阅读说明：本技术 一种从混合气中回收乙烷的系统及工艺 (System and process for recovering ethane from mixed gas ) 是由 陈光进 彭晓婉 陈婉 杨明科 于 2019-03-29 设计创作，主要内容包括：本发明提供一种从混合气中回收乙烷的系统及工艺。该系统包括分离塔、气提塔、循环闪蒸罐、解吸塔；分离塔底部设原料气入口、浆液出口,顶部设浆液入口、气体出口,用于实现原料气和浆液在塔内逐级逆流接触进行吸收-吸附；气提塔底部设浆液出口、气体入口,中部设第一浆液入口,顶部设第二浆液入口、气体出口,用于实现气体与分别从第一浆液入口、第二浆料入口进入的浆液逐级逆流接触进行吸收-吸附；循环闪蒸罐、解吸塔均分别设浆液入口、气体出口、浆液出口；分离塔浆液出口与气提塔第一浆液入口连接,气提塔浆液出口与循环闪蒸罐浆液入口连接,循环闪蒸罐气体出口与气提塔气体入口连接,循环闪蒸罐浆液出口与解吸塔浆液入口连接。(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.)

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 content of the first and second substances,

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 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 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.

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 content of the first and second substances,

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.