Method and system for optimizing energy system of xylene rectification plant

Abstract

The application provides an optimization method and an optimization system for an energy system of a xylene rectification device, the rectification device comprising a main column and multiple sub-columns. The optimization method comprises the following steps: building a heat exchange network model, the heat exchange network model comprising a heat load value of a reboiler of each sub-column, a heat load value of a feed of the main column, an energy relationship between heat supplied by the main column to the reboilers of the multiple sub-columns and heat supplied by the main column to the feed of the main column; solving a reflux ratio of each sub-column and a reflux ratio of the main column that satisfy a target function, with the concentration of key components at the top and the bottom of the multiple sub-columns and the main column, the energy relationship in the heat exchange network model and the purity of xylene as constraint conditions, and the minimum energy consumption of the rectification device as the target function. The optimization method of the application obtains the reflux ratios of each sub-column and the main column that minimize the energy consumption of the rectification device while meeting the requirements for the concentration of key components at the top and the bottom, the energy relationship in the heat exchange network model and the purity of xylene.

Description

Technical Field

[0001] This application mainly relates to the field of chemical engineering, and specifically to an optimization method and optimization system for the energy system of a xylene distillation unit. Background Technology

[0002] p-Xylene is an important organic chemical raw material, mainly used in the synthesis of terephthalic acid or dimethyl terephthalate. The polyester obtained from the reaction of terephthalic acid with ethylene glycol has excellent properties and is widely used in the preparation of fibers, films, and resins, making it a very important raw material for synthetic fibers and plastics. With the rapid development of my country's textile industry, the market demand for p-xylene has continued to rise in recent years.

[0003] The industrial production of xylene is achieved through xylene distillation units, a complex and energy-intensive process. Xylene production involves a series of transformation processes, including disproportionation and alkyl transfer, xylene distillation, adsorption separation, and isomerization. Each process takes place in a relatively independent unit, making the process complex and energy-intensive. The xylene column, as the main column, is the core distillation equipment in the entire unit. Besides providing feedstock to downstream sub-columns, the xylene column is also central to the overall heat integration of the distillation unit. The reboiler at the bottom of the xylene column is centrally heated by a furnace, and the top and bottom materials can also be used to provide heat for the sub-columns in the distillation unit.

[0004] Therefore, how to adjust the reflux ratio of the main column and the sub-column to minimize the energy consumption of the entire distillation unit is an urgent problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide an optimization method for the energy system of a xylene distillation unit, which minimizes the energy consumption of the entire distillation unit by adjusting the reflux ratio of the main column and the sub-column.

[0006] The technical solution adopted in this application to solve the above-mentioned technical problems is an optimization method for the energy system of a xylene distillation unit. The distillation unit includes a main column and multiple sub-columns. The method includes the following steps: constructing a heat exchange network model, wherein the heat exchange network model includes the heat load value of the reboiler of each sub-column, the heat load value of the feed of the main column, the heat supplied by the main column to the reboilers of the multiple sub-columns, and the heat supplied by the main column to the feed of the main column; using the concentrations of key components at the top and bottom of the multiple sub-columns and the main column, the energy relationship in the heat exchange network model, and the xylene purity as constraints, and taking the minimization of the energy consumption of the distillation unit as the objective function, solving for the reflux ratio of each sub-column and the reflux ratio of the main column that satisfy the objective function.

[0007] In one embodiment of this application, a sub-tower model corresponding to each sub-tower is constructed, and each sub-tower model calculates the concentration of the key component at the top and bottom of the sub-tower based on the reflux ratio of the corresponding sub-tower.

[0008] In one embodiment of this application, a main tower model is constructed, and the main tower model calculates the concentration of the key components at the top and bottom of the main tower based on the reflux ratio of the main tower.

[0009] In one embodiment of this application, the model is built using process simulation software.

[0010] In one embodiment of this application, the plurality of sub-towers includes a stripping tower, a benzene tower, a toluene tower, a reforming oil separation tower, an o-xylene tower, a heavy aromatics tower, a raffinate tower, an extract tower, a finished product tower, and a heptane removal tower.

[0011] In one embodiment of this application, the main tower is a xylene tower.

[0012] In one embodiment of this application, the energy relationship in the heat exchange network model is the relationship between the sum of the heat supplied by the main tower to the reboilers of the plurality of sub-towers and the heat used to heat the feed of the main tower and the sum of the heat load values ​​of the plurality of sub-towers and the heat load values ​​of the feed of the main tower.

[0013] In one embodiment of this application, the heat load value of the reboiler for each sub-tower is calculated using the formula: W1 = F S ×Q S Where W1 is the heat load value of the reboiler of the corresponding sub-tower, and F S Q is the molar flow rate corresponding to the output of the sub-tower. s This represents the latent heat of vaporization of the discharge per unit molar flow rate of the corresponding sub-tower.

