Heat integration rectification system and method for extract tower and finished product tower in p-xylene production

Abstract

The invention belongs to the field of petrochemical industry, and discloses a heat integration rectification system and method for an extract tower and a finished product tower in p-xylene production. The rectification system comprises an extract tower and a finished product tower; the top of the extract tower is connected with an extract tower top gas compressor through a pipeline, the extract tower top gas compressor is respectively connected with a finished product tower heat source reboiler I and a finished product tower heat source reboiler II through pipelines, and the finished product tower heat source reboiler I and the finished product tower heat source reboiler II are connected with an extract tower top gas air cooler through pipelines. The system also comprises an extract tower top gas preheater and an extract tower top steam generator. The system provided by the invention is improved on the basis of the existing system. The invention also discloses a rectification method. According to the system and method, effective utilization of heat is achieved, cost and energy consumption are reduced, efficiency is improved, and income benefits are increased.

Description

Technical Field

[0001] This invention belongs to the technical field of petroleum processing, specifically relating to a thermally integrated distillation system and method for extracting liquid tower and finished product tower in paraxylene production. Background Technology

[0002] The Aromatics Complex Plan (ACM) is the core unit for the production of para-xylene (PX) in the petrochemical industry. It consists of pre-hydrogenation, continuous reforming, isomerization, disproportionation, and adsorption separation units. The adsorption separation unit separates C8 aromatics from the reforming, isomerization, and disproportionation processes to obtain para-xylene (PX) with a concentration higher than 99.7%. Because C8 aromatics have similar boiling points (e.g., toluene 110.6℃, ethylbenzene 136.2℃, para-xylene 138.5℃, m-xylene 140.6℃, o-xylene 144.4℃ at atmospheric pressure), conventional distillation is very difficult, requiring a large number of trays and high energy consumption. Therefore, simulated moving bed (MMB) technology (often using para-diethylbenzene as the desorbent, with an atmospheric boiling point of 184℃) is commonly used for adsorption separation of the desired product.

[0003] The adsorption separation unit contains a simulated moving bed, an extractor column, and a product column. The extractor column separates the circulating desorbent, while the product column removes toluene to obtain PX. In the existing process, the extractor column operates at atmospheric pressure (approximately 0.05 MPa) with hot reflux (approximately 130°C), achieving a top temperature of approximately 155°C. The top of the column is cooled by air cooling, resulting in a high cooling load. The product column also operates at atmospheric pressure (approximately 0.05 MPa), with a bottom temperature of approximately 165°C. It uses a mixture of xylene from the xylene fractionation and redistillation columns (temperature approximately 225°C) and the circulating desorbent from the raffinate column (temperature approximately 195°C) as heat sources.

[0004] How to achieve thermal integration of the extractant tower and the product tower, reduce the cooling load at the top of the extractant tower, replace the heat of mixed xylene and desorbent, and generate low-pressure 0.45MPag steam from the heat of mixed xylene and desorbent, thereby achieving effective utilization of heat, reducing costs and energy consumption, improving efficiency, and increasing revenue and benefits. Summary of the Invention

[0005] To address the shortcomings of existing aromatic hydrocarbon adsorption separation units where the top gas temperature of the extractor column is high but is air-cooled, resulting in a large cooling load, while the bottom temperature of the product column is low but a higher temperature heat source is used for reboiling, this invention provides a thermally integrated distillation system and method for the extractor and product columns in paraxylene production. This invention achieves efficient heat utilization, reduces costs and energy consumption, improves efficiency, and increases revenue. This invention eliminates the direct air cooling of the extractor column top gas and achieves efficient heat utilization through an extractor column top gas compressor, extractor column top steam generator, and pressure reducing valve, ensuring stable pressure in the extractor column system and orderly product separation. This invention can displace the heat from the mixed xylene and desorbent, producing low-pressure 0.45 MPa steam along with the waste heat from the extractor column top gas. The system and method of this invention can generate high heat, ensuring stable system operation, effective product separation, and allowing excess heat to be used for other purposes.

[0006] The objective of this invention is achieved through the following technical solution: A thermally integrated distillation system for paraxylene production, comprising an extractor tower and a product tower, includes an extractor tower and a product tower. The top of the extractor tower is connected to an extractor tower top gas compressor via a pipeline. The extractor tower top gas compressor is connected to two heat source reboilers in the product tower via pipelines. The two heat source reboilers are connected to an air-cooling device at the top of the extractor tower via pipelines. The air-cooling device is connected to a liquid separator at the top of the extractor tower via a pipeline. The liquid separator is connected to a reflux and product pump at the top of the extractor tower via a pipeline. The reflux and product pump are connected to the top of the extractor tower and the product tower via pipelines, respectively. A product tower feed heat exchanger is installed on the pipeline connecting the reflux and product pump to the product tower. The bottom of the extracting liquid tower is connected to the extracting liquid tower feed heat exchanger and the extracting liquid tower bottom reboiler via pipelines. The extracting liquid tower bottom reboiler is connected to the bottom of the extracting liquid tower via a pipeline to form a reflux. The extracting liquid tower feed heat exchanger is connected to the adsorption unit via a pipeline. The outlet of the extracting liquid is connected to the extracting liquid tower feed heat exchanger via a pipeline. The extracting liquid tower feed heat exchanger is connected to the extracting liquid tower via a pipeline. The top of the finished product tower is connected to the top air-cooling unit via pipeline. The top air-cooling unit is connected to the top liquid separator via pipeline. The top liquid separator is connected to the top reflux pump via pipeline. The top reflux pump is connected to the toluene collection unit and the top of the finished product tower via pipeline. The bottom of the finished product tower is connected to the first and second heat source reboilers via pipeline. The first and second heat source reboilers are connected to the bottom of the finished product tower via pipeline, forming a reflux. The bottom of the finished product tower is also connected to the feed heat exchanger via pipeline. The feed heat exchanger is connected to the paraxylene collection unit via pipeline. A paraxylene air-cooling unit and a paraxylene water-cooling unit are sequentially installed on the pipeline between the feed heat exchanger and the paraxylene collection unit. The paraxylene air-cooling unit is located near the feed heat exchanger.

