Phthalic anhydride refining system

Abstract

The utility model provides a phthalic anhydride refining system. A crude phthalic anhydride input pipeline of the phthalic anhydride refining system is used for inputting pretreated crude phthalic anhydride; the flash evaporator is communicated with the crude phthalic anhydride input pipeline and is used for carrying out flash evaporation treatment on the pretreated crude phthalic anhydride to obtain gasified crude phthalic anhydride and discharging crude phthalic anhydride residues obtained after flash evaporation out of the flash evaporator; the refining tower is connected with the flash evaporator and is used for separating light components, phthalic anhydride and phthalic anhydride residues from the gasified crude phthalic anhydride; the light component recovery device is connected with the top of the refining tower and is used for recovering the separated light components; the phthalic anhydride recovery device is connected with the middle part of the refining tower and is used for recovering phthalic anhydride obtained by separation; the residue discharging device is connected with the bottom of the refining tower and is used for discharging phthalic anhydride residues obtained by separation out of the refining tower.

Description

Technical Field

[0001] The utility model relates to the technical field of phthalic anhydride production equipment, and particularly relates to a phthalic anhydride refining system. Background Art

[0002] At the present stage, the refining process of crude phthalic anhydride mainly includes processes such as light component separation, product separation, and residue separation. The production process is that the crude phthalic anhydride produced by the oxidation process enters the light component separation tower, product separation tower, and residue separation tower in sequence for purification by rectification after being pretreated and matured. The impurities are separated and sold externally, and finally pure phthalic anhydride meeting the quality requirements is obtained. The heavy components in the crude phthalic anhydride in the pretreatment tank pass through the light component separation tower, product separation tower, and residue separation tower in sequence and always exist in each tower during the production process, always blocking the trays and bottom heat exchangers of the towers. Moreover, the three towers separately arranged for the light component separation tower, product separation tower, and residue separation tower cause the problem of high equipment investment. Content of the Utility Model

[0003] The purpose of the embodiment of the utility model is to provide a phthalic anhydride refining system.

[0004] The embodiment of the utility model adopts the following technical scheme: A phthalic anhydride refining system includes:

[0005] A crude phthalic anhydride input pipeline, which is used for inputting the pretreated crude phthalic anhydride;

[0006] A flash evaporator, which is connected to the crude phthalic anhydride input pipeline and is used for flash evaporating the pretreated crude phthalic anhydride to obtain vaporized crude phthalic anhydride and discharging the crude phthalic anhydride residue obtained after flash evaporation from the flash evaporator;

[0007] A refining tower, which is connected to the flash evaporator and is used for separating light components, phthalic anhydride, and phthalic anhydride residue from the vaporized crude phthalic anhydride;

[0008] A light component recovery device, which is connected to the top of the refining tower and is used for recovering the separated light components;

[0009] A phthalic anhydride recovery device, which is connected to the middle of the refining tower and is used for recovering the separated phthalic anhydride;

[0010] A residue discharging device, which is connected to the bottom of the refining tower and is used for discharging the separated phthalic anhydride residue from the refining tower.

[0011] In some embodiments, an inlet valve is arranged at the inlet of the flash evaporator, and an outlet valve is arranged at the outlet of the flash evaporator;

[0012] The phthalic anhydride refining system further includes a flash bypass. One end of the flash bypass is connected to the crude phthalic anhydride input pipeline, and the other end is connected to the refining tower. A bypass valve is provided on the flash bypass. When the inlet valve of the flash evaporator is closed, the bypass valve is opened so that the pretreated crude phthalic anhydride can enter the refining tower through the flash bypass.

[0013] In some embodiments, packing and trays are sequentially arranged from top to bottom inside the refining tower.

[0014] In some embodiments, a reboiler is further provided at the bottom of the refining tower, and the reboiler provides heat source for the refining tower.

[0015] In some embodiments, the light component recovery device includes:

[0016] A condenser, which is connected to the top of the refining tower and is used for condensing the separated light components;

[0017] A trap, which is connected to the condenser and is used for trapping the condensed light components;

[0018] A light component tank, which is connected to the trap and is used for storing the light components from the trap.

[0019] In some embodiments, the light component recovery device further includes:

[0020] An ejector, which is respectively connected to the condenser and the trap to inject compressed air into the condenser and the trap so that the pressure in the condenser and the trap reaches the set negative pressure;

[0021] The trap is further connected to a cooling medium pipeline and a heating medium pipeline to trap the light components;

[0022] A nitrogen pipeline, which is connected to the trap and is used for introducing nitrogen into the trap so that the light components trapped by the trap can enter the light component tank.

