Energy saving propane dehydrogenation system and method

Abstract

The present application belongs to the field of propylene production, and discloses an energy-saving propane dehydrogenation system and method. The system comprises a raw material processing unit, a dehydrogenation unit, a compression unit and a separation refrigeration unit; raw material propane enters the dehydrogenation unit after being treated by the raw material processing unit and recovering cold energy by the separation unit, reaction gas enters the compression unit and the separation unit in sequence, and crude hydrogen gas, C2's tail gas, circulating propane and propylene product are obtained in the separation unit. The method and system can significantly save the consumption of circulating cooling water, low-pressure steam and propylene refrigerant, thereby reducing the energy consumption and operating cost of the device, and having important practical significance for realizing energy saving and consumption reduction of the propane dehydrogenation device.

Description

Technical Field

[0001] This invention pertains to the field of propylene production, and more specifically, relates to an energy-saving propane dehydrogenation system and method. Background Technology

[0002] Propylene is an important chemical raw material in the petrochemical industry, used to produce numerous downstream products such as polypropylene, acrylonitrile, butanol, octanol, isopropanol, cumene, and acrylic acid. In recent years, the demand gap for propylene both domestically and internationally has continued to widen, greatly promoting the development of the propylene industry and its production technologies.

[0003] Approximately 70% of the world's propylene comes from co-products of steam cracking units and byproducts of refinery catalytic cracking units. However, steam cracking primarily produces ethylene, with a small amount of propylene as a byproduct. While refinery catalytic cracking has the potential to increase propylene production, it comes at the cost of sacrificing the output of refined petroleum products such as gasoline, diesel, and kerosene, impacting the economics of the plant. Besides these two processes, new propylene production technologies include propane dehydrogenation (PDH), deep catalytic cracking (DCC), methanol-to-olefins / propylene (MTO / MTP), high-carbon olefin cracking, and isotope olefin conversion. Considering cost, market conditions, and current technological applications, propane dehydrogenation has become one of the most competitive propylene production processes.

[0004] In traditional propane dehydrogenation processes, on the one hand, the interstage cooler of the product gas compressor typically uses circulating cooling water as a cold source, resulting in very high cooling water consumption. On the other hand, due to layout constraints, the reboiler of the fractionation tower cannot directly recover the low-temperature waste heat from the interstage of the product gas compressor and can only use low-pressure steam as a heat source. Furthermore, propane feedstock is generally liquid-phase, while propane dehydrogenation is a gas-phase reaction, requiring a large amount of steam for vaporization. Simultaneously, the propane dehydrogenation reaction products need to be cooled and liquefied to separate propylene, propane, etc., leading to high power consumption in the propylene chiller.

[0005] In summary, existing technologies suffer from the problem of dual consumption of circulating cooling water and low-pressure steam, as well as propylene refrigerant and low-pressure steam, resulting in persistently high energy consumption in traditional propane dehydrogenation units.

[0006] Therefore, there is an urgent need to develop a more energy-efficient propane dehydrogenation system and method. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing an energy-saving propane dehydrogenation system and method. Using the method and system of this invention can significantly reduce the consumption of circulating cooling water, low-pressure steam, and propylene refrigerant, thereby reducing energy consumption and operating costs. This has significant practical implications for achieving energy conservation and consumption reduction in propane dehydrogenation units.

[0008] To achieve the above objectives, the present invention provides an energy-saving propane dehydrogenation system, which includes a raw material processing unit, a dehydrogenation unit, a compression unit, and a separation refrigeration unit.

[0009] The compression unit includes a multi-stage compressor and a propane heater;

[0010] The separation and refrigeration unit includes a cold box, a multi-stage gas-liquid separator, a propane vaporizer, an ethane stripper, and a propylene distillation column;

[0011] The propane heater is connected to the outlet of the last stage of the multi-stage compressor to achieve heat exchange between the propane feedstock and the reaction product gas discharged from the last stage of the multi-stage compressor.

[0012] The raw material processing unit is used to strip and deweigh the propane raw material after heat exchange;

[0013] The cold box is used to achieve heat exchange between the stripped propane feedstock and the reaction product gas from the compression unit, thereby achieving cooling of the reaction product gas from the compression unit and heating of the stripped propane feedstock.

[0014] The propane vaporizer is used to vaporize the heated propane feedstock.

[0015] The cold box is also used to superheat the vaporized propane feedstock;

[0016] The dehydrogenation unit is used to dehydrogenate the superheated gaseous propane feedstock.

[0017] The multi-stage compressor is used to compress and pressurize the dehydrogenated reaction product gas to obtain pressurized reaction product gas.

