A method and device for separating concentrated gas based on dry gas raw material change

Abstract

The present invention belongs to the technical field of dry gas concentration and gas separation, and discloses a method and device for separating concentrated gas after concentration based on a change in dry gas raw material. The present invention adds an expander to the top of the absorption tower, and adds an ethylene coarse separation tower after the concentration, and provides the methane hydrogen cooling capacity of the expanded absorption tower top to the coarse separation tower. The crude ethane at the bottom of the coarse separation tower meets the ethane furnace feeding conditions without consuming the cooling capacity of the public works. The crude ethylene at the top of the tower does not contain carbon triple components and does not need to pass through a depropanizer, but only needs to pass through a demethanizer and an ethylene refining tower for separation. The dry gas raw material of the dry gas concentration device is changed from the hydrocarbonized tail gas produced by the gas-phase dry gas to ethylbenzene production device to catalytic dry gas. Compared with the original process, the present invention can reduce the total energy consumption by 21.2%; through the method of separation after concentration, the liquid-phase method is used to produce ethylbenzene instead of the gas-phase method, and 1.2 tons / h of high-grade ethylbenzene can be produced; thus significantly reducing energy consumption and improving product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of dry gas concentration and gas separation, and in particular to a method and device for separating dry gas after concentration based on dry gas raw material changes. Background Art

[0002] Refinery dry gas primarily comes from primary and secondary crude oil processing, such as atmospheric and vacuum distillation, catalytic cracking, delayed coking, catalytic reforming, and alkane dehydrogenation. Its primary components are methane, ethane, ethylene, propylene, propane, and butane, with C2 being the most abundant. Currently, methods for recovering C2 from refinery dry gas include cryogenic separation, cold oil absorption, and pressure swing adsorption (PSA), each with its own advantages and disadvantages. Cold oil absorption, a form of physical absorption, utilizes the solubility differences of dry gas components in an absorbent. The absorbent is typically a mixed C4, C5, or liquefied petroleum gas. First, C2 and C3 are selectively absorbed through absorption, and then recovered through desorption. Cold oil absorption methods include medium-cold oil absorption (-40 to -20°C) and shallow-cold oil absorption (10 to 15°C). Medium-cold oil absorption offers lower energy consumption.

[0003] Refinery catalytic dry gas, the tail gas from catalytic units, is typically burned directly as fuel gas, resulting in low utilization rates. The ethylene content in catalytic dry gas is generally high (10% to 30%), and burning it as fuel gas would result in a significant waste of ethylene resources. Using the ethylene in catalytic dry gas to produce ethylbenzene can improve catalytic dry gas utilization and effectively reduce the production costs of ethylbenzene units. The vapor phase process has high reaction temperatures, numerous side reactions, and high levels of impurities such as xylene and propylbenzene in the product, resulting in relatively poor ethylbenzene product quality and high energy consumption. The liquid phase process offers milder reaction conditions, produces higher quality ethylbenzene than the vapor phase process, and consumes less energy, offering significant development advantages.

[0004] Considering the plant's current demand for low energy consumption and high-grade ethylbenzene during production, adjustments are needed to the catalytic dry gas process. This reduces the load on the vapor-phase dry gas to ethylbenzene unit, allowing more catalytic dry gas to enter the dry gas enrichment unit. However, the ethylene content in the enriched dry gas is too high to be directly fed into the ethane furnace. Furthermore, the methane hydrogen at the top of the absorption tower in the dry gas enrichment unit is characterized by high pressure and low temperature. The current treatment method involves adding a throttle valve to the methane hydrogen pipeline to reduce pressure and installing a steam heat exchanger to heat it before it enters the fuel network. This process not only consumes significant steam energy but also fails to utilize the pressure energy and inherent cooling capacity, resulting in energy waste. Summary of the Invention

[0005] The present invention relates to a post-concentration gas separation method and apparatus based on a change in dry gas feedstock. The key point is to shut down the high-energy-consuming gas-phase dry gas to ethylbenzene production unit. The feedstock for the dry gas concentrator is now changed from catalytic dry gas to ethylbenzene hydrocarbonation tail gas obtained by gas-phase dry gas to ethylbenzene production, to catalytic dry gas. By adjusting the absorbent circulation rate and process parameters of each unit, consistent process specifications are maintained for the products before and after the dry gas feedstock change. Considering that the concentrated gas from the dry gas concentrator has a high ethylene content and cannot enter the ethane furnace, a crude ethylene fractionation tower is added to perform coarse separation of the concentrated gas. The cooling capacity required for the feed precooler and overhead condenser of the crude fractionation tower is provided by high-pressure, low-temperature methane hydrogen at the top of the absorption tower via a newly added expander.

[0006] This new ethylene crude fractionator and expander not only minimizes utility cooling capacity but also recycles the cooling capacity of the methane hydrogen at the top of the absorber, improving energy efficiency. After the concentrated gas enters the crude ethylene fractionator, the ethylene content in the crude ethane at the bottom meets the requirements for ethane furnace feed. Furthermore, the crude ethylene at the top does not contain heavy components such as C3, eliminating the need for a depropanizer. Instead, it passes through a demethanizer and an ethylene refining tower. The ethylene is then used in a liquid-phase ethylbenzene production unit to produce high-quality ethylbenzene, significantly reducing energy consumption and fully utilizing C2 resources.

