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

Abstract

The invention belongs to the technical field of separation of multi-component alkanes, and relates to an energy-saving and carbon-reducing system and a separation process for separation of multi-component alkanes, and the energy-saving and carbon-reducing 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 alkane, a first condenser, a second condenser and a steam heat exchanger; the first condenser and the second condenser are arranged in parallel, the side heat exchanger is arranged at the waist of the separation tower, the steam heat exchanger is arranged at the bottom of the separation tower, and the side heat exchanger and the second condenser are connected through a heat pump system and used for recycling condensation heat generated by the second condenser and supplying the recycled heat to the side heat exchanger. When the system is used for separating multi-component alkane, a side line material liquid phase can be extracted, the heat recovery amount of tower top gas is increased, the heat utilization rate of the system is increased, the energy consumption of the system is reduced, the heat pump system adopts a heat pump working medium as a circulating heat exchange medium, the medium in the tower is not directly compressed, and the potential safety hazard of the system is reduced.

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 the traditional multi-component alkane gas purification production process, in order to achieve the effective separation of multi-component alkane gas, a double-tower separation method is generally used. Specifically, the multi-component alkane gas first enters the first separation tower, and isobutane gas is extracted from the top of the tower, while the remaining heavy component liquids such as normal butane and pentane are extracted from the bottom of the tower. Subsequently, the heavy component liquid extracted from the bottom of the first separation tower is sent to the second separation tower, and normal butane gas is extracted from the top of the second separation tower, while pentane and the remaining heavy component liquid are extracted from the bottom of the tower. The double-tower separation method not only occupies a large area, but also has high energy consumption and construction cost.

[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 bottom depends on steam heating, resulting in the degradation of high-grade steam heat 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 multi-component alkane separation towers to recover waste heat. However, since alkanes are explosion-proof media, the requirements for compressors are extremely high, requiring the compressor to have zero external leakage, which increases the cost and safety risks of the system. At the same time, due to the large temperature difference between the top of the tower and the bottom of the tower (the temperature difference between the top of the tower and the bottom of the tower is about 54°C), and the components are complex and changeable, resulting in low system efficiency, frequent fluctuations in load and operating conditions, difficulty in adjustment, and easy failure of the compressor unit. 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-reducing 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 a tower top output path is formed through the first discharge pump; the tube side outlet of the second condenser, the first side outlet of the second condenser and the third outlet of the second condenser are connected to the tower top production outlet ... 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 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 the recovered heat is supplied to the side line heat exchanger.

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

[0008] The beneficial effect of adopting the above further scheme is that the heat pump system adds a hot coupling heat exchanger and a cold coupling heat exchanger, and the system can be adjusted for hot and cold coupling without adjusting the compressor unit, so that the compressor unit can always maintain high-efficiency operation, 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 the recovered heat to the side line 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 top gas of the conventional separation tower can be increased by pressurizing the compressor unit to improve the grade, and applied to the heat input of the separation tower of this process and other separation towers of the process, thereby reducing heat waste.

[0009] Furthermore, the working fluid 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.

[0010] 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 shutdown can ensure the compressor unit to start up without pressure difference, improve the system stability, 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 hammer and damage to the compressor caused by liquid carrying problems, thereby improving the stability and reliability of the system.

[0011] Furthermore, the external device is connected in parallel with the side line heat exchanger through a pipeline to form a heat exchange circulation path of the external device, and a second regulating valve is also provided at the air inlet of the external device.

[0012] The beneficial effect of adopting the above further solution is that a part 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.

[0013] Furthermore, it also includes a third regulating valve, which is arranged on the pipeline between the second condenser and the cold-coupled heat exchanger.

[0014] The beneficial effect of adopting the above further solution is that the third regulating valve is used to adjust the flow rate of the heat pump working fluid returning to the second condenser.

[0015] Furthermore, a bypass pipeline is arranged between the inlet and the outlet of the thermal coupling heat exchanger, and a fourth regulating valve is arranged on the bypass pipeline.

[0016] 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.

[0017] 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.

[0018] A separation process for separating multi-component alkanes, using the energy-saving and carbon reduction system for separating multi-component alkanes, comprises the following steps: The multi-component alkane raw material is fed 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, the feeding is stopped. 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 inside the tower by adjusting the reflux ratio until the temperature inside 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.

[0019] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, 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 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.

[0020] 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.

[0021] The beneficial effect of adopting the above further scheme is that the side line material can be produced through the liquid phase without the need for a side line production heat exchanger, and the recoverable amount of the heat pump unit is increased, the heat recovery amount of the top gas is increased, the system heat utilization rate is increased, the investment cost is reduced, and the economy is improved.