[0014] In one embodiment of this application, the formula for calculating the heat load value of the feed to the main tower is: W2 = c × G s (T a -T b ), where W2 is the heat load value of the feed to the main tower, c is the specific heat capacity of the feed, and T a Let T be the initial temperature. b For the target temperature, G s The mass flow rate of the feed is denoted as .

[0015] To address the aforementioned technical problems, this application also proposes an optimization system for the energy system of a xylene distillation apparatus, comprising: a memory for storing instructions executable by a processor; and a processor for executing the instructions to implement the optimization method described above.

[0016] To address the aforementioned technical problems, this application also proposes a computer-readable medium storing computer program code, which, when executed by a processor, implements the optimization method described above.

[0017] The optimization method of this application can obtain the reflux ratio of each sub-tower and the main tower that minimizes the energy consumption of the distillation unit, while meeting the requirements of the concentration of key components at the top and bottom of the tower, the energy relationship in the heat exchange network model, and the purity of xylene. Attached Figure Description

[0018] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings, wherein:

[0019] Figure 1 This is a system block diagram of a xylene distillation apparatus according to an embodiment of this application;

[0020] Figure 2 This is an exemplary flowchart of an energy system optimization method for a xylene distillation apparatus according to an embodiment of this application;

[0021] Figure 3 This is a schematic diagram of the splitting of the top and bottom discharges of the main column in an energy system optimization method for a xylene distillation apparatus according to an embodiment of this application.

[0022] Figure 4 This is a system block diagram of an energy system optimization system for a xylene distillation apparatus according to an embodiment of this application. Detailed Implementation

[0023] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein, and therefore this application is not limited to the specific embodiments disclosed below.

[0025] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0026] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be construed as limiting the scope of protection of this application.

[0027] Furthermore, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of the description herein. Moreover, this application is to be understood not only by the actual terms used, but also by the meaning implied by each term.

[0028] Flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, various steps can be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0029] To facilitate understanding of the subsequent explanation of the energy system optimization method for the xylene distillation unit, a brief description of the xylene distillation unit is provided here. (Reference) Figure 1 The diagram shows a system block diagram of a xylene distillation apparatus. The xylene distillation apparatus 100 includes a disproportionation unit 110, a xylene distillation unit 120, an adsorption separation unit 130, and an isomerization unit 140.

[0030] Specifically, disproportionation unit 110 uses toluene and C9 aromatics as raw materials and performs disproportionation treatment on these raw materials to produce benzene and C8 aromatics. Disproportionation unit 110 includes three sub-towers: stripping tower 111, benzene tower 112, and toluene tower 113. Stripping tower 111 uses light hydrocarbons and aromatics as feed, with light hydrocarbons as the top product and aromatics as the bottom product. Benzene tower 112 uses the bottom product from stripping tower 111 and supplementary toluene as feed, with benzene as the top product and C7 and higher aromatics as the bottom product. Toluene tower 113 uses the bottom product from benzene tower 112 as feed, with toluene as the top product and C8 and higher aromatics as the bottom product. Figure 1 The arrows indicate the destination of the top or bottom output of the tower. For example, the arrow between stripping tower 111 and benzene tower 112 indicates that the bottom output of stripping tower 111 enters benzene tower 112 as feedstock for benzene tower 112. Figure 1 The arrows between adjacent subtowers have similar meanings to those described above, and will not be elaborated upon further below.

[0031] The xylene distillation unit 120 uses the product of the disproportionation unit 110 as raw material to separate C8 and higher aromatic hydrocarbons, while simultaneously producing o-xylene as a byproduct. For example... Figure 1As shown, the xylene distillation unit 120 includes four sub-towers: a reformate separation tower 121, a xylene tower 122, an o-xylene tower 123, and a heavy aromatics tower 124. The reformate separation tower 121 uses reformate from the continuous reforming unit as feed, with C7 and lower hydrocarbons as the top product and C8 and higher aromatics as the bottom product. The xylene tower 122 uses C8 and higher aromatics from the disproportionation unit 110 as feed, with C8 aromatics as the top product and C9 and higher aromatics as the bottom product. The top product of the xylene tower 122 is sent to the adsorption separation unit 130. The o-xylene tower 123 uses the bottom product of the xylene tower 122 as feed, with o-xylene as the top product and C9 and higher aromatics as the bottom product. The heavy aromatics tower 124 uses the bottom discharge of the o-xylene tower 123 as feed, the top discharge of the tower is C9 aromatics, and the bottom discharge of the tower is C10 heavy aromatics.

