Energy-saving process for extracting benzene by hydrogenation of crude benzene

Abstract

The invention discloses an energy-saving process for extracting benzene by hydrogenation of crude benzene. In the process, the energy-saving process for extracting benzene by hydrogenation of crude benzene is used. Hydrogenated oil obtained after crude benzene hydrogenation is preheated and enters a light component removal tower, hydrogen, hydrogen sulfide, ammonia and low-carbon hydrocarbon in the oil are separated from the top of the light component removal tower, and light component removed oil enters a pre-rectifying tower from a tower kettle. The pre-rectifying tower extracts a benzene fraction from the tower top through rectification separation for downstream continuous benzene purification, and mixed aromatic hydrocarbon subjected to debenzolization in the tower kettle is discharged after being subjected to heat recovery and cooling. The heat pump technology is adopted for pressurization and coupling of the pre-rectifying tower, low-level heat of benzene fraction steam at the top of the pre-rectifying tower is recycled, the low-level heat at the position is converted into a high-level heat source used by a light component removal tower reboiler through the heat pump, and the purposes of energy conservation and consumption reduction are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of crude benzene hydrogenation, in particular to a process for extracting benzene by distillation, and specifically to an energy-saving process for extracting benzene by hydrogenation of crude benzene. Technical Background Coking crude benzene hydrorefining technology is a widely used low-temperature, low-pressure hydrogenation process in China. This mature process features low investment and energy consumption. The general process involves two or three stages of selective hydrogenation followed by a lightness removal tower to remove light components. The crude benzene then passes through a pre-distillation tower to separate the BT from the top of the tower. The BT undergoes extractive distillation to remove non-aromatic hydrocarbons. The BT oil, free of non-aromatics, passes through a benzene purification tower to separate benzene and toluene as the main products.

[0002] The distillation process utilizes patent CN200610022714.8 to thermally couple the pre-distillation tower and the pure benzene tower, significantly reducing energy consumption. Due to the low price of toluene products in recent years, most domestic distillation schemes have been optimized and adjusted. The de-light oil separation in the pre-distillation tower has been changed from the original two-benzene separation to a single-benzene separation. Specifically, only the benzene fraction is distilled from the top of the pre-distillation tower, while the toluene and other heavy fractions are produced as mixed aromatics in the bottom of the tower. The benzene fraction is also sent to the subsequent extractive distillation, which is now a single-benzene extraction. The pure aromatics regenerated after extraction and separation directly become the pure benzene product, eliminating the need for the original pure benzene tower.

[0003] Although the adjusted process has reduced energy consumption and shortened the processing flow to a certain extent, the low-level heat at the top of the pre-distillation tower has lost its utilization value due to the use of atmospheric pressure process. Further research on new process solutions to achieve energy saving and efficiency improvement is crucial for the crude benzene hydrogenation industry. Summary of the Invention

[0004] The present invention optimizes the process and re-matches the process operating parameters based on the existing crude benzene hydrogenation benzene extraction process. By adopting heat pump technology to pressurize the pre-distillation tower and couple the light-removal tower, the low-level heat of the benzene fraction steam at the top of the pre-distillation tower is recovered. The low-level heat here is converted into a high-level heat source for the reboiler of the light-removal tower by the heat pump, thereby achieving the purpose of energy saving and consumption reduction.

[0005] In order to achieve the above object of the invention, the specific technical solutions of the present invention are as follows: A crude benzene hydrogenation and benzene extraction energy-saving process employs an energy-saving system for crude benzene hydrogenation and benzene extraction; the system comprises a light-removal tower, a pre-rectifier, a hydrogenation oil preheater, a light-removal oil preheater, a light-removal tower overhead condenser, a pre-rectifier tower overhead cooler, a pre-rectifier tower heat pump, and a logistics and control system. The hydrogenated oil after selective hydrogenation of the crude benzene is preheated in the hydrogenation oil preheater before entering the light-removal tower. The overhead gas is separated into hydrogen, hydrogen sulfide, ammonia, and light hydrocarbons by the light-removal tower overhead condenser and discharged. The light-removal oil, after light components have been removed, is then heat-recovered from the bottom of the light-removal tower via the hydrogenation oil preheater and the light-removal oil preheater before entering the pre-rectifier. The benzene fraction from the top of the pre-rectifier tower, separated by distillation, is cooled in the pre-rectifier tower overhead cooler, partially recovered, and partially sent downstream for further benzene purification. The mixed aromatics from the debenzenized bottom of the tower are heat-recovered in the light-removal oil preheater before being cooled and discharged.