[0022] Further, monitoring the cooling load state 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 coupling heat exchanger is reduced, so that the temperature of the heat pump working fluid output from the outlet of the cold coupling heat exchanger is increased, 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 line heat exchanger is reduced accordingly; When the cooling load of the second condenser is insufficient, the amount of cold source provided to the cold coupling heat exchanger is increased to reduce the temperature of the heat pump working fluid output from the outlet of the cold coupling heat exchanger, increase the supercooling of the heat pump working fluid, and increase the cooling load of the second condenser.

[0023] The beneficial effect of adopting the above further scheme is that the role of the cold-coupled heat exchanger is also reflected in reducing the heat exchange area of ​​the first condenser and reducing investment costs; at the same time, increasing the subcooling 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.

[0024] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: (1) The present invention adopts a separation tower, the tower top is provided with a tower top outlet, the side line is provided with a side line outlet, and the tower bottom is provided with a tower bottom outlet. The tower top outlet is connected to the first condenser and the second condenser, and the first condenser and the second condenser are arranged in parallel. Compared with the series arrangement, the parallel arrangement reduces the local pressure loss on the one hand, and avoids the problem of uneven gas-liquid distribution after the tower top gas passes through the first condenser and enters the second condenser on the other hand, which will lead to the problem of poor heat exchange effect of the second condenser.

[0025] 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 has the following advantages over the gas phase production: 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 the latent heat of vaporization of this part 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 and reduce land occupation and initial investment.

[0026] (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 potential 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 operating conditions will be adjusted more smoothly, making the system more stable.

[0027] (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 in 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 that only uses the tower bottom to directly treat 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, and the main evaporation task is undertaken by the intermediate heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0029] Figure 1 It is a structural schematic diagram of the present invention.

[0030] 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

[0031] The serial numbers assigned to the components in this application, such as "first" and "second", are only used to distinguish the objects described, and do not imply any priority in order or specific technical meaning. In addition, the concepts of "connection" and "coupling" mentioned in this application, unless otherwise specified, are deemed to include both direct connection (coupling) and indirect connection (coupling).

[0032] When interpreting the description of this application, it is necessary to clarify that the terms such as "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., which indicate positions or positional relationships, are based on the perspectives and layouts shown in the drawings, and are intended to facilitate explanation and simplify the description process, rather than being absolute limitations on the actual positions, construction methods, and operating modes of the devices or components. Therefore, these terms should not be understood as restrictive interpretations of the content of this application.

[0033] The principles and features of the present invention are described below in conjunction with examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] This embodiment takes the separation of a multi-component alkane feedstock containing C4 normal butane, C4 isobutane and C5 pentane as an example to introduce 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 the above-mentioned specific components, and it also has the ability to separate other multi-component alkane feedstocks.

[0035] like Figure 1As shown, an energy-saving and carbon-reducing system for separating multi-component alkanes comprises a separation system, a side-line heat exchanger 11 and a heat pump system, wherein the separation system comprises 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 liquid phase materials at the top of the tower, a second reflux tank 8 for buffering and storing liquid phase materials produced from the side line, 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 tower top production outlet, a side-line production outlet and a tower bottom production outlet; the first condenser 2 and the second condenser 3 are arranged in parallel and are both connected to the tower top production outlet for condensing the tower top gas; the first reflux tank 4 is connected to the pipe side outlet of the first condenser 2, and forms a tower 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 to heat 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 to exchange heat with 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.

[0036] The heat pump system includes a compressor unit 15, a working fluid high-pressure tank 12, a thermal coupling heat exchanger 14 and a cold coupling 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 thermal coupling heat exchanger 14 through an intake pipeline 20, and the tube side outlet of the thermal coupling 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, and 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 thermal coupling heat exchanger 14 through a pipeline, and the shell side outlet of the thermal coupling heat exchanger 14 is sequentially connected to the tube side of the cold coupling heat exchanger 17 and the shell side inlet of the second condenser 3 to form a heat pump circulation loop.

[0037] The top of the separation tower 1 is provided with a tower top outlet, a side line outlet, and a tower bottom outlet. The tower top outlet is connected to the first condenser 2 and the second condenser 3, and the first condenser 2 and the second condenser 3 are arranged in parallel. Compared with the series arrangement, the parallel arrangement reduces the local pressure loss on the one hand, and avoids the problem of uneven gas-liquid distribution after the tower top gas passes through the first condenser and enters the second condenser 3 on the other hand, which will 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 intake temperature of the tower 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, which absorbs heat and evaporates into a gas phase in the second condenser 3, and the tower top gas releases heat and condenses into a liquid phase, and then flows back to the separation tower 1 through the tower top heat exchange circulation loop 23.

