A system and process for recovering ethane from mixed gas

Abstract

The present invention provides a system and process for recovering ethane from a mixed gas. The system includes a separation tower, a gas stripping tower, a circulating flash tank, and a desorption tower; a raw gas inlet and a slurry outlet are arranged at the bottom of the separation tower, and a slurry inlet and a gas outlet are arranged at the top, so as to realize step-by-step countercurrent contact between the raw gas and the slurry in the tower for absorption-adsorption; a slurry outlet and a gas inlet are arranged at the bottom of the gas stripping tower, a first slurry inlet is arranged in the middle, and a second slurry inlet and a gas outlet are arranged at the top, so as to realize step-by-step countercurrent contact between the gas and the slurry entering from the first slurry inlet and the second slurry inlet respectively for absorption-adsorption; the circulating flash tank and the desorption tower are respectively provided with a slurry inlet, a gas outlet, and a slurry outlet; the slurry outlet of the separation tower is connected to the first slurry inlet of the gas stripping tower, the slurry outlet of the gas stripping tower is connected to the slurry inlet of the circulating flash tank, the gas outlet of the circulating flash tank is connected to the gas inlet of the gas stripping tower, and the slurry outlet of the circulating flash tank is connected to the slurry inlet of the desorption tower.

Description

Technical Field

[0001] The present invention relates to a mixed gas separation process, in particular to a process for separating methane and ethane in a natural gas light hydrocarbon recovery process, specifically to a process for recovering ethane from natural gas. Background Art

[0002] The mining and utilization of fossil fuels will produce gases containing a large amount of economic components, such as catalytic cracking dry gas and cracking dry gas. Ethane is a component with high economic value, and oil refining companies have a need to recycle and reuse it.

[0003] The separation of methane and ethane is usually involved in natural gas processing and petroleum refining. For example, the recovery of ethane in the natural gas light hydrocarbon recovery process mainly involves the separation of methane and ethane. The recovery of ethane, ethylene and other products from refinery dry gas involves the separation of methane and C2 components. For the existing separation processes for separating methane and ethane, there are mainly cryogenic distillation, pressure swing adsorption, membrane separation and hydrate separation. At present, the most widely used method is cryogenic distillation, which can achieve good separation effect and high-purity products. However, the conventional cryogenic distillation method needs to be carried out under such harsh conditions as high pressure and about -110°C, and requires more power equipment, high operating costs and equipment investment, which is not cost-effective in terms of economic benefits. Other processes, such as pressure swing adsorption and membrane separation, have problems of high cost and difficulty in operation, and have not been widely used. The hydrate separation method proposed in recent years is used to separate low-boiling gas mixtures, and can also be used to separate methane and ethane. Different gases have different degrees of difficulty in forming hydrates. By generating hydrates, the components that are easy to form hydrates can be preferentially allowed to enter the hydrate phase, thereby achieving separation of gas mixtures. The hydrate method can be carried out under mild conditions above 0°C. Compared with the cryogenic distillation method, the energy consumption is greatly reduced, but there are still problems such as high hydrate formation pressure and difficult to control formation rate. Summary of the invention

[0004] In view of the deficiencies of the prior art, the object of the present invention is to provide a system and process for recovering ethane from a mixed gas, by which ethane can be recovered from a mixed gas with a low ethane content, such as natural gas.

[0005] The present invention provides a system for recovering ethane from mixed gas, wherein the system comprises a separation tower, a gas stripping tower, a circulating flash tank, and a desorption tower; wherein:

[0006] The bottom of the separation tower is provided with a raw gas inlet and a slurry outlet, and the top is provided with a slurry inlet and a gas outlet; the separation tower is used to realize the step-by-step countercurrent contact of the raw gas entering the separation tower from the raw gas inlet and the slurry entering the separation tower from the slurry inlet in the tower for absorption-adsorption;

[0007] The gas stripping tower is provided with a slurry outlet and a gas inlet at the bottom, a first slurry inlet in the middle, and a second slurry inlet and a gas outlet at the top; wherein the middle refers to the position between the second slurry inlet and the gas inlet on the gas stripping tower; the gas stripping tower is used to realize the step-by-step countercurrent contact between the gas entering from the gas inlet and the slurry entering from the first slurry inlet and the slurry entering from the second slurry inlet for absorption-adsorption;

[0008] The circulating flash tank is provided with a slurry inlet, a gas outlet, and a slurry outlet;

[0009] The desorption tower is provided with a slurry inlet, a gas outlet, and a slurry outlet;

[0010] Among them, the slurry outlet of the separation tower is connected to the first slurry inlet of the gas stripping tower, the slurry outlet of the gas stripping tower is connected to the slurry inlet of the circulating flash tank, the gas outlet of the circulating flash tank is connected to the gas inlet of the gas stripping tower, and the slurry outlet of the circulating flash tank is connected to the slurry inlet of the desorption tower.

[0011] In the above system, preferably, the gas outlet of the circulating flash tank is arranged at the top of the circulating flash tank, and the slurry outlet of the circulating flash tank is arranged at the bottom of the circulating flash tank.

[0012] In the above system, preferably, the gas outlet of the desorption tower is arranged at the top of the desorption tower, and the slurry outlet of the desorption tower is arranged at the bottom of the desorption tower.

[0013] In the above system, preferably, the system further comprises a first cooler; the inlet of the first cooler is connected to the gas outlet of the circulating flash tank, and the outlet of the first cooler is connected to the gas inlet at the bottom of the stripping tower, so as to cool the gas flashed out of the circulating flash tank before entering the stripping tower.

[0014] In the above system, preferably, the system further comprises a gas compressor; the inlet of the gas compressor is connected to the gas outlet of the circulating flash tank, and the outlet of the gas compressor is connected to the gas inlet at the bottom of the gas stripping tower, for pressurizing the gas flashed out of the circulating flash tank and transporting it to the gas stripping tower.

[0015] In the above system, preferably, the slurry outlet at the bottom of the desorption tower is connected to the slurry inlet at the top of the separation tower and the second slurry inlet at the top of the stripping tower, respectively, so as to realize the recycling of the slurry after desorption in the desorption tower.

[0016] In the above system, when the slurry outlet at the bottom of the desorption tower is respectively connected to the slurry inlet at the top of the separation tower and the inlet of the second slurry at the top of the gas stripping tower to realize the recycling of the slurry after desorption in the desorption tower, the system preferably further includes a second cooler and a third cooler, the inlet of the second cooler is connected to the slurry outlet at the bottom of the desorption tower, the outlet of the second cooler is connected to the inlet of the slurry at the top of the separation tower, and is used to cool the slurry after desorption in the desorption tower before entering the separation tower, the inlet of the third cooler is connected to the slurry outlet at the bottom of the desorption tower, and the outlet of the third cooler is connected to the inlet of the second slurry at the top of the gas stripping tower, and is used to cool the slurry after desorption in the desorption tower before entering the gas stripping tower.

[0017] In the above system, when the slurry outlet at the bottom of the desorption tower is respectively connected to the slurry inlet at the top of the separation tower and the inlet of the second slurry at the top of the gas stripping tower to realize the recycling of the slurry after desorption in the desorption tower, the system preferably further includes a first slurry booster pump and a second slurry booster pump, the inlet of the first slurry booster pump is connected to the slurry outlet at the bottom of the desorption tower, the outlet of the first slurry booster pump is connected to the slurry inlet at the top of the separation tower, and is used to pressurize and transport the slurry after desorption in the desorption tower to the separation tower, the inlet of the second slurry booster pump is connected to the slurry outlet at the bottom of the desorption tower, and the outlet of the second slurry booster pump is connected to the inlet of the second slurry at the top of the gas stripping tower, and is used to pressurize and transport the slurry after desorption in the desorption tower to the gas stripping tower.

[0018] In the above system, preferably, the equilibrium number of stages of the separation tower is 3-5; and the equilibrium number of stages of the stripping tower is 5-10.

