Ethylene cracking gas separation system, its use and ethylene cracking gas separation method

Abstract

The application belongs to the technical field of synthesis gas separation, and particularly relates to an ethylene cracking gas separation system and application thereof and an ethylene cracking gas separation method. The system comprises, in sequence, a quenching unit, a compression separation unit and a re-separation unit, which are used for separating a separated liquid phase, hydrogen-poor gas and product hydrogen from ethylene cracking gas; wherein the compression separation unit comprises a plurality of hydrogen separation membrane units. In the application, the hydrogen separation membrane unit is coupled with the compression section, the membrane-passing pressure of the material is provided by the compression section, the separation energy is reduced, and the hydrogen yield and hydrogen purity are improved.

Description

Technical Field

[0001] This invention belongs to the field of syngas separation technology, specifically relating to an ethylene cracking gas separation system and its application, and an ethylene cracking gas separation method. Background Technology

[0002] The ethylene industry is the core of the petrochemical industry, accounting for over 75% of petrochemical products and holding a vital position in the national economy. Ethylene is typically produced using the cracking method. However, ethylene cracking gas contains a large amount of hydrogen, which reduces the yield of ethylene. Therefore, removing hydrogen from the cracking gas is crucial for ethylene purification. Hydrogen, as one of the main byproducts of ethylene cracking, can be used as a feedstock for alkyne hydrogenation, downstream gasoline hydrogenation, a blending agent in polyethylene or polypropylene production, a feedstock for oil refining hydrogenation, and even as fuel cell gas after drying and methanation. The separated hydrogen has significant economic value. Currently, the hydrogen yield in the ethylene industry is less than 90%, indicating room for resource optimization.

[0003] Improving the hydrogen yield from ethylene cracking gas to produce high-quality, high-purity, and high-value-added hydrogen products can bring considerable benefits to the ethylene industry. Currently, the ethylene industry typically uses a cold box to heat the cracking gas to 160°C, then separates the hydrogen from other components. The separated hydrogen requires further heat exchange to recover the cold energy, a process that inevitably results in significant energy loss. How to increase hydrogen yield and produce high-quality hydrogen products while reducing energy consumption remains a challenge for the ethylene industry. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of high separation energy consumption, low hydrogen yield and purity in the existing technology, and to provide an ethylene cracking gas separation system and its application and ethylene cracking gas separation method.

[0005] In this invention, by coupling the hydrogen separation membrane unit with the compression section, the compression section provides the material's transmembrane pressure, which reduces the separation energy and simultaneously improves the hydrogen yield and purity.

[0006] To achieve the above objectives, a first aspect of the present invention provides an ethylene cracking gas separation system, characterized in that the system comprises: a quenching unit, a compression separation unit, and a re-separation unit connected in sequence, for separating heavy hydrocarbons, lean hydrogen gas, and product hydrogen from the ethylene cracking gas; wherein...

[0007] The compression separation unit includes multiple hydrogen separation membrane units.

[0008] The second aspect of the present invention provides an application of the system described in the first aspect of the present invention in the separation of ethylene cracking gas.

[0009] The third aspect of the present invention provides a method for separating ethylene cracked gas, characterized in that, under separation conditions, the gas to be separated is introduced into the system described in the first aspect of the present invention for separation to obtain a separated liquid phase, a hydrogen-poor gas and product hydrogen.

[0010] Through the above technical solutions, the beneficial effects of the ethylene cracking gas separation system and its application, and the ethylene cracking gas separation method provided by the present invention are as follows:

[0011] Using the technical solution of this invention, membrane separation dehydrogenation can remove 98% of the hydrogen from ethylene cracking gas, and the hydrogen concentration of the separated product is greater than 98%. The transmembrane pressure provided by the compression section reduces energy consumption while greatly improving hydrogen yield and purity.

[0012] The membrane separation process does not require additional heat exchange and heating. The high outlet temperature of the compression section helps to improve the permeation rate. Even if the material components are in a gaseous state, there is no need to worry about the negative impact of water on the membrane.

[0013] Membrane separation technology is gentle, energy-efficient, and highly efficient. Membrane modules have a small footprint and can be easily optimized based on existing equipment. Attached Figure Description

[0014] Figure 1 This is a flow chart of the ethylene cracking gas separation system of the present invention;

[0015] Figure 2 This is a process flow diagram of the ethylene cracking gas separation system in Example 1;

[0016] Figure 3 This is a process flow diagram of the ethylene cracking gas separation system in Example 2;

[0017] Figure 4 This is a process flow diagram of the ethylene cracking gas separation system in Example 3;

[0018] Figure 5 This is a process flow diagram of the ethylene cracking gas separation system in Example 4.