[0007] The distillation system also includes a preheater for the top gas of the extraction liquid tower; the preheater for the top gas of the extraction liquid tower is installed on the pipeline connecting the first heat source reboiler of the finished product tower and the second heat source reboiler of the finished product tower to the air cooling device for the top gas of the extraction liquid tower; the preheater for the top gas of the extraction liquid tower is also installed on the pipeline connecting the top of the extraction liquid tower to the compressor for the top gas of the extraction liquid tower.

[0008] The distillation system also includes a vapor generator at the top of the extractor column; the vapor generator is installed on the pipeline connecting the vapor preheater at the top of the extractor column and the air cooler at the top of the extractor column.

[0009] The distillation system also includes a pressure reducing valve, which is installed on the pipeline connecting the steam generator at the top of the extraction liquid tower and the air-cooling device at the top of the extraction liquid tower.

[0010] The distillation system also includes a mixed xylene hot steam generator, a circulating desorbent hot steam generator, and a steam compressor; the water supply device is connected to the extractant tower top steam generator, the mixed xylene hot steam generator, and the circulating desorbent hot steam generator respectively through pipelines, and the extractant tower top steam generator, the mixed xylene hot steam generator, and the circulating desorbent hot steam generator are connected to the steam compressor through pipelines.

[0011] A thermally integrated distillation method for extracting liquid and producing product in paraxylene production includes the following steps: 1) The extracted liquid is heated by heat exchange in the feed heat exchanger of the extracted liquid tower, and then enters the extracted liquid tower. After processing in the extracted liquid tower, the overhead gas from the top of the extracted liquid tower is output and compressed by the overhead gas compressor. The compression increases the temperature and pressure of the overhead gas, resulting in compressed overhead gas. The compressed overhead gas is then sent to the product tower heat source reboiler No. 1 and the product tower heat source reboiler No. 2, respectively. The No. 2 reboiler exchanges heat with the bottom liquid of the product column, and the temperature of the compressed top gas of the extractive column decreases. Then, the compressed top gas of the extractive column enters the top gas air cooler and the top liquid separator of the extractive column in sequence. After being air cooled, the compressed top gas of the extractive column becomes liquid and is stored in the top liquid separator of the extractive column. The liquid mixture in the top liquid separator of the extractive column is transported to the top of the extractive column and the feed heat exchanger of the product column respectively through the top reflux of the extractive column and the product pump. A portion of the bottom liquid from the extractive liquid tower is sent to the extractive liquid tower feed heat exchanger, where it exchanges heat with the extractive liquid. After the heat exchange, the bottom liquid from the extractive liquid tower is cooled and enters the adsorption unit. Another portion of the bottom liquid from the extractive liquid tower is sent to the bottom reboiler of the extractive liquid tower. Through heating in the bottom reboiler, this portion of the bottom liquid from the extractive liquid tower partially vaporizes and is then returned to the bottom of the extractive liquid tower. 2) The liquid mixture fed to the product tower feed heat exchanger exchanges heat with the liquid from the bottom of the product tower, and is heated before entering the product tower. After processing in the product tower, the overhead gas is sent to the product tower overhead gas air-cooling device. After air cooling, the overhead gas is liquefied and stored in the product tower overhead separator. The liquid in the product tower overhead separator is then sent to the top of the product tower and the toluene collection device, respectively, under the control of the product tower overhead reflux product pump. A portion of the bottom liquid from the finished product column is fed to the finished product column feed heat exchanger, where it exchanges heat with the liquid mixture from the top separator of the extractor column. This portion of the bottom liquid cools down, while the liquid mixture from the top separator of the extractor column heats up. The cooled bottom liquid then passes through an air-cooling unit for paraxylene and a water-cooling unit for paraxylene before entering a paraxylene collection unit to obtain paraxylene. A portion of the bottom liquid of the finished product tower is also transported to the No. 1 and No. 2 heat source reboilers of the finished product tower. Through the heat exchange between the No. 1 and No. 2 heat source reboilers of the finished product tower and the compressed top gas of the extractable liquid tower, part of the bottom liquid of the finished product tower is vaporized. The partially vaporized bottom liquid of the finished product tower is returned to the bottom of the finished product tower.

[0012] Before the top gas of the extraction liquid tower mentioned in step 1) is output from the top of the extraction liquid tower and enters the top gas compressor, the top gas of the extraction liquid tower is heated by the top gas preheater of the extraction liquid tower. The top gas of the extraction liquid tower exchanges heat with the cooled top gas of the extraction liquid tower from the reboiler 1 and the reboiler 2 of the product tower heat source through the top gas preheater of the extraction liquid tower.

[0013] After heat exchange with the cooled extract liquid tower top gas from the reboiler 1 and reboiler 2 of the product tower heat source, the temperature of the extract liquid tower top gas decreases again; then it enters the extract liquid tower top steam generator, and the extract liquid tower top gas is cooled down again.

[0014] The gas enters the top steam generator of the extraction liquid tower. After the gas in the top steam generator is cooled down again, it is depressurized through the pressure reducing valve to maintain the stability of the pressure in the extraction liquid tower system. After depressurization, the gas in the top steam generator enters the air cooling device for air cooling.

[0015] The extractant comes from a simulated moving bed. The overhead gas from the extractant tower is a mixture containing toluene and paraxylene.

[0016] The liquid mixture in the top separator of the extraction tower refers to a liquid mixture containing toluene and paraxylene.