[0018] The multi-stage gas-liquid separator is used to achieve the step-by-step gas-liquid separation of the pressurized reaction product gas;

[0019] The deethane removal tower is used to deethane the liquid phase stream of the reaction product gas after staged cooling and gas-liquid separation.

[0020] The propylene distillation column is used for the distillation and separation of the bottom liquid feed from the deethaner column.

[0021] According to the present invention, preferably, a throttling valve is provided on the pipeline connecting the raw material processing unit and the cold box, the throttling valve being used to reduce the pressure of the propane raw material after stripping and deweighing.

[0022] According to the present invention, preferably, the equipment used for stripping and deweighting in the raw material processing unit is a single-stage or two-stage distillation tower, or a single-stage or two-stage flash tank.

[0023] According to the present invention, preferably, the compression unit further includes a quencher; the quencher is used to further cool the reaction product gas after heat exchange with the propane feedstock; the reaction product gas outlet of the quencher is connected to the inlet of the cold box.

[0024] According to the present invention, preferably, each segment of the multi-stage compressor is provided with a suction tank in front of it. Except for the outlet of the last segment of the multi-stage compressor, the outlets of the first segment of the multi-stage compressor are sequentially connected to a heat transfer medium heat exchanger, an inter-segment cooler and a suction tank, and the outlet of the suction tank of the first segment is connected to the inlet of the compressor of the next segment.

[0025] In this invention, "the front section of the multi-stage compressor" refers to all sections before the last section of the multi-stage compressor.

[0026] According to the present invention, preferably, the heat exchanger is used to convert a portion of the heat from the reaction product gas discharged from the front section of the multi-stage compressor into a stripping heat source required by the raw material processing unit; the inter-stage cooler is used to recover the remaining heat from the reaction product gas discharged from the front section of the multi-stage compressor.

[0027] In this invention, the heat exchanger is used to cool the reaction product gas discharged from the front section of the multi-stage compressor and to use the recovered heat as the stripping heat source required by the raw material processing unit; the inter-stage cooler is used to further cool the reaction product gas discharged from the front section of the multi-stage compressor.

[0028] The heat exchanger is connected to the intermediate boiler of the first-stage fractionation column, or to the reboiler of the first-stage fractionation column in the two-stage fractionation column.

[0029] According to the present invention, preferably, the multi-stage compressor is a 2-4 stage compressor.

[0030] According to the present invention, preferably, each gas-liquid separator of the separation refrigeration unit is provided with an inlet, a gas phase outlet and a liquid phase outlet, and the gas phase outlet of the previous gas-liquid separator is connected to the inlet of the next gas-liquid separator.

[0031] According to the present invention, preferably, the deethanizer is provided with a deethanizer inlet, a deethanizer top gas phase outlet and a deethanizer bottom liquid phase outlet; the liquid phase outlet of each stage gas-liquid separator is connected to the deethanizer inlet.

[0032] According to the present invention, preferably, the propylene distillation column is provided with a propylene distillation column inlet, a propylene product outlet at the top of the propylene distillation column, and a circulating propane outlet at the bottom of the propylene distillation column; the liquid phase outlet at the bottom of the deethanizer is connected to the propylene distillation column inlet.

[0033] According to the present invention, preferably, the cold box is also used to cool the gas discharged from the gas phase outlet of each stage of the gas-liquid separator and to recover the cooling capacity of the gas discharged from the top gas phase outlet of the de-ethaner tower.

[0034] According to the present invention, preferably, the separate refrigeration unit further includes a propylene refrigeration compressor and / or an ethylene refrigeration compressor for providing cooling capacity to the cold box.

[0035] In this invention, the cold box uses propylene refrigerant and ethylene refrigerant to supplement the cooling capacity.

[0036] According to the present invention, preferably, the propane vaporizer is provided with propylene refrigerant for recovering cold energy.

[0037] According to the present invention, preferably, the propane heater is further connected to a propane feedstock inlet pipeline, the other end of which is connected to the circulating propane outlet of the propylene distillation column and the fresh propane feedstock inlet, respectively.

[0038] Another aspect of the present invention provides an energy-saving propane dehydrogenation method, which employs the aforementioned energy-saving propane dehydrogenation system and includes the following steps:

[0039] S1: The propane feedstock and the reaction product gas discharged from the last stage of the multi-stage compressor are heat exchanged in the propane heater; the heat-exchanged propane feedstock is sent to the feedstock processing unit for stripping and deweighting to obtain stripped and deweighted propane feedstock and C4+ heavy components; the C4+ heavy components are discharged from the system.

[0040] S2: First, the stripped and deweighted propane feedstock is sent into the cold box to exchange heat with the reaction gas generated from the compression unit in the cold box to obtain heated propane feedstock; then, the heated propane feedstock is sent into the propane vaporizer to obtain vaporized propane feedstock; then, the vaporized propane feedstock is sent into the cold box to obtain superheated gaseous propane feedstock.

