Deep cryogenic separation of propane dehydrogenation to propylene products and hydrogen liquefaction co-production system and method

Abstract

The present invention discloses a cryogenic separation of propane dehydrogenation to propylene products and a hydrogen liquefaction co-production system and method, belonging to the technical field of refrigeration and cryogenic engineering. The system includes an atmospheric cold box, a vacuum cold box, a hydrogen compression unit, and a mixed refrigerant compression unit. The propane raw material is vaporized in the atmospheric cold box and then sent to the downstream cracking unit. The cracking products from the cracking unit are cryogenically separated in the atmospheric cold box to obtain high-purity propane / propylene products and hydrogen-rich gas. The hydrogen-rich gas is further separated, purified, and cooled in the vacuum cold box to obtain high-purity liquid hydrogen. The mixed refrigerant cycle and the hydrogen refrigeration cycle respectively provide cooling capacity for the atmospheric cold box and the vacuum cold box. The system couples the propane dehydrogenation cryogenic separation process and the hydrogen liquefaction process to achieve the efficient and energy-saving production of high-purity liquid hydrogen. The specific energy consumption of the system does not exceed 15.4 kWh / kg of liquid hydrogen, reducing the total energy consumption of the two independent processes by about 30%. The system has wide applicability and can flexibly adapt to different cracking processes, improving the single-pass conversion rate of the cracking process.

Description

Technical Field

[0001] The present invention belongs to the technical field of refrigeration and cryogenic engineering, and particularly relates to a cryogenic separation of propane dehydrogenation to propylene products and a hydrogen liquefaction co-production system and method. Background Art

[0002] As important basic chemical raw materials, olefins can promote the development of the downstream industrial chain. With the development of products such as polypropylene, acrylonitrile, and acrylic acid, as an important raw material, the demand for propylene is increasing continuously. Propane dehydrogenation (PDH) to produce propylene is an important process for olefin production, and this process can also obtain by-product hydrogen. On the one hand, the PDH cracking products need to pass through a cryogenic separation device to obtain high-purity propane / propylene products. However, almost all of the currently put into operation PDH cryogenic separation devices adopt a high-low pressure series expansion process, which has disadvantages such as a large number of equipment, complex operation, and high energy consumption. On the other hand, due to the relatively high direct storage and transportation cost of the by-product hydrogen from PDH, most of the by-product hydrogen in PDH plants can only be digested locally. Therefore, most of the by-product hydrogen is directly burned as fuel, with low added value. Liquid hydrogen and high-pressure gaseous hydrogen are the most common hydrogen storage and transportation methods at present. Since the energy storage density of liquid hydrogen is 5 times that of compressed hydrogen (20 MPa), liquid hydrogen has obvious economic advantages as a storage and transportation carrier for by-product hydrogen. With the large-scale commercial application development of global liquid hydrogen, the cryogenic separation of propane dehydrogenation to propylene products and hydrogen liquefaction co-production have broad inherent demands and energy-saving prospects.

[0003] In the PDH cryogenic separation device, the hydrogen component in the cracking products undergoes a cooling and reheating process, increasing the degree of thermodynamic irreversibility. In addition, the hydrogen-rich gas separated from the PDH cryogenic separation device needs to be processed by a pressure swing adsorption (PSA) device to obtain high-purity hydrogen. Based on hydrogen, the system energy consumption of the currently put into operation high-low pressure series expansion PDH cryogenic separation process is about 10 kWh / kg of hydrogen; and the system energy consumption of the currently put into operation double-pressure hydrogen Claude cycle hydrogen liquefaction process with liquid nitrogen precooling is about 12 kWh / kg of liquid hydrogen. The total energy consumption of these two processes is as high as 22 kWh / kg of liquid hydrogen. From the perspective of the refrigeration process, there is an overlap in the large refrigeration temperature range of these two systems. By reasonably optimizing and integrating the PDH cryogenic separation and hydrogen liquefaction processes, not only can the added value of the by-product hydrogen be improved, but also the process flow can be simplified, the number of equipment can be reduced, and the problem of high energy consumption in PDH cryogenic separation and hydrogen liquefaction production can be solved.

[0004] However, there is currently no relevant research on the PDH cryogenic separation and hydrogen liquefaction co-production process. How to creatively combine these two processes to achieve low-energy consumption operation and simultaneously meet the requirements of PDH and liquid hydrogen products has become the core problem that urgently needs to be solved in the design of the PDH cryogenic separation and hydrogen liquefaction co-production process. Summary of the Invention

[0005] The object of the present invention is to solve the deficiencies in the prior art and provide a cryogenic separation of propane dehydrogenation to propylene products and a hydrogen liquefaction co-production system and method.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In the first aspect, the present invention provides a cryogenic separation of propane dehydrogenation to propylene products and a hydrogen liquefaction co-production system, including an atmospheric cold box, a vacuum cold box, a hydrogen compression unit, and a mixed refrigerant compression unit;

[0008] Among them, the atmospheric cold box includes a primary heat exchanger, a raw gas primary separation tank, a raw gas secondary separation tank, a raw gas tertiary separation tank, a raw gas quaternary separation tank, and a cryogenic pump; the vacuum cold box includes a secondary heat exchanger, a tertiary heat exchanger, a refrigerant-hydrogen primary separation tank, a refrigerant-hydrogen secondary separation tank, a hydrogen-rich gas primary separation tank, a hydrogen-rich gas secondary separation tank, a hydrogen-rich gas tertiary separation tank, a cryogenic purifier, and an isothermal converter;

[0009] The atmospheric cold box uses the latent heat of vaporization of propane raw materials and the cold energy provided by multi-stage throttling of the mixed refrigerant to perform cryogenic separation on the cracking products from the cracking unit, thereby obtaining the target propane / propylene products and hydrogen-rich gas; the hydrogen compression unit receives the hydrogen refrigerant reheated under reduced pressure from the atmospheric cold box, compresses and cools the hydrogen refrigerant to form a hydrogen refrigeration cycle; the mixed refrigerant compression unit receives the mixed refrigerant reheated under reduced pressure from the atmospheric cold box, compresses and cools the mixed refrigerant to form a mixed refrigerant refrigeration cycle; the vacuum cold box receives the hydrogen-rich gas from the atmospheric cold box, and further separates, purifies, and cools the hydrogen-rich gas using hydrogen cycle refrigeration to obtain the target liquid hydrogen.

[0010] Preferably, the specific structure of the system is as follows:

[0011] The propane raw material from upstream is connected to the first heat side inlet of the primary heat exchanger through a first propane pipeline; the first heat side outlet of the primary heat exchanger is connected to the inlet of a second propane pipeline, and the outlet of the second propane pipeline is divided into two branches. One branch is connected to the second heat side inlet of the primary heat exchanger through a third propane pipeline, and the other branch is sequentially provided with a fourth propane pipeline, a first propane throttle valve, and a fifth propane pipeline;

[0012] The second heat side outlet of the primary heat exchanger is connected to the inlet of a sixth propane pipeline, and the outlet of the sixth propane pipeline is divided into two branches. One branch is connected to the third heat side inlet of the primary heat exchanger through a seventh propane pipeline, and the other branch is sequentially provided with an eighth propane pipeline, a second propane throttle valve, and a ninth propane pipeline;

[0013] The third hot-side outlet of the primary heat exchanger is connected to the inlet of the tenth propane pipeline. The outlet of the tenth propane pipeline has two branches. One branch is connected to the fourth hot-side inlet of the primary heat exchanger through the eleventh propane pipeline, and the other branch is successively provided with the twelfth propane pipeline, a propane three-stage throttle valve, and the thirteenth propane pipeline. The fourth hot-side outlet of the primary heat exchanger is successively provided with the fourteenth propane pipeline, a propane four-stage throttle valve, and the fifteenth propane pipeline.

[0014] The outlets of the fifth propane pipeline, the ninth propane pipeline, the thirteenth propane pipeline, and the fifteenth propane pipeline are all connected to the primary heat exchanger. After reheating in the primary heat exchanger, they converge to the first cold-side outlet of the primary heat exchanger. The first cold-side outlet of the primary heat exchanger is provided with a sixteenth propane pipeline for connecting propane vapor to the downstream cracking unit.

[0015] The cracking products from upstream are connected to the fifth hot-side inlet of the primary heat exchanger through the first raw material gas pipeline. The fifth hot-side outlet of the primary heat exchanger is connected to the raw material gas primary separation tank through the second raw material gas pipeline. The liquid phase space at the bottom of the raw material gas primary separation tank is successively connected to the inlet of the raw material gas secondary separation tank through the fourth raw material gas pipeline, a raw material gas primary throttle valve, and the fifth raw material gas pipeline. The gas phase space at the top of the raw material gas primary separation tank is connected to the sixth hot-side inlet of the primary heat exchanger through the third raw material gas pipeline. The sixth hot-side outlet of the primary heat exchanger is connected to the inlet of the raw material gas tertiary separation tank through the sixth raw material gas pipeline.

[0016] The gas phase space at the top of the raw material gas tertiary separation tank is connected to the twelfth hot-side inlet of the primary heat exchanger through the seventh raw material gas pipeline. The twelfth hot-side outlet of the primary heat exchanger leaves the atmospheric pressure cold box through the nineteenth raw material gas pipeline and enters the secondary heat exchanger in the vacuum cold box. The liquid phase space at the bottom of the raw material gas tertiary separation tank is successively connected to the second cold-side inlet of the primary heat exchanger through the eighth raw material gas pipeline, a raw material gas secondary throttle valve, and the ninth raw material gas pipeline. The second cold-side outlet of the primary heat exchanger is connected to the inlet of the raw material gas secondary separation tank through the tenth raw material gas pipeline.

[0017] The gas phase space at the top of the raw material gas secondary separation tank is connected to the seventh hot-side inlet of the primary heat exchanger through the eleventh raw material gas pipeline. The seventh hot-side outlet of the primary heat exchanger is connected to the inlet of the raw material gas quaternary separation tank through the thirteenth raw material gas pipeline.

