An absorption and stabilization process and system for increasing the yield of liquefied gas

Abstract

The present invention discloses an absorption stabilization process and system for increasing the yield of liquefied gas. The absorption process comprises: (1) the raw gas A from the catalytic cracking fractionation tower is compressed, mixed with rich absorption oil, and then enters the gas-liquid separation tank for flash evaporation; (2) the obtained gas phase enters the membrane separation unit for separation to obtain permeate gas and retentate gas containing hydrogen; (3) the obtained permeate gas enters the first gas inlet at the lower part of the absorption tower; (4) the gas obtained at the top of the absorption tower leaves the device and enters the reabsorption tower; (5) the liquid phase obtained in the gas-liquid separation tank enters the upper part of the desorption tower after heat exchange to remove the overabsorbed C2 component in the rich absorbent; (6) the desorbed gas obtained at the top of the desorption tower is cooled and then enters the absorption tower through the second gas inlet; (7) the deethanized gasoline at the bottom of the desorption tower enters the stabilization tower, and the liquefied gas product and stabilized gasoline are separated in the stabilization tower. The method of the present invention can effectively increase the yield of liquefied gas in the absorption stabilization system.

Description

Technical Field

[0001] The present invention belongs to the field of light hydrocarbon separation in the petroleum refining and chemical industry, and in particular relates to an absorption stabilization process and system for increasing the yield of liquefied gas. Background Art

[0002] As refining and chemical integration progresses, petrochemical companies are increasingly integrating their full-process processing capabilities. Consequently, the production of liquefied gas (LNG), a by-product of the refining process, is also increasing. Furthermore, the proportion of high-value-added components (such as propylene) in LNG is also increasing. Therefore, for petrochemical companies, efficient recovery of liquefied gas components is crucial for tapping potential and increasing efficiency.

[0003] Currently, petrochemical companies primarily use absorption stabilization to recover liquefied gas (LPG). This process uses a stream such as gasoline as a mass separator to remove entrained LPG components from the dry gas through physical absorption. Typical catalytic cracking units, delayed coking units, and light hydrocarbon recovery units in petrochemical companies all employ similar processes. The design specification for absorption stabilization is typically to maintain an entrained LPG content of ≤3% (V) in the dry gas product. In practice, absorption stabilization is susceptible to factors such as feedstock composition, flow rate fluctuations, and insufficient heat during the stabilization process. Consequently, many petrochemical companies experience entrained LPG content exceeding 5% (V) in their dry gas products. This high level of entrained LPG in the dry gas not only results in the loss of high-value-added components but also impacts downstream dry gas processing operations (such as fuel gas, hydrogen production, dry gas to ethylbenzene, and dry gas enrichment).

[0004] CN107278786A provides an absorption stabilization process. This invention installs a partial condenser at the top of the desorption tower to prevent the desorption tower top gas phase from entering the gas-liquid balance tank together with the rich gas and the absorption tower bottom liquid, affecting the phase equilibrium, thereby reducing the gas phase load at the absorption tower bottom. Through this invention, the C3+ content of the dry gas product of the absorption stabilization system can be reduced to 2.0%. In this technology, the liquid phase of the desorption tower partial condenser returns to the desorption tower as reflux, and the heat of the desorption tower reboiler needs to be increased to ensure the C2 content index in the deethanized gasoline. Therefore, this technology is mainly suitable for use in scenarios where the system has sufficient heat.

[0005] CN107338068A utilizes the different compositions of stabilized gasoline and crude gasoline to introduce them into different locations in the absorption tower, thereby preventing back-mixing of components within the absorption tower and enhancing absorption efficiency. Furthermore, the invention also utilizes a shell-and-tube vortex tube bundler in the reabsorption tower to convert the pressure energy of the dry gas into cold and hot flows, further reducing the C3+ content in the dry gas to approximately 1.5%. However, the shell-and-tube vortex tube bundler preferred in this invention is rarely used in the petrochemical industry, and its suitability for the high concentrations of impurities in gases and liquids in the petrochemical industry remains to be verified.

[0006] Membrane separation technology, as a highly efficient separation technology, offers energy-efficient, easy-to-use methods for gas separation and is currently widely used in petrochemical enterprises. For example, membrane separation processes for purifying hydrogen are already being used in the circulating hydrogen systems of many hydrogenation plants to improve the purity of the circulating hydrogen. Membrane separation technology primarily separates gases by exploiting the differential fluxes through the pores of polymer organic membranes. The driving force behind the separation process is the pressure difference between the feed and permeate sides.

