Separation method and system of ethane oxidative dehydrogenation product

Abstract

The invention relates to a separation method and system of an ethane oxidative dehydrogenation product, and the method comprises the following steps: condensing the ethane oxidative dehydrogenation product containing ethane, ethylene and nitrogen to-138 DEG C to-163 DEG C at 1.80-4.00 MPaG to obtain crude tail gas, a nitrogen-rich liquid phase and a hydrocarbon-rich liquid phase; and feeding the nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase into a denitrification tower (209) to remove nitrogen, extracting a tower kettle liquid phase, feeding the tower kettle liquid phase into an ethylene rectifying tower (211), extracting an ethylene product from the tower top, and extracting ethane from the tower kettle. Compared with the prior art, the method has the advantages of high C2 recovery rate, low energy consumption, small equipment number, low investment and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of ethane oxidative dehydrogenation, and relates to a method and system for separating ethane oxidative dehydrogenation products. Background Art

[0002] In recent years, the research on the oxidative dehydrogenation of low-carbon hydrocarbons, especially ethane, to produce ethylene (ODHE) has attracted more and more attention. The research on catalytic oxidative dehydrogenation of ethane began in the 1970s. As early as in 1971, GasPar et al. proposed a method for the catalytic oxidative dehydrogenation of ethane in H 2 In 1977 and 1978, Ward and Thorsteinson successively published the oxidative dehydrogenation process using Mo, Si and Mo, V mixed oxides as catalysts. The patent CN105849069A of Shell Research International Co., Ltd. discloses the use of a catalyst with the active component MoVTe(Nb)O for the oxidative dehydrogenation of alkanes with 2-6 carbon atoms, with a feed gas space velocity of 7500-15000h -1 , the reaction temperature is 320-420℃, the ethane conversion rate can reach 44%, and the corresponding ethylene selectivity is 92.2%. The patent CN105080575B of Dalian Institute of Chemical Physics of Chinese Academy of Sciences discloses the use of a catalyst with the active component of MoVTeNbO for catalytic oxidative dehydrogenation of ethane. At 350℃, the ethane conversion rate and ethylene selectivity can reach 70.5% and 95% respectively. Under the condition of using suitable catalysts, ethane has a high conversion rate even at a lower reaction temperature, and the reaction by-products are usually a small amount of acetic acid, carbon monoxide, and carbon dioxide.

[0003] For the catalytic oxidative dehydrogenation of ethane (ODHE) reaction, since the system is an oxygen-containing flammable and explosive mixed gas, and the reaction is highly exothermic, it is necessary to introduce a diluent gas to dilute the reaction heat and improve the reaction heat transfer efficiency. At the same time, the introduction of the diluent gas makes the mixed gas outside the explosion limit range, and the operation is safer. The introduction of a large amount of diluent gas is crucial to the reaction and the subsequent separation of the diluent gas. Patents such as CN105080575B, CN110963880A, CN110963879A, CN106660901B, and CN105727975B mention methods using inert gases such as water vapor, nitrogen, and carbon dioxide as diluents. The addition of these diluents has brought challenges to the separation and industrial application of this technology. Researchers in this field have found that the use of water vapor as a diluent gas has the advantage that the diluent gas and the product gas can be separated by cooling, and the separation energy consumption is low. The disadvantage is that the presence of water vapor in the raw gas will greatly increase the selectivity of the by-product acetic acid product, thereby reducing the effective utilization rate of the raw material; using CO 2As a diluent gas, it will cause a large amount of CO 2 After absorption and desorption, it is recycled back to the reactor to remove CO 2 The unit has high energy consumption and the desorbed CO 2 As the gas is at normal pressure, the energy consumption and equipment investment of compressing and recycling it back to the reactor are relatively high. In addition, a large amount of CO needs to be introduced during startup. 2 , and its material sources are limited; using nitrogen as a diluent has little effect on the selectivity of the reaction and can obtain a higher ethylene yield. In addition, since air is rich in nitrogen, cheap air or oxygen-enriched air can be used as the raw material gas for the reaction. In view of the above reasons, using nitrogen as a diluent has a high industrial application value.

[0004] The raw product gas of ODHE using air or oxygen-enriched air as the raw material gas mainly contains ethylene, unconverted ethane, nitrogen, acetic acid, carbon monoxide, carbon dioxide and water vapor. The raw product gas is passed through a deacidification device, an acetylenic removal device, compression, a carbon dioxide removal device, and a drying device to remove acetic acid, water vapor and carbon dioxide to become a pre-treated product gas. The pre-treated ODHE product gas mainly contains ethane, ethylene and nitrogen, and low-temperature distillation is usually used for product separation.

[0005] CN110248916B proposes a method and equipment for producing olefins, which uses cold energy at four temperature levels of -20℃ to -105℃ to gradually cool the pretreated ODHE product gas, condense the carbon dioxide therein and separate it from the light component gas, and send the condensate to the distillation tower to separate the carbon dioxide from the light components dissolved therein. Since the ODHE product gas using air or oxygen-enriched gas as the raw material contains a lot of nitrogen, the solubility of nitrogen in carbon dioxide at low temperature is relatively large, resulting in a large amount of light components entering the distillation tower, and the required cold energy of the distillation tower condenser is relatively large. In order to avoid the light component gas carrying too much carbon dioxide due to insufficient reflux of the distillation tower, this patent uses a stream of liquefied methane as a supplementary reflux liquid. This will cause the reflux methane to enter the nitrogen, and this part of methane is difficult to recover and can only be burned as fuel gas, resulting in a waste of methane.

[0006] CN111094221B proposes a method and device for producing ethylene, which adopts a method combining cryogenic distillation and pressure swing adsorption, and adopts cryogenic distillation at a temperature level of -40℃ to -100℃ to separate ethane, ethylene and light component gas in the pretreated ODHE product gas. Then, the ethane and ethylene entrained in the light component gas discharged from the cryogenic distillation are recovered by pressure swing adsorption, and the recovered ethane and ethylene are returned to the cryogenic distillation after compression to improve the recovery rate of ethane and ethylene in the device. For the above-mentioned ODHE product gas using air or oxygen-enriched gas as raw materials, the nitrogen gas volume fraction can reach 30% to 60%. A large amount of nitrogen entering the pressure swing adsorption will result in a larger equipment size of the pressure swing adsorption device and a higher equipment investment.

[0007] CN113166003A proposes a separation method for ethane oxidative dehydrogenation effluent, which uses two low-temperature distillation towers to separate ethane, ethylene and light component gas. The first tower uses a relatively low operating pressure of 15 to 20 bar and a relatively low grade of cold at -20°C to -40°C to separate ethylene, light components and ethane. Ethylene and light components are extracted from the top of the tower, and ethane is extracted from the bottom of the tower. The ethylene and light component gas at the top of the tower are further compressed and cooled before being sent to the second distillation tower. The second tower uses a relatively high operating pressure of 20 to 40 bar and a relatively high grade of cold at -80°C to -110°C to separate ethylene from light components. For the ODHE product gas whose nitrogen gas volume fraction can reach 30% to 60%, this patent sends all the product gas to the distillation tower, which will result in a large size of the distillation tower equipment and a high condenser load. In addition, since the critical temperature of nitrogen is -146.95°C, it cannot be condensed at the highest grade cooling capacity (-110°C) provided by this patent. Therefore, the second distillation tower of the patent cannot achieve a clear separation of ethylene and nitrogen, the amount of ethylene entrained in nitrogen is high, and the ethylene recovery rate is low.

[0008] Therefore, it is necessary to provide an ODHE product gas separation technology suitable for air or oxygen-enriched air as raw material, which has high carbon two recovery rate, low energy consumption, small number of equipment and low investment. Summary of the invention

[0009] The object of the present invention is to provide a method and system for separating ethane oxidative dehydrogenation products.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] A method for separating an ethane oxidative dehydrogenation product, comprising:

[0012] Condensing the ethane oxidative dehydrogenation product containing ethane, ethylene and nitrogen to -138°C to -163°C at 1.80 to 4.00 MPaG to obtain a crude tail gas, a nitrogen-rich liquid phase and a hydrocarbon-rich liquid phase;

[0013] The nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase are sent to a denitrification tower to remove nitrogen, and a liquid phase is taken out from the bottom of the tower and sent to an ethylene distillation tower. The ethylene product is taken out from the top of the tower, and ethane is taken out from the bottom of the tower.

[0014] Further, the method comprises:

[0015] Cooling the ethane oxidative dehydrogenation product in multiple stages, collecting the cooling liquid phase product and the inter-stage cooling liquid phase intermediate product;

[0016] The interstage cooling liquid phase intermediate product is sent to the pre-cutting tower (207) as reflux liquid, the pre-cutting gas phase is taken out from the tower top, and the pre-cutting liquid phase is taken out from the tower bottom;

[0017] The pre-cut gas phase and the cooled liquid phase product are stripped in a denitrification tower feed stripping tower (208) to obtain a stripping tower top produced gas phase and a stripping tower bottom produced liquid phase;

[0018] The gas phase produced from the top of the stripping tower is condensed to -138°C to -163°C at 1.88 to 3.88 MPaG to obtain a crude tail gas, a nitrogen-rich liquid phase, and a hydrocarbon-rich liquid phase;

[0019] The nitrogen-rich liquid phase is sent to the denitrification tower as reflux liquid together with the stripping tower kettle produced liquid phase and the hydrocarbon-rich liquid phase to obtain the denitrification tower top produced gas phase and the denitrification tower kettle produced liquid phase;

[0020] The liquid phase produced from the bottom of the denitrogenation tower and the pre-cut liquid phase are sent to an ethylene distillation tower, ethylene products are produced from the top of the tower, and ethane is produced from the bottom of the tower.