[0007] The technical solution of the present invention is: a method for separating concentrated gas based on the change of dry gas raw material, the steps are as follows:

[0008] The gaseous first-stage flash gas 7 from the first-stage flash tank B is combined with the raw dry gas 1 through the circulating dry gas compressor D to form a mixed dry gas that enters the absorption tower A. The lean solvent 2 from the bottom of the solvent regeneration tower K and the semi-lean solvent 3 from the liquid phase of the second-stage flash tank C enter the absorption tower A from the top and middle of the absorption tower A, respectively. The lean solvent 2 and the semi-lean solvent 3 come into countercurrent contact with the mixed dry gas to absorb the carbon dioxide component in the mixed dry gas. The top of the absorption tower A is the methane-hydrogen mixed gas 4, which is expanded by the newly added expander J and then heat-exchanged with the gaseous phase from the top of the ethylene crude fraction tower G through the crude fraction tower top gas-expanded gas heat exchanger H. The rich absorption liquid 5 from the bottom of the absorption tower A enters the first-stage flash tank B.

[0009] The liquid-phase primary flash bottom liquid 8 of the primary flash tank B enters the secondary flash tank C; the gas-phase secondary flash gas 9 of the secondary flash tank C is cooled by the crude fraction tower feed-crude fraction tower overhead gas heat exchanger F and then enters the upper middle position of the ethylene crude fraction tower G as the flash tank concentrated gas 12; part of the liquid-phase secondary flash bottom liquid 10 of the secondary flash tank C is used as the semi-lean solvent 3, and the remaining part is used as the solvent regeneration tower feed 11 to enter the solvent regeneration tower K;

[0010] The top of the ethylene crude fraction tower G is passed through the crude fraction tower top gas-expanded gas heat exchanger H and the crude fraction tower reflux tank I to obtain crude ethylene 13, and part of the crude ethylene is refluxed to the ethylene crude fraction tower G; the crude ethylene 13 enters the crude fraction tower feed-crude fraction tower top gas heat exchanger F for heat exchange to obtain heat-exchanged crude ethylene 17, which is successively pressurized by the crude ethylene compressor O and cooled by the demethanizer feed cooler P, and then enters the middle of the demethanizer Q as the demethanizer feed 19; the top of the demethanizer Q is passed through the demethanizer condenser R and the demethanizer reflux tank S to obtain methane 20, and part of the methane The ethane 21 is refluxed to the demethanizer Q; the bottom of the demethanizer Q is a mixed carbon dioxide 21; part of the mixed carbon dioxide 21 is refluxed to the bottom of the demethanizer Q through the demethanizer reboiler T; the mixed carbon dioxide 21 enters the ethylene refining tower U, and the top of the ethylene refining tower U is passed through the ethylene refining tower condenser V and the ethylene refining tower reflux tank W to obtain a high-purity ethylene product 22, which enters the liquid-phase ethylbenzene production unit Y to obtain an ethylbenzene product 24; part of the ethane 23 at the bottom of the ethylene refining tower U is refluxed to the bottom of the ethylene refining tower U through the ethylene refining tower reboiler X, and the rest enters the ethane furnace Z for cracking;

[0011] Crude ethane 14 is obtained at the bottom of the ethylene crude fraction tower G;

[0012] The top gas phase of the solvent regeneration tower K is passed through the solvent recovery tower top condenser L and the solvent recovery tower reflux tank M as the solvent regeneration tower top concentrated gas 15, and part of the concentrated gas is refluxed to the solvent regeneration tower K; the solvent regeneration tower top concentrated gas 15 is combined with the crude ethane 14 at the bottom of the ethylene crude fraction tower G as the ethane furnace feed 16 and enters the ethane furnace Z; the ethane furnace Z is cracked to obtain the ethane furnace output 25.

[0013] When the utility refrigerant is replenished to the top of the ethylene crude fraction tower G, the crude ethylene compressor O, the demethanizer feed cooler P, the demethanizer Q, and the ethylene refining tower U are shut down;

[0014] The gaseous first-stage flash gas 7 from the first-stage flash tank B is combined with the raw dry gas 1 through the circulating dry gas compressor D to form a mixed dry gas that enters the absorption tower A. The lean solvent 2 from the bottom of the solvent regeneration tower K and the semi-lean solvent 3 from the liquid phase of the second-stage flash tank C enter the absorption tower A from the top and middle of the absorption tower A, respectively. The lean solvent 2 and the semi-lean solvent 3 come into countercurrent contact with the mixed dry gas to absorb the carbon dioxide component in the mixed dry gas. The top of the absorption tower A is the methane-hydrogen mixed gas 4, which is expanded by the newly added expander J and then heat-exchanged with the gaseous phase from the top of the ethylene crude fraction tower G through the crude fraction tower top gas-expanded gas heat exchanger H. The rich absorption liquid 5 from the bottom of the absorption tower A enters the first-stage flash tank B.

[0015] The liquid-phase primary flash bottom liquid 8 of the primary flash tank B enters the secondary flash tank C; the gas-phase secondary flash gas 9 of the secondary flash tank C is cooled through the crude fraction tower feed-crude fraction tower overhead gas heat exchanger F and then enters the upper middle position of the ethylene crude fraction tower G as the flash tank concentrated gas 12; a portion of the liquid-phase secondary flash bottom liquid 10 of the secondary flash tank C is used as the semi-lean solvent 3, and the remaining portion is used as the solvent regeneration tower feed 11 to enter the solvent regeneration tower K; the overhead gas of the solvent regeneration tower K is passed through the solvent recovery tower top condenser L and the solvent recovery tower reflux tank M as the solvent regeneration tower overhead concentrated gas 15, and part of the concentrated gas is refluxed to the solvent regeneration tower K; the solvent regeneration tower overhead concentrated gas 15 is combined with the crude ethane 14 at the bottom of the ethylene crude fraction tower G as the ethane furnace feed 16 to enter the ethane furnace Z;

[0016] The top of the ethylene crude fraction tower G is passed through the crude fraction tower overhead gas-expanded gas heat exchanger H and the crude fraction tower reflux tank I to obtain product-grade ethylene. Part of the product-grade ethylene is refluxed to the ethylene crude fraction tower G. The product-grade ethylene enters the crude fraction tower feed-crude fraction tower overhead gas heat exchanger F for heat exchange to obtain heat-exchanged product-grade ethylene. The heat-exchanged product-grade ethylene enters the liquid-phase ethylbenzene production unit Y, and part of it is produced as ethylene product. The destination of the product-grade ethylene 17 can be flexibly adjusted according to demand. The ethane 14 at the bottom of the ethylene crude fraction tower G enters the ethane furnace Z for cracking.