[0019] Explanation of reference numerals in the attached figures

[0020] A1 - First compression stage; A2 - Second compression stage, A3 - Third compression stage, A4 - Fourth compression stage, A5 - Fifth compression stage, G1 - Gas-liquid separator in the first sub-compression separation unit, G2 - Gas-liquid separator in the second sub-compression separation unit, G3 - Gas-liquid separator in the third sub-compression separation unit, G4 - Gas-liquid separator in the fourth sub-compression separation unit, G5 - Gas-liquid separator in the fifth sub-compression separation unit, MEM1 - Hydrogen separation membrane unit in the first sub-compression separation unit, MEM2 - Hydrogen separation membrane unit in the second sub-compression separation unit, MEM3 - Hydrogen separation membrane unit in the third sub-compression separation unit, MEM4 - Hydrogen separation membrane unit in the fourth sub-compression separation unit. Gas separation membrane unit, MEM5 - hydrogen separation membrane unit in the 5th sub-compression separation unit, MEM6 - first hydrogen purification device in the re-separation unit, MEM7 - second hydrogen purification device in the re-separation unit, C1 - heat exchanger in the 2nd sub-compression separation unit, C2 - heat exchanger in the 3rd sub-compression separation unit, C3 - heat exchanger in the 4th sub-compression separation unit, C4 - heat exchanger in the 5th sub-compression separation unit, ZC1 - first heat exchanger in the re-separation unit, ZC2 - second heat exchanger in the re-separation unit, E1 - first compression device in the re-separation unit, E2 - second compression device in the re-separation unit, Z - re-separation unit, W - alkaline washing unit, J - Quenching unit, M1 - first mixer, M2 - second mixer, M3 - first mixer, S0 - separated liquid phase in the first sub-compression separation unit, S18 - separated liquid phase in the second sub-compression separation unit, S21 - separated liquid phase in the third sub-compression separation unit, S1 - separated gas phase in the first sub-compression separation unit, S17 - separated gas phase in the second sub-compression separation unit, S20 - separated gas phase in the third sub-compression separation unit, S3 - permeate gas obtained from the hydrogen separation membrane unit in the first sub-compression separation unit, S6 - permeate gas obtained from the hydrogen separation membrane unit in the second sub-compression separation unit, S4 - permeate gas obtained from the hydrogen separation membrane unit in the first sub-compression separation unit. S7 - Permeate gas obtained from the hydrogen separation membrane unit in the second sub-compression separation unit; S10 - Permeate gas obtained from the hydrogen separation membrane unit in the third sub-compression separation unit; S2 - First compressed gas; S5 - Second compressed gas; S8 - Third compressed gas; S9 - Hydrogen-lean gas; S14 - Product hydrogen; S15 - Gas to be compressed; S30 - Permeate gas; S31 - Secondary purified gas; S11 - Collected permeate gas; S12 - Purified gas; S13 - Return gas obtained from the first hydrogen purification unit; S23 - Return gas obtained from the second hydrogen purification unit; S16 - Gas-liquid mixture obtained from the heat exchanger in the second sub-compression separation unit; S19 - Gas-liquid mixture obtained from the heat exchanger in the second sub-compression separation unit. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of this invention provides an ethylene cracking gas separation system, characterized in that the system comprises: a quenching unit, a compression separation unit, and a re-separation unit connected in sequence, for separating heavy hydrocarbons, lean hydrogen gas, and product hydrogen from the ethylene cracking gas; wherein,

[0023] The compression separation unit includes multiple hydrogen separation membrane units.

[0024] According to the present invention, the compression separation unit further includes a compressor having n compression sections; wherein, corresponding to the n compression sections, the compression separation unit is provided with n sub-compression separation units, where n is an integer greater than or equal to 1.

[0025] In this invention, the pressure required by the sub-compression separation unit can be directly provided by the compression section within that unit. Compared to traditional processes, embedding polymer membrane technology into the sub-compression separation unit significantly improves hydrogen yield, enabling the recovery of the vast majority of hydrogen from the cracked gas. The recovered and purified hydrogen is collected and stored as product hydrogen or used in hydrogenation units. This also substantially reduces the load on subsequent cryogenic units. The higher compressor outlet temperature greatly enhances the permeation rate, and the gaseous state of the components eliminates concerns about the negative impact of water on the membrane. Membrane technology is gentle, energy-efficient, and highly efficient; the membrane module has a small footprint and can be directly optimized from existing equipment.

[0026] In this invention, preferably, the number n of compression sections in the compressor is 1-5.

[0027] According to the present invention, in the compression separation unit, the first sub-compression separation unit includes: a gas-liquid separator, a first compression section, and an optional hydrogen separation membrane unit connected in sequence; the (x+1)th sub-compression separation unit includes: a heat exchanger, a gas-liquid separator, the (x+1)th compression section, and an optional hydrogen separation membrane unit connected in sequence, wherein x is an integer greater than or equal to 1.

[0028] In this invention, the use of n and x does not limit the technical solution, wherein the total number of sub-compression separation units is equal to the total number of compression sections.

