CN111747816A

CN111747816A - System and process for recovering ethane from mixed gas

Info

Publication number: CN111747816A
Application number: CN201910251376.2A
Authority: CN
Inventors: 陈光进; 彭晓婉; 陈婉; 杨明科
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2019-03-29
Filing date: 2019-03-29
Publication date: 2020-10-09

Abstract

The invention provides a system and a process for recovering ethane from a mixed gas. The system comprises a separation tower, a stripping tower, a circulating flash tank and a desorption tower; the bottom of the separation tower is provided with a raw material gas inlet and a slurry outlet, and the top of the separation tower is provided with a slurry inlet and a gas outlet, so that the raw material gas and the slurry are in stepwise countercurrent contact in the tower to carry out absorption-adsorption; the bottom of the gas stripping tower is provided with a slurry outlet and a gas inlet, the middle part of the gas stripping tower is provided with a first slurry inlet, and the top of the gas stripping tower is provided with a second slurry inlet and a gas outlet, so that gas and slurry entering from the first slurry inlet and the second slurry inlet respectively are in stepwise countercurrent contact 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 with the first slurry inlet of the stripping tower, the slurry outlet of the stripping tower is connected with the slurry inlet of the circulating flash tank, the gas outlet of the circulating flash tank is connected with the gas inlet of the stripping tower, and the slurry outlet of the circulating flash tank is connected with the slurry inlet of the desorption tower.

Description

System and process for recovering ethane from mixed gas

Technical Field

The invention relates to a separation process of mixed gas, in particular to a process for separating methane and ethane in a natural gas light hydrocarbon recovery process, and specifically relates to a process for recovering ethane from natural gas.

Background

In the process of exploiting and utilizing fossil fuels, gases containing a large amount of economic components, such as catalytic cracking dry gas, cracking dry gas and the like, are associated, wherein ethane is a component with higher economic value, and oil refining enterprises all have the requirement of recycling.

The separation of methane and ethane is commonly involved in natural gas processing and petroleum refining processes. For example, the recovery of ethane in natural gas light hydrocarbon recovery processes mainly involves the separation of methane and ethane. The products of ethane and ethylene recovered from refinery dry gas relate to methane and C₂And (4) separating components. The existing separation process for separating methane and ethane mainly comprises a low-temperature rectification method, a pressure swing adsorption method, a membrane separation method and a hydrate separation method. At present, the most widely applied method is the cryogenic rectification method, which can achieve good separation effect and high-purity products, but the conventional cryogenic rectification method needs to be carried out under the harsh conditions of high pressure and about-110 ℃, and has the disadvantages of more required power equipment, higher operating cost and equipment investment and non-economical economic benefit. Other processes, such as pressure swing adsorption and membrane separation, have the problems of high cost and difficult operation, and cannot be widely applied. Hydrate separation methods proposed in recent years are used for separating low boiling point gas mixtures, and also for separating methane and ethane. The difficulty of forming hydrates by using different gases is different, and the components which are easy to form hydrates can be preferentially introduced into hydrate phases by forming the hydrates, thereby realizing the separation of gas mixtures. The hydrate method can be carried out under the mild condition of more than 0 ℃, and compared with the low-temperature rectification method, the energy consumption is greatly reduced, but the problems of higher hydrate generation pressure, difficult control of the generation rate and the like still exist.

Disclosure of Invention

In view of the shortcomings of the prior art, it is an object of the present invention to provide a system and process for recovering ethane from a gas mixture, by which ethane recovery from a gas mixture with a low ethane content, such as natural gas, can be achieved.

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

the bottom of the separation tower is provided with a raw material gas inlet and a slurry outlet, and the top is provided with a slurry inlet and a gas outlet; the separation tower is used for realizing the absorption-adsorption of the raw material gas entering the separation tower from the raw material gas inlet and the slurry entering the separation tower from the slurry inlet by the stepwise countercurrent contact in the tower;

the bottom of the gas stripping tower is provided with a slurry outlet and a gas inlet, the middle part of the gas stripping tower is provided with a first slurry inlet, and the top of the gas stripping tower is provided with a second slurry inlet and a gas outlet; wherein the middle part refers to the position from the second slurry inlet to the gas inlet on the stripping tower; the gas stripping tower is used for realizing the absorption-adsorption of the gas entering from the gas inlet, the slurry entering from the first slurry inlet and the slurry entering from the second slurry inlet in a stepwise countercurrent contact manner;

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 with the first slurry inlet of the gas stripping tower, the slurry outlet of the gas stripping tower is connected with the slurry inlet of the circulating flash tank, the gas outlet of the circulating flash tank is connected with the gas inlet of the gas stripping tower, and the slurry outlet of the circulating flash tank is connected with the slurry inlet of the desorption tower.

In the above system, preferably, the outlet of the gas of the circulation flash tank is arranged at the top of the circulation flash tank, and the slurry outlet of the circulation flash tank is arranged at the bottom of the circulation flash tank.

In the above system, preferably, the outlet of the gas of the desorption tower is provided at the top of the desorption tower, and the slurry outlet of the desorption tower is provided at the bottom of the desorption tower.

In the above system, preferably, the system further comprises a first cooler; the inlet of the first cooler is connected with the gas outlet of the circulation flash tank, the outlet of the first cooler is connected with the gas inlet at the bottom of the stripping tower, and the first cooler is used for cooling the gas flashed out from the circulation flash tank before entering the stripping tower.

In the above system, preferably, the system further comprises a gas compressor; the inlet of the gas compressor is connected with the gas outlet of the circulating flash tank, and the outlet of the gas compressor is connected with the gas inlet at the bottom of the stripping tower and used for pressurizing and conveying the gas flashed out from the circulating flash tank to the stripping tower.

In the above system, preferably, 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 second slurry inlet at the top of the stripping tower, so as to recycle the slurry desorbed by the desorption tower.

In the above system, when 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, for recycling the slurry desorbed from the desorption tower, the system preferably further comprises a second cooler and a third cooler, wherein 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 slurry inlet at the top of the separation tower, for cooling the slurry desorbed from 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 second slurry inlet at the top of the stripping tower, for cooling the slurry desorbed from the desorption tower before entering the stripping tower.

In the above system, when 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 stripper tower, respectively, for recycling the slurry desorbed from the desorption tower, the system preferably further comprises a first slurry booster pump and a second slurry booster pump, wherein the first slurry booster pump has an inlet connected to the slurry outlet at the bottom of the desorption tower, an outlet connected to the slurry inlet at the top of the separation tower for boosting and delivering the slurry desorbed from the desorption tower to the separation tower, the second slurry booster pump has an inlet connected to the slurry outlet at the bottom of the desorption tower, and the second slurry booster pump has an outlet connected to the second slurry inlet at the top of the stripper tower for boosting and delivering the slurry desorbed from the desorption tower to the stripper tower.

In the above system, preferably, the number of equilibrium stages of the separation column is 3 to 5 stages; the equilibrium number of stages of the stripping tower is 5-10 stages.