[0007] CN1580191A discloses a method for recovering liquefied gas by combining membrane separation with an absorption stabilization system. This invention separates the liquefied gas components in the raw gas through a composite membrane with silicone rubber as the separation layer. The enriched liquefied gas components are extracted from the permeation side of the membrane. The liquefied gas components are returned to the absorption stabilization system of the catalytic cracking unit through the rich gas compressor, thereby completing the recovery of the liquefied gas components. This invention can further recover liquefied gas components from gas sources such as refinery dry gas and gasholder fuel gas. The liquefied gas components obtained by membrane separation in this invention contain C2 and lower impurities, so they need to be processed in the catalytic cracking unit. On the one hand, this increases the load on the rich gas compressor and its absorption stabilization system, and on the other hand, it reduces the separation effect of the absorption stabilization system, resulting in an increase in the liquefied gas components in the catalytic cracking dry gas. Summary of the Invention

[0008] The present invention provides an absorption stabilization process and system for increasing liquefied gas yield. This process reduces the load on the absorption stabilization unit through membrane separation technology and enhances the absorption efficiency of the absorption tower by feeding the retentate gas and the gas phase at the top of the desorption tower in stages, thereby reducing the liquefied gas component lost in the dry gas and enhancing the liquefied gas recovery capacity of the process unit.

[0009] According to a first aspect of the present invention, there is provided an absorption stabilization process for increasing the yield of liquefied gas.

[0010] Specifically, an absorption stabilization process for increasing the yield of liquefied gas according to the present invention comprises the following contents:

[0011] (1) The raw gas A from the catalytic cracking fractionator is compressed by the rich gas compressor, mixed with the rich absorption oil obtained at the bottom of the absorption tower, and after cooling, enters the gas-liquid separation tank for flash evaporation. The resulting gas phase is optionally filtered and then enters the membrane separation unit for separation;

[0012] (2) The gas phase obtained in step (1) enters a membrane separation unit for separation to obtain permeate gas and retentate gas containing hydrogen;

[0013] (3) The permeate gas obtained in step (2) enters the first gas inlet at the lower part of the absorption tower, and contacts the absorbent entering the upper part of the absorption tower on the tray or packing to carry out mass and heat transfer;

[0014] (4) The top gas obtained from the absorption tower in step (3) leaves the device and enters the reabsorption tower, where it undergoes mass and heat transfer with the reabsorbent (such as light diesel, etc.). The dry gas obtained from the reabsorption tower leaves the top of the reabsorption tower, and the reabsorption rich agent obtained from the reabsorption tower leaves the device;

[0015] (5) The liquid phase obtained from the gas-liquid separation tank in step (1) enters the upper part of the desorption tower after heat exchange, thereby removing light components such as C2 that are overabsorbed in the rich absorbent, and the desorption tower gas phase is produced from the top of the desorption tower, and the deethanized gasoline is produced from the bottom of the tower;

[0016] (6) The desorbed gas obtained at the top of the desorption tower in step (5) is cooled by heat exchange and then enters the absorption tower from the second gas inlet at the bottom of the absorption tower;

[0017] (7) The deethanized gasoline at the bottom of the desorption tower in step (5) enters the stabilization tower, where it is separated into liquefied gas product and stabilized gasoline.

[0018] Furthermore, the optional filtration in step (1) means that the gas phase obtained from the gas-liquid separation tank may or may not be filtered, preferably filtered. The purpose of filtration is to filter out a small amount of solid impurities that may be contained in the gas phase, thereby preventing the solid impurities from contaminating and damaging the membrane separator. After filtration, the gas phase is heated to 60-80°C in a preheater, so that the gas phase temperature is higher than its dew point by more than 20°C, thereby preventing the gas phase from liquefying in the membrane separator.

[0019] Furthermore, in the preheating process described in step (1), the heat source can be selected to absorb the low-temperature heat that is not recovered by the stabilization system, such as the heat below 100°C of the stabilized gasoline entering the air-cooled or water-cooled system, so that the energy consumption required for the device process heating will not be increased.

