Recovery process and recovery system for refinery dry gas

Abstract

This invention provides a method and system for recovering refinery dry gas, comprising the following steps: performing a first distillation separation on the refinery dry gas to obtain a first liquid and a first gas; performing a second distillation separation on the first gas to obtain ethane and a second gas; performing low-temperature washing on the second gas to obtain a second liquid and a hydrogen-rich gas; and purifying the hydrogen-rich gas to obtain pure hydrogen product. This application utilizes the different boiling points of the constituent gases in the refinery dry gas, and through multiple distillation separations, low-temperature washing, and purification processes, gradually removes components other than hydrogen from the refinery dry gas, thereby improving the hydrogen recovery rate and purity. Furthermore, by performing multiple distillation separations, low-temperature washing, and purification processes on the refinery dry gas, the effective components in the refinery dry gas can be purified and utilized as chemical raw materials or products, thus increasing the economic benefits of the refinery dry gas.

Description

Technical Field

[0001] This invention relates to the field of low-temperature separation technology for refinery dry gas, and in particular to a method and system for recovering refinery dry gas. Background Technology

[0002] Refinery dry gas refers to non-condensable gases (also known as distilled gas) generated and recovered during the refining process in oil refineries. Its main components are hydrogen, ethylene, propylene, and methane, ethane, propane, butane, etc. Refinery dry gas primarily originates from secondary crude oil processing, such as heavy oil catalytic cracking, thermal cracking, and delayed coking. Although the light hydrocarbons and hydrogen in refinery dry gas have high utilization value, they are usually fed into the gas pipeline network as fuel gas, and some are even burned in flares, resulting in a significant waste of resources.

[0003] With the continuous commissioning of refinery hydrotreating units, the demand for hydrogen from refineries is increasing daily. If the high-value-added hydrogen in refinery dry gas is recovered, the hydrogen products can fill the gaps and shortages in the refinery's oil product upgrading and structural optimization processes. In addition, other effective components in hydrogen-rich tail gas can also bring considerable economic benefits to enterprises through fractional utilization.

[0004] Hydrogen energy, as a new type of energy, has advantages such as high calorific value and being green and pollution-free. Traditional recovery methods mainly employ pressure swing adsorption (PSA) and membrane separation technologies. However, the recovery rate and purity of hydrogen in traditional methods are relatively low. Summary of the Invention

[0005] Therefore, it is necessary to provide a method and system for recovering dry gas from refineries, addressing the problem that the recovery rate and purity of hydrogen are both low in traditional recovery methods.

[0006] The technical solution is as follows:

[0007] On the one hand, a method for recovering dry gas from refineries is provided, comprising:

[0008] The refinery dry gas is subjected to a first distillation separation to obtain a first liquid and a first gas;

[0009] The first gas is subjected to a second distillation separation to obtain ethane and a second gas;

[0010] The second gas is subjected to low-temperature washing to obtain a second liquid and a hydrogen-rich gas;

[0011] The hydrogen-rich gas is purified to obtain pure hydrogen product.

[0012] The technical solution will be further explained below:

[0013] In one embodiment, the step of performing a first distillation separation on refinery dry gas to obtain a first liquid and a first gas includes:

[0014] The refinery dry gas is pressurized and then subjected to impurity removal treatment to remove acidic impurities from the refinery dry gas.

[0015] The refinery dry gas, after removing acidic impurities, is dehydrated to obtain purified dry gas.

[0016] The purified dry gas is subjected to a first distillation separation to obtain a first liquid and a first gas.

[0017] In one embodiment, prior to the step of performing a first distillation separation on the purified dry gas to obtain the first liquid and the first gas, the method further includes:

[0018] The purified dry gas undergoes a first heat exchange to lower its temperature, while maintaining the purified dry gas in a gaseous state.

[0019] In one embodiment, the step of performing a second distillation separation on the first gas to obtain ethane and the second gas includes:

[0020] The first heat exchange medium, after undergoing a first heat exchange with the purified dry gas, is conveyed to the ethane tower, and the first gas is conveyed to the ethane tower, so that the first heat exchange medium and the first gas exchange heat in the ethane tower, thereby allowing the first gas to undergo a second distillation separation to obtain the ethane and the second gas.