[0018] The gas phase space at the top of the raw material gas quaternary separation tank is connected to the eleventh cold-side inlet of the primary heat exchanger through the fifteenth raw material gas pipeline. The eleventh cold-side outlet of the primary heat exchanger is provided with a sixteenth raw material gas pipeline for connecting the hydrogen-containing mixed gas to be recovered. The liquid phase space at the bottom of the raw material gas quaternary separation tank is connected to the inlet of the raw material gas secondary separation tank through the fourteenth raw material gas pipeline.

[0019] The liquid phase space at the bottom of the secondary separation tank of the feed gas is sequentially connected to the third cold side inlet of the primary heat exchanger through the twelfth pipeline of the feed gas, a cryogenic pump, and the seventeenth pipeline of the feed gas; the third cold side outlet of the primary heat exchanger is provided with an eighteenth pipeline of the feed gas for taking out the propane / propylene product liquid;

[0020] The outlet of the nineteenth pipeline of the feed gas is connected to the first heat side inlet of the secondary heat exchanger in the vacuum cold box; the first heat side outlet of the secondary heat exchanger is connected to the inlet of the hydrogen-rich gas primary separation tank through the twentieth pipeline of the feed gas;

[0021] The liquid phase space at the bottom of the hydrogen-rich gas primary separation tank is sequentially connected to the third cold side inlet of the secondary heat exchanger through the twenty-first pipeline of the feed gas, a hydrogen-rich methane gas primary throttle valve, and the twenty-ninth pipeline of the feed gas; the gas phase space at the top of the hydrogen-rich gas primary separation tank is sequentially connected to the second heat side inlet of the secondary heat exchanger through the twenty-second pipeline of the feed gas; the second heat side outlet of the secondary heat exchanger is connected to the inlet of the hydrogen-rich gas secondary separation tank through the twenty-third pipeline of the feed gas;

[0022] The liquid phase space at the bottom of the hydrogen-rich gas secondary separation tank is sequentially connected to the fourth cold side inlet of the secondary heat exchanger through the twenty-fourth pipeline of the feed gas, a hydrogen-rich methane gas secondary throttle valve, and the thirtieth pipeline of the feed gas; the gas phase space at the top of the hydrogen-rich gas secondary separation tank is connected to the third heat side inlet of the secondary heat exchanger through the twenty-fifth pipeline of the feed gas; the third heat side outlet of the secondary heat exchanger is connected to the inlet of the hydrogen-rich gas tertiary separation tank through the twenty-sixth pipeline of the feed gas;

[0023] The liquid phase space at the bottom of the hydrogen-rich gas tertiary separation tank is sequentially connected to the fifth cold side inlet of the secondary heat exchanger through the twenty-seventh pipeline of the feed gas, a hydrogen-rich nitrogen gas throttle valve, and the thirty-first pipeline of the feed gas; the gas phase space at the top of the hydrogen-rich gas tertiary separation tank is sequentially connected to the fourth heat side inlet of the secondary heat exchanger through a cryogenic purifier and the first pipeline of the product hydrogen; the fourth heat side outlet of the secondary heat exchanger is sequentially connected to the second pipeline of the product hydrogen, a liquid hydrogen primary throttle valve, the third pipeline of the product hydrogen, the tube side of the isothermal converter, and the fourth pipeline of the product hydrogen and then connected to the heat side inlet of the tertiary heat exchanger; the heat side outlet of the tertiary heat exchanger is sequentially connected to the fifth pipeline of the product hydrogen, a liquid hydrogen secondary throttle valve, and the sixth pipeline of the product hydrogen and then connected to the liquid hydrogen storage tank to take out the liquid hydrogen product to the liquid hydrogen storage tank;

[0024] The third cold side outlet and the fourth cold side outlet of the secondary heat exchanger are respectively provided with a thirty-second pipeline of the feed gas and a thirty-third pipeline of the feed gas. The outlet of the thirty-third pipeline of the feed gas converges with the thirty-second pipeline of the feed gas and is then connected to the ninth cold side inlet of the primary heat exchanger; the ninth cold side outlet of the primary heat exchanger is provided with a thirty-fifth pipeline of the feed gas for taking out the hydrogen-rich methane gas to the downstream;

[0025] The fifth cold side outlet of the secondary heat exchanger is connected to the tenth cold side inlet of the primary heat exchanger through the thirty-fourth raw material gas pipeline; the tenth cold side outlet of the primary heat exchanger is provided with a thirty-sixth raw material gas pipeline for taking out rich nitrogen gas to the downstream.

[0026] The eleventh hot side inlet of the primary heat exchanger is connected to the outlet of the first refrigerant hydrogen pipeline; the eleventh hot side outlet of the primary heat exchanger is connected to the fifth hot side inlet of the secondary heat exchanger through the second refrigerant hydrogen pipeline; the fifth hot side outlet of the secondary heat exchanger is provided with a third refrigerant hydrogen pipeline, and the outlet of the third refrigerant hydrogen pipeline is divided into two branches. One branch is sequentially connected to the sixth hot side inlet of the secondary heat exchanger through the fifth refrigerant hydrogen pipeline, the first-stage expander, and the sixth refrigerant hydrogen pipeline, and the other branch is connected to the seventh hot side inlet of the secondary heat exchanger through the fourth refrigerant hydrogen pipeline; the sixth hot side outlet of the secondary heat exchanger is sequentially connected to the first cold side inlet of the secondary heat exchanger through the seventh refrigerant hydrogen pipeline, the second-stage expander, and the eighth refrigerant hydrogen pipeline; the first cold side outlet of the secondary heat exchanger is connected to the seventh cold side inlet of the primary heat exchanger through the ninth refrigerant hydrogen pipeline; the seventh cold side outlet of the primary heat exchanger is provided with a tenth refrigerant hydrogen pipeline; the seventh hot side outlet of the secondary heat exchanger is sequentially connected to the inlet of the first-stage refrigerant hydrogen separation tank through the eleventh refrigerant hydrogen pipeline, the first-stage refrigerant hydrogen throttle valve, and the twelfth refrigerant hydrogen pipeline.

[0027] The outlet of the liquid phase space at the bottom of the first-stage refrigerant hydrogen separation tank is provided with two branches, namely the thirteenth refrigerant hydrogen pipeline and the fifteenth refrigerant hydrogen pipeline; the outlet of the thirteenth refrigerant hydrogen pipeline is connected to the inlet of the shell side of the isothermal converter, and the outlet of the fifteenth refrigerant hydrogen pipeline is sequentially connected to the inlet of the second-stage refrigerant hydrogen separation tank through the second-stage refrigerant hydrogen throttle valve and the seventeenth refrigerant hydrogen pipeline; the outlet of the gas phase space at the top of the first-stage refrigerant hydrogen separation tank is provided with a fourteenth refrigerant hydrogen pipeline; the outlet of the shell side of the isothermal converter is provided with a sixteenth refrigerant hydrogen pipeline; the outlets of the fourteenth refrigerant hydrogen pipeline and the sixteenth refrigerant hydrogen pipeline converge to the eighth refrigerant hydrogen pipeline.

[0028] The outlet of the liquid phase space at the bottom of the second-stage refrigerant hydrogen separation tank is connected to the cold side inlet of the tertiary heat exchanger through the eighteenth refrigerant hydrogen pipeline, and the outlet of the gas phase space at the top is connected to the second cold side inlet of the secondary heat exchanger through the nineteenth refrigerant hydrogen pipeline; the cold side outlet of the tertiary heat exchanger is provided with a twentieth refrigerant hydrogen pipeline, and the outlet of the twentieth refrigerant hydrogen pipeline converges into the nineteenth refrigerant hydrogen pipeline; the second cold side outlet of the secondary heat exchanger is connected to the eighth cold side inlet of the primary heat exchanger through the twenty-first refrigerant hydrogen pipeline; the eighth cold side outlet of the primary heat exchanger is provided with a twenty-second refrigerant hydrogen pipeline.

[0029] The mixed refrigerant compression unit includes a low-pressure MR compressor, a medium-pressure MR aftercooler, an MR primary separation tank, a medium-pressure MR compressor, a high-pressure MR aftercooler and an MR secondary separation tank; the low-pressure MR compressor receives the mixed refrigerant from the primary heat exchanger in the atmospheric cold box; the outlet of the low-pressure MR compressor is connected to the inlet of the MR primary separation tank through the second mixed refrigerant pipeline, the medium-pressure MR aftercooler and the third mixed refrigerant pipeline; the gas phase space at the top of the MR primary separation tank is connected to the inlet of the MR secondary separation tank through the fourth mixed refrigerant pipeline, the medium-pressure MR compressor, the sixth mixed refrigerant pipeline, the high-pressure MR aftercooler and the seventh mixed refrigerant pipeline in sequence; the gas phase space at the top of the MR secondary separation tank and the liquid phase space at the bottom are connected to the tenth hot side inlet and the ninth hot side inlet of the primary heat exchanger through the eighth mixed refrigerant pipeline and the ninth mixed refrigerant pipeline respectively; the liquid phase space at the bottom of the MR primary separation tank is connected to the eighth hot side inlet of the primary heat exchanger through the fifth mixed refrigerant pipeline; The tenth hot side outlet of the heat exchanger is connected to the fourth cold side inlet of the first heat exchanger through the tenth mixed refrigerant pipeline, the MR first-level throttle valve, and the eleventh mixed refrigerant pipeline in sequence; the fourth cold side outlet of the first heat exchanger is provided with a twelfth mixed refrigerant pipeline; the ninth hot side outlet of the first heat exchanger is connected to the inlet of the fourteenth mixed refrigerant pipeline through the thirteenth mixed refrigerant pipeline and the MR second-level throttle valve in sequence; the outlet of the fourteenth mixed refrigerant pipeline is connected to the fifth cold side inlet of the first heat exchanger after merging with the outlet of the twelfth mixed refrigerant pipeline; the fifth cold side outlet of the first heat exchanger is provided with a fifteenth mixed refrigerant pipeline; the eighth hot side outlet of the first heat exchanger is provided with a sixteenth mixed refrigerant pipeline, the MR third-level throttle valve and the seventeenth mixed refrigerant pipeline in sequence; the seventeenth mixed refrigerant pipeline is connected to the outlet of the fifteenth mixed refrigerant pipeline after merging with the sixth cold side inlet of the first heat exchanger; the sixth cold side of the first heat exchanger is provided with a first mixed refrigerant pipeline for transporting the mixed refrigerant to the low-pressure MR compressor, forming a mixed refrigerant refrigeration cycle;

[0030] The hydrogen compression unit includes a low-pressure hydrogen compressor, a medium-pressure hydrogen aftercooler, a medium-pressure hydrogen compressor and a high-pressure hydrogen aftercooler; the outlet of the refrigerant hydrogen pipeline No. 22 is connected to the inlet of the refrigerant hydrogen pipeline No. 24 through the low-pressure hydrogen compressor, the refrigerant hydrogen pipeline No. 23, the medium-pressure hydrogen aftercooler in sequence; the refrigerant hydrogen pipeline No. 10 is connected to the inlet of the medium-pressure hydrogen compressor after converging with the refrigerant hydrogen pipeline No. 24; the outlet of the medium-pressure hydrogen compressor is connected to the inlet of the refrigerant hydrogen pipeline No. 25 and the high-pressure hydrogen aftercooler in sequence, forming a hydrogen refrigeration cycle.