[0017] The overhead gas in the product column is toluene. The liquid in the top separator of the product column is liquid toluene. The bottom liquid in the product column is a liquid whose main component is para-xylene.

[0018] In the method of the present invention, the gas enters the top steam generator of the extraction liquid tower, and the top gas of the extraction liquid tower is cooled again. The top steam generator of the extraction liquid tower is a device that uses the top gas of the extraction liquid tower, which has been cooled by the top gas preheater of the extraction liquid tower, as a heat source to heat the deoxygenated water to generate steam. The steam generated by the deoxygenated water enters the steam compressor for compression.

[0019] The method of the present invention further includes utilizing the heat from the mixed xylene and the circulating desorbent from the adsorption separation unit. Specifically, the mixed xylene from the adsorption separation unit is used as a heat source to heat the deoxygenated water to generate steam through a mixed xylene hot steam generator; the circulating desorbent from the adsorption separation unit is used as a heat source to heat the deoxygenated water to generate steam through a circulating desorbent hot steam generator; and the steam obtained through the mixed xylene hot steam generator and the steam obtained through the circulating desorbent hot steam generator are compressed using a steam compressor.

[0020] In this invention, the pressure of the top gas from the extraction liquid tower is increased from approximately 0.05 MPa to approximately 0.2 MPa after being compressed by the top gas compressor; the temperature of the top gas from the extraction liquid tower is also increased. The compressed top gas from the extraction liquid tower is used as the reboiling heat source for the bottom of the product tower (product tower heat source reboiler No. 1 and product tower heat source reboiler No. 2, replacing the original mixed xylene heat source reboiler and the original circulating desorbent heat source reboiler in the existing adsorption separation unit with product tower heat source reboiler No. 1 and product tower heat source reboiler No. 2, the equipment remains unchanged, only the heat source is replaced).

[0021] This invention includes an extraction liquid tower top gas preheater located between the top of the extraction liquid tower and the extraction liquid tower top gas compressor. This preheater uses the cooled extraction liquid tower top gas from the reboiler 1 and reboiler 2 of the product tower heat source as a heat source to heat the extraction liquid tower top gas, raising the compressor inlet gas temperature by 5-10°C to prevent liquid carryover in the gas and thus affecting compression.

[0022] This invention includes an extractable liquid tower top steam generator installed between the extractable liquid tower top gas preheater and the extractable liquid tower top gas air cooler. The extractable liquid tower top steam generator uses the cooled extractable liquid tower top gas from the extractable liquid tower top gas preheater as a heat source to heat the deoxygenated water, producing 0.45 MPa saturated steam with a saturation temperature of 159.2°C.

[0023] A pressure reducing valve is installed between the steam generator at the top of the extraction liquid tower and the air cooler at the top of the extraction liquid tower. The pressure reducing valve releases the pressure of the gas from the top of the extraction liquid tower from the steam generator to approximately 0.045 MPa, thereby maintaining a constant operating pressure for the extraction liquid tower system.

[0024] In this invention, the temperature of the top gas of the extraction liquid tower is reduced to a level where the top air cooling of the extraction liquid tower can be shut down to maintain hot reflux operation.

[0025] This invention utilizes a mixed xylene thermal steam generator and a circulating desorbent thermal steam generator to effectively recover the heat from the displaced mixed xylene (temperature 225℃~185℃) and circulating desorbent (temperature 195℃~175℃) to produce 0.45MPag saturated steam, or to use the heat from the mixed xylene and circulating desorbent for other purposes.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) This invention realizes the thermal integration of the extraction liquid tower and the product tower. The waste heat of the extraction liquid tower is used for the product tower. The waste heat of the top gas of the extraction liquid tower is upgraded by compression. The heat of the top gas of the upgraded extraction liquid tower replaces the heat of the original equivalent 1.0 MPag steam as the reboiling heat source of the product tower. The heat is effectively utilized. (2) This invention can shut down the air cooling at the top of the extracting liquid tower, solving the problem of high cooling load; calculations show that for an 800,000-ton / year adsorption separation unit, the air cooling load at the top of the extracting liquid tower is approximately 2600 × 10⁻⁶ tons / year. 4 kcal / h; (3) This invention utilizes the compressed extractor tower top gas to replace the heat of the mixed xylene and circulating desorbent in the original adsorption separation unit, thereby achieving effective heat utilization, reducing costs and energy consumption, and improving efficiency; the heat from the replaced mixed xylene and desorbent produces 0.45 MPa of steam. Calculations show that an 800,000-ton / year adsorption separation unit can produce approximately 25 t / h of steam from its heat. (4) This invention utilizes a steam generator at the top of the extraction liquid tower to generate 0.45 MPa of steam from the remaining compressed extraction liquid tower top gas. Calculations show that for an 800,000-ton / year adsorption separation unit, the reboiling load of the finished product tower is approximately 1150 × 10⁻⁶. 4 kcal / h, so the residual heat can produce about 29t / h of steam.

[0027] (5) In this invention, the extraction liquid tower and the finished product tower do not need to be changed because the operating pressure remains unchanged; and the product distribution and product quality remain unchanged. For the renovation project, the extraction liquid tower can utilize the original air-cooled space to arrange the compressor and compressed gas vapor generator, which is convenient for implementation.