[0038] The C4 isobutane gas is extracted from the tower top outlet and condensed by the first condenser 2 before being output; the tower top gas reflux ratio is adjusted to make C4 normal butane be extracted from the side line outlet through the liquid phase. The extraction of C4 normal butane through the liquid phase has the following advantages over the extraction through the gas phase: first, there is no need to add a side line extraction heat exchanger; second, the recoverable amount of the heat pump unit is increased, and the latent heat of vaporization of this part can be transferred to the tower top, thereby increasing the heat recovery amount of the tower top gas and increasing the thermal utilization rate of the system. C5 pentane and other small amounts of heavy component impurity liquids are extracted from the tower bottom.

[0039] The heat pump system of the present invention can recover the condensation heat generated by the second condenser 3, and supply the recovered heat to the side line heat exchanger 11. 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 gas at the top of the conventional separation tower 1 is pressurized and improved by the compressor unit 15, and applied to the heat input of the separation tower 1 of this process and other process separation towers 1, thereby reducing the waste of heat. This is because the temperature difference between the top of the tower 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. The temperature of this part of the heat is too low to be used. The heat pump working fluid (such as Freon working fluid) is used to gasify and extract heat, and the compressor unit 15 is used to pressurize and heat it, and then it is supplied to the side line heat exchanger 11 for use. The excess heat can also be used according to the needs of the chemical plant area to produce steam of different pressures or hot water of different temperatures, and supply it to other process devices.

[0040] The steam heat exchanger 10 uses water vapor as a heat source to assist in starting during the startup phase and heat the material in the high-temperature section of the tower bottom during the operation phase. The present invention adds a side heat exchanger 11, and the proportion of heavy components at the installation position is relatively low, and the temperature in 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 demand. Compared with the traditional steam heat exchanger 10 in the tower bottom that only directly processes the high-heavy component and high-temperature liquid in the tower bottom, the side heat exchanger 11 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 heavy component proportions, the required pressure and energy consumption are also reduced accordingly. Compared with the use of only the steam heat exchanger 10, the energy consumption of the system can be reduced, which is of great significance for improving the economy and sustainability of the entire system.

[0041] The first discharge pump 6 is used for extracting the tower top material, the second discharge pump 7 is used for extracting the tower bottom material, and the third discharge pump 9 is used for extracting the side line material. The first reflux pump 5 is used for reflux of the tower top material.

[0042] The working fluid high pressure tank 12 is connected to the suction pipeline 20 through a pressure equalizing pipeline 21. The pressure equalizing pipeline 21 is provided with a first regulating valve 13, which is used for the inlet and outlet pressure equalization before the compressor unit 15 starts to run and after shutdown, which can ensure the pressure difference-free startup of the compressor unit 15 and improve the stability of the system. The pressure equalizing port of the suction pipeline 20 is set at the lowest point of the suction pipeline 20. The advantage of this setting method is that after the shutdown pressure equalization, the condensate of the suction pipeline 20 can flow into the working fluid high pressure tank 12 by itself, avoiding the condensate from entering the compressor. The setting position of the working fluid high pressure tank 12 needs to be lower than the side line heat exchanger 11. A certain mass of heat pump working fluid is stored in the working fluid 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 fluid will also change under this influence. However, this change is an indirect effect, and its hysteresis will produce a damping effect. The load position or frequency conversion adjustment of the compressor unit 15 can effectively eliminate the fluctuation and stabilize the temperature in the tower.

[0043] The external device is connected in parallel with the side line heat exchanger 11 through a pipeline to form an external device heat exchange circulation path 26, and a second regulating valve 16 is also provided at the air inlet of the external device. A portion of the gas phase heat pump working fluid compressed by the compressor unit 15 passes through the external device heat exchange circulation path 26 for heat demand of other process systems.

[0044] 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 adjusted by the third regulating valve 18 .