[0019] In the above system, the tower height of the separation tower and the gas stripping tower can be determined by the formula tower height = mass transfer unit height × number of mass transfer units, wherein the mass transfer unit height is 0.5m-1.5m, and the number of mass transfer units is the equilibrium stage, wherein the equilibrium stage can be determined according to the feed composition and the purity of the recovered ethane, the equilibrium stage of the separation tower is determined according to the feed composition and the purity of the gas at the top of the tower (for example, the separation of methane and ethane mixed gas is determined according to the purity requirement of methane), and the equilibrium stage of the gas stripping tower is determined according to the feed composition and the purity of ethane in the slurry at the bottom of the tower. The tower diameter of the separation tower and the gas stripping tower can be determined according to the size of the feed amount, that is, the gas-liquid phase load in the tower. The specific design method meets the conventional design requirements for the tower height and tower diameter of the adsorption tower.

[0020] In the above system, the specific position of the first slurry inlet in the stripping tower is designed according to the ethane content in the slurry entering from the first slurry inlet and the ethane content at different positions of the stripping tower under the working state, and its design meets the conventional design requirements of the feed inlet of the adsorption tower.

[0021] In the above system, a low-pressure desorption tank can be selected as the desorption tower.

[0022] The present invention also provides a process for recovering ethane from a mixed gas using the system for recovering ethane from a mixed gas, wherein the process comprises the following steps:

[0023] 1) allowing the mixed gas to enter the separation tower and contact with the slurry in reverse order step by step for absorption-adsorption to obtain a first absorption-adsorption slurry; wherein the slurry is a slurry of a ZIF-8 / water-ethylene glycol system;

[0024] 2) The first absorption-adsorption slurry enters from the middle of the stripping tower, and the slurry enters from the top of the stripping tower. The gas flashed from the circulating flash tank enters from the bottom of the stripping tower. The gas is countercurrently contacted with the slurry that absorbs and adsorbs ethane and the slurry step by step, and absorption-adsorption is carried out under the conditions of -15°C-+10°C and 1-10Mpa to obtain the second absorption-adsorption slurry; the second absorption-adsorption slurry is flashed under reduced pressure in the circulating flash tank to obtain the third absorption-adsorption slurry; the flashed gas enters the bottom of the stripping tower, participates in the absorption-adsorption of the stripping tower, and forms a cycle;

[0025] The middle part refers to the position between the slurry entry position and the gas entry position on the gas stripping tower;

[0026] 3) The third absorption slurry enters a desorption tower for desorption to obtain ethane;

[0027] In the above-mentioned process for recovering ethane, preferably, the temperature in the separation tower is -15°C to +10°C, and the pressure is 1-10 MPa; more preferably, the pressure in the separation tower is 5-10 MPa.

[0028] In the above-mentioned process for recovering ethane, preferably, the pressure in the stripping tower is 1-5 MPa.

[0029] In the above-mentioned process for recovering ethane, preferably, the process further comprises: the slurry after desorption in the desorption tower is returned to the separation tower and the gas stripping tower for recycling; more preferably, the slurry after desorption in the desorption tower is cooled before returning to the separation tower and the gas stripping tower; further preferably, the slurry after desorption in the desorption tower is cooled to the temperature inside the separation tower and the gas stripping tower before returning to the separation tower and the gas stripping tower. When the slurry after the desorption tower is returned to the separation tower and the gas stripping tower through the circulation pump, the slurry will heat up after passing through the circulation pump. At this time, the slurry can be cooled to the temperature inside the separation tower and the gas stripping tower respectively before being transported into the separation tower and the gas stripping tower. The reason is that low temperature is more conducive to the absorption-adsorption process.

[0030] In the above-mentioned process for recovering ethane, preferably, the pressure of the reduced pressure flash evaporation is 0.3-0.7 MPa.

[0031] In the above-mentioned process for recovering ethane, preferably, the content of ethane in the mixed gas is not higher than 10 mol%.

[0032] In the above-mentioned process for recovering ethane, preferably, the mixed gas is a mixed gas whose main key component is ethane; more preferably, the mixed gas is natural gas; further preferably, the mixed gas is a mixed gas of methane and ethane.

[0033] By using the ZIF-8 / water-ethylene glycol slurry system, the water-ethylene glycol solvent is the absorbent and the ZIF-8 is the adsorbent, the light gas mixture can be separated by the absorption-adsorption coupling method. Taking the separation of methane and ethane mixed gas as an example, the separation mechanism is as follows: the solvent molecules form a liquid film around the ZIF-8 particles, which has permeation selectivity for different gas molecules, and ethane is easier to enter this film than methane. In addition, the selective adsorption capacity of ZIF-8 itself for ethane is greater than that for methane, and further selectively adsorbs ethane and methane in the dissolved gas. This is equivalent to achieving the superposition of absorption-adsorption separation effects, so that the separation effect of the suspended slurry for ethane and methane is higher than that of single absorption separation or single adsorption separation. The ZIF-8 / water-ethylene glycol slurry system can not only be regenerated, but also has excellent stability. Since the slurry is flowable, multi-stage separation can be achieved in the separation tower.

[0034] The above-mentioned process for recovering ethane mainly consists of two links: gas absorption-adsorption and slurry desorption. The absorption-adsorption link uses a two-stage separation method, and absorption-adsorption is performed in a separation tower and a gas stripping tower respectively. The gas-liquid ratio in the separation tower is large, so the absorption and adsorption operation in the separation tower is used to separate methane (and other gas components in the mixed gas), and the gas-liquid ratio in the gas stripping tower is small, so the absorption and adsorption operation in the gas stripping tower is used to recover ethane. The operating pressure of the separation tower can be consistent with the raw gas pressure, which is used to maintain the pressure of the tower top rich methane (and other gas components in the mixed gas). The pressure of the gas stripping tower is lower than that of the separation tower, and the optimal pressure that is conducive to the separation of ethane from other gases in the mixed gas can be selected. The desorption link is carried out through a circulating flash tank and a desorption tower. Most of the gas evaporated from the circulating flash tank is ethane and also contains some methane (and other gas components in the mixed gas). The gas returns to the gas stripping tower, which increases the ethane concentration in the gas stripping tower, which is conducive to the absorption-adsorption of ethane in the slurry in the gas stripping tower and the separation of other gases in the mixed gas. The slurry after the cyclic flash evaporation is desorbed and recovered in a desorption tower to obtain high-purity ethane.

[0035] The system and process provided by the present invention can be applied to separating methane and ethane mixed gas, removing methane and other light components from natural gas, and recovering ethane components. However, the application scope of the process flow is not limited to the above aspects.

[0036] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0037] (1) The technical solution provided by the present invention can realize the recovery of ethane from mixed gases with low ethane content, such as natural gas.

[0038] (2) The existing process usually adopts a one-stage separation method, that is, all absorption-adsorption operations are completed in a single tower. However, when the content of ethane gas in the mixed gas is low, the one-stage method is not applicable. When the content of ethane gas in the mixed gas is low, if a single tower operation is used, due to the low ethane content in the raw gas (i.e., the mixed gas), the amount of gas flashed out of the circulating flash tank is small, and after returning to the tower, the gas phase load in the lower section of the tower is too small, and the gas phase may be completely absorbed by the slurry, resulting in insufficient gas phase and large liquid phase load, causing tower flooding. The technical solution provided by the present invention effectively avoids the above problems.

[0039] (3) In the technical solution provided by the present invention, the height and diameter of the separation tower and the gas stripping tower can be flexibly designed according to the feed and function, which is more economical and reasonable than single tower operation.

[0040] (4) Different from the conventional cryogenic distillation method, the technical solution provided by the present invention can realize the recovery of ethane in the mixed gas under mild conditions such as -15-10°C and 1-5MPa, and the absorption-adsorption process and the desorption process are operated at relatively constant temperatures, without energy consumption caused by temperature fluctuations, thereby reducing the energy consumption of the entire process, and reducing equipment investment and operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of a system for recovering ethane from a mixed gas provided in Example 1.

[0042] Figure 2 This is a schematic diagram of the system for recovering ethane from a mixed gas used in Comparative Example 1.