In the above system, the height of the separation column and the stripping column can be determined by the formula of the height of the column, namely the height of the mass transfer unit x the number of the mass transfer units, wherein the height of the mass transfer unit is 0.5m to 1.5m, and the number of the mass transfer units is an equilibrium number, wherein the equilibrium number can be determined according to the feed composition and the purity of the recovered ethane, the equilibrium number of the separation column is determined according to the feed composition and the purity of the top gas (for example, the methane is separated, and the mixed gas of the ethane is determined according to the purity requirement of the methane), and the equilibrium number of the stripping column is determined according to the feed composition and the purity of. The tower diameters of the separation tower and the stripping tower can be determined according to the feeding amount, namely the gas-liquid phase load in the tower. The specific design method meets the conventional design requirements of the height and the diameter of the adsorption tower.

In the above system, the specific location of the first slurry inlet in the stripper column is designed based on the ethane content of the slurry entering from the first slurry inlet and the ethane content at different locations in the operating state of the stripper column, and the design meets the conventional design requirements of the feed inlet of the adsorption column.

In the system, the desorption tower can be selected from a low-pressure desorption tank.

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

1) allowing the mixed gas to enter a separation tower to be in stepwise reverse contact with the slurry for absorption-adsorption to obtain first absorption-adsorption slurry; wherein the slurry is a ZIF-8/water-glycol system slurry;

2) the first absorption-adsorption slurry enters from the middle part of a stripping tower, the slurry enters from the top part of the stripping tower, gas flashed by a circulating flash tank enters from the bottom part of the stripping tower, the gas is in stepwise countercurrent contact with the slurry absorbing-adsorbing ethane and the slurry, and absorption-adsorption is carried out under the conditions of minus 15-minus-plus 10 ℃ and 1-10Mpa to obtain second absorption-adsorption slurry; carrying out reduced pressure flash evaporation on the second absorption adsorption slurry in a circulating flash tank to obtain third absorption adsorption slurry; the gas flashed out enters the bottom of the stripping tower and participates in absorption-adsorption of the stripping tower to form circulation;

wherein the middle portion refers to a location on the stripper column between the slurry entry location and the gas entry location;

3) the third absorption adsorption slurry enters a desorption tower for desorption to obtain ethane;

in the above process for recovering ethane, preferably, the temperature in the separation column is from-zero 15 ℃ to-zero 10 ℃, and the pressure is from 1 to 10 MPa; more preferably, the pressure in the separation column is between 5 and 10 MPa.

In the above process for recovering ethane, it is preferable that the pressure in the stripper is 1 to 5 MPa.

In the above process for recovering ethane, preferably, the process further comprises: the slurry desorbed by the desorption tower returns to the separation tower and the stripping tower respectively for recycling; more preferably, the slurry desorbed by the desorption tower is cooled before returning to the separation tower and the gas tower; further preferably, the slurry desorbed from the desorption tower is cooled to the temperature in the separation tower or the gas tower before being returned to the separation tower or the gas tower. When the slurry after the desorption tower returns to the separation tower and the gas stripping tower through the circulating pump, the slurry can be heated up after passing through the circulating pump, and at the moment, the slurry can be respectively cooled to the temperatures in the separation tower and the gas stripping tower and then conveyed into the separation tower and the gas stripping tower, and the reason is that the low temperature is more favorable for the absorption-adsorption process.

In the above process for recovering ethane, preferably, the pressure of the reduced-pressure flash is 0.3 to 0.7 MPa.

In the above-described process for recovering ethane, it is preferable that the content of ethane in the mixed gas is not more than 10 mol.%.

In the above process for recovering ethane, preferably, the mixed gas is a mixed gas whose critical component is ethane; more preferably, the gas mixture is natural gas; further preferably, the mixed gas is a mixed gas of methane and ethane.

A ZIF-8/water-glycol slurry system is adopted, a water-glycol solvent is used as an absorbent, and ZIF-8 is used as an adsorbent, so that the light gas mixture can be separated by an absorption-adsorption coupling method. Taking the separation of the mixed gas of methane and ethane as an example, the separation mechanism is as follows: solvent molecules form a liquid film around the ZIF-8 particles, which is permselective to different gas molecules, and ethane is more likely to enter this film than methane. And the selective adsorption capacity of ZIF-8 to ethane is larger than that to methane, so that ethane and methane in the dissolved gas are further selectively adsorbed. Equivalent to the superposition of absorption-adsorption separation effects, so that the separation effect of the suspension slurry on ethane and methane is higher than that of single absorption separation or single adsorption separation. The ZIF-8/water-glycol slurry system can be regenerated and has excellent stability. Since the slurry is flowable, multi-stage separation can be achieved in the separation column.

The process for recovering ethane mainly comprises two links of gas absorption-adsorption and slurry desorption. The absorption-adsorption link respectively performs absorption-adsorption in a separation tower and a stripping tower by using a two-stage separation mode, the gas-liquid ratio in the separation tower is large, so that the absorption-adsorption operation in the separation tower is used for separating methane (and other gas components in the mixed gas), and the gas-liquid ratio in the stripping tower is small, so that the absorption-adsorption operation in the stripping tower is used for recovering ethane. The operating pressure of the separation column can be kept the same as the pressure of the feed gas for the pressure holding of the methane-rich gas at the top of the column (and other gas components in the mixed gas). The pressure of the stripping tower is lower than that of the separation tower, and the optimal pressure for separating 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 gas evaporated by the circulating flash tank is ethane and also contains partial methane (and other gas components in the mixed gas), and the gas returns to the stripping tower, so that the ethane concentration in the stripping tower is improved, and the absorption-adsorption of the ethane in the slurry in the stripping tower and the separation of other gases in the mixed gas are facilitated. And desorbing and recovering the slurry subjected to the circulating flash evaporation in a desorption tower to obtain high-purity ethane.

The system and the process provided by the invention can be suitable for separating methane and ethane mixed gas, and can be suitable for removing methane and other light components from natural gas and recovering ethane components. The scope of applicability of the process flow is not limited to the aspects described above.

Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects:

(1) the technical scheme provided by the invention can realize the recovery of ethane from the mixed gas with low ethane content such as natural gas.

(2) The prior art usually adopts a one-stage separation mode, namely, the whole absorption-adsorption operation is completed in a single tower, but the one-stage mode cannot be applied when the content of ethane gas in the mixed gas is low. When the content of ethane gas in the mixed gas is low, if single-tower operation is adopted, because the ethane content in the raw material gas (namely the mixed gas) is low, the gas amount flashed out by the circulating flash tank is small, the gas phase load at the lower section of the tower is too small after the mixed gas returns to the tower, the gas phase can be completely absorbed by the slurry, and the gas phase is insufficient, the liquid phase load is large, so that the tower flooding is caused. The technical scheme provided by the invention effectively avoids the problems.

(3) According to the technical scheme provided by the invention, the separation tower and the stripping tower can flexibly design the tower height and the tower diameter according to different feeding and functions, and the operation is more economical and reasonable compared with single tower operation.

