Benzene-toluene treatment energy-saving method

Abstract

The invention relates to a benzene-toluene treatment energy-saving method, and belongs to the technical field of energy and chemical industry. The negative pressure tower is additionally arranged in front of the first extract tower, and a thermal coupling network between the towers is optimized, so that efficient gradient utilization of low-temperature waste heat is realized. Wherein steam at the top of the first extract tower supplies heat to the negative pressure tower reboiler; the tower top steam of the second extract tower supplies heat to the first extract tower reboiler and the middle section reboiler of the benzene-toluene tower at the same time, and low-pressure steam is byproduct through a tower top steam generator; the top steam of the raffinate tower supplies heat to the benzene-toluene tower reboiler, and the side-draw of the raffinate tower supplies heat to the second extract tower reboiler. According to the method, heat sources with the same energy level are utilized in a matched mode, low-temperature waste heat is greatly recycled, the energy consumption of the system is remarkably reduced, low-pressure steam can be produced as a byproduct for preheating, heat tracing and the like, and the remarkable energy-saving effect and economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of energy and chemical technology, specifically to an energy-saving method for benzene-toluene treatment. Background Technology

[0002] Against the backdrop of a global push for green and low-carbon transformation, energy conservation, environmental protection, and sustainable development have become core guiding principles for industrial transformation and upgrading. For refining and chemical enterprises, while continuously promoting technological innovation and equipment upgrades, optimizing resource allocation and tapping potential efficiency are key paths to achieving improved quality and efficiency. Currently, the overall energy efficiency level of my country's refining and chemical industry still lags significantly behind international benchmarks. Aromatics integrated systems, as typical high-energy-consuming systems, account for over 30% of the total energy consumption due to their multi-unit integration and complex process coupling. In-depth analysis shows that a large amount of low-temperature waste heat within the unit, ranging from 80 to 150°C, is not being utilized in a cascade manner, directly leading to high overall energy consumption indicators. Therefore, constructing a more scientific heat recovery network, further realizing heat matching and coupling within the system, and developing new low-temperature heat utilization technologies have become important breakthroughs for improving the energy efficiency level of aromatics units.

[0003] In the petroleum refining industry, thermal energy consumption accounts for a significant proportion of total energy consumption. Although high-grade thermal energy (such as high-temperature steam) has been efficiently utilized through system optimization during the unit design phase, a large amount of low-grade waste heat (usually found in fractionation tower top oil and gas, reaction products, and process cooling condensate) is still generally not effectively recovered. Due to process stability requirements, this waste heat is often directly dissipated through traditional methods such as air cooling or water cooling, which not only leads to low energy efficiency but also increases the company's operating costs and environmental burden.

[0004] Existing aromatic hydrocarbon coprocessing systems have complex processes and numerous separation steps. Typically, most distillation columns have significant amounts of low-temperature heat at their tops, and this heat is difficult to fully utilize within the system due to its low temperature. Most systems rely on air cooling or circulating water cooling, which wastes heat and increases electrical energy consumption. This approach not only exposes the high energy consumption of the system but also results in a large amount of unutilized low-temperature waste heat during operation. Furthermore, in high-temperature environments, numerous air cooling units can cause hot air recirculation and mixing between nearby units, thus affecting the overall cooling efficiency of the system. Particularly in the benzene-toluene processing within aromatic hydrocarbon coprocessing systems, the lack of proper heat coupling between the benzene-toluene column, the evaporator column, and the residual liquid column leads to a large amount of low-temperature waste heat being dissipated without efficient utilization.

[0005] Therefore, efficiently recovering low-temperature waste heat from benzene-toluene processing systems is a crucial energy-saving measure and means for petrochemical enterprises. Systematically integrating these dispersed, low-grade heat sources through low-temperature waste heat recovery technology can reduce the consumption of high-value refrigerants (such as circulating water and electricity), lower investment and maintenance pressures in cooling systems, and simultaneously reduce cooling water consumption and carbon emission intensity. From a production practice perspective, the cascade utilization of this type of heat energy not only helps enterprises achieve their energy consumption control targets but also improves economic efficiency through optimized resource allocation, thereby strengthening competitive barriers in the industry. Summary of the Invention

[0006] This invention addresses the problem of insufficient thermal coupling and unutilized low-temperature waste heat resources in the combined use of the benzene-toluene tower, extractor tower, and raffinate tower in the benzene-toluene processing section of an aromatic hydrocarbon coprocessing system. It innovatively proposes a method to achieve heat exchange and utilization by rationally and progressively utilizing the overhead steam heat from most of the distillation towers in the benzene-toluene processing system. On one hand, this invention matches and utilizes heat sources of the same energy level to achieve heat exchange, enabling heat exchange between raw materials within the system and between systems. For example, the by-product low-pressure steam can be used for preheating tower feed, pipeline heating, and heating, thus reducing investment costs and shortening the payback period to some extent. On the other hand, the energy-saving process mainly utilizes the waste heat from the tower overhead steam for thermal coupling: a negative pressure tower and its supporting equipment are added before the first extractor tower. The thermal coupling method involves the overhead steam from the first extractor tower supplying heat to the reboiler of the negative pressure tower, further reducing system heat consumption. The saved high-temperature heat source is used for the by-product low-pressure steam, achieving optimized energy matching and efficient recovery.