[0031] Furthermore, the first-stage heat exchanger, the second-stage heat exchanger and the third-stage heat exchanger are all aluminum plate-fin heat exchangers.

[0032] Further, the low-temperature purifier is a low-temperature purifier using a two-column pressure swing adsorption device. Molecular sieves or activated carbon are filled in the adsorption columns to remove nitrogen and methane impurities in the raw material gas.

[0033] Further, in the product hydrogen channels of the secondary heat exchanger and the tertiary heat exchanger, ortho-para hydrogen conversion catalysts with corresponding catalytic performance are filled according to the refrigeration temperature range.

[0034] Further, the isothermal converter adopts a shell-and-tube structure. The corresponding catalytic performance ortho-para hydrogen conversion catalyst is filled in the tube side, and the shell side is a liquid hydrogen bath.

[0035] Even further, the ortho-para hydrogen conversion catalyst is any one or a combination of several of iron hydroxide, hydrated iron oxide, and α-Fe 2 O 3 、β-Fe 2 O 3 、γ-Fe 2 O 3 crystalline forms of iron oxide.

[0036] Preferably, the mixed refrigerant is composed of 10-15 mol% methane, 28-33 mol% ethylene, 28-33 mol% propane, 2-7 mol% isopentane, and 18-23 mol% nitrogen.

[0037] In a second aspect, the present invention provides a method using the co-production system described in the first aspect, and the specific steps are as follows:

[0038] S1: Propane raw materials from upstream enter the primary heat exchanger in the atmospheric cold box through the first propane pipeline. After undergoing four-stage throttling and vaporization in the primary heat exchanger, the obtained propane vapor is transported to the downstream cracking unit through the sixteenth propane pipeline; the mixed refrigerant refrigeration cycle adopts a three-stage throttling method; propane vaporization and the mixed refrigerant refrigeration cycle provide cold energy for the atmospheric cold box;

[0039] S2: The cracking products from the cracking unit serve as raw material gas and enter the primary heat exchanger through the first raw material gas pipeline for temperature reduction, and then enter the primary raw material gas separation tank; the liquid phase at the bottom of the primary raw material gas separation tank is throttled and enters the secondary raw material gas separation tank, and the gas phase at the top of the primary raw material gas separation tank is refluxed to the primary heat exchanger for further temperature reduction and then enters the tertiary raw material gas separation tank; the hydrogen-rich gas at the top of the tertiary raw material gas separation tank is refluxed to the primary heat exchanger for further temperature reduction and then leaves the atmospheric cold box through the nineteenth raw material gas pipeline and enters the secondary heat exchanger in the vacuum cold box; the propane / propylene liquid at the bottom of the secondary raw material gas separation tank is pressurized by a cryogenic pump in sequence, reheated by the primary heat exchanger, and then transported to the downstream through the eighteenth raw material gas pipeline;

[0040] S3: After the hydrogen-rich gas enters the secondary heat exchanger for temperature reduction, it enters the first-stage hydrogen-rich gas separation tank; the gas phase at the top of the first-stage hydrogen-rich gas separation tank enters the second-stage hydrogen-rich gas separation tank after being cooled by the secondary heat exchanger; the liquid phase at the bottom of the second-stage hydrogen-rich gas separation tank and the liquid phase at the bottom of the first-stage hydrogen-rich gas separation tank are reheated through the secondary heat exchanger and the primary heat exchanger in sequence, and the methane-rich gas therein is taken out through the 35th raw material gas pipeline to the downstream; the gas phase at the top of the second-stage hydrogen-rich gas separation tank enters the third-stage hydrogen-rich gas separation tank after being cooled by the secondary heat exchanger;

[0041] The liquid nitrogen at the bottom of the third-stage hydrogen-rich gas separation tank is reheated through the secondary heat exchanger and the primary heat exchanger in sequence to become nitrogen-rich gas, and the nitrogen-rich gas is taken out through the 36th raw material gas pipeline to the downstream; the gas phase at the top of the third-stage hydrogen-rich gas separation tank is purified by a cryogenic purifier, then enters the secondary heat exchanger for temperature reduction, and the content of para-hydrogen is increased under the action of the ortho-para hydrogen conversion catalyst to obtain raw hydrogen; the raw hydrogen enters the isothermal converter after being depressurized by the first-stage liquid hydrogen throttle valve, and the content of para-hydrogen is further increased under the action of the ortho-para hydrogen conversion catalyst in the isothermal converter; subsequently, the raw hydrogen enters the tertiary heat exchanger for cooling until it is completely liquefied, and the content of para-hydrogen is further increased under the action of the ortho-para conversion catalyst; finally, it is throttled and cooled to the target temperature and pressure by the second-stage liquid hydrogen throttle valve and then connected to the liquid hydrogen storage tank.

[0042] Preferably, the parameters of the propane raw material are 40°C and 1.9 MPa; the temperatures of the propane raw material before the four-stage throttling in the primary heat exchanger are -15 to -35°C, -50 to -60°C, -75 to -95°C, and -100 to -120°C respectively; the highest operating pressure of the mixed refrigerant refrigeration cycle is 4 to 4.5 MPa, and the temperatures before the three-stage throttling are -15 to -35°C, -65 to -85°C, and -140 to -160°C respectively;

[0043] The parameters of the pyrolysis product are 40°C and 2.1 MPa, and the pyrolysis product is cooled to -25 to -45°C in the primary heat exchanger; the gas phase at the top of the first-stage raw material gas separation tank flows back into the primary heat exchanger for further cooling to -110 to -120°C, and then enters the third-stage raw material gas separation tank; the hydrogen-rich gas at the top of the third-stage raw material gas separation tank flows back into the primary heat exchanger for further cooling to -165 to -170°C and then leaves the atmospheric cold box to the vacuum cold box;

[0044] The hydrogen-rich gas enters the first-stage hydrogen-rich gas separation tank after being cooled to -170 to -173°C by the secondary heat exchanger; the gas phase at the top of the first-stage hydrogen-rich gas separation tank enters the second-stage hydrogen-rich gas separation tank after being cooled to -175 to -180°C by the secondary heat exchanger;

[0045] The gas phase at the top of the second-stage hydrogen-rich gas separation tank enters the third-stage hydrogen-rich gas separation tank after being cooled to -205 to -208°C by the secondary heat exchanger;

[0046] The purity of the hydrogen purified by the low-temperature purifier is not less than 99.99%; the purified hydrogen is cooled to -250°C in the secondary heat exchanger, and the content of para-hydrogen is increased from 25% to more than 85% under the action of the ortho-para hydrogen conversion catalyst;

[0047] The raw material hydrogen is depressurized to 0.2 - 0.7 MPa through the liquid hydrogen primary throttle valve, and then enters the isothermal converter, where the content of para-hydrogen is further increased to more than 95% under the action of the ortho-para hydrogen conversion catalyst; the raw material hydrogen is further increased to more than 98% in the tertiary heat exchanger under the action of the ortho-para conversion catalyst.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The system provided by the present invention highly couples the propane dehydrogenation cryogenic separation process and the hydrogen liquefaction process, and can produce liquid hydrogen with a para-hydrogen content of not less than 98% while realizing the cryogenic separation of the propane dehydrogenation to propylene product, solving the problem of the destination of the by-product hydrogen;

[0050] (2) The system provided by the present invention saves the raw material hydrogen compressor device, the high-low pressure series hydrogen expander device for propane dehydrogenation cryogenic separation, and the pressure swing adsorption device for rich hydrogen purification, reduces the total number of cold boxes, and has less initial investment and less project land occupation for the project;

[0051] (3) The specific energy consumption of the system provided by the present invention does not exceed 15.4 kWh / kg of liquid hydrogen, which is about 30% lower than the total energy consumption of the two independent processes, solves the problem of high energy consumption in propane dehydrogenation cryogenic separation and hydrogen liquefaction, and greatly reduces the co-production cost of propane dehydrogenation to propylene and liquid hydrogen.