(4) Different from the conventional low-temperature rectification method, the technical scheme provided by the invention can realize the recovery of ethane in the mixed gas under the mild conditions of-15 to-10 ℃ and 1 to 5MPa, and the temperature of the absorption-adsorption process and the desorption process is relatively constant, so that the energy consumption caused by temperature fluctuation is avoided, and the energy consumption of the whole process is low, and the equipment investment and the operation cost are low.

Drawings

Fig. 1 is a schematic diagram of a system for recovering ethane from a mixed gas provided in example 1.

Fig. 2 is a schematic diagram of a system for recovering ethane from a mixed gas used in comparative example 1.

Fig. 3 is a schematic diagram of a system for recovering ethane from a mixed gas used in comparative example 2.

Fig. 4 is a schematic diagram of a system for recovering ethane from a mixed gas used in comparative example 3.

FIG. 5 is a schematic diagram of a system for recovering ethane from a mixed gas used in comparative example 4.

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.

In the following examples and comparative examples, the desorbed slurry is recycled, and fig. 1 to 5 and the abstract drawing are schematic views in a recycling state, wherein a slurry outlet at the bottom of the low-pressure desorption tank V102 is directly connected with a slurry inlet at the top of the separation column T101 and/or the stripper column T102. It is noted that, in the stage where the stable circulation is not formed, the slurry entering from the slurry inlet at the top of the separation column T101 and/or the stripper column T102 is supplied by the slurry supply apparatus entirely or partially according to the actual situation, and the slurry supply apparatus stops supplying the slurry after the circulation is stabilized.

Example 1

The present embodiment provides a system for recovering ethane from a mixed gas, and the structure of the system is shown in fig. 1.

The system comprises a separation tower T101, a 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 stripping tower T102 is a long and thin tower;

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

the bottom of the stripping tower T102 is provided with a slurry outlet and a gas inlet, the middle part is provided with a first slurry inlet, and the top is provided with a second slurry inlet and a gas outlet; the gas stripping tower T102 is used for realizing the absorption-adsorption of the gas entering from the gas inlet, the slurry entering from the first slurry inlet and the slurry entering from the second slurry inlet in the step-by-step countercurrent contact;

a slurry inlet of the circulating flash tank V101, wherein the top of the circulating flash tank is provided with a gas outlet, and the bottom of the circulating flash tank is provided with a slurry outlet;

the low-pressure desorption tank V102 is provided with a slurry inlet, the top of the low-pressure desorption tank is provided with a gas outlet, and the bottom of the low-pressure desorption tank is provided with a slurry outlet;

the slurry leaving the separation column T101 at the slurry outlet at the bottom of the separation column T101 is fed to the middle of the stripper column T102;

wherein, a slurry outlet at the bottom of the separation tower T101 is connected with a first slurry inlet at the middle part of the stripping tower T102; the slurry outlet at the bottom of the stripper T102 is connected with the slurry inlet of the circulating flash tank V101; a gas outlet at the top of the circulating flash tank V101 is connected with an input port of a circulating compressor K101, an output port of the circulating compressor K101 is connected with an input port of a circulating gas cooler E101, and an output port of the circulating gas cooler E101 is connected with a gas inlet at the top of a stripping tower T102; a slurry outlet at the bottom of the circulating flash tank V101 is connected with a slurry inlet of the low-pressure desorption tank V102; slurry outlets at the bottom of the low-pressure desorption tank V102 are respectively connected with inlets of circulating slurry booster pumps P101 and P102, wherein an outlet of the circulating slurry booster pump P101 is connected with an inlet of a cooler E102, an outlet of the cooler E102 is connected with an inlet of second slurry at the top of the stripper T102, an outlet of the circulating slurry booster pump P102 is connected with an inlet of a cooler E103, and an outlet of the cooler E103 is connected with a slurry inlet at the top of the separation tower T101, so that the slurry desorbed from the low-pressure desorption tank V102 can be recycled.

In addition, according to actual conditions, the gas outlets of the separation tower T101, the stripping tower T102 and the pressure desorption tank V102 are connected with compressors for conveying the gas therein into a gas conveying pipeline network, for example, as shown in fig. 1, the gas outlet of the stripping tower T102 is connected with a compressor K102 for conveying the methane gas therein into the methane gas conveying pipeline network.

This embodiment provides a slave nailAlkane (CH)₄) Ethane (C)₂H₆) The process for recovering ethane from the mixed gas is carried out by using the system for recovering ethane from the mixed gas provided by the embodiment (wherein, the height of the separation tower T101 is 1.5-2.5m, and the diameter of the tower is 1-1.5 m; the height of the stripping tower T102 is 2.5-5m, the diameter of the stripping tower is 0.5-1m), and the method comprises the following steps:

1) the raw gas entering the separation tower T101 from the raw gas inlet at the bottom of the separation tower T101 and the slurry entering the separation tower T101 from the top are in stepwise countercurrent contact in the tower, so that the absorption-adsorption of the gas in the slurry of a ZIF-8/water-glycol system is realized, and a first absorption-adsorption slurry and methane are obtained; wherein the methane gas directly enters a methane conveying pipe network,

wherein the feed gas contains 94 mol% of CH₄And 6 mol% of C₂H₆The temperature in the separation tower T101 is 0-5 ℃, and the pressure is 5-10 MPa;

2) conveying the first absorption-adsorption slurry in the step 1) from a slurry outlet at the bottom of a separation tower T101 to a first slurry inlet of a stripping tower T102 to enter the stripping tower T102, pressurizing circulating flash gas obtained by pressure reduction flash evaporation of a circulating flash tank V101 through a circulating compressor K101, then cooling the circulating flash gas to the temperature in the stripping tower T102 through a circulating gas cooler E101, and then entering the stripping tower T102 through a gas inlet at the bottom of the stripping tower T102, wherein the circulating flash gas entering the stripping tower, the first absorption-adsorption slurry and the slurry entering from a second slurry inlet at the top of the stripping tower T102 are subjected to stepwise countercurrent contact in the tower to carry out absorption-adsorption to obtain second absorption-adsorption slurry and methane gas; the methane gas is enriched at the top of the stripping tower T102, the methane enriched at the top of the stripping tower T102 is collected through a gas outlet at the top of the stripping tower T102, the methane gas enters a methane conveying pipe network after passing through a compressor K102, the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and the second absorption-adsorption slurry is conveyed to a circulating flash tank V101 connected with the second absorption-adsorption slurry through a slurry outlet at the bottom of the stripping tower T102; the second absorption-adsorption slurry enters a circulating flash tank V101 for decompression flash evaporation to obtain circulating flash vapor and third absorption-adsorption slurry, wherein the circulating flash vapor obtained by decompression flash evaporation of the circulating flash tank V101 enters a stripping tower T102 through a circulating compressor K101 and a circulating gas cooler E101 to participate in absorption-adsorption of the stripping tower T102, so as to form circulation;

wherein the temperature in the stripping tower T102 is 0-5 ℃ and the pressure is 1 Mpa; the pressure of the pressure reduction flash evaporation of the circulating flash tank V101 is 0.3-0.7 Mpa;

3) the third absorption and adsorption slurry is conveyed from a slurry outlet at the bottom of the circulating flash tank V101 to a slurry inlet of the low-pressure desorption tank V102 and enters the low-pressure desorption tank V102 for desorption to obtain ethane; and respectively pressurizing the slurry obtained after desorption by circulating slurry booster pumps P101 and P102, cooling to 0 ℃ by coolers E102 and E103, and respectively conveying to a slurry inlet at the top of the separation tower T101 and a slurry inlet at the top of the stripping tower T102.

