System and method for removing VOC (Volatile Organic Compounds) from polyolefin resin powder

Abstract

The invention provides a system and a method for removing VOC (Volatile Organic Compounds) from polyolefin resin powder, and belongs to the field of production of polyolefin resin powder. The system comprises a high-temperature degassing bin; a filter; the tail gas recoverer is communicated with the filter; the inlet end of the first-stage nitrogen supply loop is communicated with the nitrogen recovery outlet and a fresh nitrogen source, and the outlet end of the first-stage nitrogen supply loop is connected to the middle upper part of the high-temperature degassing bin through a first-stage nitrogen heater and a first-stage nitrogen distributor; the inlet end of the multi-stage nitrogen supply loop is communicated with a fresh nitrogen source, and the outlet end of the multi-stage nitrogen supply loop is connected to the bottom or the lower part of the high-temperature degassing bin. According to the system for removing the VOC in the polyolefin resin powder, the function design of the core component of the system for removing the VOC in the polyolefin resin powder is optimized, the material flow of the polyolefin resin powder and the airflow of the nitrogen are cooperatively matched, and finally the removal effect of the VOC in the polyolefin resin powder is effectively improved.

Description

Technical Field

[0001] This application relates to the field of polyolefin resin powder production technology, and in particular to a system and method for removing VOCs from polyolefin resin powder. Background Technology

[0002] In the production process of polyolefins, after the polyolefin resin powder produced from the reactor is processed by a low-pressure separation system, most of the unreacted monomers and solvents are separated from the polyolefin resin powder. The separated unreacted monomers and solvents are sent to the tail gas recovery section for recycling. The polyolefin resin powder still carries and adsorbs unreacted monomers and solvents on its surface; these unreacted monomers and solvents are defined as volatile organic compounds (VOCs). The polyolefin resin powder needs to be further processed by a powder product treatment system to remove the VOCs carried and adsorbed on its surface.

[0003] Currently, there are two main methods for removing volatile organic compounds (VOCs) from powder product processing systems: The first method involves low-pressure steam treatment. This involves introducing low-pressure steam into the polyolefin resin powder, which carries away unreacted monomers and solvents entrained in or adsorbed on the surface. The polyolefin resin powder carrying water vapor then enters a drying unit, where hot nitrogen is used to dry the moisture. This low-pressure steam treatment method is quite effective at removing VOCs from polyolefin resin powder, and the odor level of the treated polyolefin resin powder is typically below level 3.

[0004] The second method involves purging with low-temperature nitrogen. The specific operation of this method is as follows: Low-temperature nitrogen gas at a temperature not exceeding 70°C is used to purge the polyolefin resin powder. This low-temperature nitrogen carries away unreacted monomers and solvents adsorbed on the surface of the polyolefin resin powder. The low-temperature nitrogen carrying the unreacted monomers and solvents then enters the VOC and monomer separation and recovery section for further treatment. To deactivate the catalyst and triethylaluminum in the polyolefin resin powder, a small amount of steam is added to the low-temperature nitrogen. This low-temperature nitrogen purging method is not ideal for removing volatile organic compounds (VOCs) from polyolefin resin powder. The odor level of the treated polyolefin resin powder reaches level 4 or higher, which cannot meet the requirements of applications with high VOC removal efficiency.

[0005] In summary, among existing methods for removing VOCs from polyolefin resin powders, low-temperature nitrogen purging has significant limitations in VOC removal efficiency. While low-pressure steam treatment is more effective, it cannot fully meet the VOC removal requirements of all polyolefin production scenarios. Therefore, a stable and efficient technical solution for improving VOC removal efficiency remains lacking in polyolefin production processes. Improving VOC removal efficiency in polyolefin resin powders has become a pressing technical challenge in polyolefin production. Summary of the Invention

[0006] This application provides a system and method for removing VOCs from polyolefin resin powder to solve the following technical problem: how to improve the VOC removal effect in polyolefin resin powder.