[0007] This invention is achieved through the following technical solution: This invention provides an energy-saving method for benzene-toluene treatment, comprising the following steps: Materials with benzene and toluene as the main components are transported to the benzene-toluene tower, and the material is collected from the bottom of the benzene-toluene tower; Material from the adsorption separation device is conveyed to a negative pressure tower, and material collected from the bottom of the negative pressure tower is conveyed to a first extraction liquid tower; material collected from the bottom of the first extraction liquid tower is conveyed to a second extraction liquid tower. The first extraction liquid tower returns the extracted liquid from the first extraction liquid tower side line to the adsorption separation device through the first extraction liquid tower side sampling pipeline, and the negative pressure tower returns the extracted liquid from the negative pressure tower side line to the adsorption separation device through the negative pressure tower side sampling pipeline. The top steam of the first extracting liquid tower is heated by the reboiler of the negative pressure tower and then refluxed back to the top of the first extracting liquid tower. The top steam of the second extracting liquid tower is heated by three branches: the reboiler of the first extracting liquid tower, the top steam generator of the second extracting liquid tower, and the intermediate reboiler of the benzene-toluene tower, and then the materials are combined. Part of the combined material is refluxed back to the top of the second extracting liquid tower, and the other part is refluxed back to the adsorption separation unit. Material is collected from the bottom of the second extracting liquid tower. Low-pressure steam is produced as a byproduct by the top steam generator of the second extracting liquid tower. The material from the adsorption separation unit and the material from the F351 convection section of the aromatic hydrocarbon coprocessing system are transported to the raffinate tower. The material collected through the side line of the raffinate tower is heated by the reboiler of the second raffinate tower and then returned to the raffinate tower. The top vapor of the raffinate tower is heated by the reboiler of the benzene-toluene tower, and part of it is returned to the top of the raffinate tower, while the other part is returned to the adsorption separation unit.

[0008] This invention achieves heat exchange and utilization by rationally and progressively utilizing the overhead steam heat of most distillation columns in a benzene-toluene treatment energy-saving system. On one hand, it utilizes heat at the same energy level, using water as a medium to exchange heat between raw materials within the unit and between units or the system. For example, the low-pressure steam byproduct from the overhead steam generator of the second extracting liquid tower in this invention can be used for heating the feed to the preheating tower in the aromatics co-processing system, pipeline heating, and general heating. This method can reduce investment costs and shorten the payback period to some extent. Furthermore, the energy-saving process mainly utilizes the waste heat from the overhead steam for heat coupling: based on existing technology, this invention adds a negative pressure tower and its supporting equipment before the first extracting liquid tower; the heat coupling method is that the overhead steam of the first extracting liquid tower heats the reboiler of the negative pressure tower, further reducing system heat consumption, efficiently utilizing different levels of heat at each stage, reducing the amount of low-pressure steam produced while fully utilizing it, and achieving rational and efficient progressive heat utilization.

[0009] As a further option, the top steam of the second extracting liquid tower is divided into three streams by three branches and heated by the reboiler of the first extracting liquid tower, the top steam generator of the second extracting liquid tower, and the intermediate reboiler of the benzene-toluene tower at a flow ratio of (2.3~2.7):(1.9~2.3):1, respectively. After heating, the steam is returned to the top of the second extracting liquid tower and transported to the adsorption separation device at a flow ratio of (4~5):1.

[0010] As a further embodiment, the top steam of the raffinate tower is heated by the benzene-toluene tower reboiler and then refluxed back to the top of the raffinate tower and transported to the adsorption separation device at a flow ratio of (1.5~2):1.

[0011] As a further embodiment, the top temperature of the benzene-toluene tower is 90~92℃, and the top pressure of the benzene-toluene tower is 0.02~0.06 MPag; the top temperature of the negative pressure tower is 92~94℃, and the top pressure of the negative pressure tower is -0.06~-0.02 MPag; the top temperature of the first extractive liquid tower is 121~123℃, and the top pressure of the first extractive liquid tower is 0.02~0.06 MPag; the top temperature of the second extractive liquid tower is 166~168℃, and the top pressure of the second extractive liquid tower is 0.27~0.31 MPag; the top temperature of the raffinate tower is 223~225℃, and the top pressure of the raffinate tower is 1.01~1.05 MPag.

[0012] As a further embodiment, the adsorption separation device includes an adsorption separation unit and a rotary valve.

[0013] As a further embodiment, the material transported to the negative pressure tower via the negative pressure tower feed pipeline includes toluene with a mass percentage of ≥99.8 wt%; the material transported to the raffinate tower via the raffinate tower feed pipeline includes toluene with a mass percentage of 40 wt% to 50 wt%, m-xylene with a mass percentage of 30 wt% to 40 wt%, and o-xylene with a mass percentage of 10 wt% to 20 wt%.

[0014] In this invention, the precise extraction of components can be achieved through the rotary valve in the adsorption separation device; this dynamic control method ensures the stable composition of the material delivered to the negative pressure tower and the evacuation tank, realizing the full-process automated control, which is beneficial to improving the stability and economic benefits of the system.

[0015] As a further preferred embodiment, the materials transported to the negative pressure tower by the negative pressure tower feed pipeline also include octane, 3-methylheptane, 1,1-dimethylcyclohexane, isopropylcyclopentane, m-xylene, 2-methyloctane, etc.

[0016] As a further preferred embodiment, the material transported to the raffinate tower via the feed pipeline also includes p-xylene, ethylbenzene, and C9 aromatics.

[0017] As a further embodiment, the bottom material of the benzene-toluene tower flows back to the bottom of the benzene-toluene tower via the cold side of the benzene-toluene tower reboiler, the bottom material of the negative pressure tower flows back to the bottom of the negative pressure tower via the cold side of the negative pressure tower reboiler, the bottom material of the first extractable liquid tower flows back to the bottom of the first extractable liquid tower via the cold side of the first extractable liquid tower reboiler, and the bottom material of the second extractable liquid tower flows back to the bottom of the second extractable liquid tower via the cold side of the second extractable liquid tower reboiler.

