Thermal joint energy-saving method, energy-saving system and application of styrene device

Abstract

The invention discloses a thermal joint energy-saving method and system for a styrene device and application of the thermal joint energy-saving method and system. The method comprises the following steps: a styrene tower kettle is provided with a first reboiler and a second reboiler, a hot side medium in the second reboiler is a benzene toluene tower top gas phase material, and a cold side medium in the second reboiler is a styrene tower kettle material; a hot-side medium in the first reboiler is external low-pressure steam, and a cold-side medium in the first reboiler is a styrene tower kettle material; and converting the gas-phase material at the top of the benzene-toluene tower after heat exchange from the second reboiler into a liquid-state material, and refluxing the liquid-state material into the benzene-toluene tower for recycling. According to the method disclosed by the invention, on the premise of ensuring stable operation of a styrene device, the gas phase at the top of the benzene-toluene tower is used as a heat source of the reboiler at the tower kettle of the styrene tower, heat contained in the gas phase at the top of the benzene-toluene tower is fully utilized, and the consumption of steam for heating the reboiler at the tower kettle and circulating water for cooling the gas phase at the top of the tower in the original technological process is saved; and the purposes of energy conservation and consumption reduction are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical process, and more particularly to a method, system and application of heat-combined energy saving for a styrene device. Background Art

[0002] In petrochemical plants, the temperature of the gas phase at the top of the tower is relatively high, and its condensation reflux process requires a large amount of circulating cooling water to cool it. The tower bottom reboiler requires an external heat source for heating, and this process consumes a large amount of steam. In this process, the heat rich in the high-temperature tower top gas phase is difficult to be fully utilized, resulting in heat waste. At the same time, the heating of the tower bottom material also requires additional steam consumption. In the traditional process flow, there is no good match between users who need heat and users rich in low-temperature heat. While consuming a large amount of steam, a large amount of low-temperature heat source is also wasted.

[0003] To solve this problem, a method for better utilization of energy needs to be provided. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention proposes a method, system and application of heat combined energy saving in a styrene device. The present invention provides a method for comprehensively utilizing low-temperature heat in a styrene device. On the premise of ensuring the stable operation of the styrene device, the gas phase at the top of the benzene toluene tower is used as the heat source of the reboiler of the styrene tower kettle, and the heat contained in the gas phase at the top of the benzene toluene tower is fully utilized, saving the steam used for heating the kettle reboiler and the circulating water used for cooling the gas phase at the top of the tower in the original process flow, thereby achieving the purpose of energy saving and consumption reduction.

[0005] One of the objects of the present invention is to provide a method for heat-combined energy saving of a styrene device, comprising the following steps:

[0006] (1) The styrene tower kettle is provided with a first reboiler and a second reboiler, wherein the hot side medium in the second reboiler is the gas phase material at the top of the benzene and toluene tower, and the cold side medium is the styrene tower kettle material; the hot side medium in the first reboiler is the low-pressure steam from the outside, and the cold side medium is the styrene tower kettle material;

[0007] (2) The gas phase material at the top of the benzene toluene tower after heat exchange in the second reboiler is converted into a liquid material and refluxed to the benzene toluene tower for reuse.

[0008] In the method for heat-combined energy saving of a styrene device according to the present invention, preferably,

[0009] The materials in the kettle of the styrene tower are divided into two parts, one part enters the first reboiler, and the other part enters the second reboiler;

[0010] Taking the total mass of the styrene tower bottom material as 100%, the bottom material allocated to the second reboiler accounts for 10% to 100%. In the present invention, the bottom material allocated to the second reboiler accounts for 10% to 100%. Under normal operation, the newly added second reboiler is used as the main reboiler, which can save steam consumption to the greatest extent and achieve the purpose of energy saving.

[0011] In the method for heat-combined energy saving of a styrene device according to the present invention, preferably,

[0012] In step (2), the gaseous material at the top of the benzene toluene tower after heat exchange in the second reboiler is collected, the gaseous phase is condensed into liquid and mixed with the collected liquid phase material, and refluxed to the benzene toluene tower for reuse.