[0021] In one embodiment, after the first distillation separation of refinery dry gas to obtain a first liquid and a first gas, the method further includes:

[0022] The first liquid is subjected to a third distillation separation to obtain light oil and liquefied petroleum gas.

[0023] In one embodiment, prior to the step of performing a second distillation separation on the first gas to obtain ethane and the second gas, the method further includes:

[0024] The first gas undergoes a second heat exchange and a first gas-liquid separation to remove the first liquid from the first gas.

[0025] In one embodiment, prior to the step of low-temperature washing of the second gas to obtain the second liquid and hydrogen-rich gas, the method further includes:

[0026] The second gas undergoes a third heat exchange and a second gas-liquid separation to remove ethane from the second gas.

[0027] In one embodiment, after the step of performing a third heat exchange and a second gas-liquid separation on the second gas to remove ethane from the second gas, the method further includes:

[0028] The second gas undergoes a fourth heat exchange to lower its temperature while maintaining its gaseous state.

[0029] And / or, the second gas is subjected to a fifth heat exchange with a nitrogen cycle refrigeration device to reduce the temperature of the second gas, while the second gas is able to maintain its gaseous state.

[0030] In one embodiment, after the step of performing low-temperature washing on the second gas to obtain a second liquid and a hydrogen-rich gas, the method further includes:

[0031] The second liquid is subjected to a fourth distillation separation to obtain methane and fuel gas.

[0032] On the other hand, a recovery system for refinery dry gas is provided. The recovery system includes an ethane stripper, an ethane stripper, a cryogenic scrubbing tower, and a pressure swing adsorption (PSA) device, wherein the ethane stripper, ethane stripper, cryogenic scrubbing tower, and PSA device are sequentially connected. The ethane stripper is used to perform a first distillation separation on the refinery dry gas to obtain a first liquid and a first gas. The ethane stripper is used to perform a second distillation separation on the first gas to obtain ethane and a second gas. The cryogenic scrubbing tower is used to perform cryogenic scrubbing on the second gas to obtain a second liquid and a hydrogen-rich gas. The PSA device is used to purify the hydrogen-rich gas to obtain pure hydrogen.

[0033] Compared with traditional recovery methods, the recovery method and system for refinery dry gas in this application have at least the following advantages: (1) By utilizing the different boiling points of the constituent gases in the refinery dry gas, the refinery dry gas is subjected to multiple distillation separations, low-temperature washing and purification treatments to gradually remove other components in the refinery dry gas except for hydrogen, which greatly improves the recovery rate and purity of hydrogen recovered from the refinery dry gas. (2) By subjecting the refinery dry gas to multiple distillation separations, low-temperature washing and purification treatments, the effective components in the refinery dry gas can be purified and utilized as chemical raw materials or products, and fully utilized, thereby increasing the economic benefits of the refinery dry gas. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of a method for recovering dry gas from a refinery, as exemplified by one embodiment.

[0037] Figure 2 A flowchart of a method for recovering refinery dry gas, according to another embodiment.

[0038] Figure 3 This is a schematic diagram of a structure for a dry gas recovery system for a refinery, according to one embodiment.

[0039] Explanation of reference numerals in the attached figures:

[0040] 10. Recovery system; 101. Ethane removal tower; 102. Ethane tower; 103. Low-temperature scrubbing tower; 104. Pressure swing adsorption unit; 105. Pressurization unit; 106. Deacidification unit; 107. Dehydration unit; 108. First heat exchanger; 109. Liquefied petroleum gas tower; 110. Second heat exchanger; 111. First separator; 112. First condensate pump; 113. Third heat exchanger; 114. Second separator; 115. Second condensate pump; 116. Fourth heat exchanger; 117. Fifth heat exchanger; 118. Nitrogen cycle refrigeration unit; 119. Mixed cycle refrigeration unit; 120. Methane tower. Detailed Implementation

[0041] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0042] like Figure 1 As shown, in one embodiment, a method for recovering refinery dry gas is provided, comprising the following steps:

[0043] S100. The refinery dry gas is subjected to a first distillation separation to obtain a first liquid and a first gas. In this way, taking advantage of the different boiling points of the various components of the refinery dry gas, some of the higher boiling point gases in the refinery dry gas are condensed and liquefied, so that the hydrogen and other components in the refinery dry gas can be recovered and reused in the later stage.

