heat pump working fluid as the circulating heat exchange medium, rather than directly compressing the medium within the tower, thereby reducing system safety risks.

Description

Technical Field

[0001] The invention relates to an energy-saving and carbon-reducing system and a separation process for separating multi-component alkanes, belonging to the technical field of separation of multi-component alkanes in the chemical and petrochemical industries. Background Art

[0002] In traditional multi-component alkane gas purification processes, a dual-tower separation approach is commonly used to effectively separate these gases. Specifically, the multi-component alkane gas first enters a first separation tower, where isobutane gas is extracted from the top and remaining heavy liquid components such as n-butane and pentane are extracted from the bottom. The heavy liquid extracted from the bottom of the first separation tower is then fed to a second separation tower, where n-butane gas is extracted from the top and pentane and the remaining heavy liquid components are extracted from the bottom. This dual-tower separation approach not only requires a large footprint but also has high energy consumption and construction costs.

[0003] In order to solve the above problems, the existing process also adopts single-tower separation. However, in the existing production process, the condensation and heat dissipation of the gas extracted from the top of the tower is usually provided by a water-cooled condenser, while the heating of the tower kettle depends on steam heating. As a result, the high-grade steam heat is degraded to low-grade cooling water heat after mass transfer. A large amount of energy cannot be recovered, resulting in significant waste.

[0004] Some chemical and petrochemical plants have also introduced heat pump distillation systems in their multi-component alkane separation towers to recover waste heat. However, since alkanes are explosion-proof media, the compressors must meet extremely stringent requirements, requiring zero external leakage, which increases system costs and safety risks. Furthermore, the large temperature difference between the tower top and bottom (approximately 54°C) and the complex and variable composition of the components lead to low system efficiency, frequent fluctuations in load and operating conditions, difficulty in adjustment, and prone to compressor failure. Summary of the Invention

[0005] The purpose of the present invention is to provide a new technical solution to improve or solve the technical problems existing in the prior art as described above.

[0006] The technical solution provided by the present invention is as follows: an energy-saving and carbon reduction system for separating multi-component alkanes, comprising a separation system, a side line heat exchanger and a heat pump system, wherein the separation system comprises a separation tower for separating multi-component alkanes, a first condenser, a second condenser, a steam heat exchanger, a first reflux tank, a second reflux tank, a first reflux pump, a first discharge pump, a second discharge pump and a third discharge pump; the separation tower is provided with a feed inlet, a tower top production outlet, a side line production outlet and a tower bottom production outlet; the first condenser and the second condenser are arranged in parallel and are both connected to the tower top production outlet for condensing the tower top gas; the first reflux tank is connected to the tube side outlet of the first condenser and forms a tower top output path through the first discharge pump; the tube side outlet of the second condenser, the second reflux tank and the third reflux tank are connected to the tower top output path; the first reflux tank and the second condenser ... A reflux tank, the first reflux pump and the separation tower are connected in sequence to form a tower top heat exchange circulation loop; the second reflux tank is connected to the side line production port, and a side line output path is formed through the third discharge pump, and the side line production port adopts a liquid phase production method; the second discharge pump is connected to the tower bottom production port to form a tower bottom output path; the steam heat exchanger is connected to the bottom of the separation tower to heat the tower bottom material to form a tower bottom heat exchange circulation loop; the side line heat exchanger is connected to the waist of the separation tower to exchange heat with the material in the tower to form a side line heat exchange circulation loop; the side line heat exchanger and the second condenser are connected through the heat pump system to recover the condensation heat generated by the second condenser, and supply the recovered heat to the side line heat exchanger.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows:

[0008] Furthermore, the heat pump system includes a compressor unit, a working fluid high-pressure tank, a thermal coupling heat exchanger and a cold coupling heat exchanger connected to form a heat pump circulation loop through pipelines, the shell-side outlet of the second condenser is connected to the tube-side inlet of the thermal coupling heat exchanger through an intake pipeline, the tube-side outlet of the thermal coupling heat exchanger is connected to the inlet of the compressor unit, the outlet of the compressor unit is connected to the shell-side inlet of the side-line heat exchanger through a pipeline, and the shell-side outlet of the side-line heat exchanger is connected to the working fluid high-pressure tank through a pipeline; the outlet of the working fluid high-pressure tank is connected to the shell-side inlet of the thermal coupling heat exchanger through a pipeline, and the shell-side outlet of the thermal coupling heat exchanger is connected to the tube-side of the cold coupling heat exchanger and the shell-side inlet of the second condenser in sequence to form a heat pump circulation loop.