[0043] Figure 3 This is a schematic diagram of the system for recovering ethane from the mixed gas used in Comparative Example 2.

[0044] Figure 4 This is a schematic diagram of the system for recovering ethane from the mixed gas used in Comparative Example 3.

[0045] Figure 5 This is a schematic diagram of the system for recovering ethane from the mixed gas used in Comparative Example 4. DETAILED DESCRIPTION

[0046] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0047] In the following examples and comparative examples, the desorbed slurry was recycled. Figure 1-Figure 5 The abstract and the accompanying drawings are schematic diagrams under the circulation state, wherein the slurry outlet at the bottom of the low-pressure desorption tank V102 is directly connected to the slurry inlet at the top of the separation tower T101 and / or the stripping tower T102. It is explained here that in the stage where a stable circulation is not formed, the slurry entering from the slurry inlet at the top of the separation tower T101 and / or the stripping tower T102 is fully provided or partially supplemented by the slurry supply device according to the actual situation, and the slurry supply device stops supplying slurry after the circulation is stable.

[0048] Example 1

[0049] This embodiment provides a system for recovering ethane from a mixed gas, and its structure is as follows: Figure 1 shown.

[0050] The system comprises a separation tower T101, a gas stripping tower T102, a circulating flash tank V101, a low-pressure desorption tank V102, a circulating compressor K101, a circulating gas cooler E101, circulating slurry coolers E102 and E103, and circulating slurry booster pumps P101 and P102; wherein the separation tower T101 is a short and thick tower, and the gas stripping tower T102 is a slender tower;

[0051] The separation tower T101 is provided with a raw gas inlet and a slurry outlet at the bottom, and a slurry inlet and a gas outlet at the top. The separation tower T101 can realize the step-by-step countercurrent contact of the raw gas entering the separation tower T101 from the bottom raw gas inlet and the slurry entering the separation tower T101 from the top slurry inlet in the tower for absorption-adsorption;

[0052] The gas stripping tower T102 is provided with a slurry outlet and a gas inlet at the bottom, a first slurry inlet in the middle, and a second slurry inlet and a gas outlet at the top; the gas stripping tower T102 is used to realize the step-by-step countercurrent contact between the gas entering from the gas inlet and the slurry entering from the first slurry inlet and the slurry entering from the second slurry inlet for absorption-adsorption;

[0053] The circulating flash tank V101 has a slurry inlet, a gas outlet at the top and a slurry outlet at the bottom;

[0054] The low-pressure desorption tank V102 is provided with a slurry inlet, a gas outlet at the top, and a slurry outlet at the bottom;

[0055] The slurry outlet at the bottom of the separation tower T101 The slurry leaving the separation tower T101 is sent to the middle of the stripping tower T102;

[0056] The slurry outlet at the bottom of the separation tower T101 is connected to the first slurry inlet in the middle of the stripping tower T102; the slurry outlet at the bottom of the stripping tower T102 is connected to the slurry inlet of the circulating flash tank V101; the gas outlet at the top of the circulating flash tank V101 is connected to the input port of the circulating compressor K101, the output port of the circulating compressor K101 is connected to the input port of the circulating gas cooler E101, and the output port of the circulating gas cooler E101 is connected to the gas inlet at the top of the stripping tower T102; the slurry outlet at the bottom of the circulating flash tank V101 is connected to the slurry inlet of the low-pressure desorption tank V102. The inlet is connected; the slurry outlet at the bottom of the low-pressure desorption tank V102 is respectively connected to the input ports of the circulating slurry booster pumps P101 and P102, wherein the output port of the circulating slurry booster pump P101 is connected to the input port of the cooler E102, the output port of the cooler E102 is connected to the inlet of the second slurry at the top of the stripping tower T102, the output port of the circulating slurry booster pump P102 is connected to the input port of the cooler E103, the output port of the cooler E103 is connected to the slurry inlet at the top of the separation tower T101, so as to realize the recycling of the slurry after desorption in the low-pressure desorption tank V102.

[0057] In addition, the system can connect compressors to the gas outlets of the separation tower T101, the gas stripping tower T102, and the compression desorption tank V102 according to actual conditions to transport the gas therein into the gas transmission network, for example Figure 1 As shown, the gas outlet of the gas stripping tower T102 is connected to the compressor K102 to transport the methane gas therein into the methane gas transmission pipeline network.

[0058] This embodiment provides a process for recovering ethane from a mixed gas of methane (CH4) and ethane (C2H6). The process is carried out using the system for recovering ethane from a mixed gas provided in this embodiment (wherein the separation tower T101 has a tower height of 1.5-2.5 m and a tower diameter of 1-1.5 m; the gas stripping tower T102 has a tower height of 2.5-5 m and a tower diameter of 0.5-1 m). The specific steps are as follows:

[0059] 1) The raw gas entering the separation tower T101 from the raw gas inlet at the bottom of the separation tower T101 is countercurrently contacted with the slurry entering the separation tower T101 from the top in the tower step by step, so as to realize the absorption-adsorption of the gas in the slurry of the ZIF-8 / water-ethylene glycol system, and obtain the first absorption-adsorption slurry and methane; wherein the methane gas directly enters the methane transmission pipeline network,

[0060] The raw gas contains 94 mol% CH4 and 6 mol% C2H6, and the temperature in the separation tower T101 is 0-5°C and the pressure is 5-10MPa;

[0061] 2) The first absorption-adsorption slurry in step 1) is transported from the slurry outlet at the bottom of the separation tower T101 to the first slurry inlet of the stripping tower T102 and enters the stripping tower T102. The circulating flash gas obtained by the reduced-pressure flash evaporation of the circulating flash tank V101 is pressurized by the circulating compressor K101, enters the circulating gas cooler E101 to be cooled to the temperature in the stripping tower T102, and then enters the stripping tower T102 from the gas inlet at the bottom of the stripping tower T102. The circulating flash gas entering the stripping tower is countercurrently contacted with the first absorption-adsorption slurry and the slurry entering from the second slurry inlet at the top of the stripping tower T102 in the tower step by step for absorption-adsorption, thereby obtaining a second absorption-adsorption slurry and methane gas; wherein, the methane gas in the stripping tower The methane is enriched at the top of the stripping tower T102, and the methane enriched at the top of the stripping tower T102 is collected through the gas outlet at the top of the stripping tower T102. The methane gas enters the methane transmission network after passing through the compressor K102. The second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and is transported to the circulating flash tank V101 connected thereto through the slurry outlet at the bottom of the stripping tower T102; the second absorption-adsorption slurry enters the circulating flash tank V101 for reduced pressure flash evaporation to obtain circulating flash gas and the third absorption-adsorption slurry, wherein the circulating flash gas obtained by the reduced pressure flash evaporation in the circulating flash tank V101 enters the stripping tower T102 through the circulating compressor K101 and the circulating gas cooler E101 to participate in the absorption-adsorption of the stripping tower T102, forming a cycle;

[0062] Among them, the temperature in the stripping tower T102 is 0-5℃ and the pressure is 1Mpa; the pressure of the reduced pressure flash evaporation in the circulating flash tank V101 is 0.3-0.7Mpa;

[0063] 3) The third absorption and adsorption slurry is transported from the slurry outlet at the bottom of the circulating flash tank V101 to the slurry inlet of the low-pressure desorption tank V102, and enters the low-pressure desorption tank V102 for desorption to obtain ethane; the slurry obtained after desorption is pressurized by the circulating slurry booster pumps P101 and P102, respectively, and then cooled to 0°C by coolers E102 and E103 respectively, and then transported to the slurry inlet at the top of the separation tower T101 and the slurry inlet at the top of the stripping tower T102 respectively.

[0064] The purity of the ethane recovered in this embodiment is not less than 96%.