[0029] According to the present invention, when the sub-compression separation unit does not include the hydrogen separation membrane unit, the outlet of the xth compression section is connected to the inlet of the heat exchanger in the (x+1)th sub-compression separation unit;

[0030] When the sub-compression separation unit includes the hydrogen separation membrane unit, the hydrogen separation membrane unit in the xth sub-compression separation unit is used to perform gas separation to obtain the xth residual gas and the xth permeate gas; and the hydrogen separation membrane unit in the xth sub-compression separation unit is connected to the heat exchanger in the (x+1)th sub-compression separation unit, and is used to send the xth residual gas into the heat exchanger in the (x+1)th sub-compression separation unit.

[0031] In this invention, "permeate gas" refers to the gas in the separation device that does not permeate through the separation membrane; "permeate gas" refers to the gas in the separation device that permeates through the separation membrane, and the same applies below.

[0032] According to the present invention, the re-separation unit includes m hydrogen purification devices for separating the collected permeate gas formed by the combined permeate gas obtained from each hydrogen separation membrane unit, to obtain product hydrogen and reflux gas, where m is a positive integer; wherein,

[0033] When m≥2, m hydrogen purification devices are connected in series. The purified permeate gas separated by the (m-1)th hydrogen purification device is sent to the mth hydrogen purification device. The collected permeate gas is separated by the m hydrogen purification devices in sequence to obtain the product hydrogen and m streams of reflux gas.

[0034] The reflux gas is mixed with the separated gas phase obtained by the gas-liquid separator in the first sub-compression and separation unit, and then sent to the first compression section.

[0035] In this invention, the re-separation unit described above has the following advantages: it further purifies hydrogen and yields the target high-purity hydrogen.

[0036] According to the present invention, the re-separation unit further includes a compression heat exchange unit, which includes a compression device and a heat exchange device connected in sequence, and is used to compress and heat the material fed into the hydrogen purification device.

[0037] According to the present invention, the separation coefficient of H2 and CH4 of the separation membrane provided in the hydrogen separation membrane unit is 150-800.

[0038] According to the present invention, the separation coefficient of H2 and CH4 of the separation membrane provided in the re-separation unit is 150-800.

[0039] According to the present invention, the separation membranes respectively provided in the hydrogen separation membrane unit and the re-separation unit are each independently selected from at least one of polysulfone membrane, polyethersulfone membrane, polyimide membrane, polypropylene membrane, polyethylene membrane, synthetic resin membrane, polyvinylidene fluoride membrane, polytetrafluoroethylene membrane, polyetheretherketone membrane, polybenzimidazole membrane, cellulose acetate membrane, polycarbonate membrane, polymethyl methacrylate membrane, silica membrane, zeolite molecular sieve membrane and carbon molecular sieve membrane.

[0040] In this invention, the separation membranes in the hydrogen separation membrane unit and the re-separation unit are selected from at least one of homogeneous membranes, heterogeneous membranes, and composite membranes. The separation membranes in the hydrogen separation membrane unit and the re-separation unit are selected from at least one of spiral wound membranes, hollow fiber membranes, flat sheet membranes, and tubular membranes.

[0041] The second aspect of the present invention provides an application of the system described in the first aspect of the present invention in the separation of ethylene cracking gas.

[0042] The third aspect of the present invention provides a method for separating ethylene cracked gas, characterized in that, under separation conditions, the gas to be separated is introduced into the system described in the first aspect of the present invention for separation to obtain a separated liquid phase, a hydrogen-poor gas and product hydrogen.

[0043] According to the present invention, the separation conditions include a membrane pressure of 0.15-4 MPa. Preferably, the membrane separation temperature in the present invention is 80-120°C.

[0044] The following is in conjunction with the present invention Figure 1 and Figure 2 The process flow of this invention is briefly described below:

[0045] Figure 1 This is a flow chart of the ethylene cracking gas separation system of the present invention. Figure 1 As can be seen, a typical pyrolysis gas compressor is a five-stage compression unit (i.e., the compression separation unit includes five sub-compression separation units; where corresponds to five compression stages). By progressively increasing the pressure of the ethylene pyrolysis gas, the ethylene pyrolysis gas is processed by the quench unit J to obtain quench gas, which is then processed sequentially through each sub-compression separation unit. An alkaline scrubbing unit can be installed between the third and fourth sub-compression separation units to remove acidic gases from the gas mixture. A hydrogen separation membrane unit can optionally be installed after the outlet of the compression stage. The permeate obtained from the hydrogen separation membrane unit is then heat-exchanged before entering the next sub-compression separation unit.

[0046] Figure 2 , Figure 3 , Figure 4 and Figure 5 This is a process flow diagram of the ethylene cracking gas separation system in the embodiment.