[0041] S3: The superheated gaseous propane feedstock is sequentially fed into the dehydrogenation unit and the compression unit, and dehydrogenation and compression are performed sequentially to obtain the reaction product gas of the compression unit, which is then sent into the cold box.

[0042] S4: The reaction product gas of the compression unit is cooled and separated into gas and liquid stages in the cold box and multi-stage gas-liquid separator. The liquid phase streams obtained from each stage of gas-liquid separation are sent to the de-ethanizer for de-ethanization treatment to obtain C2's tail gas and the bottom liquid of the de-ethanizer. The bottom liquid of the de-ethanizer is sent to the propylene distillation column for distillation separation to obtain recycled propane and propylene products.

[0043] According to the present invention, preferably, in step S1:

[0044] The propane feedstock includes fresh propane feed and recycled propane;

[0045] The concentration of C4+ heavy components in the stripped propane feedstock (at least partially liquid phase) is not greater than 0.1–5 mol%, preferably not greater than 1.0–2.0 mol%.

[0046] According to the present invention, preferably, in step S2:

[0047] The stripped and deweighed propane feedstock is then fed into the cold box after being throttled and depressurized.

[0048] The propane feedstock after stripping and deweighing is depressurized to 0.2-0.6 MPaG, preferably to 0.2-0.3 MPaG;

[0049] According to the present invention, preferably, in step S3:

[0050] The reaction product gas after dehydrogenation is compressed and pressurized to 1.0-2.0 MPaG in the multi-stage compressor, preferably to 1.4-1.6 MPaG;

[0051] During the compression and pressurization process of the dehydrogenated reaction product gas in the multi-stage compressor, except for the reaction product gas discharged from the last stage of the multi-stage compressor, part of the heat of the reaction product gas discharged from the first stage of the multi-stage compressor is converted into the stripping heat source required for stripping and deweighting through the heat medium heat exchanger, and the remaining part is recovered through the inter-stage cooler.

[0052] The reaction product gas discharged from the last stage of the multi-stage compressor is cooled sequentially by the propane heater and the quencher, and finally sent into the cold box through the reaction product gas outlet of the quencher.

[0053] In the heat exchanger, the heat of the reaction product gas discharged from the front section of the multi-stage compressor is converted into the heat source required for stripping and deweighting. The heat medium is selected from circulating hot water and / or oil.

[0054] The inter-section cooler uses circulating cooling water as its cooling source.

[0055] The quencher uses propylene refrigerant as its cold source.

[0056] According to the present invention, preferably, in step S4:

[0057] The gas obtained from the gas phase outlet of the last stage gas-liquid separator is crude hydrogen.

[0058] The C2's tail gas is obtained at the top gas outlet of the deethanizer; the liquid phase at the bottom of the deethanizer is fed into the propylene distillation column, where the recycled propane is obtained at the bottom of the propylene distillation column, and the propylene product is obtained at the top of the propylene distillation column.

[0059] The crude hydrogen and C2 exhaust gases are returned to the cold box to provide cooling.

[0060] The technical solution of the present invention has the following beneficial effects:

[0061] (1) Before entering the raw material processing unit, the raw material propane first enters the compression unit to recover the waste heat at the outlet of the last stage of the multi-stage compressor, thereby reducing the consumption of circulating cooling water.

[0062] (2) After the raw material propane is deweighted, it is throttled and enters the separation and refrigeration unit before entering the dehydrogenation unit to provide cooling capacity and is heated and vaporized at the same time, thereby reducing the consumption of low-pressure steam and propylene refrigerant.

[0063] (3) The compression unit uses heat medium to recover the waste heat from the outlet of the first stage compressor of the multi-stage compressor except the last stage, and uses it as the main heat source of the raw material processing unit to reduce the steam consumption of raw material stripping and de-weighting treatment.

[0064] In summary, the method of this invention can significantly reduce the consumption of circulating cooling water, low-pressure steam, and propylene refrigerant, thereby reducing the energy consumption and operating costs of the unit, which is of great practical significance for achieving energy saving and consumption reduction in propane dehydrogenation units.

[0065] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0066] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0067] Figure 1 A schematic diagram of an energy-saving propane dehydrogenation system provided in Embodiment 1 of the present invention is shown.

[0068] Figure 2 A schematic diagram of the compression unit of an energy-saving propane dehydrogenation system provided in Embodiment 1 of the present invention is shown.

[0069] Figure 3 A schematic diagram of the separation unit of an energy-saving propane dehydrogenation system provided in Embodiment 1 of the present invention is shown.