[0017] A concentrated gas separation device based on dry gas raw material change is used to implement the concentrated gas separation method based on dry gas raw material change; the concentrated gas separation device based on dry gas raw material change comprises an absorption tower A, a primary flash tank B, a secondary flash tank C, a circulating dry gas compressor D, an ethylene crude fraction tower reboiler E, a crude fraction tower feed-crude fraction tower top gas heat exchanger F, an ethylene crude fraction tower G, a crude fraction tower top gas-expanded gas heat exchanger H, a crude fraction tower reflux tank I, Newly added expansion machine J, solvent recovery tower K, solvent recovery tower top condenser L, solvent recovery tower reflux tank M, solvent recovery tower reboiler N, crude ethylene compressor O, demethanizer feed cooler P, demethanizer Q, demethanizer condenser R, demethanizer reflux tank S, demethanizer reboiler T, ethylene refining tower U, ethylene refining tower condenser V, ethylene refining tower reflux tank W, ethylene refining tower reboiler X, liquid phase ethylbenzene production unit Y, and ethane furnace unit Z;

[0018] The raw dry gas enters the bottom of the absorption tower A; the top of the absorption tower A is connected in sequence to the newly added expander J and the crude fraction tower top gas-expanded gas heat exchanger H; the absorption tower A is connected to the first-stage flash tank B; the top of the first-stage flash tank B is connected in sequence to the circulating dry gas compressor D and the bottom of the absorption tower A; the bottom of the first-stage flash tank B is connected to the second-stage flash tank C; the bottom of the second-stage flash tank C is divided into two branches, one is connected to the middle of the absorption tower A, and the other is connected to the solvent recovery tower K; the top of the solvent recovery tower K is connected in sequence to the solvent recovery tower top condenser L and the solvent recovery tower reflux tank M, the solvent recovery tower reflux tank M is divided into two branches, one is connected back to the solvent recovery tower K, and the other is connected to the ethane furnace device Z; the bottom of the solvent recovery tower K is divided into two branches, one is connected to the solvent recovery tower reboiler N and back to the solvent recovery tower K, and the other is connected to the top of the absorption tower A;

[0019] The top of the secondary flash tank C is connected to the coarse fraction tower feed-coarse fraction tower overhead gas heat exchanger F; the coarse fraction tower feed-coarse fraction tower overhead gas heat exchanger F is respectively connected to the ethylene coarse fraction tower G and the crude ethylene compressor O; the top of the ethylene coarse fraction tower G is connected to the coarse fraction tower overhead gas-expanded gas heat exchanger H; the crude fraction tower overhead gas-expanded gas heat exchanger H extracts the product and connects it to the coarse fraction tower reflux tank I; the coarse fraction tower reflux tank I is divided into two branches, one of which is connected back to the top of the ethylene coarse fraction tower G, and the other loop is connected to the coarse fraction tower feed-coarse fraction tower overhead gas heat exchanger F; the bottom of the ethylene coarse fraction tower G is divided into two branches, one of which is connected to the ethylene coarse fraction tower reboiler E and then connected back to the ethylene coarse fraction tower G, and the other branch is connected to the ethane furnace device Z;

[0020] The crude ethylene compressor O is connected to the demethanizer feed cooler P and the demethanizer Q in sequence; the top of the demethanizer Q is connected to the demethanizer condenser R and the demethanizer reflux tank S in sequence; the demethanizer reflux tank S is divided into two branches, one of which is connected back to the demethanizer Q, and the other is used for production; the bottom of the demethanizer reflux tank S is divided into two branches, one of which is connected to the demethanizer reboiler T and is connected back, and the other is connected to the ethylene refining tower U; the top of the ethylene refining tower U is connected to the ethylene refining tower condenser V and the ethylene refining tower reflux tank W in sequence; the ethylene refining tower reflux tank W is divided into two branches, one of which is connected back to the ethylene refining tower U, and the other is connected to the liquid-phase ethylbenzene production unit Y; the bottom of the ethylene refining tower U is divided into two branches, one of which is connected to the ethylene refining tower reboiler X and is connected back to the ethylene refining tower U, and the other is connected to the ethane furnace unit Z.

[0021] When utility refrigerant reaches the top of ethylene crude fraction tower G, shut down crude ethylene compressor O, demethanizer feed cooler P, demethanizer Q, and ethylene refining tower U; raw dry gas enters the bottom of absorption tower A; the top of absorption tower A is connected in sequence to newly added expander J and the first inlet of crude fraction tower top gas-expanded gas heat exchanger H; the bottom of absorption tower A is connected to the first-stage flash tank B; the top of the first-stage flash tank B is connected in sequence to the circulating dry gas compressor D and the bottom of absorption tower A; the bottom of the first-stage flash tank B is connected to the second-stage flash tank C; the second-stage flash tank The bottom of tank C is divided into two branches, one of which is connected to the middle of absorption tower A, and the other is connected to solvent recovery tower K; the top of solvent recovery tower K is connected in sequence to solvent recovery tower top condenser L and solvent recovery tower reflux tank M, and the solvent recovery tower reflux tank M is divided into two branches, one of which is connected back to solvent recovery tower K, and the other is connected to the middle and lower part of ethylene crude fraction tower G; the bottom of solvent recovery tower K is divided into two branches, one of which is connected to solvent recovery tower reboiler N and back to solvent recovery tower K, and the other is connected to the top of absorption tower A;