[0009] The beneficial effect of adopting the above further solution is that the heat pump system adds a hot-coupled heat exchanger and a cold-coupled heat exchanger, which can adjust the hot and cold coupling of the system without adjusting the compressor unit, so that the compressor unit can always operate at a high-efficiency working condition, while also improving system efficiency, increasing system stability, and reducing the failure rate of the compressor unit. The heat pump system of the present invention can recover the condensation heat generated by the second condenser and supply this recovered heat to the side heat exchanger. The excess heat can also be used according to the needs of the chemical plant area, that is, the low-grade heat generated by the condensation of the overhead gas of the conventional separation tower can be increased by pressurizing the compressor unit to increase the quality and apply it to the heat input of the separation tower of this process and the separation tower of other processes, thereby reducing heat waste.

[0010] Furthermore, the working medium high-pressure tank is connected to the air intake pipeline via a pressure equalizing pipeline, and a first regulating valve is provided on the pressure equalizing pipeline.

[0011] The beneficial effect of adopting the above-mentioned further scheme is that the inlet and outlet pressure equalization before the compressor unit starts running and after it stops can ensure the compressor unit to start up without pressure difference, improve the stability of the system, and prevent the unseparated droplets of the second condenser and the condensed liquid formed in the suction pipeline due to heat dissipation with the environment from entering the compressor by adjusting the valve, pressure equalization pipeline and thermal coupling heat exchanger, thereby avoiding the risk of liquid shock and damage to the compressor caused by liquid carrying problems, thereby improving the stability and reliability of the system.

[0012] Furthermore, the external device is connected in parallel with the side line heat exchanger through a pipeline to form an external device heat exchange circulation path, and a second regulating valve is also provided at the air inlet of the external device.

[0013] The beneficial effect of adopting the above further solution is that a portion of the gas phase heat pump working fluid compressed by the compressor unit is used for the heat demand of other process systems through the heat exchange circulation path of the external equipment.

[0014] Furthermore, it also includes a third regulating valve, which is arranged on the pipeline between the second condenser and the cold-coupled heat exchanger.

[0015] The beneficial effect of adopting the above further solution is that the third regulating valve is used to regulate the flow rate of the heat pump working medium returning to the second condenser.

[0016] Furthermore, a bypass pipeline is provided between the inlet and the outlet of the thermally coupled heat exchanger, and a fourth regulating valve is provided on the bypass pipeline.

[0017] The beneficial effect of adopting the above further solution is that the fourth regulating valve is used to adjust the load of the thermally coupled heat exchanger.

[0018] Furthermore, the first condenser is connected to an external cold source, and the cold source of the second condenser is a heat pump working fluid.

[0019] A separation process for separating multi-component alkanes, utilizing the energy-saving and carbon reduction system for separating multi-component alkanes, comprises the following steps:

[0020] Feed the multi-component alkane raw material from the feed port of the separation tower. When the liquid level in the tower bottom rises to 65% to 80% of the total capacity, stop feeding.

[0021] Start the steam heat exchanger to heat the tower kettle until the internal pressure of the separation tower reaches 60% to 70% of the design pressure;

[0022] Open the first condenser, adjust the pressure in the tower to the design value by adjusting the cold source flow, and then resume feeding into the separation tower;

[0023] Start the compressor unit and reduce the flow of heat source into the steam heat exchanger at the same time; turn on the first reflux pump, start the reflux operation, and control the temperature in the tower by adjusting the reflux ratio until the temperature in the tower drops to the design value; adjust the heat source flow of the steam heat exchanger and the cold source flow of the first condenser until the separation products output from the top output path and the side line output path are qualified, fix the hot and cold supply ratio of the steam heat exchanger and the first condenser, and maintain stable operation of the separation tower.

[0024] On the basis of the above technical solution, the present invention can also be improved as follows:

[0025] Furthermore, the circulation process of the heat pump working fluid in the heat pump circulation loop includes:

[0026] The liquid phase heat pump working fluid evaporates in the second condenser and then flows through the thermally coupled heat exchanger for superheating;

[0027] The superheated gas phase heat pump working fluid enters the compressor unit for compression, and the temperature and pressure increase accordingly;

[0028] The compressed gas phase heat pump working fluid enters the side line heat exchanger, exchanges heat with the material in the tower, and condenses into high-pressure liquid;

[0029] The high-pressure liquid is transported to the working fluid high-pressure tank for storage;

[0030] The high-pressure liquid released from the working medium high-pressure tank flows through the hot-coupled heat exchanger and the cold-coupled heat exchanger in sequence for cooling;

[0031] Finally, the cooled heat pump working fluid returns to the second condenser, completing a cycle.