[0007] In a first aspect, embodiments of this application provide a system for removing VOCs from polyolefin resin powder, the system comprising: A high-temperature degassing chamber is used to contain and transport polyolefin resin powder, which flows from the top to the bottom of the high-temperature degassing chamber (1) in the form of a plunger flow inside the high-temperature degassing chamber (1). A filter, which is connected to the top of the high-temperature degassing chamber, is used to filter the gas discharged from the top of the high-temperature degassing chamber; A tail gas recovery unit, which is connected to the filter, is used to recover nitrogen, unreacted monomers and solvents discharged from the high-temperature degassing chamber; A primary nitrogen supply circuit is provided, the inlet of which is connected to the nitrogen recovery outlet of the tail gas recovery unit and the fresh nitrogen source. The outlet of the primary nitrogen supply circuit is connected to the upper middle part of the high-temperature degassing chamber through a primary nitrogen heater and a primary nitrogen distributor. This circuit is used to supply primary hot nitrogen to the high-temperature degassing chamber, and the primary hot nitrogen comes into counter-current contact with the downward-flowing polyolefin resin powder to perform primary degassing. A multi-stage nitrogen supply circuit is provided, wherein the inlet end of the multi-stage nitrogen supply circuit is connected to a fresh nitrogen source, and the outlet end of the multi-stage nitrogen supply circuit is connected to the bottom or lower part of the high-temperature degassing chamber through a corresponding multi-stage nitrogen heater and a multi-stage nitrogen distributor, for supplying multi-stage hot nitrogen to the high-temperature degassing chamber, and the multi-stage hot nitrogen comes into counter-current contact with the polyolefin resin powder after primary degassing to perform multi-stage degassing; the injection stage of the multi-stage nitrogen supply circuit is two or more stages.

[0008] Optionally, the number of injection stages in the multi-stage nitrogen supply circuit is two to five.

[0009] Optionally, the primary nitrogen distributor and the multi-stage nitrogen distributor adopt a cross beam structure or an inverted cone structure.

[0010] Optionally, the outer wall of the high-temperature degassing chamber is equipped with a heater.

[0011] Optionally, the heater may be in the form of a coil, a half-tube, or an electric heating strip.

[0012] In a second aspect, embodiments of this application provide a method for removing VOCs from polyolefin resin powder, the method being adaptable to the system described in any embodiment of the first aspect, the method comprising: Polyolefin resin powder from the reaction unit enters the high-temperature degassing chamber from the top and flows downward in the form of a plunger flow within the high-temperature degassing chamber; unreacted monomers and solvents are adsorbed on the surface and in the internal pores of the polyolefin resin powder. Primary hot nitrogen gas is introduced into the high-temperature degassing chamber through a distributor in the upper part of the chamber. The primary hot nitrogen gas comes into counter-current contact with the downward-flowing polyolefin resin powder to perform primary degassing. Multi-stage hot nitrogen gas is introduced into the high-temperature degassing chamber from a distributor at the bottom or lower part of the chamber. The multi-stage hot nitrogen gas comes into counter-current contact with the polyolefin resin powder after primary degassing to perform multi-stage degassing. The multi-stage hot nitrogen gas has two or more stages.

[0013] Optionally, the residence time of the polyolefin resin powder in the high-temperature degassing chamber is 1 to 6 hours.

[0014] Optionally, the temperature of the primary hot nitrogen gas, the temperature of the multi-stage hot nitrogen gas, and the internal temperature of the high-temperature degassing chamber are all lower than the Vicat softening point temperature of the polyolefin resin powder.

[0015] Optionally, the primary hot nitrogen gas contains a polar medium for deactivating the catalyst and co-catalyst, wherein the polar medium is water or an alcohol.

[0016] Optionally, the ratio of the flow rate V1 of the primary hot nitrogen to the flow rate M of the polyolefin resin powder, V1:M, is (5-40):1. The ratio of the total flow rate V2 of the multi-stage hot nitrogen gas to the flow rate M of the polyolefin resin powder, V2:M, is (1~10):1. Where the units of V1 and V2 are both Nm 3 If M is / h, then the unit of M is t / h.

[0017] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a system for removing VOCs from polyolefin resin powder. By optimizing the functional design of the core components of the system and coordinating the flow of polyolefin resin powder with the flow of nitrogen, this application addresses the technical problem of improving the removal efficiency of volatile organic compounds (VOCs) from polyolefin resin powder from three aspects: Firstly, a stable degassing environment is constructed using the high-temperature degassing chamber 1: the polyolefin resin powder flows from the top to the bottom of the high-temperature degassing chamber 1 in the form of a plunger flow. This flow method avoids local flow short circuits and uneven residence time of the polyolefin resin powder, ensuring that each part of the polyolefin resin powder can fully contact the subsequently introduced primary and secondary hot nitrogen gas, providing uniform and sufficient contact conditions for the removal of volatile organic compounds (VOCs) in the polyolefin resin powder, thereby laying a foundation for efficient removal at the material flow level of the polyolefin resin powder.