[0028] In summary, this invention achieves efficient utilization of heat, reduces costs and energy consumption, improves efficiency, and increases revenue and benefits. Attached Figure Description

[0029] Figure 1 Schematic diagram of an existing extractable liquid tower and product tower separation system for comparison; 1-Extractable liquid tower feed heat exchanger, 2-Extractable liquid tower, 3-Extractable liquid tower top air cooling device, 4-Extractable liquid tower top separator, 5-Extractable liquid tower top reflux and product pump, 6-Extractable liquid tower bottom reboiler, 7-Product tower feed heat exchanger, 8-Product tower, 9-Product tower top air cooling device, 10-Product tower top separator, 11-Product tower top reflux product pump, 12-Product tower mixed xylene heat source reboiler, 13-Product tower desorbent heat source reboiler, 14-Product para-xylene air cooling device, 15-Product para-xylene water cooling device; Figure 2This is a schematic diagram of the integrated thermal distillation system for the extracting liquid tower and the finished product tower in the production of paraxylene according to the present invention; 1- Extracting liquid tower feed heat exchanger, 2- Extracting liquid tower, 3- Extracting liquid tower top gas air cooling device, 4- Extracting liquid tower top separator, 5- Extracting liquid tower top reflux and product pump, 6- Extracting liquid tower bottom reboiler, 7- Finished product tower feed heat exchanger, 8- Finished product tower, 9- Finished product tower top gas air cooling device, 10- Finished product tower top separator, 11- Finished product tower top reflux product pump, 12- Finished product tower heat source reboiler No. 1, 13- Finished product tower heat source reboiler No. 2, 14- Product paraxylene air cooling device, 15- Product paraxylene water cooling device, 16- Extracting liquid tower top gas preheater, 17- Extracting liquid tower top gas compressor, 18- Extracting liquid tower top steam generator, 19- Pressure reducing valve; Figure 3 This is a process diagram for the utilization of heat from mixed xylene and heat from the circulating desorbent in Example 2; 20 - Mixed xylene thermal steam generator, 21 - Circulating desorbent thermal steam generator, 22 - Steam compressor. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0031] A schematic diagram of a thermally integrated distillation system for extracting liquid and finishing product in the production of paraxylene, as described in this invention, is shown below. Figure 2 As shown, the system includes an extraction liquid tower 2 and a finished product tower 8. The top of the extraction liquid tower is connected to an extraction liquid tower top gas compressor 17 via a pipeline. The extraction liquid tower top gas compressor 17 is connected to the finished product tower heat source reboiler 12 and finished product tower heat source reboiler 2 13 via pipelines. The finished product tower heat source reboiler 12 and finished product tower heat source reboiler 2 13 are connected to the extraction liquid tower top gas air cooling device 3 via pipelines. The extraction liquid tower top gas air cooling device 3 is connected to the extraction liquid tower top liquid separator 4 via a pipeline. The extraction liquid tower top liquid separator 4 is connected to the extraction liquid tower top reflux and product pump 5 via a pipeline. The extraction liquid tower top reflux and product pump 5 is connected to the top of the extraction liquid tower 2 and the finished product tower 8 via pipelines. A finished product tower feed heat exchanger 7 is installed on the pipeline connecting the extraction liquid tower top reflux and product pump 5 to the finished product tower 8. The bottom of the extraction liquid tower 2 is connected to the extraction liquid tower feed heat exchanger 1 and the extraction liquid tower bottom reboiler 6 through pipelines respectively. The extraction liquid tower feed heat exchanger 1 is connected to the extraction liquid tower 2 through pipelines, and the extraction liquid tower bottom reboiler 6 is connected to the bottom of the extraction liquid tower 2 through pipelines. The top of product tower 8 is connected to the top air-cooling device 9 via a pipeline. The top air-cooling device 9 is connected to the top liquid separator 10 via a pipeline. The top liquid separator 10 is connected to the top reflux pump 11 via a pipeline. The top reflux pump 11 is connected to the toluene collection device and the top of product tower 8 via pipelines. The bottom of product tower 8 is connected to the first reboiler 12 and the second reboiler 13 via pipelines. The first reboiler 12 and the second reboiler 13 of the product tower heat source are connected to the bottom of the product tower 8 through pipelines; the bottom of the product tower 8 is also connected to the product tower feed heat exchanger 7 through pipelines, and the product tower feed heat exchanger 7 is connected to the paraxylene collection device through pipelines. The product paraxylene air cooling device 14 and the product paraxylene water cooling device 15 are sequentially installed on the pipeline between the product tower feed heat exchanger 7 and the paraxylene collection device; the product paraxylene air cooling device 14 is close to the product tower feed heat exchanger 7.

[0032] The distillation system also includes an extractable liquid tower top gas preheater 16; the extractable liquid tower top gas preheater 16 is installed on the pipeline connecting the product tower heat source reboiler 12 and the product tower heat source reboiler 2 13 to the extractable liquid tower top gas air cooling device 3; the extractable liquid tower top gas preheater 16 is also installed on the pipeline connecting the top of the extractable liquid tower 2 to the extractable liquid tower top gas compressor 17.

[0033] The distillation system also includes a vapor generator 18 at the top of the extractor column; the vapor generator 18 is installed on the pipeline connecting the vapor preheater 16 at the top of the extractor column and the air cooler 3 at the top of the extractor column.

[0034] The distillation system also includes a pressure reducing valve 19, which is installed on the pipeline connecting the liquid tower top steam generator 18 and the liquid tower top air cooling device 3.

[0035] The distillation system also includes a mixed xylene steam generator 20, a circulating desorbent steam generator 21, and a steam compressor 22. A water supply device is connected via pipelines to the extractant column top steam generator 18, the mixed xylene steam generator 20, and the circulating desorbent steam generator 21, respectively. The extractant column top steam generator 18, the mixed xylene steam generator 20, and the circulating desorbent steam generator 21 are connected via pipelines to the steam compressor 22. A schematic diagram of this part of the distillation system is shown below. Figure 3 As shown.