[0032] Furthermore, the top gas reflux ratio is increased to reduce the gas proportion at the side line production port, and the liquid phase separation product is produced from the side line production port.

[0033] The beneficial effect of adopting the above further scheme is that the side line material can be extracted through the liquid phase, without the need for a side line extraction heat exchanger, and the recoverable amount of the heat pump unit is increased, the heat recovery amount of the tower top gas is increased, the system heat utilization rate is increased, the investment cost is reduced, and the economy is improved.

[0034] Furthermore, the cooling load status of the second condenser is monitored to determine whether there is an excess or insufficient cooling load;

[0035] When the cooling load of the second condenser is excessive, the amount of cold source provided to the cold-coupled heat exchanger is reduced, so that the temperature of the heat pump working fluid output from the outlet of the cold-coupled heat exchanger increases, the subcooling degree of the heat pump working fluid is reduced, the cooling load of the second condenser is reduced, and the heat load of the side heat exchanger is reduced accordingly;

[0036] When the cooling load of the second condenser is insufficient, the amount of cold source provided to the cold-coupled heat exchanger is increased to reduce the temperature of the heat pump working fluid output from the outlet of the cold-coupled heat exchanger, increase the subcooling degree of the heat pump working fluid, and increase the cooling load of the second condenser.

[0037] The beneficial effect of adopting the above-mentioned further scheme is that the role of the cold-coupled heat exchanger is also reflected in that it can reduce the heat exchange area of ​​the first condenser and reduce investment costs; at the same time, increasing the subcooling degree of the supply liquid can ensure that the heat pump working fluid will not be decompressed and flash during the supply liquid process, avoiding the vibration problem of the supply liquid pipeline and making the system more stable.

[0038] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0039] (1) The present invention uses a separation tower with a top outlet provided at the top of the tower, a side outlet provided at the side line, and a bottom outlet provided at the bottom of the tower. The top outlet is connected to a first condenser and a second condenser, and the first condenser and the second condenser are arranged in parallel. Compared with the series arrangement, the parallel arrangement reduces local pressure loss on the one hand, and avoids the problem of uneven gas-liquid distribution when the gas-liquid two-phase fluid after the top gas passes through the first condenser and enters the second condenser on the other hand, which leads to poor heat exchange effect of the second condenser.

[0040] The gas from the top of the tower is condensed through the first condenser and then output; the reflux ratio of the gas from the top of the tower can be adjusted to allow the liquid phase of the side-line material to be produced without the need for a side-line production heat exchanger. The side-line material is produced through the liquid phase rather than through the gas phase, which has the following advantages: first, there is no need to add a side-line production heat exchanger; second, the recoverable amount of the heat pump unit is increased, and this part of the latent heat of vaporization can be transferred to the top of the tower, thereby increasing the heat recovery amount of the top gas and increasing the thermal utilization rate of the system; the liquid phase material and other small amounts of heavy component impurity liquid are produced from the bottom of the tower; the present invention adopts a single-tower multi-line production method to simplify the process flow, reduce land occupation and initial investment.

[0041] (2) The heat pump system of the present invention uses heat pump working fluid as the circulating heat exchange medium, does not directly compress the medium in the tower, reduces the safety hazards of the system, and has low requirements for the compressor; at the same time, when the temperature or pressure in the tower fluctuates, it will be preferentially transferred to the heat pump working fluid in the second condenser. Since there are more heat pump working fluids in the second condenser and the entire system, the fluctuations will be buffered, and the load and working condition adjustments will be carried out more smoothly, making the system more stable.

[0042] (3) The present invention adds a side heat exchanger, and the proportion of heavy components at the installation position is relatively low, and the temperature inside the tower is also low. At this position, the working fluid in the tower only needs to be pressurized to a lower pressure to meet the evaporation requirements. Compared with the steam heat exchanger in the tower bottom that directly processes the high-heavy component and high-temperature liquid in the tower bottom, the side heat exchanger can more effectively evaporate the light components (such as C4 butane) in the falling liquid while keeping the heavy components (such as C5 pentane) falling to the tower bottom, thereby optimizing the separation efficiency in the tower. And because the intermediate heat exchanger processes liquids with lower temperatures and lower proportions of heavy components, the required pressure and energy consumption are also reduced accordingly. Compared with the use of only steam heat exchangers, the energy consumption of the system can be reduced, which is of great significance for improving the economy and sustainability of the entire system. The setting of the intermediate heat exchanger allows the system to be adjusted according to different operating conditions and separation requirements. For example, during the startup phase, the steam heat exchanger can only pass a small amount of steam for auxiliary purposes, while the main evaporation task is undertaken by the intermediate heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0044] Figure 1 It is a structural schematic diagram of the present invention.