[0023] In some embodiments, the light component recovery device further includes:

[0024] A light component return pipe, one end of which is connected to the bottom of the condenser and the other end is connected to the refining tower. A return pump is provided on the light component return pipe. When the return pump is turned on, part of the light components at the bottom of the condenser can flow back to the refining tower through the light component return pipe;

[0025] A light component extraction pipe, one end of which is connected to the light component return pipe and the other end is connected to the light component tank to transport part of the light components in the condenser to the light component tank.

[0026] In some embodiments, the light component recovery device further includes:

[0027] A low-pressure steam drum, which is connected to the condenser. The demineralized water in the low-pressure steam drum can enter the condenser to form a siphon, so as to form low-pressure steam in the condenser and receive the low-pressure steam from the condenser;

[0028] A low-pressure steam pipe network, which is connected to the low-pressure steam drum to transport the low-pressure steam from the low-pressure steam drum to the system pipe network.

[0029] In some embodiments, the phthalic anhydride recovery device includes:

[0030] A phthalic anhydride extraction pipeline, one end of which is communicated with the middle part of the refining tower;

[0031] A cooler, which is arranged on the phthalic anhydride extraction pipeline to cool the phthalic anhydride from the refining tower;

[0032] A finished product tank, which is communicated with the other end of the phthalic anhydride extraction pipeline to receive the cooled phthalic anhydride.

[0033] In some embodiments, the phthalic anhydride recovery device further includes:

[0034] A nitrogen system pipeline, which is respectively connected to the finished product tank and the light component tank to introduce nitrogen into the finished product tank and the light component tank respectively.

[0035] The beneficial effects of the embodiments of the present utility model are as follows:

[0036] Before the pretreated crude phthalic anhydride enters the refining tower, it can first enter a flash evaporator. After all the crude anhydride is flashed into gas, it is then sent into the refining tower. The crude phthalic anhydride residue after flashing in the flash evaporator is discharged in advance, which can solve the problem of blockage at the bottom of the refining tower. Integrating the functions of the component separation tower, product separation tower, and residue separation tower in one refining tower reduces equipment investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or related technologies. Obviously, the drawings in the following description are only some embodiments recorded in the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 It is a schematic structural diagram of the phthalic anhydride refining system of the present utility model.

[0039] Reference numerals: 1, crude phthalic anhydride input pipeline; 2, inlet valve; 3, flash evaporator; 3-1, oil inlet pipe; 3-2, oil outlet pipe; 4, outlet valve; 5, bypass valve; 6, water inlet valve; 7, water outlet valve; 8, in-tower reflux pipeline; 9, phthalic anhydride extraction pipeline; 10-1, refining tower; 10-2, reboiler; 11, residue kettle; 12, slag discharge valve; 13, phthalic anhydride slag box; 14, condenser; 15, low-pressure steam drum; 16, light component reflux pipe; 17, light component extraction pipe; 18, reflux pump; 19, cooler; 20, make-up water system; 20-1, low-pressure steam pipe network; 21, negative pressure connection pipeline; 22, capture box; 24, cooling medium water pipeline; 25, steam pipeline; 26, nitrogen; 29, compressed air; 30, ejector; 31, regenerative incineration; 32, light component connection pipeline; 33, nitrogen system pipeline; 34, finished product tank; 35, finished product transfer pump; 36, light component tank. Detailed implementation manners

[0040] Reference is made herein to the accompanying drawings to describe the various aspects and features of the present application.

[0041] It should be understood that various modifications can be made to the embodiments claimed herein. Accordingly, the above description should not be construed as limiting, but merely as exemplary of the embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present application.

[0042] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.

[0043] These and other features of the present application will become apparent from the following description of the preferred forms of the embodiments, given by way of non-limiting example with reference to the accompanying drawings.

[0044] It should also be understood that, although the present application has been described with reference to some specific examples, those skilled in the art can surely implement many other equivalent forms of the present application.

[0045] When considered in conjunction with the accompanying drawings, the above and other aspects, features and advantages of the present application will become more apparent in view of the following detailed description.

[0046] Specific embodiments of the present application will be described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments claimed are merely examples of the present application and may be implemented in various ways. Well-known and / or repetitive functions and structures are not described in detail to avoid obscuring the present application with unnecessary or redundant details. Accordingly, the specific structural and functional details claimed herein are not intended to be limiting, but rather are merely a basis and representative basis for the claims to teach those skilled in the art to use the present application in substantially any suitable detailed structure in a variety of ways.

