Energy-saving process and system suitable for large-temperature-difference rectifying tower

Abstract

The energy-saving process comprises the following steps that a gas-phase raw material enters a depropanizing tower and is divided into two parts at a tower top outlet, and a small part of the gas-phase raw material enters a condenser and enters a reflux tank after being cooled; most gas-phase materials enter a condensation evaporator and enter a reflux tank after being condensed, one part of reflux liquid in the reflux tank enters a depropanizing tower, and the other part of the reflux liquid enters a tower top product unit; a liquid-phase material in the depropanizing tower is divided into three parts at a tower bottom outlet, the first part is used as a product to enter a liquid-phase product unit, the second part enters a tower bottom reboiler to be reboiled and then returns to the depropanizing tower, the third part enters a primary booster, and the cooled material is decompressed and cooled by a regulating valve and then enters a condensation evaporator; and the flashed material enters a second-stage booster, and the heated gas-phase material returns to the bottom of the depropanizing tower. The energy-saving requirement under the working condition of large temperature difference between the tower top and the tower kettle of the rectifying tower can be met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy-saving process for rectifying column, and particularly relates to an energy-saving process and system suitable for rectifying column with large temperature difference. BACKGROUND

[0002] In order to reduce energy consumption, some refineries at home and abroad use heat pump rectification technology in rectifying devices. Heat pump rectification changes the temperature level of the working medium through compression and heat exchange to complete the heat exchange between the overhead and bottom streams. In this way, the heating heat source of the rectifying column reboiler and part of the heat load of the overhead condenser are saved, achieving the purpose of energy saving.

[0003] Chinese patent CN113440882A discloses a device and method applied to a styrene separation system, which uses one of A-type open heat pump and B-type open heat pump of steam compression heat pump rectification, cancels the overhead condenser and the bottom reboiler, and saves energy consumption and operating costs. The temperature difference between the overhead and the bottom of the ethylbenzene / styrene column is less than 20℃.

[0004] Chinese utility model patent CN220385815U discloses a BOD heat pump rectifying column system, which directly draws out the overhead gas phase, pressurizes and warms it by a compressor to serve as a heat source for heat exchange with the column bottom reboiler (A-type open), releases heat to condense part of the gas, reduces the pressure and temperature by a throttle valve, and then enters the reflux tank after being cooled by an auxiliary condenser, thereby fully utilizing the waste heat of the system and effectively saving cold energy consumption and heat energy consumption. The temperature difference between the overhead and the bottom of the BOD purification column is about 15℃.

[0005] The overhead gas is directly compressed for rectification (A-type open), and the overhead material is used as a working medium to exchange heat with the bottom material. The column bottom liquid is flashed and reboiled for rectification (B-type open), and the bottom material is used as a working medium to exchange heat with the overhead gas. Both of the above heat pump types are suitable for rectification processes with a temperature difference between the overhead and the bottom of less than 20℃. For a rectifying column with a temperature difference between the overhead and the bottom of nearly 30℃, the existing heat pump scheme is no longer economical. The reason is that the larger the temperature difference, the higher the energy consumption.

[0006] The overhead temperature of the depropanizer in the gas separation device is about 46-50℃, and the bottom temperature is about 96-103℃, with a temperature difference of 50℃ between the overhead and the bottom. The existing heat pump scheme cannot meet the energy-saving needs of heat exchange between the overhead and the bottom materials. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide an energy-saving process and system suitable for rectifying column with large temperature difference, which can meet the energy-saving needs of rectifying column with large temperature difference between the overhead and the bottom.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0009] An energy-saving process suitable for large temperature difference distillation columns includes the following steps:

[0010] The gaseous feed enters the propane stripper and is divided into two parts at the top outlet. A small portion of the gaseous material enters the condenser and is cooled before entering the reflux tank. The majority of the gaseous material enters the condenser-evaporator and is condensed before entering the reflux tank. Part of the reflux liquid in the reflux tank enters the propane stripper, and the other part enters the top product unit.

[0011] The liquid material in the propane stripper is divided into three parts at the bottom outlet. The first part enters the liquid product unit as the product; the second part enters the bottom reboiler for reboiling and then returns to the propane stripper; the third part enters the primary booster. Device, increase cooling After being depressurized and cooled by the regulating valve, the material enters the condenser-evaporator. The flash-evaporated material then enters the secondary enrichment stage. Device, increase heat The gaseous material is then returned to the bottom of the propane stripper.