[0065] The gas-liquid ratio in the separation tower T101 is large, so the operation in the separation tower T101 is mainly used to recover methane. The absorption-adsorption amount of ethane in the slurry is larger than that of methane. More ethane enters the slurry, and the methane gas is enriched at the top of the tower, which can maintain the pressure of the methane-rich top of the tower and can be transported out without compression. Because the molar composition of methane in the raw gas accounts for a large proportion, high-purity methane can be obtained in only one or two equilibrium stages, so short and thick towers such as the separation tower T101 are suitable for the operation requirements of step 1).

[0066] The gas-liquid ratio in the stripping tower T102 is small, so the operation in the stripping tower T102 is mainly used to recover ethane with a small content. The gas obtained by the reduced pressure flash evaporation of the circulating flash tank V101 is returned to the bottom of the stripping tower T102 to increase the ethane content in the stripping tower T102, and the ethane recovery rate in the tower and the purity of ethane in the slurry are increased by utilizing the hindering effect of ethane on the adsorption of methane. Because the ethane content is small, more equilibrium stages are required to achieve high purity requirements, so slender towers such as the stripping tower T102 are suitable for the operation requirements of step 2).

[0067] Example 2

[0068] This embodiment provides a process for recovering ethane from a methane and ethane mixed gas, wherein the methane and ethane mixed gas contains 94 mol% CH4 and 6 mol% C2H6, the pressure is 5.5 MPa, the temperature is 0°C, and the mixed gas processing scale is 1 kmol / h; the gas transmission pressure of the separated methane is 5.5 MPa; the slurry is a slurry of the ZIF-8 / water-ethylene glycol system; the process is carried out using the system for recovering ethane from a mixed gas provided in Example 1, wherein the separation tower T101 has a tower height of 1.5 m, a tower diameter of 1.2 m, and a separation tower T101 equilibrium stage number of 3; the gas stripping tower T102 has 8 equilibrium stages, the gas stripping tower T102 has a tower height of 4 m, a tower diameter of 0.8 m, and the first slurry inlet of the gas stripping tower T102 is set at the third equilibrium stage position. The specific steps of the process are as follows:

[0069] 1) The methane and ethane mixed gas output from the raw gas inlet at the bottom of the separation tower T101 and entering the separation tower T101 is countercurrently contacted step by step in the tower with the slurry entering the separation tower T101 from the top, so as to realize the absorption-adsorption of the gas in the slurry, and obtain the first absorption-adsorption slurry and methane gas; wherein, the methane gas is enriched at the top of the separation tower T101, and the methane enriched at the top of the separation tower T101 is collected through the gas outlet at the top of the separation tower T101, and the methane gas directly enters the methane transmission pipeline network, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

[0070] The slurry temperature is 0°C, the pressure is 5.5 MPa, and the flow rate of the slurry entering the separation tower T101 is 0.24 m 3 / h;

[0071] The temperature in separation tower T101 is 0-1°C and the pressure is 5.5MPa;

[0072] The purity of the methane gas collected through the gas outlet at the top of the separation tower T101 is 98.75%, the flow rate is 0.58 kmol / h, the temperature is 0°C, and the pressure is 5.5 MPa;

[0073] The ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 is 14.3 mol% (based on the total amount of gas absorbed-adsorbed in the first slurry as 100%), the temperature is 0.7° C., and the pressure is 5.5 MPa;

[0074] 2) The first absorption-adsorption slurry in step 1) is transported from the slurry outlet at the bottom of separation tower T101 to the first slurry inlet of stripping tower T102 and enters stripping tower T102. The circulating flash gas obtained by reduced-pressure flash evaporation in circulating flash tank V101 is pressurized to 1 MPa (the temperature rises to 72°C) by circulating compressor K101, enters circulating gas cooler E101 to cool down to 2.8°C, and then enters stripping tower T102 from the gas inlet at the bottom of stripping tower T102. The circulating flash gas entering stripping tower T102 is countercurrently contacted with the first absorption-adsorption slurry and the slurry entering from the second slurry inlet at the top of stripping tower T102 in the tower step by step for absorption-adsorption, thereby obtaining a second absorption-adsorption slurry and methane gas; wherein, methane The gas is enriched at the top of the stripping tower T102, and the methane enriched at the top of the stripping tower T102 is collected through the gas outlet at the top of the stripping tower T102. The methane gas enters the methane transportation network after passing through the compressor K102. The second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102 and is transported to the circulating flash tank V101 connected thereto through the slurry outlet at the bottom of the stripping tower T102; the second absorption-adsorption slurry enters the circulating flash tank V101 for reduced pressure flash evaporation to obtain circulating flash gas and the third absorption-adsorption slurry, wherein the circulating flash gas obtained by the reduced pressure flash evaporation in the circulating flash tank V101 enters the stripping tower T102 through the circulating compressor K101 and the circulating gas cooler E101 to participate in the absorption-adsorption of the stripping tower T102, forming a cycle;

[0075] Among them, the temperature in the stripping tower T102 is 0-3°C and the pressure is 1Mpa;

[0076] The flow rate of the first absorption-adsorption slurry entering the stripping tower T102 is 0.256m 3 / h;

[0077] The flow rate of the slurry entering the stripping tower T102 from the second slurry inlet at the top of the stripping tower T102 is 0.14m 3 / h, temperature is 0℃, pressure is 1MPa;

[0078] The purity of the methane gas collected through the gas outlet at the top of the stripping tower T102 is 98.65 mol%, the flow rate is 0.34 kmol / h, the temperature is 0°C, and the pressure is 1 MPa;

[0079] The ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripping tower T102 is 96 mol% (the total amount of gas absorbed-adsorbed in the second slurry is 100%), the temperature is 2.8°C, the pressure is 1 MPa, and the flow rate of the second absorption-adsorption slurry transported to the circulating flash tank V101 is 0.41 m 3 / h;

[0080] The pressure of the reduced pressure flash evaporation in the circulating flash tank V101 is 0.5MPa, and the temperature is slightly lower than the tower bottom temperature at 2.6℃;

[0081] The circulating flash gas flashed out of the circulating flash tank V101 accounts for 0.5% of the raw gas volume, that is, the flow rate of the circulating flash gas entering the stripping tower T102 is 0.005 kmol / h, of which the ethane composition is 81 mol%;

[0082] The third absorption slurry obtained by flash evaporation in the circulating flash tank V101 has a temperature of 2.6°C, a pressure of 0.5 MPa, and an ethane composition of 98 mol%;

[0083] 3) The third absorption slurry is transported from the slurry outlet at the bottom of the circulating flash tank V101 to the slurry inlet of the low-pressure desorption tank V102, and enters the low-pressure desorption tank V102 for desorption to obtain the desorbed slurry and ethane gas; wherein, the ethane gas is enriched at the top of the low-pressure desorption tank V102, and the ethane enriched at the top of the low-pressure desorption tank V102 is collected through the gas outlet at the top of the low-pressure desorption tank V102, and the desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the desorbed slurry is divided into two streams, one of which has a flow rate of 0.24m 3 / h, the circulating slurry booster pump P102 pressurizes it to 5.5MPa, and then cools it to 0℃ through the cooler E103 and transports it to the slurry inlet at the top of the separation tower T101. The other stream flow rate is 0.14m 3 / h, the circulating slurry booster pump P101 increases the pressure to 1MPa, and then cools it to 0℃ through E102 before being transported to the second slurry inlet at the top of the stripping tower T102;

[0084] Among them, the temperature of the low-pressure desorption tank V102 is 0°C and the pressure is normal pressure;

[0085] The flow rate of the third absorption-adsorption slurry entering the low-pressure desorption tank V102 is 0.38m 3 / h;

[0086] The purity of the ethane gas collected through the gas outlet at the top of the low-pressure desorption tank V102 is 97 mol%, and the flow rate is 0.058 kmol / h.