[0045] In the figure, 1. separation tower; 2. first condenser; 3. second condenser; 4. first reflux tank; 5. first reflux pump; 6. first discharge pump; 7. second discharge pump; 8. second reflux tank; 9. third discharge pump; 10. steam heat exchanger; 11. side-line heat exchanger; 12. working medium high-pressure tank; 13. first regulating valve; 14. thermal coupling heat exchanger; 15. compressor unit; 16. second regulating valve; 17. cold coupling heat exchanger; 18. third regulating valve; 19. fourth regulating valve; 20. suction pipeline; 21. equalizing pressure pipeline; 22. tower top output path; 23. tower top heat exchange circulation loop; 24. side-line output path; 25. side-line heat exchange circulation loop; 26. external equipment heat exchange circulation path; 27. bypass pipeline. DETAILED DESCRIPTION

[0046] Component numbers herein, such as "first" and "second," are used solely to distinguish the components being described and do not imply any sequential priority or specific technical meaning. Furthermore, unless otherwise specified, the terms "connected" and "coupled" used in this application encompass both direct and indirect connections.

[0047] When interpreting the description of this application, it is important to clarify that the directions or positional relationships indicated by terms such as "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," "clockwise," and "counterclockwise" are based on the perspectives and layouts shown in the accompanying drawings and are intended to facilitate explanation and simplify the description process. They are not intended to be absolute limitations on the actual directions, constructions, and operating modes of the devices or components described. Therefore, these terms should not be construed as restrictive of the content of this application.

[0048] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0049] This example uses the separation of a multi-component alkane feedstock containing C4 n-butane, C4 isobutane, and C5 pentane as an example to illustrate the energy-saving and carbon reduction system and separation process for multi-component alkane separation of the present invention. Of course, the energy-saving and carbon reduction system of the present invention is not limited to the separation of these specific components; it is also capable of separating other multi-component alkane feedstocks.

[0050] like Figure 1As shown, an energy-saving and carbon reduction system for separating multi-component alkanes includes a separation system, a side line heat exchanger 11 and a heat pump system. The separation system includes a separation tower 1 for separating multi-component alkanes, a first condenser 2, a second condenser 3, a steam heat exchanger 10, a first reflux tank 4 for buffering and storing the top liquid phase material, a second reflux tank 8 for buffering and storing the side line produced liquid phase material, a first reflux pump 5, a first discharge pump 6, a second discharge pump 7 and a third discharge pump 9; the separation tower 1 is provided with a feed inlet, a top production outlet, a side line production outlet and a bottom production outlet; the first condenser 2 and the second condenser 3 are arranged in parallel and are both connected to the top production outlet for condensing the top gas; the first reflux tank 4 is connected to the pipe side outlet of the first condenser 2, and forms a top output path 22 through the first discharge pump 6; the second condenser 3 The pipe-side outlet, the first reflux tank 4, the first reflux pump 5 and the separation tower 1 are connected in sequence to form a tower top heat exchange circulation loop 23; the second reflux tank 8 is connected to the side line production outlet, and forms a side line output path 24 through the third discharge pump 9, and the side line production outlet adopts a liquid phase production method; the second discharge pump 7 is connected to the tower bottom production outlet to form a tower bottom output path; the steam heat exchanger 10 is connected to the bottom of the separation tower 1 for heating the bottom material to form a tower bottom heat exchange circulation loop; the side line heat exchanger 11 is connected to the waist of the separation tower 1 for heat exchange of the material in the tower to form a side line heat exchange circulation loop 25; the side line heat exchanger 11 and the second condenser 3 are connected through the heat pump system to recover the condensation heat generated by the second condenser 3 and supply the recovered heat to the side line heat exchanger 11.

[0051] The heat pump system includes a compressor unit 15, a working fluid high-pressure tank 12, a thermally coupled heat exchanger 14, and a cold-coupled heat exchanger 17 connected to form a heat pump circulation loop through pipelines. The shell-side outlet of the second condenser 3 is connected to the tube-side inlet of the thermally coupled heat exchanger 14 through an intake pipeline 20. The tube-side outlet of the thermally coupled heat exchanger 14 is connected to the inlet of the compressor unit 15. The outlet of the compressor unit 15 is connected to the shell-side inlet of the side-line heat exchanger 11 through a pipeline. The shell-side outlet of the side-line heat exchanger 11 is connected to the working fluid high-pressure tank 12 through a pipeline. The outlet of the working fluid high-pressure tank 12 is connected to the shell-side inlet of the thermally coupled heat exchanger 14 through a pipeline. The shell-side outlet of the thermally coupled heat exchanger 14 is connected to the tube-side of the cold-coupled heat exchanger 17 and the shell-side inlet of the second condenser 3 in sequence to form a heat pump circulation loop.