[0036] A thermally integrated distillation method for extracting liquid and producing product in paraxylene production includes the following steps: 1) The extracted liquid is heated by heat exchange in the feed heat exchanger 1 of the extracted liquid tower, and then enters the extracted liquid tower 2. After processing in the extracted liquid tower 2, the overhead gas from the top of the extracted liquid tower 2 is output and compressed by the overhead gas compressor 17. The compression increases the temperature and pressure of the overhead gas, resulting in compressed overhead gas. The compressed overhead gas is then sent to the product tower heat source reboiler 12 and the product tower heat source reboiler 23, respectively. Heat exchange occurs between the reboiler 2 (13) and the bottom liquid of the product column 8, causing the temperature of the compressed extractor gas to decrease. Subsequently, the compressed extractor gas enters the extractor gas air cooler 3 and the extractor gas separator 4 in sequence. After air cooling, the compressed extractor gas becomes liquid and is stored in the extractor gas separator 4. The liquid mixture in the extractor gas separator 4 is transported to the top of the extractor and the product column feed heat exchanger 7 respectively by the extractor reflux and product pump 5. A portion of the bottom liquid from the extractive liquid tower is sent to the extractive liquid tower feed heat exchanger 1, where it exchanges heat with the extractive liquid. After heat exchange, the bottom liquid from the extractive liquid tower cools down and enters the adsorption unit. Another portion of the bottom liquid from the extractive liquid tower is sent to the bottom reboiler 6, where it is heated and partially vaporized. This vaporized portion is then returned to the bottom of the extractive liquid tower. 2) The liquid mixture fed to the product tower feed heat exchanger 7 exchanges heat with the bottom liquid from the product tower, and is heated before entering the product tower 8. After being processed by the product tower 8, the top gas of the product tower is fed to the top gas air cooler 9. After being air cooled, the top gas of the product tower becomes liquid and is stored in the top liquid separator 10 of the product tower. The liquid in the top liquid separator 10 of the product tower is controlled by the product reflux pump 11 to be transported to the top of the product tower and the toluene collection device respectively. A portion of the bottom liquid from the finished product tower is fed to the finished product tower feed heat exchanger 7, where it exchanges heat with the liquid mixture from the top separator 4 of the extractor tower. This portion of the bottom liquid from the finished product tower cools down, while the liquid mixture from the top separator 4 of the extractor tower heats up. The cooled bottom liquid from the finished product tower then passes through the air cooling unit 14 for product paraxylene and the water cooling unit 15 for product paraxylene, before entering the paraxylene collection unit to obtain paraxylene. A portion of the bottom liquid from the finished product column is also transported to the finished product column heat source reboiler 1 (12) and the finished product column heat source reboiler 2 (13). Through the finished product column heat source reboiler 1 (12) and the finished product column heat source reboiler 2 (13), heat is exchanged with the compressed extractor column top gas. This portion of the bottom liquid from the finished product column is heated and partially vaporized. The heated and partially vaporized bottom liquid from the finished product column is then returned to the bottom of the finished product column.

[0037] Before the top gas of the extraction liquid tower described in step 1) is output from the top of the extraction liquid tower and enters the top gas compressor 17, the top gas of the extraction liquid tower is heated by the top gas preheater 16. The top gas of the extraction liquid tower exchanges heat with the cooled top gas of the extraction liquid tower from the reboiler 12 and the reboiler 2 of the product tower heat source through the top gas preheater 16.

[0038] After the cooled gas from the top of the extraction liquid tower from the reboiler 12 and the reboiler 2 of the product tower heat source exchanges heat, its temperature drops again; then it enters the steam generator 18 at the top of the extraction liquid tower, where it is cooled down again.

[0039] The vapor enters the top steam generator 18 of the extraction liquid tower. After the top gas of the extraction liquid tower is cooled again, it is depressurized through the pressure reducing valve 19 to maintain the stability of the system pressure of the extraction liquid tower 2. After depressurization, the top gas of the extraction liquid tower enters the top gas air cooling device 3 for air cooling. The top gas air cooling device of the extraction liquid tower can be shut down.

[0040] The extractant comes from a simulated moving bed. The overhead gas from the extractant tower is a mixture containing toluene and paraxylene.

[0041] The liquid mixture in the top separator of the extraction tower refers to a liquid mixture containing toluene and paraxylene.

[0042] The overhead gas in the product column is toluene. The liquid in the top separator of the product column is liquid toluene. The bottom liquid in the product column is a liquid whose main component is para-xylene.

[0043] After the extracted liquid is heated by heat exchange, it enters from the middle of the extracted liquid tower. The liquid mixture conveyed to the feed heat exchanger of the finished product tower is heated by heat exchange and then enters the finished product tower from the upper middle part.

[0044] In the method of the present invention, the gas enters the top steam generator 18 of the extraction liquid tower, and the top gas of the extraction liquid tower is cooled again. The top steam generator 18 is a device that uses the top gas of the extraction liquid tower, which has been cooled by the top gas preheater 16 of the extraction liquid tower, as a heat source to heat the deoxygenated water to generate steam. The steam generated by the deoxygenated water enters the steam compressor 22 for compression.

[0045] The method of the present invention further includes utilizing the heat from the mixed xylene and the circulating desorbent from the adsorption separation unit. Specifically, the mixed xylene from the adsorption separation unit is used as a heat source to heat the deoxygenated water to generate steam through the mixed xylene hot steam generator 20; the circulating desorbent from the adsorption separation unit is used as a heat source to heat the deoxygenated water to generate steam through the circulating desorbent hot steam generator 21; and the steam obtained through the mixed xylene hot steam generator 20 and the steam obtained through the circulating desorbent hot steam generator 21 are compressed using a steam compressor 22.