[0012] Preferably, the ratio of gaseous material entering the condenser to gaseous material entering the condenser-evaporator is (5:95) to (30:70); the top temperature of the propane removal tower is 40 to 55°C, the pressure is 1.55 to 1.75 MPa, the bottom temperature is 90 to 105°C, and the pressure is 1.55 to 1.75 MPa.

[0013] Specifically, the ratio of gaseous material entering the condenser to gaseous material entering the condenser-evaporator can be 5:95, 10:90, 15:85, 20:80, 25:75, or 30:70. The top temperature of the propane removal column can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, or 55℃, and the pressure can be 1.55MPag, 1.6MPag, 1.65MPag, 1.7MPag, or 1.75MPag. These values ​​are not limited to those listed, and other unlisted values ​​within the range are also applicable.

[0014] Preferably, the ratio of reflux liquid entering the propane stripper from the reflux tank to the product unit at the top of the tower is (1:1) to (4:1); the temperature of the reflux tank is 40 to 55°C, and the pressure is 1.55 to 1.75 MPa.

[0015] Specifically, the ratio of reflux liquid entering the propane stripper from the reflux tank to the product entering the top product unit can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. The temperature of the reflux tank can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, or 55℃, and the pressure can be 1.55MPag, 1.6MPag, 1.65MPag, 1.7MPag, or 1.75MPag. These values ​​are not limited to those listed, and other unlisted values ​​within the range are also applicable.

[0016] Preferably, it enters the liquid phase product unit, the reboiler, and the first-stage enhancement stage. The liquid phase material ratio of the device is (40:5:55) to (20:10:70).

[0017] Specifically, it enters the liquid product unit, the reboiler, and the first-stage enhancement stage. The liquid phase material ratio of the apparatus is 40:5:55, 35:5:60, 35:10:55, 30:5:60, 30:10:60, 25:5:70, 25:10:65, 20:10:70, and is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the material temperature after passing through the reboiler is 90–105°C, and the material passes through a single-stage intensifier. The material temperature after the booster is 50–90℃, and the material temperature after the regulating valve is 26–45℃. The material pressure is 0.2–0.7 MPa. The material is then passed through a two-stage booster. The temperature of the material after the device is 90-105℃.

[0019] Specifically, the material temperature after passing through the reboiler can be 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, or 105℃, through a first-stage increase... The material temperatures after the booster are 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, and 90℃. The material temperatures after the regulating valve are 26℃, 28℃, 30℃, 32℃, 34℃, 36℃, 38℃, 40℃, 42℃, 44℃, and 45℃. The material pressures are 0.2MPag, 0.3MPag, 0.4MPag, 0.5MPag, 0.6MPag, and 0.7MPag. The material is then passed through a two-stage booster. The material temperature after the device can be 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, or 105℃, and is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] This invention also protects an energy-saving system for implementing the process described above in a large temperature difference distillation column, comprising a propane stripper, wherein the top outlet of the propane stripper is divided into two paths by a pipeline, one path being connected to the inlet of a condenser-evaporator and the other path being connected to the inlet of a condenser, the outlets of the condenser-evaporator and the condenser being connected by a pipeline to the inlet of a reflux tank, and the outlet of the reflux tank being connected by a pipeline to the propane stripper at one end and to the top product unit at the other end.

[0021] The bottom outlet of the propane stripper is divided into three branches via pipelines: the first branch connects to the inlet of the reboiler, the second branch connects to the inlet of the liquid product unit, and the third branch connects to the first-stage increaser. The device inlet, the first-stage increase The outlet of the heat exchanger is connected to the inlet of the condenser-evaporator via a pipe, and the outlet of the condenser-evaporator is connected to the secondary booster via a pipe. The entrance to the device, secondary enhancement The outlet of the device is connected to the bottom inlet of the propane stripper via a pipeline.

[0022] Preferably, the first-level increase A regulating valve is also installed between the evaporator and the condenser.

[0023] Preferably, the reboiler is also connected to a steam inlet pipe and a steam condensate outlet pipe.

[0024] Preferably, the condenser is also connected to a cooling circulating water inlet pipe and a cooling circulating water outlet pipe.

[0025] In this invention, the first-level increase The heat exchanger can be any type of heat exchanger, with air coolers being the preferred option.

[0026] In this invention, the secondary enhancement The device can be any type of additional equipment, with a compressor being the preferred choice.