[0006] As a better embodiment of the present application, the light-removal tower is provided with a light-removal tower reboiler; the heat source used in the light-removal tower reboiler is low-pressure steam.

[0007] As a preferred embodiment of the present application, a pre-distillation tower reboiler is provided on the pre-distillation tower; the heat source used in the pre-distillation tower reboiler is medium-pressure steam.

[0008] As a better embodiment of the present application, the heat source of the de-lightening tower reboiler in the system is low-pressure steam.

[0009] As a preferred embodiment of the present application, medium-pressure steam is used as the heat source for the reboiler of the pre-distillation tower.

[0010] As a better implementation method in the present application, after the medium-pressure steam is condensed by heat exchange in the pre-distillation tower reboiler, part of the condensed water is sent to the condensed water recovery system, and part is sent to the pre-tower heat pump after adjustment as a high-level heat source for the heat pump to replenish water. After heat recovery by the pre-tower heat pump, low-pressure steam is produced. The produced low-pressure steam is directly used as the heat source for the de-light tower reboiler, and the surplus part is sent to the low-pressure steam pipeline network, or can be directly sent downstream to be used as the heat source for the extraction distillation tower reboiler.

[0011] In the present invention, in order to achieve thermal coupling between the pre-distillation tower and the light-removal tower, a large amount of research and demonstration was conducted on the adaptation and selection of the heat pump unit by continuously changing the process configuration and coupling under different operating conditions. After a large number of engineering simulation calculations, the process configuration and control parameters that can significantly save energy and increase efficiency were selected. The key control parameters were verified in the industrial device and the simulation calculation model was repeatedly revised to finally determine the process configuration and preferred operating parameters of the present invention.

[0012] As a preferred embodiment of the present application, the top pressure of the pre-distillation tower is 0.10-0.40 MPa, and more preferably controlled to be 0.2-0.3 MPaG.

[0013] As a preferred embodiment of the present application, the top pressure of the lightness removal tower is 0.25 to 0.50 MPa, and more preferably controlled to be 0.3 to 0.40 MPaG.

[0014] As a better embodiment of the present application, the circulating hot water inlet temperature of the pre-tower heat pump is 100-130°C, preferably controlled at 110-120°C; the circulating hot water outlet temperature is 70-90°C, preferably controlled at 75-85°C.

[0015] As a better embodiment of the present application, the high-temperature heat energy of the pre-tower heat pump can be provided by deoxygenated water under the same conditions, and the pressure of the by-product high-temperature heat source low-pressure steam is 0.6~0.8MPaG, preferably controlled at 0.7~0.8MPaG.

[0016] Compared with the existing technology, the beneficial effects of the present invention are embodied in: 1) Compared with the non-pressurized and coupled heat pump process, a large amount of low-grade heat is converted into high-grade heat and can be used as a heat source. The overall system heat energy consumption is reduced by more than 20%, with significant energy-saving effects.

[0017] 2) Compared with the non-pressurized and coupled heat pump process, the cooling consumption of the heat recovery system is reduced, and the cooling consumption of the overall system is reduced by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the energy-saving process for extracting benzene by hydrogenation of crude benzene described in the examples.

[0019] Among them: T1 de-lightening tower; T2 pre-distillation tower; E1 hydrogenation oil preheater; E2 de-lightening tower reboiler; E3 de-lightening oil preheater; E4 pre-distillation tower reboiler; E5 de-lightening tower top condenser; E6 pre-distillation tower top cooler; X1 pre-tower heat pump. DETAILED DESCRIPTION

[0020] To better explain the content of the present invention, the present invention is further described below through specific examples. However, it should not be understood that the scope of protection of the present invention is limited to these examples. All features disclosed in the summary of the present invention, or all steps in the disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any manner. Any feature disclosed in the present invention, unless otherwise stated, can be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0021] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] In the present invention, some conventional operating equipment, devices and components are omitted or only briefly described.