[0013] In the method for heat-combined energy saving of a styrene device according to the present invention, preferably,

[0014] The temperature of the gas phase material at the top of the benzene toluene tower before heat exchange is 123-125°C; and / or,

[0015] The temperature of the gas phase material at the top of the benzene toluene tower after heat exchange is 100-102.92°C; and / or,

[0016] The temperature of the material in the kettle of the styrene tower after heat exchange is 90-93.26℃.

[0017] The second object of the present invention is to provide a thermal combined energy-saving system for a styrene device, the system comprising a benzene toluene tower and a styrene tower;

[0018] The bottom of the styrene tower is provided with a first reboiler and a second reboiler; the top gas phase material outlet of the benzene toluene tower is connected to the hot side medium material inlet of the second reboiler, and the hot side medium material outlet of the second reboiler is connected to the material inlet of the benzene toluene tower through a reflux device; the cold side medium material inlets of the first reboiler and the second reboiler are respectively connected to the bottom material outlet of the styrene tower, and the hot side medium material inlet of the first reboiler is connected to the material outlet of the external low-pressure steam pipeline.

[0019] In the heat-combined energy-saving system for a styrene device of the present invention, preferably,

[0020] A liquid distribution system for distributing the styrene tower kettle material is also provided between the first reboiler and the second reboiler;

[0021] Preferably,

[0022] The liquid distribution system includes a first liquid level measuring device arranged on the reflux tank of the first reboiler and a flow control device arranged at the outlet of the styrene tower kettle; the flow control device includes a flow meter and a regulating pump, and the first liquid level measuring device, the flow meter and the regulating pump are electrically connected; wherein the flow meter receives the signal of the first liquid level measuring device, and sends a signal to the regulating pump to control the outlet flow of the regulating pump, thereby distributing the liquid amount of the styrene tower kettle material flowing into the first reboiler and the second reboiler.

[0023] In the heat-combined energy-saving system for a styrene device of the present invention, preferably,

[0024] The second reboiler is selected from a thermosyphon reboiler; and / or,

[0025] The first liquid level measuring device is a liquid level gauge; and / or,

[0026] The flow meter is a flow meter with remote transmission function; and / or,

[0027] The regulating pump is a regulating pump with a regulating valve.

[0028] In the heat-combined energy-saving system for a styrene device of the present invention, preferably,

[0029] The reflux device comprises a second reboiler reflux tank and a benzene toluene tower reflux tank; the hot side medium material outlet of the second reboiler is connected to the material inlet of the second reboiler reflux tank; the gas phase outlet of the second reboiler reflux tank is connected to the condensate material inlet of the benzene toluene tower reflux tank; the liquid phase outlet of the second reboiler reflux tank is connected to the liquid phase inlet of the benzene toluene tower reflux tank; the liquid phase outlet of the benzene toluene tower reflux tank is connected to the material inlet of the benzene toluene tower;

[0030] Preferably, a condenser is also provided on the connecting pipe between the second reboiler reflux tank and the benzene toluene tower reflux tank.

[0031] In the heat-combined energy-saving system for a styrene device of the present invention, preferably,

[0032] Controlling the liquid level in the first reboiler to be 60%-70% of the height of the first reboiler;

[0033] Preferably,

[0034] The second reboiler reflux drum is also provided with a second liquid level measuring device.

[0035] When the liquid level fluctuation of the second liquid level measuring device exceeds the warning value, the technicians can promptly know the operating status of the system and can promptly adjust the liquid distribution in the liquid distribution system to ensure that the bottom reboiler operates smoothly and controllably.

[0036] The third object of the present invention is to provide an application of the energy-saving method as described in one of the objects of the present invention or the energy-saving system as described in the second object of the present invention in styrene production.

[0037] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be considered as specifically disclosed in this article.

[0038] Compared with the prior art, the present invention has at least the following advantages:

[0039] The present invention proposes for the first time a highly efficient way to utilize the low-temperature heat of the gas phase at the top of the benzene toluene tower. By matching the heat energy in the styrene unit, adding a second reboiler for heat exchange, and using the low-temperature heat for tower kettle heating, the steam consumption is further reduced, and energy integration for emergency use is achieved while achieving the purpose of energy saving and consumption reduction.