The purity of ethane recovered in this example was not less than 96%.

The gas-liquid ratio in the separation column T101 is large, and therefore the operation in the separation column T101 is mainly for recovering methane. The absorption-adsorption capacity of ethane is larger than that of methane in the slurry, more ethane enters the slurry, and methane gas is enriched at the tower top, so that the pressure of methane-enriched at the tower top can be maintained, and the ethane can be conveyed outwards without compression. Because the molar composition of methane in the feed gas is large, high-purity methane can be obtained only by one to two equilibrium stages, and therefore a short coarse tower such as the separation tower T101 is suitable for the operation requirement of the step 1).

The gas-to-liquid ratio in the stripper T102 is small, and therefore the operation in the stripper T102 is mainly for recovering ethane having a small content. The gas obtained by decompression flash of the circulating flash tank V101 returns to the bottom of the stripping tower T102 so as to increase the content of ethane in the stripping tower T102, and the methane recovery rate in the tower and the ethane purity in the slurry are increased by utilizing the inhibition effect of ethane on methane adsorption. An elongated column such as stripper T102 is suitable for the operating requirements of step 2) because of the low ethane content and therefore the need for more equilibrium stages to achieve high purity.

Example 2

This example provides a process for recovering ethane from a methane and ethane mixture, wherein the methane and ethane mixture contains 94 mol% CH₄And 6 mol% of C₂H₆Pressure ofThe force is 5.5MPa, the temperature is 0 ℃, and the treatment scale of the mixed gas is 1 kmol/h; the gas output pressure of the separated methane is 5.5 MPa; the slurry is a ZIF-8/water-glycol system slurry; the process was carried out using the system for recovering ethane from a mixed gas provided in example 1, in which the height of the separation column T101 was 1.5m, the column diameter was 1.2m, and the equilibrium number of stages of the separation column T101 was 3; the stripper T102 has 8 equilibrium stages, the stripper T102 has a height of 4m and a diameter of 0.8m, and the first slurry inlet of the stripper T102 is provided at the position of the third equilibrium stage. The process comprises the following specific steps:

1) the methane and ethane mixed gas which is output from a raw gas inlet at the bottom of the separation tower T101 and enters the separation tower T101 and the slurry which enters the separation tower T101 from the top are in stepwise countercurrent contact in the tower, so that the absorption-adsorption of the gas in the slurry is realized, and the first absorption-adsorption slurry and methane gas are obtained; 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 a gas outlet at the top of the separation tower T101, the methane gas directly enters a methane conveying pipe network, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

wherein the temperature of the slurry is 0 ℃, the pressure is 5.5MPa, and the flow of the slurry entering the separation tower T101 is 0.24m³/h；

The temperature in the separation tower T101 is 0-1 ℃, and the pressure is 5.5 MPa;

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 0.58kmol/h, the temperature is 0 ℃, and the pressure is 5.5 MPa;

the ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 was 14.3 mol% (based on 100% of the total amount of the gas absorbed-adsorbed in the first slurry), the temperature was 0.7 ℃, and the pressure was 5.5 MPa;

2) the first absorption-adsorption slurry in the step 1) is conveyed from a slurry outlet at the bottom of a separation tower T101 to a first slurry inlet of a stripping tower T102 to enter the stripping tower T102, the circulating flash gas obtained by pressure reduction flash evaporation of a circulating flash tank V101 is pressurized to 1MPa (at the moment, the temperature is raised to 72 ℃) through a circulating compressor K101, then enters a circulating gas cooler E101 to be cooled to 2.8 ℃, and then enters the stripping tower T102 from a gas inlet at the bottom of the stripping tower T102, and the circulating flash gas entering the stripping tower T102, the first absorption-adsorption slurry and the slurry entering from a second slurry inlet at the top of the stripping tower T102 are in stepwise countercurrent contact in the tower to carry out absorption-adsorption, so that second absorption-adsorption slurry and methane gas are obtained; the methane gas is enriched at the top of the stripping tower T102, the methane enriched at the top of the stripping tower T102 is collected through a gas outlet at the top of the stripping tower T102, the methane gas enters a methane conveying pipe network after passing through a compressor K102, the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and the second absorption-adsorption slurry is conveyed to a circulating flash tank V101 connected with the second absorption-adsorption slurry through a slurry outlet at the bottom of the stripping tower T102; the second absorption-adsorption slurry enters a circulating flash tank V101 for decompression flash evaporation to obtain circulating flash vapor and third absorption-adsorption slurry, wherein the circulating flash vapor obtained by decompression flash evaporation of the circulating flash tank V101 enters a stripping tower T102 through a circulating compressor K101 and a circulating gas cooler E101 to participate in absorption-adsorption of the stripping tower T102, so as to form circulation;

wherein the temperature in the stripping tower T102 is 0-3 ℃ and the pressure is 1 Mpa;

the flow rate of the first absorption-adsorption slurry into the stripper T102 was 0.256m³/h；

The flow rate of the slurry entering the stripper column T102 through the second slurry inlet at the top of the stripper column T102 was 0.14m³H, the temperature is 0 ℃, and the pressure is 1 MPa;

the purity of the methane gas collected through a gas outlet at the top of the stripping tower T102 is 98.65 mol%, the flow rate is 0.34kmol/h, the temperature is 0 ℃, and the pressure is 1 MPa;

the ethane content in the second absorption-adsorption slurry enriched at the bottom of the gas stripping tower T102 is 96 mol% (based on the total amount of the absorption-adsorption gas in the second slurry as 100%), the temperature is 2.8 ℃, the pressure is 1MPa, the flow of the second absorption-adsorption slurry which is output to the circulating flash tank V101 is 0.41m³/h；

The pressure of the pressure reduction flash evaporation of the circulating flash tank V101 is 0.5MPa, and the temperature is slightly lower than the temperature of the bottom of the tower and is 2.6 ℃;

the circulating flash gas flashed from the circulating flash tank V101 accounts for 0.5% of the raw material gas amount, namely the flow of the circulating flash gas entering the stripper T102 is 0.005kmol/h, wherein the ethane content is 81 mol%;

the temperature of the third absorption adsorption slurry obtained by flash evaporation of the circulating flash tank V101 is 2.6 ℃, the pressure is 0.5MPa, and the ethane composition is 98 mol%;