[0087] Comparative Example 1

[0088] This comparative example provides a process for recovering ethane from a methane-ethane mixed gas, wherein the methane-ethane mixed gas contains 94 mol% CH4 and 6 mol% C2H6, the pressure is 5.5 MPa, the temperature is 0°C, and the mixed gas processing scale is 1 kmol / h; the gas transmission pressure of the separated methane is 5.5 MPa; the slurry is a slurry of a ZIF-8 / water-ethylene glycol system; the process uses Figure 2 The system for recovering ethane from mixed gas shown in the figure is carried out, wherein the separation tower T101 has a tower height of 4m, a tower diameter of 1.5m, and a separation tower T101 equilibrium stage number of 3; the gas stripping tower T102 has 8 equilibrium stages, the gas stripping tower T102 has a tower height of 4m, a tower diameter of 0.8m, and the first slurry inlet of the gas stripping tower T102 is set at the first equilibrium stage position. The specific steps of the process are as follows:

[0089] 1) The methane and ethane mixed gas output from the raw gas inlet at the bottom of the separation tower T101 and the first circulating gas generated after gas stripping by the gas stripping tower T102, output through the gas outlet at the top of the gas stripping tower T102, cooled by the cooler E101, and entering the separation tower T101 through the circulating gas inlet at the bottom of the separation tower T101 are contacted with the slurry entering the separation tower T101 from the slurry inlet at the top of the separation tower T101 in the tower step by step in countercurrent, so as to realize the absorption-adsorption of the gas in the slurry, and obtain the first absorption-adsorption slurry and methane gas; wherein, the methane gas is enriched at the top of the separation tower T101, the methane enriched at the top of the separation tower T101 is collected through the gas outlet at the top of the separation tower T101, the methane gas enters the methane transportation pipeline after passing through the compressor K102, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

[0090] The slurry temperature is 0°C, the pressure is 1MPa, and the flow rate of the slurry entering the separation tower T101 is 0.38m 3 / h;

[0091] The temperature in separation tower T101 is 0-1°C and the pressure is 1MPa;

[0092] The purity of the methane gas collected through the gas outlet at the top of the separation tower T101 is 95%, the flow rate is 0.92 kmol / h, the temperature is 0°C, and the pressure is 1 MPa;

[0093] The ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 is 14.3 mol% (based on the total amount of gas absorbed-adsorbed in the first slurry as 100%), the temperature is 0.7° C., and the pressure is 1 MPa;

[0094] The first circulating gas after cooling by cooler E101 has a temperature of 0°C, a pressure of 1 MPa, a flow rate of 0.01 kmol / h, and a methane composition of 94.5 mol%;

[0095] 2) The first absorption-adsorption slurry in step 1) is transported from the slurry outlet at the bottom of the separation tower T101 to the heater E102, heated by the heater E102, and then transported to the slurry inlet at the top of the stripping tower T102 to enter the stripping tower T102. A portion of the ethane gas (the second circulating gas) obtained by desorption in the low-pressure desorption tank V102 is compressed to 1 MPa by the circulating compressor K101 and cooled to 0°C by the circulating gas cooler E104, and then enters the stripping tower T102 through the gas inlet at the bottom of the stripping tower T102. In tower T102, the second circulating gas entering the stripping tower T102 is countercurrently contacted with the first absorption-adsorption slurry in the stripping tower T102 step by step for stripping, thereby obtaining the second absorption-adsorption slurry and the first circulating gas; wherein, the first circulating gas is output through the gas outlet at the top of the stripping tower T102, cooled by the cooler E101, and then enters the separation tower T101 to participate in the absorption-adsorption of the separation tower T101, thus forming a cycle; the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102;

[0096] Among them, the temperature in the stripping tower T102 is 10°C and the pressure is 1Mpa;

[0097] The flow rate of the first absorption-adsorption slurry entering the stripping tower T102 is 0.4m 3 / h;

[0098] The purity of methane in the first circulating gas outputted through the gas outlet at the top of the stripping tower T102 is 94.5 mol%, the flow rate is 0.01 kmol / h, the temperature is 10°C, and the pressure is 1 MPa;

[0099] The ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripping tower T102 is 93 mol% (based on the total amount of gas absorbed-adsorbed in the second slurry as 100%), the temperature is 2.8°C, the pressure is 1 MPa, and the outflow rate of the second absorption-adsorption slurry is 0.41 m 3 / h;

[0100] 3) The second absorption adsorption slurry is transported from the slurry outlet at the bottom of the stripping tower T102 to the cooler E103 and cooled to 0°C. It then enters the low-pressure desorption tank V102 through the slurry inlet for desorption to obtain the desorbed slurry and ethane gas; wherein the ethane gas is enriched at the top of the low-pressure desorption tank V102, and the ethane enriched at the top of the low-pressure desorption tank V102 is collected through the gas outlet at the top of the low-pressure desorption tank V102. The ethane gas is divided into two parts, one of which (accounting for 0.5% of the molar amount of the raw gas) , i.e. the flow rate is 0.005 kmol / h) is pressurized by the circulating compressor K101, cooled to 0°C by the circulating gas cooler E104, and enters the stripping tower T102 from the gas inlet at the bottom of the stripping tower T102 to participate in the gas stripping of the stripping tower T102 to form a cycle, and the other part is transported out as a product; the desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102, pressurized to 1 MPa by the circulating slurry booster pump P102, and then cooled to 0°C by the cooler E105 and transported to the slurry inlet at the top of the separation tower T101;

[0101] Among them, the temperature of the low-pressure desorption tank V102 is 0°C and the pressure is normal pressure;

[0102] The flow rate of the second absorption-adsorption slurry entering the low-pressure desorption tank V102 is 0.41m 3 / h;

[0103] The purity of the ethane gas collected through the gas outlet at the top of the low-pressure desorption tank V102 is 92.5 mol%, and the flow rate of the ethane gas exported as a product is 0.056 kmol / h.

[0104] It can be seen that the operating temperature of the stripping tower T102 in this process is 10°C. For temperature-raising stripping, the energy consumption of the heater E102 is more than that of Example 2. In addition, since the operating pressure of the separation tower T101 is 1MPa, and the external transmission pressure of the methane-rich gas is 5.5MPa, the methane-rich gas needs to be compressed for external transmission. In Example 2, the pressure of the methane-rich gas in the separation tower T101 is consistent with the external transmission pressure, and can be externally transmitted without compression. For detailed results of the energy consumption and ethane recovery rate comparison between Example 2 and Comparative Example 1, please refer to Table 1.

[0105] Table 1 Comparison of energy consumption and ethane recovery rate

[0106] Example 2 Comparative Example 1 Circulation pump energy consumption / kW 1.3360 0.3213 Energy consumption of circulating compressor / kW 0.0447 0.1156 Compression transmission energy consumption / kW 0.6083 1.6383 Heat exchanger energy consumption / kW 0.0609 3.9712 Total energy consumption / kW 2.0499 6.0464 Ethane recovery rate / % 93.7 93.4

[0107] *The energy consumption of the circulating pump refers to the energy consumption of the circulating slurry booster pumps P101 and P102 in Example 2, and the energy consumption of the circulating slurry booster pump P101 in the comparative example; *The energy consumption of the circulating compressor refers to the energy consumption of K101 in Example 2, and the energy consumption of K101 in the comparative example 1;

[0108] *Compression transmission energy consumption refers to the energy consumption of K102 in Example 2 and the energy consumption of K102 in Comparative Example 1;

[0109] *The energy consumption of the heat exchanger refers to the energy consumption of coolers E101, E102, and E103 in Example 2, and the energy consumption of E101, E102, E103, E104, and E105 in Comparative Example 1;

[0110] The ethane recovery rate refers to the ratio of the molar amount of ethane in the finally recovered ethane gas to the molar amount of ethane in the feed.

[0111] Compared with the process flow of comparative example 1, the process flow of recovering ethane from a mixed gas provided in Example 2 has an operating pressure of 5.5 MPa for the separation tower T101, which is the same as the methane output pressure, and the power consumption of the output compressor can be saved by 1.03 kW. The stripping tower T102 does not need to be heated for stripping, but is stripped by reducing pressure, which has no energy consumption and can save 3.91 kW of energy consumption. The total energy consumption of comparative example 1 is much higher than that of example 1.