[0022] The top of the secondary flash tank C is connected to the coarse fraction tower feed-coarse fraction tower top gas heat exchanger F; the coarse fraction tower feed-coarse fraction tower top gas heat exchanger F is respectively connected to the middle part of the ethylene coarse fraction tower G and the liquid phase ethylbenzene production unit Y; the top of the ethylene coarse fraction tower G is connected to the second inlet of the coarse fraction tower top gas-expanded gas heat exchanger H; the first outlet of the coarse fraction tower top gas-expanded gas heat exchanger H produces the product, and the second outlet is connected to the coarse fraction tower reflux tank I; the coarse fraction tower reflux tank I is divided into two branches, one branch is connected back to the top of the ethylene coarse fraction tower G, and the other loop is connected to the coarse fraction tower feed-coarse fraction tower top gas heat exchanger F; the bottom of the ethylene coarse fraction tower G is divided into two branches, one branch is connected to the ethylene coarse fraction tower reboiler E and then connected back to the ethylene coarse fraction tower G, and the other branch is connected to the ethane furnace device Z.

[0023] The present invention has the following beneficial effects: the newly added ethylene crude fractionation tower and expander not only minimize utilities' cooling capacity but also recycle the cooling capacity of the methane hydrogen at the top of the absorption tower, thereby improving energy efficiency. After the concentrated gas enters the ethylene crude fractionation tower, the ethylene content in the crude ethane at the bottom meets the requirements for ethane furnace feed. Furthermore, the crude ethylene at the top of the tower contains no heavy components such as C3, eliminating the need for a depropanizer. Instead, the ethylene only needs to pass through a demethanizer and an ethylene refining tower. The ethylene is then used in a liquid-phase ethylbenzene production unit to produce high-quality ethylbenzene, significantly reducing energy consumption and achieving efficient utilization of C2 resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart of a method for separating concentrated gas based on the change of dry gas raw materials.

[0025] Figure 2 This is a flow chart of the method when utility refrigerant is added to the top of the ethylene crude fractionator.

[0026] Logistics in the figure: 1 raw dry gas; 2 lean solvent; 3 semi-lean solvent; 4 methane-hydrogen mixed gas; 5 rich absorbent; 6 newly added expander outlet gas; 7 primary flash gas; 8 primary flash bottom liquid; 9 secondary flash gas; 10 secondary flash bottom liquid; 11 solvent regeneration tower feed; 12 concentrated gas from flash tank; 13 crude ethylene; 14 crude ethane from tower bottom; 15 concentrated gas from solvent regeneration tower top; 16 ethane furnace feed; 17 crude ethylene after heat exchange; 18 crude ethylene from compressor outlet; 19 demethanizer feed; 20 methane; 21 mixed carbon dioxide; 22 ethylene product; 23 ethane; 24 ethylbenzene product; 25 ethane furnace discharge.

[0027] Equipment in the figure: A absorption tower; B primary flash tank; C secondary flash tank; D circulating dry gas compressor; E ethylene crude fraction tower reboiler; F crude fraction tower feed-crude fraction tower overhead gas heat exchanger; G ethylene crude fraction tower; H crude fraction tower overhead gas-expanded gas heat exchanger; I crude fraction tower reflux tank; J newly added expander; K solvent recovery tower; L solvent recovery tower overhead condenser; M solvent recovery tower reflux tank; N solvent recovery tower reboiler; O crude ethylene compressor; P demethanizer feed cooler; Q demethanizer; R demethanizer condenser; S demethanizer reflux tank; T demethanizer reboiler; U ethylene refining tower; V ethylene refining tower condenser; W ethylene refining tower reflux tank; X ethylene refining tower reboiler; Y liquid phase ethylbenzene production unit; Z ethane furnace unit. DETAILED DESCRIPTION

[0028] The following is a detailed and complete description of the technical solution of the present invention, based on the example of a petrochemical company that shuts down its gas-phase dry gas to ethylbenzene production unit, where the raw material for the dry gas enrichment unit is changed from ethylbenzene hydrocarbonation tail gas to catalytic dry gas. Figure 1 Taking the example of FIG. 1 , the separation process of concentrated gas after the dry gas raw material change of the present invention is described in detail.

[0029] After desulfurization, the catalytic dry gas is combined with dry gas from other devices to form the raw dry gas 1, which enters the process of the present invention. This raw dry gas 1 combines with the gas phase 7 from flash tank B to form a mixed dry gas that enters absorption tower A. Lean solvent 2 from the bottom of solvent regeneration tower K and semi-lean solvent 3 from the liquid phase of secondary flash tank C enter absorption tower A from the top and middle of the tower, respectively, where they come into countercurrent contact with the mixed dry gas, absorbing the C2 component from the dry gas. The top of absorption tower A produces a methane-hydrogen mixture 4, which is expanded by a newly added expander J. After this, it exchanges heat with the gas phase from the top of ethylene crude fraction tower G via the crude fraction tower overhead gas-expanded gas heat exchanger H. The rich absorbent liquid 5 from the bottom of absorption tower A enters the primary flash tank B.