3) the third absorption and adsorption slurry is conveyed from a slurry outlet at the bottom of the circulating flash tank V101 to a slurry inlet of the low-pressure desorption tank V102 and enters the low-pressure desorption tank V102 to be desorbed to obtain desorbed slurry and ethane gas; wherein ethane gas is enriched at the top of the low-pressure desorption tank V102, ethane enriched at the top of the low-pressure desorption tank V102 is collected through a gas outlet at the top of the low-pressure desorption tank V102, and desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the desorbed slurry was divided into two streams, one of which had a flow rate of 0.24m³H, pressurizing to 5.5MPa by a circulating slurry booster pump P102, cooling to 0 ℃ by a cooler E103, conveying to a slurry inlet at the top of a separation tower T101, and enabling the flow rate of the other stream to be 0.14m³The pressure is increased to 1MPa by a circulating slurry booster pump P101, and the temperature is reduced to 0 ℃ by E102 and then the slurry is conveyed to a second slurry inlet at the top of an air stripping tower T102;

wherein the temperature of the low-pressure desorption tank V102 is 0 ℃, and the pressure is normal pressure;

the flow rate of the third absorption-adsorption slurry into the low-pressure desorption tank V102 was 0.38m³/h；

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

Comparative example 1

This comparative example provides a process for recovering ethane from a methane ethane mixture comprising 94 mol% CH₄And 6 mol% of C₂H₆The pressure is 5.5MPa, the temperature is 0 ℃, and the treatment scale of the mixed gas is 1 kmol/h; the gas output pressure of the separated methane is 5.5 MPa; the slurry is a ZIF-8/water-glycol system slurry; the process is carried out by using a system for recovering ethane from a mixed gas as shown in FIG. 2, wherein the height of a separation tower T101 is 4m, the diameter of the tower is 1.5m, and the equilibrium stage number of the separation tower T101 is 3; gas stripping towerT102 has 8 equilibrium stages, the height of the stripping tower T102 is 4m, the diameter of the stripping tower T102 is 0.8m, and the first slurry inlet of the stripping tower T102 is arranged at the position of the first equilibrium stage. The process comprises the following specific steps:

1) the methane and ethane mixed gas which is externally conveyed into the separation tower T101 from a raw gas inlet at the bottom of the separation tower T101, and the methane and ethane mixed gas which is stripped by the stripping tower T102 and then is output from a gas outlet at the top of the stripping tower T102, is cooled by the cooler E101, and is conveyed into the separation tower T101 from a circulating gas inlet at the bottom of the separation tower T101 are in stepwise countercurrent contact with the slurry which enters the separation tower T101 from a slurry inlet at the top of the separation tower T101 in the tower, so that the absorption-adsorption of the gas in the slurry is realized, and the first absorption-adsorption slurry and methane gas are obtained; 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 a gas outlet at the top of the separation tower T101, the methane gas enters a methane conveying pipe network after passing through a compressor K102, and the first absorption-adsorption slurry is enriched at the bottom of the separation tower T101;

wherein the temperature of the slurry is 0 ℃, the pressure is 1MPa, and the flow of the slurry entering the separation tower T101 is 0.38m³/h；

The temperature in the separation tower T101 is 0-1 ℃, and the pressure is 1 MPa;

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 0.92kmol/h, the temperature is 0 ℃, and the pressure is 1 MPa;

the ethane content in the first absorption-adsorption slurry enriched at the bottom of the separation tower T101 was 14.3 mol% (based on 100% of the total amount of the gas absorbed-adsorbed in the first slurry), the temperature was 0.7 ℃, and the pressure was 1 MPa;

the temperature of the first circulating gas cooled by the cooler E101 is 0 ℃, the pressure is 1MPa, the flow is 0.01kmol/h, and the methane composition is 94.5 mol%;

2) conveying the first absorption-adsorption slurry in the step 1) from a slurry outlet at the bottom of a separation tower T101 to a heater E102, heating the first absorption-adsorption slurry by the heater E102, conveying the heated first absorption-adsorption slurry to a slurry inlet at the top of a stripping tower T102, then conveying the heated first absorption-adsorption slurry to the slurry inlet at the top of the stripping tower T102, allowing a part (second circulating gas) of ethane gas obtained by desorption of a low-pressure desorption tank V102 to enter the stripping tower T102 through a circulating compressor K101, cooling the part to 0 ℃ by a circulating gas cooler E104, allowing the part to enter the stripping tower T102 through a gas inlet at the bottom of the stripping tower T102, and allowing the second circulating gas entering the stripping tower T102 and the first absorption-adsorption slurry to be in stepwise countercurrent contact for stripping in the stripping tower T102 to obtain second absorption-adsorption; wherein, the first circulating gas is output through a gas outlet at the top of the stripping tower T102, is cooled by a cooler E101, enters the separation tower T101, and participates in the absorption-adsorption of the separation tower T101 to form circulation; the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102;

wherein the temperature in the stripper T102 is 10 ℃ and the pressure is 1 Mpa;

the flow rate of the first absorption-adsorption slurry into the stripper T102 was 0.4m³/h；

The purity of methane in the first circulating gas output through a gas outlet at the top of the stripping tower T102 is 94.5 mol%, the flow rate is 0.01kmol/h, the temperature is 10 ℃, and the pressure is 1 MPa;

the ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripper T102 was 93 mol% (based on 100% of the total amount of the gas absorbed and adsorbed in the second slurry), the temperature was 2.8 deg.C, the pressure was 1MPa, and the output flow rate of the second absorption-adsorption slurry was 0.41m³/h；

3) The second absorption and adsorption slurry is conveyed to a cooler E103 from a slurry outlet at the bottom of the stripper T102 and is cooled to 0 ℃, and then enters the low-pressure desorption tank V102 from a slurry inlet of the low-pressure desorption tank V102 to be desorbed to obtain desorbed slurry and ethane gas; wherein ethane gas is enriched at the top of the low-pressure desorption tank V102, ethane enriched at the top of the low-pressure desorption tank V102 is collected through a gas outlet at the top of the low-pressure desorption tank V102, the ethane gas is divided into two parts, one part (accounting for 0.5 percent of the molar weight of raw material gas, namely the flow is 0.005kmol/h) is pressurized through a circulating compressor K101, a circulating gas cooler E104 is cooled to 0 ℃, and enters the stripping tower T102 from a gas inlet at the bottom of the stripping tower T102 to participate in stripping of the stripping tower T102 so as to form circulation, and the other part is output as a product; the desorbed slurry is enriched at the bottom of a low-pressure desorption tank V102, pressurized to 1MPa by a circulating slurry booster pump P102, cooled to 0 ℃ by a cooler E105 and then conveyed to a slurry inlet at the top of a separation tower T101;

the flow rate of the second absorption-adsorption slurry into the low-pressure desorption tank V102 was 0.41m³/h；

The purity of the ethane gas collected through the gas outlet at the top of the low-pressure stripping tank V102 was 92.5 mol%, and the flow rate of the ethane gas to be exported as a product was 0.056 kmol/h.

It can be seen that the operating temperature of the stripping tower T102 in the process is 10 ℃, and compared with example 2, the energy consumption of the heater E102 is consumed more for raising the temperature of stripping. And the operation pressure of the separation tower T101 is 1MPa, and the outward transportation pressure of the rich methane is 5.5MPa, so the rich methane needs to be compressed and transported outward, and the pressure of the rich methane of the separation tower T101 in the embodiment 2 is consistent with the outward transportation pressure, and the rich methane can be transported outward without being compressed. See table 1 for detailed results comparing energy consumption and ethane recovery for example 2 with comparative example 1.