[0052] The top of the separation tower 1 is provided with a top outlet, a side outlet is provided with a side outlet, and a bottom outlet is provided with a bottom outlet. The top outlet is connected to the first condenser 2 and the second condenser 3. The first condenser 2 and the second condenser 3 are arranged in parallel. Compared with the series arrangement, the parallel arrangement reduces local pressure loss on the one hand, and on the other hand avoids reducing the gas-liquid two-phase fluid of the top gas after passing through the first condenser and entering the second condenser 3, which will cause the problem of uneven gas-liquid distribution and lead to the problem of poor heat exchange effect of the second condenser 3. The first condenser 2 is cooled by an external cold source, which is circulating cooling water; the inlet temperature of the top gas is controlled by the flow rate of cooling water. The cold source of the second condenser 3 is a heat pump working fluid. The heat pump working fluid absorbs heat and evaporates into a gas phase in the second condenser 3. The top gas releases heat and condenses into a liquid phase, and then flows back to the separation tower 1 through the top heat exchange circulation loop 23.

[0053] C4 isobutane gas is extracted from the tower top outlet and condensed in the first condenser 2 before being output. Adjusting the tower top gas reflux ratio allows C4 normal butane to be extracted from the side outlet in the liquid phase. Producing C4 normal butane in the liquid phase rather than in the gas phase offers the following advantages: first, it eliminates the need for a side-extraction heat exchanger; second, it increases the heat recovery capacity of the heat pump unit, transferring this latent heat of vaporization to the tower top, increasing the heat recovery capacity of the tower top gas and improving the system's thermal efficiency. C5 pentane and other small amounts of heavy component impurities are extracted from the tower bottom.

[0054] The heat pump system of the present invention can recover the condensation heat generated by the second condenser 3 and supply this recovered heat to the side heat exchanger 11. Excess heat can also be used to meet the needs of the chemical plant. That is, the low-grade heat generated by the condensation of the gas at the top of the conventional separation tower 1 can be pressurized and increased in quality by the compressor unit 15 and applied to the heat input of the separation tower 1 of this process and other separation towers 1 of the process, thereby reducing heat waste. This is because the temperature difference between the top and the bottom of the tower in the present invention is 54°C, and the isobutane gas in the top condenser condenses and releases heat, which is too low to be used. Heat is extracted by vaporizing the heat pump working fluid (such as Freon working fluid), and after being pressurized and heated by the compressor unit 15, it is supplied to the side heat exchanger 11 for use. Excess heat can also be used to produce steam of different pressures or hot water of different temperatures according to the needs of the chemical plant to supply other process equipment.

[0055] Steam heat exchanger 10 uses steam as a heat source to assist with startup during the startup phase and heat the high-temperature section of the tower bottom during operation. The present invention adds a side heat exchanger 11, installed at a location where the heavy component ratio is relatively low and the tower temperature is also lower. At this location, the working fluid in the tower can be pressurized to a lower pressure to meet evaporation requirements. Compared to conventional methods that use the steam heat exchanger 10 in the tower bottom to directly process the high-heavy component, high-temperature liquid in the tower bottom, side heat exchanger 11 can more effectively evaporate light components (such as C4 butane) in the falling liquid while allowing heavy components (such as C5 pentane) to fall to the bottom, thereby optimizing separation efficiency within the tower. Furthermore, because the intermediate heat exchanger processes liquid with a lower temperature and a lower heavy component ratio, the required pressure and energy consumption are also reduced. Compared to using only the steam heat exchanger 10, this can reduce system energy consumption, which is of great significance for improving the economic efficiency and sustainability of the entire system.

[0056] The first discharge pump 6 is used for collecting the tower top material, the second discharge pump 7 is used for collecting the tower bottom material, and the third discharge pump 9 is used for collecting the side line material. The first reflux pump 5 is used for the reflux of the tower top material.