[0047] This specification may use the phrases "in one embodiment", "in another embodiment", "in yet another embodiment", or "in other embodiments", all of which may refer to one or more of the same or different embodiments according to the present application.

[0048] Before introducing the present utility model, the phthalic anhydride and its refining principle will be described first.

[0049] Phthalic anhydride is abbreviated as PA, with a freezing point of 130.5 °C and a molecular formula of C8H4O3. Phthalic acid can be dehydrated at 200 °C to form phthalic anhydride, and phthalic anhydride is a colorless needle-like and small flaky rhombic or monoclinic crystal. Industrial phthalic anhydride is in the form of white flakes or in a molten state, has sublimability, and has a special slight pungent odor.

[0050] The light components of phthalic anhydride are mainly maleic anhydride and benzoic acid, and the heavy components are mainly by-products such as naphthoquinone, phthalimide, and tar substances.

[0051] Phthalic anhydride refining principle: Utilizing the different volatilities of the components in the mixture, the material is heated by the tube bundle heater at the bottom of the distillation column to generate an ascending gas phase, which makes full countercurrent contact with the reflux liquid condensed at the top of the column on the trays, and a mass transfer and heat transfer process occurs. The volatile components are vaporized into the gas phase, and the less volatile components are condensed into the liquid phase. In this way, the components in the mixture are fully separated through multiple repetitions. The liquid mixture is partially vaporized multiple times, and at the same time, the generated gas phase is partially condensed multiple times to separate the required components.

[0052] To solve the problems in the background art, the present utility model provides a phthalic anhydride refining system, combined with Figure 1 , the system includes a crude phthalic anhydride input pipeline 1, a flash evaporator 3, a refining column 10-1, a light component recovery device, a phthalic anhydride recovery device, and a residue discharge device.

[0053] Among them, the crude phthalic anhydride input pipeline 1 is used to input the pretreated crude phthalic anhydride. Specifically, the crude phthalic anhydride input pipeline 1 is connected to the pretreatment system of the crude phthalic anhydride, and the crude phthalic anhydride after being processed by the crude phthalic anhydride pretreatment system enters the phthalic anhydride refining system of the embodiment of the present application through the crude phthalic anhydride input pipeline 1.

[0054] The flash evaporator 3 is connected to the crude phthalic anhydride input pipeline 1 and is used for flash evaporation of the pretreated crude phthalic anhydride to obtain vaporized crude phthalic anhydride, and discharging the crude phthalic anhydride residue obtained after flash evaporation from the flash evaporator 3. A flash evaporator 3 is added before entering the refining tower 10-1 after the pretreatment process. After all the liquid crude phthalic anhydride is heated and flash evaporated into gas in the flash evaporator 3, it enters the refining tower 10-1 through pipeline structures such as a gas guide cylinder.

[0055] The flash evaporator 3 can be heated by heat transfer oil, with a working pressure of slightly negative pressure and a vertical structure. It has tube bundles, and the slag is discharged at the lower part and flows into the bottom of the residue tower by gravity, and the slag discharge rate is 10-20%. Of course, it can be understood that the flash evaporator 3 can also adopt a horizontal structure, and the specific structure is not limited. The heat exchange area of the gas guide cylinder at the upper part of the flash evaporator 3 can be about 100 m 2 or so. Of course, the specific heat exchange area can be set according to specific production needs. After adding the flash evaporator 3 to this phthalic anhydride refining system, the crude phthalic anhydride residue can be removed in advance, avoiding the heavy components in the crude phthalic anhydride from causing blockage of structures such as the bottom reboiler 10-2 of the refining tower 10-1, and can solve the blockage problems of structures such as the bottom reboiler 10-2 of the refining tower 10-1.

[0056] The flash evaporator 3 also includes a water inlet valve 6 and a water outlet valve 7 to realize the cooling of the flash evaporator 3.

[0057] The refining tower 10-1 is connected to the flash evaporator 3 and is used for separating light components, phthalic anhydride and phthalic anhydride residue from the vaporized crude phthalic anhydride. A reboiler 10-2 is also provided at the bottom of the refining tower 10-1, and the reboiler 10-2 provides heat source for the refining tower 10-1.

[0058] Specifically, the bottom reboiler 10-2 of the refining tower 10-1 heats the circulating material to provide heat source for the bottom of the tower. Packings and trays are installed in the refining tower 10-1 from top to bottom. Light components are separated at the top of the tower, phthalic anhydride is separated in the middle, and sub-heavy phthalic anhydride (phthalic anhydride residue) is separated at the bottom of the tower.