[0021] Preferably, the crude tail gas and the gas phase extracted from the top of the denitrification tower are expanded, separated into gas and liquid, and heated to obtain tail gas and circulating gas.

[0022] Preferably, after expansion, the gas phase pressure is 0.10 MPaG to 0.50 MPaG.

[0023] Preferably, the crude tail gas and the gas phase produced from the top of the denitrification tower undergo multi-stage heat exchange with the ethane oxidative dehydrogenation product during the heating and rewarming process.

[0024] Preferably, during the multi-stage cooling process, the pressure of the ethane oxidative dehydrogenation product is 2.00 MPa to 4.00 MPaG. After the multi-stage cooling, the temperature of the ethane oxidative dehydrogenation product is -95°C to -101°C.

[0025] Preferably, the pressure at the top of the pre-cutting tower is 1.90 MPa to 3.90 MPaG.

[0026] Preferably, the pressure at the top of the denitrification tower feed stripping tower is 1.88 MPa to 3.88 MPaG;

[0027] Preferably, the pressure at the top of the denitrification tower is 1.75 MPaG to 3.75 MPaG.

[0028] Preferably, the pressure at the top of the ethylene distillation tower is 0.60 MPaG to 2.00 MPaG.

[0029] An ethane oxidative dehydrogenation product separation system for implementing the method as described above comprises:

[0030] A gas-liquid-liquid condenser is used to condense the ethane oxidative dehydrogenation product containing ethane, ethylene and nitrogen to -138°C to -163°C at 1.80 to 4.00 MPaG to obtain a condensed ODHE product material;

[0031] A gas-liquid-liquid separation device is used to separate the condensed ODHE product material into gas-liquid-liquid three-phases, extract the upper liquid phase to obtain a nitrogen-rich liquid phase, and extract the lower liquid phase to obtain a hydrocarbon-rich liquid phase;

[0032] A denitrification tower is used to further remove nitrogen from the nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase and produce a bottom liquid phase; and

[0033] The ethylene distillation tower is used to separate the ethylene product and ethane from the liquid phase in the tower bottom.

[0034] Furthermore, the nitrogen-rich liquid phase is introduced into the denitrification tower as reflux liquid, and the hydrocarbon-rich liquid phase is introduced into the denitrification tower as a feed.

[0035] Furthermore, a denitrogenation tower feed stripping tower is provided before the gas-liquid-liquid condenser, and the gas phase extracted from the top of the denitrogenation tower feed stripping tower enters the gas-liquid-liquid condenser, and the liquid phase extracted from the bottom of the tower enters the denitrogenation tower.

[0036] Further, the system also includes an exhaust gas expansion element and an expansion gas-liquid separator;

[0037] The exhaust gas expansion component includes an exhaust gas expander or an exhaust gas throttle valve;

[0038] The gas phase extracted from the gas-liquid-liquid separation device and the gas phase extracted from the top of the denitrification tower pass through the tail gas expansion piece and the expansion gas-liquid separator in sequence to obtain tail gas material and circulating material.

[0039] Furthermore, the gas-liquid-liquid condenser is provided with a product gas condensation channel connected to the inlet of the gas-liquid-liquid separation device, a hydrocarbon-rich liquid phase heat exchange channel connected to the hydrocarbon-rich liquid phase outlet of the gas-liquid-liquid separation device, a crude tail gas rewarming channel connected to the gas phase outlet of the gas-liquid-liquid separation device, a tail gas rewarming channel connected to the tail gas material outlet of the expansion gas-liquid separator, and a circulating material rewarming channel connected to the circulating material outlet of the expansion gas-liquid separator.

[0040] Further, the system also includes a precooling unit for precooling the ethane oxidative dehydrogenation product;

[0041] The precooling unit includes a precooling heat exchanger;

[0042] The tail gas material and the circulating material produced by the expansion gas-liquid separator are heat exchanged with the ethane oxidation dehydrogenation product through a precooling unit to obtain tail gas and circulating gas.

[0043] Preferably, the precooling unit comprises a single precooling heat exchanger or a plurality of precooling heat exchangers arranged in series.

[0044] Preferably, the pre-cooling unit includes a first heat exchanger, a second heat exchanger and a third heat exchanger which are arranged in series in sequence, and the first heat exchanger, the second heat exchanger and the third heat exchanger are respectively provided with a product gas deep cooling channel, a circulating gas rewarming channel, an exhaust gas rewarming channel and a refrigerant channel.

[0045] Furthermore, a pre-cutting unit is provided between the pre-cooling unit and the denitrification tower feed stripping tower, and the pre-cutting unit comprises

[0046] A multi-stage pre-cutting heat exchanger group is used for multi-stage cooling of the ethane oxidative dehydrogenation product, comprising a plurality of pre-cutting heat exchangers arranged in series; the outlet end of the multi-stage pre-cutting heat exchanger group is connected to the feed end of the denitrification tower feed stripping tower;

[0047] A pre-cutting gas-liquid separator is used to separate the ethane oxidative dehydrogenation product after cooling in the pre-cooling unit, or the cooling intermediate material in the process of cooling the ethane oxidative dehydrogenation product in the multi-stage pre-cutting heat exchanger group, into a gas-liquid phase of the ethane oxidative dehydrogenation product and a liquid phase of the ethane oxidative dehydrogenation product, and the ethane oxidative dehydrogenation product gas phase is sent to the next stage pre-cutting heat exchanger; and

[0048] The pre-cutting tower is used to remove nitrogen from the liquid phase of the ethane oxidation dehydrogenation product. The gas phase produced from the top of the tower is sent to the denitrogenation tower feed stripping tower, and the liquid phase produced from the bottom of the tower is sent to the ethylene distillation tower.

[0049] Furthermore, the multi-stage pre-cutting heat exchanger group includes a fourth heat exchanger, a fifth heat exchanger, and a sixth heat exchanger which are sequentially arranged in series; the outlet end of the sixth heat exchanger is connected to the feed end of the denitrification tower feed stripping tower;

[0050] The pre-cutting gas-liquid separator includes a first gas-liquid separator and a second gas-liquid separator, the first gas-liquid separator is arranged between the pre-cooling unit and the fourth heat exchanger, and the second gas-liquid separator is arranged between the fourth heat exchanger and the fifth heat exchanger; or, the first gas-liquid separator is arranged between the fourth heat exchanger and the fifth heat exchanger, and the second gas-liquid separator is arranged between the fifth heat exchanger and the sixth heat exchanger.

[0051] Furthermore, the pre-cutting heat exchanger is provided with a product gas deep cooling channel, a circulating gas rewarming channel, an exhaust gas rewarming channel and a refrigerant channel.

[0052] Preferably, when the pre-cutting gas-liquid separator is arranged between adjacent pre-cutting heat exchangers, the upper pre-cutting heat exchanger among the adjacent pre-cutting heat exchangers is further provided with a condensate rewarming channel connected to the pre-cutting gas-liquid separator.

[0053] Preferably, when a pre-cutting heat exchanger is provided in front of the adjacent pre-cutting heat exchanger, the pre-cutting heat exchanger is provided with an upper-level condensate rewarming channel connected to the lower-level condensate rewarming channel; the liquid phase outlet of the pre-cutting gas-liquid separator is connected in sequence to the condensate rewarming channel in the previous pre-cutting heat exchanger.

[0054] Preferably, when a hydrocarbon-rich liquid phase heat exchange channel is provided in the gas-liquid-liquid condenser, a hydrocarbon-rich liquid phase pre-cutting heat exchange channel connected to the hydrocarbon-rich liquid phase heat exchange channel is provided in the last stage pre-cutting heat exchanger in the multi-stage pre-cutting heat exchanger group.

[0055] The present invention provides a separation system for separating ethane oxidative dehydrogenation products, comprising: a heat exchanger and a gas-liquid separator for graded condensation and phase separation of ethane oxidative dehydrogenation product gas, a pre-cutting tower, a denitrogenation tower feed stripping tower and a denitrogenation tower for separating carbon dioxide and nitrogen, a tail gas expander or a tail gas throttle valve for tail gas expansion, and an ethylene distillation tower for separating ethane and ethylene. The present invention also provides a separation method for separating components such as product ethylene, unconverted ethane and diluent nitrogen from ethane oxidative dehydrogenation product gas, which has high carbon dioxide recovery rate, low energy consumption, few equipment, low investment and simple operation.