[0044] It should be noted that the first liquid refers to propylene and heavier components after condensation and liquefaction, and the first gas refers to ethane and lighter components (such as ethylene and methane).

[0045] like Figure 2 As shown, specifically in this embodiment, in step S110, the refinery dry gas is pressurized and then subjected to impurity removal treatment to remove acidic impurities. This pressurization of the refinery dry gas allows it to flow along a predetermined path, improving the reliability of the recovery method. Furthermore, the deacidification device 106 removes acidic impurities such as carbon dioxide and hydrogen sulfide from the refinery dry gas, improving the purity of the recovered hydrogen and other products.

[0046] S120. The refinery dry gas, after removing acidic impurities, is dehydrated to obtain purified dry gas. This removes moisture from the refinery dry gas, improving the purity of hydrogen and other products recovered by the recycling method.

[0047] S130. The purified dry gas is subjected to a first distillation separation to obtain a first liquid and a first gas. In this way, taking advantage of the different boiling points of the constituent gases in the purified gas, some of the gases with higher boiling points are condensed and liquefied so that the constituent gases such as hydrogen can be recovered and reused in the future.

[0048] S200: The first gas undergoes a second distillation separation to obtain ethane and a second gas. This allows ethane to be recovered from the first gas, avoiding waste of ethane in refinery dry gas and improving the economic efficiency of refinery dry gas. Furthermore, by removing ethane from the first gas to obtain the second gas, the hydrogen content in the second gas increases, improving the convenience, purity, and recovery rate of the hydrogen recovery method.

[0049] It should be noted that the second gas refers to the remaining gas after ethane has been separated from the first gas, including methane, hydrogen, carbon monoxide, and nitrogen.

[0050] like Figure 2 As shown, specifically in this embodiment, in step S210, the first heat exchange medium, after undergoing a first heat exchange with the purified dry gas, is conveyed to the ethane tower 102, and the first gas is also conveyed to the ethane tower 102. This allows the first heat exchange medium and the first gas to exchange heat within the ethane tower 102, thereby enabling the first gas to undergo a second distillation separation to obtain ethane and the second gas. In this way, the heat required by the ethane tower 102 can be derived from the heat exchange with the purified gas, eliminating the need for an external heating source. This effectively achieves comprehensive energy utilization and reduces the recovery cost of the recovery method.

[0051] S300: The second gas is subjected to low-temperature washing to obtain a second liquid and a hydrogen-rich gas. In this way, hydrogen-rich gas is extracted from the second gas to ensure that hydrogen of higher purity can be recovered from the hydrogen-rich gas.

[0052] It should be noted that the second liquid is formed by the condensation and liquefaction of gases other than hydrogen in the second gas.

[0053] S400 purifies the hydrogen-rich gas to obtain pure hydrogen products. This increases both the hydrogen recovery rate and purity, improving the economic efficiency of the refinery's dry gas.

[0054] like Figure 2 As shown, in one embodiment, before the step of performing a first distillation separation on the purified dry gas to obtain a first liquid and a first gas, the following step is further included:

[0055] S500: The purified dry gas undergoes a first heat exchange to lower its temperature while maintaining it in a gaseous state. This lowers the temperature of the purified gas to slightly above the boiling point of the first liquid before the first distillation separation, ensuring that the purified dry gas can undergo the first distillation separation to obtain the first liquid and the first gas, thus improving the reliability of the recovery method.

[0056] like Figure 2 As shown, in one embodiment, after the first distillation separation of refinery dry gas to obtain a first liquid and a first gas, the following steps are further included:

[0057] S600: The first liquid is subjected to a third distillation separation to obtain light oil and liquefied petroleum gas. In this way, light oil and liquefied petroleum gas can be recovered from the first liquid, avoiding the waste of light oil and liquefied petroleum gas in the refinery dry gas and improving the economic efficiency of the refinery dry gas.

[0058] like Figure 2 As shown, in one embodiment, prior to the step of performing a second distillation separation on the first gas to obtain ethane and the second gas, the method further includes:

[0059] S700: The first gas undergoes a second heat exchange and a first gas-liquid separation to remove the first liquid from the first gas. This further removes the first liquefaction from the first gas, improving the purity of the recovered hydrogen and ethane products.