[0112] Comparative Example 2

[0113] This comparative example provides a process for recovering ethane from a methane-ethane mixture, wherein the methane-ethane mixture contains 94 mol% CH4 and 6 mol% C2H6, the pressure is 5.5 MPa, the temperature is 0°C, and the mixed gas processing scale is 1 kmol / h; the gas transmission pressure of the separated methane is 5.5 MPa; the slurry is a slurry of the ZIF-8 / water-ethylene glycol system; wherein the separation tower T101 has a tower height of 1.5 m, a tower diameter of 1.2 m, and a separation tower T101 equilibrium stage number of 3; the gas stripping tower T102 has 3 equilibrium stages, the gas stripping tower T102 has a tower height of 1.5 m, a tower diameter of 0.8 m, and the first slurry inlet of the gas stripping tower T102 is set at the third equilibrium stage position. This process uses Figure 3 The system for recovering ethane from the mixed gas shown in the figure is carried out. The difference between this comparative example and Example 2 is that the circulating flash tank V101 is not added, and the amount of absorption-adsorption liquid and the operating conditions of the separation tower T101, the stripping tower T102, and the low-pressure desorption tank V102 are consistent with those of Example 2. The specific steps of the process are as follows:

[0114] 1) The methane and ethane mixed gas output from the raw gas inlet at the bottom of the separation tower T101 and entering the separation tower T101 is countercurrently contacted step by step in the tower with the slurry entering the separation tower T101 from the top to achieve absorption-adsorption of the gas in the slurry, and obtain a first absorption-adsorption slurry and methane gas; wherein the methane gas is enriched at the top of the separation tower T101, and the methane enriched at the top of the separation tower T101 is collected through the gas outlet at the top of the separation tower T101, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

[0115] The slurry temperature is 0°C, the pressure is 5.5 MPa, and the flow rate of the slurry entering the separation tower T101 is 0.24 m 3 / h;

[0116] The temperature in separation tower T101 is 0-1°C and the pressure is 5.5MPa;

[0117] The purity of the methane gas collected through the gas outlet at the top of the separation tower T101 is 98.75%, the flow rate is 0.58 kmol / h, the temperature is 0°C, and the pressure is 5.5 MPa;

[0118] The ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 is 14.3 mol% (based on the total amount of gas absorbed-adsorbed in the first slurry as 100%), the temperature is 0.7° C., and the pressure is 5.5 MPa;

[0119] 2) The first absorption-adsorption slurry in step 1) is transported from the slurry outlet at the bottom of the separation tower T101 to the first slurry inlet of the stripping tower T102 and enters the stripping tower T102. The first absorption-adsorption slurry and the slurry entering from the second slurry inlet at the top of the stripping tower T102 are subjected to countercurrent contact step by step in the tower for absorption-adsorption to obtain a second absorption-adsorption slurry and methane gas; wherein the methane gas is enriched at the top of the stripping tower T102, and the methane enriched at the top of the stripping tower T102 is collected through the gas outlet at the top of the stripping tower T102, and the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102;

[0120] Among them, the temperature in the stripping tower T102 is 0-3°C and the pressure is 1Mpa;

[0121] The flow rate of the first absorption-adsorption slurry entering the stripping tower T102 is 0.256m 3 / h;

[0122] The flow rate of the slurry entering the stripping tower T102 from the second slurry inlet at the top of the stripping tower T102 is 0.14m 3 / h, temperature is 0℃, pressure is 1MPa;

[0123] The purity of the methane gas collected through the gas outlet at the top of the stripping tower T102 is 95 mol%, the flow rate is 0.21 kmol / h, the temperature is 0°C, and the pressure is 1 MPa;

[0124] The ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripping tower T102 reached 13.8 mol% (based on the total amount of gas absorbed-adsorbed in the second slurry as 100%), the temperature was 2.8°C, the pressure was 1 MPa, and the flow rate of the second absorption-adsorption slurry was 0.41 m 3 / h;

[0125] 3) The second absorption adsorption slurry is transported from the slurry outlet at the bottom of the gas stripping tower T102 to the slurry inlet of the low-pressure desorption tank V102, and enters the low-pressure desorption tank V102 for desorption to obtain the desorbed slurry and ethane gas; wherein, the ethane gas is enriched at the top of the low-pressure desorption tank V102, and the ethane enriched at the top of the low-pressure desorption tank V102 is collected through the gas outlet at the top of the low-pressure desorption tank V102, and the desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the desorbed slurry is divided into two streams, one of which has a flow rate of 0.24m 3 / h, the circulating slurry booster pump P102 increases the pressure to 5.5MPa, and then cools it to 0℃ through the cooler E102 and transports it to the slurry inlet at the top of the separation tower T101. The other stream flow rate is 0.14m 3 / h, the circulating slurry booster pump P101 increases the pressure to 1MPa, and then cools it to 0℃ through E101 before being transported to the second slurry inlet at the top of the stripping tower T102;

[0126] Among them, the temperature of the low-pressure desorption tank V102 is 0°C and the pressure is normal pressure;

[0127] The flow rate of the second absorption-adsorption slurry entering the low-pressure desorption tank V102 is 0.38m 3 / h;

[0128] The purity of the ethane gas collected through the gas outlet at the top of the low-pressure desorption tank V102 is 13.5 mol%, and the flow rate is 0.416 kmol / h.

[0129] It can be seen that compared with Example 2, the failure to add the circulating flash tank V101 will result in a significant decrease in the ethane composition in the slurry entering the low-pressure desorption tank, from 98 mol% to 13.8 mol%, thereby resulting in a decrease in the purity of the recovered ethane, from 97 mol% to 13.5 mol%.

[0130] Comparative Example 3

[0131] This comparative example provides a process for recovering ethane from a methane-ethane mixture, wherein the methane-ethane mixture contains 94 mol% CH4 and 6 mol% C2H6, the pressure is 5.5 MPa, the temperature is 0°C, and the mixed gas processing scale is 1 kmol / h; the gas transmission pressure of the separated methane is 5.5 MPa; the slurry is a slurry of the ZIF-8 / water-ethylene glycol system; wherein the separation tower T101 has a tower height of 1.5 m, a tower diameter of 1.2 m, and a separation tower T101 equilibrium stage number of 3; the gas stripping tower T102 has 5 equilibrium stages, the gas stripping tower T102 has a tower height of 2.5 m, a tower diameter of 0.8 m, and the first slurry inlet of the gas stripping tower T102 is set at the first equilibrium stage position. This process uses Figure 4The system for recovering ethane from mixed gas shown in the figure is carried out. The difference between this comparative example and Example 2 is that the stripping tower T102 is not filled with fresh slurry. For the convenience of comparison, the amount of absorption-adsorption liquid and the operating conditions are consistent with those of Example 2. The specific steps of the process are as follows:

[0132] 1) The methane-rich mixed gas output from the raw gas inlet at the bottom of the separation tower T101 and entering the separation tower T101 is countercurrently contacted step by step in the tower with the slurry entering the separation tower T101 from the top, so as to realize absorption-adsorption of the gas in the slurry, and obtain a first absorption-adsorption slurry and methane gas; wherein the methane gas is enriched at the top of the separation tower T101, and the methane enriched at the top of the separation tower T101 is collected through the gas outlet at the top of the separation tower T101, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

[0133] The slurry temperature is 0°C, the pressure is 5.5 MPa, and the flow rate of the slurry entering the separation tower is 0.38 m 3 / h;

[0134] The temperature in separation tower T101 is 0-1°C and the pressure is 5.5MPa;

[0135] The purity of the methane gas collected through the gas outlet at the top of the separation tower T101 is 98.97%, the flow rate is 0.55 kmol / h, the temperature is 0°C, and the pressure is 5.5 MPa;

[0136] The ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 is 14.3 mol% (based on the total amount of gas absorbed-adsorbed in the first slurry as 100%), the temperature is 0.7° C., and the pressure is 5.5 MPa;