[0059] The light component recovery device is connected to the top of the refining tower 10-1 and is used for recovering the separated light components.

[0060] In some embodiments, the light component recovery device may include a condenser 14, a trap and a light component tank 36.

[0061] Among them, the condenser 14 is connected to the top of the refining tower 10-1 and is used for condensing the separated light components.

[0062] The trap is connected to the condenser 14 and is used for trapping the condensed light components. There may be two traps, one for standby and one for use, and they can be switched regularly. The trap can adopt the structural form of a trap box 22. The condenser 14 can be connected to the trap by a negative pressure pipeline.

[0063] The light component tank 36 is connected to the trap and is used to store the light components from the trap.

[0064] In some embodiments, the light component recovery device further includes:

[0065] An ejector 30, which is respectively connected to the condenser 14 and the trap, to inject compressed air 29 into the condenser 14 and the trap, so that the pressure inside the condenser 14 and the trap reaches the set negative pressure.

[0066] The trap is also connected to a cooling medium pipeline (cooling medium water pipeline 24) and a heating medium pipeline (steam pipeline 25) to capture the light components.

[0067] The nitrogen pipeline is connected to the trap and is used to introduce nitrogen 26 into the trap, so that the light components captured by the trap can enter the light component tank 36.

[0068] In some embodiments, the light component recovery device further includes:

[0069] A light component reflux pipe 16, one end of which is communicated with the bottom of the condenser 14, and the other end of which is communicated with the refining tower 10-1. A reflux pump 18 is arranged on the light component reflux pipe 16. When the reflux pump 18 is turned on, part of the light components at the bottom of the condenser 14 can flow back into the refining tower 10-1 through the light component reflux pipe 16.

[0070] A light component extraction pipe 17, one end of which is communicated with the light component reflux pipe 16, and the other end of which is communicated with the light component tank 36, to transport part of the light components in the condenser 14 to the light component tank 36.

[0071] In some embodiments, the light component recovery device further includes:

[0072] A low-pressure steam drum 15, which is connected to the condenser 14. The demineralized water in the low-pressure steam drum 15 can enter the condenser 14 to form a siphon, so as to form low-pressure steam in the condenser 14 and receive the low-pressure steam from the condenser 14.

[0073] A low-pressure steam pipe network 20-1, which is connected to the low-pressure steam drum 15 to transport the low-pressure steam from the low-pressure steam drum 15 to the system pipe network.

[0074] In one embodiment, the light components separated from the top of the tower enter the condenser 14. The cooling medium of the condenser 14 is connected to the low-pressure steam drum 15. The demineralized water in the low-pressure steam drum 15 enters the condenser 14 to form a siphon, generating low-pressure steam that enters the low-pressure steam drum 15. The water replenishing system 20 of the low-pressure steam drum 15 maintains the low-pressure steam drum 15 at a certain liquid level, and the generated low-pressure steam (for example, with a pressure of 0.3 Mpa) is transported to the system pipe network through the low-pressure steam pipe network 20-1.

[0075] The condenser 14 is connected to the capture tank 22 through a negative pressure connection pipe 21. The capture tank 22 has one in use and one in reserve, and they are switched regularly. The light components are captured and recycled. Compressed air 29 at 150 °C uses an ejector 30 to draw a negative pressure of the condenser 14 and the capture tank 22 system to -90 Kpa. The outlet of the ejector 30 is connected to a regenerative incinerator 31 to treat waste gas. Cooling medium water is introduced into the capture tank 22 to cool down and capture the light components for recycling. After the fins in the capture tank 22 are full of captured components, the standby capture tank 22 is put into use. The cooling medium water pipe 24 of this capture tank 22 is closed, and steam is introduced into the steam pipe 25 to heat and melt the materials. Nitrogen 26 is used to blow and press the melted light components into the light component tank 36 through the light component connection pipe 32.

[0076] The reflux pump 18 extracts the light components in the condenser 14. Part of them forms a reflux into the refining tower 10-1 through the light component reflux pipe 16, and part of them goes into the light component tank 36 through the light component extraction pipe 17.

[0077] The phthalic anhydride recovery device is connected to the middle part of the refining tower 10-1 for recovering the phthalic anhydride obtained by separation.

[0078] In some embodiments, the phthalic anhydride recovery device includes:

[0079] The phthalic anhydride extraction pipe 9, one end of which communicates with the middle part of the refining tower 10-1.