[0045] A bypass pipe 27 is provided between the inlet and outlet of the thermal coupling heat exchanger 14, and a fourth regulating valve 19 is provided on the bypass pipe 27. The fourth regulating valve 19 is used to adjust the load of the thermal coupling heat exchanger 14. The thermal coupling heat exchanger 14 has two functions: one is to adjust and 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 side of the thermal coupling heat exchanger 14 is increased. Under the condition of constant suction and exhaust pressure of the same size compressor unit 15, the density of the heat pump working fluid will be reduced. For the compressor unit 15, the mass flow rate of the heat pump working fluid will be reduced, thereby reducing the heat load provided to the side line heat exchanger 11; conversely, reducing the outlet temperature of the gas phase side of the thermal coupling heat exchanger 14 can increase the heat load of the side line heat exchanger 11, so that the heat load of the side line heat exchanger 11 can be adjusted under the condition of ensuring that the compressor itself is stationary. At the same time, since the heat source of the thermal coupling heat exchanger 14 mainly comes from the high-pressure heat pump working fluid liquid, reducing the high-pressure heat pump working fluid liquid 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 longer suction line 20 and the ambient heat dissipation will be heated and evaporated after entering the thermally coupled heat exchanger 14, avoiding the liquid hammer phenomenon caused by the liquid droplets directly entering the compressor, making the system more stable and reliable.

[0046] A separation process for separating multi-component alkanes, using the energy-saving and carbon reduction system for separating multi-component alkanes, comprises the following steps: The multi-component alkane raw material is fed from the feed port of the separation tower 1, and the feeding is stopped when the liquid level in the tower bottom rises to 65% to 80% of the total capacity; The steam heat exchanger 10 is started to heat the tower kettle until the internal pressure of the separation tower 1 reaches 60% to 70% of the design pressure; 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; 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, 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 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, fix the cold and hot supply ratio of the steam heat exchanger 10 and the first condenser 2, and maintain the stable operation of the separation tower 1; 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 by the circulation of the heat pump working medium, and the recovered heat is transferred to the side line heat exchanger 11; A part 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 part of the top gas releases heat through the second condenser 3 and is stored in the first reflux tank 4. A part of the liquid phase separation product in the first reflux tank 4 is refluxed to the separation tower 1 through the top heat exchange circulation loop 23, and the other part is output through the top output path 22.

[0047] 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 3 and then flows through the thermally coupled heat exchanger 14 for superheating; The superheated gas phase heat pump working fluid enters the compressor unit 15 for compression, and the temperature and pressure increase accordingly; The compressed gas phase heat pump working fluid enters the side line heat exchanger 11, exchanges heat with the material in the tower, and is condensed into a high-pressure liquid; The high-pressure liquid is transported to the working fluid high-pressure tank 12 for storage; 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; Finally, the cooled heat pump working fluid returns to the second condenser 3, completing a cycle.

[0048] Increase the tower 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. The side line C4 n-butane is produced through the liquid phase, without the need for a side line 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.

[0049] The cold coupling 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 cold load of the second condenser 3 is excessive, the amount of cold source provided to the cold coupling heat exchanger 17 is reduced, so that the temperature of the heat pump working fluid output from the outlet of the cold coupling heat exchanger 17 is increased, the supercooling of the heat pump working fluid is reduced, the cold load of the second condenser 3 is reduced, and the heat load of the side line heat exchanger 11 is reduced accordingly; when the cold load of the second condenser 3 is insufficient, the amount of cold source provided to the cold coupling heat exchanger 17 is increased, so that the temperature of the heat pump working fluid output from the outlet of the cold coupling heat exchanger 17 is reduced, the supercooling of the heat pump working fluid is increased, and the cold load of the second condenser 3 is increased.

[0050] 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: 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 additional cooling capacity left.

[0051] 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 tower top gas. In other words, due to insufficient cooling capacity, part of the gas in the tower top gas cannot be condensed into liquid and still remains in gaseous state.

[0052] 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.

[0053] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An energy-saving and carbon-reducing system for separating multi-component alkanes, comprising a separation system, a side line heat exchanger (11) and a heat pump system, characterized in that: The separation system comprises a separation tower (1), a first condenser (2), a second condenser (3), a steam heat exchanger (10), a first reflux tank (4), a second reflux tank (8), 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 tower top outlet, a side line outlet and a tower bottom outlet; The first condenser (2) and the second condenser (3) are arranged in parallel and are both connected to the tower top production outlet; The first reflux tank (4) is connected to the pipe-side outlet of the first condenser (2), and forms a tower top output path (22) through a first discharge pump (6); The tube side outlet of the second condenser (3), the first reflux tank (4), the first reflux pump (5) and the separation tower (1) are sequentially connected 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); The second discharge pump (7) is connected to the tower bottom outlet to form a tower bottom outlet path; The steam heat exchanger (10) is connected to the bottom of the separation tower (1) 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) to form a side line heat exchange circulation loop (25); The side line heat exchanger (11) and the second condenser (3) are connected via the heat pump system, and are used to recover condensation heat generated by the second condenser (3), and supply the recovered heat to the side line heat exchanger (11).