[0047] In this invention, the number of sub-compression and separation units can be set according to process conditions. Taking three sub-compression and separation units as an example, after the ethylene cracking gas is processed by the quench unit J, quench gas is obtained. After the quench gas is processed by the gas-liquid separator G1 in the first sub-compression and separation unit, separated gas phase S1 and separated liquid phase S0 are obtained. The separated gas phase S1 and the reflux gas obtained from the re-separation unit Z are mixed by the second mixer M2 to obtain the gas to be compressed S15. The gas to be compressed S15 is compressed by the first compression section A1 in the first sub-compression and separation unit and then discharged as the first compressed gas S2. The discharged first compressed gas S2 can be directly sent to the heat exchanger C1 in the second sub-compression and separation unit for cooling, and then sent to the gas-liquid separator G2 in the second sub-compression and separation unit for processing (e.g., Figure 3 and Figure 5 (as shown); or, the first compressed gas S2 is fed into the hydrogen separation membrane unit MEM1 in the first sub-compression separation unit for separation. After the first compressed gas S2 is separated by the hydrogen separation membrane unit MEM1 in the first sub-compression separation unit, permeate gas S3 and permeate gas S4 (as shown) are obtained. Figure 2 and Figure 4 (As shown).

[0048] The permeate gas S3 obtained from the hydrogen separation membrane unit MEM1 in the first sub-compression separation unit is cooled by the heat exchanger C1 in the second sub-compression separation unit to obtain a gas-liquid mixture S16. This gas-liquid mixture S16 is then processed by the gas-liquid separator G2 in the second sub-compression separation unit to obtain a separated gas phase S17 and a separated liquid phase S18. The separated gas phase S17 is then compressed by the second compression section A2 in the second sub-compression separation unit, and a second compressed gas S5 is discharged. The second compressed gas S5 is then separated by the hydrogen separation membrane unit MEM2 in the second sub-compression separation unit to obtain permeate gas S6 and permeate gas S7.

[0049] The permeate gas S6 obtained from the hydrogen separation membrane unit MEM2 in the second sub-compression separation unit is cooled by the heat exchanger C2 in the third sub-compression separation unit to obtain a gas-liquid mixture S19. The gas-liquid mixture S19 is processed by the gas-liquid separator G3 in the third sub-compression separation unit to obtain a separated gas phase S20 and a separated liquid phase S21. The separated gas phase S20 is compressed by the third compression section A3 in the third sub-compression separation unit and discharged as a third compressed gas S8. The third compressed gas S8 is separated by the hydrogen separation membrane unit MEM3 in the third sub-compression separation unit to obtain a hydrogen-lean gas S9 and a permeate gas S10. The hydrogen-lean gas S9 enters the alkaline washing unit W for further processing.

[0050] The permeate gas separated by the hydrogen separation membrane unit in each sub-compression and separation unit is mixed by the first mixer M1 to obtain the collected permeate gas S11. The collected permeate gas S11 is pressurized by the first compression device E1 in the re-separation unit, and then heat-exchanged by the first heat exchange device ZC1 in the re-separation unit to obtain the gas to be purified S12.

[0051] When there is only one hydrogen purification unit, the first heat exchanger MEM6 in the re-separation unit is used to separate the gas to be purified S12, obtaining the product hydrogen S14 and the reflux gas S13 obtained from the first hydrogen purification unit (e.g., Figure 2 and Figure 3 (As shown in the attached diagram). When there are multiple hydrogen purification devices, they are connected sequentially, as can be seen from the attached diagram (e.g.). Figure 4 and Figure 5 The first hydrogen purification unit MEM6 on the left separates the gas to be purified, S12, to obtain reflux gas S13 and purified permeate gas S30 from the first hydrogen purification unit. The purified permeate gas S30 is then processed by the second compression unit E2 and the second heat exchanger ZC2 in the re-separation unit to obtain secondary gas to be purified, S31. The secondary gas to be purified, S31, is then processed by the second hydrogen purification unit MEM7 to obtain reflux gas S23 and product hydrogen S14. The collected permeate gas S11 is then separated by multiple hydrogen purification units to obtain product hydrogen S14 and multiple streams of reflux gas. The multiple streams of reflux gas are mixed by the third mixer M3 and then sent to the second mixer M2 to mix with the separated gas phase S1 in the first sub-compression and separation unit.

[0052] The present invention will be described in detail below through embodiments.

[0053] Example 1

[0054] The components of the ethylene cracked gas entering the quench unit are: hydrogen, methane, ethylene, ethane, propane, n-butane, carbon monoxide, n-hexane, benzene, toluene, and water, with volume percentages of 15.12%, 23.66%, 29.48%, 6.28%, 8.98%, 4.33%, 0.22%, 2.04%, 2.44%, 2.06%, and 5.38%, respectively; the inlet flow rate is 4000 Nm³. 3 / h.

[0055] The separation membrane in the hydrogen separation membrane unit and the separation membrane in the hydrogen purification device are selected from PBI hollow fiber membranes, with a separation coefficient of 200 for H2 and CH4.

[0056] The hydrogen purification unit consists of one unit. The composition of each stream in the system is shown in Table 1. The specific method is as follows: from... Figure 2 As can be seen from the above, ethylene cracked gas is processed by a quench unit to obtain quenched gas.