[0030] The gas phase 7 of the first-stage flash tank B is pressurized by the compressor D and merged with the raw gas 1 to return to the absorption tower A as a mixed dry gas. The liquid phase 8 of the first-stage flash tank B enters the second-stage flash tank C. The gas phase 9 of the second-stage flash tank C is cooled by the coarse fraction tower feed-coarse fraction tower top gas heat exchanger F and then enters the coarse fraction tower G as the flash tank concentrated gas 12. The liquid phase part of the second-stage flash tank C returns to the absorption tower A as the semi-lean solvent 3, and the rest enters the solvent regeneration tower K.

[0031] Flash tank concentrated gas 12 enters ethylene crude fractionator G at the upper center of the tower, producing crude ethylene 13 and crude ethane 14 at the top and bottom, respectively. Lean solvent 2 produced in the bottom of solvent regeneration tower K enters the top of absorption tower A. The overhead gas, acting as concentrated gas 15, merges with crude ethane 14 at the bottom of ethylene crude fractionator G and enters ethane furnace Z.

[0032] Optionally, when there is refrigerant replenishment from the utility, the concentrated gas 16 at the top of the solvent regeneration tower can be pre-cooled and then passed into the lower middle position of the ethylene crude fraction tower G. When the cooling capacity is sufficient, product-grade ethylene can be obtained directly at the top of the ethylene crude fraction tower G, without having to pass the crude ethylene 13 at the top of the crude fraction tower G into the demethanizer Q and the ethylene refining tower U for further separation.

[0033] The crude ethylene 13 at the top of the crude ethylene fractionator G is pressurized by the crude ethylene compressor O and cooled by the demethanizer feed cooler P before entering the middle of the demethanizer Q. Methane 20 is obtained at the top of the demethanizer Q, and mixed carbon dioxide 21 is obtained at the bottom of the demethanizer Q. The mixed carbon dioxide 21 at the bottom of the demethanizer Q enters the ethylene refining tower U. The high-purity ethylene product 22 obtained at the top of the ethylene refining tower U enters the liquid-phase ethylbenzene production unit Y, producing ethylbenzene product 24. The ethane 23 at the bottom of the tower enters the ethane furnace Z for cracking, producing the cracking product 25.

[0034] Optionally, part of the high-purity ethylene product 22 obtained at the top of the ethylene refining tower U can enter the liquid-phase ethylbenzene production unit Y, and part can be produced as an ethylene product. The destination of the ethylene product 22 can be flexibly adjusted according to demand.

[0035] Example:

[0036] A petrochemical company used a 9,377 kg / h dry gas volume, including desulfurized catalytic dry gas with an ethylene content of 18.94% (volume fraction), for a gas-phase dry gas to ethylbenzene unit. Due to the high energy consumption and poor product quality of the gas-phase process, the company proposed shutting down the gas-phase dry gas to ethylbenzene unit and integrating the catalytic dry gas into a dry gas enrichment unit. The dry gas enrichment unit used a different feedstock and then separated the enriched gas. This improved energy utilization, significantly reduced energy consumption, and achieved efficient utilization of C2 resources. The details are as follows:

[0037] The composition of the catalytic dry gas is shown in Table 1:

[0038] Table 1 Catalytic dry gas composition

[0039] Components Volume fraction / % Mass fraction / % <![CDATA[H2]]> 18.48 1.87 <![CDATA[CO2]]> 0.87 1.93 <![CDATA[O2]]> 0.33 0.53 <![CDATA[N2]]> 18.41 25.99 <![CDATA[CH4]]> 32.19 26.02 <![CDATA[C2H6]]> 8.74 13.25 <![CDATA[C2H4]]> 18.94 26.77 <![CDATA[C3H8]]> 0.08 0.18 <![CDATA[C3H6]]> 1.08 2.29 C4 and C4+ 0.16 0.48 H2O 0.67 0.6

[0040] The present invention proposes a method for separating concentrated gas based on the change of dry gas raw material. The specific process is as follows:

[0041] The desulfurized catalytic dry gas is combined with dry gas from other devices to form dry gas feed 1, which enters the process of the present invention. Dry gas feed 1 has a mass flow rate of 30,367 kg / h and combines with the gas phase 7 from flash tank B to form a mixed dry gas. The mixed dry gas has a mass flow rate of 34,172 kg / h and a temperature of -35°C. It enters absorption tower A at feed position 30, using a theoretical plate number of 30 and a controlled top pressure of 3.6 MPa. Lean solvent 2 from the bottom of solvent regeneration tower K and semi-lean solvent 3 from the liquid phase of secondary flash tank C enter absorption tower A from the top and middle of the tower, respectively, countercurrently contacting the mixed dry gas and absorbing the C2 component from the dry gas. The top of absorption tower A contains a methane-hydrogen mixed gas 4 at -32°C. After passing through the newly added expander J, the temperature reaches -69.5°C. It then exchanges heat with the gas phase from the top of ethylene crude fractionator G via the crude fractionator overhead gas-expanded gas heat exchanger H. The rich absorbent liquid 5 from the bottom of absorption tower A enters the primary flash tank B at a mass flow rate of 76,217 kg / h.

[0042] The gas phase 7 of the first-stage flash tank B has a pressure of 0.5 MPag and is pressurized to 3.64 MPag by compressor D, and then merged with the raw gas 1 as a mixed dry gas and returned to the absorption tower A. The liquid phase 8 of the first-stage flash tank B enters the second-stage flash tank C. The gas phase 9 of the second-stage flash tank C has a temperature of -64°C. After being cooled by the coarse fraction tower feed-coarse fraction tower top gas heat exchanger F, it is used as the flash tank concentrated gas 12 with a mass flow rate of 6066 kg / h and a temperature of -18°C and enters the coarse fraction tower G. The liquid phase part of the second-stage flash tank C returns to the absorption tower A as the semi-lean solvent 3, and the rest enters the solvent regeneration tower K.