[0060] like Figure 2 As shown, in one embodiment, prior to the step of cryogenically washing the second gas to obtain the second liquid and hydrogen-rich gas, the following steps are also included:

[0061] S800: The second gas undergoes a third heat exchange and a second gas-liquid separation to remove ethane. This further removes ethane from the second gas, improving the purity of the recovered hydrogen and other products.

[0062] like Figure 2 As shown, in one embodiment, after the step of performing a third heat exchange and a second gas-liquid separation on the second gas to remove ethane from the second gas, the following step is further included:

[0063] S900: A fourth heat exchange is performed on the second gas to lower its temperature while maintaining its gaseous state. This lowers the temperature of the second gas to slightly above the boiling point of the second liquid, ensuring that the second gas can be subjected to low-temperature washing to obtain the second liquid and hydrogen-rich gas, thus improving the reliability of the recovery method.

[0064] In step S1000, the second gas undergoes a fifth heat exchange with the nitrogen cycle refrigeration device 118 to lower its temperature while maintaining its gaseous state. This allows the nitrogen cycle refrigeration device 118 to reduce the temperature of the second gas to an even lower range, ensuring thorough removal of low-boiling-point components such as carbon monoxide, methane, and nitrogen, thus improving the purity of the recovered hydrogen.

[0065] like Figure 2 As shown, in one embodiment, after the step of performing low-temperature washing on the second gas to obtain the second liquid and hydrogen-rich gas, the following step is further included:

[0066] S1100: The second liquid undergoes a fourth distillation separation to obtain methane and fuel gas. This allows for the recovery of methane and fuel gas from the second liquid, preventing waste of methane and fuel gas in refinery dry gas and improving the economic efficiency of refinery dry gas.

[0067] Compared with traditional recovery methods, the recovery method in this application has at least the following advantages: (1) By utilizing the different boiling points of the constituent gases in the refinery dry gas, the refinery dry gas is subjected to multiple distillation separations, low-temperature washing and purification treatments to gradually remove other components in the refinery dry gas except for hydrogen, which greatly improves the recovery rate and purity of hydrogen recovered from the refinery dry gas. (2) By subjecting the refinery dry gas to multiple distillation separations, low-temperature washing and purification treatments, the effective components in the refinery dry gas can be purified and utilized as chemical raw materials or products, and fully utilized, thereby increasing the economic benefits of the refinery dry gas.

[0068] like Figure 3As shown, in one embodiment, a recovery system 10 for refinery dry gas is provided. The recovery system 10 includes an ethane stripper 101, an ethane stripper 102, a cryogenic scrubbing tower 103, and a pressure swing adsorption (PSA) device 104. The ethane stripper 101, ethane stripper 102, cryogenic scrubbing tower 103, and PSA device 104 are sequentially connected. The ethane stripper 101 is used to perform a first distillation separation on the refinery dry gas to obtain a first liquid and a first gas. The ethane stripper 102 is used to perform a second distillation separation on the first gas to obtain ethane and a second gas. The cryogenic scrubbing tower 103 is used to perform cryogenic scrubbing on the second gas to obtain a second liquid and a hydrogen-rich gas. The PSA device 104 is used to purify the hydrogen-rich gas to obtain pure hydrogen products.

[0069] In the above-described recovery system 10, the refinery dry gas is first subjected to a first distillation separation using an ethane stripper 101 to obtain a first liquid and a first gas. Then, the first gas is subjected to a second distillation separation using an ethane stripper 102 to obtain ethane and a second gas. Next, the second gas is subjected to low-temperature washing using a low-temperature scrubbing tower 103 to obtain a second liquid and a hydrogen-rich gas. Finally, the hydrogen-rich gas is purified using a pressure swing adsorption device 104 to obtain pure hydrogen. Compared to traditional recovery methods, the recovery system 10 of this application can perform multiple distillation separations, low-temperature washing, and purification processes on the refinery dry gas, significantly improving the recovery rate and purity of hydrogen from the refinery dry gas. Furthermore, by performing multiple distillation separations, low-temperature washing, and purification processes on the refinery dry gas, the effective components in the refinery dry gas can be purified and utilized as chemical raw materials or products, thus increasing the economic benefits of the refinery dry gas.