[0020] Furthermore, in step (2), the preheated gas phase enters the membrane separator and is separated in the membrane separator. After the membrane separation operation, the permeate gas obtained mainly contains H2, CH4 and a small amount of C2 and other components, among which the content of C3 and above components is relatively low and can be directly sent out of the device boundary area. The concentration of C3+ components in the retentate gas obtained by membrane separation increases, and the partial pressure of C3+ components in the retentate gas increases accordingly, which is beneficial to the subsequent absorption process. The retentate gas is cooled to 30-40°C and then sent to the first gas inlet of the absorption tower.

[0021] Furthermore, the operating conditions of the membrane separator in step (2) are common knowledge among those skilled in the art. For example, the membrane separation operating conditions include: an operating pressure of 1.00-3.00 MPaG, an osmotic pressure of 0.01-0.50 MPaG, and a retentate pressure that is substantially consistent with the pressure of the membrane separator. The membrane separator can be made of various materials used in common hydrogen separation membranes, such as polyimide membranes and other membrane materials commonly used in the field of hydrogen separation. The membrane assembly of the membrane separator can be in the form of hollow fiber, spiral wound, plate-and-frame flat plate, etc. The installation form can be horizontal or vertical. In order to reduce the contamination and damage of the membrane by residual impurities in the gas phase, the vertical type is preferred.

[0022] Furthermore, in step (3), stabilized gasoline and / or crude gasoline can be used as absorbent in the absorption tower.

[0023] Furthermore, in step (4), the rich reabsorbent extracted from the bottom of the reabsorption tower can be used in a separate regeneration tower, or can be returned to the main fractionation tower for regeneration. Furthermore, the operating conditions of the absorption tower are common knowledge in the art.

[0024] Furthermore, in step (6), the second gas inlet and the first gas inlet can both be set at the bottom of the tower for feeding, or they can be located at different theoretical plates. In the present invention, since the gas phase at the top of the desorption tower is rich in C2 components, in order to avoid the light components such as C2 in the gas phase of the desorption tower reducing the partial pressure of the C3+ components in the retentate gas, thereby weakening the effect of the membrane separation process on the absorption effect, preferably, the second gas inlet is higher than the first gas inlet, and the difference between the two is at least one theoretical plate; more preferably, the gas phase at the top of the desorption tower is set to be fed 2-4 theoretical plates above the bottom of the absorption tower, while the retentate gas is fed at the bottom of the absorption tower. In the present invention, since the content of C3+ components in the retentate gas after treatment by the membrane separation unit increases, the segmented feeding of the above two gas phases is more consistent with the gradient distribution of the gas phase composition in the absorption tower, which can effectively reduce the back mixing of the components in the tower and reduce the overabsorption of the C2 component during the absorption process, thereby reducing the cumulative amount of the absorption tower-desorption tower logistics cycle, and further improving the processing capacity of the absorption tower.

[0025] According to a second aspect of the present invention, the present invention also provides an absorption stabilization process system for increasing the yield of liquefied gas.

[0026] The absorption stabilization process system of the present invention comprises:

[0027] The gas-liquid separation tank is used to flash the compressed and cooled rich gas and rich absorption oil to obtain the flash tank gas phase and the flash tank liquid phase;

[0028] A membrane separation unit is used to separate the gas phase obtained from the flash tank and obtain permeate gas and retentate gas rich in hydrogen, CH4 and C2;

[0029] An absorption tower is used for mass and heat transfer between the retentate gas obtained by separation of the absorbent and the membrane and the desorption tower top gas on the tower plates or packing, and to obtain absorption tower top gas and rich absorption oil; the absorption tower includes an absorbent inlet at the top, a tower top gas removal pipeline, a tower bottom rich absorption oil removal pipeline, a first gas inlet and a second gas inlet;

[0030] The reabsorption tower is used to absorb the tower top gas and light diesel oil for mass and heat transfer, and obtain the tower top dry gas and rich light diesel oil;

[0031] The desorption tower is used to desorb the liquid phase of the flash tank obtained from the gas-liquid separation tank, and obtain the desorption tower top gas and desorption tower bottom oil;

[0032] The stabilizer is used to fractionate the oil at the bottom of the desorption tower and obtain liquefied gas products and stabilized gasoline.

[0033] Furthermore, the first gas inlet and the second gas inlet may be located together at the bottom of the tower, or the first gas inlet may be located at the bottom of the tower and the second gas inlet may be located several theoretical plates above the bottom of the tower; preferably, the second gas inlet is higher than the first gas inlet; further, preferably, the second gas inlet is located 2-4 theoretical plates above the bottom of the self-absorption tower.