[0032] The adsorption separation unit 130 uses the top product of the xylene distillation unit 120 as raw material to separate para-xylene from other xylenes. For example... Figure 1 As shown, the adsorption separation unit 130 includes three sub-towers: an extractor tower 131, a product tower 132, and a raffinate tower 133. The raffinate tower 133 is fed with a mixture containing a large amount of xylene and p-diethylbenzene. The top product is C8 aromatics, destined for the isomerization unit 140, while the bottom product, p-diethylbenzene, is recycled as a desorption agent. The extractor tower 131 is fed with a mixture containing a large amount of p-xylene and p-diethylbenzene. The top product is crude p-xylene, and the bottom product, p-diethylbenzene, is recycled as a desorption agent. The product tower 132 is fed with the top product from the extractor tower. The top product is toluene, and the bottom product is high-purity p-xylene.

[0033] Isomerization unit 140 converts the lean p-xylene mixture from adsorption separation unit 130 into a concentration-equilibrium mixed xylene, which is then used as feedstock for xylene tower 122. Isomerization unit 140 includes a sub-tower: deheptane tower 141. Deheptane tower 141 receives a mixture containing C8 aromatics as feed, with light hydrocarbons as the top product and C8 aromatics as the bottom product, both destined for xylene tower 122.

[0034] The top and bottom feeds of the xylene column 122, which serves as the main column, can be used to heat the reboilers of other sub-columns and to heat its own feed. The optimization method of this application can obtain the reflux ratios of the main column and each sub-column that minimize the energy consumption of the entire distillation unit.

[0035] The optimization method and control system of this application will be described below through specific embodiments.

[0036] Figure 2 This is an exemplary flowchart of a method for optimizing the energy system of a xylene distillation apparatus according to an embodiment of this application. (Reference) Figure 2 As shown, the optimization of this embodiment includes the following steps:

[0037] Step S210: Build a heat exchange network model. The heat exchange network model includes the heat load value of the reboiler of each sub-tower, the heat load value of the feed to the main tower, the energy relationship between the heat supplied by the main tower to the reboilers of multiple sub-towers and the heat supplied by the main tower to the feed to the main tower.

[0038] Step S220: Using the concentrations of key components at the top and bottom of multiple sub-towers and the main tower, the energy relationships in the heat exchange network model, and the purity of xylene as constraints, and taking the minimum energy consumption of the distillation unit as the objective function, solve for the reflux ratio of each sub-tower and the reflux ratio of the main tower that satisfy the objective function.

[0039] The following details steps S210 and S220.

[0040] Combination Figure 1 and Figure 2 As shown, the xylene distillation apparatus in this application includes a main column and multiple sub-columns. Figure 1 In this embodiment, the main tower is implemented as xylene tower 122, and the multiple sub-towers are implemented as stripping tower 111, benzene tower 112, toluene tower 113, reformate separator 121, o-xylene tower 123, heavy aromatics tower 124, raffinate tower 133, extract tower 131, product tower 132, and heptane removal tower 141. It should be noted that in some other embodiments, the multiple sub-towers may also be... Figure 1 Any and more sub-towers, not limited to Figure 1 All the sub-towers. For example, in another embodiment, the multiple sub-towers are implemented as stripping tower 111, o-xylene tower 123, heavy aromatics tower 124, raffinate tower 133, extract tower 131, product tower 132 and heptane removal tower 141, excluding Figure 1 The benzene tower 112, toluene tower 113, and reforming oil separator 121 are included.

[0041] In step S110, a heat exchange network model is constructed. The heat exchange network model includes the energy relationship between the heat load value of the reboiler of each sub-tower, the heat load value of the feed to the main tower, the heat supplied by the main tower to the reboilers of multiple sub-towers, and the heat supplied by the main tower to the feed to the main tower. It should be noted that "each sub-tower" in step S110 refers to the sub-tower participating in the heat exchange network, not just the sub-towers themselves. Figure 1All the sub-towers. In other words, "each sub-tower," as a link in the heat exchange network, has its top or bottom feed from the main tower used to heat the reboiler of the sub-tower within the network. Additionally, the main tower's feed also heats its own feed. In other words, the heat exchange network includes a main tower and multiple sub-towers. The main tower has a reboiler, through which it can be heated. The top and bottom feeds of the main tower have specific temperatures. Within the heat exchange network, the main tower's top and bottom feeds are divided into multiple streams, each used to heat the corresponding sub-tower's reboiler and the main tower's own feed, respectively.

[0042] In one embodiment, the heat load value of the reboiler for each sub-tower is calculated using the formula: W1 = F S ×Q S Where W1 is the heat load value of the reboiler of the corresponding sub-tower, and F S Q is the molar flow rate corresponding to the output of the sub-tower. s This refers to the latent heat of vaporization of the product per unit molar flow rate in the corresponding sub-tower. Taking a heptane removal tower as an example, its top product is light hydrocarbons and its bottom product is C8 aromatics. Therefore, the molar flow rate of the product from the heptane removal tower is the sum of the molar flow rates of the top and bottom products. Multiplying this sum by the latent heat of vaporization of the product per unit molar flow rate yields the heat load value of the reboiler in the heptane removal tower.