[0070] It should be noted that the ethane recovery purity in this application can reach over 95%, and the ethane recovery rate can reach over 95%. The hydrogen recovery purity in the hydrogen-rich gas in this application is approximately 80%. The pure hydrogen product recovery rate in this application can reach over 98%, and the pure hydrogen product recovery purity can reach over 99.9%.

[0071] Specifically, in this embodiment, the temperature in the deethaner 101 decreases from bottom to top. The temperature at the bottom of the deethaner 101 is 84°C, the first liquid is located at the bottom of the deethaner 101, the temperature at the top of the deethaner 101 is -33°C, and the first gas is located at the top of the deethaner 101. Similarly, the temperature in the ethaner 102 decreases from bottom to top. The temperature at the bottom of the ethaner 102 is 4°C, ethane is located at the bottom of the ethaner 102, the temperature at the top of the ethaner 102 is -118°C, and the second gas is located at the top of the ethaner 102. Likewise, the temperature in the cryogenic scrubbing tower 103 decreases from bottom to top. The temperature at the bottom of the cryogenic scrubbing tower 103 is -175°C, the second liquid is located at the bottom of the cryogenic scrubbing tower 103, the temperature at the top of the cryogenic scrubbing tower 103 is -180°C, and the hydrogen-rich gas is located at the top of the cryogenic scrubbing tower 103.

[0072] like Figure 3 As shown, the recovery system 10 further includes a pressurization component 105, a deacidification device 106, and a dehydration device 107. The pressurization component 105, deacidification device 106, and dehydration device 107 are sequentially connected. The dehydration device 107 is connected to the ethane removal tower 101. The pressurization component 105 is used to pressurize the refinery dry gas; the deacidification device 106 is used to remove impurities from the refinery dry gas to remove acidic impurities; and the dehydration system is used to dehydrate the refinery dry gas to obtain purified dry gas. Thus, the pressurization component 105 can pressurize the refinery dry gas, allowing it to flow along a preset path, improving the reliability of the recovery system 10. In addition, the deacidification device 106 can remove acidic impurities such as carbon dioxide and hydrogen sulfide from the refinery dry gas, and the dehydration device 107 can remove moisture from the refinery dry gas, improving the purity of the recovered hydrogen and other products.

[0073] It should be noted that the pressurizing component 105 can be a booster pump, compressor, or other pressurizing structure. The deacidification device 106 can be a spray tower or existing deacidification equipment capable of removing acidic gases such as carbon dioxide and hydrogen sulfide. The dehydration device 107 can be a distillation tower, gas dehydration equipment, or existing equipment for removing moisture from gases.

[0074] like Figure 3 As shown, optionally, the recovery system 10 also includes a first heat exchanger 108. One end of the first heat exchanger 108 is connected to the dehydration device 107, and the other end is connected to the deethaner 101. Thus, the first heat exchanger 108 can perform the first heat exchange on the purified dry gas, lowering its temperature to slightly above the boiling point of the first liquid. This ensures that the deethaner 101 can perform the first distillation separation of the purified dry gas to obtain the first liquid and the first gas, improving the reliability of the recovery system 10.

[0075] It should be noted that the first heat exchanger 108 can be a heat exchanger, a reboiler, or other heat exchange structure. Specifically, in this embodiment, the first heat exchanger 108 is configured as a first reboiler, which can cool the purified gas at 40°C to 14°C.

[0076] like Figure 3 As shown, optionally, the first heat exchanger 108 is provided with a first heat exchange channel for conveying the first heat exchange medium, and the ethane tower 102 is provided with a second heat exchange channel for conveying the first heat exchange medium. The first heat exchange channel and the second heat exchange channel are correspondingly connected. In this way, the first heat exchange medium, after exchanging heat with the purified gas in the first heat exchanger 108, can flow into the ethane tower 102, so that the first heat exchange medium can exchange heat with the second gas in the ethane tower 102. Thus, the heat required by the ethane tower 102 can be obtained from the heat exchange with the purified gas, without the need for an external heating source, which can effectively realize the comprehensive utilization of energy and reduce the recovery cost of the recovery system 10.