[0034] Furthermore, the membrane separation unit typically includes a preheater, a filter, a membrane separator, and a cooler. The membrane separator can be made of various materials commonly used in hydrogen separation membranes, such as polyimide membranes. The membrane separator can be constructed using various types of hollow fiber, spiral wound, plate-and-frame flat-plate, and other membrane modules. Installation options include horizontal or vertical installation. Vertical installation is preferred to minimize contamination and damage to the membrane from residual impurities in the gas phase.

[0035] In the present invention, the absorption stabilization process and system are suitable for separation of rich gas in absorption stabilization systems of processes such as catalytic cracking, delayed coking, and light hydrocarbon recovery.

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

[0037] 1. The present invention provides a process for improving the existing absorption stabilization system. By setting up a membrane separator, the gas phase obtained from the compressed rich gas gas-liquid separation tank is subjected to membrane separation operation, thereby reducing the hydrogen partial pressure, C1 and C2 partial pressure in the absorption tower feed, and making C3 + The components are more easily absorbed by the absorbent within the absorption tower. Simultaneously, by adjusting the positions of the two gaseous feed streams, the overabsorption of C2 components during the absorption process is reduced, thereby reducing the cumulative volume of absorber-desorber logistics circulation. This increases the absorption of C3+ components at a constant absorbent circulation rate. In summary, the present invention can effectively increase the liquefied gas yield of the absorption stabilization system.

[0038] 2. When the two gas phases of the absorption tower are preferably fed separately, the amount of C2 overabsorbed during the absorption process is reduced, and the output of the desorption tower gas phase is also reduced. Therefore, the present invention can also reduce the heat load of the desorption tower reboiler to a certain extent.

[0039] 3. The permeate gas obtained in the membrane separation process of the present invention has a high hydrogen purity and can be sent to the hydrogen recovery unit (such as PSA) in the plant for recovery, thereby improving the hydrogen recovery rate of the entire plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a process flow chart of the process of the present invention, wherein the gas phase of the desorption tower is fed into the second gas inlet, and the second gas inlet is located at the bottom of the absorption tower.

[0041] In the figure, the numerical marks correspond to: 1-rich gas compressor; 2-water cooler; 3-gas-liquid separation tank; 4-filter; 5-preheater; 6-membrane separator; 7-cooler; 8-absorption tower; 9-reabsorption tower; 10-desorption tower; 11-stabilization tower; 12-desorption tower gas phase cooler; 13-first gas inlet; 14-second gas inlet; A-raw gas; B-permeate gas; C-retentate gas; D-dry gas product; E-liquefied gas product; F-stabilized gasoline; G-reabsorption of lean diesel; H-reabsorption of rich diesel; I-desorption tower gas phase.

[0042] Figure 2 2 is a process flow chart of the process of the present invention, wherein the gas phase of the desorption tower is fed into the second gas inlet, and the second gas inlet is located several theoretical plates above the bottom of the absorption tower.

[0043] In the figure, the numerical marks correspond to: 1-rich gas compressor; 2-water cooler; 3-gas-liquid separation tank; 4-filter; 5-preheater; 6-membrane separator; 7-cooler; 8-absorption tower; 9-reabsorption tower; 10-desorption tower; 11-stabilization tower; 12-desorption tower gas phase cooler; 13-first gas inlet; 14-second gas inlet; A-raw gas; B-permeate gas; C-retentate gas; D-dry gas product; E-liquefied gas product; F-stabilized gasoline; G-reabsorption of lean diesel; H-reabsorption of rich diesel; I-desorption tower gas phase. DETAILED DESCRIPTION

[0044] The method and system of the present invention are described in more detail below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1 As shown, feed gas A is compressed by rich gas compressor 1 and cooled by water cooler 2. The cooled feed gas enters gas-liquid separator 3 for flash evaporation. The gas phase from gas-liquid separator 3 is then sent to a membrane separation unit for separation. The membrane separation unit typically consists of a preheater 5, a filter 4, a membrane separator 6, and a cooler 7.

[0046] The gas phase separated by the gas-liquid separator 3 first enters the filter 4 to filter out a small amount of solid impurities in the gas phase. After filtration, it is heated to 60-80°C by the preheater 5. The preheated gas phase enters the membrane separator 6, where it is separated. The separated permeate gas B is directly sent out of the device boundary area, and the separated retentate gas C is cooled to 30-40°C by the cooler 7 and then sent to the absorption tower 8. In order to reduce the processing capacity of the membrane separation unit, the desorption tower gas phase I in the present invention does not enter the gas-liquid separator 3, but is cooled by the desorption tower gas phase cooler 12 and then sent to the absorption tower 8. Optionally, the retentate gas C and the desorption tower gas phase I can be fed in stages at different positions of the absorption tower.