[0018] As a further option, the mixed aromatics are fed to the benzene-toluene tower via the first feed pipeline of the benzene-toluene tower, and the material from the bottom of the stripping tower of the disproportionation unit in the aromatics coprocessing system is fed to the benzene-toluene tower via the second feed pipeline of the benzene-toluene tower.

[0019] As a further option, the benzene-toluene tower extracts materials through a benzene-toluene tower side sampling pipeline.

[0020] As a further preferred option, the benzene-toluene tower extracts benzene through a first side sampling line, and the benzene-toluene tower extracts toluene through a second side sampling line.

[0021] As a further option, the material is extracted from the bottom of the benzene-toluene tower through the bottom extraction pipeline.

[0022] As a further preferred embodiment, the material collected from the bottom of the benzene-toluene tower is transported to the A8 stripping tower in the aromatic hydrocarbon coprocessing system via the bottom collection pipeline of the benzene-toluene tower.

[0023] As a further embodiment, the overhead vapor of the benzene-toluene tower is returned to the benzene-toluene tower via the overhead vapor reflux pipeline.

[0024] As a further embodiment, the overhead vapor of the benzene-toluene tower flows sequentially through the benzene-toluene tower overhead condenser, the benzene-toluene tower reflux tank, and the benzene-toluene tower reflux pump via the benzene-toluene tower overhead vapor reflux pipeline, and then returns to the benzene-toluene tower.

[0025] As a further embodiment, the material from the adsorption separation device is transported to the negative pressure tower via the negative pressure tower feed pipeline, and the material at the bottom of the negative pressure tower is transported to the first extraction liquid tower via the negative pressure tower bottom collection pipeline.

[0026] As a further embodiment, the top steam of the negative pressure tower is returned to the negative pressure tower through the top steam return pipeline.

[0027] As a further embodiment, the top steam of the negative pressure tower flows sequentially through the top steam return pipeline of the negative pressure tower, the top condenser of the negative pressure tower, the return tank of the negative pressure tower, and the return pump of the negative pressure tower, and then returns to the negative pressure tower.

[0028] As a further option, the vapor at the top of the first extraction tower is used to heat the reboiler of the negative pressure tower through the top extraction pipeline of the first extraction tower and then flows back to the top of the first extraction tower.

[0029] As a further preferred embodiment, the steam at the top of the first extraction tower heats the reboiler of the negative pressure tower through the steam return pipeline at the top of the first extraction tower, and then flows sequentially through the return tank of the first extraction tower and the return pump of the first extraction tower back to the top of the first extraction tower.

[0030] This invention adds a negative pressure tower and its supporting equipment, and optimizes the heat coupling method of the hot benzene-toluene treatment energy-saving system. At this time, there is no need to set up a condensation device at the top of the first liquid extraction tower, which further makes efficient use of the heat at different levels in each stage, realizes full utilization of heat, reduces heat consumption in the system, and reduces condensation load.

[0031] As a further option, the material at the bottom of the first extraction tower is transported to the second extraction tower via the bottom extraction pipeline of the first extraction tower.

[0032] As a further embodiment, the top vapor of the second extracting liquid tower is heated by three branches: the reboiler of the first extracting liquid tower, the top vapor generator of the second extracting liquid tower, and the reboiler in the middle section of the benzene-toluene tower, and then the combined materials are combined. The combined materials flow sequentially through the reflux tank of the second extracting liquid tower and the reflux pump of the second extracting liquid tower. Part of the material is returned to the top of the second extracting liquid tower, and the other part is returned to the adsorption separation device.

[0033] As a further embodiment, the bottom material of the second extraction liquid tower is refluxed back to the bottom of the second extraction liquid tower through the second extraction liquid tower reboiler.

[0034] As a further embodiment, the bottom material of the second extraction liquid tower flows through the bottom reflux pump of the second extraction liquid tower and is returned to the bottom of the second extraction liquid tower through the reboiler of the second extraction liquid tower.

[0035] As a further option, the second extraction tower extracts paraxylene through the side extraction pipeline of the second extraction tower.

[0036] As a further option, the material is extracted from the bottom of the second extraction tower through the bottom extraction pipeline.

[0037] As a further embodiment, the bottom material of the raffinate column is refluxed back to the bottom of the raffinate column through the raffinate column reboiler.

[0038] As a further embodiment, the bottom material of the raffinate tower flows through the bottom reflux pump of the raffinate tower and is returned to the bottom of the raffinate tower through the reboiler of the raffinate tower.

[0039] As a further embodiment, the material is extracted from the bottom of the evaporator through the bottom extraction pipeline of the evaporator.

[0040] As a further embodiment, the vapor from the top of the raffinate tower is used to heat the benzene-toluene tower reboiler via the raffinate tower top extraction pipeline. After passing through the raffinate tower top reflux tank and the raffinate tower top reflux pump in sequence, a portion of the vapor is returned to the top of the raffinate tower, and the other portion is returned to the adsorption separation device.

[0041] As a further option, the material extracted through the side-line extraction pipeline of the evaporator is used to heat the reboiler of the second extraction tower, and then flows sequentially through the side-line extraction return tank and the side-line extraction return pump of the evaporator before returning to the evaporator.

[0042] As a further embodiment, the material with benzene and toluene as the main components includes mixed aromatics and material from the bottom of the stripping tower in the disproportionation unit of the aromatics complex.

[0043] As a further preferred embodiment, the mixed aromatics include benzene and toluene, wherein the mass percentage of benzene and toluene is greater than 99%.