[0040] The system of the present invention is particularly suitable for domestically operated styrene units, and only relevant operating parameters need to be adjusted accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a system diagram for the heat-combined energy saving of the styrene device of the present invention.

[0042] Description of reference numerals:

[0043] 1-styrene tower, 2-first reboiler, 3-second reboiler, 4-first delivery pump, 5-second reboiler reflux tank, 6-second delivery pump, 7-condenser, 8-benzene toluene tower reflux tank, 9-third delivery pump, 10-benzene toluene tower, 11-benzene toluene tower reboiler, 12-fourth delivery pump. DETAILED DESCRIPTION

[0044] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0045] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0046] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0047] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0048] Comparative Example 1

[0049] The system of the present invention is used in a device for producing styrene, and benzene and toluene are byproducts of producing styrene. After the reaction of producing styrene is completed, it first enters a light component removal tower to separate crude styrene and light components. The top material of the light component removal tower enters a benzene and toluene tower, and the bottom material enters a styrene tower. Finally, byproduct benzene and toluene and the desired product styrene are separated. In the prior art, in the original system of the device for producing styrene, there is no connection between the styrene tower and the benzene and toluene tower.

[0050] In the original system of the benzene toluene tower of a certain styrene device in the prior art: the gas phase at the top of the benzene toluene tower is cooled by two circulating water coolers and then enters the reflux tank, and the liquid phase returns to the benzene toluene tower for further separation. The gas phase is discharged from the top of the tank and enters the subsequent process flow. In the original system of the styrene tower, the crude styrene from the previous process flow enters the styrene tower for separation, and the heat source of the styrene tower kettle reboiler comes from low-pressure steam. It can be seen that in the original process flow, the gas phase at the top of the benzene toluene tower exchanges heat with the circulating cooling water. This process requires the consumption of a large amount of circulating cooling water. At the same time, the low-temperature heat source rich in the gas phase at the top of the tower is not fully utilized, resulting in a large amount of heat energy waste.

[0051] In addition, in the prior art, if the top gas of styrene is passed into the reboiler of its tower kettle as a heating heat source, or the top gas of benzene and toluene is passed into the reboiler of its tower kettle as a heating heat source, the heat pump technology needs to add a compressor, the investment of the equipment itself will be greatly increased, the required floor space will also be greatly increased, and the consumption of other public engineering materials and power consumption will also increase a lot; and benzene and toluene are highly toxic media, and the use and selection requirements of the compressor itself are also very high. However, the present invention only adds a second reboiler to the tower kettle of styrene, and uses the top gas phase of the benzene and toluene tower as the heat source of the tower kettle reboiler of the styrene tower. Not only does it not need to add equipment such as compressors, but it can also make full use of the heat contained in the top gas phase of the benzene and toluene tower, saving the steam used for heating the tower kettle reboiler and the circulating water used for cooling the top gas phase in the original process flow, so as to achieve the purpose of energy saving and consumption reduction. Therefore, the energy-saving method used in the present invention saves equipment investment, and the requirements for equipment layout and floor space are also very low.

[0052] Example 1

[0053] To solve the above problems, the present invention proposes Figure 1 The system diagram of the thermal combined energy saving of the benzene-toluene-styrene device of the present invention is shown. The thermal combined energy saving system of the styrene device comprises a benzene-toluene tower 10 and a styrene tower 1; the bottom of the styrene tower is provided with a first reboiler 2 and a second reboiler 3, and the second reboiler is selected from a thermal siphon reboiler; the top gas phase material outlet of the benzene-toluene tower is connected to the hot side medium material inlet of the second reboiler, and the hot side medium material outlet of the second reboiler is connected to the material inlet of the benzene-toluene tower through a reflux device; the cold side medium material inlets of the first reboiler and the second reboiler are respectively connected to the bottom material outlet of the styrene tower, and the hot side medium material inlet of the first reboiler is connected to the material outlet of the external low-pressure steam pipeline. The material in the bottom of the styrene tower can also be transported out through the first delivery pump 4 later.