[0046] Comparative Example A schematic diagram of the existing extractor and product separation system is shown below. Figure 1 As shown, it includes an extraction liquid tower 2 and a finished product tower 8. The top of the extraction liquid tower 2 is connected to an air-cooled device 3 at the top of the extraction liquid tower via a pipeline. The air-cooled device 3 at the top of the extraction liquid tower is connected to a liquid separator 4 at the top of the extraction liquid tower via a pipeline. The liquid separator 4 at the top of the extraction liquid tower is connected to a reflux and product pump 5 at the top of the extraction liquid tower via a pipeline. The reflux and product pump 5 at the top of the extraction liquid tower is connected to the top of the extraction liquid tower 2 and the finished product tower 8 via pipelines respectively. A finished product tower feed heat exchanger 7 is installed on the pipeline connecting the reflux and product pump 5 at the top of the extraction liquid tower and the finished product tower 8. The bottom of the extraction liquid tower 2 is connected to the extraction liquid tower feed heat exchanger 1 and the extraction liquid tower bottom reboiler 6 respectively through pipelines. The extraction liquid tower feed heat exchanger 1 is connected to the extraction liquid tower 2 through a pipeline, and the extraction liquid tower bottom reboiler 6 is connected to the bottom of the extraction liquid tower 2 through a pipeline. The top of product column 8 is connected to the top air-cooling unit 9 via a pipeline. The top air-cooling unit 9 is connected to the top liquid separator 10 via a pipeline. The top liquid separator 10 is connected to the top reflux product pump 11 via a pipeline. The top reflux product pump 11 is connected to the toluene collection unit and the top of product column 8 via pipelines. The bottom of product column 8 is connected to the mixed xylene heat source reboiler 12 and the circulating desorbent heat source reboiler No. 2 13 via pipelines. The reboiler 12 for the mixed xylene heat source of the finished product tower and the reboiler 13 for the desorbent heat source of the finished product tower are connected to the bottom of the finished product tower 8 through pipelines; the bottom of the finished product tower 8 is also connected to the finished product tower feed heat exchanger 7 through pipelines, and the finished product tower feed heat exchanger 7 is connected to the para-xylene collection device through pipelines. The product para-xylene air cooling device 14 and the product para-xylene water cooling device 15 are sequentially installed on the pipeline between the finished product tower feed heat exchanger 7 and the para-xylene collection device; the product para-xylene air cooling device 14 is close to the finished product tower feed heat exchanger 7.

[0047] The existing separation system operates the extractor column at atmospheric pressure with hot reflux, where the overhead gas is condensed and cooled by air cooling. The product column operates at atmospheric pressure, with a bottom temperature above 160°C, using a mixture of xylene and a desorbent as a reheat source. The temperature of the xylene mixture ranges from 225°C to 185°C, and the temperature of the desorbent ranges from 195°C to 175°C, thus its energy level is equivalent to 1.0 MPa steam. The main energy problem is that the relatively high-temperature overhead gas in the extractor column is cooled, while the relatively low-temperature product column uses the equivalent of 1.0 MPa steam as a heat source. Therefore, possible solutions are to increase the pressure of the extractor column or decrease the pressure of the product column. However, the former might lead to exceeding the design pressure, requiring column replacement, which is too costly; the latter would require switching to negative pressure operation, which involves significant changes.

[0048] Taking an 800,000-ton / year adsorption separation unit of an aromatics complex in a petrochemical enterprise as an example, the parameters and energy consumption of the extractor and product towers using the existing separation system are shown in Table 1.

[0049] Table 1. Main operating parameters and energy consumption of the extracting liquid tower and the finished product tower. It can be seen that the total cooling load at the top of the two towers is 3967.9 × 10⁻⁶. 4 kcal / h; Reboiling load at the bottom of the raffinate column: 2612 × 10 4 kcal / h, bottom temperature 213.7℃, equivalent to consuming approximately 42t / h of medium-pressure 3.5MPa steam as a heat source; the reboiling load at the bottom of the product column is 1143.4×10 4 With a heat output of kcal / h and a bottom temperature of 162.9℃, this is equivalent to consuming approximately 20 t / h of low-pressure 1.0 MPa steam as a heat source. The total steam consumption is approximately 62 t / h, indicating extremely high energy consumption.

[0050] Table 2 shows the composition of the crude p-xylene product at the top of the extraction column.

[0051] Table 2. Composition of crude p-xylene product at the top of the extract column Table 3 shows the composition of the para-xylene product at the bottom of the finished product tower.

[0052] Table 3 Composition of p-xylene products from the bottom of the finished product tower Example 1 This embodiment of a thermally integrated distillation system for paraxylene production, comprising an extraction liquid tower and a product tower, includes an extraction liquid tower and a product tower. The top of the extraction liquid tower is connected to an extraction liquid tower top gas compressor via a pipeline. An extraction liquid tower top gas preheater is installed on the pipeline connecting the extraction liquid tower top to the extraction liquid tower top gas compressor. The extraction liquid tower top gas compressor is connected via pipelines to two heat source reboilers in the product tower, respectively. These two heat source reboilers are connected via pipelines to the extraction liquid tower top gas preheater. The pipeline connects to the steam generator at the top of the extractive liquid tower, which in turn connects to the air cooler at the top of the extractive liquid tower via another pipeline. A pressure reducing valve is installed on the pipeline connecting the steam generator and the air cooler. The air cooler at the top of the extractive liquid tower connects to the liquid separator at the top of the extractive liquid tower via another pipeline. The liquid separator is connected to the reflux and product pumps at the top of the extractive liquid tower via another pipeline. The reflux and product pumps are connected to the top of the extractive liquid tower and the finished product tower, respectively, via pipelines. A product tower feed heat exchanger is installed on the pipeline connecting the reflux and product pumps to the finished product tower. The bottom of the extraction liquid tower is connected to the extraction liquid tower feed heat exchanger and the extraction liquid tower bottom reboiler through pipelines respectively. The extraction liquid tower feed heat exchanger is connected to the extraction liquid tower through a pipeline, and the extraction liquid tower bottom reboiler is connected to the bottom of the extraction liquid tower through a pipeline. The top of the finished product tower is connected to the top air-cooled product tower via a pipeline. The top air-cooled product tower is connected to the top liquid separator via a pipeline. The top liquid separator is connected to the top reflux product pump via a pipeline. The top reflux product pump is connected to the toluene collection unit and the top of the finished product tower via pipelines. The bottom of the finished product tower is connected to the first and second heat source reboilers via pipelines. The first and second heat source reboilers are connected to the bottom of the finished product tower via pipelines. The bottom of the finished product tower is also connected to the feed heat exchanger via a pipeline. The feed heat exchanger is connected to the paraxylene collection unit via a pipeline. The pipelines connecting the feed heat exchanger and the paraxylene collection unit are equipped with paraxylene air coolers and paraxylene water coolers in sequence. The paraxylene air coolers are located near the feed heat exchanger.