[0025] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0026] Example 1: A crude benzene hydrogenation and benzene extraction energy-saving process employs an energy-saving system for crude benzene hydrogenation and benzene extraction; the system comprises: a lightness removal column T1, a pre-rectifier T2, a hydrogenation oil preheater E1, a lightness removal oil preheater E3, a lightness removal column overhead condenser E5, a pre-rectifier overhead cooler E6, a pre-rectifier heat pump X1, and a logistics conveying and control system. The hydrogenated oil, after selective hydrogenation of the crude benzene, is preheated in the hydrogenation oil preheater E1 and then enters the lightness removal column T1. The overhead gas passes through the lightness removal column overhead condenser E5 to separate hydrogen, hydrogen sulfide, ammonia, and light hydrocarbons, and is discharged. The lightness removal oil, after light components have been removed, is then transported from the bottom of the lightness removal column T1 through the hydrogenation oil preheater E1 and the lightness removal oil preheater E3 for heat recovery before entering the pre-rectifier T2. The benzene fraction at the top of the pre-distillation tower (T2) is partially recovered after being distilled and separated, and part of it is cooled in the pre-distillation tower top cooler E6, and the rest is sent downstream to continue to purify benzene. The mixed aromatics after debenzenization in the tower bottom are heat recovered and cooled in the de-light oil preheater E3 before being sent out.

[0027] Furthermore, a light-removal tower reboiler E2 is provided on the light-removal tower T1; and the heat source used in the light-removal tower reboiler E2 is low-pressure steam.

[0028] Furthermore, the pre-distillation tower T2 is provided with a pre-distillation tower reboiler E4; the heat source used in the pre-distillation tower reboiler E4 is medium-pressure steam.

[0029] Furthermore, after the medium-pressure steam is condensed through heat exchange in the pre-distillation tower reboiler E4, part of the condensed water is sent to the condensed water recovery system, and part is sent to the pre-tower heat pump X1 after adjustment as a high-level heat source for the heat pump to make up water. After heat recovery by the pre-tower heat pump X1, low-pressure steam is produced. The produced low-pressure steam is directly used as the heat source for the de-light tower reboiler E2, and the surplus is sent to the low-pressure steam pipeline network.

[0030] Furthermore, the high temperature heat energy of the pre-tower heat pump X1 can be supplied by deoxygenated water under the same conditions. The specific process steps carried out on the basis of this system are: Feed hydrogenation oil, temperature 40℃, pressure 0.6MPaG, flow rate 43m 3 / h, with a mass composition of hydrogen: 0.02%, methane: 0.09%, hydrogen sulfide: 0.51%, ammonia: 0.06%, butane: 0.03%, isopentane: 0.40%, cyclopentane: 0.05%, cyclohexane: 0.64%, benzene: 75.21%, methylcyclohexane: 0.05%, toluene: 16.26%, ethylbenzene: 1.41%, xylene: 4.22%, and heavy components: 1.05%. See the schematic diagram of the energy-saving process for crude benzene hydrogenation and benzene extraction for details. Figure 1 .

[0031] In order to achieve thermal coupling between the pre-distillation tower and the lightness removal tower, a large amount of research and demonstration was conducted on the adaptation and selection of the heat pump unit by continuously changing the process configuration and coupling under different operating conditions. After a large number of engineering simulation calculations, the process configuration and control parameters that can significantly save energy and increase efficiency were selected. The key control parameters were verified in an industrial device and the simulation calculation model was repeatedly revised. Finally, the process configuration and optimal operating parameters of the present invention were determined. The key control parameters of this embodiment are as follows: 1) The top pressure of the lightness removal tower T1 is 0.40 MPaG and the temperature is 112°C. The top pressure of the pre-distillation tower T2 is 0.25 MPaG and the temperature is 127°C. The gas phase flow rate of the top benzene fraction is 56 t / h and the produced benzene fraction is 28 t / h.