[0070] Figure 4A schematic diagram of the feedstock processing unit of an energy-saving propane dehydrogenation system provided in Embodiment 1 of the present invention is shown.

[0071] Figure 5 A schematic diagram of a propane dehydrogenation system provided in Comparative Example 1 of the present invention is shown.

[0072] The annotations in the attached figures are explained as follows:

[0073] S1 - Raw material processing unit; S2 - Dehydrogenation unit; S3 - Compression unit; S4 - Separation and refrigeration unit;

[0074] E1 - Propane vaporizer; E2 - Heat exchanger; E3 - Propane heater; E4 - Quencher; E5 - Interstage cooler; E6 - Medium boiler; E7 - Condenser; E8 - Reflux tank;

[0075] T1 - Deethanizer; T2 - Propylene distillation column; T3 - Cold box; T4 - Stage 1-4 gas-liquid separator; T5 - Suction tank; T6 - Inlet; T7 - ​​Gas phase outlet; T8 - Liquid phase outlet; T9 - Deethanizer inlet; T10 - Deethanizer top gas phase outlet; T11 - Deethanizer bottom liquid phase outlet; T12 - Propylene distillation column inlet; T13 - Propylene product outlet at the top of the propylene distillation column; T14 - Propylene distillation column bottom circulating propane outlet; T15 - First-stage fractionation column.

[0076] P1 - Fresh propane feed; P2 - Recycled propane; P3 - Propane feed after heat exchange; P4 - Propane feed after stripping and deweighting; P4a - Propane feed after throttling; P4b - Heated propane feed; P4c - Propane feed after vaporization; P5 - Superheated gaseous propane feed; P6 - Reaction product gas; P7 - Reaction product gas after pressurization; P8 - Propylene product; P9 - Crude hydrogen; P10 - C2 tail gas; P11 - C4+ recombinant gas P12 - Circulating heat medium of the self-heating medium circulation unit; P13 - Circulating heat medium after heat extraction; P14 - Circulating heat medium after heat recovery; P15 - Propane gaseous feedstock; P16 - Steam of grade 0.4~0.5MPaG; P17 - Circulating cooling water; P18 - Propylene refrigerant providing cooling capacity; P19 - Ethylene refrigerant; P20 - Propylene refrigerant with recovered cooling capacity; P21 - Liquid phase stream obtained from gas-liquid separation at each stage; LS - Low-pressure steam.

[0077] V1 - Throttling valve. Detailed Implementation

[0078] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0079] Example 1

[0080] This embodiment provides an energy-saving propane dehydrogenation system, such as Figure 1-3 As shown, the system includes a raw material processing unit S1, a dehydrogenation unit S2, a compression unit S3, and a separation and refrigeration unit S4.

[0081] The compression unit includes a 3-stage compressor, a suction tank T5, a heat transfer medium heat exchanger E2, an inter-stage cooler E5, a propane heater E3, and a quencher E4.

[0082] The separation unit includes a cold box T3, a 1-4 stage gas-liquid separator T4, an ethane stripper T1, a propylene distillation column T2, and a propane vaporizer E1.

[0083] The propane heater E3 is connected to the outlet of the last stage of the three-stage compressor to achieve heat exchange between the propane feedstock and the reaction product gas discharged from the last stage of the three-stage compressor.

[0084] The raw material processing unit S1 is used to strip and deweigh the propane raw material after heat exchange; the equipment used for stripping and deweighing in the raw material processing unit S1 is a primary fractionation tower T15.

[0085] A throttling valve V1 is provided between the raw material processing unit S1 and the cold box T3. The throttling valve is used to reduce the pressure of the propane raw material after stripping and deweighing.

[0086] The cold box T3 is used to realize heat exchange between the propane feedstock after throttling and depressurization and the reaction product gas from the compression unit S3, thereby realizing the cooling of the reaction product gas after pressurization from the compression unit S3 and the heating of the propane feedstock after throttling and depressurization.

[0087] The propane vaporizer E1 is used to vaporize the heated propane feedstock.

[0088] The cold box T3 is also used to superheat the vaporized propane feedstock;

[0089] The dehydrogenation unit S2 is used to dehydrogenate the superheated gaseous propane feedstock.

[0090] The three-stage compressor is used to compress and pressurize the reaction product gas after dehydrogenation treatment to obtain the pressurized reaction product gas; the quencher E4 is used to further cool the reaction product gas after heat exchange with the propane feedstock; the quencher E4 includes a reaction product gas outlet, which is connected to the inlet of the cold box T3.

[0091] The first to fourth stage gas-liquid separators T4 are used to achieve the staged gas-liquid separation of the reaction gas generated by the compression unit S3;

[0092] The deethanizer T1 is used to deethanize the liquid phase stream of the reaction product gas after staged cooling and gas-liquid separation.