[0047] Conventional processes can be used for the remaining processes of the absorption and stabilization system of the present invention. For example, absorption tower 8 can use stabilized gasoline or crude gasoline as the absorbent. The dry gas from the top of the absorption tower enters reabsorption tower 9, where the reabsorbent absorbs the gasoline components entrained in the dry gas. The absorbed gas phase exits as dry gas product D. Reabsorption-rich agent H is extracted from the bottom of reabsorption tower 9 and returned to the main fractionation tower for regeneration. The liquid phase at the bottom of absorption tower 8 is transported to gas-liquid separator 3, which is then pumped to the top of desorption tower 10. The deethanized gasoline at the bottom of desorption tower 10 is then transported to stabilization tower 11, where it is separated into liquefied gas product E and stabilized gasoline F.

[0048] The operating pressure of the membrane separator mentioned in the above process method is 1.00-3.00 MPaG, the osmotic pressure is 0.01-0.50 MPaG, and the retentate side pressure is basically the same as the pressure of the membrane separator.

[0049] The absorption tower gas phase mentioned in the above process method is fed in stages, and the first gas inlet 13 for the retentate gas feed is set at the bottom of the tower for feeding, and the second gas inlet 14 for the desorption tower gas phase is fed several theoretical plates upward from the bottom of the tower. The feeding position is determined according to the specific composition at the time of use, preferably 2-4 theoretical plates from bottom to top.

[0050] Example 1

[0051] In the absorption stabilization system of a 1 million tons / year catalytic cracking unit, the process for increasing the liquefied gas yield of the absorption stabilization system provided by the present invention is adopted. The process is as follows: Figure 1 The raw gas A is compressed by the rich gas compressor 1 and then cooled by the water cooler 2. The cooled raw gas enters the gas-liquid separation tank 3 for flash evaporation, and the gas phase of the gas-liquid separation tank 3 is sent to the membrane separation unit for separation.

[0052] The gas phase from the gas-liquid separator 3 has a mass flow rate of 28,947 kg / h and a molar flow rate of 22,642 Nm³ / h. It first enters filter 4 to filter out small amounts of solid impurities in the gas phase, thereby preventing contamination and damage to the membrane separator. After filtration, it is heated to 70°C in a preheater 5, raising the gas phase temperature to at least 20°C above its dew point to prevent liquefaction in the membrane separator. The preheated gas then enters membrane separator 6, where separation occurs. The membrane separator is a vertical hollow fiber membrane made of polyimide. The feed gas pressure is 1.58 MPaG, and the permeate pressure is 0.03 MPaG. The separated retentate gas C is cooled to 30-40°C in a cooler 7 and then fed to the first gas inlet 13 at the bottom of the absorption tower 8 of the absorption stabilization system. The desorption tower gas phase I, extracted from the desorption tower 10, is cooled to 40°C and then fed to the second gas inlet 14 at the bottom of the absorption tower 8.

[0053] The remaining process is identical to the conventional absorption and stabilization process. Absorption tower 8 uses stabilized gasoline and crude gasoline as absorbents. The dry gas from the top enters reabsorption tower 9, where the diesel absorbent absorbs entrained gasoline components. The absorbed gas exits as dry gas product D. The reabsorbed diesel-rich H is extracted and reabsorbed at the bottom of reabsorption tower 9 and returned to the main fractionation tower for regeneration. The liquid phase at the bottom of absorption tower 8 is transported to separator 3, where it is pumped to the top of desorption tower 10. The deethanized gasoline at the bottom of desorption tower 10 is then transported to stabilization tower 11, where it is separated into the liquefied gas product and stabilized gasoline.

[0054] Table 1 shows the flow rate, composition and other data of some gas phases in Example 1. The relevant data were calculated using Aspen Plus simulation software.