[0027] In this invention, a first-level increment is set. The device increased cooling The decompression of the material at the bottom of the column allows it to provide sufficient cooling to the gaseous material at the top, causing it to condense; the secondary booster is designed to... The device increased heat This allows the gaseous material returning to the tower to carry enough heat to offset most of the heat provided by the original reboiler.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention provides an energy-saving process suitable for large temperature difference distillation columns, wherein the bottom material first enters a primary enrichment stage. Device, increase cooling After acquiring sufficient cooling capacity, the gaseous material at the top of the column can be condensed after pressure reduction and cooling; after absorbing the heat from the material at the top of the column, the vaporized material enters the secondary booster. Device, increase heat After accumulating sufficient heat, the steam returns to the bottom of the column, reducing the steam used by the original reboiler. Furthermore, the technical solution of this invention retains the original top condenser and bottom reboiler. Compared to a simple heat pump solution, it adds flexible control methods during start-up, changes in column throughput, and normal operation (controlling the bottom process parameters by adjusting the steam flow and the top process parameters by adjusting the circulating water flow), which is more conducive to the stable operation and control of the distillation column and is more suitable for retrofitting older columns. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the energy-saving system structure applicable to large temperature difference distillation columns in Embodiment 1 of the present invention;

[0031] Figure 2 This is a schematic diagram of the system structure of the distillation column of Comparative Example 1 of the present invention.

[0032] The components are as follows: 1. Gas feedstock; 2. Propane stripper; 3. Condenser; 4. Reflux tank; 5. Top product unit; 6. Bottom outlet; 7. Reboiler; 8. Liquid product unit; 9. Cooling water inlet pipe; 10. Cooling water outlet pipe; 11. Steam inlet pipe; 12. Steam condensate outlet pipe; 13. Top outlet; 14. First inlet; 15. Condensate evaporator; 16. First outlet; 17. First stage increaser. Device; 18. Control valve; 19. Second inlet; 20. Second outlet; 21. Secondary booster Utensils. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] An energy-saving system suitable for large temperature difference distillation columns includes a propane stripper 2. The top outlet 13 of the propane stripper 2 is divided into two paths by a pipeline. One path is connected to the first inlet 14 of a condenser-evaporator 15, and the other path is connected to the inlet of a condenser 3. The first outlet 16 of the condenser-evaporator 15 and the outlet of the condenser 3 are connected to the inlet of a reflux tank 4 by a pipeline. The outlet of the reflux tank 4 is connected to the propane stripper 2 at one end and to the gas phase product unit 5 at the other end by a pipeline.

[0036] The bottom outlet 6 of the propane removal column 2 is divided into three branches via pipelines: the first branch connects to the inlet of the reboiler 7, the second branch connects to the inlet of the liquid product unit 8, and the third branch connects to the first-stage increaser. Inlet of device 17, the first-stage enhancement The outlet of evaporator 17 is connected to the second inlet 19 of condenser-evaporator 15 via a pipe, and the second outlet 20 of condenser-evaporator 15 is connected to the secondary booster via a pipe. The entrance to device 21, secondary enhancement The outlet of device 21 is connected to the bottom inlet of the depropanizer 2 via a pipeline.

[0037] In this embodiment, the first inlet 14 and the first outlet 16 of the condenser evaporator 15 are the same pipeline, and the second inlet 19 and the second outlet 20 of the condenser evaporator 15 are the same pipeline, and the two pipelines are not connected.

[0038] In this embodiment, the first-level enhancement A regulating valve 18 is also provided between the evaporator 17 and the condenser 15.

[0039] In this embodiment, the reboiler 7 is also connected to a steam inlet pipe 11 and a steam condensate outlet pipe 12.

[0040] In this embodiment, the condenser 4 is also connected to a cooling circulating water inlet pipe 9 and a cooling circulating water outlet pipe 10.

[0041] In this embodiment, the first-level enhancement Unit 17 is an air cooler.

[0042] In this embodiment, the secondary enhancement Device 21 is a compressor.