[0054] Preferably, a liquid distribution system for distributing styrene tower kettle material is also provided between the first reboiler and the second reboiler; the liquid distribution system comprises a first liquid level measuring device arranged on the reflux tank of the first reboiler and a flow control device arranged at the outlet of the styrene tower kettle; the flow control device comprises a flow meter and a regulating pump, the first liquid level measuring device is a liquid level meter; the flow meter is a flow meter with a remote transmission function; the regulating pump is a regulating pump with a regulating valve, and the first liquid level measuring device, the flow meter and the regulating pump are electrically connected; wherein the flow meter receives a signal from the first liquid level measuring device, and sends a signal to the regulating pump to control the outlet flow of the regulating pump, thereby distributing the liquid amount of the styrene tower kettle material flowing into the first reboiler and the second reboiler.

[0055] Preferably, the reflux device includes a second reboiler reflux tank 5 and a benzene toluene tower reflux tank 8; the hot side medium material outlet of the second reboiler is connected to the material inlet of the second reboiler reflux tank; the gas phase outlet of the second reboiler reflux tank is connected to the condensate material inlet of the benzene toluene tower reflux tank; the liquid phase outlet of the second reboiler reflux tank is connected to the liquid phase inlet of the benzene toluene tower reflux tank, and the two are transported liquid phase materials through the second delivery pump 6; the liquid phase outlet of the benzene toluene tower reflux tank is connected to the material inlet of the benzene toluene tower, and the two are transported liquid phase materials through the third delivery pump 9; the connecting pipeline between the second reboiler reflux tank and the benzene toluene tower reflux tank is also provided with a circulating water condenser 7. The benzene toluene tower kettle is provided with a benzene toluene tower reboiler 11, and the materials in the benzene toluene tower kettle are transported out through the fourth delivery pump 12.

[0056] Preferably, the liquid level in the first reboiler is controlled to be 60%-70% of the height of the first reboiler;

[0057] Preferably, the second reboiler reflux drum is also provided with a second liquid level measuring device (i.e., Figure 1 LC in the figure is a liquid level controller). Other symbols in the drawings of the present invention are commonly used abbreviations in the art.

[0058] As can be seen from the above, the present invention adds a second reboiler on the basis of the original first reboiler of the styrene tower and uses it together with the original tower kettle reboiler as the styrene tower kettle reboiler. The newly added second reboiler heat source comes from the gas phase at the top of the benzene toluene tower, which returns to the second reboiler reflux tank after heat exchange with the styrene tower kettle material. The gas phase enters the benzene toluene tower reflux tank after being cooled by the circulating water cooler from the top of the second reboiler reflux tank, and the liquid phase is discharged from the bottom of the second reboiler reflux tank and transported to the benzene toluene tower reflux tank through the second reboiler reflux pump. After liquid separation in the benzene toluene tower reflux tank, the gas phase is discharged from the top of the tank, and the liquid phase is transported back to the benzene toluene tower as the top reflux of the benzene toluene tower through the benzene toluene tower reflux pump for subsequent separation. The newly added second reboiler shares the heat load of the original styrene tower kettle reboiler to a certain extent, reducing the consumption of external low-pressure steam in the original process flow. At the same time, the top gas phase of the benzene toluene tower exchanges heat with the bottom material of the styrene tower, which also reduces the consumption of circulating cooling water required for cooling the top gas phase of the benzene toluene tower.

[0059] In order to ensure that the device operates smoothly and controllably, multiple control points are set in the entire process flow. A liquid level control point is added to the reflux tank of the original tower kettle reboiler, and a flow control point is set at the outlet of the styrene tower kettle. The set value of the flow control point is given by the original tower kettle reboiler liquid level controller. The amount of styrene tower kettle material entering the newly added second reboiler is adjusted by setting the above control points, so that it can bear part of the heat load of the tower kettle reboiler, reduce the amount of steam, and achieve the purpose of energy saving and consumption reduction. Furthermore, the second reboiler reflux tank is also provided with a second liquid level measuring device. When the liquid level of the second reboiler reflux tank cannot be maintained within the normal value range by adjusting the flow of the original tower kettle reboiler reflux pump, the set value of the flow control point will be reset to keep the entire system running smoothly and the operation controllable.