[0032] 2) The benzene fraction of the pre-distillation tower top cooler E6 is cooled to 85℃, the circulating hot water inlet temperature is 75℃, the circulating hot water outlet temperature is 110℃, and the circulation flow rate is 165t / h.

[0033] 3) The circulating water of the pre-tower heat pump X1 adopts circulating water with an inlet of 0.4MPa and 32℃ and an outlet of 0.25MPa and 40℃, with a circulating water volume of 492m 3 / h; the total by-product 0.8MPaG low-pressure saturated steam flow rate is: 3.8t / h, of which the steam flow rate for the lightness removal tower reboiler E2 is: 2.7t / h, and the surplus 1.1t / h low-pressure steam is sent to the downstream extractive distillation tower reboiler for use.

[0034] 4) The heat source for reboiler E3 is medium-pressure saturated steam at 2.0 MPaG, with a steam flow rate of 14.8 t / h. After condensation in regeneration tower reboiler E3, some of the condensed water is sent to the condensate recovery system, while the remaining condensed water is conditioned and sent to the lean liquid heat pump X1 as high-level heat source feed water.

[0035] Under the condition that other conditions remain unchanged, the energy-saving process of crude benzene hydrogenation and benzene extraction can save 0.8MPaG low-pressure saturated steam, 3.8t / h, and the system steam energy saving rate is 21.7%; the circulating cooling water is reduced by 253m 3 / h, the total cooling capacity of the tower top of the comprehensive system is reduced by about 26.2% in the cooling capacity of the entire system.

[0036] Example 2 A crude benzene hydrogenation benzene energy-saving process was carried out on the basis of the same system as in Example 1. The specific process steps are as follows: Feed hydrogenated oil, temperature 40℃, pressure 0.65MPaG, flow rate 22.4m 3 / h, with a mass composition of hydrogen: 0.01%, methane: 0.09%, hydrogen sulfide: 0.51%, ammonia: 0.06%, butane: 0.03%, pentane: 0.40%, cyclopentane: 0.05%, cyclohexane: 0.60%, benzene: 75.25%, methylcyclohexane: 0.03%, heptane: 0.02%, toluene: 16.25%, ethylbenzene: 1.42%, xylene: 4.12%, and heavy components: 1.16%. See the schematic diagram of the energy-saving process for crude benzene hydrogenation and benzene extraction for details. Figure 1 .

[0037] When the feed hydrogenation oil flow rate is low, in order to achieve the same level of energy saving and efficiency improvement as Example 1, after a large number of engineering simulation calculations and continuous verification in industrial equipment, the top control pressure of the light removal tower and the pre-distillation tower should be optimized and adjusted. The key control parameters of this embodiment are as follows: 1) The pressure at the top of the lightness removal tower T1 is 0.35 MPaG and the temperature is 108°C. The pressure at the top of the pre-distillation tower T2 is 0.30 MPaG and the temperature is 132.8°C. The gas phase flow rate of the benzene fraction at the top is 28 t / h and the produced benzene fraction is 14 t / h.

[0038] 2) The benzene fraction of the pre-distillation tower top cooler E6 is cooled to 85℃, the circulating hot water inlet temperature is 75℃, the circulating hot water outlet temperature is 115℃, and the circulation flow rate is 72t / h.

[0039] 3) The circulating water of the pre-tower heat pump X1 adopts circulating water with an inlet of 0.4MPa and 32℃ and an outlet of 0.25MPa and 40℃, with a circulating water volume of 243m 3 / h; the total by-product 0.8MPaG low-pressure saturated steam flow rate is: 1.9t / h, of which the steam flow rate for the de-light tower reboiler E2 is: 1.5t / h, and the surplus 0.4t / h low-pressure steam is sent to the downstream extractive distillation tower reboiler for use.

[0040] 4) The reboiler (E3) heat source uses medium-pressure saturated steam at 2.0 MPaG and a steam flow rate of 7.5 t / h. After heat exchange and condensation in the regeneration tower reboiler E3, part of the condensate is sent to the condensate recovery system, while the remaining condensate is conditioned and sent to the lean liquid heat pump X1 as high-level heat source feed water.