[0056] Compared with the prior art, the present invention has the following characteristics:

[0057] 1. The inventors found in their research that by setting up a pre-cutting tower, about 60% to 80% of the carbon two in the product gas can be "cut" through the pre-cutting tower and sent directly to the ethylene distillation tower. This part of carbon two will no longer be cooled step by step and will not enter the denitrification tower, thus reducing the cooling consumption of the device. In addition, the temperature of the pre-cutting tower is relatively high, and ordinary carbon steel can be used. Since the operating temperature of the denitrification tower is relatively low, stainless steel must be used. Setting up a pre-cutting tower can reduce the tower diameter of the denitrification tower, thereby reducing the investment in the device.

[0058] 2. The inventors found in their research that by setting up a denitrogenation tower feed stripping tower, the nitrogen content in the denitrogenation tower feed can be significantly reduced, so that the reflux amount required by the denitrogenation tower is reduced, and the refrigeration consumption is reduced. In addition, since the amount of nitrogen entering the denitrogenation tower is reduced, the entrainment of ethylene in the tower top nitrogen can be reduced, and the ethylene loss rate of the device can be reduced.

[0059] 3. The inventors found through experimental research that the ethane-ethylene-nitrogen mixed liquid phase system has a large non-ideality. The attraction between the same molecules in the mixed liquid phase greatly exceeds the attraction between different molecules. Under a specific temperature and pressure, the solution will undergo phase splitting within a certain composition range to form two liquid phases, a hydrocarbon-rich liquid phase and a nitrogen-rich liquid phase. The nitrogen-rich liquid phase has a lower density and is located above the solution; the hydrocarbon-rich liquid phase has a higher density and is located below the solution. Tables 1 and 2 respectively list the temperatures at which the ethane-nitrogen and ethylene-nitrogen mixtures begin to undergo liquid phase splitting at different pressures.

[0060] Table 1 Liquid phase splitting temperature of ethane and nitrogen mixture at different pressures

[0061] Pressure, MPa 1.04 1.39 1.81 2.34 2.94 3.66 4.42 Phase splitting temperature, °C -168 -163 -158 -153 -148 -143 -138

[0062] Table 2 Liquid phase splitting temperature of ethylene and nitrogen mixture at different pressures

[0063] Pressure, MPa 1.03 1.37 1.79 2.29 2.88 3.51 4.11 Phase splitting temperature, °C -168 -163 -158 -153 -148 -143 -138

[0064] Table 3 Liquid phase law of nitrogen containing 5 mol% ethane at 1.9 MPaG

[0065]

[0066]

[0067] Table 4 Liquid phase law of nitrogen containing 5 mol% ethylene at 1.9 MPaG

[0068]

[0069]

[0070] Table 3 lists the liquid phase data of nitrogen containing 5 mol% ethane at 1.90 MPaG, and Table 4 lists the liquid phase data of nitrogen containing 5 mol% ethylene at 1.90 MPaG. The inventors found the following rules:

[0071] 1) When there are two liquid phases, the system temperature remains constant as the total liquid fraction increases;

[0072] 2) When there are two liquid phases, as the total liquid phase fraction increases, the volume ratio of the two liquid phases changes relatively, the nitrogen-rich liquid phase ratio gradually increases, and the hydrocarbon-rich liquid phase ratio gradually decreases;

[0073] 3) When two liquid phases are present, the compositions of the nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase do not change;

[0074] 4) When there are two liquid phases, the nitrogen-rich liquid phase contains a higher proportion of nitrogen;

[0075] According to the law exhibited by the above-mentioned ethane-ethylene-nitrogen mixed liquid, the present invention innovatively proposes to use the nitrogen-rich liquid phase with a higher nitrogen content as the reflux liquid of the denitrification tower. The volume flow rate of the nitrogen-rich liquid phase can be controlled by simply controlling the load of the gas-liquid-liquid condenser, and its composition ratio can be kept constant as the volume flow rate of the nitrogen-rich liquid phase changes, thereby ensuring the flow controllability and composition stability of the reflux of the denitrification tower.

[0076] This design can generate an additional reflux liquid suitable for the denitrification tower during the step-by-step condensation of the product gas. The denitrification tower does not need to be equipped with a corresponding condenser and reflux tank, thus reducing the number of equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like streams or components in the exemplary embodiments of the present invention.

[0078] Figure 1 This is a schematic diagram of the product gas separation device used in Example 1;

[0079] Figure 2 This is a schematic diagram of the product gas separation device used in Example 2;

[0080] Figure 3 This is a schematic diagram of the product gas separation device used in Example 3;

[0081] Figure 4 This is a schematic diagram of the product gas separation device used in Comparative Example 1;

[0082] Figure 5 It is a simplified flow chart of an ethane oxidative dehydrogenation device according to an embodiment of the present invention;

[0083] Logistics markings in the figure:

[0084] a-ethane feedstock; b-pretreated ethane feedstock; c-oxidant; d-dilution gas, e-crude product gas; f-deacidified water product gas; g-acid water; h-acetic acid; i-dealkyne product gas; j-compressed product gas; k-deCO 2 Product gas; l-carbon dioxide; m-product gas after pretreatment; n-ethylene product; o-tail gas; p-circulating ethane; q-circulating gas; r-heavy hydrocarbons; s-light hydrocarbons;

[0085] Device markings in the figure:

[0086] 101-Raw material pretreatment device; 102-Ethane oxidative dehydrogenation device; 103-Acid water separation device; 104-Acetic acid recovery device; 105-Deacetylenic device; 106-Product gas compression device; 107-DeCO2 Device; 108-drying device; 109-product gas separation device;

[0087] 201a-first heat exchanger, 201b-second heat exchanger, 201c-third heat exchanger, 202a-fourth heat exchanger, 202b-fifth heat exchanger, 202c-sixth heat exchanger, 203-gas-liquid-liquid condenser; 204a-first gas-liquid separator, 204b-second gas-liquid separator, 205-gas-liquid-liquid separation device; 206-expansion gas-liquid separator; 207-pre-cutting tower; 208-denitrogenation tower feed stripping tower, 209-denitrogenation tower; 210-tail gas expander; 211-ethylene distillation tower; 212-tail gas throttle valve; 213-gas-liquid separator. DETAILED DESCRIPTION

[0088] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0089] A separation system for ethane oxidative dehydrogenation products comprises a gas-liquid-liquid condenser 203, a gas-liquid-liquid separation device 205, a denitrification tower 209 and an ethylene distillation tower 211 which are connected in sequence. The gas-liquid-liquid condenser 203 is used to condense the ethane oxidative dehydrogenation products containing ethane, ethylene and nitrogen to -138°C to -163°C at 1.80 to 4.00 MPaG to obtain a condensed ODHE product material; the gas-liquid-liquid separation device 205 is used to perform gas-liquid-liquid three-phase separation on the condensed ODHE product material, extract the upper liquid phase to obtain a nitrogen-rich liquid phase, and extract the lower liquid phase to obtain a hydrocarbon-rich liquid phase; the denitrification tower 209 is used to further remove nitrogen from the nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase, and extract the tower bottom liquid phase; the ethylene distillation tower 211 is used to obtain ethylene products and ethane by distillation and separation from the tower bottom liquid phase.

[0090] Furthermore, the nitrogen-rich liquid phase is introduced into the denitrification tower 209 as reflux liquid, and the hydrocarbon-rich liquid phase is introduced into the denitrification tower 209 in a feeding manner, that is, the hydrocarbon-rich liquid phase is introduced into the denitrification tower 209 from the upper part.

[0091] In some specific embodiments, the bottom outlet of the denitrification tower 209 is connected to the ethylene distillation tower 211 .

[0092] Furthermore, a denitrogenation tower feed stripping tower 208 for preliminarily separating the carbon two products (ethane, ethylene) from nitrogen is provided before the gas-liquid-liquid condenser 203. The gas phase extracted from the top of the denitrogenation tower feed stripping tower 208 enters the gas-liquid-liquid condenser 203, and the liquid phase extracted from the bottom of the tower enters the denitrogenation tower 209.

[0093] Further, the system also includes an exhaust gas expansion element and an expansion gas-liquid separator;

[0094] The exhaust gas expansion element includes an exhaust gas expander 210 or an exhaust gas throttle valve 212;

[0095] The gas phase extracted from the gas-liquid-liquid separation device 205 and the gas phase extracted from the top of the denitrification tower 209 pass through the tail gas expansion element and the expansion gas-liquid separator in sequence to obtain tail gas material and circulating material.

[0096] The tail gas material is heated to obtain tail gas, and the circulating material is heated to obtain circulating gas.

[0097] Furthermore, the gas-liquid-liquid condenser 203 is provided with a product gas condensation channel connected to the inlet of the gas-liquid-liquid separation device 205, a hydrocarbon-rich liquid phase heat exchange channel connected to the hydrocarbon-rich liquid phase outlet of the gas-liquid-liquid separation device 205, a crude tail gas rewarming channel connected to the gas phase outlet of the gas-liquid-liquid separation device 205, a tail gas rewarming channel connected to the tail gas material outlet of the expansion gas-liquid separator 206, and a circulating gas rewarming channel connected to the circulating material outlet of the expansion gas-liquid separator 206.

[0098] Furthermore, the gas-liquid-liquid separation device 205 is provided with a gas phase outlet, a nitrogen-rich liquid phase outlet, and a hydrocarbon-rich liquid phase outlet.