[0060] In addition, if the second reboiler is not increased, the benzene toluene tower overhead gas is directly passed into the first reboiler hot side, the first is that the benzene toluene tower overhead gas will bring in more water in a relatively long time, which has a great impact on the subsequent separation link. The second is that it is difficult to achieve in control, if the feeding condition fluctuation of the tower mentioned at the beginning occurs, when the temperature of the benzene toluene tower overhead gas phase temperature and the styrene tower reactor material changes, there will be no means of regulation, so that the operation of the two towers is returned to stability. So the present invention adopts the mode of increasing the second reboiler, if the fluctuation can be through the distribution of a heat load, that is, the increase or reduction of the external low-pressure steam heat source, it is ensured that the heat provided can meet the requirement of the tower whose operating conditions have changed.

[0061] Comparative Example 2

[0062] The benzene toluene tower involved in this application is a positive pressure tower, the tower top operating pressure is 80kPaG, the benzene toluene tower top gas phase flow rate is 32t / h, and the temperature is 127.6°C. In the original process flow of Comparative Example 1, the tower top gas phase is cooled to 115°C by two circulating cooling water heat exchangers before entering the subsequent process flow. The heat load of the circulating water heat exchanger used to cool the tower top gas phase is 4.0MW.

[0063] Example 2

[0064] The benzene toluene tower involved in this application is a positive pressure tower, the top operating pressure is 80kPaG, the top gas flow rate of the benzene toluene tower is 32t / h, and the temperature is 127.6℃. Figure 1The device shown adopts the improved process flow of Example 1, and the gas phase at the top of the benzene toluene tower is used as the heat source of the newly added thermal syphon reboiler of the styrene tower to heat the styrene tower kettle material. The average temperature of the styrene tower kettle material after heat exchange is about 91.38°C, and the temperature of the gas phase material at the top of the benzene toluene tower after heat exchange is between 100-102.92°C. By adding liquid level control to the original tower kettle reboiler, the flow distribution of the styrene tower kettle material between the two reboilers is controlled. Depending on the operation of the system, after the system is stably operated, the total mass of the styrene tower kettle material is 100%, and the proportion of the tower kettle material allocated to the second reboiler is 70%, so that the newly added thermal syphon reboiler shares part of the heat load of the tower kettle while ensuring that the device operates smoothly and controllably. This process saves 328t of cooling water consumption and 3.5MW of energy consumption.

[0065] Comparative Example 3

[0066] The gas phase flow rate of the benzene and toluene tower top is 19.2t / h, the tower top operating pressure is 80kPaG, and the temperature is 127.6°C. In the original process flow of Comparative Example 1, the tower top gas phase is cooled to 115°C by two circulating cooling water heat exchangers before entering the subsequent process flow. The heat load of the circulating water heat exchanger used to cool the tower top gas phase is 2.4MW.

[0067] Example 3

[0068] The gas phase flow rate of the benzene and toluene tower top is 19.2t / h, the tower top operating pressure is 80kPaG, and the temperature is 127.6℃. Figure 1 The device shown adopts the improved process flow of Example 1, and the gas phase at the top of the benzene toluene tower is used as the heat source of the newly added thermal syphon reboiler of the styrene tower to heat the styrene tower kettle material. The average temperature of the styrene tower kettle material after heat exchange is about 91.38°C, and the temperature of the gas phase material at the top of the benzene toluene tower after heat exchange is between 100-102.92°C. By adding liquid level control to the original tower kettle reboiler, the flow distribution of the styrene tower kettle material between the two reboilers is controlled. Depending on the operation of the system, after the system is stably operated, the total mass of the styrene tower kettle material is 100%, and the proportion of the tower kettle material allocated to the second reboiler is 40%, so that the newly added thermal syphon reboiler shares part of the heat load of the tower kettle while ensuring that the device operates smoothly and controllably. This process saves 196.8t of cooling water consumption and 2.1MW of energy consumption.

[0069] Based on the above results, the method of the present invention is used for process heating, which reduces the consumption of steam and circulating cooling water and realizes the joint utilization of heat between devices.

[0070] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0071] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0072] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0073] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

Claims

1. A method for heat-combined energy saving in a styrene device, characterized in that: The following steps are involved: (1) The styrene tower kettle is provided with a first reboiler and a second reboiler, wherein the hot side medium in the second reboiler is the gas phase material at the top of the benzene and toluene tower, and the cold side medium is the styrene tower kettle material; the hot side medium in the first reboiler is the low-pressure steam from the outside, and the cold side medium is the styrene tower kettle material; (2) The gas phase material at the top of the benzene toluene tower after heat exchange in the second reboiler is converted into a liquid material and refluxed to the benzene toluene tower for reuse.