[0055] Table 1

[0056]

[0057] Example 2

[0058] In the absorption stabilization system of a 1 million tons / year catalytic cracking unit, the process for increasing the liquefied gas yield of the absorption stabilization system provided by the present invention is adopted. The process is as follows: Figure 2 The raw gas A is compressed by the rich gas compressor 1 and then cooled by the water cooler 2. The cooled raw gas enters the gas-liquid separation tank 3 for flash evaporation, and the gas phase of the gas-liquid separation tank 3 is sent to the membrane separation unit for separation.

[0059] The gas phase from gas-liquid separator 3 has a mass flow rate of 28,947 kg / h and a molar flow rate of 22,642 Nm³ / h. It first enters filter 4 to filter out small amounts of solid impurities in the gas phase, thereby preventing contamination and damage to the membrane separator. After filtration, it is heated to 70°C in preheater 5, raising the gas phase temperature to at least 20°C above its dew point to prevent liquefaction in the membrane separator. The preheated gas phase enters membrane separator 6, where it undergoes separation. The membrane separator is a vertical hollow fiber membrane made of polyimide. The feed gas pressure is 1.58 MPaG, and the permeate pressure is 0.03 MPaG. The flow rates and composition of the membrane separator feed gas, permeate gas B, and retentate gas C are shown in Table 2. The separated retentate gas C is cooled to 40°C by the cooler 7 and then fed into the first gas inlet 13 at the bottom of the absorption tower 8 of the absorption stabilization system. The desorption tower gas phase I produced by the desorption tower 10 enters the second gas inlet 14 of the absorption tower 8, which is set at the fourth theoretical plate upward from the bottom of the tower.

[0060] The remaining process is identical to the conventional absorption and stabilization process. Absorption tower 8 uses stabilized gasoline and crude gasoline as absorbents. The dry gas from the top enters reabsorption tower 9, where the diesel absorbent absorbs entrained gasoline components. The absorbed gas exits as dry gas product D. The reabsorbed diesel-rich H is extracted and reabsorbed at the bottom of reabsorption tower 9 and returned to the main fractionation tower for regeneration. The liquid phase at the bottom of absorption tower 8 is transported to separator 3, where it is pumped to the top of desorption tower 10. The deethanized gasoline at the bottom of desorption tower 10 is then transported to stabilization tower 11, where it is separated into the liquefied gas product and stabilized gasoline.

[0061] Table 2 shows the flow rate, composition and other data of some gas phases in Example 2. The relevant data are all calculated using AspenPlus simulation software.

[0062] Table 2

[0063]

[0064] Comparative Example 1

[0065] Taking the absorption stabilization system of the 1 million tons / year catalytic cracking unit as a comparative example, the absorption stabilization system of the unit adopts conventional technology, and the data of the catalytic dry gas product flow rate, composition, etc. are calculated by Aspen Plus simulation software, see Table 3.

[0066] Table 3

[0067]

[0068] Table 4 compares the process parameters of the absorption towers in the Examples and Comparative Examples. As can be seen from Table 4, Examples 1 and 2 were compared with the Comparative Examples under the same absorbent dosage and absorption pressure. As can be seen from Example 1 and the Comparative Examples in Table 4, the present invention can pre-separate light components such as hydrogen through a membrane separation unit, thereby reducing the gas phase feed rate to the absorption tower, which is beneficial to the absorption process. As can be seen from Example 1 and Example 2 in Table 4, Example 2 preferably utilizes the process discussed in the present invention of feeding the retentate gas and the desorption tower gas phase separately, thereby further reducing the total gas phase amount entering the absorption tower.

[0069] Table 4

[0070]

[0071] Table 5 shows the liquefied gas flow rate and liquefied gas yield in Examples 1, 2, and Comparative Example 1. As shown in Table 5, by using the process provided by the present invention in this catalytic cracking unit, by coupling membrane separation technology with an absorption stabilization system, the liquefied gas content in the catalytic dry gas can be reduced from 3.1% (Comparative Example) to 1.48% (Example 1), and the liquefied gas yield in the absorption stabilization system can be increased from 97.70% in the Comparative Example to 98.64%. Furthermore, by using separate gas-phase feeding in Example 1, the liquefied gas content in the catalytic dry gas can be further reduced to 1.29% (Example 2), and the liquefied gas yield in the absorption stabilization system is now 98.71%.