[0041] Under the condition that other conditions remain unchanged, the patented pressurized coupled heat pump energy-saving process saves 0.8MPaG low-pressure saturated steam, 1.9t / h, and the system steam energy saving rate is 21.1%; the circulating cooling water is reduced by 125m 3 / h, the total cooling capacity of the system top tower is integrated, and the cooling capacity consumption of the entire system is reduced by about 27.6%.

[0042] The aforementioned basic examples and their respective further alternatives may be freely combined to form a plurality of embodiments, all of which are applicable and claimed embodiments of the present invention. Each alternative in the present invention may be arbitrarily combined with any other basic examples and alternatives. Those skilled in the art will appreciate the numerous possible combinations.

[0043] The above embodiments are merely preferred embodiments of the present invention. The implementation and scope of protection of the present invention are not limited to the above embodiments. Any design and technical solution based on the concept of the present invention shall fall within the scope of protection of the present invention. It should be noted that for those skilled in the art, certain modifications without departing from the design principles of the present invention should also be considered within the scope of protection of the present invention. The present invention extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. An energy-saving process for extracting benzene from crude benzene by hydrogenation, characterized in that: The process utilizes an energy-saving system for hydrogenating benzene from crude benzene. The system comprises a light-removal column (T1), a pre-distillation column (T2), a hydrogenation oil preheater (E1), a light-removal oil preheater (E3), a light-removal column overhead condenser (E5), a pre-distillation column overhead cooler (E6), a pre-tower heat pump (X1), and a logistics and control system. The hydrogenated oil from the selective hydrogenation of crude benzene is preheated in the hydrogenation oil preheater (E1) before entering the light-removal column (T1). The top gas produced by the light components removal tower (T1) is separated into hydrogen, hydrogen sulfide, ammonia and light hydrocarbons by the light components removal tower top condenser (E5) and then discharged; the light components removal oil from the bottom of the light components removal tower (T1) is heat recovered in the hydrogenation oil preheater (E1) and the light components removal oil preheater (E3) in sequence and then enters the pre-distillation tower (T2); the benzene fraction at the top of the pre-distillation tower (T2) is cooled by the pre-distillation tower top cooler (E6) and partially recovered, and part is sent downstream to continue benzene purification. The mixed aromatics after the debenzenization in the bottom of the tower are heat recovered and cooled by the light components removal oil preheater (E3) and then sent out.

2. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 1, characterized in that: The light-removal tower (T1) is provided with a light-removal tower reboiler (E2); the heat source used in the light-removal tower reboiler (E2) is low-pressure steam.

3. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 1, characterized in that: A pre-distillation tower reboiler (E4) is provided on the pre-distillation tower (T2); a heat source used in the pre-distillation tower reboiler (E4) is medium-pressure steam.

4. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 3, characterized in that: After the medium-pressure steam is condensed by heat exchange in the pre-distillation tower reboiler (E4), part of the condensed water is sent to the condensed water recovery system, and part is sent to the pre-tower heat pump (X1) after adjustment as the high-level heat source water for the heat pump.

5. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 1 or 2, characterized in that: The top pressure of the light-removal tower (T1) is 0.25-0.50 MPa.

6. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 1 or 3, characterized in that: The top pressure of the pre-distillation tower (T2) is 0.10-0.40 MPa.

7. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 2 or 4, characterized in that: After heat recovery by the pre-tower heat pump (X1), low-pressure steam is produced. The produced low-pressure steam is directly used as the heat source of the de-light tower reboiler (E2), and the surplus is sent to the low-pressure steam pipeline network.

8. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 1 or 4, characterized in that: The circulating hot water inlet temperature of the pre-tower heat pump (X1) is 100-130°C, and the circulating hot water outlet temperature is 70-90°C.

9. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 8, characterized in that: The high-temperature heat energy of the pre-tower heat pump (X1) is provided by deoxygenated water with the same conditions as the make-up water.

10. The energy-saving process for extracting benzene by hydrogenation of crude benzene according to claim 9, characterized in that: The low-pressure steam pressure of the high-temperature heat source produced as a by-product of the pre-tower heat pump (X1) is 0.6 to 0.8 MPaG.

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