[0080] The cooler 19 is arranged on the phthalic anhydride extraction pipe 9 to cool the phthalic anhydride from the refining tower 10-1.

[0081] The finished product tank 34 is communicated with the other end of the phthalic anhydride extraction pipe 9 to receive the cooled phthalic anhydride.

[0082] The phthalic anhydride recovery device further includes: a nitrogen system pipe 33, which is respectively connected to the finished product tank 34 and the light component tank 36 to introduce nitrogen into the finished product tank 34 and the light component tank 36 respectively.

[0083] The phthalic anhydride product passes through the extraction pipe. Since the temperature of the extraction pipe is relatively high, it is cooled to 160 °C - 180 °C by the product cooler 19 and then sent to the finished product tank 34. The finished product tank 34 is connected to the finished product transfer pump 35 for external sale or sent to flaking.

[0084] The nitrogen system pipe 33 is introduced into the finished product tank 34 to form a nitrogen seal to prevent air from entering and forming an explosive space. When the nitrogen system pipe 33 is introduced into the light component tank 36, the phthalic anhydride is pressed into the light component separation system again for separation and recovery by relying on the nitrogen pressure.

[0085] The residue discharge device is connected to the bottom of the refining tower 10-1 for discharging the phthalic anhydride residue obtained by separation from the refining tower 10-1.

[0086] The phthalic anhydride refining system may further include a residue kettle 11, which is respectively connected to the bottom of the flash evaporator 3 and the bottom of the refining tower 10-1 to receive the crude phthalic anhydride residue from the flash evaporator 3 and the phthalic anhydride residue from the refining tower 10-1. When the phthalic anhydride purity in the residue kettle 11 is lower than 40%, it is discharged into the phthalic anhydride residue tank 13 and can be sold after solidification.

[0087] The refining tower 10-1 may further include an internal reflux pipeline 8 to realize the cyclic refining of crude phthalic anhydride in the refining tower 10-1.

[0088] In some embodiments, an inlet valve 2 is provided at the inlet of the flash evaporator 3, and an outlet valve 4 is provided at the outlet of the flash evaporator 3.

[0089] The phthalic anhydride refining system further includes a flash bypass. One end of the flash bypass is connected to the crude phthalic anhydride input pipeline 1, and the other end is connected to the refining tower 10-1. A bypass valve is provided on the flash bypass. When the inlet valve 2 of the flash evaporator 3 is closed, the bypass valve is opened so that the pretreated crude phthalic anhydride can enter the refining tower 10-1 through the flash bypass.

[0090] The crude phthalic anhydride enters the flash evaporator 3 through the inlet valve 2 of the flash evaporator 3 from the crude phthalic anhydride input pipeline 1. The heat transfer oil for heating the flash evaporator 3 is heated through the oil inlet pipe 3-1 into the flash evaporator 3, and the crude phthalic anhydride in the flash evaporator 3 is heated and vaporized and enters the refining tower 10-1. The heat transfer oil can return to the electric heater through the oil outlet pipe 3-2 of the flash evaporator 3 for heating circulation.

[0091] When the flash evaporator 3 is under maintenance, the inlet valve 2 and the outlet valve 4 of the flash evaporator 3 are closed, the bypass valve of the flash evaporator 3 is opened to enter the refining tower 10-1 for normal production, the bottom slag discharge valve 12 of the refining tower 10-1 is closed, and the valve to the residue kettle 11 is opened for slag evaporation. When the flash evaporator 3 is in normal use, the bottom slag discharge valve 12 is normally open at intervals, and the residue can be sent to the pretreatment system, and after pretreatment, it circulates into the phthalic anhydride refining system to recycle phthalic anhydride again.

[0092] The phthalic anhydride refining system can solve the problem of blockage of phthalic anhydride refining equipment, avoid steaming the tower, boiling the tower or shutting down to replace the tower trays and packing, and extend the operation cycle of the device. The refining and separation process has the efficiency of three towers in one (combining the light component tower, the product tower and the residue tower into one tower), and has the characteristics of low investment, low energy consumption and excellent product quality. Before the crude phthalic anhydride enters the refining tower 10-1, it first enters the flash evaporator 3. After all the liquid crude anhydride is flashed into gas in the flash evaporator 3, it enters the light component tower through the gas guide cylinder. The residue after adding the flash evaporator 3 can be discharged in advance, which can solve the problem of blockage of the bottom reboiler 10-2 of the refining tower 10-1. When the flash evaporator 3 is regularly cleaned, it directly enters the refining tower 10-1 from the pretreatment plus bypass pipeline. Such a design extends the operation time of the refining process.

