Method for reducing energy consumption in heavy aromatics separation process

Abstract

The invention discloses a method for reducing energy consumption in a heavy aromatics separation process. The method comprises the following steps: performing heat exchange on fresh C9 < + > aromatic hydrocarbon and a tower top gas phase of a heavy aromatic hydrocarbon separation tower, and separating in a gas-liquid separator to obtain a separator liquid phase and a separator gas phase; a gas phase and a liquid phase of the separator respectively enter from the upper part and the lower part of the same side of the heavy aromatics separation tower, and C9 + aromatics of an upstream section enters from the middle part of the other side of the heavy aromatics separation tower. According to the method, fresh C9 + aromatic hydrocarbon exchanges heat with a gas phase at the top of a heavy aromatic hydrocarbon separation tower, heat in the gas phase at the top of the heavy aromatic hydrocarbon separation tower is effectively recovered, a separator gas phase and a separator liquid phase are generated in a separator and enter the heavy aromatic hydrocarbon separation tower from different positions of the heavy aromatic hydrocarbon separation tower, the load capacity of the separation tower is effectively reduced, and the separation efficiency is improved. Therefore, the energy consumption required in the separation process is reduced to the greatest extent.

Description

Technical Field

[0001] The present invention relates to a method for separating heavy aromatics, and specifically to a method for reducing the energy consumption in the process of separating heavy aromatics, belonging to the technical field of chemical engineering. Background Art

[0002] Aromatics are an important class of basic organic chemical raw materials and have wide applications in multiple industrial fields. An aromatics complex aims to improve the output value and product quality by separating and upgrading the aromatic compounds in the raw materials. The process of the aromatics complex is complex, with a large amount of recycled materials and high energy consumption. Especially in the product rectification and separation stage, due to the high purity requirements for aromatic products and the close boiling points of components, the rectification tower often requires a large heat load.

[0003] The heavy aromatics separation tower is an important part of the rectification and separation stage in the aromatics complex, and its purpose is to separate the unreacted C9 + aromatics and heavy substances in the reaction products and avoid the accumulation of heavy substances in the reaction system. For the heavy aromatics separation tower, reducing the operating pressure is beneficial to reducing the reflux ratio, thereby reducing the loads of the bottom reboiler and the top condenser. Therefore, the heavy aromatics separation tower usually operates under negative pressure. However, due to the low top temperature, it is difficult to recover and utilize the large amount of heat contained in the top gas by conventional methods such as generating steam. At the same time, the fresh C9 + aromatics in the reaction raw materials usually need to be sent to the heavy aromatics separation tower to remove the moisture and heavy substances carried therein before entering the reaction system. The fresh C9 + aromatics at a low temperature further increase the heat load of the bottom reboiler. Even if the heavy aromatics separation tower operates under high vacuum, the operating energy consumption remains high.

[0004] In traditional aromatics complexes, for the high-temperature gas generated at the top of the heavy aromatics separation tower, it is usually only condensed by a simple cooling method, resulting in a large amount of wasted heat energy. If this part of heat can be effectively recovered and utilized, it can not only reduce energy consumption and improve energy utilization efficiency, but also contribute to improving the economy and sustainability of the aromatics complex.

[0005] In order to fully recover and utilize the heat at the top of the rectification and separation tower and reduce the energy consumption of the rectification tower, Chinese invention patent CN105176582A discloses an aromatics complex, which uses the method of generating steam to recover the low-temperature waste heat in the device and realizes the optimal utilization of energy through reasonable matching of temperature levels. However, this method has the risk of steam contamination of process media due to internal leakage of the heat exchanger. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method for reducing the energy consumption in the process of separating heavy aromatics. This method involves fresh C9 +The gas phase at the top of the aromatic hydrocarbon and heavy aromatic hydrocarbon separation column exchanges heat, effectively recovering the heat in the gas phase at the top of the heavy aromatic hydrocarbon separation column. Then, separator gas phase and separator liquid phase are generated in the separator and enter the column from different positions of the heavy aromatic hydrocarbon separation column, effectively reducing the load of the separation column, thereby minimizing the energy consumption required for the separation process.

[0007] To achieve the above technical objectives, the present invention provides a method for reducing the energy consumption in the heavy aromatic hydrocarbon separation process. Fresh C9 + aromatic hydrocarbons exchange heat with the gas phase at the top of the heavy aromatic hydrocarbon separation column and then enter a gas-liquid separator to be separated into separator liquid phase and separator gas phase; the separator gas phase and liquid phase enter from the upper and lower parts on the same side of the heavy aromatic hydrocarbon separation column respectively, and C9 + aromatic hydrocarbons from the upstream section enter from the middle of the other side of the heavy aromatic hydrocarbon separation column.

[0008] As a preferred solution, the environment at the top of the heavy aromatic hydrocarbon separation column is under negative pressure, and the conditions are: the operating pressure is -0.1 MPaG to -0.01 MPaG, and the temperature is 110 to 170 °C.

[0009] As a preferred solution, the environment at the top of the heavy aromatic hydrocarbon separation column is under negative pressure, and the conditions are: the operating pressure is -0.09 MPaG to -0.08 MPaG, and the temperature is 130 to 150 °C.