[0057] After the quenched gas is processed by the gas-liquid separator in the first sub-compression and separation unit, a separated gas phase S1 and a separated liquid phase S0 are obtained. The separated gas phase S1 and the reflux gas separated by the hydrogen purification device MEM4 are mixed by the second mixer M2 to obtain the gas to be compressed S15.

[0058] After the compressed gas S15 is compressed in the compression section of the first sub-compression separation unit, the pressure increases from 50 kPa to 206 kPa and the temperature rises from 42°C to 92°C, and the first compressed gas S2 is discharged.

[0059] After the first compressed gas S2 is separated by the hydrogen separation membrane unit in the first sub-compression separation unit, a permeate gas S3 with a hydrogen concentration of 17% and a permeate gas S4 with a hydrogen concentration of 35% are obtained. After the permeate gas S3 is cooled by a heat exchanger, a gas-liquid mixture S16 is obtained.

[0060] After the gas-liquid mixture S16 is processed by the gas-liquid separator in the second sub-compression and separation unit, the separated gas phase S17 and the separated liquid phase S18 are obtained.

[0061] After the separated gas phase S17 is compressed in the compression section of the second sub-compression separation unit, the pressure reaches 492 kPa, and the second compressed gas S5 is discharged.

[0062] The second compressed gas S5 is separated by the hydrogen separation membrane unit in the second sub-compression separation unit to obtain permeate gas S6 with a hydrogen concentration of 11% and permeate gas S7 with a hydrogen concentration of 66.97%. After being cooled by a heat exchanger, permeate gas S6 is obtained as a gas-liquid mixture S19.

[0063] After the gas-liquid mixture S19 is processed by the gas-liquid separator in the third sub-compression and separation unit, the separated gas phase S20 and the separated liquid phase S21 are obtained.

[0064] After the separated gas phase S20 is compressed in the compression section of the third sub-compression separation unit, the pressure reaches 983 kPa, and the third compressed gas S8 is discharged. After the third compressed gas S8 is separated by the hydrogen separation membrane unit in the third sub-compression separation unit, a hydrogen-lean gas S9 with a hydrogen concentration of 0.87% and a permeate gas S10 with a hydrogen concentration of 40% are obtained. S9 enters the alkaline washing unit for treatment.

[0065] Permeate gas S4, permeate gas S7 and permeate gas S10 are mixed by the first mixer M1 to obtain collected permeate gas S11. Collected permeate gas S11 is pressurized by the compression device E1 in the compression heat exchange unit, and then heat exchanged by the heat exchange device to obtain purified gas S12 with a pressure of 600 kPa.

[0066] After the purified gas S12 is purified by the hydrogen purification device, product hydrogen S14 with a hydrogen concentration of 98% and reflux gas S13 with a hydrogen concentration of 48% are obtained. The hydrogen recovery rate in the system is 95%.

[0067] Example 2

[0068] The components of the ethylene cracked gas entering the quench unit are: hydrogen, methane, ethylene, ethane, propane, n-butane, carbon monoxide, n-hexane, benzene, toluene, and water, with volume percentages of 16.08%, 28.71%, 24.97%, 7.74%, 6.36%, 3.54%, 0.22%, 2.13%, 2.60%, 2.23%, and 5.42%, respectively; the inlet flow rate is 4000 Nm³. 3 / h.

[0069] The separation membrane in the hydrogen separation membrane unit and the separation membrane in the hydrogen purification device are selected from PBI hollow fiber membranes, with a separation coefficient of 800 for H2 and CH4.

[0070] The hydrogen purification unit consists of one unit. The composition of each stream in the system is shown in Table 2. The specific method is as follows: from... Figure 3 As can be seen from the above, ethylene cracked gas is processed by a quench unit to obtain quenched gas.

[0071] After the quenched gas is processed by the gas-liquid separator in the first sub-compression and separation unit, a separated gas phase S1 and a separated liquid phase S0 are obtained. The separated gas phase S1 and the reflux gas separated by the hydrogen purification device MEM4 are mixed by the second mixer M2 to obtain the gas to be compressed S15.

[0072] After the compressed gas S15 is compressed in the compression section of the first sub-compression separation unit, the pressure increases from 50 kPa to 206 kPa and the temperature rises from 42°C to 92°C, and the first compressed gas S2 is discharged.

[0073] After the first compressed gas S2 is cooled by a heat exchanger, a gas-liquid mixture S16 is obtained.

[0074] After the gas-liquid mixture S16 is processed by the gas-liquid separator in the second sub-compression and separation unit, the separated gas phase S17 and the separated liquid phase S18 are obtained.

[0075] After the separated gas phase S17 is compressed in the compression section of the second sub-compression separation unit, the pressure reaches 492 kPa, and the second compressed gas S5 is discharged.

[0076] The second compressed gas S5 is separated by the hydrogen separation membrane unit in the second sub-compression separation unit to obtain permeate gas S6 with a hydrogen concentration of 11% and permeate gas S7 with a hydrogen concentration of 69%. After being cooled by a heat exchanger, permeate gas S6 yields a gas-liquid mixture S19.