[0044] As a further preferred embodiment, the mixed aromatics also include one or more of C3-C7 alkanes, ethylbenzene, xylene, and C9-C10 aromatics.

[0045] As a further embodiment, the mass percentage of benzene and toluene in the material from the bottom of the stripping tower of the disproportionation unit in the aromatic hydrocarbon complex is greater than 45%, and the mass percentage of xylene is greater than 35%.

[0046] As a further embodiment, the overhead vapor of the first extraction tower contains ≥99.9% toluene.

[0047] As a further embodiment, the material at the bottom of the first extraction liquid tower includes 40wt%~50wt% toluene and 50wt%~55wt% p-xylene by mass.

[0048] As a further option, the material at the bottom of the first extraction tower also includes ethylbenzene, m-xylene, o-xylene, and o-m-p-ethyltoluene.

[0049] The features and beneficial effects of this invention are as follows: (1) This method uses thermal coupling technology to optimize the heat exchange network and improve energy-saving potential; (2) Compared with the traditional single-tower extract distillation tower, this method can reduce the energy consumption of the first extract tower by 42%, and its by-product steam can be used for preheating tower feed, pipeline heating, heating, etc. This invention can maximize and efficiently recover the low-temperature thermal energy of the aromatic hydrocarbon complex to generate low-pressure steam, thereby reducing the energy consumption of the unit and the entire plant. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 An energy-saving system for benzene-toluene treatment in a factory.

[0052] Figure 2 This invention relates to an improved energy-saving system for benzene-toluene treatment.

[0053] Figure 3 This is a schematic diagram of the low-pressure steam produced as a byproduct of this invention.

[0054] in: T1 - Benzene-Toluene Tower, T2 - Negative Pressure Tower, T3 - First Extraction Liquid Tower, T4 - Second Extraction Liquid Tower, T5 - Residual Liquid Tower, T6 - Adsorption Separation Unit; X101 - First feed line of benzene-toluene tower, X102 - Second feed line of benzene-toluene tower, X103 - First side sampling line of benzene-toluene tower, X104 - Second side sampling line of benzene-toluene tower, X105 - Bottom sampling line of benzene-toluene tower, X106 - Top steam reflux line of benzene-toluene tower; Q101 - Benzene-toluene tower reboiler, Q102 - Benzene-toluene tower overhead condenser, Q103 - Benzene-toluene tower reflux tank, Q104 - Benzene-toluene tower reflux pump, Q105 - Benzene-toluene tower intermediate reboiler. X201 - Feed pipeline of negative pressure tower, X202 - Bottom outlet pipeline of negative pressure tower, X203 - Steam return pipeline of negative pressure tower top, X204 - Side outlet pipeline of negative pressure tower; Q201 - Reboiler of negative pressure tower, Q202 - Condenser at the top of negative pressure tower, Q203 - Reflux tank of negative pressure tower, Q204 - Reflux pump of negative pressure tower; X301 - Side sampling pipeline of the first extraction liquid tower; X302 - Bottom sampling pipeline of the first extraction liquid tower; X303 - Top vapor return pipeline of the first extraction liquid tower; Q301 - Reboiler of the first extraction liquid tower, Q302 - Condenser at the top of the first extraction liquid tower, Q303 - Reflux tank of the first extraction liquid tower, Q304 - Reflux pump of the first extraction liquid tower. X401 - Side sampling pipeline of the second extraction tower; X402 - Bottom sampling pipeline of the second extraction tower; Q401 - Second extracting liquid tower reboiler, Q402 - Second extracting liquid tower reflux tank, Q403 - Second extracting liquid tower reflux pump; Q404 - Second extracting liquid tower reboiler, Q405 - Second extracting liquid tower top steam generator, Q406 - Second extracting liquid tower bottom reflux pump. X501 - First feed line of the evaporator; X502 - Second feed line of the evaporator; X503 - Side sampling line of the evaporator; X504 - Top steam return line of the evaporator; X505 - Bottom sampling line of the evaporator. Q501 - Side reflux tank for raffinate tower; Q502 - Side reflux pump for raffinate tower; Q503 - Top reflux tank for raffinate tower; Q504 - Top reflux pump for raffinate tower; Q505 - Reboiler for raffinate tower; Q506 - Bottom reflux pump for raffinate tower. Q601 - Adsorption separation unit; Q602 - Rotary valve. Detailed Implementation

[0055] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0056] As a specific example of the implementation of this invention, detailed cases are provided below.

[0057] This embodiment uses Figure 1 Based on the energy-saving system for benzene-toluene processing in a certain factory, a negative pressure tower T2 is added before the first extraction tower T3, and a second extraction tower top steam generator Q405 is installed at the top of the second extraction tower T4, as detailed below. Figure 2 As shown.

[0058] The following combination Figure 2 The specific embodiments of the present invention will be described in detail below. It should be noted that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0059] This invention provides an energy-saving method for benzene-toluene treatment, comprising the following steps: The benzene-toluene treatment energy-saving system of the present invention includes a benzene-toluene tower T1, a negative pressure tower T2, a first extractor tower T3, a second extractor tower T4, a residual extractor tower T5, and an adsorption separation device T6.

[0060] Materials with benzene and toluene as the main components are transported to benzene-toluene tower T1; Specifically, the mixed aromatics are fed to the benzene-toluene tower T1 through the first feed line X101 at a temperature of 127℃ and a flow rate of 111.4 t / h. The material from the bottom of the stripping tower of the disproportionation unit in the aromatics co-processing system is fed to the benzene-toluene tower T1 through the second feed line X102 at a temperature of 179℃ and a flow rate of 496.1 t / h. The mixed aromatics include benzene, toluene, C3-C7 alkanes, ethylbenzene, xylene, and C9-C10 aromatics, wherein the mass percentage of benzene and toluene is >99%; The material from the bottom of the stripping tower in the disproportionation unit of the aromatics coprocessing system includes 4.3 wt% benzene, 42 wt% toluene, 36.8 wt% xylene, and 16.9 wt% aromatics with C8 or higher.