[0018] Secondly, a "one-stage + multi-stage" stepwise reverse degassing structure is designed to enhance degassing efficiency: the first-stage nitrogen supply circuit 4 heats the recovered nitrogen from the nitrogen recovery outlet of the tail gas recovery unit 3 or the fresh nitrogen from the fresh nitrogen source into first-stage hot nitrogen through the first-stage nitrogen heater 41. This first-stage hot nitrogen is then transported to the upper middle part of the high-temperature degassing chamber 1 via the first-stage nitrogen distributor 42, allowing it to directly and counter-currently contact the downward-flowing polyolefin resin powder. The VOC carrying capacity of the first-stage hot nitrogen is utilized to preferentially remove the higher content of VOCs in the polyolefin resin powder. Based on this, the multi-stage nitrogen supply circuit 5... Fresh nitrogen from a fresh nitrogen source is heated into multi-stage hot nitrogen by a multi-stage nitrogen heater 51. The multi-stage hot nitrogen is then transported to the bottom or lower part of the high-temperature degassing chamber 1 via a multi-stage nitrogen distributor 52. This allows the multi-stage hot nitrogen to come into counter-current contact with the polyolefin resin powder after primary degassing, thus deeply purifying the residual volatile organic compounds (VOCs) in the polyolefin resin powder. By adopting a step-by-step approach of "first removing a large amount of high-content VOCs from the polyolefin resin powder, and then deeply purifying the residual VOCs in the polyolefin resin powder," the overall removal efficiency of VOCs in the polyolefin resin powder is significantly improved.

[0019] Thirdly, the degassing process is stabilized through component coordination: the primary nitrogen supply circuit 4 is connected to both the nitrogen recovery outlet of the tail gas recovery unit (3) and the fresh nitrogen source. By prioritizing the use of nitrogen recovered by the tail gas recovery unit 3 and supplementing the insufficient portion with fresh nitrogen, the primary hot nitrogen supply is ensured to be continuous and sufficient, avoiding interruption or insufficient degassing of the polyolefin resin powder due to insufficient primary hot nitrogen. The filter 2 filters the gas containing nitrogen, unreacted monomers and solvents discharged from the top of the high-temperature degassing chamber 1, preventing polyolefin resin powder particles entrained in the gas from entering the tail gas recovery unit 3 and causing blockage of the tail gas recovery unit 3, ensuring the normal operation of the tail gas recovery unit 3, indirectly maintaining the stability of the nitrogen supply in the primary nitrogen supply circuit 4, further ensuring the continuous and efficient degassing process of the polyolefin resin powder, and ultimately improving the removal effect of volatile organic compounds (VOCs) in the polyolefin resin powder. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a system for removing VOCs from polyolefin resin powder, provided in an embodiment of this application. Figure 2 A schematic flowchart illustrating a method for removing VOCs from polyolefin resin powder, provided in an embodiment of this application; Figure label: 1-High temperature degassing chamber, 11-Heater, 2-Filter, 3-Tail gas recovery unit, 4-Primary nitrogen supply circuit, 41-Primary nitrogen heater, 42-Primary nitrogen distributor, 5-Multi-stage nitrogen supply circuit, 51-Multi-stage nitrogen heater, 52-Multi-stage nitrogen distributor. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0025] Figure 1 This is a schematic diagram of a system for removing VOCs from polyolefin resin powder, provided in an embodiment of this application.