[0099] In some specific embodiments, the top outlet of the denitrification tower feed stripping tower 208 is connected to the product gas deep cooling channel of the gas-liquid-liquid condenser 203 and the inlet of the gas-liquid-liquid separation device 205 in sequence, and the bottom outlet is connected to the denitrification tower 209.

[0100] In some specific embodiments, the outlet of the crude tail gas rewarming channel of the gas-liquid-liquid condenser 203 and the top outlet of the denitrification tower 209 are connected to the inlet of the tail gas expander 210 , and the outlet of the tail gas expander 210 is connected to the inlet of the expansion gas-liquid separator 206 .

[0101] Further, the system also includes a precooling unit for precooling the ethane oxidative dehydrogenation product;

[0102] The precooling unit includes a precooling heat exchanger;

[0103] The tail gas material and the circulating material produced by the expansion gas-liquid separator are heat exchanged with the ethane oxidation dehydrogenation product through a precooling unit to obtain tail gas and circulating gas.

[0104] Preferably, the precooling unit comprises a single precooling heat exchanger or a plurality of precooling heat exchangers arranged in series.

[0105] Preferably, the pre-cooling unit includes a first heat exchanger 201a, a second heat exchanger 201b and a third heat exchanger 201c which are arranged in series in sequence, and the first heat exchanger 201a, the second heat exchanger 201b and the third heat exchanger 201c are respectively provided with a product gas deep cooling channel, a circulating gas rewarming channel, an exhaust gas rewarming channel and a refrigerant channel.

[0106] Furthermore, a pre-cutting unit for preliminarily separating the C2 products (ethane, ethylene) from nitrogen is provided between the pre-cooling unit and the denitrification tower feed stripping tower 208. The pre-cutting unit includes

[0107] A multi-stage pre-cutting heat exchanger group, used for multi-stage cooling of the ethane oxidative dehydrogenation product, comprises a plurality of pre-cutting heat exchangers arranged in series; the outlet end of the multi-stage pre-cutting heat exchanger group is connected to the feed end of the denitrification tower feed stripping tower 208;

[0108] A pre-cutting gas-liquid separator is used to separate the ethane oxidative dehydrogenation product after cooling in the pre-cooling unit, or the cooling intermediate material in the process of cooling the ethane oxidative dehydrogenation product in the multi-stage pre-cutting heat exchanger group, into a gas-liquid phase of the ethane oxidative dehydrogenation product and a liquid phase of the ethane oxidative dehydrogenation product, and the ethane oxidative dehydrogenation product gas phase is sent to the next stage pre-cutting heat exchanger; and

[0109] The pre-cutting tower 207 is used to remove nitrogen from the liquid phase of the ethane oxidative dehydrogenation product. The gas phase produced from the top of the tower is sent to the denitrogenation tower feed stripping tower 208, and the liquid phase produced from the bottom of the tower is sent to the ethylene distillation tower 211.

[0110] In some specific embodiments, the top outlet of the pre-cutting tower 207 is connected to the bottom inlet of the denitrogenation tower feed stripping tower 208 , and the bottom outlet is connected to the ethylene distillation tower 211 .

[0111] Furthermore, the multi-stage pre-cutting heat exchanger group includes a fourth heat exchanger 202a, a fifth heat exchanger 202b, and a sixth heat exchanger 202c which are sequentially arranged in series; the outlet end of the sixth heat exchanger 202c is connected to the feed end of the denitrification tower feed stripping tower 208.

[0112] Preferably, the pre-cutting gas-liquid separator includes a first gas-liquid separator 204a and a second gas-liquid separator 204b, wherein the first gas-liquid separator 204a is disposed between the pre-cooling unit and the fourth heat exchanger 202a, and the second gas-liquid separator 204b is disposed between the fourth heat exchanger 202a and the fifth heat exchanger 202b;

[0113] Alternatively, the first gas-liquid separator 204a is disposed between the fourth heat exchanger 202a and the fifth heat exchanger 202b, and the second gas-liquid separator 204b is disposed between the fifth heat exchanger 202b and the sixth heat exchanger 202c.

[0114] Furthermore, the pre-cutting heat exchanger is provided with a product gas deep cooling channel, a circulating gas rewarming channel, an exhaust gas rewarming channel and a pre-cutting refrigeration channel.

[0115] In some specific embodiments, the outlet of the product gas deep cooling channel of the sixth heat exchanger 202c is connected to the top inlet of the denitrification tower feed stripping tower 208.

[0116] In some specific embodiments, the product gas cryogenic channel outlet of the third heat exchanger 201c is connected to the first gas-liquid separator 204a, the top outlet of the first gas-liquid separator 204a is connected to the product gas cryogenic channel of the fourth heat exchanger 202a, and the bottom outlet is connected to the upper inlet of the pre-cutting tower 207;

[0117] The product gas deep cooling channel outlet of the fourth heat exchanger 202a is connected to the second gas-liquid separator 204b, the top outlet of the second gas-liquid separator 204b is connected to the product gas deep cooling channel of the fifth heat exchanger 202b, and the bottom outlet is connected to the top inlet of the pre-cutting tower 207.

[0118] Preferably, when the pre-cutting gas-liquid separator is arranged between adjacent pre-cutting heat exchangers, the upper pre-cutting heat exchanger among the adjacent pre-cutting heat exchangers is further provided with a condensate rewarming channel connected to the pre-cutting gas-liquid separator.

[0119] Preferably, when a pre-cutting heat exchanger is provided in front of the adjacent pre-cutting heat exchanger, the pre-cutting heat exchanger is provided with an upper-level condensate rewarming channel connected to the lower-level condensate rewarming channel; the liquid phase outlet of the pre-cutting gas-liquid separator is connected in sequence to the condensate rewarming channel in the previous pre-cutting heat exchanger.

[0120] In some specific embodiments, the fourth heat exchanger 202a and the fifth heat exchanger 202b are further provided with a condensate rewarming channel;

[0121] The product gas cryogenic channel outlet of the fourth heat exchanger 202a is connected to the first gas-liquid separator 204a, the top outlet of the first gas-liquid separator 204a is connected to the product gas cryogenic channel of the fifth heat exchanger 202b, and the bottom outlet is connected to the condensate rewarming channel of the fourth heat exchanger 202a and the upper inlet of the pre-cutting tower 207 in sequence;

[0122] The outlet of the product gas deep cooling channel of the fifth heat exchanger 202b is connected to the second gas-liquid separator 204b, the top outlet of the second gas-liquid separator 204b is connected to the product gas deep cooling channel of the sixth heat exchanger 202c, and the bottom outlet is connected to the condensate rewarming channel of the fifth heat exchanger 202b, the condensate rewarming channel of the fourth heat exchanger 202a and the top inlet of the pre-cutting tower 207 in sequence.

[0123] Preferably, when a hydrocarbon-rich liquid phase heat exchange channel is provided in the gas-liquid-liquid condenser 203, a hydrocarbon-rich liquid phase heat exchange channel connected to the hydrocarbon-rich liquid phase heat exchange channel is provided in the last stage pre-cutting heat exchanger in the multi-stage pre-cutting heat exchanger group.

[0124] In some specific embodiments, the gas phase outlet of the gas-liquid-liquid separator 205 is connected to the crude tail gas rewarming channel of the gas-liquid-liquid condenser 203, the hydrocarbon-rich liquid phase outlet is connected to the condensate rewarming channel of the gas-liquid-liquid condenser 203 and the denitrification tower 209 in sequence, and the nitrogen-rich liquid phase outlet is connected to the denitrification tower 209. Preferably, the sixth heat exchanger 202c is further provided with a hydrocarbon-rich liquid phase heat exchange channel;

[0125] The gas phase outlet of the gas-liquid-liquid separator 205 is connected to the raw tail gas rewarming channel of the gas-liquid-liquid condenser 203, the hydrocarbon-rich liquid phase outlet is connected to the hydrocarbon-rich liquid phase heat exchange channel of the gas-liquid-liquid condenser 203, the hydrocarbon-rich liquid phase heat exchange channel of the sixth heat exchanger 202c and the denitrification tower 209 in sequence, and the nitrogen-rich liquid phase outlet is connected to the denitrification tower 209.

[0126] In some specific embodiments, the top outlet of the expansion gas-liquid separator is sequentially connected to the corresponding tail gas rewarming channels in the gas-liquid-liquid condenser 203, the pre-cutting heat exchanger, and the pre-cooling heat exchanger, and the bottom outlet is sequentially connected to the corresponding circulating gas rewarming channels in the gas-liquid-liquid condenser 203, the pre-cutting heat exchanger, and the pre-cooling heat exchanger. For example, the top outlet of the expansion gas-liquid separator is sequentially connected to the corresponding tail gas rewarming channels in the gas-liquid-liquid condenser 203, the sixth heat exchanger 202c, the fifth heat exchanger 202b, the fourth heat exchanger 202a, the third heat exchanger 201c, the second heat exchanger 201b, and the first heat exchanger 201a, and the bottom outlet is sequentially connected to the corresponding circulating gas rewarming channels in the gas-liquid-liquid condenser 203, the sixth heat exchanger 202c, the fifth heat exchanger 202b, the fourth heat exchanger 202a, the third heat exchanger 201c, the second heat exchanger 201b, and the first heat exchanger 201a. The tail gas and circulating gas need to pass through all seven heat exchangers in reverse to recover the cold to 37℃.