[0061] The benzene-toluene tower T1 extracts benzene through the first side sampling pipeline X103 of the benzene-toluene tower; The benzene-toluene tower T1 extracts toluene through the second side sampling pipeline X104 of the benzene-toluene tower; The X105 bottom-out pipeline of the benzene-toluene tower transports the bottom-out material of the benzene-toluene tower to the A8 stripping tower in the aromatic hydrocarbon coprocessing system.

[0062] The overhead vapor of the benzene-toluene tower T1 flows through the benzene-toluene tower overhead vapor reflux pipeline X106, sequentially through the benzene-toluene tower overhead condenser Q102, the benzene-toluene tower reflux tank Q103, and the benzene-toluene tower reflux pump Q104, and then returns to the benzene-toluene tower T1.

[0063] The material from the adsorption separation device T6 is transported to the negative pressure tower T2 through the negative pressure tower feed pipeline X201; The material conveyed to negative pressure tower T2 through negative pressure tower feed pipeline X201 includes toluene with a mass ratio of 99.87 wt%, and other components including octane, 3-methylheptane, 1,1-dimethylcyclohexane, isopropylcyclopentane, m-xylene, and 2-methyloctane. The negative pressure tower T2 returns the side-stream sampled liquid of the negative pressure tower to the adsorption separation device T6 through the negative pressure tower side-stream sampled liquid X204; The material at the bottom of the negative pressure tower T2 is transported to the first extraction tower T3 through the bottom extraction pipeline X202 of the negative pressure tower.

[0064] The top steam of the negative pressure tower T2 flows through the negative pressure tower top steam return pipeline X203, sequentially through the negative pressure tower top condenser Q202, the negative pressure tower return tank Q203, and the negative pressure tower return pump Q204, and then returns to the negative pressure tower T2.

[0065] The first extraction tower T3 returns the extracted liquid from the side line of the first extraction tower to the adsorption separation device T6 through the first extraction tower side sampling pipeline X301. The material at the bottom of the first extraction tower T3 is transported to the second extraction tower T4 through the bottom extraction pipeline X302.

[0066] The top steam of the first extraction liquid tower T3 heats the reboiler Q201 of the negative pressure tower through the top steam return pipeline X303 of the first extraction liquid tower, and then flows sequentially through the first extraction liquid tower return tank Q303 and the first extraction liquid tower return pump Q304, and returns to the first extraction liquid tower T3.

[0067] This invention adds a negative pressure tower T2 and its supporting equipment, and optimizes the heat coupling method of the hot benzene-toluene treatment energy-saving system. At this time, the top of the first extraction liquid tower T3 does not need to be equipped with a condensation device, which further makes efficient use of the heat at different levels in each stage, realizes full utilization of heat, reduces heat consumption in the system, and reduces condensation load.

[0068] As a further embodiment, the top steam of the second extractable liquid tower T4 is provided with three branches. The three branches supply heat to the reboiler Q301 of the first extractable liquid tower, the top steam generator Q405 of the second extractable liquid tower, and the intermediate reboiler Q105 of the benzene-toluene tower. The materials heated by the reboiler Q301 of the first extractable liquid tower and the top steam generator Q405 of the second extractable liquid tower are combined and then combined with the materials heated by the intermediate reboiler Q105 of the benzene-toluene tower. The combined materials flow sequentially through the reflux tank Q402 of the second extractable liquid tower and the reflux pump Q403 of the second extractable liquid tower. Part of the reflux is returned to the top of the second extractable liquid tower T4, and the other part is returned to the adsorption separation device T6. The top steam of the second extracting liquid tower T4 is distributed into three streams via three branches at flow rates of 385.1 t / h, 321.6 t / h, and 152.2 t / h, respectively, to heat the reboiler Q301 of the first extracting liquid tower, the top steam generator Q405 of the second extracting liquid tower, and the intermediate reboiler Q105 of the benzene-toluene tower. Then, it is returned to the top of the second extracting liquid tower and transported to the adsorption separation unit at flow rates of 858.9 t / h and 321.6 t / h, respectively. The material at the bottom of the second extraction liquid tower T4 flows through the bottom reflux pump Q406 and is returned to the bottom of the second extraction liquid tower T4 via the reboiler Q404. The second extraction tower T4 extracts paraxylene through the second extraction tower side sampling pipeline X401; The material is extracted from the bottom of the second extraction tower T4 through the bottom extraction pipeline X402.

[0069] Material from the adsorption separation device T6 is transported to the raffinate tower T5 through the first feed line X501 of the raffinate tower, and material from the convection section F351 of the aromatic hydrocarbon coprocessing system is transported to the raffinate tower T5 through the second feed line X502 of the raffinate tower.

[0070] The material collected through the side-line sampling pipeline X503 of the raffinate tower, after heating the reboiler Q401 of the second raffinate tower, flows through the side-line sampling reflux tank Q501 and the side-line sampling reflux pump Q502 of the raffinate tower, and then returns to the raffinate tower T5. The overhead vapor of the raffinate tower T5, after heating the benzene-toluene tower reboiler Q101 through the overhead vapor reflux pipeline X504 of the raffinate tower, flows through the overhead reflux tank Q503 and the overhead reflux pump Q504 of the raffinate tower. Part of it returns to the top of the raffinate tower T5, and the other part returns to the adsorption separation unit T6; the flow rate returning to the top of the raffinate tower T5 is 834.8 t / h, and the flow rate returning to the adsorption separation unit T6 is 467.1 t / h.