[0043] Example 2

[0044] An energy-saving process suitable for large temperature difference distillation columns includes the following steps:

[0045] Desulfurized liquefied petroleum gas feedstock 1 enters the propane removal tower 2, and is divided into two parts at the top outlet 13. A small portion of the gaseous material enters the condenser 3, and after cooling, it enters the reflux tank 4. The majority of the gaseous material enters the condenser-evaporator 15, and after condensation, it enters the reflux tank 4. Part of the reflux liquid in the reflux tank 4 enters the propane removal tower 2, and the other part enters the top product unit 5. Circulating water enters the condenser 3 from the cooling circulating water inlet pipe 9 to provide cooling capacity, and returns to the pipeline network from the cooling circulating water outlet pipe 10.

[0046] The liquid material in the propane stripper 2 is divided into three parts at the bottom outlet 6. The first part enters the liquid product unit 8 as the product, the second part enters the bottom reboiler 7 for reboiling and then returns to the propane stripper 2, and the third part enters the primary booster. Unit 17, increases cooling After being depressurized and cooled by regulating valve 18, the material enters condenser-evaporator 15. The flash-evaporated material then enters the secondary booster. Device 21, increases heat The gaseous material is returned to the bottom of the propane stripper 2, and the steam enters the reboiler 7 from the steam inlet pipe 11 to provide heat, and returns to the pipeline network from the steam condensate outlet pipe 12.

[0047] In this embodiment, the ratio of gaseous material entering the condenser 3 to gaseous material entering the condenser-evaporator 15 is 15:85; the top temperature of the propane removal tower 2 is 45°C and the pressure is 1.65 MPa, and the bottom temperature is 100°C and the pressure is 1.65 MPa.

[0048] In this embodiment, the ratio of reflux liquid entering the propane stripper 2 to entering the top product unit 5 in the reflux tank 4 is 1:1; the temperature of the reflux tank 4 is 45°C and the pressure is 1.65 MPa.

[0049] In this embodiment, the product enters the liquid phase product unit 8, the reboiler 7, and the first-stage enhancer. The liquid phase material ratio of device 17 is 30:10:60.

[0050] In this embodiment, the material temperature after reboiler 7 is 100°C, and it passes through a first-stage intensifier. The material temperature after valve 17 is 60℃, and the material temperature after regulating valve 18 is 35℃. The material pressure is 0.4MPa. The material is then supplied via a two-stage booster. The material temperature after device 21 is 100℃.

[0051] In this embodiment, the load on condenser 3 is approximately -500kW, the load on reboiler 7 is approximately 900kW, and the first-stage booster... Unit 17 has a load of approximately -1500kW, and is a secondary booster. The power of the 21-shaft unit is approximately 1500kW. (Single-stage increaser) Unit 17 increases cooling 260kW, secondary boost Device 21 increases heat 1200kW.

[0052] Comparative Example 1

[0053] like Figure 2 As shown, a distillation process for a propane removal column includes the following steps:

[0054] Desulfurized liquefied petroleum gas feedstock 1 enters propane removal tower 2, where C3 and C4 components are separated by the action of the top condenser 3 and the bottom reboiler 7.

[0055] Among them, the gaseous material at the top of the tower goes to the condenser 3 through the top outlet 13, and after condensation, it enters the reflux tank 4. Part of the reflux liquid in the reflux tank 4 is returned to the propane removal tower, and the other part enters the top product unit 5. The circulating water enters the condenser 3 from the cooling circulating water inlet pipe 9 to provide cooling capacity, and returns to the pipeline network from the cooling circulating water outlet pipe 10.

[0056] The liquid material at the bottom of the tower is divided into two parts at the bottom outlet 6. One part enters the liquid product unit 8 as a product, and the other part enters the bottom reboiler 7 for reboiling and then returns to the propane removal tower 2. Steam enters the reboiler 7 from the steam inlet pipe 11 to provide heat, and returns to the pipeline network from the steam condensate outlet pipe 12.

[0057] In this comparative example, the ratio of reflux liquid entering propane dehydrogenator 2 to entering top product unit 5 in reflux tank 4 is 1:1; the temperature of reflux tank 4 is 45°C and the pressure is 1.65 MPa.

[0058] In this comparative example, in this embodiment, the ratio of liquid phase material entering the liquid phase product unit 8 to liquid phase material entering the reboiler 7 is 75:25.

[0059] In this comparative example, the load of condenser 3 is approximately -5100kW; the load of reboiler 7 is approximately 5600kW.

[0060] Compared to Comparative Example 1, Example 2 reduced the cooling load by 3100kW, the heating load by 4700kW, and the electrical power increased by 1500kW. A detailed comparison of the economic benefits of Example 2 and Comparative Example 1 is shown in Table 1.