[0127] In some specific embodiments, the refrigerant flowing in the refrigerant channel is propylene refrigerant or ethylene refrigerant; for example: the medium flowing in the refrigerant channels of the first heat exchanger 201a, the second heat exchanger 201b and the third heat exchanger 201c is propylene refrigerant; the medium flowing in the refrigerant channels of the fourth heat exchanger 202a, the fifth heat exchanger 202b and the sixth heat exchanger 202c is ethylene refrigerant.

[0128] A method for separating an ethane oxidative dehydrogenation product, comprising:

[0129] Condensing the ethane oxidative dehydrogenation product containing ethane, ethylene and nitrogen to -138°C to -163°C at 1.80 to 4.00 MPaG to obtain a crude tail gas, a nitrogen-rich liquid phase and a hydrocarbon-rich liquid phase;

[0130] The nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase are sent to a denitrification tower 209 to remove nitrogen, and a liquid phase is produced from the bottom of the tower, and sent to an ethylene distillation tower 211, and an ethylene product is produced from the top of the tower, and ethane is produced from the bottom of the tower.

[0131] Further, the method comprises:

[0132] Cooling the ethane oxidative dehydrogenation product in multiple stages, collecting the cooling liquid phase product and the inter-stage cooling liquid phase intermediate product;

[0133] The interstage cooling liquid phase intermediate product is sent to the pre-cutting tower 207 as reflux liquid, the pre-cut gas phase is taken out from the tower top, and the pre-cut liquid phase is taken out from the tower bottom;

[0134] The pre-cut gas phase and the cooled liquid phase product are stripped in the denitrification tower feed stripping tower 208 to obtain a gas phase produced at the top of the stripping tower and a liquid phase produced at the bottom of the stripping tower;

[0135] The gas phase produced from the top of the stripping tower is condensed to -138°C to -163°C at 1.88 to 3.88 MPaG to obtain a crude tail gas, a nitrogen-rich liquid phase, and a hydrocarbon-rich liquid phase;

[0136] The nitrogen-rich liquid phase is sent to the denitrification tower 209 as reflux liquid together with the stripping tower kettle produced liquid phase and the hydrocarbon-rich liquid phase to obtain the denitrification tower top produced gas phase and the denitrification tower kettle produced liquid phase;

[0137] The liquid phase produced from the bottom of the denitrogenation tower and the pre-cut liquid phase are sent to the ethylene distillation tower 211, and the ethylene product is produced from the top of the tower, and ethane is produced from the bottom of the tower.

[0138] Preferably, the crude tail gas and the gas phase extracted from the top of the denitrification tower are expanded, separated into gas and liquid, and heated to obtain tail gas and circulating gas.

[0139] Preferably, after expansion, the gas phase pressure is 0.10 MPaG to 0.50 MPaG.

[0140] Preferably, the crude tail gas and the gas phase produced from the top of the denitrification tower undergo multi-stage heat exchange with the ethane oxidative dehydrogenation product during the heating and rewarming process.

[0141] Preferably, during the multi-stage cooling process, the pressure of the ethane oxidative dehydrogenation product is 2.00 MPa to 4.00 MPaG. After the multi-stage cooling, the temperature of the ethane oxidative dehydrogenation product is -95°C to -101°C.

[0142] Preferably, the pressure at the top of the pre-cutting tower 207 is 1.90 MPa to 3.90 MPaG.

[0143] Preferably, the pressure at the top of the denitrification tower feed stripping tower 208 is 1.88 MPa to 3.88 MPaG;

[0144] Preferably, the pressure at the top of the denitrification tower 209 is 1.75 MPaG to 3.75 MPaG.

[0145] Preferably, the pressure at the top of the ethylene distillation tower 211 is 0.60 MPaG to 2.00 MPaG.

[0146] Furthermore, the method comprises the following steps:

[0147] S1: The pretreated gaseous ethane oxidative dehydrogenation product m is sequentially passed through the first heat exchanger 201a, the second heat exchanger 201b, the third heat exchanger 201c, the fourth heat exchanger 202a, the fifth heat exchanger 202b and the sixth heat exchanger 202c, and the product gas is graded and condensed under the cooling effect of propylene refrigerant, ethylene refrigerant, tail gas, circulating gas and condensate.

[0148] S2: The ethane oxidative dehydrogenation product m is subjected to the first gas-liquid separation in the first gas-liquid separator 204a, the gas phase is sent to the next stage heat exchanger, and the liquid phase is sent to the upper part of the pre-cutting tower 207 directly or after reheating in the fourth heat exchanger 202b;

[0149] S3: The ethane oxidative dehydrogenation product m is subjected to second-stage gas-liquid separation in the second gas-liquid separator 204a, the gas phase is sent to the next stage heat exchanger, and the liquid phase is sent to the top of the pre-cutting tower 207 directly or after being reheated in the fifth heat exchanger 202c and the fourth heat exchanger 202b;

[0150] S4: The condensate from the first gas-liquid separator 204a and the second gas-liquid separator 204b is separated from nitrogen in the pre-cutting tower 207. The bottom liquid of the pre-cutting tower does not contain nitrogen, and the bottom liquid is sent to the ethylene tower 211, and the top gas is sent to the bottom of the denitrification tower feed stripping tower 208;

[0151] S5: The ethane oxidative dehydrogenation product m is cooled by the sixth heat exchanger 202c and then sent to the top of the denitrification tower feed stripping tower 208. The third gas-liquid separation is achieved at the top of the denitrification tower feed stripping tower 208. The liquid phase and the rising gas phase in the tower bottom are contacted in countercurrent heat and mass transfer. The gas phase at the top of the tower is sent to the gas-liquid-liquid condenser 203, and the liquid phase in the tower bottom is sent to the denitrification tower 209;

[0152] S6: The gas phase at the top of the denitrification tower feed stripping tower 208 is cooled by the gas-liquid-liquid condenser 203 and then sent to the gas-liquid-liquid separator 205, and the fourth-stage gas-liquid-liquid separation is realized in the gas-liquid-liquid separator 205, wherein the gas phase returns to the gas-liquid-liquid condenser 203 for reheating and merges with the gas phase at the top of the denitrification tower 209 and is sent to the tail gas expander 210 or the tail gas throttle valve 212, the first liquid phase is sent to the denitrification tower 209 after being reheated by the gas-liquid-liquid condenser 203 or by the gas-liquid-liquid condenser 203 and the sixth heat exchanger 202c, and the second liquid phase is directly sent to the top of the denitrification tower 209 as reflux liquid;

[0153] S7: The kettle liquid of the denitrogenation tower feed stripping tower 208 and the first and second liquid phases of the gas-liquid-liquid separator 205 are separated from carbon dioxide and nitrogen in the denitrogenation tower 209. The kettle liquid of the denitrogenation tower does not contain nitrogen and is sent to the ethylene tower 211.

[0154] S8: The outlet of the tail gas expander 210 or the tail gas throttle valve 212 forms a gas-liquid two-phase and is sent to the expansion gas-liquid separator 206 to achieve the fifth stage of gas-liquid separation. The gas phase and the liquid phase respectively pass through the heat exchangers 203, 202c, 202b, 202a, 201c, 201b and 202a in sequence to recover the cold and become tail gas and circulating gas. The tail gas is directly discharged or discharged after being treated, and the circulating gas returns to the product gas compression device 106;

[0155] S9: The kettle liquid of the pre-cutting tower 207 and the kettle liquid of the denitrification tower 209 are clearly separated from ethylene and ethane in the ethylene tower 211, and the product ethylene n is produced from the top of the ethylene tower, and the circulating ethane p is produced from the bottom of the tower.

[0156] In some specific embodiments, the gas-liquid-liquid separation device 205 is a gas-liquid-liquid three-phase separation device, the first liquid phase is a hydrocarbon-rich phase with a high carbon content, and the second liquid phase is a nitrogen-rich phase with a high nitrogen content.

[0157] In some specific embodiments, the pretreated ethane oxidative dehydrogenation product gas m contains at least nitrogen, ethane and ethylene, and the pressure range is 2.00MPa to 4.00MPaG;

[0158] The temperature of the product gas m after passing through the third heat exchanger 201c is set in the range of -35°C to -41°C;

[0159] The temperature of the product gas m after passing through the sixth heat exchanger 202c is set in the range of -95°C to -101°C;

[0160] The temperature setting range of the product gas m after passing through the gas-liquid-liquid condenser 203 is -138°C to -163°C;

[0161] The pressure setting range of the top of the pre-cutting tower 207 is 1.90MPa~3.90MPaG;

[0162] The pressure setting range of the top of the denitrification tower feed stripping tower 208 is 1.88MPa to 3.88MPaG;

[0163] The pressure setting range of the top of the denitrification tower 209 is 1.75MPaG to 3.75MPaG;

[0164] The pressure setting range of the top of the ethylene tower 209 is 0.60MPaG~2.00MPaG;

[0165] The outlet pressure of the tail gas expander 210 is set in the range of 0.10 MPaG to 0.50 MPaG;

[0166] The outlet pressure of the exhaust throttle valve 212 is set in the range of 0.10 MPaG to 0.50 MPaG.