2. The method for heat-combined energy saving of a styrene device according to claim 1, characterized in that: The materials in the kettle of the styrene tower are divided into two parts, one part enters the first reboiler, and the other part enters the second reboiler; Based on the total mass of the bottom material of the styrene tower being 100%, the proportion of the bottom material allocated to the second reboiler is 10% to 100%.

3. The method for heat-combined energy saving of a styrene device according to claim 1, characterized in that: In step (2), the gaseous material at the top of the benzene toluene tower after heat exchange in the second reboiler is collected, the gaseous phase is condensed into liquid and mixed with the collected liquid phase material, and refluxed to the benzene toluene tower for reuse.

4. The method for heat-combined energy saving of a styrene device according to claim 1, characterized in that: The temperature of the gas phase material at the top of the benzene toluene tower before heat exchange is 123-125°C; and / or, The temperature of the gas phase material at the top of the benzene toluene tower after heat exchange is 100-102.92°C; and / or, The temperature of the material in the kettle of the styrene tower after heat exchange is 90-93.26℃.

5. A heat-combined energy-saving system for a styrene plant, characterized in that: The system includes a benzene toluene tower and a styrene tower; The bottom of the styrene tower is provided with a first reboiler and a second reboiler; the top gas phase material outlet of the benzene toluene tower is connected to the hot side medium material inlet of the second reboiler, and the hot side medium material outlet of the second reboiler is connected to the material inlet of the benzene toluene tower through a reflux device; the cold side medium material inlets of the first reboiler and the second reboiler are respectively connected to the bottom material outlet of the styrene tower, and the hot side medium material inlet of the first reboiler is connected to the material outlet of the external low-pressure steam pipeline.

6. The heat-combined energy-saving system for a styrene plant according to claim 5, characterized in that: A liquid distribution system for distributing the styrene tower kettle material is also provided between the first reboiler and the second reboiler; Preferably, The liquid distribution system includes a first liquid level measuring device arranged on the reflux tank of the first reboiler and a flow control device arranged at the outlet of the styrene tower kettle; the flow control device includes a flow meter and a regulating pump, and the first liquid level measuring device, the flow meter and the regulating pump are electrically connected; wherein the flow meter receives the signal of the first liquid level measuring device, and sends a signal to the regulating pump to control the outlet flow of the regulating pump, thereby distributing the liquid amount of the styrene tower kettle material flowing into the first reboiler and the second reboiler.

7. The heat-combined energy-saving system for a styrene plant according to claim 6, characterized in that: The second reboiler is selected from a thermosyphon reboiler; and / or, The first liquid level measuring device is a liquid level gauge; and / or, The flow meter is a flow meter with remote transmission function; and / or, The regulating pump is a regulating pump with a regulating valve.

8. The heat-combined energy-saving system for a styrene plant according to claim 5, characterized in that: The reflux device comprises a second reboiler reflux tank and a benzene toluene tower reflux tank; the hot side medium material outlet of the second reboiler is connected to the material inlet of the second reboiler reflux tank; the gas phase outlet of the second reboiler reflux tank is connected to the condensate material inlet of the benzene toluene tower reflux tank; the liquid phase outlet of the second reboiler reflux tank is connected to the liquid phase inlet of the benzene toluene tower reflux tank; the liquid phase outlet of the benzene toluene tower reflux tank is connected to the material inlet of the benzene toluene tower; Preferably, a condenser is also provided on the connecting pipe between the second reboiler reflux tank and the benzene toluene tower reflux tank.

9. The heat-combined energy-saving system for a styrene device according to claim 8, characterized in that: Controlling the liquid level in the first reboiler to be 60%-70% of the height of the first reboiler; Preferably, The second reboiler reflux drum is also provided with a second liquid level measuring device.

10. Use of the energy-saving method according to any one of claims 1 to 4 or the energy-saving system according to any one of claims 5 to 9 in styrene production.

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