[0137] 2) The first absorption-adsorption slurry in step 1) is transported from the slurry outlet at the bottom of the separation tower T101 to the first slurry inlet of the stripping tower T102 and enters the stripping tower T102. The circulating flash gas obtained by the reduced pressure flash evaporation of the circulating flash tank V101 is pressurized to 1 MPa (the temperature rises to 72°C at this time) by the circulating compressor K101, enters the circulating gas cooler E101 to cool down to 2.8°C, and then enters the stripping tower from the gas inlet at the bottom of the stripping tower T102. The circulating flash gas entering the stripping tower is countercurrently contacted with the first absorption-adsorption slurry and the slurry entering from the second slurry inlet at the top of the stripping tower T102 in the tower step by step for absorption-adsorption, thereby obtaining a second absorption-adsorption slurry and methane. gas; wherein, methane gas is enriched at the top of the stripping tower T102, and the methane enriched at the top of the stripping tower T102 is collected through the gas outlet at the top of the stripping tower T102, and the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and is transported to the circulating flash tank V101 connected thereto through the slurry outlet at the bottom of the stripping tower T102; the second absorption-adsorption slurry enters the circulating flash tank V101 for reduced pressure flash evaporation to obtain circulating flash gas and the third absorption-adsorption slurry, wherein the circulating flash gas obtained by the reduced pressure flash evaporation in the circulating flash tank V101 enters the stripping tower T102 through the circulating compressor K101 and the circulating gas cooler E101 to participate in the absorption-adsorption of the stripping tower T102, forming a cycle;

[0138] Among them, the temperature in the stripping tower T102 is 0-3°C and the pressure is 1Mpa;

[0139] The flow rate of the first absorption-adsorption slurry entering the stripping tower T102 is 0.39m 3 / h;

[0140] The purity of the methane gas collected through the gas outlet at the top of the stripping tower T102 is 94 mol%, the flow rate is 0.38 kmol / h, the temperature is 0°C, and the pressure is 1 MPa;

[0141] The ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripping tower T102 is 94 mol% (the total amount of gas absorbed-adsorbed in the second slurry is 100%), the temperature is 2.8°C, the pressure is 1 MPa, and the flow rate of the second absorption-adsorption slurry transported to the circulating flash tank V101 is 0.41 m 3 / h;

[0142] The pressure of the reduced pressure flash evaporation in the circulating flash tank V101 is 0.5MPa, and the temperature is slightly lower than the tower bottom temperature at 2.6℃;

[0143] The circulating flash gas flashed out from the circulating flash tank V101 accounts for 0.5% of the raw gas, of which the ethane composition is 81 mol%;

[0144] The third absorption slurry obtained by flash evaporation in the circulating flash tank V101 has a temperature of 2.6°C, a pressure of 0.5 MPa, and an ethane composition of 95 mol%;

[0145] 3) The third absorption slurry is transported from the slurry outlet at the bottom of the circulating flash tank V101 to the slurry inlet of the low-pressure desorption tank V102, and enters the low-pressure desorption tank V102 for desorption to obtain the desorbed slurry and ethane gas; wherein, the ethane gas is enriched at the top of the low-pressure desorption tank V102, and the ethane enriched at the top of the low-pressure desorption tank V102 is collected through the gas outlet at the top of the low-pressure desorption tank V102, and the desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the flow rate of the desorbed slurry is 0.38m 3 / h, the circulating slurry booster pump P101 increases the pressure to 5.5MPa, and then cools it to 0°C through the cooler E102 before being transported to the slurry inlet at the top of the separation tower T101;

[0146] Among them, the temperature of the low-pressure desorption tank V102 is 0°C and the pressure is normal pressure;

[0147] The flow rate of the third absorption-adsorption slurry entering the low-pressure desorption tank V102 is 0.38m 3 / h;

[0148] The purity of the ethane gas collected through the gas outlet at the top of the low-pressure desorption tank V102 is 94.3 mol%, and the flow rate is 0.062 kmol / h.

[0149] It can be seen that compared with Example 2, failure to charge fresh slurry will result in a decrease in the methane content at the top of the stripping tower T102 from 98.65 mol% to 94 mol%, thereby resulting in a decrease in ethane purity from 97 mol% to 94.3 mol%.

[0150] Comparative Example 4

[0151] This comparative example provides a process for recovering ethane from a methane-ethane mixture, wherein the methane-ethane mixture contains 94 mol% CH4 and 6 mol% C2H6, the pressure is 5.5 MPa, the temperature is 0°C, and the mixed gas processing scale is 1 kmol / h; the methane gas after separation has an external transmission pressure of 5.5 MPa; the slurry is a slurry of a ZIF-8 / water-ethylene glycol system; wherein the separation tower T101 has a tower height of 1.5 m, a tower diameter of 1.2 m, and a separation tower T101 equilibrium stage number of 3; the gas stripping tower T102 has 9 equilibrium stages, the gas stripping tower T102 has a tower height of 4.5 m, a tower diameter of 0.5 m, and the first slurry inlet of the gas stripping tower T102 is set at the third equilibrium stage position. This process uses Figure 5The system for recovering ethane from the mixed gas shown in the comparative example is carried out. The difference between this comparative example and Example 2 is that the circulating flash tank V101 is removed, and a part of the ethane gas desorbed in the low-pressure desorption tank V102 is returned to the bottom of the stripping tower T102 to participate in the absorption-adsorption in the stripping tower T102. For the convenience of comparison, the absorption-adsorption liquid amount and operating conditions are consistent with those in Example 2. The specific steps of the process are as follows:

[0152] 1) The methane and ethane mixed gas output from the raw gas inlet at the bottom of the separation tower T101 and entering the separation tower T101 is countercurrently contacted step by step in the tower with the slurry entering the separation tower T101 from the top, so as to realize the absorption-adsorption of the gas in the slurry, and obtain the first absorption-adsorption slurry and methane gas; wherein, the methane gas is enriched at the top of the separation tower T101, and the methane enriched at the top of the separation tower T101 is collected through the gas outlet at the top of the separation tower T101, and the methane gas directly enters the methane transmission pipeline network, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

[0153] The slurry temperature is 0°C, the pressure is 5.5 MPa, and the flow rate of the slurry entering the separation tower T101 is 0.26 m 3 / h;

[0154] The temperature in separation tower T101 is 0-1°C and the pressure is 5.5MPa;

[0155] The purity of the methane gas collected through the gas outlet at the top of the separation tower T101 is 98.75%, the flow rate is 0.63 kmol / h, the temperature is 0°C, and the pressure is 5.5 MPa;

[0156] The ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 is 14.3 mol% (based on the total amount of gas absorbed-adsorbed in the first slurry as 100%), the temperature is 0.7° C., and the pressure is 5.5 MPa;

[0157] 2) The first absorption-adsorption slurry in step 1) is transported from the bottom slurry outlet of separation tower T101 to the first slurry inlet of stripping tower T102 and enters stripping tower T102. A portion of the ethane gas desorbed by the low-pressure desorption tank is used as circulating gas and is pressurized to 1 MPa (the temperature rises to 72°C) by circulating compressor K101, then enters circulating gas cooler E101 to cool down to 2.9°C, and then enters stripping tower T102 from the gas inlet at the bottom of stripping tower T102. The circulating gas entering stripping tower T102 is mixed with the first absorption-adsorption slurry at The slurry entering from the second slurry inlet at the top of the stripping tower T102 is subjected to countercurrent contact step by step in the tower for absorption-adsorption to obtain a second absorption-adsorption slurry and methane gas; wherein, the methane gas is enriched at the top of the stripping tower T102, and the methane enriched at the top of the stripping tower T102 is collected through the gas outlet at the top of the stripping tower T102, and the methane gas enters the methane transmission pipeline after passing through the compressor K102, and the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and is transported to the low-pressure desorption tank V102 connected thereto through the slurry outlet at the bottom of the stripping tower T102;

[0158] Among them, the temperature in the stripping tower T102 is 0-3°C and the pressure is 1Mpa;

[0159] The flow rate of the first absorption-adsorption slurry entering the stripping tower T102 is 0.277m 3 / h;