TABLE 1 energy consumption and ethane recovery comparison

	Example 2	Comparative example 1
			Energy consumption/kW of circulating pump	1.3360	0.3213
Energy consumption/kW of circulating compressor	0.0447	0.1156
			Compression output energy consumption/kW	0.6083	1.6383
Energy consumption/kW of heat exchanger	0.0609	3.9712
			Total energy consumption/kW	2.0499	6.0464
Ethane recovery/%	93.7	93.4

The circulating pump energy consumption 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; cycle compressor energy consumption refers to the energy consumption of K101 in example 2, the energy consumption of K101 in comparative example 1;

compressed export energy consumption refers to the energy consumption of K102 in example 2, the energy consumption of K102 in comparative example 1;

heat exchanger energy consumption refers to the energy consumption of the coolers E101, E102, E103 in example 2, and E101, E102, E103, E104, E105 in comparative example 1;

ethane recovery refers to the ratio of the moles of ethane in the ethane gas ultimately recovered to the moles of ethane in the feed.

Compared with the process flow of the comparative example 1, the process flow for recovering ethane from the mixed gas provided by the embodiment 2 has the advantages that the operation pressure of the separation tower T101 is 5.5MPa, the operation pressure is the same as the methane output pressure, the power consumption of an output compressor can be saved by 1.03kW, the gas stripping tower T102 does not need to be used for raising the temperature and stripping the gas, but is used for reducing the pressure and stripping the gas, the energy consumption is not required, and the energy consumption can be saved by 3.91 kW. And the total energy consumption of comparative example 1 is much higher than that of example 1.

Comparative example 2

This comparative example provides a process for recovering ethane from a methane ethane mixture comprising 94 mol% CH₄And 6 mol% of C₂H₆The pressure is 5.5MPa, the temperature is 0 ℃, and the treatment scale of the mixed gas is 1 kmol/h; the gas output pressure of the separated methane is 5.5 MPa; the slurry is a ZIF-8/water-glycol system slurry; wherein the height of the separation tower T101 is 1.5m, the diameter of the tower is 1.2m, and the number of the equilibrium stages of the separation tower T101 is 3; the stripper T102 had 3 equilibrium stages, the height of the stripper T102 was 1.5m, the diameter of the column was 0.8m, and the first slurry inlet of the stripper T102 was located at the third equilibrium stage. The process was carried out using the system for recovering ethane from a mixed gas shown in FIG. 3, and this comparative example differs from example 2 in that the circulating flash tank V101 was not added, the amount of absorption-adsorption liquid and the operating conditions of the separation column T101, the stripper column T102, and the low-pressure stripper tank V102 were the same as those of example 2. The process comprises the following specific steps:

1) the methane and ethane mixed gas which is output from a raw gas inlet at the bottom of the separation tower T101 and enters the separation tower T101 and the slurry which enters the separation tower T101 from the top are in stepwise countercurrent contact in the tower, so that the absorption-adsorption of the gas in the slurry is realized, and the first absorption-adsorption slurry and methane gas are obtained; 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 a 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;

2) the first absorption-adsorption slurry in the step 1) is conveyed from a slurry outlet at the bottom of the separation tower T101 to a first slurry inlet of the stripper T102 to enter the stripper T102, and the first absorption-adsorption slurry and the slurry entering from a second slurry inlet at the top of the stripper T102 are in stepwise countercurrent contact in the tower for absorption-adsorption to obtain second absorption-adsorption slurry and methane gas; wherein, methane gas is enriched at the top of the stripping tower T102, methane enriched at the top of the stripping tower T102 is collected through a gas outlet at the top of the stripping tower T102, and second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102;

the purity of the methane gas collected through a gas outlet at the top of the stripping tower T102 is 95 mol%, the flow rate is 0.21kmol/h, the temperature is 0 ℃, and the pressure is 1 MPa;

the ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripper T102 reached 13.8 mol% (based on the total amount of the gas absorbed and adsorbed in the second slurry as 100%), the temperature was 2.8 deg.C, the pressure was 1MPa, and the flow rate of the second absorption-adsorption slurry was 0.41m³/h；

3) The second absorption and adsorption slurry is conveyed from a slurry outlet at the bottom of the stripper T102 to a slurry inlet of the low-pressure desorption tank V102 and enters the low-pressure desorption tank V102 for desorption to obtain desorbed slurry and ethane gas; wherein ethane gas is enriched at the top of the low-pressure desorption tank V102, ethane enriched at the top of the low-pressure desorption tank V102 is collected through a gas outlet at the top of the low-pressure desorption tank V102, and desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the desorbed slurry was divided into two streams, one of which had a flow rate of 0.24m³H, pressurizing to 5.5MPa by a circulating slurry booster pump P102, cooling to 0 ℃ by a cooler E102, and deliveringSending to the top slurry inlet of a separation tower T101, and the flow rate of the other stream is 0.14m³The pressure is increased to 1MPa by a circulating slurry booster pump P101, and the temperature is reduced to 0 ℃ by E101 and then the slurry is conveyed to a second slurry inlet at the top of an air stripping tower T102;

the flow rate of the second absorption-adsorption slurry into the low-pressure desorption tank V102 was 0.38m³/h；

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

It can be seen that the absence of the addition of the recycle flash tank V101 results in a significant drop in the ethane composition in the slurry entering the low pressure stripping tank from 98 mol% to 13.8 mol% compared to example 2, resulting in a reduction in the recovered ethane purity from 97 mol% to 13.5 mol%.

Comparative example 3

This comparative example provides a process for recovering ethane from a methane ethane mixture comprising 94 mol% CH₄And 6 mol% of C₂H₆The pressure is 5.5MPa, the temperature is 0 ℃, and the treatment scale of the mixed gas is 1 kmol/h; the gas output pressure of the separated methane is 5.5 MPa; the slurry is a ZIF-8/water-glycol system slurry; wherein the height of the separation tower T101 is 1.5m, the diameter of the tower is 1.2m, and the number of the equilibrium stages of the separation tower T101 is 3; the stripper T102 had 5 equilibrium stages, the height of the stripper T102 was 2.5m and the diameter was 0.8m, and the first slurry inlet of the stripper T102 was located at the first equilibrium stage. The process was carried out using the system for recovering ethane from a mixed gas shown in FIG. 4, and this comparative example differs from example 2 in that the stripper T102 was not charged with a fresh slurry, and for convenience of comparison, the amount of absorption-adsorption liquid and the operating conditions were the same as those in example 2. The process comprises the following specific steps:

1) the methane-rich mixed gas which is externally conveyed into the separation tower T101 from a raw gas inlet at the bottom of the separation tower T101 and the slurry which enters the separation tower T101 from the top are in stepwise countercurrent contact in the tower, so that the absorption-adsorption of the gas in the slurry is realized, and a first absorption-adsorption slurry and methane gas are obtained; 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 a 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;

wherein the temperature of the slurry is 0 ℃, the pressure is 5.5MPa, and the flow of the slurry entering the separation tower is 0.38m³/h；

the purity of the methane gas collected through the gas outlet at the top of the separation column T101 is 98.97%, the flow rate is 0.55kmol/h, the temperature is 0 ℃, and the pressure is 5.5 MPa;