[0072] Table 5

[0073]

Claims

1. An absorption stabilization process for increasing the yield of liquefied gas, characterized in that: Includes the following: (1) The raw gas A from the catalytic cracking fractionator is compressed by the rich gas compressor, mixed with the rich absorption oil obtained at the bottom of the absorption tower, and after cooling, enters the gas-liquid separation tank for flash evaporation. The resulting gas phase is optionally filtered and then enters the membrane separation unit for separation; (2) The gas phase obtained in step (1) enters a membrane separation unit for separation to obtain permeate gas and retentate gas containing hydrogen; (3) The permeate gas obtained in step (2) enters the first gas inlet at the lower part of the absorption tower, and contacts the absorbent entering the upper part of the absorption tower on the tray or packing to carry out mass and heat transfer; (4) The top gas obtained from the absorption tower in step (3) leaves the device and enters the reabsorption tower, where it undergoes mass and heat transfer with the reabsorbent. The dry gas obtained from the reabsorption tower leaves the top of the reabsorption tower, and the reabsorbent rich agent obtained from the reabsorption tower leaves the device; (5) The liquid phase obtained in the gas-liquid separation tank in step (1) enters the upper part of the desorption tower after heat exchange, and the desorption tower gas phase is produced from the top of the desorption tower, and the de-ethanized gasoline is produced from the bottom of the tower; (6) The desorbed gas obtained at the top of the desorption tower in step (5) is cooled by heat exchange and then enters the absorption tower from the second gas inlet at the bottom of the absorption tower; (7) The deethanized gasoline at the bottom of the desorption tower in step (5) enters the stabilization tower, where it is separated into liquefied gas product and stabilized gasoline.

2. The absorption stabilization process according to claim 1, characterized in that: The optional filtration in step (1) means that the gas phase obtained from the gas-liquid separation tank needs to be filtered or not.

3. The absorption stabilization process according to claim 2, characterized in that: The gas phase is heated to 60-80°C before entering the membrane separator, so that the gas phase temperature is 20°C higher than its dew point.

4. The absorption stabilization process according to claim 1, characterized in that: The retentate gas obtained in step (2) is cooled to 30-40° C. and then fed into the first gas inlet of the absorption tower.

5. The absorption stabilization process according to claim 1, characterized in that: The operating conditions of the membrane separator in step (2) include: an operating pressure of 1.00-3.00 MPaG, an osmotic pressure of 0.01-0.50 MPaG, and a retentate pressure that is substantially consistent with the pressure of the membrane separator.

6. The absorption stabilization process according to claim 1, characterized in that: In step (3), stabilized gasoline and / or crude gasoline is used as absorbent in the absorption tower.

7. The absorption stabilization process according to claim 1, characterized in that: The first gas inlet and the second gas inlet are both located at the bottom of the tower, or the first gas inlet is located at the bottom of the tower, and the second gas inlet is located several theoretical plates above the bottom of the tower.

8. An absorption stabilization system for increasing the yield of liquefied gas, characterized in that: include: The gas-liquid separation tank is used to flash the compressed and cooled rich gas and rich absorption oil to obtain the flash tank gas phase and the flash tank liquid phase; A membrane separation unit is used to separate the gas phase obtained from the flash tank and obtain permeate gas and retentate gas rich in hydrogen, CH4 and C2; An absorption tower is used for mass and heat transfer between the retentate gas obtained by separation of the absorbent and the membrane and the desorption tower top gas on the tower plates or packing, and to obtain absorption tower top gas and rich absorption oil; the absorption tower includes an absorbent inlet at the top, a tower top gas removal pipeline, a tower bottom rich absorption oil removal pipeline, a first gas inlet and a second gas inlet; The reabsorption tower is used to absorb the tower top gas and light diesel oil for mass and heat transfer, and obtain the tower top dry gas and rich light diesel oil; The desorption tower is used to desorb the liquid phase of the flash tank obtained from the gas-liquid separation tank, and obtain the desorption tower top gas and desorption tower bottom oil; The stabilizer is used to fractionate the oil at the bottom of the desorption tower and obtain liquefied gas products and stabilized gasoline.

9. The absorption stabilization system according to claim 8, characterized in that The first gas inlet and the second gas inlet are both located at the bottom of the tower.

10. The absorption stabilization system according to claim 8, characterized in that The first gas inlet is located at the bottom of the tower, and the second gas inlet is located several theoretical plates above the bottom of the tower.

11. The absorption stabilization system according to claim 10, characterized in that The second gas inlet is located 2-4 theoretical plates above the bottom of the absorption tower.

12. The absorption stabilization system according to claim 8, characterized in that The membrane separation unit includes a preheater, a filter, a membrane separator and a cooler.

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