[0167] The following embodiments are implemented based on the above technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0168] In this document, unless otherwise specified, % can be regarded as molar percentage.

[0169] In order to facilitate understanding of the embodiments of the present invention, the following describes the ethane oxidative dehydrogenation process of the embodiment of the present invention:

[0170] Figure 5 This is a schematic diagram of the entire process of the ethane oxidative dehydrogenation device according to the embodiment of the present invention. An ethane feedstock a containing methane and heavy component impurities is fed into a feedstock pretreatment device 101, and the ethane feedstock a is separated into pretreated ethane feedstock b, light hydrocarbons s containing methane impurities, and heavy hydrocarbons r containing carbon three, wherein the light hydrocarbons s and heavy hydrocarbons r are discharged as products.

[0171] The pretreated ethane feedstock b and circulating ethane p are fed into an ethane oxidative dehydrogenation (ODHE) unit 102 together with air or oxygen-enriched air c and a small amount of water vapor d. Ethane and oxygen react with a catalyst to generate product ethylene and a small amount of over-oxidation by-products such as acetic acid, carbon monoxide, and carbon dioxide. The ODHE crude product gas e includes ethylene, unreacted ethane and oxygen, acetic acid, carbon monoxide, carbon dioxide, nitrogen and water vapor.

[0172] The ODHE crude product gas e after the reaction is sent to the acid-water separation device 103. After the ODHE crude product gas e is cooled and separated, the acetic acid and water therein are separated into acid water g. The acid water g is sent to the acetic acid recovery device 104 to recover the acetic acid h therein.

[0173] The deacidified ODHE product gas f after acid-water separation is sent to the deacetylenic device 105 to remove trace amounts of acetylenes. The deacetylenic ODHE product gas i is successively sent to the product gas compression device 106, the deCO 2 The device 107 and the drying device 108 remove carbon dioxide l and residual water from the ODHE product gas i to obtain the pretreated ODHE product gas m. The pretreated ODHE product gas mainly contains components such as ethylene, ethane, and nitrogen.

[0174] The pre-treated ODHE product gas m produced by the drying device 108 is sent to the product gas separation device 109 to be separated into ethylene product n, tail gas o, circulating ethane p, and circulating gas q. The circulating ethane p is sent back to the ODHE reaction device 102, and the circulating gas q is sent back to the product gas compression device 106.

[0175] The following mentioned system and method for separating the products of ethane oxidative dehydrogenation include the product gas separation device 109 in the above process.

[0176] Example 1

[0177] In this embodiment, the process of the product gas separation device 109 is shown in Figure 1 After pretreatment, the ODHE product gas m is cooled to -37°C step by step through the first heat exchanger 201a, the second heat exchanger 201b and the third heat exchanger 201c, and then sent to the fourth heat exchanger 202a. The product gas is cooled to -66°C in the fourth heat exchanger 202a to form a gas-liquid two-phase, and the gas-liquid two-phase is separated in the first gas-liquid separator 204a. The liquid phase returns to the fourth heat exchanger and is reheated to -41°C and then sent to the upper part of the pre-cutting tower 207. The gas phase is sent to the fifth heat exchanger 202b. The gas phase is cooled to -82°C in the fifth heat exchanger to form a gas-liquid two-phase, which is then separated in the second gas-liquid separator 204b. The liquid phase is successively reheated to -50°C through the fifth heat exchanger and the fourth heat exchanger and then sent to the top of the pre-cutting tower 207 as reflux liquid. The gas phase is sent to the sixth heat exchanger 202c for further cooling.

[0178] The operating pressure of the pre-cutting tower 207 is 1.90 MPaG, the tower top temperature is -49°C, and a reboiler is set at the bottom of the tower to control the nitrogen content in the kettle liquid. The top gas phase is sent to the lower part of the denitrogenation tower feed stripping tower 208, and the kettle liquid is sent to the ethylene distillation tower 211.

[0179] The product gas m is cooled to -98°C in the sixth heat exchanger 202c to form gas-liquid two-phases, and both the gas and liquid phases are sent to the top of the denitrification tower feed stripping tower 208 to separate the gas phase and the liquid phase, wherein the liquid phase is countercurrently contacted with the gas phase rising from the tower bottom for heat and mass transfer. The liquid phase itself is heated, and part of the nitrogen dissolved in the liquid phase enters the gas phase; the gas phase is cooled, and part of the carbon dioxide in the gas phase enters the liquid phase. The operating pressure of the denitrification tower feed stripping tower is 1.88MPaG, the top gas phase is sent to the gas-liquid-liquid condenser 203, and the bottom liquid phase is sent to the denitrification tower 209.

[0180] The product gas m is cooled to -156°C by the gas-liquid-liquid condenser 203 and then sent to the gas-liquid-liquid separator 205 to achieve gas-liquid-liquid three-phase separation. The operating pressure of the gas-liquid-liquid separator is 1.9 MPaG, and the gas phase composition is: N 2 :98.4%、O 2 :0.4%, CO:1.1%, C 2 :0.1%, the hydrocarbon-rich liquid phase composition is: N 2 :21.9%、C 2 :77.9%、O 2 :0.1%, CO:0.1%, the nitrogen-rich liquid phase composition is: N 2 :89.5%、C 2 :8.8%, CO:1.1%, O 2 The gas phase returns to the gas-liquid-liquid condenser 203 and is reheated to -135°C, then merged with the gas phase at the top of the denitrification tower 209 and sent to the tail gas expander 210. The first liquid phase (hydrocarbon-rich liquid phase) is reheated to -85°C through the gas-liquid-liquid condenser 203 and the sixth heat exchanger 202c and sent to the denitrification tower 209. The second liquid phase (nitrogen-rich liquid phase) is directly sent to the top of the denitrification tower 209 as reflux liquid.

[0181] The denitrogenation tower feed stripping tower 208 kettle liquid and the first and second liquid phases of the gas-liquid-liquid separator 205 are separated from carbon dioxide and nitrogen in the denitrogenation tower 209. The operating pressure of the denitrogenation tower is 1.75MPaG, and a reboiler is set in the kettle to control the nitrogen content in the kettle liquid, and the kettle liquid is sent to the ethylene distillation tower 211.

[0182] The outlet pressure of the tail gas expander 210 is set to 0.1 MPaG, and gas-liquid two-phases are formed at the outlet of the expander, and are sent to the expansion gas-liquid separator 206 to realize gas-liquid separation. The carbon dioxide content in the gas phase is less than 10 ppm, and it passes through the heat exchangers 203, 202c, 202b, 202a, 201c, 201b and 202a in sequence to recover the cold to 37°C and become tail gas o, which is discharged into the atmosphere after being treated to meet the standards; the liquid phase passes through the heat exchangers 203, 202c, 202b, 202a, 201c, 201b and 202a in sequence to recover the cold and become circulating gas q, and the circulating gas returns to the product gas compression device 106.

[0183] The bottom liquid of the pre-cutting tower 207 and the bottom liquid of the denitrification tower 209 are used to realize clear separation of ethylene and ethane in the ethylene distillation tower 211. The operating pressure of the ethylene distillation tower is 0.60 MPaG. The product ethylene n is produced from the top of the tower, and the circulating ethane p is produced from the bottom of the tower. The circulating ethane is returned to the ODHE reaction unit 102.

[0184] The flow rate and composition of the main logistics in this example are shown in Table 5.

[0185] Table 5

[0186]

[0187]

[0188] Example 2

[0189] In this embodiment, the process of the product gas separation device 109 is shown in Figure 2 After pretreatment, the ODHE product gas m is cooled to -38°C in stages through the first heat exchanger 201a, the second heat exchanger 201b and the third heat exchanger 201c to form a gas-liquid two-phase. The gas-liquid two-phase is separated in the first gas-liquid separator 204a, the liquid phase is sent to the upper part of the pre-cutting tower 207, and the gas phase is sent to the fourth heat exchanger 202a. The product gas is cooled to -66°C in the fourth heat exchanger 202a to form a gas-liquid two-phase, which is then separated in the second gas-liquid separator 204b, the liquid phase is sent to the top of the pre-cutting tower 207 as reflux liquid, and the gas phase is sent to the fifth heat exchanger 202b for further cooling.

[0190] The operating pressure of the pre-cutting tower 207 is 2.90 MPaG, the tower top temperature is -66°C, and a reboiler is set at the bottom of the tower to control the nitrogen content in the kettle liquid. The top gas phase is sent to the lower part of the denitrogenation tower feed stripping tower 208, and the kettle liquid is sent to the ethylene distillation tower 211.

[0191] The product gas m passes through the fifth heat exchanger 202b and the sixth heat exchanger 202c in turn, and is cooled to -98°C to form gas-liquid two-phases. The gas and liquid phases are sent to the top of the denitrification tower feed stripping tower 208 to separate the gas phase and the liquid phase. The liquid phase is countercurrently contacted with the gas phase rising from the bottom of the tower for heat and mass transfer. The liquid phase itself is heated, and part of the nitrogen dissolved in the liquid phase enters the gas phase; the gas phase is cooled, and part of the carbon dioxide in the gas phase enters the liquid phase. The operating pressure of the denitrification tower feed stripping tower is 2.88MPaG, the top gas phase is sent to the gas-liquid-liquid condenser 203, and the bottom liquid phase is sent to the denitrification tower 209.