2) the first absorption-adsorption slurry in the step 1) is conveyed from a slurry outlet at the bottom of a separation tower T101 to a first slurry inlet of a stripping tower T102 to enter the stripping tower T102, the circulating flash gas obtained by pressure reduction flash evaporation of a circulating flash tank V101 is pressurized to 1MPa (the temperature is raised to 72 ℃) through a circulating compressor K101, then enters a circulating gas cooler E101 to be cooled to 2.8 ℃, and then enters the stripping tower from a gas inlet at the bottom of the stripping tower T102, and the circulating flash gas entering the stripping tower, the first absorption-adsorption slurry and the slurry entering from a second slurry inlet at the top of the stripping tower T102 are in stepwise countercurrent contact in the tower for absorption-adsorption to obtain second absorption-adsorption slurry and methane gas; the methane gas is enriched at the top of the stripping tower T102, the methane enriched at the top of the stripping tower T102 is collected through a gas outlet at the top of the stripping tower T102, the second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and the second absorption-adsorption slurry is conveyed to a circulating flash tank V101 connected with the second absorption-adsorption slurry through a slurry outlet at the bottom of the stripping tower T102; the second absorption-adsorption slurry enters a circulating flash tank V101 for decompression flash evaporation to obtain circulating flash vapor and third absorption-adsorption slurry, wherein the circulating flash vapor obtained by decompression flash evaporation of the circulating flash tank V101 enters a stripping tower T102 through a circulating compressor K101 and a circulating gas cooler E101 to participate in absorption-adsorption of the stripping tower T102, so as to form circulation;

the flow rate of the first absorption-adsorption slurry into the stripper T102 was 0.39m³/h；

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

the ethane content in the second absorption-adsorption slurry enriched at the bottom of the gas stripping tower T102 is 94 mol% (based on the total amount of the absorption-adsorption gas in the second slurry as 100%), the temperature is 2.8 ℃, the pressure is 1MPa, the flow of the second absorption-adsorption slurry which is output to the circulating flash tank V101 is 0.41m³/h；

circulating flash gas flashed from the circulating flash tank V101 accounts for 0.5% of the gas content of the raw material, wherein the ethane content is 81 mol%;

the temperature of the third absorption adsorption slurry obtained by flash evaporation of the circulating flash tank V101 is 2.6 ℃, the pressure is 0.5MPa, and the ethane composition is 95 mol%;

3) the third absorption and adsorption slurry is conveyed from a slurry outlet at the bottom of the circulating flash tank V101 to a slurry inlet of the low-pressure desorption tank V102 and enters the low-pressure desorption tank V102 to be desorbed to obtain desorbed slurry and ethane gas; wherein ethane gas is enriched at the top of the low-pressure desorption tank V102, ethane enriched at the top of the low-pressure desorption tank V102 is collected through a gas outlet at the top of the low-pressure desorption tank V102, and desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the flow rate of the slurry after desorption was 0.38m³The pressure is increased to 5.5MPa by a circulating slurry booster pump P101, and the temperature is reduced to 0 ℃ by a cooler E102 and then the slurry is conveyed to a slurry inlet at the top of a separation tower T101;

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

It can be seen that compared to example 2, the absence of fresh slurry feed results in a reduction of the methane content at the top of stripper T102 from 98.65 mol% to 94 mol%, and thus in a reduction of the ethane purity from 97 mol% to 94.3 mol%.

Comparative example 4

This comparative example provides a process for recovering ethane from a methane ethane mixture comprising 94 mol% CH₄And 6 mol% of C₂H₆The pressure is 5.5MPa, the temperature is 0 ℃, and the treatment scale of the mixed gas is 1 kmol/h; the output pressure of the separated methane gas is 5.5 MPa; the slurry is a ZIF-8/water-glycol system slurry; wherein the height of the separation tower T101 is 1.5m, the diameter of the tower is 1.2m, and the number of the equilibrium stages of the separation tower T101 is 3; the stripper T102 had 9 equilibrium stages, the height of the stripper T102 was 4.5m, the diameter of the column was 0.5m, and the first slurry inlet of the stripper T102 was provided at the position of the third equilibrium stage. The process was carried out using the system for recovering ethane from a mixed gas shown in fig. 5, and this comparative example differs from example 2 in that the circulating flash tank V101 was removed, and a part of the ethane gas desorbed in the low-pressure desorption tank V102 was returned to the bottom of the stripper T102 to participate in absorption-adsorption in the stripper T102. For comparison, the amount of the absorption-adsorption liquid and the operation conditions were the same as those in example 2. The process comprises the following specific steps:

wherein the temperature of the slurry is 0 ℃, the pressure is 5.5MPa, and the flow of the slurry entering the separation tower T101Is 0.26m³/h；

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 0.63kmol/h, the temperature is 0 ℃, and the pressure is 5.5 MPa;

2) conveying the first absorption-adsorption slurry in the step 1) from a slurry outlet at the bottom of a separation tower T101 to a first slurry inlet of a stripping tower T102, allowing the first absorption-adsorption slurry to enter the stripping tower T102, pressurizing a part of ethane gas obtained by desorption in a low-pressure desorption tank to 1MPa (at the moment, the temperature is raised to 72 ℃) by a circulating compressor K101 as circulating gas, allowing the part of ethane gas to enter a circulating gas cooler E101 to be cooled to 2.9 ℃, and allowing the part of ethane gas to enter the stripping tower T102 from a gas inlet at the bottom of the stripping tower T102, wherein the circulating gas entering the stripping tower T102, the first absorption-adsorption slurry and the slurry entering from a second slurry inlet at the top of the stripping tower T102 are subjected to stepwise countercurrent contact in the tower for absorption-adsorption to obtain second absorption-adsorption slurry and methane gas; the methane gas is enriched at the top of the stripping tower T102, the methane enriched at the top of the stripping tower T102 is collected through a gas outlet at the top of the stripping tower T102, the methane gas enters a methane conveying pipe network after passing through a compressor K102, second absorption-adsorption slurry is enriched at the bottom of the stripping tower T102, and the second absorption-adsorption slurry is conveyed into a low-pressure desorption tank V102 connected with the second absorption-adsorption slurry through a slurry outlet at the bottom of the stripping tower T102;

the flow rate of the first absorption-adsorption slurry into the stripper T102 was 0.277m³/h；

The flow rate of the slurry entering the stripper column T102 through the second slurry inlet at the top of the stripper column T102 was 0.12m³H, the temperature is 0 ℃, and the pressure is 1 MPa;

the purity of the methane gas collected through a gas outlet at the top of the stripping tower T102 is 98.65 mol%, the flow rate is 0.29kmol/h, the temperature is 0 ℃, and the pressure is 1 MPa;

the ethane content in the second absorption-adsorption slurry enriched at the bottom of the stripper T102 is 96.4 mol% (based on the total amount of the gas absorbed and adsorbed in the second slurry as 100%), the temperature is 2.9 ℃, the pressure is 1MPa, and the flow rate of the second absorption-adsorption slurry conveyed into the low-pressure desorption tank V102 is 0.41m³/h；