[0052] (4) The system provided by the present invention has a wider application range, can flexibly match the hydrogen-hydrocarbon ratio according to the upstream cracking process, and is even applicable to no hydrogen circulation, which helps to improve the single-pass conversion rate of the cracking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the propane dehydrogenation to propylene product cryogenic separation and hydrogen liquefaction co-production system provided by this embodiment;

[0054] In the figure: primary heat exchanger HX1, secondary heat exchanger HX2, tertiary heat exchanger HX3, primary raw gas separation tank D1, secondary raw gas separation tank D2, tertiary raw gas separation tank D3, quaternary raw gas separation tank D4, primary MR separation tank D5, secondary MR separation tank D6, primary refrigerant hydrogen separation tank D7, secondary refrigerant hydrogen separation tank D8, primary hydrogen-rich gas separation tank D9, secondary hydrogen-rich gas separation tank D10, tertiary hydrogen-rich gas separation tank D11, cryogenic pump CP, low-pressure MR compressor K1, medium-pressure MR after-cooler C1, medium-pressure MR compressor K2, high-pressure MR after-cooler C2, low-pressure hydrogen compressor K3, medium-pressure hydrogen after-cooler C3, medium-pressure hydrogen compressor K4, high-pressure hydrogen after-cooler C4, primary expander E1, secondary expander E2, cryogenic purifier T, isothermal converter R, first propane pipeline P1, second propane pipeline P2, third propane pipeline P3, fourth propane pipeline P4, fifth propane pipeline P5, sixth propane pipeline P6, seventh propane pipeline P7, eighth propane pipeline P8, ninth propane pipeline P9, tenth propane pipeline P10, eleventh propane pipeline P11, twelfth propane pipeline P12, thirteenth propane pipeline P13, fourteenth propane pipeline P14, fifteenth propane pipeline P15, sixteenth propane pipeline P16, first mixed refrigerant pipeline M1, second mixed refrigerant pipeline M2, third mixed refrigerant pipeline M3, fourth mixed refrigerant pipeline M4, fifth mixed refrigerant pipeline M5, sixth mixed refrigerant pipeline M6, seventh mixed refrigerant pipeline M7, eighth mixed refrigerant pipeline M8, ninth mixed refrigerant pipeline M9, tenth mixed refrigerant pipeline M10, eleventh mixed refrigerant pipeline M11, twelfth mixed refrigerant pipeline M12, thirteenth mixed refrigerant pipeline M13, fourteenth mixed refrigerant pipeline M14, fifteenth mixed refrigerant pipeline M15, sixteenth mixed refrigerant pipeline M16, seventeenth mixed refrigerant pipeline M17, first raw gas pipeline F1, second raw gas pipeline F2, third raw gas pipeline F3, fourth raw gas pipeline F4, fifth raw gas pipeline F5, sixth raw gas pipeline F6, seventh raw gas pipeline F7, eighth raw gas pipeline F8, ninth raw gas pipeline F9, tenth raw gas pipeline F10, eleventh raw gas pipeline F11, twelfth raw gas pipeline F12, thirteenth raw gas pipeline F13, fourteenth raw gas pipeline F14, fifteenth raw gas pipeline F15, sixteenth raw gas pipeline F16, seventeenth raw gas pipeline F17, eighteenth raw gas pipeline F18, nineteenth raw gas pipeline F19, twentieth raw gas pipeline F20, twenty-first raw gas pipeline F21, twenty-second raw gas pipeline F22, twenty-third raw gas pipeline F23, twenty-fourth raw gas pipeline F24, twenty-fifth raw gas pipeline F25, twenty-sixth raw gas pipeline F26, twenty-seventh raw gas pipeline F27, twenty-eighth raw gas pipeline F28, twenty-ninth raw gas pipeline F29, thirtieth raw gas pipeline F30, thirty-first raw gas pipeline F31The thirty-second raw material gas pipeline F32, the thirty-third raw material gas pipeline F33, the thirty-fourth raw material gas pipeline F34, the thirty-fifth raw material gas pipeline F35, the thirty-sixth raw material gas pipeline F36, the first refrigerant hydrogen pipeline A1, the second refrigerant hydrogen pipeline A2, the third refrigerant hydrogen pipeline A3, the fourth refrigerant hydrogen pipeline A4, the fifth refrigerant hydrogen pipeline A5, the sixth refrigerant hydrogen pipeline A6, the seventh refrigerant hydrogen pipeline A7, the eighth refrigerant hydrogen pipeline A8, the ninth refrigerant hydrogen pipeline A9, the tenth refrigerant hydrogen pipeline A10, the eleventh refrigerant hydrogen pipeline A11, the twelfth refrigerant hydrogen pipeline A12, the thirteenth refrigerant hydrogen pipeline A13, the fourteenth refrigerant hydrogen pipeline A14, the fifteenth refrigerant hydrogen pipeline A15, the sixteenth refrigerant hydrogen pipeline A16, the seventeenth refrigerant hydrogen pipeline A17, the eighteenth refrigerant hydrogen pipeline A18, the nineteenth refrigerant hydrogen pipeline A19, the twentieth refrigerant hydrogen pipeline A20, the twenty-first refrigerant hydrogen pipeline A21, the twenty-second refrigerant hydrogen pipeline A22, the twenty-third refrigerant hydrogen pipeline A23, the twenty-fourth refrigerant hydrogen pipeline A24, the twenty-fifth refrigerant hydrogen pipeline A25, the first product hydrogen pipeline H1, the second product hydrogen pipeline H2, the third product hydrogen pipeline H3, the fourth product hydrogen pipeline H4, the fifth product hydrogen pipeline H5, the sixth product hydrogen pipeline H6, the first-stage propane throttle valve V1, the second-stage propane throttle valve V2, the third-stage propane throttle valve V3, the fourth-stage propane throttle valve V4, the first-stage raw material gas throttle valve V5, the second-stage raw material gas throttle valve V6, the first-stage MR throttle valve V7, the second-stage MR throttle valve V8, the third-stage MR throttle valve V9, the first-stage refrigerant hydrogen throttle valve V10, the second-stage refrigerant hydrogen throttle valve V11, the second-stage rich methane gas throttle valve V12, the second-stage rich methane gas throttle valve V13, the rich nitrogen gas throttle valve V14, the first-stage liquid hydrogen throttle valve V15, the second-stage liquid hydrogen throttle valve V16. Detailed implementation manners

[0055] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following describes the detailed implementation manners of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflict.

[0056] In the description of the present invention, it should be understood that when an element is considered to be "connected" to another element, it can be directly connected to the other element or indirectly connected, that is, there is an intermediate element. On the contrary, when an element is referred to as being "directly" connected to another element, there is no intermediate element.

[0057] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for the purpose of distinguishing descriptions, and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features.

[0058] In the description of the present invention, it should be understood that the terms "low temperature" and "high temperature" both refer to high temperature or low temperature compared to the temperature of the same medium in the same passage, and cannot be construed as indicating or implying relative importance or implicitly specifying the temperature value of the indicated technical features. Similarly, the terms "high pressure" and "low pressure" both refer to high pressure or low pressure compared to the pressure of the same medium in the same passage, and cannot be construed as indicating or implying relative importance or implicitly specifying the pressure value of the indicated technical features.

[0059] As Figure 1 shown, in a preferred embodiment of the present invention, a cryogenic separation of propane dehydrogenation to propylene product and hydrogen liquefaction co-production system is provided, which specifically includes an atmospheric pressure cold box, a vacuum cold box, a hydrogen compression unit, a mixed refrigerant compression unit, a propane pipeline, a raw material gas pipeline, a product hydrogen pipeline, a refrigerant hydrogen pipeline, and a mixed refrigerant pipeline.

[0060] In the system of the present invention, the atmospheric pressure cold box includes a first-stage heat exchanger HX1, a raw material gas first-stage separation tank D1, a raw material gas second-stage separation tank D2, a raw material gas third-stage separation tank D3, a raw material gas fourth-stage separation tank D4, and a cryogenic pump CP, which are connected to each other through pipelines.

[0061] The mixed refrigerant compression unit includes a low-pressure MR compressor K1, a medium-pressure MR after-cooler C1, an MR first-stage separation tank D5, a medium-pressure MR compressor K2, a high-pressure MR after-cooler C2, and an MR second-stage separation tank D6, which are connected to each other through pipelines.

[0062] The hydrogen compression unit includes a low-pressure hydrogen compressor K3, a medium-pressure hydrogen after-cooler C3, a medium-pressure hydrogen compressor K4, and a high-pressure hydrogen after-cooler C4, which are connected to each other through pipelines.

[0063] The vacuum cold box includes a second-stage heat exchanger HX2, a third-stage heat exchanger HX3, a refrigerant hydrogen first-stage separation tank D7, a refrigerant hydrogen second-stage separation tank D8, a hydrogen-rich gas first-stage separation tank D9, a hydrogen-rich gas second-stage separation tank D10, a hydrogen-rich gas third-stage separation tank D11, a cryogenic purifier T, and an isothermal converter R, which are connected to each other through pipelines.

[0064] In the system of the present invention, the atmospheric pressure cold box uses the vaporization latent heat of the propane raw material and the cooling capacity provided by the multi-stage throttling of the mixed refrigerant to deeply cool and separate the pyrolysis products from the pyrolysis unit, thereby obtaining the target propane / propylene products and hydrogen-rich gas. The hydrogen compression unit receives the hydrogen refrigerant after pressure reduction and reheating in the atmospheric pressure cold box, compresses and cools the hydrogen refrigerant to form a hydrogen refrigeration cycle. The mixed refrigerant compression unit receives the mixed refrigerant after pressure reduction and reheating in the atmospheric pressure cold box, compresses and cools the mixed refrigerant to form a mixed refrigerant refrigeration cycle. The vacuum cold box receives the hydrogen-rich gas from the atmospheric pressure cold box, and further separates, purifies and cools the hydrogen-rich gas by using the hydrogen cycle refrigeration to obtain the target liquid hydrogen.

[0065] It should be noted that aluminum has good corrosion resistance and high heat conduction efficiency. In addition, the plate-fin design allows the heat exchanger to provide a large heat exchange area in a small space. Therefore, in this embodiment, the primary heat exchanger HX1, the secondary heat exchanger HX2, and the tertiary heat exchanger HX3 are all aluminum plate-fin heat exchangers. Among them, in the product hydrogen channels of the secondary heat exchanger HX2 and the tertiary heat exchanger HX3, ortho-para hydrogen conversion catalysts with corresponding catalytic properties are filled according to the refrigeration temperature range. Those skilled in the art can select a suitable heat exchanger according to the actual working conditions.