[0093] The propylene distillation column T2 is used for the distillation and separation of the bottom liquid feed from the deethaner column.

[0094] In compression unit S3:

[0095] Each of the three-stage compressors is equipped with a suction tank T5 before each compressor stage. Except for the outlet of the last stage of the three-stage compressor, the outlets of the first two stages of the multi-stage compressor are sequentially connected to a heat exchanger E2, an interstage cooler E5, and a suction tank T5. The outlet of the suction tank T5 of the first stage is connected to the inlet of the compressor of the next stage. The heat exchanger E2 is used to convert part of the heat of the reaction product gas discharged from the first two stages of the three-stage compressor into the stripping heat source required by the raw material processing unit S1. The interstage cooler E5 is used to recover the remaining heat of the reaction product gas discharged from the first two stages of the three-stage compressor.

[0096] The heat exchanger E2 is connected to the intermediate boiler E6 of the first-stage fractionation tower T15.

[0097] The propane heater E3 is also connected to a propane feedstock P1 input pipeline, the other end of which is connected to the circulating propane outlet T14 of the propylene distillation column and the fresh propane feed inlet.

[0098] In the separate refrigeration unit S4:

[0099] Each gas-liquid separator in the separation refrigeration unit S4 is provided with an inlet T6, a gas phase outlet T7, and a liquid phase outlet T8. The gas phase outlet T7 of the previous gas-liquid separator is connected to the inlet T6 of the next gas-liquid separator.

[0100] The deethanizer is equipped with a deethanizer inlet T9, a deethanizer top gas phase outlet T10, and a deethanizer bottom liquid phase outlet T11; the liquid phase outlet T8 of each stage gas-liquid separator is connected to the deethanizer inlet T9.

[0101] The propylene distillation column is equipped with a propylene distillation column inlet T12, a propylene product outlet at the top of the propylene distillation column T13, and a circulating propane outlet at the bottom of the propylene distillation column T14; the liquid phase outlet T11 at the bottom of the deethanizer is connected to the propylene distillation column inlet T12.

[0102] The cold box T3 is used to cool the gas discharged from the gas phase outlet T6 of each stage of the gas-liquid separator and to recover the cooling capacity of the gas discharged from the top gas phase outlet T10 of the deethanizer.

[0103] The propane vaporizer is equipped with propylene refrigerant (propylene refrigerant P20 that recovers cold energy);

[0104] The separate refrigeration unit also includes a propylene refrigeration compressor (propylene refrigerant P18 providing cooling capacity) and an ethylene refrigeration compressor (ethylene refrigerant P19) for providing cooling capacity to the cold box.

[0105] The propane dehydrogenation method using the above system includes the following steps:

[0106] S1: The propane feedstock and the reaction product P7 discharged from the last stage of the 3-stage compressor are heat-exchanged in the propane heater E3; the heat-exchanged propane feedstock P3 is sent to the feedstock processing unit S1 for stripping and deweighting to obtain stripped propane feedstock P4 and C4+ heavy component P11; the C4+ heavy component P11 is discharged from the system.

[0107] The propane feedstock includes fresh propane feed P1 and recycled propane P2;

[0108] The concentration of C4+ heavy components in the stripped propane feedstock P4 is ≤2.0 mol%.

[0109] S2: First, the stripped and deweighed propane feedstock P4 is throttled and depressurized to 0.3 MPaG, then fed into the cold box T3 to exchange heat with the reaction product gas P7 from the compression unit in the cold box T3, to obtain heated propane feedstock; then the heated propane feedstock is fed into the propane vaporizer E1 to obtain vaporized propane feedstock; then the vaporized propane feedstock is fed into the cold box T3 to obtain superheated gaseous propane feedstock P5;

[0110] S3: The superheated gaseous propane feedstock P5 is sequentially fed into the dehydrogenation unit S2 and the compression unit S3 for sequential dehydrogenation and compression pressurization, and the reaction product gas P7 (pressure 1.4 MPaG) discharged from the last stage of the 3-stage compressor is sent into the cold box T3.

[0111] During the compression and pressurization process of the dehydrogenated gas P6 (mainly containing propylene reaction product gas) in the three-stage compressor, except for the reaction product gas P7 discharged from the last stage of the three-stage compressor, part of the heat of the reaction product gas discharged from the other stages of the three-stage compressor is converted into the stripping heat source required for stripping and deweighting through the heat medium heat exchanger E2, and the remaining part is recovered through the interstage cooler E5.