[0043] Flash tank concentrated gas 12 enters ethylene crude fractionator G at feed position 20, using a theoretical plate number of 40. The tower's top pressure is controlled at 1.62 MPa. Crude ethylene 13 and crude ethane 14 are produced at mass flow rates of 4200 kg / h and 1866 kg / h, respectively, at the top and bottom of the tower, respectively. Lean solvent 2, produced in the bottom of solvent regeneration tower K, enters the top of absorption tower A. The overhead gas, acting as concentrated gas 15, merges with crude ethane 14 at the bottom of ethylene crude fractionator G to form ethane furnace feed 16 at a mass flow rate of 8834 kg / h and enters ethane furnace Z.

[0044] The crude ethylene 13 at the top of the ethylene crude fractionator G is pressurized to 3.2 MPag by the crude ethylene compressor O and cooled to -35°C by the demethanizer feed cooler P to enter the demethanizer Q, with a feed position of 25 and a theoretical plate number of 50 for calculation. The top pressure is controlled at 3.0 MPag. Methane 20 with a mass flow rate of 339 kg / h is obtained at the top of the tower, and mixed carbon dioxide 21 is obtained at the bottom of the tower. The mixed carbon dioxide 21 at the bottom of the demethanizer Q enters the ethylene refining tower U, with a feed position of 40 and a theoretical plate number of 60 for calculation. The top pressure is controlled at 1.62 MPag. High-purity ethylene product 22 is obtained at the top of the ethylene refining tower U and enters the liquid-phase ethylbenzene production unit Y. Ethylbenzene product 24 has a mass flow rate of 8700 kg / h. Ethane 23 at the bottom of the tower enters the ethane furnace Z for cracking, and the cracking product 25 is obtained.

[0045] Compared with the original process in which the catalytic dry gas first passes through the gas phase dry gas to ethylbenzene device to obtain the ethylbenzene hydrocarbon tail gas and then enters the dry gas concentration device, the process of the present invention shuts down the gas phase dry gas to ethylbenzene device and the catalytic dry gas directly enters the dry gas concentration device. The total energy consumption and product indicators of the process are shown in Table 2.

[0046] Table 2 Comparison of total energy consumption and product indicators

[0047]

[0048] Compared with the original process, the total energy consumption of the process of the present invention is reduced by 21.2%, the xylene content in ethylbenzene is lower, and it is a high-grade ethylbenzene product. It can also produce an additional 1.2t / h of ethylbenzene; it significantly reduces energy consumption, improves product quality, and realizes the efficient utilization of carbon dioxide resources.

[0049] This embodiment is merely illustrative and not a complete set of embodiments. All other embodiments improved or adjusted by those skilled in the art are within the scope of protection of the present invention.

Claims

1. A method for separating concentrated gas based on dry gas raw material change, characterized in that: Here are the steps: The gas phase of the first flash gas (7) from the first flash tank (B) is combined with the raw material dry gas (1) through the circulating dry gas compressor (D) to form a mixed dry gas and enter the absorption tower (A); the lean solvent (2) from the bottom of the solvent recovery tower (K) and the semi-lean solvent (3) from the liquid phase of the second flash tank (C) enter the absorption tower (A) from the top and the middle of the absorption tower (A) respectively; the lean solvent (2) and the semi-lean solvent (3) are in countercurrent contact with the mixed dry gas to absorb the carbon two components in the mixed dry gas; the top of the absorption tower (A) is the methane hydrogen mixed gas (4), which is expanded by the newly added expander (J) and then heat-exchanged with the gas phase at the top of the ethylene crude fraction tower (G) through the crude fraction tower top gas-expanded gas heat exchanger (H); The rich absorption liquid (5) in the bottom of the absorption tower (A) enters the first-stage flash tank (B); The liquid-phase primary flash bottom liquid (8) of the primary flash tank (B) enters the secondary flash tank (C); the gas-phase secondary flash gas (9) of the secondary flash tank (C) is cooled by the crude fraction tower feed-crude fraction tower top gas heat exchanger (F) and then enters the upper middle position of the ethylene crude fraction tower (G) as the flash tank concentrated gas (12); part of the liquid-phase secondary flash bottom liquid (10) of the secondary flash tank (C) is used as the semi-lean solvent (3), and the remaining part is used as the solvent recovery tower feed (11) to enter the solvent recovery tower (K); The top of the ethylene crude fraction tower (G) is passed through the crude fraction tower top gas-expanded gas heat exchanger (H) and the crude fraction tower reflux tank (I) to obtain crude ethylene (13), and part of the crude ethylene is refluxed to the ethylene crude fraction tower (G); the crude ethylene (13) enters the crude fraction tower feed-crude fraction tower top gas heat exchanger (F) for heat exchange to obtain heat-exchanged crude ethylene (17), which is successively entered into the crude ethylene compressor (O) for pressurization and the demethanizer feed cooler (P) for cooling, and then enters the middle part of the demethanizer (Q) as the demethanizer feed (19); the top of the demethanizer (Q) is passed through the demethanizer condenser (R) and the demethanizer reflux tank (S) to obtain methane (20), and part of the methane is refluxed to Demethanizer (Q); the bottom of the demethanizer (Q) is mixed carbon dioxide (21); part of the mixed carbon dioxide (21) is refluxed to the bottom of the demethanizer (Q) through the demethanizer reboiler (T); the mixed carbon dioxide (21) enters the ethylene refining tower (U), the top of the ethylene refining tower (U) is passed through the ethylene refining tower condenser (V) and the ethylene refining tower reflux tank (W) to obtain a high-purity ethylene product (22), which enters the liquid phase ethylbenzene production device (Y) to obtain an ethylbenzene product (24); part of the ethane (23) at the bottom of the ethylene refining tower (U) is refluxed to the bottom of the ethylene refining tower (U) through the ethylene refining tower reboiler (X), and the rest enters the ethane furnace device (Z) for cracking; The crude ethane (14) is obtained at the bottom of the crude ethylene fractionation tower (G); The top gas phase of the solvent recovery tower (K) is passed through the solvent recovery tower top condenser (L) and the solvent recovery tower reflux tank (M) as the solvent recovery tower top concentrated gas (15), and part of the concentrated gas is refluxed to the solvent recovery tower (K); the solvent recovery tower top concentrated gas (15) is combined with the crude ethane (14) at the bottom of the ethylene crude fraction tower (G) as the ethane furnace feed (16) to enter the ethane furnace device (Z); the ethane furnace device (Z) is cracked to obtain the ethane furnace output (25).