[0043] In one embodiment, the formula for calculating the heat load value of the feed to the main tower is: W2 = c × G s (T a -T b ), where W2 is the heat load value of the feed to the main tower, c is the specific heat capacity of the feed, and T a Let T be the initial temperature. b For the target temperature, G s This refers to the mass flow rate of the feed. When the main tower is implemented as... Figure 1 When the xylene tower is used, the feed is C8 and above aromatics, and the initial temperature is T. a The target temperature T that the feed needs to be heated to is 98℃. b The specific heat capacity c and mass flow rate G of the feed can be obtained through simulation or by looking up a table, given a temperature of 204℃. s The heat load value of the xylene tower feed can be obtained based on the above parameters.

[0044] In one embodiment, the energy relationship in the heat exchanger network model is the relationship between the sum of the heat supplied by the main column to the reboilers of multiple sub-columns and the heat used to heat the feed to the main column, and the sum of the heat load values ​​of the multiple sub-columns and the heat load value of the feed to the main column. Within the heat exchanger network, to ensure that the heat received by the reboilers of the sub-columns is equal to or greater than their heat load, and to ensure that the feed to the main column can be heated to the target temperature, it is necessary to ensure that the heat supplied by the main column to the reboilers of the sub-columns through its discharge is equal to or greater than the heat load of the sub-columns, and it is also necessary to ensure that the discharge of the main column can heat its own feed temperature to the target temperature. Therefore, in optimizing the energy system of the xylene distillation unit, one of the constraints of the optimization method is that the energy relationship in the heat exchanger network model is that the sum of the heat supplied by the main column to the reboilers of multiple sub-columns and the heat used to heat the feed to the main column is equal to or greater than the sum of the heat load values ​​of the multiple sub-columns and the heat load value of the feed to the main column. The constraints involved in the optimization method will be explained in detail later and will not be repeated here.

[0045] In one embodiment, before step S110, the method further includes: constructing a sub-tower model corresponding to each sub-tower, and calculating the concentrations of key components at the top and bottom of the sub-tower based on the reflux ratio of the corresponding sub-tower. In another embodiment, before step S110, the method further includes: constructing a main tower model, and calculating the concentrations of key components at the top and bottom of the main tower based on the reflux ratio of the main tower. By constructing the sub-tower models and the main tower model, the concentrations of key components at the top and bottom of the tower can be calculated based on the reflux ratio, and other parameters (such as top pressure, bottom pressure, top temperature, bottom temperature, and reflux ratio) can be analyzed.

[0046] Tables 1 to 8 show the simulation results of the sub-tower model and main tower model based on this application, and the comparison with the calibration values.

[0047] Table 1 compares the simulation results of the stripping tower sub-tower model. The feed for the stripping tower sub-tower model was set as a mixture of light hydrocarbons and aromatics, with a feed pressure of 0.91 MPa and a feed molar flow rate of 1412 kmol / h. The number of trays was set to 45, the feed position to the 23rd tray, and the condenser was set to partial condensation. Other parameters used default values. Then, simulation calculations were performed on the stripping tower. In the table, "calibration value" refers to the design value of the sub-tower process parameters, "simulated calculation value" refers to the numerical value of the process parameters simulated by the sub-tower model, and "relative error" indicates the closeness between the "simulated calculation value" and the "calibration value"; the smaller the value, the closer the "simulated calculation value" is to the "calibration value".

[0048] Table 1 Comparison of Simulation Calculation Results of Stripping Tower Sub-tower Model

[0049]

[0050]

[0051] Table 2 compares the simulation results of the o-xylene column sub-tower model. The feed for the o-xylene column sub-tower model was set to bottom discharge from the xylene column, the feed pressure to 0.2 MPa, and the feed molar flow rate to 706 kmol / h. The theoretical number of trays was set to 100, the feed location was set to the 37th tray, the condenser was set to full condensation, and other parameters used default values. Simulation calculations were then performed on the o-xylene column.

[0052] Table 2 Comparison of Simulation Results of o-xylene Tower Subtotal Model

[0053] process parameters Calibration value Simulated values Relative error / % Tower top pressure / MPa 0.118 0.12 1.7 Tower bottom pressure / MPa 0.185 0.19 2.7 Tower top temperature / ℃ 147.7 146.3 0.9 Tower bottom temperature / ℃ 197 200.2 1.6 <![CDATA[Return flow rate / (t*h -1 )]]> 140.6 140.6 0 Top-of-the-Tower Recombinant Components / % 0.2 0.2 0 Light components at the bottom of the tower / % 0.1 0.1 0

[0054] Table 3 compares the simulation results of the heavy aromatics tower sub-tower model. The feed for the heavy aromatics tower sub-tower model was set to the bottom discharge of the o-xylene tower, the feed pressure to 0.34 MPa, and the feed molar flow rate to 597 kmol / h. The theoretical number of trays was set to 40, the feed location was set to the 27th tray, the condenser was set to total condensation, and other parameters used default values. Simulation calculations were then performed on the heavy aromatics tower.