[0192] The product gas m is cooled to -148°C by the gas-liquid-liquid condenser 203 and then sent to the gas-liquid-liquid separator 205 to achieve gas-liquid-liquid three-phase separation. The operating pressure of the gas-liquid-liquid separator 205 is 2.8MPaG, and the gas phase composition is: N 2 :99.5%、C2 :0.4%、CH 4 :0.1%, the hydrocarbon-rich liquid phase composition is: N 2 :25.1%、C 2 :74.5%、CH 4 :0.4%, the nitrogen-rich liquid phase composition is: N 2 :91.7%、C 2 :8.0%、CH 4 :0.3%. The gas phase returns to the gas-liquid-liquid condenser 203 to be reheated to -138°C and then merged with the gas phase at the top of the denitrification tower 209 and sent to the tail gas expander 210. The first liquid phase (hydrocarbon-rich liquid phase) is reheated to -101°C by the gas-liquid-liquid condenser 203 and then sent to the denitrification tower 209. The second liquid phase (nitrogen-rich liquid phase) is directly sent to the top of the denitrification tower 209 as reflux liquid.

[0193] The denitrogenation tower feed stripping tower 208 kettle liquid and the first and second liquid phases of the gas-liquid-liquid separator 205 are separated from carbon dioxide and nitrogen in the denitrogenation tower 209. The operating pressure of the denitrogenation tower is 2.75MPaG, and a reboiler is set in the kettle to control the nitrogen content in the kettle liquid, and the kettle liquid is sent to the ethylene distillation tower 211.

[0194] The outlet pressure of the tail gas expander 210 is set to 0.5MPaG, and gas-liquid two-phases are formed at the outlet of the expander, and are sent to the expansion gas-liquid separator 206 to realize gas-liquid separation. The carbon dioxide content in the gas phase is less than 50ppm. It passes through the gas-liquid-liquid condenser 203, the sixth heat exchanger 202c, the fifth heat exchanger 202b, the fourth heat exchanger 202a, the third heat exchanger 201c, the second heat exchanger 201b and the first heat exchanger 201a in sequence to recover the cold to 37°C and then become tail gas o directly discharged into the atmosphere; the liquid phase passes through the heat exchangers 203, 202c, 202b, 202a, 201c, 201b and 202a in sequence to recover the cold to 37°C and then become circulating gas q, and the circulating gas returns to the product gas compression device 106.

[0195] The liquid in the kettle of the pre-cutting tower 207 and the liquid in the kettle of the denitrification tower 209 are used to clearly separate ethylene and ethane in the ethylene distillation tower 211. The operating pressure of the ethylene distillation tower is 1.70 MPaG. The product ethylene n is produced from the top of the tower, and the circulating ethane p is produced from the kettle. The circulating ethane is returned to the ODHE reaction device 102. The flow rate and composition of the main logistics in this embodiment are shown in Table 6.

[0196] Table 6

[0197]

[0198] Example 3

[0199] In this embodiment, the process of the product gas separation device 109 is shown in Figure 3The difference between this embodiment and embodiment 2 is that:

[0200] 1) After pretreatment, the ODHE product gas pressure is 4.00MPaG and the molar composition is N 2 :45.1%、C 2 H 4 :26.9%、C 2 H 6 :28.0%;

[0201] 2) The operating pressure of the pre-cutting tower 207 is 3.90 MPaG, and the tower top temperature is -65°C;

[0202] 3) The operating pressure of the denitrification tower feed stripping tower 208 is 3.88 MPaG;

[0203] 4) The product gas m is cooled to -142°C by the gas-liquid-liquid condenser 203 and then sent to the gas-liquid-liquid separator 205 to achieve gas-liquid-liquid three-phase separation. The operating pressure of the gas-liquid-liquid separator is 3.8 MPaG, and the gas phase composition is: N 2 :98.8%、C 2 :1.2%, the hydrocarbon-rich liquid phase composition is: N 2 :27.1%、C 2 :72.9%, the nitrogen-rich liquid phase composition is: N 2 :95.0%、C 2 :5.0%. The gas phase returns to the gas-liquid-liquid condenser 203 and is reheated to -122°C, then merges with the gas phase at the top of the denitrification tower 209 and is sent to the tail gas throttle valve 212;

[0204] 5) The operating pressure of the denitrification tower 209 is 3.75 MPaG;

[0205] 6) The outlet pressure of the exhaust gas throttle valve 212 is set to 0.15MPaG, and gas-liquid two-phases are formed at the outlet of the exhaust gas throttle valve, which are sent to the expansion gas-liquid separator 206 to achieve gas-liquid separation. The carbon dioxide content in the gas phase is less than 0.3%. It passes through the gas-liquid-liquid condenser 203, the sixth heat exchanger 202c, the fifth heat exchanger 202b, the fourth heat exchanger 202a, the third heat exchanger 201c, the second heat exchanger 201b and the first heat exchanger 201a in sequence to recover the cold to 37°C and then become exhaust gas. After the exhaust gas is treated to meet the standards, it is discharged into the atmosphere.

[0206] 7) The operating pressure of the ethylene distillation tower 211 is 2.00 MPaG.

[0207] The flow rate and composition of the main logistics in this example are shown in Table 7.

[0208] Table 7

[0209]

[0210] Comparative Example 1

[0211] This comparative example is compared with Example 1 to compare the effects of setting a cutting tower and a denitrification tower feed stripping tower. The process of the product gas separation device 109 in this comparative example is shown in FIG. Figure 4 , which is different from Example 1, in this comparative example, the pre-cutting tower 207 is not provided, and the gas-liquid separator 213 is used to replace the denitrification tower feed stripping tower 208, and the liquid phase discharge of the gas-liquid separator 213, and the discharge of the first gas-liquid separator 204a, 204b-the second gas-liquid separator after being heated by the pre-cutting heat exchanger are sent to the denitrification tower 209. In this comparative example, the ODHE product gas m conditions are the same as those in Example 1, and the temperature settings of each stage of the heat exchanger (the first heat exchanger 201a, the second heat exchanger 201b, the third heat exchanger 201c, the fourth heat exchanger 202a, the fifth heat exchanger 202b, and the sixth heat exchanger 202c), the operating pressures of the denitrification tower 209 and the ethylene distillation tower 211, and the outlet pressure of the tail gas expander 210 are all the same as those in Example 1.

[0212] The cooling capacity consumption of each stage in the above-mentioned heat exchangers in Comparative Example 1 and Example 1 is shown in Table 8.

[0213] Table 8

[0214] Cold quality 6℃ -12℃ -41℃ -69℃ -85℃ -101℃ Comparative Example 1 Consumption (kW) 954 739 1005 3394 2226 734 Example 1 Consumption (kW) 957 741 1008 3397 2228 579

[0215] It can be seen from the above table that by setting the pre-cutting tower 207 and the denitrification tower feed stripping tower 208, the cooling consumption at the temperature of -101°C can be significantly reduced without affecting the cooling consumption at other temperatures, thereby achieving the purpose of reducing separation energy consumption.

[0216] In Comparative Example 1 and Example 1, the reflux rate of the denitrogenation tower is shown in Table 9, and the flow rate and composition of the top gas phase are shown in Table 10.

[0217] Table 9

[0218] Denitrification tower reflux rate, kg / h Comparative Example 1 11042.5 Example 1 4150.6

[0219] Table 10

[0220]

[0221]

[0222] It can be seen from Tables 9 and 10 that by setting the pre-cutting tower 207 and the denitrification tower feed stripping tower 208, the nitrogen mass flow rate in the denitrification tower feed is reduced to less than 1 / 2 of the original, which also reduces the reflux required by the denitrification tower to less than 1 / 2 of the original, reducing the refrigeration consumption. In addition, due to the reduction of nitrogen discharged from the top of the denitrification tower, the entrainment of ethylene in the top nitrogen is reduced to less than 1 / 2 of the original, reducing the ethylene loss rate of the device.

[0223] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for separating ethane oxidative dehydrogenation products, characterized in that: include: Condensing the ethane oxidative dehydrogenation product containing ethane, ethylene and nitrogen to -138°C to -163°C at 1.80 to 4.00 MPaG to obtain a crude tail gas, a nitrogen-rich liquid phase and a hydrocarbon-rich liquid phase; The nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase are sent to a denitrogenation tower (209) to remove nitrogen, and a liquid phase is taken out from the bottom of the tower and sent to an ethylene distillation tower (211). An ethylene product is taken out from the top of the tower, and ethane is taken out from the bottom of the tower.