[0077] like Figure 3 As shown, in one embodiment, the recovery system 10 further includes a liquefied petroleum gas (LPG) tower 109, which is connected to a deethaner 101. The LPG tower 109 is used to perform a third distillation separation on the first liquid to obtain light oil and LPG. Thus, the LPG tower 109 can separate the light oil and LPG in the first liquid, avoiding waste of light oil and LPG in the refinery dry gas and improving the economic efficiency of the refinery dry gas.

[0078] Specifically, in this embodiment, the temperature in the liquefied petroleum gas tower 109 tends to decrease from bottom to top. The temperature at the bottom of the liquefied petroleum gas tower 109 is 144°C, and light oil is located at the bottom of the liquefied petroleum gas tower 109. The temperature at the top of the liquefied petroleum gas tower 109 is 40°C to 50°C, and liquefied petroleum gas is located at the top of the liquefied petroleum gas tower 109.

[0079] like Figure 3In one embodiment, the recovery system 10 further includes a second heat exchanger 110, a first separator 111, and a first condensate pump 112. The first separator 111 has a first gas inlet, a first gas outlet, and a first liquid outlet. One end of the second heat exchanger 110 is connected to the ethane stripper 101, and the other end is connected to the first gas inlet. The first gas outlet is connected to the ethane stripper 102, and the first liquid outlet is connected to the first condensate pump 112. The first condensate pump 112 is also connected to the ethane stripper 101. Thus, the second heat exchanger 110 can exchange heat with the first gas, and the first separator 111 can separate the first liquid from the first gas, improving the purity of hydrogen and ethane recovered by the recovery system 10. Furthermore, the separated first liquid can be pumped back to the ethane stripper 101 via the first condensate pump 112, avoiding waste and improving the recovery rate of light oil recovered by the recovery system 10.

[0080] It should be noted that the second heat exchanger 110 can be a heat exchanger, a reboiler, or other heat exchange structures. The heat exchange temperature of the second heat exchanger 110 can be flexibly adjusted according to actual usage needs, as long as it can liquefy and separate the first liquid from the first gas. Specifically, in this embodiment, the second heat exchanger 110 is set as the first heat exchanger, which can cool the first gas from -33°C to -65°C.

[0081] like Figure 3 As shown, the recovery system 10 further includes a third heat exchanger 113, a second separator 114, and a second condensate pump 115. The second separator 114 has a second inlet, a second outlet, and a second liquid outlet. One end of the third heat exchanger 113 is connected to the ethane tower 102, and the other end is connected to the second inlet. The second outlet is connected to the low-temperature scrubbing tower 103, and the second liquid outlet is connected to the second condensate pump 115. The second condensate pump 115 is also connected to the ethane tower 102. Thus, the third heat exchanger 113 can exchange heat with the second gas, and the second separator 114 can separate ethane from the second gas, improving the purity of hydrogen and ethane recovered by the recovery system 10. Furthermore, the separated ethane can be returned to the ethane tower 102 via the second condensate pump 115, avoiding ethane waste and improving the ethane recovery rate of the recovery system 10.

[0082] It should be noted that the third heat exchanger 113 can be a heat exchanger, a reboiler, or other heat exchange structure.

[0083] In other embodiments, the recovery system 10 further includes a second reboiler, one end of which is connected to a third heat exchanger, and the other end of which is connected to a second separator 114. Thus, the second reboiler can cool the first gas again, ensuring that the ethane column 102 can perform a second distillation separation of the first gas to obtain ethane and the second gas, thereby improving the reliability of the recovery system 10.

[0084] It should be noted that the heat exchange temperature of the second heat exchanger 110 and the heat exchange temperature of the second reboiler can be flexibly adjusted according to actual usage needs, as long as they can liquefy and separate ethane from the second gas. Specifically, in this embodiment, the second heat exchanger 110 is configured as the first heat exchanger, which can reduce the temperature of the first gas from -74°C to -94°C, and the second reboiler can reduce the temperature of the first gas from -94°C to -118°C.