[0055] Table 3 Comparison of Simulation Calculation Results for Heavy Aromatic Hydrocarbon Tower

[0056] process parameters Calibration value Simulated values Relative error / % Tower top pressure / MPa 0.14 0.14 0 Tower bottom pressure / MPa 0.25 0.26 4 Tower top temperature / ℃ 203 203.8 0.4 Tower bottom temperature / ℃ 237 237.9 0.4 Return flow rate / (t*h-1) 54.75 54.75 0 Top-of-the-Tower Recombinant Components / % 0.23 0.23 0 Light components at the bottom of the tower / % 0.3 0.3 0

[0057] Table 4 compares the simulation results of the raffinate column sub-column model. The feed for the raffinate column sub-column model was set to a mixture containing large amounts of xylene and p-diethylbenzene, with a feed pressure of 0.88 MPa and a feed molar flow rate of 5818 kmol / h. The theoretical number of trays was set to 69, the feed location was set to the 35th tray, the condenser was set to full condensation, and other parameters used default values. Simulation calculations were then performed on the raffinate column.

[0058] Table 4 Comparison of Simulation Calculation Results for Residue Extraction Tower

[0059] process parameters Calibration value Simulated values Relative error / % Tower top pressure / MPa 0.242 0.25 3.3 Tower bottom pressure / MPa 0.407 0.417 2.6 Tower top temperature / ℃ 177.4 179.5 1.2 Tower bottom temperature / ℃ 249.4 249.2 0.1 <![CDATA[Reflux rate / (t*h -1 )]]> 542.5 542.5 0 Top-of-the-Tower Recombinant Components / % 0.005 0.005 0 Light components at the bottom of the tower / % 0.01 0.01 0

[0060] Table 5 compares the simulation results of the extractant column sub-model. The feed to the extractant column sub-model was set to a mixture containing large amounts of p-xylene and p-diethylbenzene, with a feed pressure of 0.88 MPa and a feed molar flow rate of 1649 kmol / h. The theoretical number of trays was set to 59, the feed location was set to the 31st tray, the condenser was set to full condensation, and other parameters used default values. Simulation calculations were then performed on the extractant column.

[0061] Table 5 Comparison of Simulation Calculation Results for Extraction Tank

[0062] process parameters Calibration value Simulated values Relative error / % Tower top pressure / MPa 0.274 0.27 1.5 Tower bottom pressure / MPa 0.339 0.34 0.3 Tower top temperature / ℃ 177.8 178.6 0.5 Tower bottom temperature / ℃ 236.2 242.4 2.6 <![CDATA[Reflux flow rate / (t*h -1 )]]> 112.7 112.7 0 Top-of-the-Tower Recombinant Components / % 0.005 0.005 0 Light components at the bottom of the tower / % 0.05 0.04996 0

[0063] Table 6 compares the simulation results of the finished product column sub-column model. The feed for the finished product column sub-column model was set to the top discharge of the extractor column, the feed pressure to 0.35 MPa, and the feed molar flow rate to 622 kmol / h. The theoretical number of trays was set to 66, the feed location was set to the 23rd tray, the condenser was set to full condensation, and other parameters used default values. Simulation calculations were then performed on the finished product column.

[0064] Table 6 Comparison of Simulation Calculation Results for Finished Towers

[0065] process parameters Calibration value Simulated values Relative error / % Tower top pressure / MPa 0.121 0.12 0.8 Tower bottom pressure / MPa 0.16 0.16 0 Tower top temperature / ℃ 112.9 116 2.7 Tower bottom temperature / ℃ 154.1 155.4 0.8 <![CDATA[Reflux rate / (t*h -1 )]]> 79.63 79.63 0 Top-of-the-Tower Recombinant Components / % 0.75 0.75 0 Light components at the bottom of the tower / % 0.02 0.02 0

[0066] Table 7 compares the simulation results of the heptane removal column sub-column model. The feed for the heptane removal column sub-column model was set to C8 aromatics containing a small amount of light hydrocarbons, the feed pressure was set to 0.866 MPa, and the feed molar flow rate was set to 2883 kmol / h. The theoretical number of trays was set to 46, the feed location was set to the 23rd tray, the condenser was set to partial condensation, and other parameters used default values. Then, simulation calculations were performed on the heptane removal column.