2. The method for separating concentrated gas based on dry gas feedstock change according to claim 1, characterized in that: A high-purity ethylene product (22) is obtained at the top of the ethylene refining tower (U), part of which enters the liquid-phase ethylbenzene production unit (Y) and part is produced as an ethylene product. The destination of the ethylene product (22) is adjusted according to demand.

3. The method for separating concentrated gas based on dry gas feedstock change according to claim 1 or 2, characterized in that: When utility refrigerant is added to the top of the ethylene crude fraction tower (G), the crude ethylene compressor (O), demethanizer feed cooler (P), demethanizer (Q), and ethylene refining tower (U) are shut down; The gas phase of the first flash gas (7) from the first flash tank (B) is combined with the raw material dry gas (1) through the circulating dry gas compressor (D) to form a mixed dry gas and enter the absorption tower (A); the lean solvent (2) from the bottom of the solvent recovery tower (K) and the semi-lean solvent (3) from the liquid phase of the second flash tank (C) enter the absorption tower (A) from the top and the middle of the absorption tower (A) respectively; the lean solvent (2) and the semi-lean solvent (3) are in countercurrent contact with the mixed dry gas to absorb the carbon two components in the mixed dry gas; the top of the absorption tower (A) is the methane hydrogen mixed gas (4), which is expanded by the newly added expander (J) and then heat-exchanged with the gas phase at the top of the ethylene crude fraction tower (G) through the crude fraction tower top gas-expanded gas heat exchanger (H); The rich absorption liquid (5) in the bottom of the absorption tower (A) enters the first-stage flash tank (B); The liquid-phase primary flash bottom liquid (8) of the primary flash tank (B) enters the secondary flash tank (C); the gas-phase secondary flash gas (9) of the secondary flash tank (C) is cooled by the crude fraction tower feed-crude fraction tower top gas heat exchanger (F) and then enters the middle and upper position of the ethylene crude fraction tower (G) as the flash tank concentrated gas (12); part of the liquid-phase secondary flash bottom liquid (10) of the secondary flash tank (C) is used as the semi-lean solvent (3), and the remaining part is used as the solvent recovery tower feed (11) to enter the solvent recovery tower (K); the top gas of the solvent recovery tower (K) is passed through the solvent recovery tower top condenser (L) and the solvent recovery tower reflux tank (M) as the solvent recovery tower top concentrated gas (15), and part of the concentrated gas is refluxed to the solvent recovery tower (K); the solvent recovery tower top concentrated gas (15) is combined with the crude ethane (14) at the bottom of the ethylene crude fraction tower (G) as the ethane furnace feed (16) to enter the ethane furnace device (Z); The top of the ethylene crude fraction tower (G) is passed through a crude fraction tower top gas-expanded gas heat exchanger (H) and a crude fraction tower reflux tank (I) to obtain product-grade ethylene, part of which is refluxed to the ethylene crude fraction tower (G), and the product-grade ethylene enters a crude fraction tower feed-crude fraction tower top gas heat exchanger (F) for heat exchange to obtain product-grade ethylene after heat exchange, and the product-grade ethylene after heat exchange enters a liquid-phase ethylbenzene production unit (Y), part of which is extracted as an ethylene product, and the destination of the product-grade ethylene is flexibly adjusted according to demand; the crude ethane (14) at the bottom of the ethylene crude fraction tower (G) enters an ethane furnace unit (Z) for cracking.