[0085] like Figure 3 As shown, optionally, the recovery system 10 also includes a fourth heat exchanger 116, a fifth heat exchanger 117, a nitrogen cycle refrigeration device 118, and a mixed cycle refrigeration device 119. One end of the fourth heat exchanger 116 is connected to the second gas outlet, and the other end of the fourth heat exchanger 116 is connected to one end of the fifth heat exchanger 117. The other end of the fifth heat exchanger 117 is connected to the cryogenic scrubbing tower 103. The mixed cycle refrigeration device 119 is connected to the second heat exchanger 110, the third heat exchanger 113, and the fourth heat exchanger 116. The nitrogen cycle refrigeration device 118 is connected to the second heat exchanger 110, the third heat exchanger 113, the fourth heat exchanger 116, and the fifth heat exchanger 117. In this way, the fourth heat exchanger 116 and the fifth heat exchanger 117 can work together to lower the temperature of the second gas to slightly higher than the boiling point temperature of the second liquid, ensuring that the cryogenic scrubbing tower 103 can perform cryogenic scrubbing on the second gas to obtain the second liquid and hydrogen-rich gas, thereby improving the reliability of the recovery system 10. In addition, the nitrogen cycle refrigeration device 118 can reduce the temperature of the second gas to a lower range, ensuring that the low-temperature scrubbing tower 103 can deeply remove low-boiling-point components such as carbon monoxide, methane and nitrogen, thereby improving the purity of the hydrogen recovered by the recovery system 10.

[0086] It should be noted that the fourth heat exchanger 116 and the fifth heat exchanger 117 can both be heat exchangers, reboilers, subcoolers, or other heat exchange structures. Specifically, in this embodiment, the fourth heat exchanger 116 is configured as a third heat exchanger, and the fifth heat exchanger 117 is configured as a subcooler. The third heat exchanger can reduce the temperature of the second gas from -118°C to -165°C, and the subcooler can reduce the temperature of the second gas from -165°C to -171°C.

[0087] It should be noted that the refrigerant in the mixed cycle refrigeration unit 119 can be a multi-component mixture (such as methane, nitrogen, propane, ethylene, isopentane, etc.), and the combination ratio can be adjusted according to the different dry gas compositions of the refinery, so the refrigeration components and composition are flexible and varied.

[0088] It should be noted that the exhaust gas from the pressure swing adsorption device 104 is mainly nitrogen, which can be recycled into the nitrogen cycle refrigeration device 118, with any shortfall supplemented by external sources. The nitrogen cycle refrigeration device 118 can reduce the temperature of the second gas to -180°C.

[0089] like Figure 3 As shown, in one embodiment, the recovery system 10 further includes a methane tower 120, which is connected to a cryogenic scrubbing tower 103. The cryogenic scrubbing tower 103 is used to perform a fourth distillation separation on the second liquid to obtain methane and fuel gas. Thus, the methane tower 120 can separate the methane and fuel gas in the second liquid, avoiding waste of methane and fuel gas in the refinery dry gas and improving the economic efficiency of the refinery dry gas.

[0090] Specifically, in this embodiment, the methane recovery purity can reach over 93%, and the methane recovery rate can reach over 99%. The fuel gas can be reheated by sequentially passing through a cooler, a third heat exchanger, a second heat exchanger, and a first heat exchanger, and then used as unit fuel gas or returned to the refinery fuel system for utilization.

[0091] In other embodiments, the hydrogen-rich gas in the low-temperature scrubbing tower 103 is sequentially reheated by passing through a cooler, a third heat exchanger, a second heat exchanger, and a first heat exchanger before being transported to the pressure swing adsorption (PSA) device 104. This ensures that the PSA device 104 can extract high-purity hydrogen.

[0092] Specifically, in this embodiment, the temperature in the methane tower 120 tends to decrease from the bottom to the top. The temperature at the bottom of the methane tower 120 is -130°C, where methane is located. The temperature at the top of the methane tower 120 is -172°C, where fuel gas is located.

[0093] Furthermore, the second reboiler is provided with a third heat exchange channel for conveying the second heat exchange medium, and the methane tower 120 is provided with a fourth heat exchange channel for conveying the second heat exchange medium. The third heat exchange channel and the fourth heat exchange channel are correspondingly connected. In this way, the second heat exchange medium, after exchanging heat with the first gas in the second reboiler, can flow into the methane tower 120 and exchange heat with the second liquid in the methane tower 120. This allows the heat required by the methane tower 120 to be obtained from the heat exchange with the first gas, eliminating the need for an external heating source. This effectively achieves comprehensive energy utilization and reduces the recovery cost of the recovery system 10.