[0061] Table 1

[0062]

[0063] Note: Annual operating hours of the unit are calculated based on 8400 hours; "-" indicates a decrease; "+" indicates an increase.

[0064] As can be seen from Table 1, the modification scheme of the present invention can save 9.3 million yuan per year, which is a significant economic benefit.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An energy-saving process suitable for large temperature difference distillation columns, characterized in that, Includes the following steps: The gaseous feedstock (1) enters the propane stripper (2) and is divided into two parts at the top outlet (13). A small portion of the gaseous material enters the condenser (3), and after cooling, it enters the reflux tank (4). The majority of the gaseous material enters the condenser-evaporator (15), and after condensation, it enters the reflux tank (4). Part of the reflux liquid in the reflux tank (4) enters the propane stripper (2), and the other part enters the top product unit (5). The liquid material in the propane stripper (2) is divided into three parts at the bottom outlet (6). The first part enters the liquid product unit (8) as product, the second part enters the bottom reboiler (7) for reboiling and then returns to the propane stripper (2), and the third part enters the primary booster. Device (17), increase cooling After being depressurized and cooled by regulating valve (18), the material enters the condenser-evaporator (15), and the flash-evaporated material enters the secondary enrichment stage. Device (21), increasing heat The gaseous material is then returned to the bottom of the propane stripper (2).

2. The process according to claim 1, characterized in that, The ratio of gaseous material entering the condenser (3) to gaseous material entering the condenser-evaporator (15) is (5:95) to (30:70); the top temperature of the propane removal tower (2) is 40 to 55°C, the pressure is 1.55 to 1.75 MPa, the bottom temperature is 90 to 105°C, and the pressure is 1.55 to 1.75 MPa.

3. The process according to claim 1, characterized in that, The ratio of reflux liquid entering the propane stripper (2) from the reflux tank (4) to the product unit (5) at the top of the tower is (1:1) to (4:1); the temperature of the reflux tank (4) is 40 to 55°C and the pressure is 1.55 to 1.75 MPa.

4. The process according to claim 1, characterized in that, It enters the liquid product unit (8), the reboiler (7), and the first-stage growth regulator. The liquid phase material ratio of the device (17) is (40:5:55) to (20:10:70).

5. The process according to claim 1, characterized in that, The material temperature after passing through the reboiler (7) is 90-105℃, and after passing through the first stage of intensification... The material temperature after the device (17) is 50-90℃, and the material temperature after the regulating valve (18) is 26-45℃. The material pressure is 0.2-0.7 MPa. The material is then subjected to a two-stage increase... The material temperature after the device (21) is 90-105℃.

6. An energy-saving system for implementing the process described in any one of claims 1-5, suitable for large temperature difference distillation columns, characterized in that, The system includes a propane stripper (2), the top outlet (13) of which is divided into two paths by a pipeline, one path being connected to the first inlet (14) of a condenser evaporator (15) and the other path being connected to the inlet of a condenser (3). The first outlet (16) of the condenser evaporator (15) and the outlet of the condenser (3) are connected to the inlet of a reflux tank (4) by a pipeline. The outlet of the reflux tank (4) is connected to the propane stripper (2) at one end and to the top product unit (5) at the other end by a pipeline. The bottom outlet (6) of the propane removal column (2) is divided into three branches via pipelines: the first branch connects to the inlet of the reboiler (7), the second branch connects to the inlet of the liquid product unit (8), and the third branch connects to the first-stage increaser. The inlet of device (17), the first-stage increaser The outlet of the evaporator (17) is connected via a pipe to the second inlet (19) of the condenser-evaporator (15), and the second outlet (20) of the condenser-evaporator (15) is connected via a pipe to the secondary booster. The inlet of device (21), secondary enhancement The outlet of the device (21) is connected to the bottom inlet of the depropane tower (2) via a pipeline.

7. The system according to claim 6, characterized in that, The first-level increase A regulating valve (18) is also provided between the evaporator (17) and the condenser (15).

8. The system according to claim 6, characterized in that, The reboiler (7) is also connected to a steam inlet pipe (11) and a steam condensate outlet pipe (12).

9. The system according to claim 6, characterized in that, The condenser (3) is also connected to a cooling water inlet pipe (9) and a cooling water outlet pipe (10).

10. The system according to claim 6, characterized in that, The first-level increase The device (17) is an air cooler; the secondary booster... The device (21) is a compressor.

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