[0053] The main operating parameters and energy consumption of the raffinate tower and the finished product tower in this embodiment are shown in Table 4.

[0054] Table 4. Main operating parameters and energy consumption of the extracting liquid tower and product tower in Example 1 It can be seen that the overhead gas from the extraction liquid tower is compressed from 0.05 MPa to 0.2 MPa and 184.7℃ in a superheated state by the compressor, based on an isentropic efficiency of 75%, consuming 2372.5 kW of shaft power. The compressed gas is then used as the reboiling heat source for the finished product tower, with a heat load of 1173 × 10⁻⁶ kW. 4 kcal / h, corresponding to the heat generated from displacing mixed xylene and desorbent, can produce 24.3 t / h of saturated steam at a rate of 0.45 MPa; the heat load of the steam generator at the top of the extraction liquid tower is 1410 × 10⁻⁶ kcal / h. 4 The capacity is kcal / h, which can produce 29.2 t / h of 0.45 MPa saturated steam. Based on a steam price of 185 yuan / t at 0.45 MPa, an electricity price of 0.65 yuan / kWh, and an annual operating time of 8400 hours, the new dual-tower heat pump distillation integrated process will increase efficiency by 68.995 million yuan / year. See Table 5 for details.

[0055] Table 5 Energy Saving Benefits of Example 1

Claims

1. A thermally integrated distillation system for the extracting liquid tower and the finished product tower in the production of paraxylene, characterized in that: It includes an extracting liquid tower and a finished product tower. The top of the extracting liquid tower is connected to the top gas compressor via a pipeline. The top gas compressor is connected to the first and second heat source reboilers of the finished product tower via pipelines. The first and second heat source reboilers of the finished product tower are connected to the air-cooling device at the top of the extracting liquid tower via pipelines. The air-cooling device is connected to the top liquid separator at the top of the extracting liquid tower via pipelines. The top liquid separator is connected to the top reflux and product pumps of the extracting liquid tower via pipelines. The top reflux and product pumps are connected to the top of the extracting liquid tower and the finished product tower via pipelines, respectively. A finished product tower feed heat exchanger is installed on the pipeline connecting the top reflux and product pumps of the extracting liquid tower to the finished product tower. The bottom of the extracting liquid tower is connected to the extracting liquid tower feed heat exchanger and the extracting liquid tower bottom reboiler via pipelines. The extracting liquid tower bottom reboiler is connected to the bottom of the extracting liquid tower via a pipeline to form a reflux. The extracting liquid tower feed heat exchanger is connected to the adsorption unit via a pipeline. The extracting liquid outlet of the simulated moving bed is connected to the extracting liquid tower feed heat exchanger via a pipeline. The extracting liquid tower feed heat exchanger is connected to the extracting liquid tower via a pipeline. The top of the finished product tower is connected to the top air-cooled unit via a pipeline. The top air-cooled unit is connected to the top liquid separator via a pipeline. The top liquid separator is connected to the top reflux pump via a pipeline. The top reflux pump is connected to the toluene collection unit and the top of the finished product tower via pipelines. The bottom of the finished product tower is connected to reboilers No. 1 and No. 2 via pipelines. Reboilers No. 1 and No. 2 are connected to the bottom of the finished product tower via pipelines, forming a reflux. The bottom of the finished product tower is also connected to the feed heat exchanger via a pipeline. The feed heat exchanger is connected to the paraxylene collection unit via a pipeline. A paraxylene air-cooling unit and a paraxylene water-cooling unit are sequentially installed on the pipelines connecting the feed heat exchanger and the paraxylene collection unit. The paraxylene air-cooling unit is located near the feed heat exchanger.

2. The integrated thermal distillation system for extracting liquid and producing product in the production of paraxylene according to claim 1, characterized in that: It also includes a preheater for the top gas of the extraction liquid tower; the preheater for the top gas of the extraction liquid tower is installed on the pipeline connecting the first heat source reboiler of the finished product tower and the second heat source reboiler of the finished product tower to the air cooling device for the top gas of the extraction liquid tower; the preheater for the top gas of the extraction liquid tower is also installed on the pipeline connecting the top of the extraction liquid tower to the compressor for the top gas of the extraction liquid tower.

3. The thermally integrated distillation system for the extraction liquid tower and the finished product tower in the production of paraxylene according to claim 2, characterized in that: It also includes a vapor generator at the top of the extraction liquid tower; the vapor generator at the top of the extraction liquid tower is installed on the pipeline connecting the vapor preheater at the top of the extraction liquid tower and the air cooling device at the top of the extraction liquid tower.

4. The thermally integrated distillation system for extracting liquid and finishing product in paraxylene production according to claim 3, characterized in that: It also includes a pressure reducing valve, which is installed on the pipeline connecting the top steam generator of the liquid tower and the air-cooling device of the top gas of the extraction liquid tower.

5. The thermally integrated distillation system for the extraction liquid tower and the finished product tower in the production of paraxylene according to claim 4, characterized in that: The distillation system also includes a mixed xylene hot steam generator, a circulating desorbent hot steam generator, and a steam compressor; the water supply device is connected to the extractant tower top steam generator, the mixed xylene hot steam generator, and the circulating desorbent hot steam generator respectively through pipelines, and the extractant tower top steam generator, the mixed xylene hot steam generator, and the circulating desorbent hot steam generator are connected to the steam compressor through pipelines.