The recycle gas accounts for 0.42 percent of the raw gas, namely the flow of the recycle gas entering the stripping tower T102 is 0.0042kmol/h, wherein the ethane composition is 95mol percent;

3) the second absorption and adsorption slurry is conveyed from a slurry outlet at the bottom of the low-pressure desorption tank V102 to a slurry inlet of the low-pressure desorption tank V102 and enters the low-pressure desorption tank V102 for desorption to obtain desorbed slurry and ethane gas; wherein, ethane gas is enriched at the top of the low-pressure desorption tank V102, ethane enriched at the top of the low-pressure desorption tank V102 is collected through a gas outlet at the top of the low-pressure desorption tank V102, a part of ethane-enriched gas is circulated back to a stripper, and desorbed slurry is enriched at the bottom of the low-pressure desorption tank V102; the desorbed slurry was divided into two streams, one of which had a flow rate of 0.26m³H, pressurizing to 5.5MPa by a circulating slurry booster pump P102, cooling to 0 ℃ by a cooler E103, conveying to a slurry inlet at the top of a separation tower T101, and enabling the flow rate of the other stream to be 0.12m³The pressure is increased to 1MPa by a circulating slurry booster pump P101, and the temperature is reduced to 0 ℃ by E102 and then the slurry is conveyed to a second slurry inlet at the top of an air stripping tower T102;

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

It can be seen that in example 2, a circulating flash tank is provided, and the dry-basis concentration of ethane in the slurry after circulating flash evaporation is increased from 96 mol% to 98 mol%, so that the ethane product with higher purity can be obtained after desorption, wherein the dry-basis concentration of ethane in the slurry is 97 mol%. When a portion of the recycle gas is taken directly from the ethane-rich stream, the purity of the ethane product can only reach 95 mol%. And a circulating flash tank is not arranged, the ethane content in the circulating gas is increased from 81 mol% to 96.4 mol%, and in order to avoid back mixing, a balance stage is additionally arranged in the stripper so as to increase the ethane content at the bottom of the tower and increase the equipment cost.

Claims

1. A system for recovering ethane from mixed gas comprises a separation tower, a stripping tower, a circulating flash tank and a desorption tower; wherein,

the bottom of the separation tower is provided with a raw material gas inlet and a slurry outlet, and the top of the separation tower is provided with a slurry inlet and a gas outlet;

the bottom of the gas stripping tower is provided with a slurry outlet and a gas inlet, the middle part of the gas stripping tower is provided with a first slurry inlet, and the top of the gas stripping tower is provided with a second slurry inlet and a gas outlet; wherein the middle part refers to the position from the second slurry inlet to the gas inlet on the stripping tower;

the slurry outlet of the separation tower is connected with the first slurry inlet of the stripping tower, the slurry outlet of the stripping tower is connected with the slurry inlet of the circulation flash tank, the gas outlet of the circulation flash tank is connected with the gas inlet of the stripping tower, and the slurry outlet of the circulation flash tank is connected with the slurry inlet of the desorption tower.

2. The system of claim 1, further comprising a first cooler;

the inlet of the first cooler is connected with the gas outlet of the circulation flash tank, and the outlet of the first cooler is connected with the gas inlet at the bottom of the stripping tower.

3. The system of claim 1, further comprising a gas compressor;

and the inlet of the gas compressor is connected with the gas outlet of the circulating flash tank, and the outlet of the gas compressor is connected with the gas inlet at the bottom of the stripping tower.

4. The system of claim 1, wherein a slurry outlet at the bottom of the desorption tower is respectively connected with a slurry inlet at the top of the separation tower and a second slurry inlet at the top of the stripping tower, so as to realize the recycling of the slurry desorbed from the desorption tower;

preferably, the system further comprises a second cooler, a third cooler; the inlet of the second cooler is connected with the slurry outlet at the bottom of the desorption tower, and the outlet of the second cooler is connected with the slurry inlet at the top of the separation tower; the inlet of the third cooler is connected with the slurry outlet at the bottom of the desorption tower, and the outlet of the third cooler is connected with the inlet of the second slurry at the top of the stripping tower;

preferably, the system further comprises a first slurry booster pump, a second slurry booster pump; an inlet of the first slurry booster pump is connected with a slurry outlet at the bottom of the desorption tower, and an outlet of the first slurry booster pump is connected with an inlet of the slurry at the top of the separation tower; the inlet of the second slurry booster pump is connected with the slurry outlet at the bottom of the desorption tower, and the outlet of the second slurry booster pump is connected with the inlet of the second slurry at the top of the stripping tower.

5. The system of claim 1, wherein the separation column has a number of equilibrium stages of 3-5 stages; the equilibrium number of stages of the stripping tower is 5-10 stages.

6. A process for the recovery of ethane from a gas mixture using the system of any one of claims 1-5, wherein the process comprises the steps of:

1) enabling the mixed gas and the slurry to be in stepwise countercurrent contact in a separation tower for absorption-adsorption to obtain first absorption-adsorption slurry; wherein the slurry is a ZIF-8/water-glycol system slurry; preferably, the temperature in the separation tower is 15 ℃ below zero to 10 ℃ above zero, and the pressure is 1 to 10 MPa; more preferably, the pressure in the separation column is from 5 to 10 MPa;

2) the first absorption-adsorption slurry enters from the middle part of the stripping tower, the slurry enters from the top part of the stripping tower, the gas flashed by the circulating flash tank enters from the bottom part of the stripping tower, the gas is in stepwise countercurrent contact with the first absorption-adsorption slurry and the slurry, and absorption-adsorption is carried out under the conditions of minus 15-minus-plus 10 ℃ and 1-10MPa to obtain second absorption-adsorption slurry; carrying out reduced pressure flash evaporation on the second absorption adsorption slurry in a circulating flash tank to obtain third absorption adsorption slurry; the gas flashed out enters the bottom of the stripping tower and participates in absorption-adsorption of the stripping tower to form circulation;

wherein the middle portion refers to a location on the stripper column between the slurry entry location and the gas entry location; preferably, the pressure in the stripper column is from 1 to 5 MPa;

3) and the third absorption and adsorption slurry enters a desorption tower for desorption to obtain ethane.

7. The process of claim 6, further comprising: the slurry desorbed by the desorption tower returns to the separation tower and the stripping tower respectively for recycling;

preferably, the slurry desorbed by the desorption tower is cooled before returning to the separation tower and the gas tower;

more preferably, the slurry desorbed from the desorption tower is cooled to the temperature in the separation tower and the temperature in the gas tower before being returned to the separation tower and the gas tower, respectively.

8. The process of claim 6, wherein the pressure of the reduced pressure flash is from 0.3 to 0.7 MPa.

9. The process of claim 6, wherein the mixed gas has an ethane content of not more than 10 mol.%.

10. The process of claim 6, wherein the mixed gas is a mixed gas with a heavy key component of ethane; preferably, the mixed gas is natural gas; more preferably, the mixed gas is a mixed gas of methane and ethane.