[0112] The reaction product gas P7 discharged from the last stage of the three-stage compressor is cooled to 13°C by passing through the propane heater E3 and the quencher E4 in sequence, and finally sent into the cold box T3 through the reaction product gas outlet of the quencher E4.

[0113] Inside the heat exchanger E2, the heat from the reaction gas discharged from the first two stages of the three-stage compressor is converted into circulating hot water, which is the heat source required for stripping and deweighting. The circulating hot water is heated from 65°C to 100°C by the outlet gas from the first two stages of the compressor, and then used as the heat source for the intermediate boiling unit E6 of the first-stage fractionation tower T15 of the raw material processing unit S1. The circulating hot water provides heat while being cooled to 65°C and sent out.

[0114] The inter-section cooler uses circulating cooling water P17 as its cold source.

[0115] The quencher E4 uses propylene refrigerant P18 as its cold source.

[0116] S4: The reaction product gas P7 discharged from the last stage of the 3-stage compressor is cooled and separated into gas and liquid in the cold box T3 and the 4-stage gas-liquid separator T4. The liquid phase stream P21 obtained from each stage of gas-liquid separation is sent to the deethanizer T1 for deethanization treatment to obtain C2's tail gas P10 and the bottom liquid of the deethanizer. The bottom liquid of the deethanizer is sent from the bottom liquid outlet T11 of the deethanizer to the inlet T12 of the propylene distillation column for distillation separation to obtain recycled propane P2 and propylene product P8.

[0117] The gas obtained from the gas phase outlet of the final gas-liquid separator is crude hydrogen P9; the C2's tail gas P10 is obtained from the gas phase outlet T10 at the top of the deethanizer; the liquid phase from the bottom of the deethanizer is sent to the propylene distillation column T2, where the recycled propane P2 is obtained from the bottom of the propylene distillation column T2, and propylene product P8 is obtained from the top of the propylene distillation column; the crude hydrogen P9 and the C2's tail gas P10 are returned to the cold box T3 to provide cooling.

[0118] Comparative Example 1

[0119] This comparative example provides a propane dehydrogenation method. The propane dehydrogenation process of this comparative example is as follows: Figure 4 As shown, the propane dehydrogenation method in this comparative example includes the following steps:

[0120] S1: The propane feedstock is fed into the feedstock processing unit S1 for stripping and deweighting to obtain stripped propane feedstock P4 and C4+ heavy component P11; the C4+ heavy component P11 is discharged from the system.

[0121] The heat source used for stripping and deweighting is steam of grade 0.4–0.5 MPaG;

[0122] The propane feedstock includes fresh propane feed P1 and recycled propane P2;

[0123] The concentration of C4+ heavy components in the stripped propane feedstock P4 is ≤2.0 mol%.

[0124] S2: The stripped propane feedstock P4 is heated and vaporized using steam P16 at a pressure of 0.4–0.5 MPaG to obtain gaseous propane feedstock P15, which enters the dehydrogenation unit S2 for reaction, generating reaction product gas P6. This product gas then enters the compression unit S3 for pressurization, resulting in the final stage of the three-stage compressor, which discharges reaction product gas P7 (pressure 1.4 MPaG), into the cold box. The compression unit S3 has three compressor stages, each with a cooler and a suction tank at its outlet. The first two stages use circulating cooling water as the cooling source for the coolers; the third stage compressor outlet cooler is sequentially cooled by circulating cooling water and propylene refrigerant, ultimately reaching a temperature of 13°C.

[0125] S3: The reaction product gas P7 discharged from the last stage of the 3-stage compressor is cooled and separated into gas and liquid in the cold box T3 and the 1st to 4th stage gas-liquid separator T4. The liquid phase stream P21 obtained from each stage of gas-liquid separation is sent to the de-ethanizer T1 and the propylene distillation tower T2 for de-ethanization and distillation separation to obtain C2's tail gas P10, recycled propane P2 and propylene product P8.

[0126] The gas obtained from the gas phase outlet of the final gas-liquid separator is crude hydrogen P9; the C2's tail gas P10 is obtained from the gas phase outlet T10 at the top of the deethanizer; the liquid phase from the bottom of the deethanizer is sent to the propylene distillation column T2, where the recycled propane P2 is obtained from the bottom of the propylene distillation column T2, and propylene product P8 is obtained from the top of the propylene distillation column; the crude hydrogen P9 and the C2's tail gas P10 are returned to the cold box T3 to provide cooling.