[0160] The flow rate of slurry entering the stripping tower T102 from the second slurry inlet at the top of the stripping tower T102 is 0.12m 3 / h, temperature is 0℃, pressure is 1MPa;

[0161] The purity of the methane gas collected through the gas outlet at the top of the stripping tower T102 is 98.65 mol%, the flow rate is 0.29 kmol / h, the temperature is 0°C, and the pressure is 1 MPa;

[0162] The ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripping tower T102 is 96.4 mol% (the total amount of gas absorbed-adsorbed in the second slurry is 100%), the temperature is 2.9°C, the pressure is 1 MPa, and the flow rate of the second absorption-adsorption slurry transported to the low-pressure desorption tank V102 is 0.41 m 3 / h;

[0163] The circulating gas accounts for 0.42% of the raw gas, that is, the flow rate of the circulating gas entering the stripping tower T102 is 0.0042 kmol / h, of which the ethane composition is 95 mol%;

[0164] 3) The second absorption adsorption slurry is transported from the slurry outlet at the bottom of the low-pressure desorption tank V102 to the slurry inlet of the low-pressure desorption tank V102 and enters the low-pressure desorption tank V102 for desorption to obtain the desorbed slurry and ethane gas; wherein, the ethane gas is enriched at the top of the low-pressure desorption tank V102, and the ethane enriched at the top of the low-pressure desorption tank V102 is collected through the gas outlet at the top of the low-pressure desorption tank V102, and a part of the ethane-rich gas is recycled back to the gas stripping tower, and the desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the desorbed slurry is divided into two streams, one of which has a flow rate of 0.26m 3 / h, the circulating slurry booster pump P102 increases the pressure to 5.5MPa, and then cools it to 0℃ through the cooler E103 and transports it to the slurry inlet at the top of the separation tower T101. The other stream flow rate is 0.12m 3 / h, the circulating slurry booster pump P101 increases the pressure to 1MPa, and then cools it to 0℃ through E102 before being transported to the second slurry inlet at the top of the stripping tower T102;

[0165] Among them, the temperature of the low-pressure desorption tank V102 is 0°C and the pressure is normal pressure;

[0166] The flow rate of the second absorption-adsorption slurry entering the low-pressure desorption tank V102 is 0.41m 3 / h;

[0167] The purity of the ethane gas collected through the gas outlet at the top of the low-pressure desorption tank V101 is 95 mol%, the flow rate is 0.052 kmol / h, and the circulating gas flow rate is 0.0042 kmol / h.

[0168] It can be seen that in Example 2, a circulating flash tank is provided, and the ethane dry basis concentration in the slurry after the circulating flash is increased from 96 mol% to 98 mol%, so that a higher purity ethane product of 97 mol% can be obtained after desorption. When a portion of the circulating gas is directly separated from the ethane-rich stream, the purity of the ethane product can only reach 95 mol%. In addition, without a circulating flash tank, the ethane content in the circulating gas increases from 81 mol% to 96.4 mol%. In order to avoid back mixing, an additional equilibrium stage needs to be provided in the stripping tower to increase the ethane content at the bottom of the tower, which increases the equipment cost.

Claims

1. A system for recovering ethane from a mixed gas, characterized in that: The system includes a separation tower, a gas stripping tower, a circulating flash tank, a desorption tower, and a first cooler; wherein, The separation tower is provided with a raw gas inlet and a slurry outlet at the bottom, and a slurry inlet and a gas outlet at the top; The stripping tower is provided with a slurry outlet and a gas inlet at the bottom, a first slurry inlet in the middle, and a second slurry inlet and a gas outlet at the top; wherein the middle refers to the position between the second slurry inlet and the gas inlet on the stripping tower; The circulating flash tank is provided with a slurry inlet, a gas outlet, and a slurry outlet; The desorption tower is provided with a slurry inlet, a gas outlet, and a slurry outlet; The slurry outlet of the separation tower is connected to the first slurry inlet of the gas stripping tower, the slurry outlet of the gas stripping tower is connected to the slurry inlet of the circulating flash tank, the gas outlet of the circulating flash tank is connected to the gas inlet of the gas stripping tower, and the slurry outlet of the circulating flash tank is connected to the slurry inlet of the desorption tower; The slurry outlet at the bottom of the desorption tower is connected to the slurry inlet at the top of the separation tower and the second slurry inlet at the top of the gas stripping tower, respectively, so as to realize the recycling of the slurry after desorption in the desorption tower; The inlet of the first cooler is connected to the gas outlet of the circulating flash tank, and the outlet of the first cooler is connected to the gas inlet at the bottom of the stripping tower.

2. The system according to claim 1, characterized in that The system further includes a gas compressor; The inlet of the gas compressor is connected to the gas outlet of the circulating flash tank, and the outlet of the gas compressor is connected to the gas inlet at the bottom of the gas stripping tower.

3. The system according to claim 1, characterized in that The system further includes a second cooler and a third cooler; the inlet of the second cooler is connected to the slurry outlet at the bottom of the desorption tower, and the outlet of the second cooler is connected to the slurry inlet at the top of the separation tower; the inlet of the third cooler is connected to the slurry outlet at the bottom of the desorption tower, and the outlet of the third cooler is connected to the inlet of the second slurry at the top of the stripping tower.

4. The system according to claim 1, characterized in that The system further comprises a first slurry booster pump and a second slurry booster pump; the inlet of the first slurry booster pump is connected to the slurry outlet at the bottom of the desorption tower, and the outlet of the first slurry booster pump is connected to the slurry inlet at the top of the separation tower; The inlet of the second slurry booster pump is connected to the slurry outlet at the bottom of the desorption tower, and the outlet of the second slurry booster pump is connected to the inlet of the second slurry at the top of the stripping tower.

5. The system according to claim 1, characterized in that The equilibrium number of the separation tower is 3-5; the equilibrium number of the stripping tower is 5-10.

6. A process for recovering ethane from a mixed gas using the system according to any one of claims 1 to 5, characterized in that: The process includes the following steps: 1) The mixed gas and the slurry are contacted with each other in a separation tower in a countercurrent manner to perform absorption-adsorption, so as to obtain a first absorption-adsorption slurry; wherein the slurry is a slurry of a ZIF-8 / water-ethylene glycol system; wherein the temperature in the separation tower is -15°C to +10°C, and the pressure is 5-10MPa; 2) The first absorption-adsorption slurry enters from the middle of the stripping tower, and the slurry enters from the top of the stripping tower. The gas flashed from the circulating flash tank enters from the bottom of the stripping tower. The gas contacts the first absorption-adsorption slurry and the slurry in countercurrent step by step, and absorbs and adsorbs at -15℃-10℃ and 1-5 MPa to obtain the second absorption-adsorption slurry; the second absorption-adsorption slurry is flashed under reduced pressure in the circulating flash tank to obtain the third absorption-adsorption slurry; the flashed gas enters the bottom of the stripping tower to participate in the absorption-adsorption of the stripping tower to form a cycle; The middle part refers to the position between the slurry entry position and the gas entry position on the gas stripping tower; 3) The adsorbed slurry enters the desorption tower for desorption to obtain ethane. The slurry after desorption in the desorption tower is returned to the separation tower and the stripping tower for recycling.

7. The process according to claim 6, characterized in that The slurry after desorption in the desorption tower is cooled before returning to the separation tower and the gas tower.

8. The process according to claim 6, characterized in that The slurry after desorption in the desorption tower is cooled to the temperature in the separation tower and the gas tower respectively before returning to the separation tower and the gas tower.

9. The process according to claim 6, characterized in that The pressure of the reduced pressure flash evaporation is 0.3-0.7 MPa.

10. The process according to claim 6, characterized in that The ethane content in the mixed gas is not higher than 10 mol.%.

11. The process according to claim 6, characterized in that The mixed gas is a mixed gas whose main key component is ethane.

12. The process according to claim 6, characterized in that The mixed gas is natural gas.

13. The process according to claim 6, characterized in that The mixed gas is a mixed gas of methane and ethane.

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