[0066] The ortho-para hydrogen conversion catalyst in the heat exchanger is used to promote the conversion of ortho-hydrogen in hydrogen to para-hydrogen. In this embodiment, the ortho-para hydrogen conversion catalyst can be ferric hydroxide, hydrated ferric oxide, and α-Fe 2 O 3 , β-Fe 2 O 3 , γ-Fe 2 O 3 or any combination of several of the iron oxide crystal forms. Those skilled in the art can also select other ortho-para hydrogen conversion catalysts according to the actual working conditions.

[0067] It should be noted that the low-temperature purifier T is a device for separating and purifying gases, and it works by utilizing the adsorption differences of different gases on the adsorbent. During the low-temperature purification process, the mixed gas passes through the adsorbent, and these adsorbed components are removed from the gas stream, thereby achieving purification. In this embodiment, the low-temperature purifier T adopts a low-temperature purifier with a two-tower pressure swing adsorption device. In this device, there are usually two adsorption towers that alternately perform the adsorption and regeneration processes to continuously provide purified gas. The adsorption towers are filled with molecular sieves or activated carbon to remove nitrogen and methane impurities in the raw gas.

[0068] It should be noted that in this embodiment, the isothermal converter R adopts a shell-and-tube structure. This converter usually consists of a shell side and a tube side. The tube side is filled with an ortho-para hydrogen conversion catalyst with corresponding catalytic properties, and the shell side is a liquid hydrogen bath.

[0069] Next, the specific connection methods of the components in the system provided by the present invention will be described.

[0070] In the system of the present invention, the propane raw material from the upstream is connected to the first heat side inlet of the primary heat exchanger HX1 through the first propane pipeline P1. The first heat side outlet of the primary heat exchanger HX1 is connected to the inlet of the second propane pipeline P2. The outlet of the second propane pipeline P2 is divided into two branches. One branch is connected to the second heat side inlet of the primary heat exchanger HX1 through the third propane pipeline P3, and the other branch is successively provided with a fourth propane pipeline P4, a first-stage propane throttle valve V1, and a fifth propane pipeline P5.

[0071] The second heat side outlet of the primary heat exchanger HX1 is connected to the inlet of the sixth propane pipeline P6. The outlet of the sixth propane pipeline P6 is divided into two branches. One branch is connected to the third heat side inlet of the primary heat exchanger HX1 through the seventh propane pipeline P7, and the other branch is successively provided with an eighth propane pipeline P8, a second-stage propane throttle valve V2, and a ninth propane pipeline P9.

[0072] The third heat side outlet of the primary heat exchanger HX1 is connected to the inlet of the tenth propane pipeline P10. The outlet of the tenth propane pipeline P10 is provided with two branches. One branch is connected to the fourth heat side inlet of the primary heat exchanger HX1 through the eleventh propane pipeline P11, and the other branch is successively provided with a twelfth propane pipeline P12, a third-stage propane throttle valve V3, and a thirteenth propane pipeline P13. The fourth heat side outlet of the primary heat exchanger HX1 is successively provided with a fourteenth propane pipeline P14, a fourth-stage propane throttle valve V4, and a fifteenth propane pipeline P15.

[0073] The outlets of the fifth propane pipeline P5, the ninth propane pipeline P9, the thirteenth propane pipeline P13, and the fifteenth propane pipeline P15 are all connected to the primary heat exchanger HX1, and after reheating in the primary heat exchanger HX1, they converge to the first cold side outlet of the primary heat exchanger HX1. The first cold side outlet of the primary heat exchanger HX1 is provided with a sixteenth propane pipeline P16.

[0074] After the propane raw material from the upstream is gasified through the above four-stage throttling, the obtained propane vapor is transported to the downstream cracking unit through the sixteenth propane pipeline P16, and the propane gasification process provides cold energy for the atmospheric cold box.

[0075] In the system of the present invention, the cracking products from the upstream are connected to the fifth hot-side inlet of the first-stage heat exchanger HX1 through the first raw gas pipeline F1. The fifth hot-side outlet of the first-stage heat exchanger HX1 is connected to the first-stage raw gas separation tank D1 through the second raw gas pipeline F2. The liquid phase space at the bottom of the first-stage raw gas separation tank D1 is sequentially connected to the inlet of the second-stage raw gas separation tank D2 through the fourth raw gas pipeline F4, the first-stage raw gas throttle valve V5, and the fifth raw gas pipeline F5. The gas phase space at the top of the first-stage raw gas separation tank D1 is connected to the sixth hot-side inlet of the first-stage heat exchanger HX1 through the third raw gas pipeline F3. The sixth hot-side outlet of the first-stage heat exchanger HX1 is connected to the inlet of the third-stage raw gas separation tank D3 through the sixth raw gas pipeline F6.

[0076] The gas phase space at the top of the third-stage raw gas separation tank D3 is connected to the twelfth hot-side inlet of the first-stage heat exchanger HX1 through the seventh raw gas pipeline F7. The twelfth hot-side outlet of the first-stage heat exchanger HX1 leaves the atmospheric cold box through the nineteenth raw gas pipeline F19 and enters the second-stage heat exchanger HX2 in the vacuum cold box. The liquid phase space at the bottom of the third-stage raw gas separation tank D3 is sequentially connected to the second cold-side inlet of the first-stage heat exchanger HX1 through the eighth raw gas pipeline F8, the second-stage raw gas throttle valve V6, and the ninth raw gas pipeline F9. The second cold-side outlet of the first-stage heat exchanger HX1 is connected to the inlet of the second-stage raw gas separation tank D2 through the tenth raw gas pipeline F10.

[0077] The gas phase space at the top of the second-stage raw gas separation tank D2 is connected to the seventh hot-side inlet of the first-stage heat exchanger HX1 through the eleventh raw gas pipeline F11. The seventh hot-side outlet of the first-stage heat exchanger HX1 is connected to the inlet of the fourth-stage raw gas separation tank D4 through the thirteenth raw gas pipeline F13.

[0078] The gas phase space at the top of the fourth-stage raw gas separation tank D4 is connected to the eleventh cold-side inlet of the first-stage heat exchanger HX1 through the fifteenth raw gas pipeline F15. The eleventh cold-side outlet of the first-stage heat exchanger HX1 is provided with a sixteenth raw gas pipeline F16 for taking out and recovering the hydrogen-containing mixed gas. The liquid phase space at the bottom of the fourth-stage raw gas separation tank D4 is connected to the inlet of the second-stage raw gas separation tank D2 through the fourteenth raw gas pipeline F14.

[0079] The liquid phase space at the bottom of the second-stage raw gas separation tank D2 is sequentially connected to the third cold-side inlet of the first-stage heat exchanger HX1 through the twelfth raw gas pipeline F12, the cryogenic pump CP, and the seventeenth raw gas pipeline F17. The third cold-side outlet of the first-stage heat exchanger HX1 is provided with an eighteenth raw gas pipeline F18 for taking out the propane / propylene product liquid.

[0080] The mixed refrigerant undergoes a three-stage throttling cycle in the first-stage heat exchanger HX1 to provide cooling capacity for the atmospheric cold box. It should be noted that the mixed refrigerant used in this embodiment is composed of 10 - 15 mol% methane, 28 - 33 mol% ethylene, 28 - 33 mol% propane, 2 - 7 mol% isopentane, and 18 - 23 mol% nitrogen.

[0081] In the system of the present invention, the outlet of the nineteenth pipeline F19 of the raw material gas is connected to the first heat side inlet of the second-stage heat exchanger HX2 in the vacuum cold box. The first heat side outlet of the second-stage heat exchanger HX2 is connected to the inlet of the first-stage hydrogen-rich gas separation tank D9 through the twentieth pipeline F20 of the raw material gas.

[0082] The liquid phase space at the bottom of the first-stage hydrogen-rich gas separation tank D9 is sequentially connected to the third cold side inlet of the second-stage heat exchanger HX2 through the twenty-first pipeline F21 of the raw material gas, the first-stage methane-rich gas throttle valve V12, and the twenty-ninth pipeline F29 of the raw material gas. The gas phase space at the top of the first-stage hydrogen-rich gas separation tank D9 is sequentially connected to the second heat side inlet of the second-stage heat exchanger HX2 through the twenty-second pipeline F22 of the raw material gas. The second heat side outlet of the second-stage heat exchanger HX2 is connected to the inlet of the second-stage hydrogen-rich gas separation tank D10 through the twenty-third pipeline F23 of the raw material gas.

[0083] The liquid phase space at the bottom of the second-stage hydrogen-rich gas separation tank D10 is sequentially connected to the fourth cold side inlet of the second-stage heat exchanger HX2 through the twenty-fourth pipeline F24 of the raw material gas, the second-stage methane-rich gas throttle valve V13, and the thirtieth pipeline F30 of the raw material gas. The gas phase space at the top of the second-stage hydrogen-rich gas separation tank D10 is connected to the third heat side inlet of the second-stage heat exchanger HX2 through the twenty-fifth pipeline F25 of the raw material gas. The third heat side outlet of the second-stage heat exchanger HX2 is connected to the inlet of the third-stage hydrogen-rich gas separation tank D11 through the twenty-sixth pipeline F26 of the raw material gas.

[0084] The liquid phase space at the bottom of the third-stage hydrogen-rich gas separation tank D11 is sequentially connected to the fifth cold side inlet of the second-stage heat exchanger HX2 through the twenty-seventh pipeline F27 of the raw material gas, the nitrogen-rich gas throttle valve V14, and the thirty-first pipeline F31 of the raw material gas. The gas phase space at the top of the third-stage hydrogen-rich gas separation tank D11 is sequentially connected to the fourth heat side inlet of the second-stage heat exchanger HX2 through the low-temperature purifier T and the first pipeline H1 of the product hydrogen. The fourth heat side outlet of the second-stage heat exchanger HX2 is sequentially connected to the second pipeline H2 of the product hydrogen, the first-stage liquid hydrogen throttle valve V15, the third pipeline H3 of the product hydrogen, the tube side of the isothermal converter R, and the fourth pipeline H4 of the product hydrogen to the heat side inlet of the third-stage heat exchanger HX3. The heat side outlet of the third-stage heat exchanger HX3 is sequentially connected to the fifth pipeline H5 of the product hydrogen, the second-stage liquid hydrogen throttle valve V16, and the sixth pipeline H6 of the product hydrogen to the liquid hydrogen storage tank, and the liquid hydrogen product is taken out to the liquid hydrogen storage tank.