[0057] The working medium high pressure tank 12 is connected to the suction line 20 through a pressure equalizing pipe 21. The pressure equalizing pipe 21 is provided with a first regulating valve 13 for equalizing the inlet and outlet pressures before and after the compressor unit 15 starts running, which can ensure that the compressor unit 15 starts without pressure difference and improves system stability. The suction line 20 pressure equalizing port is set at the lowest point of the suction line 20. The advantage of this setting method is that after the shutdown pressure equalization, the condensate in the suction line 20 can flow into the working medium high pressure tank 12 by itself, avoiding the condensate from entering the compressor. The setting position of the working medium high pressure tank 12 needs to be lower than the side line heat exchanger 11. A certain mass of heat pump working medium is stored in the working medium high pressure tank 12 and the second condenser 3. When the temperature or pressure in the tower fluctuates, the phase change load of the heat pump working medium will also change under this influence. However, this change is an indirect effect. Its hysteresis will produce a damping effect. Cooperating with the load position or frequency conversion regulation of the compressor unit 15 can effectively eliminate fluctuations and stabilize the temperature in the tower.

[0058] The external device is connected in parallel to the side heat exchanger 11 via piping to form an external device heat exchange circulation path 26. A second regulating valve 16 is also provided at the air inlet of the external device. A portion of the gaseous heat pump working fluid, compressed by the compressor unit 15, passes through this external device heat exchange circulation path 26 to meet the heat needs of other process systems.

[0059] A third regulating valve 18 is provided on the pipeline between the second condenser 3 and the cold-coupled heat exchanger 17 , and the flow rate of the heat pump working medium returning to the second condenser 3 can be regulated by the third regulating valve 18 .

[0060] A bypass line 27 is provided between the inlet and outlet of the thermally coupled heat exchanger 14, and a fourth regulating valve 19 is installed on the bypass line 27. The fourth regulating valve 19 is used to adjust the load of the thermally coupled heat exchanger 14. The thermally coupled heat exchanger 14 has two functions: first, it is used to fine-tune the load of the side-line heat exchanger 11. By adjusting the fourth regulating valve 19, the outlet temperature of the gas phase of the thermally coupled heat exchanger 14 is increased. For the same size compressor unit 15, under the condition of constant suction and discharge pressure, the density of the heat pump working fluid is reduced, and the mass flow rate of the heat pump working fluid for the compressor unit 15 is reduced, thereby reducing the heat load provided to the side-line heat exchanger 11. Conversely, lowering the outlet temperature of the gas phase of the thermally coupled heat exchanger 14 can increase the heat load of the side-line heat exchanger 11. This allows the heat load of the side-line heat exchanger 11 to be adjusted while ensuring that the compressor itself remains stationary. Furthermore, since the heat source of the thermally coupled heat exchanger 14 primarily comes from the high-pressure heat pump working fluid, reducing the high-pressure heat pump working fluid will improve the efficiency of the compressor unit 15. Secondly, during operation, the liquid droplets not separated by the second condenser 3 and the liquid formed by the heat dissipation of the longer suction pipe 20 and the environment will be heated and evaporated after entering the thermally coupled heat exchanger 14, avoiding the liquid hammer phenomenon caused by the droplets directly entering the compressor, making the system more stable and reliable.

[0061] A separation process for separating multi-component alkanes, utilizing the energy-saving and carbon reduction system for separating multi-component alkanes, comprises the following steps:

[0062] Feed the multi-component alkane raw material from the feed port of separation tower 1. When the liquid level in the bottom of the tower rises to 65% to 80% of the total capacity, stop feeding.

[0063] Start the steam heat exchanger 10 to heat the tower kettle until the internal pressure of the separation tower 1 reaches 60% to 70% of the design pressure;

[0064] Open the first condenser 2, adjust the pressure in the tower to the design value by adjusting the cold source flow, and then resume feeding into the separation tower 1;

[0065] Start the compressor unit 15 and reduce the flow rate of the heat source entering the steam heat exchanger 10 at the same time; start the first reflux pump 5 to start the reflux operation, and control the temperature in the tower by adjusting the reflux ratio until the temperature in the tower drops to the designed value; adjust the heat source flow rate of the steam heat exchanger 10 and the cold source flow rate of the first condenser 2 until the separation product output from the tower top output path 22 and the side line output path 24 is qualified, and fix the hot and cold supply ratio of the steam heat exchanger 10 and the first condenser 2 to maintain stable operation of the separation tower 1;

[0066] The first condenser 2 is cooled by an external cold source, and the cold source of the second condenser 3 is a heat pump working medium. The heat pump working medium is circulated in the heat pump circulation loop of the heat pump system. The condensation heat generated by the second condenser 3 is recovered through the circulation of the heat pump working medium, and the recovered heat is transferred to the side line heat exchanger 11.

[0067] A portion of the top gas separated from the top outlet is condensed into a liquid phase separation product by the first condenser 2 and stored in the first reflux tank 4; another portion of the top gas releases heat through the second condenser 3 and is stored in the first reflux tank 4. A portion of the liquid phase separation product in the first reflux tank 4 is refluxed into the separation tower 1 through the top heat exchange circulation loop 23, and the other portion is output through the top output path 22.