[0127] Test case

[0128] This test case, based on the propane dehydrogenation processes of Example 1 and Comparative Example 1, performs material and heat balance calculations on a 600,000-ton / year propane dehydrogenation system. The calculation results, using Comparative Example 1 as a benchmark, are listed in Table 1. The calculation results show that, compared to Comparative Example 1, Example 1, using the method and system of this invention, can save 2200 t / h of circulating water, 45 t / h of low-pressure steam, 22 t / h of propylene refrigerant (recovered propylene refrigerant P20) in the propane vaporizer, and 4922 kW of power savings in the propylene refrigeration compressor and ethylene refrigeration compressor. The system energy consumption can be reduced by an average of 70 kgEo / t propylene, resulting in operating cost savings of approximately RMB 103.7 million per year. Therefore, using the method and system of this invention can significantly save on the consumption of circulating cooling water, low-pressure steam, and propylene refrigerant, thereby reducing system energy consumption and operating costs, which has significant practical implications for energy saving and consumption reduction in propane dehydrogenation systems.

[0129] Table 1

[0130]

[0131] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An energy-saving propane dehydrogenation system, characterized in that, The system includes a raw material processing unit, a dehydrogenation unit, a compression unit, and a separation and refrigeration unit; The compression unit includes a multi-stage compressor and a propane heater; The separation and refrigeration unit includes a cold box, a multi-stage gas-liquid separator, a propane vaporizer, an ethane stripper, and a propylene distillation column; The propane heater is connected to the outlet of the last stage of the multi-stage compressor to achieve heat exchange between the propane feedstock and the reaction product gas discharged from the last stage of the multi-stage compressor. The raw material processing unit is used to strip and deweigh the propane raw material after heat exchange; The cold box is used to achieve heat exchange between the stripped propane feedstock and the reaction product gas from the compression unit, thereby achieving cooling of the reaction product gas from the compression unit and heating of the stripped propane feedstock. The propane vaporizer is used to vaporize the heated propane feedstock. The cold box is also used to superheat the vaporized propane feedstock; The dehydrogenation unit is used to dehydrogenate the superheated gaseous propane feedstock. The multi-stage compressor is used to compress and pressurize the dehydrogenated reaction product gas to obtain pressurized reaction product gas. The multi-stage gas-liquid separator is used to achieve the step-by-step gas-liquid separation of the pressurized reaction product gas; The deethane removal tower is used to deethane the liquid phase stream of the reaction product gas after staged cooling and gas-liquid separation. The propylene distillation column is used for the distillation and separation of the bottom liquid feed from the deethaner column.

2. The energy-saving propane dehydrogenation system according to claim 1, wherein, A throttling valve is installed on the pipeline connecting the raw material processing unit and the cold box. The throttling valve is used to reduce the pressure of the propane raw material after stripping and deweighing. The raw material processing unit is equipped with a single or two-stage distillation tower for stripping and deweighting, or a single or two-stage flash tank. The compression unit also includes a quencher; the quencher is used to further cool the reaction product gas after heat exchange with the propane feedstock; the reaction product gas outlet of the quencher is connected to the inlet of the cold box; Each stage of the multi-stage compressor is equipped with a suction tank before it. Except for the outlet of the last stage of the multi-stage compressor, the outlets of the first stage of the multi-stage compressor are connected in sequence to a heat transfer medium heat exchanger, an inter-stage cooler and a suction tank. The outlet of the suction tank of the first stage is connected to the inlet of the compressor of the next stage. The heat exchanger is used to convert a portion of the heat from the reaction product gas discharged from the front section of the multi-stage compressor into the stripping heat source required by the raw material processing unit; the inter-stage cooler is used to recover the remaining heat from the reaction product gas discharged from the front section of the multi-stage compressor. The heat exchanger is connected to the intermediate boiler of the first-stage fractionation column, or to the reboiler of the first-stage fractionation column in the two-stage fractionation column.

3. The energy-saving propane dehydrogenation system according to claim 2, wherein, The multi-stage compressor is a 2-4 stage compressor.

4. The energy-saving propane dehydrogenation system according to claim 2, wherein, Each gas-liquid separator in the separation refrigeration unit is equipped with an inlet, a gas phase outlet, and a liquid phase outlet. The gas phase outlet of the previous gas-liquid separator is connected to the inlet of the next gas-liquid separator. The deethanizer is provided with a deethanizer inlet, a deethanizer top gas phase outlet, and a deethanizer bottom liquid phase outlet; the liquid phase outlet of each stage gas-liquid separator is connected to the deethanizer inlet; The propylene distillation column is equipped with a propylene distillation column inlet, a propylene product outlet at the top of the propylene distillation column, and a circulating propane outlet at the bottom of the propylene distillation column; the liquid phase outlet at the bottom of the deethanizer is connected to the propylene distillation column inlet; The cold box is also used to cool the gas discharged from the gas phase outlet of each stage of the gas-liquid separator and to recover the cooling capacity of the gas discharged from the top gas phase outlet of the deethaner column.