[0071] The bottom material of the raffinate tower T5 flows through the bottom reflux pump Q506 and is returned to the bottom of the second extraction tower T5 through the reboiler Q505. The material is extracted from the bottom of the raffinate tower through the X505 bottom extraction pipeline.

[0072] The benzene-toluene tower T1 has a top temperature of 91°C and a top pressure of 0.04 MPa; the negative pressure tower T2 has a top temperature of 93°C and a top pressure of -0.06 to -0.02 MPa; the first extractant tower T3 has a top temperature of 121 to 123°C and a top pressure of 0.02 to -0.06 MPa; the second extractant tower T4 has a top temperature of 166 to 168°C and a top pressure of 0.27 to -0.31 MPa; and the raffinate tower T5 has a top temperature of 224°C and a top pressure of 1.03 MPa.

[0073] The adsorption separation device T6 includes an adsorption separation unit Q601 and a rotary valve Q602; The material transported from the negative pressure tower feed pipeline X201 to the negative pressure tower T2 includes toluene with a mass percentage of ≥99.87wt%; other components include octane, 3-methylheptane, 1,1-dimethylcyclohexane, isopropylcyclopentane, m-xylene, 2-methyloctane, etc.

[0074] The material transported to the raffinate tower T5 by the first feed pipeline X501 includes 43.9 wt% toluene, 35.9 wt% m-xylene, 15.6 wt% o-xylene, 0.5 wt% p-xylene, 2.7 wt% ethylbenzene, and 1.3 wt% C9 aromatics.

[0075] The second feed line X502 of the raffinate tower delivers to a mixture comprising 43 wt% toluene, 3 wt% ethylbenzene, 1 wt% p-xylene, 37 wt% m-xylene, and 16 wt% o-xylene.

[0076] In this invention, the rotary valve Q602 serves, but is not limited to, the precise distribution and extraction of material components in the adsorption separation device T6.

[0077] The materials transported from the negative pressure tower feed pipeline X201 to the negative pressure tower T2 also include octane, 3-methylheptane, 1,1-dimethylcyclohexane, isopropylcyclopentane, m-xylene, 2-methyloctane, etc.

[0078] The bottom material of the benzene-toluene tower T1 flows back to the bottom of the benzene-toluene tower T1 via the cold side of the benzene-toluene tower reboiler Q101. The bottom material of the negative pressure tower T2 flows back to the bottom of the negative pressure tower T2 via the cold side of the negative pressure tower reboiler Q201. The bottom material of the first extractable liquid tower T3 flows back to the bottom of the first extractable liquid tower T3 via the cold side of the first extractable liquid tower reboiler Q301. The bottom material of the second extractable liquid tower T4 flows back to the bottom of the second extractable liquid tower T4 via the cold side of the second extractable liquid tower reboiler Q401.

[0079] The materials with benzene and toluene as the main components include mixed aromatics and materials from the bottom of the stripping tower in the disproportionation unit of the aromatics complex.

[0080] The mixed aromatics include benzene and toluene, wherein the mass percentage of benzene and toluene is greater than 99%.

[0081] The mixed aromatics also include one or more of the following: C3-C7 alkanes, ethylbenzene, xylene, and C9-C10 aromatics.

[0082] The mass percentage of benzene and toluene from the bottom of the stripping tower in the disproportionation unit of the aromatics complex is >45%, and the mass percentage of xylene is >35%.

[0083] The overhead vapor of the first extraction tower T3 contains ≥99.9% toluene. The material at the bottom of the first extraction tower T3 includes 40wt%~50wt% toluene and 50wt%~55wt% para-xylene by mass.

[0084] The materials at the bottom of the first extraction tower T3 also include ethylbenzene, m-xylene, o-xylene, and o-m-p-ethyltoluene.

[0085] In this invention, the material transported from the adsorption separation device T6 to the raffinate tower T5 via the first feed pipeline X501 and the material transported from the negative pressure tower feed pipeline X201 to the negative pressure tower T2 originates from other processing units in the aromatic hydrocarbon complex.

[0086] This invention adds a negative pressure tower T2 and its auxiliary equipment before the first extraction liquid tower T3. Before being fed into the first extraction liquid tower T3, the feed is separated by the newly added negative pressure tower T2 and then connected in series to the first extraction liquid tower T3. The reboiler Q201 of the newly added negative pressure tower is heated by the steam from the top of the first extraction liquid tower T3, meeting the heat requirements of the reboiler Q201. The negative pressure tower T2 can share 42% of the original heat load of the first extraction liquid tower. The heat for the reboiler Q301 of the first extraction liquid tower is provided by the higher-grade oil and gas from the top of the tower downstream, thus saving 42% of the high-grade heat source. The higher-grade heat source can further produce low-pressure saturated steam as a byproduct, which can be effectively recovered and utilized.

[0087] In this embodiment, a specific application is provided. The negative pressure tower T2 is fed at 157℃ and 615.946t / h. Before the modification, the heat load of the first extracting liquid tower bottom was >62MW. After the modification, the heat load of the first extracting liquid tower bottom was 34.55MW. The operating heat loads of each tower after the modification are shown in Table 1 below:

[0088] Depend on Figure 3 It can be seen that the low-pressure steam produced as a byproduct of this invention can be used for preheating tower feed, pipeline heat tracing, heating, etc. This type of method can reduce investment costs and shorten the payback period to some extent.