[0085] The third cold side outlet and the fourth cold side outlet of the secondary heat exchanger HX2 are respectively provided with a raw gas thirty-second pipeline F32 and a raw gas thirty-third pipeline F33. The outlet of the raw gas thirty-third pipeline F33 converges with the raw gas thirty-second pipeline F32 and is connected to the ninth cold side inlet of the primary heat exchanger HX1. The ninth cold side outlet of the primary heat exchanger HX1 is provided with a raw gas thirty-fifth pipeline F35 for taking out rich methane gas to the downstream.

[0086] The fifth cold side outlet of the secondary heat exchanger HX2 is connected to the tenth cold side inlet of the primary heat exchanger HX1 through a raw gas thirty-fourth pipeline F34. The tenth cold side outlet of the primary heat exchanger HX1 is provided with a raw gas thirty-sixth pipeline F36 for taking out rich nitrogen gas to the downstream.

[0087] The eleventh hot side inlet of the primary heat exchanger HX1 is connected to the outlet of the refrigerant hydrogen first pipeline A1. The eleventh hot side outlet of the primary heat exchanger HX1 is connected to the fifth hot side inlet of the secondary heat exchanger HX2 through a refrigerant hydrogen second pipeline A2. The fifth hot side outlet of the secondary heat exchanger HX2 is provided with a refrigerant hydrogen third pipeline A3. The outlet of the refrigerant hydrogen third pipeline A3 is divided into two branches. One branch is sequentially connected to the sixth hot side inlet of the secondary heat exchanger HX2 through a refrigerant hydrogen fifth pipeline A5, a primary expander E1, and a refrigerant hydrogen sixth pipeline A6. The other branch is connected to the seventh hot side inlet of the secondary heat exchanger HX2 through a refrigerant hydrogen fourth pipeline A4. The sixth hot side outlet of the secondary heat exchanger HX2 is sequentially connected to the first cold side inlet of the secondary heat exchanger HX2 through a refrigerant hydrogen seventh pipeline A7, a secondary expander E2, and a refrigerant hydrogen eighth pipeline A8. The first cold side outlet of the secondary heat exchanger HX2 is connected to the seventh cold side inlet of the primary heat exchanger HX1 through a refrigerant hydrogen ninth pipeline A9. The seventh cold side outlet of the primary heat exchanger HX1 is provided with a refrigerant hydrogen tenth pipeline A10. The seventh hot side outlet of the secondary heat exchanger HX2 is sequentially connected to the inlet of the refrigerant hydrogen first separation tank D7 through a refrigerant hydrogen eleventh pipeline A11, a refrigerant hydrogen primary throttle valve V10, and a refrigerant hydrogen twelfth pipeline A12.

[0088] The bottom liquid phase space outlet of the refrigerant hydrogen first separation tank D7 is provided with two branches, namely a refrigerant hydrogen thirteenth pipeline A13 and a refrigerant hydrogen fifteenth pipeline A15. The outlet of the refrigerant hydrogen thirteenth pipeline A13 is connected to the shell side inlet of the isothermal converter R. The outlet of the refrigerant hydrogen fifteenth pipeline A15 is sequentially connected to the inlet of the refrigerant hydrogen second separation tank D8 through a refrigerant hydrogen secondary throttle valve V11 and a refrigerant hydrogen seventeenth pipeline A17. The top gas phase space outlet of the refrigerant hydrogen first separation tank D7 is provided with a refrigerant hydrogen fourteenth pipeline A14. The shell side outlet of the isothermal converter R is provided with a refrigerant hydrogen sixteenth pipeline A16. The outlets of the refrigerant hydrogen fourteenth pipeline A14 and the refrigerant hydrogen sixteenth pipeline A16 converge to the refrigerant hydrogen eighth pipeline A8.

[0089] The liquid-phase space outlet at the bottom of the refrigerant hydrogen secondary separation tank D8 is connected to the cold-side inlet of the tertiary heat exchanger HX3 through the eighteenth refrigerant hydrogen pipeline A18, and the gas-phase space outlet at the top is connected to the second cold-side inlet of the secondary heat exchanger HX2 through the nineteenth refrigerant hydrogen pipeline A19. The cold-side outlet of the tertiary heat exchanger HX3 is provided with a twentieth refrigerant hydrogen pipeline A20, and the outlet of the twentieth refrigerant hydrogen pipeline A20 converges into the nineteenth refrigerant hydrogen pipeline A19. The second cold-side outlet of the secondary heat exchanger HX2 is connected to the eighth cold-side inlet of the primary heat exchanger HX1 through the twenty-first refrigerant hydrogen pipeline A21. The eighth cold-side outlet of the primary heat exchanger HX1 is provided with a twenty-second refrigerant hydrogen pipeline A22.

[0090] In the system of the present invention, the low-pressure MR compressor K1 in the mixed refrigerant compression unit receives the mixed refrigerant from the primary heat exchanger HX1 in the atmospheric cold box. The outlet of the low-pressure MR compressor K1 is connected to the inlet of the MR primary separation tank D5 through the second mixed refrigerant pipeline M2, the medium-pressure MR aftercooler C1, and the third mixed refrigerant pipeline M3. The gas-phase space at the top of the MR primary separation tank D5 sequentially passes through the fourth mixed refrigerant pipeline M4, the medium-pressure MR compressor K2, the sixth mixed refrigerant pipeline M6, the high-pressure MR aftercooler C2, and the seventh mixed refrigerant pipeline M7 and is connected to the inlet of the MR secondary separation tank D6. The gas-phase space and the liquid-phase space at the top and bottom of the MR secondary separation tank D6 are respectively connected to the tenth hot-side inlet and the ninth hot-side inlet of the primary heat exchanger HX1 through the eighth mixed refrigerant pipeline M8 and the ninth mixed refrigerant pipeline M9. The liquid-phase space at the bottom of the MR primary separation tank D5 is connected to the eighth hot-side inlet of the primary heat exchanger HX1 through the fifth mixed refrigerant pipeline M5. The tenth hot-side outlet of the primary heat exchanger HX1 sequentially passes through the tenth mixed refrigerant pipeline M10, the MR primary throttle valve V7, and the eleventh mixed refrigerant pipeline M11 and is connected to the fourth cold-side inlet of the primary heat exchanger HX1. The fourth cold-side outlet of the primary heat exchanger HX1 is provided with a twelfth mixed refrigerant pipeline M12. The ninth hot-side outlet of the primary heat exchanger HX1 sequentially passes through the thirteenth mixed refrigerant pipeline M13 and the MR secondary throttle valve V8 and is connected to the inlet of the fourteenth mixed refrigerant pipeline M14. The outlet of the fourteenth mixed refrigerant pipeline M14 and the outlet of the twelfth mixed refrigerant pipeline M12 converge and are connected to the fifth cold-side inlet of the primary heat exchanger HX1. The fifth cold-side outlet of the primary heat exchanger HX1 is provided with a fifteenth mixed refrigerant pipeline M15. The eighth hot-side outlet of the primary heat exchanger HX1 is sequentially provided with a sixteenth mixed refrigerant pipeline M16, an MR tertiary throttle valve V9, and a seventeenth mixed refrigerant pipeline M17. The seventeenth mixed refrigerant pipeline M17 and the outlet of the fifteenth mixed refrigerant pipeline M15 converge and are connected to the sixth cold-side inlet of the primary heat exchanger HX1. The sixth cold-side of the primary heat exchanger HX1 is provided with a first mixed refrigerant pipeline M1 for delivering the mixed refrigerant to the low-pressure MR compressor K1, forming a mixed refrigerant refrigeration cycle.

[0091] In the system of the present invention, the inlet of the low-pressure hydrogen compressor K3 in the hydrogen compression unit is connected to the refrigerant hydrogen second twenty-second pipeline A22 at the outlet of the eighth cold side of the primary heat exchanger HX1, and the outlet of the low-pressure hydrogen compressor K3 is sequentially connected to the inlet of the refrigerant hydrogen twenty-third pipeline A23, the medium-pressure hydrogen aftercooler C3, and the refrigerant hydrogen twenty-fourth pipeline A24. After the refrigerant hydrogen tenth pipeline A10 at the outlet of the seventh cold side of the primary heat exchanger HX1 converges with the refrigerant hydrogen twenty-fourth pipeline A24, it is connected to the inlet of the medium-pressure hydrogen compressor K4. The outlet of the medium-pressure hydrogen compressor K4 is sequentially connected to the refrigerant hydrogen twenty-fifth pipeline A25, the high-pressure hydrogen aftercooler C4, and the refrigerant hydrogen first pipeline A1 inlet to form a hydrogen refrigeration cycle.

[0092] In another preferred embodiment of the present invention, a method for utilizing the above-mentioned cryogenic separation of propane dehydrogenation to propylene products and hydrogen liquefaction co-production system is provided, and the specific steps are as follows:

[0093] S1: Propane raw materials at 40°C and 1.9 MPa from upstream enter the primary heat exchanger HX1 in the atmospheric cold box through the propane first pipeline P1, and the temperatures before the four-stage throttling are -15 to -35°C, -50 to -60°C, -75 to -95°C, and -100 to -120°C respectively. After four-stage throttling and gasification in the primary heat exchanger HX1, propane vapor is obtained, and the propane vapor is transported to the downstream cracking unit through the propane sixteenth pipeline P16.

[0094] The mixed refrigerant refrigeration cycle adopts a three-stage throttling method, with a maximum operating pressure of 4 to 4.5 MPa, and the temperatures before the three-stage throttling are -15 to -35°C, -65 to -85°C, and -140 to -160°C respectively. The cold energy of the atmospheric cold box is provided by propane gasification and the mixed refrigerant refrigeration cycle.