[0077] After the gas-liquid mixture S19 is processed by the gas-liquid separator in the third sub-compression and separation unit, the separated gas phase S20 and the separated liquid phase S21 are obtained.

[0078] After the separated gas phase S20 is compressed in the compression section of the third sub-compression separation unit, the pressure reaches 983 kPa, and the third compressed gas S8 is discharged. After the third compressed gas S8 is separated by the hydrogen separation membrane unit in the third sub-compression separation unit, a hydrogen-lean gas S9 with a hydrogen concentration of 0.8% and a permeate gas S10 with a hydrogen concentration of 41% are obtained. S9 enters the alkaline washing unit for treatment.

[0079] After permeate gas S7 and permeate gas S10 are mixed by the first mixer M1, a collected permeate gas S11 is obtained. The collected permeate gas S11 is pressurized by the compression device E1 in the compression heat exchange unit, and then heat exchanged by the heat exchange device to obtain a purified gas S12 with a pressure of 600 kPa.

[0080] After the purified gas S12 is purified by the hydrogen purification device, product hydrogen S14 with a hydrogen concentration of 98% and reflux gas S13 with a hydrogen concentration of 50% are obtained. The hydrogen recovery rate in the system is 96%.

[0081] Example 3

[0082] The components of the ethylene cracked gas entering the quench unit are: hydrogen, methane, ethylene, ethane, propane, n-butane, carbon monoxide, n-hexane, benzene, toluene, and water, with volume percentages of 15.73%, 24.45%, 27.39%, 8.80%, 6.16%, 3.91%, 0.24%, 2.45%, 2.84%, 2.35%, and 5.67%, respectively; the inlet flow rate is 4000 Nm³. 3 / h.

[0083] The separation membrane in the hydrogen separation membrane unit and the separation membrane in the hydrogen purification device are selected from PBI hollow fiber membranes, with a separation coefficient of 230 for H2 and CH4.

[0084] The hydrogen purification unit consists of one unit. The composition of each stream in the system is shown in Table 3. The specific method is as follows: from... Figure 4 As can be seen from the above, ethylene cracked gas is processed by a quench unit to obtain quenched gas.

[0085] After the quenched gas is processed by the gas-liquid separator in the first sub-compression and separation unit, the separated gas phase S1 and the separated liquid phase S0 are obtained. The separated gas phase S1 and the reflux gas separated by the hydrogen purification devices MEM4 and MEM5 are mixed by the second mixer M2 to obtain the gas to be compressed S15.

[0086] After the compressed gas S15 is compressed in the compression section of the first sub-compression separation unit, the pressure increases from 50 kPa to 206 kPa and the temperature rises from 42°C to 92°C, and the first compressed gas S2 is discharged.

[0087] After the first compressed gas S2 is separated by the hydrogen separation membrane unit in the first sub-compression separation unit, residual gas S3 with a hydrogen concentration of 18% and permeate gas S4 with a hydrogen concentration of 37% are obtained; after the residual gas S3 is cooled by the heat exchanger, a gas-liquid mixture S16 is obtained.

[0088] After the gas-liquid mixture S16 is processed by the gas-liquid separator in the second sub-compression and separation unit, the separated gas phase S17 and the separated liquid phase S18 are obtained.

[0089] After the separated gas phase S17 is compressed in the compression section of the second sub-compression separation unit, the pressure reaches 492 kPa, and the second compressed gas S5 is discharged.

[0090] The second compressed gas S5 is separated by the hydrogen separation membrane unit in the second sub-compression separation unit to obtain permeate gas S6 with a hydrogen concentration of 11% and permeate gas S7 with a hydrogen concentration of 69%. After being cooled by a heat exchanger, permeate gas S6 yields a gas-liquid mixture S19.

[0091] After the gas-liquid mixture S19 is processed by the gas-liquid separator in the third sub-compression and separation unit, the separated gas phase S20 and the separated liquid phase S21 are obtained.

[0092] After the separated gas phase S20 is compressed in the compression section of the third sub-compression separation unit, the pressure reaches 983 kPa, and the third compressed gas S8 is discharged. After the third compressed gas S8 is separated by the hydrogen separation membrane unit in the third sub-compression separation unit, a hydrogen-lean gas S9 with a hydrogen concentration of 0.8% and a permeate gas S10 with a hydrogen concentration of 41% are obtained. S9 enters the alkaline washing unit for treatment.

[0093] Permeate gas S4, permeate gas S7 and permeate gas S10 are mixed by the first mixer M1 to obtain collected permeate gas S11. Collected permeate gas S11 is pressurized by the compression device E1 in the compression heat exchange unit, and then heat exchanged by the heat exchange device to obtain purified gas S12 with a pressure of 600 kPa.