[0089] Based on an annual operating time of 8000 hours, a steam price of 200 yuan / ton, an electricity price of 0.6 yuan / kW, and a circulating water price of 0.15 yuan / ton, the preliminary estimate of the annual economic benefit from the high-grade heat source recovery of low-pressure steam after the renovation is approximately 80.566 million yuan, which is quite considerable, with energy savings of 42%. For new markets, the investment is small, the operation is highly feasible, and energy-saving measures such as optimizing heat recovery through heat exchange networks significantly reduce energy consumption.

[0090] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. An energy-saving method for benzene-toluene processing, comprising the following steps: conveying materials with benzene and toluene as the main components to a benzene-toluene tower (T1), and collecting the material from the bottom of the benzene-toluene tower (T1); The material from the adsorption separation device (T6) is conveyed to the negative pressure tower (T2), and the material collected from the bottom of the negative pressure tower (T2) is conveyed to the first extraction liquid tower (T3); the material collected from the bottom of the first extraction liquid tower (T3) is conveyed to the second extraction liquid tower (T4). The first extraction tower (T3) returns the extracted liquid from the first extraction tower side line to the adsorption separation device (T6) through the first extraction tower side sampling line (X301), and the negative pressure tower (T2) returns the extracted liquid from the negative pressure tower side line to the adsorption separation device (T6) through the negative pressure tower side sampling line (X204). The steam at the top of the first extracting liquid tower (T3) is heated by the reboiler (Q201) of the negative pressure tower and then refluxed back to the top of the first extracting liquid tower (T3). The steam at the top of the second extracting liquid tower (T4) is heated by three branches: the reboiler (Q301) of the first extracting liquid tower, the steam generator (Q405) at the top of the second extracting liquid tower, and the reboiler (Q105) in the middle section of the benzene-toluene tower. The combined materials are then combined. Part of the combined materials are refluxed back to the top of the second extracting liquid tower (T4), and the other part is refluxed back to the adsorption separation unit (T6). The material is collected from the bottom of the second extracting liquid tower (T4). The steam generator (Q405) at the top of the second extracting liquid tower produces low-pressure steam as a byproduct. The material from the adsorption separation unit (T6) and the material from the convection section of F351 in the aromatic hydrocarbon coprocessing system are transported to the raffinate tower (T5). The material collected through the side line of the raffinate tower (X503) is used to heat the reboiler (Q401) of the second raffinate tower and then returned to the raffinate tower (T5). The top vapor of the raffinate tower (T5) is used to heat the reboiler (Q101) of the benzene-toluene tower. Part of the vapor is returned to the top of the raffinate tower (T5) and the other part is returned to the adsorption separation unit (T6).

2. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The top steam of the second extraction liquid tower (T4) is divided into three streams by three branches and heated by the first extraction liquid tower reboiler (Q301), the second extraction liquid tower top steam generator (Q405), and the benzene-toluene tower intermediate reboiler (Q105) at a flow ratio of (2.3~2.7):(1.9~2.3):1 respectively. After heating, the steam is returned to the top of the second extraction liquid tower (T4) and transported to the adsorption separation unit (T6) at a flow ratio of (4~5):1 respectively. Preferably, the top steam of the raffinate column (T5) is heated by the benzene-toluene column reboiler (Q101) and then refluxed back to the top of the raffinate column (T5) and transported to the adsorption separation device (T6) at a flow ratio of (1.5~2):

1. Preferably, the top temperature of the benzene-toluene tower (T1) is 90~92℃, and the top pressure of the benzene-toluene tower (T1) is 0.02~0.06 MPag; the top temperature of the negative pressure tower (T2) is 92~94℃, and the top pressure of the negative pressure tower (T2) is -0.06~-0.02 MPag; the top temperature of the first extractable liquid tower (T3) is 121~123℃, and the top pressure of the first extractable liquid tower (T3) is 0.02~0.06 MPag; the top temperature of the second extractable liquid tower (T4) is 166~168℃, and the top pressure of the second extractable liquid tower (T4) is 0.27~0.31 MPag; the top temperature of the raffinate tower (T5) is 223~225℃, and the top pressure of the raffinate tower (T5) is 1.01~1.05 MPag.

3. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The adsorption separation device (T6) includes an adsorption separation unit (Q601) and a rotary valve (Q602). Preferably, the material conveyed to the negative pressure tower (T2) through the negative pressure tower feed pipeline (X201) includes toluene with a mass percentage of ≥99.8 wt%; The material transported to the raffinate tower (T5) via the first feed pipeline (X501) includes 40wt%~50wt% toluene, 30wt%~40wt% m-xylene, and 10wt%~20wt% o-xylene by mass.

4. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The bottom material of the benzene-toluene tower (T1) flows back to the bottom of the benzene-toluene tower (T1) through the cold side of the benzene-toluene tower reboiler (Q101), the bottom material of the negative pressure tower (T2) flows back to the bottom of the negative pressure tower (T2) through the cold side of the negative pressure tower reboiler (Q201), the bottom material of the first extractable liquid tower (T3) flows back to the bottom of the first extractable liquid tower (T3) through the cold side of the first extractable liquid tower reboiler (Q301), and the bottom material of the second extractable liquid tower (T4) flows back to the bottom of the second extractable liquid tower (T4) through the cold side of the second extractable liquid tower reboiler (Q401).

5. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, Mixed aromatics are fed to the benzene-toluene tower (T1) via the first feed line (X101), and the material from the bottom of the stripping tower of the disproportionation unit in the aromatics combined processing system is fed to the benzene-toluene tower (T1) via the second feed line (X102). Preferably, the benzene-toluene tower (T1) extracts material through a side sampling pipeline of the benzene-toluene tower; Preferably, benzene is extracted from the benzene-toluene tower (T1) through the first side sampling line (X103), and toluene is extracted from the benzene-toluene tower (T1) through the second side sampling line (X104). Preferably, the benzene-toluene tower (T1) collects material through the bottom collection pipeline (X105); Preferably, the overhead vapor of the benzene-toluene tower (T1) is returned to the benzene-toluene tower (T1) through the overhead vapor reflux pipeline (X106). More preferably, the overhead vapor of the benzene-toluene tower (T1) flows sequentially through the benzene-toluene tower overhead vapor reflux pipeline (X106) and passes through the benzene-toluene tower overhead condenser (Q102), the benzene-toluene tower reflux tank (Q103), and the benzene-toluene tower reflux pump (Q104) before returning to the benzene-toluene tower (T1).

6. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, Material from the adsorption separation device (T6) is transported to the negative pressure tower (T2) through the negative pressure tower feed pipeline (X201), and the material at the bottom of the negative pressure tower (T2) is transported to the first extraction liquid tower (T3) through the negative pressure tower bottom collection pipeline (X202). Preferably, the top steam of the negative pressure tower (T2) is returned to the negative pressure tower (T2) through the negative pressure tower top steam return pipeline (X203). More preferably, the top steam of the negative pressure tower (T2) flows through the negative pressure tower top steam return pipeline (X203) in sequence through the negative pressure tower top condenser (Q202), the negative pressure tower return tank (Q203), and the negative pressure tower return pump (Q204) and returns to the negative pressure tower (T2).

7. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The steam at the top of the first extraction tower (T3) is heated by the steam return pipeline (X303) at the top of the first extraction tower to the top of the negative pressure tower reboiler (Q201) and then returned to the top of the first extraction tower (T3). Preferably, the steam at the top of the first extraction tower (T3) is used to heat the reboiler (Q201) of the negative pressure tower through the steam return pipeline (X303) at the top of the first extraction tower, and then flows back to the top of the first extraction tower (T3) through the first extraction tower return tank (Q303) and the first extraction tower return pump (Q304). Preferably, the material at the bottom of the first extraction tower (T3) is transported to the second extraction tower (T4) through the bottom extraction pipeline (X302).

8. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The steam at the top of the second extracting liquid tower (T4) has three branches. The three branches are the first extracting liquid tower reboiler (Q301), the second extracting liquid tower top steam generator (Q405), and the benzene-toluene tower intermediate reboiler (Q105). After being heated, the materials are combined. The combined materials flow sequentially through the second extracting liquid tower reflux tank (Q402) and the second extracting liquid tower reflux pump (Q403). Part of the material flows back to the top of the second extracting liquid tower (T4), and the other part flows back to the adsorption separation unit (T6). Preferably, the bottom material of the second extraction liquid tower (T4) is refluxed to the bottom of the second extraction liquid tower (T4) through the second extraction liquid tower reboiler (Q404); Preferably, the bottom material of the second extraction liquid tower (T4) flows through the bottom reflux pump (Q406) of the second extraction liquid tower and is returned to the bottom of the second extraction liquid tower (T4) through the reboiler (Q404) of the second extraction liquid tower; Preferably, the second extraction tower (T4) extracts paraxylene through the second extraction tower side sampling pipeline (X401); Preferably, the material is extracted from the bottom of the second extraction tower (T4) through the bottom extraction pipeline (X402).

9. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The bottom material of the raffinate column (T5) is returned to the bottom of the raffinate column (T5) through the raffinate column reboiler (Q505); Preferably, the bottom material of the raffinate tower (T5) flows through the bottom reflux pump (Q506) and is returned to the bottom of the raffinate tower (T5) via the reboiler (Q505). Preferably, the material is collected from the bottom of the raffinate tower (T5) through the bottom collection pipeline (X505); Preferably, the top vapor of the raffinate tower (T5) is heated by the top vapor reflux pipeline (X504) of the raffinate tower to supply heat to the benzene-toluene tower reboiler (Q101), and then flows sequentially through the top reflux tank (Q503) and the top reflux pump (Q504) of the raffinate tower. Part of the vapor then flows back to the top of the raffinate tower (T5), and the other part flows back to the adsorption separation unit (T6). Preferably, the material extracted through the side line extraction pipeline (X503) of the evaporator is used to heat the reboiler (Q401) of the second evaporator, and then flows back to the evaporator (T5) after passing through the side extraction return tank (Q501) and the side extraction return pump (Q502) of the evaporator in sequence.

10. The energy-saving method for benzene-toluene treatment according to claim 1, characterized in that, The materials with benzene and toluene as the main components include mixed aromatics and materials from the bottom of the stripping tower in the disproportionation unit of the aromatics complex. Preferably, the mixed aromatics include benzene and toluene, wherein the mass percentage of benzene and toluene is >99%; More preferably, the mixed aromatics further include one or more of C3-C7 alkanes, ethylbenzene, xylene, and C9-C10 aromatics; Preferably, the mass percentage of benzene and toluene in the material from the bottom of the stripping tower of the disproportionation unit in the aromatics complex is >45%, and the mass percentage of xylene is >35%. Preferably, the overhead vapor of the first extraction tower (T3) comprises ≥99.9% toluene; Preferably, the material at the bottom of the first extraction liquid tower (T3) includes 40wt%~50wt% toluene and 50wt%~55wt% p-xylene by mass. More preferably, the material at the bottom of the first extraction liquid tower (T3) also includes ethylbenzene, m-xylene, o-xylene, and o-m-p-ethyltoluene.

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