[0093] The above has described multiple embodiments of the present utility model in detail. However, the present utility model is not limited to these specific embodiments. Based on the concept of the present utility model, those skilled in the art can make various variations and modifications to the embodiments, and these variations and modifications should all fall within the scope of protection required by the present utility model.

Claims

1. A phthalic anhydride refining system, characterized in that, Comprising: A crude phthalic anhydride input pipeline for inputting pretreated crude phthalic anhydride; A flash evaporator connected to the crude phthalic anhydride input pipeline, for flash-evaporating the pretreated crude phthalic anhydride to obtain vaporized crude phthalic anhydride, and discharging the crude phthalic anhydride residue obtained after flash evaporation from the flash evaporator; A refining tower connected to the flash evaporator, for separating light components, phthalic anhydride, and phthalic anhydride residue from the vaporized crude phthalic anhydride; A light component recovery device connected to the top of the refining tower, for recovering the separated light components; A phthalic anhydride recovery device connected to the middle of the refining tower, for recovering the separated phthalic anhydride; A residue discharge device connected to the bottom of the refining tower, for discharging the phthalic anhydride residue separated from the refining tower.

2. The phthalic anhydride refining system according to claim 1, characterized in that, An inlet valve is provided at the inlet of the flash evaporator, and an outlet valve is provided at the outlet of the flash evaporator; The phthalic anhydride refining system further includes a flash bypass. One end of the flash bypass is connected to the crude phthalic anhydride input pipeline, and the other end is connected to the refining tower. A bypass valve is provided on the flash bypass. When the inlet valve of the flash evaporator is closed, the bypass valve is opened so that the pretreated crude phthalic anhydride can enter the refining tower through the flash bypass.

3. The phthalic anhydride refining system according to claim 1, characterized in that, Packing and trays are sequentially arranged from top to bottom inside the refining tower.

4. The phthalic anhydride refining system according to claim 1 or 3, characterized in that, A reboiler is further provided at the bottom of the refining tower, and the reboiler provides heat source for the refining tower.

5. The phthalic anhydride refining system according to claim 1, wherein The light component recovery device includes: A condenser connected to the top of the refining tower, for condensing the separated light components; A trap connected to the condenser, for trapping the condensed light components; A light component tank connected to the trap, for storing the light components from the trap.

6. The phthalic anhydride refining system according to claim 5, wherein The light component recovery device further includes: An ejector connected to the condenser and the trap respectively, for injecting compressed air into the condenser and the trap so that the pressure inside the condenser and the trap reaches the set negative pressure; The trap is further connected to a cooling medium pipeline and a heating medium pipeline to trap the light components; A nitrogen pipeline connected to the trap, for introducing nitrogen into the trap so that the light components trapped by the trap can enter the light component tank.

7. The phthalic anhydride refining system according to claim 5, characterized in that, The light component recovery device further includes: A light component return pipe, one end of which is communicated with the bottom of the condenser, and the other end is communicated with the refining tower. A return pump is provided on the light component return pipe. When the return pump is turned on, part of the light components at the bottom of the condenser can flow back to the refining tower through the light component return pipe; A light component extraction pipe, one end of which is communicated with the light component return pipe, and the other end is communicated with the light component tank to transport part of the light components in the condenser to the light component tank.

8. The phthalic anhydride refining system according to claim 5, wherein, The light component recovery device further includes: A low-pressure steam drum connected to the condenser. The demineralized water in the low-pressure steam drum can enter the condenser to form a siphon, so as to form low-pressure steam in the condenser and receive the low-pressure steam from the condenser; A low-pressure steam pipe network, which is connected to the low-pressure steam drum to transport the low-pressure steam from the low-pressure steam drum to the system pipe network.

9. The phthalic anhydride refining system according to claim 5, wherein, The phthalic anhydride recovery device includes: A phthalic anhydride extraction pipeline, one end of which is communicated with the middle part of the refining tower; A cooler, which is arranged on the phthalic anhydride extraction pipeline to cool the phthalic anhydride from the refining tower; A finished product tank, which is communicated with the other end of the phthalic anhydride extraction pipeline to receive the cooled phthalic anhydride.

10. The phthalic anhydride refining system according to claim 9, wherein, The phthalic anhydride recovery device further includes: A nitrogen system pipeline, which is respectively connected to the finished product tank and the light component tank to introduce nitrogen into the finished product tank and the light component tank respectively.

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