6. A thermally integrated distillation method for the extracting liquid tower and the finished product tower in the production of paraxylene, characterized in that: Includes the following steps: 1) The extracted liquid is heated by heat exchange in the feed heat exchanger of the extracted liquid tower, and then enters the extracted liquid tower. After processing in the extracted liquid tower, the overhead gas from the top of the extracted liquid tower is output and compressed by the overhead gas compressor. The compression increases the temperature and pressure of the overhead gas, resulting in compressed overhead gas. The compressed overhead gas is then sent to the product tower heat source reboiler No. 1 and the product tower heat source reboiler No. 2, respectively. The No. 2 reboiler exchanges heat with the bottom liquid of the product column, and the temperature of the compressed top gas of the extractive column decreases. Then, the compressed top gas of the extractive column enters the top gas air cooler and the top liquid separator of the extractive column in sequence. After being air cooled, the compressed top gas of the extractive column becomes liquid and is stored in the top liquid separator of the extractive column. The liquid mixture in the top liquid separator of the extractive column is transported to the top of the extractive column and the feed heat exchanger of the product column respectively through the top reflux of the extractive column and the product pump. A portion of the bottom liquid from the extractive liquid tower is sent to the extractive liquid tower feed heat exchanger, where it exchanges heat with the extractive liquid. After heat exchange, the bottom liquid from the extractive liquid tower cools down and enters the adsorption unit. Another portion of the bottom liquid from the extractive liquid tower is sent to the bottom reboiler of the extractive liquid tower. Through heating in the bottom reboiler, this portion of the bottom liquid from the extractive liquid tower is heated up and partially vaporized, and then refluxed back to the bottom of the extractive liquid tower. 2) The liquid mixture fed to the product tower feed heat exchanger exchanges heat with the bottom liquid from the product tower, raising its temperature, and then enters the product tower. After processing in the product tower, the overhead gas from the product tower is sent to the product tower overhead gas air cooler. After air cooling, the overhead gas from the product tower becomes liquid and is stored in the product tower overhead separator. The liquid in the product tower overhead separator is controlled by the product tower overhead reflux pump to be separately transported to the top of the product tower and the toluene collection device. A portion of the bottom liquid from the finished product column is fed to the finished product column feed heat exchanger, where it exchanges heat with the liquid mixture from the top separator of the extractor column. This portion of the bottom liquid cools down, while the liquid mixture from the top separator of the extractor column heats up. The cooled bottom liquid then passes through an air-cooling unit for paraxylene and a water-cooling unit for paraxylene before entering a paraxylene collection unit to obtain paraxylene. A portion of the bottom liquid of the finished product tower is also sent to the No. 1 and No. 2 heat source reboilers of the finished product tower. Through the heat exchange between the No. 1 and No. 2 heat source reboilers of the finished product tower and the compressed top gas of the extractable liquid tower, the bottom liquid of the finished product tower is partially vaporized after the temperature rises. The bottom liquid of the finished product tower after the temperature rises is returned to the bottom of the finished product tower. The method is implemented using the thermally integrated distillation system for extracting liquid tower and finished product tower in the production of paraxylene as described in any one of claims 1 to 5.

7. The thermally integrated distillation method for the extracting liquid tower and the finished product tower in the production of paraxylene according to claim 6, characterized in that: Before the top gas of the extraction liquid tower mentioned in step 1) is output from the top of the extraction liquid tower and enters the top gas compressor, the top gas of the extraction liquid tower is heated by the top gas preheater of the extraction liquid tower. The top gas of the extraction liquid tower exchanges heat with the cooled top gas of the extraction liquid tower from the reboiler 1 and the reboiler 2 of the product tower heat source through the top gas preheater of the extraction liquid tower.

8. The thermally integrated distillation method for the extracting liquid tower and the finished product tower in the production of paraxylene according to claim 7, characterized in that: After heat exchange with the cooled extract liquid tower top gas from the reboiler 1 and reboiler 2 of the product tower heat source, the temperature of the extract liquid tower top gas decreases again; then it enters the extract liquid tower top steam generator, and the extract liquid tower top gas is cooled down again.

9. The thermally integrated distillation method for the extracting liquid tower and the finished product tower in the production of paraxylene according to claim 8, characterized in that: The gas enters the top steam generator of the extraction liquid tower. After the gas in the top steam generator of the extraction liquid tower is cooled again, it is depressurized through the pressure reducing valve to maintain the stability of the pressure of the extraction liquid tower system. After depressurization, the gas in the top steam generator of the extraction liquid tower enters the air cooling device of the top steam generator of the extraction liquid tower for air cooling or the air cooling of the top steam generator of the extraction liquid tower is stopped.

10. The thermally integrated distillation method for the extracting liquid tower and the finished product tower in the production of paraxylene according to claim 9, characterized in that: The gas enters the steam generator at the top of the extraction liquid tower, where it is cooled again. The steam generator at the top of the extraction liquid tower uses the cooled gas from the top of the extraction liquid tower (which has been preheated by the gas preheater) as a heat source to heat the deoxygenated water and generate steam. The steam generated by the deoxygenated water is then compressed by the steam compressor. The method further includes utilizing the heat from the mixed xylene and circulating desorbent from the adsorption separation unit. Specifically, the mixed xylene from the adsorption separation unit is used as a heat source to heat the deoxygenated water to generate steam through a mixed xylene hot steam generator; the circulating desorbent from the adsorption separation unit is used as a heat source to heat the deoxygenated water to generate steam through a circulating desorbent hot steam generator; and the steam obtained from the mixed xylene hot steam generator and the steam obtained from the circulating desorbent hot steam generator are compressed using a steam compressor.

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