[0095] S2: The cracking products at 40°C and 2.1 MPa from the cracking unit, as raw material gas, enter the primary heat exchanger HX1 through the raw material gas first pipeline F1 to be cooled to -25 to -45°C, and then enter the raw material gas primary separation tank D1. The liquid phase at the bottom of the raw material gas primary separation tank D1 is throttled and then enters the raw material gas secondary separation tank D2. The gas phase at the top of the raw material gas primary separation tank D1 is refluxed to the primary heat exchanger HX1 to be further cooled to -110 to -120°C, and then enters the raw material gas tertiary separation tank D3. The hydrogen-rich gas at the top of the raw material gas tertiary separation tank D3 is refluxed to the primary heat exchanger HX1 to be further cooled to -165 to -170°C, and leaves the atmospheric cold box through the raw material gas nineteenth pipeline F19 and enters the secondary heat exchanger HX2 in the vacuum cold box. The propane / propylene liquid at the bottom of the raw material gas secondary separation tank D2 is sequentially pressurized by the cryogenic pump CP and reheated by the primary heat exchanger HX1 to obtain high-purity propane / propylene products, which are sent to the downstream through the raw material gas eighteenth pipeline F18.

[0096] S3: After the hydrogen-rich gas enters the secondary heat exchanger HX2 and is cooled to -170 to -173 °C, it enters the first-stage hydrogen-rich gas separation tank D9. The liquid phase at the bottom of the first-stage hydrogen-rich gas separation tank D9 mainly consists of methane, ethane, and ethylene. After reheating through the secondary heat exchanger HX2 and the primary heat exchanger HX1 in sequence, the methane-rich gas therein is taken out through the thirty-fifth raw material gas pipeline F35 to the downstream. The gas phase at the top of the first-stage hydrogen-rich gas separation tank D9 is cooled to -175 to -180 °C through the secondary heat exchanger HX2 and enters the second-stage hydrogen-rich gas separation tank D10. The liquid phase at the bottom of the second-stage hydrogen-rich gas separation tank D10 also passes through the secondary heat exchanger HX2 and the primary heat exchanger HX1 for reheating in sequence and is then taken out through the thirty-fifth raw material gas pipeline F35 to the downstream. The gas phase at the top of the second-stage hydrogen-rich gas separation tank D10 is cooled to -205 to -208 °C through the secondary heat exchanger HX2 and then enters the third-stage hydrogen-rich gas separation tank D11.

[0097] The liquid nitrogen at the bottom of the third-stage hydrogen-rich gas separation tank D11 becomes nitrogen-rich gas after reheating through the secondary heat exchanger HX2 and the primary heat exchanger HX1 in sequence, and the nitrogen-rich gas is taken out through the thirty-sixth raw material gas pipeline F36 to the downstream. The gas phase at the top of the third-stage hydrogen-rich gas separation tank D11 is purified by the cryogenic purifier T to obtain high-purity hydrogen with a purity of not less than 99.99%. The high-purity hydrogen enters the secondary heat exchanger HX2 and is cooled to -250 °C, and under the action of the ortho-para hydrogen conversion catalyst, the ortho-hydrogen content is increased from 25% to more than 85% to obtain raw hydrogen. The raw hydrogen is depressurized to 0.2 to 0.7 MPa through the first-stage liquid hydrogen throttle valve V15 and then enters the isothermal converter R. Under the action of the ortho-para hydrogen conversion catalyst in the isothermal converter R, the ortho-hydrogen content is further increased to more than 95%. Subsequently, the raw hydrogen enters the tertiary heat exchanger HX3 and is cooled to complete liquefaction, and under the action of the ortho-para conversion catalyst, the ortho-hydrogen content is further increased to more than 98%. Finally, it is throttled and cooled to the target temperature and pressure through the second-stage liquid hydrogen throttle valve V16 and then connected to the liquid hydrogen storage tank.

[0098] Using the system provided by the present invention, the raw material gas from the upstream cracking unit is multi-stage cryogenically separated in the atmospheric pressure cold box to obtain high-purity propane / propylene products. The hydrogen-rich gas is multi-stage cryogenically separated and cryogenically purified in the vacuum cold box to obtain high-purity hydrogen, which is directly used as the raw material gas for liquid hydrogen. The atmospheric pressure cold box provides cooling capacity by four-stage throttling of propane raw materials and three-stage throttling of mixed refrigerants. The vacuum cold box provides cooling capacity by a dual-pressure hydrogen Claude cycle refrigeration. The hydrogen by-produced from propane dehydrogenation to propylene is directly liquefied as a product.

[0099] The present invention provides a co-production system that efficiently integrates the cryogenic separation of propane dehydrogenation to propylene and the hydrogen liquefaction process. It can achieve the cryogenic separation of the products of propane dehydrogenation to propylene while producing liquid hydrogen with a secondary hydrogen content of not less than 98%, improving the added value of the by-product hydrogen. This system saves the raw material hydrogen compressor device, the high-low pressure series hydrogen expander device for PDH cryogenic separation, and the two-column pressure swing adsorption device (PSA) for rich hydrogen purification, reduces the total number of cold boxes, and has less initial project investment and less project land occupation. From a process perspective, this system has a wider scope of application and can flexibly match the hydrogen-hydrocarbon ratio according to the upstream cracking process, and is even applicable to hydrogen-free recycling, which helps to improve the single-pass conversion rate of the cracking process. From an energy consumption perspective, the specific energy consumption of the system does not exceed 15.4 kWh / kg of liquid hydrogen, reducing the total energy consumption of the two independent processes by about 30%, solving the problem of high energy consumption in PDH cryogenic separation and hydrogen liquefaction, and significantly reducing the co-production cost of propane dehydrogenation to propylene and liquid hydrogen.

[0100] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A system for the cryogenic separation and hydrogen liquefaction of propane dehydrogenation products to produce propylene, characterized in that: It comprises a normal pressure cold box, a hydrogen compression unit, a mixed refrigerant compression unit and a vacuum cold box; the normal pressure cold box utilizes the vaporization latent heat of the propane raw material and the cooling capacity provided by the multi-stage throttling of the mixed refrigerant to perform deep cold separation on the cracking product from the cracking unit to obtain the target propane / propylene product and hydrogen-rich gas; the hydrogen compression unit receives the hydrogen refrigerant after decompression and reheating from the normal pressure cold box, compresses and cools the hydrogen refrigerant to form a hydrogen refrigeration cycle; the mixed refrigerant compression unit receives the mixed refrigerant after decompression and reheating from the normal pressure cold box, compresses and cools the mixed refrigerant to form a mixed refrigerant refrigeration cycle; the vacuum cold box receives the hydrogen-rich gas from the normal pressure cold box, separates, purifies and cools the hydrogen-rich gas by utilizing the hydrogen cycle refrigeration to obtain the target liquid hydrogen; The atmospheric cold box includes a primary heat exchanger, a primary separation tank for raw gas, a secondary separation tank for raw gas, a tertiary separation tank for raw gas, a quaternary separation tank for raw gas and a cryogenic pump; the vacuum cold box includes a secondary heat exchanger, a tertiary heat exchanger, a primary separation tank for cryogen hydrogen, a secondary separation tank for cryogen hydrogen, a primary separation tank for rich hydrogen, a secondary separation tank for rich hydrogen, a tertiary separation tank for rich hydrogen, a cryogenic purifier and an isothermal converter; the upstream propane raw material provides cooling capacity for the atmospheric cold box through a four-stage throttling method in the primary heat exchanger; the mixed refrigerant in the mixed refrigerant compression unit provides cooling capacity for the atmospheric cold box through a three-stage throttling method; the upstream cracking product is cooled in the primary heat exchanger and then flashed in the primary separation tank for raw gas and the tertiary separation tank for raw gas in turn; the hydrogen-rich gas obtained at the top outlet of the primary separation tank for raw gas and the tertiary separation tank for raw gas is cooled in the secondary heat exchanger , the bottom outlet liquid phase is throttled to the secondary separation tank of raw gas; the liquid phase at the bottom outlet of the secondary separation tank of raw gas is pressurized by a cryogenic pump and then goes to the downstream as a propane / propylene product, and the top outlet gas phase goes to the fourth-stage separation tank of raw gas, flashes to obtain low-pressure hydrogen-rich gas and goes to the downstream to recover hydrogen; the hydrogen-rich gas cooled in the secondary heat exchanger is flashed in the hydrogen-rich primary separation tank, the hydrogen-rich secondary separation tank and the hydrogen-rich tertiary separation tank in turn, and then enters the low-temperature purifier for purification to obtain high-purity hydrogen; the liquid at the bottom outlet of the hydrogen-rich primary separation tank and the hydrogen-rich secondary separation tank is throttled and reheated to obtain methane-rich gas; the liquid at the bottom outlet of the hydrogen-rich tertiary separation tank is throttled and reheated to obtain nitrogen-rich gas; the high-purity hydrogen is returned to the secondary heat exchanger for cooling and then throttled to the isothermal converter for normal-parahydrogen conversion; the converted high-purity hydrogen is liquefied in the tertiary heat exchanger and then decompressed to go to the liquid hydrogen storage tank; The hydrogen compression unit comprises a low-pressure hydrogen compressor, a medium-pressure hydrogen aftercooler, a medium-pressure hydrogen compressor and a high-pressure hydrogen aftercooler; the refrigerant hydrogen compressed and cooled by the hydrogen compression unit is cooled in the primary heat exchanger and the secondary heat exchanger in turn and then divided into two paths, one path is expanded and cooled in the primary expander and the secondary expander in turn, and the other path is cooled and liquefied and then throttled to go to the refrigerant hydrogen primary separation tank; the liquid phase at the bottom outlet of the refrigerant hydrogen primary separation tank is divided into two paths, one path is provided for the isothermal converter to vaporize and then merge with the gas phase at the top outlet of the refrigerant hydrogen primary separation tank and the gas phase at the secondary expander outlet to be reheated and returned to the inlet of the medium-pressure hydrogen compressor, and the other path is throttled to go to the refrigerant hydrogen secondary separation tank; the liquid phase at the bottom outlet of the refrigerant hydrogen secondary separation tank is provided for the tertiary heat exchanger to vaporize and then merge with the gas phase at the top outlet of the refrigerant hydrogen secondary separation tank to be reheated and returned to the inlet of the low-pressure hydrogen compressor, forming a hydrogen refrigeration cycle.

2. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene according to claim 1, characterized in that: The upstream propane feedstock provides cooling capacity for the atmospheric cold box through a four-stage throttling method in the primary heat exchanger, as follows: The upstream propane feedstock is divided into two branches after heat exchange through the first hot side inlet of the primary heat exchanger, one branch continues to enter the second hot side inlet of the primary heat exchanger for heat exchange, and the other branch enters the primary heat exchanger through the propane primary throttle valve; The second hot side outlet of the first-stage heat exchanger is divided into two branches, one branch continues to enter the third hot side inlet of the first-stage heat exchanger for heat exchange, and the other branch enters the first-stage heat exchanger through the propane secondary throttle valve; The third hot side outlet of the first-stage heat exchanger is divided into two branches, one branch continues to enter the fourth hot side inlet of the first-stage heat exchanger through a pipeline for heat exchange, and the other branch enters the first-stage heat exchanger through a propane third-stage throttle valve; The fourth hot side outlet of the primary heat exchanger enters the primary heat exchanger through a propane fourth-stage throttle valve.

3. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene according to claim 2, characterized in that: The mixed refrigerant compression unit includes a low-pressure MR compressor, a medium-pressure MR aftercooler, an MR primary separation tank, a medium-pressure MR compressor, a high-pressure MR aftercooler and an MR secondary separation tank; the mixed refrigerant in the mixed refrigerant compression unit adopts a three-stage throttling method to provide cooling capacity for the atmospheric pressure cold box, as follows: The low-pressure MR compressor receives the mixed refrigerant from the primary heat exchanger in the atmospheric cold box; the outlet of the low-pressure MR compressor is connected to the inlet of the MR primary separation tank through a pipeline provided with a medium-pressure MR aftercooler; the gas phase space at the top of the MR primary separation tank is connected to the inlet of the MR secondary separation tank through pipelines provided with a medium-pressure MR compressor and a high-pressure MR aftercooler in sequence; the gas phase space at the top and the liquid phase space at the bottom of the MR secondary separation tank are respectively connected to the tenth hot side inlet and the ninth hot side inlet of the primary heat exchanger through pipelines; the liquid phase space at the bottom of the MR primary separation tank is connected to the eighth hot side inlet of the primary heat exchanger through a pipeline; The tenth hot side outlet of the first-stage heat exchanger is connected to the fourth cold side inlet of the first-stage heat exchanger through a pipeline provided with an MR first-stage throttle valve; the ninth hot side outlet of the first-stage heat exchanger is connected to the fifth cold side inlet of the first-stage heat exchanger after being converged by a pipeline provided with an MR second-stage throttle valve and a pipeline of the fourth cold side outlet of the first-stage heat exchanger; the eighth hot side outlet of the first-stage heat exchanger is connected to the sixth cold side inlet of the first-stage heat exchanger after being converged by a pipeline provided with an MR third-stage throttle valve and a pipeline of the fifth cold side outlet of the first-stage heat exchanger; the sixth cold side of the first-stage heat exchanger is provided with a pipeline for transporting the mixed refrigerant to the low-pressure MR compressor, forming a mixed refrigerant refrigeration cycle.

4. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene according to claim 3, characterized in that: The first-stage heat exchanger, the second-stage heat exchanger and the third-stage heat exchanger are all aluminum plate-fin heat exchangers.

5. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene according to claim 3, characterized in that: The low-temperature purifier adopts a low-temperature purifier of a two-tower pressure swing adsorption device, and the adsorption tower is filled with molecular sieve or activated carbon to remove nitrogen and methane impurities in the raw gas.

6. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene according to claim 3, characterized in that: The product hydrogen channels of the secondary heat exchanger and the tertiary heat exchanger are filled with ortho-para-hydrogen conversion catalysts with corresponding catalytic properties according to the refrigeration temperature zone.

7. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene products according to claim 3, characterized in that: The isothermal converter adopts a shell-and-tube structure, the tube side is filled with a normal-parahydrogen conversion catalyst with corresponding catalytic performance, and the shell side is a liquid hydrogen bath.

8. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene products according to claim 6 or 7, characterized in that: The ortho-parahydrogen conversion catalyst is any one or a combination of ferric hydroxide, hydrous ferric oxide, and ferric oxide in the crystal form of α-Fe2O3, β-Fe2O3, and γ-Fe2O3.

9. The system for cryogenic separation and hydrogen liquefaction of propane dehydrogenation to produce propylene according to claim 1, characterized in that: The mixed refrigerant consists of 10-15 mol% methane, 28-33 mol% ethylene, 28-33 mol% propane, 2-7 mol% isopentane and 18-23 mol% nitrogen.

10. A method for co-production of cryogenic separation and hydrogen liquefaction of propylene products from propane dehydrogenation, which utilizes the co-production system of claim 3, characterized in that: The specific steps are as follows: S1: The propane raw material from the upstream enters the primary heat exchanger, and after the four-stage throttling gasification in the primary heat exchanger, the obtained propane vapor is transported to the downstream cracking unit through a pipeline; the mixed refrigerant refrigeration cycle adopts a three-stage throttling method; the propane gasification and mixed refrigerant refrigeration cycle provide cooling capacity for the atmospheric pressure cold box; S2: The cracking product from the cracking unit is used as raw gas, which enters the primary heat exchanger through a pipeline for cooling, and then enters the primary separation tank of the raw gas; the liquid phase at the bottom of the primary separation tank of the raw gas enters the secondary separation tank of the raw gas after throttling, and the gas phase at the top of the primary separation tank of the raw gas returns to the primary heat exchanger for cooling, and then enters the tertiary separation tank of the raw gas; the hydrogen-rich gas at the top of the tertiary separation tank of the raw gas returns to the primary heat exchanger for cooling, and then leaves the atmospheric pressure cold box through a pipeline and enters the secondary heat exchanger in the vacuum cold box; the propane / propylene liquid at the bottom of the secondary separation tank of the raw gas is pressurized by a cryogenic pump, reheated by the primary heat exchanger, and then passes through a pipeline to the downstream; S3: After the hydrogen-rich gas enters the secondary heat exchanger for cooling, it enters the hydrogen-rich primary separation tank; after the gas phase at the top of the hydrogen-rich primary separation tank passes through the secondary heat exchanger for cooling, it enters the hydrogen-rich secondary separation tank; after the liquid phase at the bottom of the hydrogen-rich secondary separation tank and the liquid phase at the bottom of the hydrogen-rich primary separation tank pass through the secondary heat exchanger and the primary heat exchanger for reheating in turn, the methane-rich gas therein is connected to the downstream through a pipeline; after the gas phase at the top of the hydrogen-rich secondary separation tank passes through the secondary heat exchanger for cooling, it enters the hydrogen-rich tertiary separation tank; The liquid nitrogen at the bottom of the hydrogen-rich three-stage separation tank is reheated in the secondary heat exchanger and the primary heat exchanger in turn to become nitrogen-rich gas, and the nitrogen-rich gas is connected to the downstream through a pipeline; the gas phase at the top of the hydrogen-rich three-stage separation tank is purified by a low-temperature purifier, and then enters the secondary heat exchanger for cooling, and the para-hydrogen content is increased under the action of the normal-para-hydrogen conversion catalyst to obtain raw hydrogen; the raw hydrogen enters the isothermal converter after throttling and pressure reduction, and the para-hydrogen content is increased under the action of the normal-para-hydrogen conversion catalyst in the isothermal converter; then the raw hydrogen enters the three-stage heat exchanger to be cooled to complete liquefaction, and the para-hydrogen content is increased under the action of the normal-para-hydrogen conversion catalyst; finally, it is throttled and cooled to the target temperature and pressure and then connected to the liquid hydrogen storage tank.

11. The method for co-production of cryogenic separation and hydrogen liquefaction of the product of propylene produced by dehydrogenation of propane according to claim 10, characterized in that: The parameters of the propane raw material are 40°C and 1.9MPa; the temperatures of the propane raw material before the four-stage throttling in the primary heat exchanger are -15~-35°C, -50~-60°C, -75~-95°C and -100~-120°C respectively; the maximum operating pressure of the mixed refrigerant refrigeration cycle is 4~4.5MPa, and the temperatures before the three-stage throttling are -15~-35°C, -65~-85°C and -140~-160°C respectively; The parameters of the cracking product are 40°C and 2.1MPa. The cracking product is cooled to -25~-45°C in the primary heat exchanger; the gas phase at the top of the primary separation tank of the raw gas is refluxed to the primary heat exchanger and cooled to -110~-120°C, and then enters the third-stage separation tank of the raw gas; the hydrogen-rich gas at the top of the third-stage separation tank of the raw gas is refluxed to the primary heat exchanger and cooled to -165~-170°C, and then leaves the atmospheric pressure cold box and goes to the vacuum cold box; The hydrogen-rich gas is cooled to -170~-173°C by the secondary heat exchanger and then enters the hydrogen-rich primary separation tank; the gas phase at the top of the hydrogen-rich primary separation tank is cooled to -175~-180°C by the secondary heat exchanger and then enters the hydrogen-rich secondary separation tank; The gas phase at the top of the hydrogen-rich secondary separation tank is cooled to -205~-208°C by the secondary heat exchanger and then enters the hydrogen-rich tertiary separation tank; The purity of the hydrogen purified by the cryogenic purifier is not less than 99.99%; the purified hydrogen is cooled to -250°C in the secondary heat exchanger, and the para-hydrogen content is increased from 25% to more than 85% under the action of the normal-para-hydrogen conversion catalyst; The raw hydrogen is throttled and depressurized to 0.2-0.7 MPa, and then enters the isothermal converter, where the para-hydrogen content is increased to more than 95% under the action of the normal-para-hydrogen conversion catalyst; the raw hydrogen is increased to more than 98% under the action of the normal-para-hydrogen conversion catalyst in the three-stage heat exchanger.

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