[0067] Table 7 Comparison of Simulation Calculation Results for the Heptane Removal Tower

[0068] process parameters Calibration value Simulated values Relative error / % Tower top pressure / MPa 0.545 0.568 4.2 Tower bottom pressure / MPa 0.614 0.63 2.6 Tower top temperature / ℃ 116 112.7 2.8 Tower bottom temperature / ℃ 220 222 0.9 <![CDATA[Reflux flow rate / (t*h -1 )]]> 36.33 36.33 0 Top-of-the-Tower Recombinant Components / % 0.03 0.02994 0 Light components at the bottom of the tower / % 0.05 0.0499 0

[0069] Table 8 compares the simulation results of the xylene column sub-tower model. The feed for the xylene column sub-tower model was set to C8 and above aromatics from the disproportionation and alkylation unit and the isomerization unit. The feed pressure was set to 1.6 MPa. The feed molar flow rate from the disproportionation unit was set to 1290 kmol / h, and the feed molar flow rate from the isomerization unit was set to 2876 kmol / h. The theoretical number of trays was set to 175. The feed positions from the disproportionation and isomerization units were set to the 120th and 56th trays, respectively. The condenser was set to full condensation. Other parameters used default values. Simulation calculations were then performed on the xylene column.

[0070] Table 8 Comparison of Xylene Tower Simulation Calculation Results

[0071] process parameters Calibration value Simulated values relative error Tower top pressure / MPa 1.277 1.286 0.7 Tower bottom pressure / MPa 1.64 1.622 1.1 Tower top temperature / ℃ 271.2 266 1.9 Tower bottom temperature / ℃ 316 312.9 1 <![CDATA[Reflux rate / (t*h -1 )]]> <![CDATA[1.3*10 3 ]]> <![CDATA[1.3*10 3 ]]> 0 Top-of-the-Tower Recombinant Components / % 0.05 0.05 0 Light components at the bottom of the tower / % 13.41 13.41 0

[0072] The comparison results in Tables 1 to 8 show that the simulated values ​​and calibration values ​​of the sub-tower model are basically consistent, and the relative errors are all within the allowable range. Therefore, the model can be used to optimize and analyze the actual production equipment.

[0073] In step S220, the reflux ratios of each sub-tower and the main tower are determined using the concentrations of key components at the top and bottom of the multiple sub-towers and the main tower, the energy relationships in the heat exchange network model, and the xylene purity as constraints. The objective function is to minimize the energy consumption of the distillation unit. Specifically, the energy consumption of the distillation unit is calculated by adjusting the reflux ratios of each sub-tower and the main tower, and these calculated energy consumptions are compared to obtain the minimum energy consumption value of the distillation unit. The reflux ratios of each sub-tower and the main tower corresponding to this minimum energy consumption value are the reflux ratios that satisfy the objective function. It is important to note that in determining the reflux ratios of each sub-tower and the main tower that satisfy the objective function, the reflux ratio of each sub-tower must ensure that the concentrations of key components at the top and bottom of the sub-tower meet the requirements, and the reflux ratio of the main tower must ensure that the concentrations of key components at the top and bottom of the main tower meet the requirements. Furthermore, the purity of the xylene output from the distillation unit must also meet the requirements.

[0074] In one embodiment, step S220 is described as a mathematical expression in the form of:

[0075] minE(x(1)

[0076] stG(y(2)

[0077] x=x1,x2,x3,……,x7,x8](3)

[0078] y = y1, y2, y3, ..., x 18 ,x 19 (4)

[0079] Wherein, in formula (1): minE(x) represents the energy consumption of the distillation unit; in formula (2): stG(y) represents the constraint condition y; in formula (3): x1 to x8 represent the reflux ratio of 7 sub-towers and 1 main tower; in formula (4): y1 to y 16 This represents the concentrations of the critical components at the top and bottom of the seven sub-towers and one main tower, y. 17 and y 18 y represents the heat of the material discharged from the top and bottom of the main tower. 19 This indicates the purity of the xylene output from the distillation unit. It should be noted that in the above embodiments, the number of sub-columns is seven, which does not constitute a limitation on this application; the number of sub-columns can be increased or decreased as needed. In some embodiments, the constraint on the xylene is a purity equal to or greater than 99.7%.

[0080] In some embodiments, the key components at the top and bottom of the sub-tower and main tower are shown in Table 9. The concentrations of the key components at the top and bottom of the main tower and each sub-tower can be set according to requirements.

[0081] Table 9 Key components at the top and bottom of the sub-tower and main tower

[0082] Tower Name Key components at the top of the tower Key components at the bottom of the tower Stripping Tower Top toluene n-Pentane Xylene tower C9 aromatics at the top of the tower o-xylene o-xylene tower Top of the tower isopropylbenzene C8 aromatics Heavy Aromatics Tower Top Naphthalene C9 aromatics evaporator diethylbenzene at the top of the tower o-xylene Extraction tower C9 aromatics at the top of the tower p-xylene Finished tower Top p-xylene Toluene deheptane tower Top-of-the-column xylene benzene

[0083] In one embodiment, in step S220, after solving for the reflux ratio of each sub-tower and the reflux ratio of the main tower that satisfy the objective function, the flow rates of the main tower for heating the sub-tower reboiler and for heating its own feed streams through the top and bottom discharges can be determined.