[0094] After the gas to be purified, S12, is purified by the first hydrogen purification unit, a permeate gas, S30, with a hydrogen concentration of 98% and a reflux gas, S13, with a hydrogen concentration of 50% is obtained. The permeate gas, S30, is processed by the compression heat exchange unit to obtain a secondary gas to be purified, S31. The secondary gas to be purified, S31, is sent to the second hydrogen purification unit for purification to obtain product hydrogen, S14, with a hydrogen concentration of 99%. The hydrogen recovery rate in the system is 95%.

[0095] Example 4

[0096] The components of the ethylene cracked gas entering the quench unit are: hydrogen, methane, ethylene, ethane, propane, n-butane, carbon monoxide, n-hexane, benzene, toluene, and water, with volume percentages of 15.73%, 24.45%, 27.39%, 8.80%, 6.16%, 3.91%, 0.24%, 2.45%, 2.84%, 2.35%, and 5.67%, respectively; the inlet flow rate is 4000 Nm³. 3 / h.

[0097] The separation membrane in the hydrogen separation membrane unit and the separation membrane in the hydrogen purification device are selected from PI block copolymer mixed MOFs heterogeneous flat sheet membranes, with a separation coefficient of 150 for H2 and CH4.

[0098] The hydrogen purification unit consists of one unit. The composition of each stream in the system is shown in Table 4. The specific method is as follows: from... Figure 5 As can be seen from the above, ethylene cracked gas is processed by a quench unit to obtain quenched gas.

[0099] After the quenched gas is processed by the gas-liquid separator in the first sub-compression and separation unit, the separated gas phase S1 and the separated liquid phase S0 are obtained. The separated gas phase S1 and the reflux gas separated by the hydrogen purification devices MEM4 and MEM5 are mixed by the second mixer M2 to obtain the gas to be compressed S15.

[0100] After the compressed gas S15 is compressed in the compression section of the first sub-compression separation unit, the pressure increases from 50 kPa to 206 kPa and the temperature rises from 42°C to 92°C, and the first compressed gas S2 is discharged.

[0101] After the first compressed gas S2 is cooled by a heat exchanger, a gas-liquid mixture S16 is obtained.

[0102] After the gas-liquid mixture S16 is processed by the gas-liquid separator in the second sub-compression and separation unit, the separated gas phase S17 and the separated liquid phase S18 are obtained.

[0103] After the separated gas phase S17 is compressed in the compression section of the second sub-compression separation unit, the pressure reaches 492 kPa, and the second compressed gas S5 is discharged.

[0104] The second compressed gas S5 is separated by the hydrogen separation membrane unit in the second sub-compression separation unit to obtain permeate gas S6 with a hydrogen concentration of 11% and permeate gas S7 with a hydrogen concentration of 68%. After being cooled by a heat exchanger, permeate gas S6 yields a gas-liquid mixture S19.

[0105] After the gas-liquid mixture S19 is processed by the gas-liquid separator in the third sub-compression and separation unit, the separated gas phase S20 and the separated liquid phase S21 are obtained.

[0106] After the separated gas phase S20 is compressed in the compression section of the third sub-compression separation unit, the pressure reaches 983 kPa, and the third compressed gas S8 is discharged. After the third compressed gas S8 is separated by the hydrogen separation membrane unit in the third sub-compression separation unit, a hydrogen-lean gas S9 with a hydrogen concentration of 0.8% and a permeate gas S10 with a hydrogen concentration of 40% are obtained. S9 enters the alkaline washing unit for treatment.

[0107] After permeate gas S7 and permeate gas S10 are mixed by the first mixer M1, a collected permeate gas S11 is obtained. The collected permeate gas S11 is pressurized by the compression device E1 in the compression heat exchange unit, and then heat exchanged by the heat exchange device to obtain a purified gas S12 with a pressure of 600 kPa.

[0108] After the gas to be purified, S12, is purified by the first hydrogen purification unit, a permeate gas, S30, with a hydrogen concentration of 98% and a reflux gas, S13, with a hydrogen concentration of 49% is obtained. The permeate gas, S30, is processed by the compression heat exchange unit to obtain a secondary gas to be purified, S31. The secondary gas to be purified, S31, is sent to the second hydrogen purification unit for purification to obtain product hydrogen, S14, with a hydrogen concentration of 99.9%. The hydrogen recovery rate in the system is 95%.

[0109] Comparative Example 1

[0110] In existing technologies, dehydrogenation relies on cryogenic units. Although cold energy is recovered, cold energy loss is unavoidable during the cryogenic process. Removing hydrogen is crucial for improving ethylene yield. Traditional sequential separation processes achieve a maximum hydrogen yield of about 90% by volume and a hydrogen purity of about 95% by volume, while the CO concentration is greater than 0.1% by volume. Methanation treatment is also required, and the hydrogen cooling box temperature needs to be around -160°C, consuming a huge amount of energy. C5+ requires additional cold energy and a butanizer tower needs to be installed.

[0111]

[0112]

[0113]

[0114]

[0115]

[0116] The contents of hydrogen, methane, ethylene, ethane, propane, n-butane, carbon monoxide, n-hexane, benzene, toluene, and water in each stream of the material listed in Tables 1-4 are all volume percentages.