[0010] As a preferred solution, the fresh C9 + aromatic hydrocarbons contain C9 - C12 aromatic hydrocarbons, and the content of C9 aromatic hydrocarbons is 40 - 80 wt%.

[0011] As a preferred solution, the minimum temperature difference in the heat exchange process is 5 - 10 °C; the gas fraction of the fresh C9 + aromatic hydrocarbons after heat exchange is 5 - 20 wt%.

[0012] As a preferred solution, the number of theoretical plates of the heavy aromatic hydrocarbon separation column is 10 - 60, and the reflux ratio is 1.0 - 3.0. Further preferably, the reflux ratio of the heavy aromatic hydrocarbon separation column is 1.5 - 2.5.

[0013] As a preferred solution, the heavy aromatic hydrocarbon separation column is fed with separator gas phase, C9 + aromatic hydrocarbons from the upstream section, and separator liquid phase in sequence from top to bottom.

[0014] As a preferred solution, the separator gas phase enters the heavy aromatic hydrocarbon separation column from the 3rd to 10th plates from top to bottom.

[0015] As a preferred solution, the C9 + aromatic hydrocarbons from the upstream section enter the heavy aromatic hydrocarbon separation column from the 5th to 30th plates from top to bottom.

[0016] As a preferred solution, the liquid phase of the separator enters the heavy aromatics separation column from the 8th to 50th trays from top to bottom.

[0017] As a preferred solution, the upstream section C9 + aromatics contain C9 - C12 aromatics, where the content of C9 aromatics is 50 - 90 wt%.

[0018] As a preferred solution, the heat exchange between the fresh C9 + aromatics and the gas phase at the top of the heavy aromatics separation column is carried out through a shell-and-tube heat exchanger and / or a plate heat exchanger.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] 1) In the method provided by the present invention, the heat in the gas phase at the top of the heavy aromatics separation column is effectively recovered by heat exchange between the fresh C9 + aromatics and the gas phase at the top of the heavy aromatics separation column. Then, a separator gas phase and a separator liquid phase are generated in the separator and enter the column from different positions of the heavy aromatics separation column, effectively reducing the load of the separation column, thereby minimizing the energy consumption required for the separation process.

[0021] 2) In the method provided by the present invention, the separator can be regarded as a theoretical tray, and the heat required for its rectification process all comes from the gas phase at the top of the heavy aromatics separation column, without the need for an additional heat source; by controlling the heat exchange amount in the heat exchange process, the separator can control the gas and liquid fractions in the separator, so as to ensure that the separator gas phase and the separator liquid phase entering the heavy aromatics separation column from the corresponding positions will not increase the heat load of the separation column again. While ensuring the separation effect of heavy aromatics, the energy consumption is minimized to the greatest extent.

[0022] 3) In the technical solution provided by the present invention, by using the top heat exchange and the multi-shunt injection method, on the one hand, the heat in the gas phase at the top of the separation column is effectively recovered and utilized, and on the other hand, the injection method for specific sites can also reduce the heat load of the separation column. After testing, when using the method provided by the present invention under the same throughput, the energy consumption can be reduced by about 20% compared with the traditional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the process flow chart of the method adopted in the embodiment of the present invention;

[0024] Among them, 1 - heavy aromatics separation column; 2 - gas-liquid separator, 3 - reboiler of heavy aromatics separation column; 4 - top heat recovery heat exchanger of heavy aromatics separation column; 5 - top condenser of heavy aromatics separation column; 6 - reflux drum of heavy aromatics separation column; 7 - post-cooler at the top of heavy aromatics separation column; 8 - vacuum pump of heavy aromatics separation column. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be further described below in conjunction with specific embodiments. However, it should be understood that these embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of the present invention. The test methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages and parts are by weight.

[0026] Example 1

[0027] The heat recovery at the top of the heavy aromatics separation column in the rectification section of a certain device adopts Figure 1 the process technology shown. The heavy aromatics separation column has a total of 40 trays. The operating pressure at the top of the column is -0.08 MPaG, the operating temperature at the top of the column is 140 °C, the reflux ratio is 2.0. The heat recovery heat exchanger at the top of the column adopts a shell-and-tube heat exchanger, and the minimum temperature difference inside it is 7 °C. The weight flow rate of fresh C9 + aromatics is 60 t / h, and the weight percentage composition is 70% C9 aromatics and 30% C 10 + aromatics. The weight flow rate of C9 + aromatics from the upstream section is 10 t / h, and the weight percentage composition is 55% C9 aromatics and 45% C 10 + aromatics. The gaseous C9 + aromatics separated by the gas-liquid separator enters the heavy aromatics column from the 10th tray from top to bottom, and the liquid C9 + aromatics enters the heavy aromatics column from the 30th tray from top to bottom. The C9 + aromatics from the upstream section enters the heavy aromatics column from the 20th tray from top to bottom. The gas-phase fraction of the fresh C9 + aromatics after heat exchange is 12 wt%. The heat load of this heavy aromatics reboiler is 8.2 MW.