[0068] The circulation process of the heat pump working medium in the heat pump circulation loop includes:

[0069] The liquid phase heat pump working fluid evaporates in the second condenser 3 and then flows through the thermally coupled heat exchanger 14 for superheating;

[0070] The superheated gas phase heat pump working fluid enters the compressor unit 15 for compression, and the temperature and pressure increase accordingly;

[0071] The compressed gas phase heat pump working fluid enters the side line heat exchanger 11, exchanges heat with the material in the tower, and condenses into high pressure liquid;

[0072] The high-pressure liquid is transported to the working medium high-pressure tank 12 for storage;

[0073] The high-pressure liquid released from the working medium high-pressure tank 12 flows through the hot-coupled heat exchanger 14 and the cold-coupled heat exchanger 17 in sequence for cooling;

[0074] Finally, the cooled heat pump working medium returns to the second condenser 3, completing a cycle.

[0075] Increasing the overhead gas reflux ratio reduces the gas proportion at the side outlet, allowing the liquid phase separation product to be produced from the side outlet. This allows the sideline C4 n-butane to be produced in the liquid phase, eliminating the need for a side outlet heat exchanger. This increases the recoverable capacity of the heat pump unit, increases the heat recovery capacity of the overhead gas, improves the system's thermal utilization rate, reduces investment costs, and improves economic efficiency.

[0076] The cold-coupled heat exchanger 17 has two main functions. One is that it can be used to couple the load of the second condenser 3 with the heat of the side-line heat exchanger 11. When the cooling load of the second condenser 3 is in excess, the amount of cold source provided to the cold-coupled heat exchanger 17 is reduced, so that the temperature of the heat pump working fluid output from the outlet of the cold-coupled heat exchanger 17 increases, the supercooling of the heat pump working fluid is reduced, the cooling load of the second condenser 3 is reduced, and the heat load of the side-line heat exchanger 11 is reduced accordingly; when the cooling load of the second condenser 3 is insufficient, the amount of cold source provided to the cold-coupled heat exchanger 17 is increased, so that the temperature of the heat pump working fluid output from the outlet of the cold-coupled heat exchanger 17 is reduced, the supercooling of the heat pump working fluid is increased, and the cooling load of the second condenser 3 is increased.

[0077] It should be further explained that the terms "excess cooling load" and "insufficient cooling load" are used to describe whether the cooling capacity provided by the second condenser 3 to the top gas is sufficient during the condensation process. Specifically:

[0078] The excess cooling load of the second condenser 3 means that the cooling capacity provided by the second condenser 3 exceeds the cooling capacity required to completely condense the tower top gas. In this case, the tower top gas can be completely condensed and there may even be extra cooling capacity left.

[0079] The insufficient cooling load of the second condenser 3 means that the cooling capacity provided by the second condenser 3 is insufficient to completely condense the overhead gas. In other words, due to insufficient cooling capacity, part of the overhead gas cannot be condensed into liquid and remains in gaseous state.

[0080] In addition, another function of the cold-coupled heat exchanger 17 is to reduce the heat exchange area of ​​the first condenser 2 and reduce investment costs; at the same time, increasing the subcooling degree of the liquid supply can ensure that the heat pump working fluid will not be decompressed and flash during the liquid supply process, avoiding the vibration problem of the liquid supply pipeline and making the system more stable.

[0081] 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 in the scope of protection of the present invention.

Claims

1. An energy-saving and carbon reduction system for separating multi-component alkanes, comprising a separation system, a side heat exchanger and a heat pump system, characterized in that: The separation system includes a separation tower, a first condenser, a second condenser, a steam heat exchanger, a first reflux tank, a second reflux tank, a first reflux pump, a first discharge pump, a second discharge pump and a third discharge pump; the separation tower is provided with a feed inlet, a tower top production outlet, a side line production outlet and a tower bottom production outlet; the first condenser and the second condenser are arranged in parallel and are both connected to the tower top production outlet; the first reflux tank is connected to the pipe-side outlet of the first condenser, and forms a tower top output path through the first discharge pump; the pipe-side outlet of the second condenser, the first reflux tank, the first reflux pump and the separation tower are connected in sequence to form a tower top heat exchange circulation loop; the second reflux tank is connected to the side line production outlet, and forms a side line output path through the third discharge pump; the second discharge pump is connected to the tower bottom production outlet to form a tower bottom output path; the steam heat exchanger is connected to the bottom of the separation tower, A heat exchange circulation loop is formed in the tower bottom; the side heat exchanger is connected to the waist of the separation tower to form a side heat exchange circulation loop; the side heat exchanger and the second condenser are connected through a heat pump system to recover the condensation heat generated by the second condenser and supply the recovered heat to the side heat exchanger; the heat pump system includes a compressor unit, a working fluid high-pressure tank, a thermal coupling heat exchanger and a cold coupling heat exchanger, the shell side outlet of the second condenser is connected to the thermal coupling heat exchanger, the thermal coupling heat exchanger is connected to the compressor unit, the outlet of the compressor unit is connected to the side heat exchanger, and the side heat exchanger is connected to the working fluid high-pressure tank; the working fluid high-pressure tank is connected to the thermal coupling heat exchanger, and the thermal coupling heat exchanger is sequentially connected to the cold coupling heat exchanger and the second condenser to form a heat pump circulation loop; the working fluid high-pressure tank is connected to the suction pipeline through a pressure equalizing pipeline, and a first regulating valve is provided on the pressure equalizing pipeline.