[0094] Optionally, the recovery system 10 also includes a cold box, in which the ethane tower 102, the low-temperature scrubbing tower 103, and the methane tower 120 are all housed. In this way, the cold box effectively ensures the cooling effect of the ethane tower 102, the low-temperature scrubbing tower 103, and the methane tower 120, reduces the loss of cooling capacity, and improves the reliability of the recovery system 10.

[0095] In other embodiments, the first separator 111, the second separator 114, and the methane tower 120 can also be housed within a cold box. This improves the reliability of the recovery system 10.

[0096] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0097] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0098] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0099] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0100] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0101] It should also be understood that, in interpreting the connection or positional relationships of components, although not explicitly described, connection and positional relationships are interpreted to include a range of error, which should be within the acceptable deviation range of a specific value as determined by a person skilled in the art. For example, "approximately," "about," or "substantially" can mean within one or more standard deviations, without limitation herein.

[0102] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0103] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for recovering dry gas from a refinery, characterized in that, include: The refinery dry gas is pressurized and then subjected to impurity removal treatment to remove acidic impurities from the refinery dry gas. The refinery dry gas, after removing acidic impurities, is dehydrated to obtain purified dry gas. The purified dry gas undergoes a first heat exchange to lower its temperature, while maintaining the purified dry gas in a gaseous state. The purified dry gas is subjected to a first distillation separation to obtain a first liquid and a first gas; The first heat exchange medium, after undergoing a first heat exchange with the purified dry gas, is conveyed to the ethane tower, and the first gas is conveyed to the ethane tower, so that the first heat exchange medium and the first gas exchange heat in the ethane tower, thereby allowing the first gas to undergo a second distillation separation to obtain ethane and the second gas. The second gas is subjected to low-temperature washing to obtain a second liquid and a hydrogen-rich gas; The hydrogen-rich gas is purified to obtain pure hydrogen product.

2. The method for recovering refinery dry gas according to claim 1, characterized in that, Following the initial distillation separation of refinery dry gas to obtain a first liquid and a first gas, the process also includes: The first liquid is subjected to a third distillation separation to obtain light oil and liquefied petroleum gas.

3. The method for recovering refinery dry gas according to claim 1, characterized in that, Before the step of performing a second distillation separation on the first gas to obtain ethane and the second gas, the method further includes: The first gas undergoes a second heat exchange and a first gas-liquid separation to remove the first liquid from the first gas.

4. The method for recovering refinery dry gas according to claim 1, characterized in that, Before the step of performing low-temperature washing on the second gas to obtain the second liquid and hydrogen-rich gas, the method further includes: The second gas undergoes a third heat exchange and a second gas-liquid separation to remove ethane from the second gas.

5. The method for recovering refinery dry gas according to claim 4, characterized in that, After the step of performing a third heat exchange and a second gas-liquid separation on the second gas to remove ethane from the second gas, the process further includes: The second gas undergoes a fourth heat exchange to lower its temperature while maintaining its gaseous state. And / or, the second gas is subjected to a fifth heat exchange with a nitrogen cycle refrigeration device to reduce the temperature of the second gas, while the second gas is able to maintain its gaseous state.

6. The method for recovering refinery dry gas according to any one of claims 1 to 5, characterized in that, After the step of performing low-temperature washing on the second gas to obtain the second liquid and hydrogen-rich gas, the method further includes: The second liquid is subjected to a fourth distillation separation to obtain methane and fuel gas.

7. A system for recovering dry gas from a refinery, characterized in that, The recovery system includes an ethane stripper, an ethane stripper, a cryogenic scrubbing tower, and a pressure swing adsorption (PSA) unit, which are sequentially connected. The ethane stripper is used for the first distillation separation of refinery dry gas to obtain a first liquid and a first gas. The ethane stripper is used for the second distillation separation of the first gas to obtain ethane and a second gas. The cryogenic scrubbing tower is used for cryogenic scrubbing of the second gas to obtain a second liquid and a hydrogen-rich gas. The PSA unit is used for purifying the hydrogen-rich gas to obtain pure hydrogen.

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