4. A post-enrichment gas separation device based on dry gas raw material change, characterized in that: The method for separating concentrated gas based on dry gas raw material change according to any one of claims 1 to 3 is used; the separation device for separating concentrated gas based on dry gas raw material change comprises an absorption tower (A), a primary flash tank (B), a secondary flash tank (C), a circulating dry gas compressor (D), an ethylene crude fraction tower reboiler (E), a crude fraction tower feed-crude fraction tower top gas heat exchanger (F), an ethylene crude fraction tower (G), a crude fraction tower top gas-expanded gas heat exchanger (H), a crude fraction tower reflux tank (I), a newly added expander (J), a solvent recovery unit (C), a solvent recovery unit (D), a solvent recovery unit (E ... Tower (K), solvent recovery tower top condenser (L), solvent recovery tower reflux tank (M), solvent recovery tower reboiler (N), crude ethylene compressor (O), demethanizer feed cooler (P), demethanizer (Q), demethanizer condenser (R), demethanizer reflux tank (S), demethanizer reboiler (T), ethylene refining tower (U), ethylene refining tower condenser (V), ethylene refining tower reflux tank (W), ethylene refining tower reboiler (X), liquid phase ethylbenzene production unit (Y), ethane furnace unit (Z); The raw dry gas is transported to the bottom of the absorption tower (A); the top of the absorption tower (A) is connected in sequence to the newly added expander (J) and the crude fraction tower top gas-expanded gas heat exchanger (H); the absorption tower (A) is connected to the first-stage flash tank (B); the top of the first-stage flash tank (B) is connected in sequence to the circulating dry gas compressor (D) and the bottom of the absorption tower (A); the bottom of the first-stage flash tank (B) is connected to the second-stage flash tank (C); the bottom of the second-stage flash tank (C) is divided into two branches, one of which is connected to the middle of the absorption tower (A) and the other is connected to the second-stage flash tank (C). connected to the solvent recovery tower (K); the top of the solvent recovery tower (K) is connected to the solvent recovery tower top condenser (L) and the solvent recovery tower reflux tank (M) in sequence, the solvent recovery tower reflux tank (M) is divided into two branches, one branch is connected back to the solvent recovery tower (K), and the other branch is connected to the ethane furnace device (Z); the bottom of the solvent recovery tower (K) is divided into two branches, one branch is connected to the solvent recovery tower reboiler (N) and back to the solvent recovery tower (K), and the other branch is connected to the top of the absorption tower (A); The top of the secondary flash tank (C) is connected to the crude fraction tower feed-crude fraction tower overhead gas heat exchanger (F); the crude fraction tower feed-crude fraction tower overhead gas heat exchanger (F) is respectively connected to the ethylene crude fraction tower (G) and the crude ethylene compressor (O); the top of the ethylene crude fraction tower (G) is connected to the crude fraction tower overhead gas-expanded gas heat exchanger (H); the crude fraction tower overhead gas-expanded gas heat exchanger (H) extracts the product and connects it to the crude fraction tower reflux tank (I); the crude fraction tower reflux tank (I) is divided into two branches, one of which is connected back to the top of the ethylene crude fraction tower (G), and the other loop is connected to the crude fraction tower feed-crude fraction tower overhead gas heat exchanger (F); the bottom of the ethylene crude fraction tower (G) is divided into two branches, one of which is connected to the ethylene crude fraction tower reboiler (E) and then connected back to the ethylene crude fraction tower (G), and the other branch is connected to the ethane furnace device (Z); The crude ethylene compressor (O) is connected to the demethanizer feed cooler (P) and the demethanizer (Q) in sequence; the top of the demethanizer (Q) is connected to the demethanizer condenser (R) and the demethanizer reflux tank (S) in sequence; the demethanizer reflux tank (S) is divided into two branches, one of which is connected back to the demethanizer (Q) and the other is used for extraction; the bottom of the demethanizer reflux tank (S) is divided into two branches, one of which is connected to the demethanizer reboiler (T) and back, and the other is connected to the ethylene refining Tower (U); the top of the ethylene refining tower (U) is connected to the ethylene refining tower condenser (V) and the ethylene refining tower reflux tank (W) in sequence; the ethylene refining tower reflux tank (W) is divided into two branches, one branch is connected back to the ethylene refining tower (U), and the other branch is connected to the liquid phase ethylbenzene production device (Y); the bottom of the ethylene refining tower (U) is divided into two branches, one branch is connected to the ethylene refining tower reboiler (X) and back to the ethylene refining tower (U), and the other branch is connected to the ethane furnace device (Z).

5. The concentrated gas separation device based on dry gas feedstock change according to claim 4 is characterized in that: When utility refrigerant reaches the top of the ethylene crude fraction tower (G), shut down the crude ethylene compressor (O), demethanizer feed cooler (P), demethanizer (Q), and ethylene refining tower (U); the raw dry gas is passed to the bottom of the absorption tower (A); the top of the absorption tower (A) is connected in sequence to the newly added expander (J) and the first inlet of the crude fraction tower top gas-expanded gas heat exchanger (H); the bottom of the absorption tower (A) is connected to the first-stage flash tank (B); the top of the first-stage flash tank (B) is connected in sequence to the circulating dry gas compressor (D) and the bottom of the absorption tower (A); the bottom of the first-stage flash tank (B) is connected to the second-stage flash tank (C); The bottom of the flash tank (C) is divided into two branches, one of which is connected to the middle of the absorption tower (A), and the other is connected to the solvent recovery tower (K); the top of the solvent recovery tower (K) is connected in sequence to the solvent recovery tower top condenser (L) and the solvent recovery tower reflux tank (M), and the solvent recovery tower reflux tank (M) is divided into two branches, one of which is connected back to the solvent recovery tower (K), and the other is connected to the middle and lower part of the ethylene crude fraction tower (G); the bottom of the solvent recovery tower (K) is divided into two branches, one of which is connected to the solvent recovery tower reboiler (N) and back to the solvent recovery tower (K), and the other is connected to the top of the absorption tower (A); The top of the secondary flash tank (C) is connected to the feed of the crude fraction tower-crude fraction tower top gas heat exchanger (F); the feed of the crude fraction tower-crude fraction tower top gas heat exchanger (F) is respectively connected to the middle part of the ethylene crude fraction tower (G) and the liquid phase ethylbenzene production device (Y); the top of the ethylene crude fraction tower (G) is connected to the second inlet of the crude fraction tower top gas-expansion gas heat exchanger (H); the first outlet of the crude fraction tower top gas-expansion gas heat exchanger (H) produces the product, and the second outlet is connected to the crude fraction tower reflux tank (I); the crude fraction tower reflux tank (I) is divided into two branches, one of which is connected back to the top of the ethylene crude fraction tower (G), and the other loop is connected to the feed of the crude fraction tower-crude fraction tower top gas heat exchanger (F); the bottom of the ethylene crude fraction tower (G) is divided into two branches, one of which is connected to the ethylene crude fraction tower reboiler (E) and then connected back to the ethylene crude fraction tower (G), and the other branch is connected to the ethane furnace device (Z).

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