[0084] Figure 3 This is a schematic diagram illustrating the separation of the top and bottom feed streams in the energy system optimization method of a xylene distillation apparatus according to an embodiment of this application. (Reference) Figure 3 As shown, the top discharge 310 of the xylene tower is divided into four streams, which serve as heat sources for the reboilers of the raffinate tower 311, the extract tower 312, the finished product tower 323, and the o-xylene tower 313, respectively. The bottom discharge 320 is divided into five streams, which serve as heat sources for the reboilers of the stripping tower 321, the extract tower 322, the heptane removal tower 323, and the heavy aromatics tower 324, respectively, and as a heat source for heating the xylene tower feed 325. It is understood that the diversion method of the top and bottom discharges of the main tower in this application is not limited to the above embodiment and can be adjusted according to requirements.

[0085] Table 10 shows a comparison between the reflux ratios of each sub-tower and the main tower obtained by the optimization method according to the present invention and the calibration values. As shown in Table 10, the comparison results show that, through the energy optimization method of the present invention, while ensuring that the purity of paraxylene meets the requirements, the energy consumption of the distillation unit is reduced from 4.33×10⁸ kJ / h to 3.85×10⁸ kJ / h, resulting in a 11.09% reduction in the overall energy consumption of the distillation unit, demonstrating a significant optimization effect.

[0086] Table 10 Calibration values ​​and optimization results of this invention

[0087] Calibration value Optimization results of this invention stripping tower reflux ratio 5.15 8.62 o-xylene tower reflux ratio 12.21 12.3 Heavy Aromatics Tower Reflux Ratio 0.83 0.83 Reflux ratio of evaporator 1.86 1.86 Reflux ratio of extraction tower 1.71 1.76 Product tower reflux ratio 48.92 40.9 heptane removal tower reflux ratio 5.72 5.7 xylene tower reflux ratio 3.66 3 PX purity of finished product tower / % 99.73 99.7 Energy consumption of distillation unit / kJ / h <![CDATA[4.33×10 8 ]]> <![CDATA[3.85×10 8 ]]>

[0088] The optimization method of this application uses the concentrations of key components at the top and bottom of multiple sub-towers and the main tower, the energy relationship in the heat exchange network model, and the purity of xylene as constraints, and takes the minimum energy consumption of the distillation unit as the objective function. It solves for the reflux ratio of each sub-tower and the reflux ratio of the main tower that satisfy the objective function, thereby minimizing the energy consumption of the distillation unit.

[0089] This application also includes an optimization system for the energy system of a xylene distillation unit, comprising a memory and a processor. The memory stores instructions executable by the processor, which then executes these instructions to implement the optimization method described above. This optimization system uses the concentrations of key components at the top and bottom of multiple sub-towers and the main tower, the energy relationships in the heat exchange network model, and xylene purity as constraints, and minimizes the energy consumption of the distillation unit as the objective function. It solves for the reflux ratio of each sub-tower and the reflux ratio of the main tower that satisfy the objective function, thereby minimizing the energy consumption of the distillation unit.

[0090] Figure 4 This is a system block diagram of the energy system optimization system of a xylene distillation apparatus according to an embodiment of this application. (Reference) Figure 4 As shown, the optimization system 400 may include an internal communication bus 410, a processor 420, a read-only memory (ROM) 430, a random access memory (RAM) 440, and a communication port 450. When applied to a personal computer, the optimization system 400 may also include a hard disk 460. The internal communication bus 410 enables data communication between the components of the optimization system 400. The processor 420 can make judgments and issue prompts. In some embodiments, the processor 420 may consist of one or more processors. The communication port 450 enables data communication between the optimization system 400 and external systems. In some embodiments, the optimization system 400 can send and receive information and data from a network through the communication port 450. The optimization system 400 may also include different forms of program storage units and data storage units, such as the hard disk 460, the read-only memory (ROM) 430, and the random access memory (RAM) 440, capable of storing various data files used for computer processing and / or communication, as well as possible program instructions executed by the processor 420. The processor executes these instructions to implement the main part of the method. The results processed by the processor are transmitted to the user device through the communication port and displayed on the user interface.

[0091] The above optimization method can be implemented as a computer program, stored in the hard disk 460, and loaded into the processor 420 for execution to implement the input system log optimization method of this application.

[0092] This application also includes a computer-readable medium storing computer program code that, when executed by a processor, implements the optimization methods described above.

[0093] When the optimization method is implemented as a computer program, it can also be stored as an article of art in a computer-readable storage medium. For example, computer-readable storage media can include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, magnetic stripes), optical discs (e.g., compact discs (CDs), digital multifunction discs (DVDs)), smart cards, and flash memory devices (e.g., electrically erasable programmable read-only memory (EPROM), cards, sticks, key drives). Furthermore, the various storage media described herein can represent one or more devices and / or other machine-readable media for storing information. The term "machine-readable medium" can include, but is not limited to, wireless channels and various other media (and / or storage media) capable of storing, containing, and / or carrying code and / or instructions and / or data.