[0117] In this invention, the pressure required by the sub-compression separation unit can be directly provided by the compression section within the sub-compression separation unit. Compared to traditional processes, embedding polymer membrane technology into the sub-compression separation unit significantly improves hydrogen recovery, enabling the recovery of the vast majority of hydrogen from the cracked gas. The recovered and purified hydrogen is collected and stored as product hydrogen or used in a hydrogenation unit, and the load on the subsequent cryogenic unit is greatly reduced. In Examples 1-4 of this invention, the hydrogen recovery rate is greater than or equal to 95%, and the purity of the product hydrogen is greater than or equal to 98%, while in the prior art (Comparative Example 1), the highest hydrogen recovery rate is only 90%, and the purity of the product hydrogen is only 95%. The higher compressor outlet temperature greatly enhances the permeation rate, and since the components are in a gaseous state, there is no need to worry about the negative impact of water on the membrane. Membrane technology is gentle, energy-efficient, and highly efficient, and the membrane module has a small footprint, allowing for direct optimization of existing equipment.

[0118] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An ethylene cracking gas separation system, characterized in that, The system comprises: a quenching unit, a compression separation unit, and a re-separation unit connected in sequence, used to separate heavy hydrocarbons, lean hydrogen gas, and product hydrogen from ethylene cracking gas; wherein... The compression separation unit includes: multiple hydrogen separation membrane units; The compression separation unit further includes a compressor having n compression sections; wherein, corresponding to the n compression sections, the compression separation unit is provided with n sub-compression separation units, where n is an integer greater than or equal to 1; The compression separation unit includes, in the first sub-compression separation unit, a gas-liquid separator, a first compression section, and an optional hydrogen separation membrane unit connected in sequence; the (x+1)th sub-compression separation unit includes, in the x+1th sub-compression separation unit, a heat exchanger, a gas-liquid separator, a (x+1)th compression section, and an optional hydrogen separation membrane unit connected in sequence, where x is an integer greater than or equal to 1. The re-separation unit includes m hydrogen purification devices, used to separate the collected permeate gas formed by the combined permeate gas obtained from each hydrogen separation membrane unit, to obtain product hydrogen and reflux gas, where m is a positive integer; where... When m≥2, m hydrogen purification devices are connected in series. The purified permeate gas separated by the (m-1)th hydrogen purification device is sent to the mth hydrogen purification device. The collected permeate gas is separated by the m hydrogen purification devices in sequence to obtain the product hydrogen and m streams of reflux gas. The reflux gas is mixed with the separated gas phase obtained by the gas-liquid separator in the first sub-compression and separation unit, and then sent to the first compression section.

2. The system according to claim 1, wherein, When the sub-compression separation unit does not include the hydrogen separation membrane unit, the outlet of the xth compression section is connected to the inlet of the heat exchanger in the (x+1)th sub-compression separation unit; When the sub-compression separation unit includes the hydrogen separation membrane unit, the hydrogen separation membrane unit in the xth sub-compression separation unit is used to perform gas separation to obtain the xth residual gas and the xth permeate gas; and the hydrogen separation membrane unit in the xth sub-compression separation unit is connected to the heat exchanger in the (x+1)th sub-compression separation unit, and is used to send the xth residual gas into the heat exchanger in the (x+1)th sub-compression separation unit.

3. The system according to claim 1, wherein, The re-separation unit further includes a compression heat exchange unit, which includes a compression device and a heat exchange device connected in sequence. The compression heat exchange unit is used to compress and heat the material fed into the hydrogen purification device.

4. The system according to any one of claims 1-3, wherein, The separation coefficient of H2 and CH4 in the separation membrane of the hydrogen separation membrane unit is 150-800.

5. The system according to claim 4, wherein, The separation coefficient of H2 and CH4 in the separation membrane set in the re-separation unit is 150-800.

6. The system according to any one of claims 1-3, wherein, The separation membranes in the hydrogen separation membrane unit and the re-separation unit are each independently selected from at least one of the following: polysulfone membrane, polyethersulfone membrane, polyimide membrane, polypropylene membrane, polyethylene membrane, synthetic resin membrane, polyvinylidene fluoride membrane, polytetrafluoroethylene membrane, polyether ether ketone membrane, polybenzimidazole membrane, cellulose acetate membrane, polycarbonate membrane, polymethyl methacrylate membrane, silica membrane, zeolite molecular sieve membrane, and carbon molecular sieve membrane.

7. The application of the ethylene cracking gas separation system according to any one of claims 1-6 in the separation of ethylene cracking gas.

8. A method for separating ethylene cracked gas, characterized in that, Under separation conditions, the gas to be separated is introduced into the ethylene cracking gas separation system according to any one of claims 1-6 for separation to obtain a separated liquid phase, a hydrogen-lean gas and product hydrogen.

9. The method according to claim 8, wherein, The separation conditions include: membrane pressure of 0.15-4 MPa.

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