2. The energy-saving and carbon-reducing system for separation of multi-component alkanes according to claim 1, characterized in that: The heat pump system comprises a compressor unit (15), a working fluid high-pressure tank (12), a heat-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 heat-coupled heat exchanger (14) through an air intake pipeline (20); the tube-side outlet of the heat-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 heat-coupled heat exchanger (14) through a pipeline; the shell-side outlet of the heat-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, forming a heat pump circulation loop.

3. The energy-saving and carbon-reducing system for separation of multi-component alkanes according to claim 2, characterized in that: The working medium high-pressure tank (12) is connected to the air intake pipeline (20) via a pressure equalizing pipeline (21), and a first regulating valve (13) is provided on the pressure equalizing pipeline (21).

4. The energy-saving and carbon-reducing system for separation of multi-component alkanes according to claim 3, characterized in that: The external device is connected in parallel with the side line heat exchanger (11) through a pipeline to form an external device heat exchange circulation path (26), and a second regulating valve (16) is also provided at the air inlet of the external device.

5. The energy-saving and carbon-reducing system for separation of multi-component alkanes according to claim 4, characterized in that: It also includes a third regulating valve (18), wherein the third regulating valve (18) is arranged on the pipeline between the second condenser (3) and the cold-coupled heat exchanger (17).

6. The energy-saving and carbon-reducing system for separation of multi-component alkanes according to claim 5, characterized in that: A bypass pipeline (27) is provided between the inlet and the outlet of the thermal coupling heat exchanger (14), and a fourth regulating valve (19) is provided on the bypass pipeline (27).

7. 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 6 comprises the following steps: Multi-component alkanes are fed from the feed port of the separation tower (1), and when the liquid level in the bottom of the tower rises to 65% to 80% of the total capacity, the feeding is stopped; The steam heat exchanger (10) is started to heat the tower kettle until the internal pressure of the separation tower (1) reaches 60% to 70% of the design pressure; Open the first condenser (2), adjust the pressure in the tower to the design value by adjusting the flow rate of the cold source, and then resume feeding the separation tower (1); The compressor unit (15) is started, and the flow rate of the heat source entering the steam heat exchanger (10) is reduced at the same time; the first reflux pump (5) is turned on, the reflux operation is started, and the temperature in the tower is controlled by adjusting the reflux ratio until the temperature in the tower drops to the design value; the heat source flow rate of the steam heat exchanger (10) and the cold source flow rate of the first condenser (2) are adjusted until the separation product output from the tower top output path (22) and the side line output path (24) are qualified, and the hot and cold supply ratios of the steam heat exchanger (10) and the first condenser (2) are fixed to maintain the stable operation of the separation tower (1).

8. The separation process for separating multi-component alkanes according to claim 7, 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 (3), and then flows through the thermal coupling heat exchanger (14) for superheating; The superheated gas phase heat pump working fluid enters the compressor unit (15) for compression, and the temperature and pressure increase accordingly; The compressed gas phase heat pump working fluid enters the side line heat exchanger (11), exchanges heat with the material in the tower, and is condensed into a high-pressure liquid; The high-pressure liquid is transported to the working fluid high-pressure tank (12) for storage; The high-pressure liquid released from the working fluid high-pressure tank (12) flows through the hot coupling heat exchanger (14) and the cold coupling heat exchanger (17) in sequence for cooling; Finally, the cooled heat pump working fluid returns to the second condenser (3), completing a cycle.

9. The separation process for separating multi-component alkanes according to claim 8, characterized in that: Increase the top gas reflux ratio to reduce the gas proportion at the side line production outlet, and produce the liquid phase separation product from the side line production outlet.

10. The separation process for separating multi-component alkanes according to claim 9, characterized in that: Monitoring the cooling load status of the second condenser (3) to determine whether there is an excess or insufficient cooling load; When the cooling load of the second condenser (3) is excessive, the amount of cold source provided to the cold coupling heat exchanger (17) is reduced, so that the temperature of the heat pump working fluid output from the outlet of the cold coupling heat exchanger (17) increases, the degree of subcooling 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 coupling heat exchanger (17) is increased, so that the temperature of the heat pump working fluid output from the outlet of the cold coupling heat exchanger (17) is reduced, the degree of subcooling of the heat pump working fluid is increased, and the cooling load of the second condenser (3) is increased.

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