[0094] It should be understood that the embodiments described above are merely illustrative. The embodiments described herein may be implemented in hardware, software, firmware, middleware, microcode, or any combination thereof. For hardware implementation, the processor may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and / or other electronic units designed to perform the functions described herein, or combinations thereof.

[0095] Some aspects of this application can be executed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The aforementioned hardware or software may be referred to as a "data block," "module," "engine," "unit," "component," or "system." The processor may be one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. Furthermore, aspects of this application may manifest as computer products residing in one or more computer-readable media, including computer-readable program code. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, magnetic tapes, etc.), optical discs (e.g., compressed CDs, digital multifunction DVDs, etc.), smart cards, and flash memory devices (e.g., cards, sticks, key drives, etc.).

[0096] A computer-readable medium may contain a propagated data signal containing computer program code, for example, on baseband or as part of a carrier wave. This propagated signal may take various forms, including electromagnetic, optical, and so on, or suitable combinations thereof. A computer-readable medium can be any computer-readable medium other than a computer-readable storage medium, which can be connected to an instruction execution system, apparatus, or device to enable communication, propagation, or transmission of a program for use. The program code located on the computer-readable medium can be propagated through any suitable medium, including radio, cable, fiber optic cable, radio frequency signals, or similar media, or any combination of the above media.

[0097] The basic concepts have been described above. Obviously, for those skilled in the art, the above disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore remain within the spirit and scope of the exemplary embodiments of this application.

[0098] Furthermore, this application uses specific terms to describe embodiments of the application. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of the application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0099] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of scope in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

Claims

1. A method for optimizing the energy system of a xylene distillation unit, the distillation unit comprising a main column and multiple sub-columns, characterized in that, The method includes the following steps: A heat exchange network model is constructed, which includes energy relationships, wherein the energy relationships include the heat load value of the reboiler of each sub-tower, the heat load value of the feed of the main tower, the heat supplied by the main tower to the reboilers of the multiple sub-towers, and the heat supplied by the main tower to the feed of the main tower. Using the concentrations of key components at the top and bottom of the multiple sub-towers and the main tower, the energy relationships in the heat exchange network model, and the purity of xylene as constraints, and with the goal of minimizing the energy consumption of the distillation unit, the reflux ratio of each sub-tower and the reflux ratio of the main tower that satisfy the objective function are solved.

2. The optimization method as described in claim 1, characterized in that, Also includes: Construct a sub-tower model corresponding to each of the sub-towers, and calculate the concentrations of the key components at the top and bottom of the sub-tower based on the reflux ratio of the corresponding sub-tower.

3. The optimization method as described in claim 2, characterized in that, Also includes: A main tower model is constructed, and the concentration of the key components at the top and bottom of the main tower is calculated based on the reflux ratio of the main tower.

4. The optimization method as described in claim 2 or 3, characterized in that, The model was built using process simulation software.

5. The optimization method as described in claim 1, characterized in that, The multiple sub-towers include a stripping tower, a benzene tower, a toluene tower, a reforming oil separator, an o-xylene tower, a heavy aromatics tower, a raffinate tower, an extract tower, a finished product tower, and a heptane removal tower.

6. The optimization method as described in claim 5, characterized in that, The main tower is a xylene tower.

7. The optimization method as described in claim 1, characterized in that, The energy relationship in the heat exchange network model is the relationship between the sum of the heat supplied by the main tower to the reboilers of the multiple sub-towers and the heat used to heat the feed to the main tower, and the sum of the heat load values ​​of the multiple sub-towers and the heat load values ​​of the feed to the main tower.

8. The optimization method as described in claim 1, characterized in that, The formula for calculating the heat load value of the reboiler for each sub-tower is as follows: ,in, This represents the heat load value of the reboiler corresponding to the sub-tower. To correspond to the molar flow rate of the sub-tower discharge, This represents the latent heat of vaporization of the discharge per unit molar flow rate of the corresponding sub-tower.

9. The optimization method as described in claim 1, characterized in that, The formula for calculating the heat load value of the feed to the main tower is as follows: ,in, Let c be the heat load value of the feed to the main tower, and c be the specific heat capacity of the feed. The initial temperature, For the target temperature, The mass flow rate of the feed is denoted as .

10. An optimization system for the energy system of a xylene distillation unit, characterized in that, include: Memory is used to store instructions that can be executed by the processor; A processor for executing the instructions to implement the optimization method as described in any one of 1-9.

11. A computer-readable medium storing computer program code that, when executed by a processor, implements the optimization method as described in any one of 1-9.

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