2. The energy-saving and carbon reduction system for separating multi-component alkanes according to claim 1, characterized in that: The external equipment is connected in parallel with the side line heat exchanger through a pipeline to form an external equipment heat exchange circulation path, and a second regulating valve is also provided at the air inlet of the external equipment.

3. The energy-saving and carbon reduction system for separating multi-component alkanes according to claim 2, characterized in that: The device further includes a third regulating valve, which is arranged on a pipeline between the second condenser and the cold-coupled heat exchanger.

4. The energy-saving and carbon reduction system for separating multi-component alkanes according to claim 3, characterized in that: A bypass pipeline is provided between the inlet and the outlet of the thermal coupling heat exchanger, and a fourth regulating valve is provided on the bypass pipeline.

5. A separation process for separating multi-component alkanes, characterized in that: The energy-saving and carbon reduction system for separating multi-component alkanes according to any one of claims 1 to 4 comprises the following steps: Feed multi-component alkanes from the feed port of the separation tower. When the liquid level in the tower bottom rises to 65% to 80% of the total capacity, stop feeding. Start the steam heat exchanger to heat the tower kettle until the internal pressure of the separation tower reaches 60% to 70% of the design pressure; Open the first condenser, adjust the pressure in the tower to the design value by adjusting the cold source flow, and then resume feeding into the separation tower; Start the compressor unit and reduce the flow of heat source into the steam heat exchanger at the same time; turn on the first reflux pump, start the reflux operation, and control the temperature in the tower by adjusting the reflux ratio until the temperature in the tower drops to the design value; adjust the heat source flow of the steam heat exchanger and the cold source flow of the first condenser until the separation products output from the top output path and the side line output path are qualified, fix the hot and cold supply ratio of the steam heat exchanger and the first condenser, and maintain stable operation of the separation tower.

6. The separation process for separating multi-component alkanes according to claim 5, characterized in that: The circulation process of the heat pump working fluid in the heat pump circulation loop includes: The liquid phase heat pump working fluid evaporates in the second condenser and then flows through the thermally coupled heat exchanger for superheating; The superheated gas phase heat pump working fluid enters the compressor unit for compression, and the temperature and pressure increase accordingly; The compressed gas phase heat pump working fluid enters the side line heat exchanger, exchanges heat with the material in the tower, and condenses into high-pressure liquid; The high-pressure liquid is transported to the working fluid high-pressure tank for storage; The high-pressure liquid released from the working medium high-pressure tank flows through the hot-coupled heat exchanger and the cold-coupled heat exchanger in sequence for cooling; Finally, the cooled heat pump working fluid returns to the second condenser, completing a cycle.

7. The separation process for separating multi-component alkanes according to claim 6, characterized in that: Increase the top gas reflux ratio to reduce the gas proportion at the side line outlet, and produce the liquid phase separation product from the side line outlet.

8. The separation process for separating multi-component alkanes according to claim 7, characterized in that: Monitor the cooling load status of the second condenser to determine whether there is an excess or insufficient cooling load; When the cooling load of the second condenser is excessive, the amount of cold source provided to the cold-coupled heat exchanger is reduced, so that the temperature of the heat pump working fluid output from the outlet of the cold-coupled heat exchanger increases, the subcooling degree of the heat pump working fluid is reduced, the cooling load of the second condenser is reduced, and the heat load of the side heat exchanger is reduced accordingly; When the cooling load of the second condenser is insufficient, the amount of cold source provided to the cold-coupled heat exchanger is increased to reduce the temperature of the heat pump working fluid output from the outlet of the cold-coupled heat exchanger, increase the subcooling degree of the heat pump working fluid, and increase the cooling load of the second condenser.

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