[0028] Example 2

[0029] The heat recovery at the top of the heavy aromatics separation column in the rectification section of a certain device adopts Figure 1 the process technology shown. The heavy aromatics separation column has a total of 50 trays. The operating pressure at the top of the column is -0.09 MPaG, the operating temperature at the top of the column is 150 °C, the reflux ratio is 2.5. The heat recovery heat exchanger at the top of the column adopts a shell-and-tube heat exchanger, and the minimum temperature difference inside it is 10 °C. The weight flow rate of fresh C9 + aromatics is 15 t / h, and the weight percentage composition is 70% C9 aromatics and 30% C 10 + aromatics. The weight flow rate of C9 + aromatics from the upstream section is 65 t / h, and the weight percentage composition is 55% C9 aromatics and 45% C 10 + aromatics. The gaseous C9 +The aromatic hydrocarbons enter the heavy aromatic hydrocarbon column from the 15th tray from top to bottom, and the liquid-phase C9 + The aromatic hydrocarbons enter the heavy aromatic hydrocarbon column from the 35th tray from top to bottom, and the C9 from the upstream section + The aromatic hydrocarbons enter the heavy aromatic hydrocarbon column from the 25th tray from top to bottom, and the fresh C9 after heat exchange + The gas fraction of the aromatic hydrocarbons is 15 wt%. The heat load of the heavy aromatic hydrocarbon reboiler is 8.8 MW.

[0030] Example 3

[0031] The top heat recovery of the heavy aromatic hydrocarbon separation column in the distillation section of a certain device adopts Figure 1 The process technology shown. The plate heat exchanger is used for the top heat recovery heat exchanger of the heavy aromatic hydrocarbon column, and other conditions are the same as those in Example 1. The heat load of the heavy aromatic hydrocarbon reboiler is 8.3 MW.

[0032] Comparative Example 1

[0033] In a certain device, the gas phase at the top of the heavy aromatic hydrocarbon separation column in the distillation section directly enters the air cooler and the water cooler for condensation and cooling. The fresh C9 + The aromatic hydrocarbons and the C9 from the upstream section + The aromatic hydrocarbons are directly mixed and then enter the heavy aromatic hydrocarbon column from the 20th tray from top to bottom, and other conditions are the same as those in Example 1. The heat load of the heavy aromatic hydrocarbon reboiler is 10.5 MW.

[0034] The above examples and comparative examples are only for better illustrating the technical solutions claimed in the present invention, and should not be construed as limitations on the technical solutions; after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for reducing the energy consumption in the process of separating heavy aromatics, characterized in that: Fresh C9 + After the gas phase at the top of the separation column for separating aromatic hydrocarbons from heavy aromatic hydrocarbons exchanges heat, it enters a gas-liquid separator for separation to obtain the liquid phase and gas phase of the separator; the gas phase and liquid phase of the separator enter from the upper and lower parts on the same side of the heavy aromatic hydrocarbon separation column respectively, and the C9 + aromatic hydrocarbons from the upstream section enter from the middle of the other side of the heavy aromatic hydrocarbon separation column.

2. The method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, wherein: The environment at the top of the heavy aromatics separation column is under negative pressure, and the conditions are as follows: the operating pressure is -0.1 MPaG to -0.01 MPaG, and the temperature is 110 to 170 °C.

3. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, characterized in that: The environment at the top of the heavy aromatics separation column is under negative pressure, and the conditions are as follows: the operating pressure is -0.09 MPaG to -0.08 MPaG, and the temperature is 130 to 150 °C.

4. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, characterized in that: The fresh C9 + aromatic hydrocarbons contain C9-C12 aromatic hydrocarbons, with the C9 aromatic hydrocarbon content being 40-80 wt%.

5. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, characterized in that: The minimum temperature difference during the heat exchange process is 5 to 10 °C; the fresh C9 + aromatic hydrocarbon has a gas phase fraction of 5 to 20 wt% after heat exchange.

6. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, characterized in that: The number of theoretical trays of the heavy aromatics separation column is 10 to 60, and the reflux ratio is 1.0 to 3.

0.

7. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 6, characterized in that: The heavy aromatic hydrocarbon separation column is fed with gas from the feed separator and C9 aromatic hydrocarbons from the upstream section in sequence from top to bottom, and liquid from the separator. + ​ 8. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 7, characterized in that: The vapor of the separator enters the heavy aromatics separation column from the 3rd to the 10th tray from top to bottom; the C9 aromatics in the upstream section + enter the heavy aromatics separation column from the 5th to the 30th tray from top to bottom; the liquid of the separator enters the heavy aromatics separation column from the 8th to the 50th tray from top to bottom.

9. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, characterized in that: The upstream section C9 + The aromatic hydrocarbons contain C9-C12 aromatic hydrocarbons, wherein the content of C9 aromatic hydrocarbons is 50-90 wt%.

10. A method for reducing the energy consumption in the process of separating heavy aromatics according to claim 1, characterized in that: The fresh C9 + The heat exchange between the gas phase at the top of the separation column for separating aromatic hydrocarbons from heavy aromatic hydrocarbons is carried out through a shell-and-tube heat exchanger and / or a plate heat exchanger.

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