2. The method for separating ethane oxidative dehydrogenation products according to claim 1, characterized in that: The method includes: The ethane oxidative dehydrogenation product is subjected to multi-stage cooling, and the cooling liquid phase product and the inter-stage cooling liquid phase intermediate product are collected; The interstage cooling liquid phase intermediate product is sent to the pre-cutting tower (207) as reflux liquid, the pre-cutting gas phase is taken out from the tower top, and the pre-cutting liquid phase is taken out from the tower bottom; The pre-cut gas phase and the cooled liquid phase product are stripped in a denitrification tower feed stripping tower (208) to obtain a gas phase produced at the top of the stripping tower and a liquid phase produced at the bottom of the stripping tower; The gas phase produced from the top of the stripping tower is condensed to -138°C to -163°C at 1.88 to 3.88 MPaG to obtain a crude tail gas, a nitrogen-rich liquid phase, and a hydrocarbon-rich liquid phase; The nitrogen-rich liquid phase is sent as reflux liquid to a denitrification tower (209) together with a stripping tower kettle produced liquid phase and a hydrocarbon-rich liquid phase to obtain a denitrification tower top produced gas phase and a denitrification tower kettle produced liquid phase; The liquid phase extracted from the bottom of the denitrogenation tower and the pre-cut liquid phase are sent to an ethylene distillation tower (211), and the ethylene product is extracted from the top of the tower, and ethane is extracted from the bottom of the tower. Preferably, the crude tail gas and the gas phase extracted from the top of the denitrification tower are expanded, separated into gas and liquid, and heated to obtain tail gas and circulating gas. Preferably, after expansion, the gas phase pressure is 0.10 MPaG to 0.50 MPaG. Preferably, the crude tail gas and the gas phase produced from the top of the denitrification tower undergo multi-stage heat exchange with the ethane oxidative dehydrogenation product during the heating and rewarming process. Preferably, during the multi-stage cooling process, the pressure of the ethane oxidative dehydrogenation product is 2.00 MPa to 4.00 MPaG. After the multi-stage cooling, the temperature of the ethane oxidative dehydrogenation product is -95°C to -101°C. Preferably, the pressure at the top of the pre-cutting tower (207) is 1.90 MPa to 3.90 MPaG. Preferably, the pressure at the top of the denitrification tower feed stripping tower (208) is 1.88 MPa to 3.88 MPaG; Preferably, the pressure at the top of the denitrification tower (209) is 1.75 MPaG to 3.75 MPaG. Preferably, the pressure at the top of the ethylene distillation tower (211) is 0.60 MPaG to 2.00 MPaG.

3. An ethane oxidative dehydrogenation product separation system for implementing the method according to claim 1 or 2, characterized in that: include: A gas-liquid-liquid condenser (203) is used to condense the ethane oxidative dehydrogenation product containing ethane, ethylene and nitrogen to -138°C to -163°C at 1.80 to 4.00 MPaG to obtain a condensed ODHE product material; A gas-liquid-liquid separation device (205) is used to separate the condensed ODHE product material into gas-liquid-liquid three phases, extract the upper liquid phase to obtain a nitrogen-rich liquid phase, and extract the lower liquid phase to obtain a hydrocarbon-rich liquid phase; A denitrification tower (209) is used to further remove nitrogen from the nitrogen-rich liquid phase and the hydrocarbon-rich liquid phase, and to produce a bottom liquid phase; as well as, The ethylene distillation tower (211) is used to separate the ethylene product and ethane from the liquid phase in the bottom of the tower.

4. The ethane oxidative dehydrogenation product separation system according to claim 3, characterized in that: The nitrogen-rich liquid phase is introduced into the denitrification tower (209) as reflux liquid, and the hydrocarbon-rich liquid phase is introduced into the denitrification tower (209) as a feed. Preferably, a denitrification tower feed stripping tower (208) is provided before the gas-liquid-liquid condenser (203), and the gas phase extracted from the top of the denitrification tower feed stripping tower (208) enters the gas-liquid-liquid condenser (203), and the liquid phase extracted from the bottom of the tower enters the denitrification tower (209).

5. The ethane oxidative dehydrogenation product separation system according to claim 3, characterized in that: The system also includes an exhaust expansion element and an expansion gas-liquid separator; The exhaust gas expansion component includes an exhaust gas expander (210) or an exhaust gas throttle valve (212); The gas phase extracted from the gas-liquid-liquid separation device (205) and the gas phase extracted from the top of the denitrification tower (209) pass through the tail gas expansion element and the expansion gas-liquid separator (206) in sequence to obtain tail gas material and circulating material.

6. The ethane oxidative dehydrogenation product separation system according to claim 5, characterized in that: The gas-liquid-liquid condenser (203) is provided with a product gas condensation channel connected to the inlet of the gas-liquid-liquid separation device (205), a hydrocarbon-rich liquid phase heat exchange channel connected to the hydrocarbon-rich liquid phase outlet of the gas-liquid-liquid separation device (205), a raw tail gas rewarming channel connected to the gas phase outlet of the gas-liquid-liquid separation device (205), a tail gas rewarming channel connected to the tail gas material outlet of the expansion gas-liquid separator (206), and a circulating material rewarming channel connected to the circulating material outlet of the expansion gas-liquid separator (206).

7. The ethane oxidative dehydrogenation product separation system according to claim 5, characterized in that: The system also includes a precooling unit for precooling the ethane oxidative dehydrogenation product; The precooling unit includes a precooling heat exchanger; The tail gas material and the circulating material produced by the expansion gas-liquid separator are heat exchanged with the ethane oxidation dehydrogenation product through a precooling unit to obtain tail gas and circulating gas. Preferably, the precooling unit comprises a single precooling heat exchanger or a plurality of precooling heat exchangers arranged in series. Preferably, the precooling unit comprises a first heat exchanger (201a), a second heat exchanger (201b) and a third heat exchanger (201c) which are arranged in series in sequence, and the first heat exchanger (201a), the second heat exchanger (201b) and the third heat exchanger (201c) are respectively provided with a product gas deep cooling channel, a circulating gas rewarming channel, an exhaust gas rewarming channel and a refrigerant channel.

8. The ethane oxidative dehydrogenation product separation system according to claim 7, characterized in that: A pre-cutting unit is further provided between the pre-cooling unit and the denitrification tower feed stripping tower (208), wherein the pre-cutting unit comprises a multi-stage pre-cutting heat exchanger group for performing multi-stage cooling on the ethane oxidation dehydrogenation product, and comprises a plurality of pre-cutting heat exchangers arranged in series; the outlet end of the multi-stage pre-cutting heat exchanger group is connected to the feed end of the denitrification tower feed stripping tower (208); A pre-cutting gas-liquid separator is used to separate the ethane oxidative dehydrogenation product after cooling in the pre-cooling unit, or the cooling intermediate material in the process of cooling the ethane oxidative dehydrogenation product in the multi-stage pre-cutting heat exchanger group, into a gas-liquid phase of the ethane oxidative dehydrogenation product and a liquid phase of the ethane oxidative dehydrogenation product, and the ethane oxidative dehydrogenation product gas phase is sent to the next stage pre-cutting heat exchanger; and The pre-cutting tower (207) is used to remove nitrogen from the liquid phase of the ethane oxidative dehydrogenation product. The gas phase produced from the top of the tower is sent to the denitrogenation tower feed stripping tower (208), and the liquid phase produced from the bottom of the tower is sent to the ethylene distillation tower (211).

9. The ethane oxidative dehydrogenation product separation system according to claim 8, characterized in that: The multi-stage pre-cutting heat exchanger group comprises a fourth heat exchanger (202a), a fifth heat exchanger (202b), and a sixth heat exchanger (202c) which are sequentially arranged in series; the outlet end of the sixth heat exchanger (202c) is connected to the feed end of the denitrification tower feed stripping tower (208); The pre-cutting gas-liquid separator comprises a first gas-liquid separator (204a) and a second gas-liquid separator (204b), wherein the first gas-liquid separator (204a) is arranged between the pre-cooling unit and the fourth heat exchanger (202a), and the second gas-liquid separator (204b) is arranged between the fourth heat exchanger (202a) and the fifth heat exchanger (202b); or, the first gas-liquid separator (204a) is arranged between the fourth heat exchanger (202a) and the fifth heat exchanger (202b), and the second gas-liquid separator (204b) is arranged between the fifth heat exchanger (202b) and the sixth heat exchanger (202c).

10. The ethane oxidative dehydrogenation product separation system according to claim 8, characterized in that: The pre-cutting heat exchanger is provided with a product gas deep cooling channel, a circulating gas rewarming channel, a tail gas rewarming channel and a refrigerant channel. Preferably, when the pre-cutting gas-liquid separator is arranged between adjacent pre-cutting heat exchangers, the upper pre-cutting heat exchanger among the adjacent pre-cutting heat exchangers is further provided with a condensate rewarming channel connected to the pre-cutting gas-liquid separator. Preferably, when a pre-cutting heat exchanger is provided in front of the adjacent pre-cutting heat exchanger, the pre-cutting heat exchanger is provided with an upper-level condensate rewarming channel connected to the lower-level condensate rewarming channel; the liquid phase outlet of the pre-cutting gas-liquid separator is connected in sequence to the condensate rewarming channel in the previous pre-cutting heat exchanger. Preferably, when a hydrocarbon-rich liquid phase heat exchange channel is provided in the gas-liquid-liquid condenser (203), a hydrocarbon-rich liquid phase heat exchange channel connected to the hydrocarbon-rich liquid phase heat exchange channel is provided in the last stage pre-cutting heat exchanger in the multi-stage pre-cutting heat exchanger group.

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