5. The energy-saving propane dehydrogenation system according to claim 4, wherein, The propane vaporizer is equipped with propylene refrigerant for recovering cold energy; The separate refrigeration unit also includes a propylene refrigeration compressor and / or an ethylene refrigeration compressor for providing cooling capacity to the cold box.

6. The energy-saving propane dehydrogenation system according to claim 1, wherein, The propane heater is also connected to a propane feedstock inlet pipeline, the other end of which is connected to the circulating propane outlet of the propylene distillation column and the fresh propane feedstock inlet.

7. An energy-saving propane dehydrogenation method, characterized in that, This method employs the energy-saving propane dehydrogenation system described in any one of claims 1-6, and includes the following steps: S1: The propane feedstock and the reaction product gas discharged from the last stage of the multi-stage compressor are heat exchanged in the propane heater; the heat-exchanged propane feedstock is sent to the feedstock processing unit for stripping and deweighting to obtain stripped and deweighted propane feedstock and C4+ heavy components; the C4+ heavy components are discharged from the system. S2: First, the stripped and deweighted propane feedstock is fed into the cold box to exchange heat with the reaction gas generated from the compression unit in the cold box to obtain heated propane feedstock; then, the heated propane feedstock is fed into the propane vaporizer to obtain vaporized propane feedstock; then, the vaporized propane feedstock is fed into the cold box to obtain superheated gaseous propane feedstock. S3: The superheated gaseous propane feedstock is sequentially fed into the dehydrogenation unit and the compression unit, and dehydrogenation and compression are performed sequentially to obtain the reaction product gas of the compression unit, which is then sent into the cold box. S4: The reaction product gas of the compression unit is cooled and separated into gas and liquid in the cold box and multi-stage gas-liquid separator in stages, and the liquid phase stream obtained from each stage of gas-liquid separation is sent to the de-ethanizer for de-ethanization treatment to obtain C2's tail gas and bottom liquid of the de-ethanizer. The bottom liquid of the de-ethanizer is sent to the propylene distillation column for distillation separation to obtain recycled propane and propylene products.

8. The energy-saving propane dehydrogenation method according to claim 7, wherein, In step S1: The propane feedstock includes fresh propane feed and recycled propane; The concentration of C4+ heavy components in the stripped propane feedstock is no greater than 0.1~5 mol.

9. The energy-saving propane dehydrogenation method according to claim 8, wherein, The concentration of C4+ heavy components in the stripped propane feedstock is no greater than 1.0~2.0 mol.

10. The energy-saving propane dehydrogenation method according to claim 7, wherein, In step S2: The stripped and deweighed propane feedstock is then fed into the cold box after being throttled and depressurized. The propane feedstock after stripping and deweighing is depressurized to 0.2~0.6 MPaG.

11. The energy-saving propane dehydrogenation method according to claim 10, wherein, The pressure of the stripped propane feedstock was reduced to 0.2~0.3 MPaG.

12. The energy-saving propane dehydrogenation method according to claim 7, wherein, In step S3: The reaction product gas after dehydrogenation is compressed and pressurized to 1.0~2.0 MPaG in the multi-stage compressor; During the compression and pressurization process of the dehydrogenated reaction product gas in the multi-stage compressor, except for the reaction product gas discharged from the last stage of the multi-stage compressor, part of the heat of the reaction product gas discharged from the first stage of the multi-stage compressor is converted into the stripping heat source required for stripping and deweighting through the heat medium heat exchanger, and the remaining part is recovered through the inter-stage cooler. The reaction product gas discharged from the last stage of the multi-stage compressor is cooled sequentially by the propane heater and the quencher, and finally sent into the cold box through the reaction product gas outlet of the quencher. In the heat exchanger, the heat of the reaction product gas discharged from the front section of the multi-stage compressor is converted into the heat source required for stripping and deweighting. The heat medium is selected from circulating hot water and / or oil. The inter-section cooler uses circulating cooling water as its cooling source. The quencher uses propylene refrigerant as its cold source.

13. The energy-saving propane dehydrogenation method according to claim 12, wherein, The dehydrogenated reaction product gas is compressed and pressurized to 1.4~1.6 MPaG in the multi-stage compressor.

14. The energy-saving propane dehydrogenation method according to claim 7, wherein, In step S4: The gas obtained from the gas phase outlet of the last stage gas-liquid separator is crude hydrogen. The C2's tail gas is obtained at the top gas outlet of the deethanizer; the liquid phase at the bottom of the deethanizer is fed into the propylene distillation column, where the recycled propane is obtained at the bottom of the propylene distillation column, and the propylene product is obtained at the top of the propylene distillation column. The crude hydrogen and C2 exhaust gases are returned to the cold box to provide cooling.

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