[0026] like Figure 1 As shown in the figure, this application provides a system for removing VOCs from polyolefin resin powder. The system includes: The high-temperature degassing chamber 1 is used to contain and transport polyolefin resin powder. The polyolefin resin powder flows from the top to the bottom of the high-temperature degassing chamber 1 in the form of a plunger flow inside the high-temperature degassing chamber 1. Filter 2 is connected to the top of the high-temperature degassing chamber 1 and is used to filter the gas discharged from the top of the high-temperature degassing chamber 1. Tail gas recovery unit 3 is connected to filter 2 and is used to recover nitrogen, unreacted monomers and solvents discharged from high temperature degassing chamber 1. The primary nitrogen supply circuit 4 has its inlet end connected to the nitrogen recovery outlet of the tail gas recovery unit 3 and the fresh nitrogen source. The outlet end of the primary nitrogen supply circuit 4 is connected to the upper middle part of the high temperature degassing chamber 1 through the primary nitrogen heater 41 and the primary nitrogen distributor 42. It is used to supply primary hot nitrogen to the high temperature degassing chamber 1, and the primary hot nitrogen comes into counter-current contact with the downward flowing polyolefin resin powder to perform primary degassing. The multi-stage nitrogen supply circuit 5 has its inlet end connected to a fresh nitrogen source, and its outlet end connected to the bottom or lower part of the high-temperature degassing chamber 1 via a corresponding multi-stage nitrogen heater 51 and a multi-stage nitrogen distributor 52. This circuit is used to supply multi-stage hot nitrogen to the high-temperature degassing chamber 1, and the multi-stage hot nitrogen comes into counter-current contact with the polyolefin resin powder after primary degassing to perform multi-stage degassing. The multi-stage nitrogen supply circuit 5 has two or more injection stages.

[0027] In some implementations, the number of injection stages in the multi-stage nitrogen supply circuit 5 is two to five.

[0028] In some embodiments, the primary nitrogen distributor 42 and the multi-stage nitrogen distributor 52 adopt a crossbeam structure or an inverted cone structure.

[0029] In some embodiments, a heater 11 is provided on the outer wall of the high-temperature degassing chamber 1.

[0030] In some embodiments, the heater 11 is in the form of a coil, a half-tube, or an electric heating belt.

[0031] It should be noted that this application rationally designs the various components of the VOC removal system for polyolefin resin powder, and the functions of each component are as follows: The high-temperature degassing chamber 1 is used to contain and transport polyolefin resin powder, providing space for VOC removal. The polyolefin resin powder flows from the top to the bottom of the high-temperature degassing chamber 1 in the form of a plunger flow, ensuring that the polyolefin resin powder has sufficient residence time to contact with hot nitrogen gas, providing flow conditions for VOC removal. A heater 11 is provided on the outer wall of the high-temperature degassing chamber 1, which can maintain the internal temperature of the high-temperature degassing chamber 1 by heating, promoting the desorption of unreacted monomers and solvents adsorbed on the surface and internal pores of the polyolefin resin powder.

[0032] Filter 2 is connected to the top of the high-temperature degassing chamber 1 and is used to filter the gas discharged from the top of the high-temperature degassing chamber 1, remove polyolefin resin powder particles that may be entrained in the gas, and prevent polyolefin resin powder particles from entering the tail gas recovery device 3 and causing pollution or blockage of the tail gas recovery device 3.

[0033] The exhaust gas recovery unit 3 is connected to the filter 2 and is used to recover nitrogen, unreacted monomers and solvents discharged from the high-temperature degassing chamber 1 after being filtered by the filter 2, so as to realize the recycling of nitrogen and the recovery of unreacted monomers and solvents, and reduce resource waste.

[0034] The inlet of the primary nitrogen supply circuit 4 is connected to the nitrogen recovery outlet of the tail gas recovery unit 3 and the fresh nitrogen source. The nitrogen recovered by the tail gas recovery unit 3 can be used as the primary nitrogen source first, and the insufficient part can be supplemented by fresh nitrogen to save nitrogen. The outlet is connected to the middle and upper part of the high temperature degassing chamber 1 through the primary nitrogen heater 41 and the primary nitrogen distributor 42. The primary nitrogen heater 41 is used to heat the nitrogen to the required temperature (the temperature is lower than the Vicat softening point temperature of the polyolefin resin). The primary nitrogen distributor 42 (adopting a cross beam structure or an inverted cone structure) is used to evenly disperse the primary hot nitrogen into the high temperature degassing chamber 1. The primary hot nitrogen comes into countercurrent contact with the downward flowing polyolefin resin powder, which can perform primary degassing of the polyolefin resin powder. At the same time, polar media such as water or alcohol can be added to the primary hot nitrogen in proportion to deactivate the catalyst and co-catalyst contained in the polyolefin resin powder.

[0035] The inlet of the multi-stage nitrogen supply circuit 5 is connected to a fresh nitrogen source, and the outlet is connected to the bottom or lower part of the high-temperature degassing chamber 1 through a corresponding multi-stage nitrogen heater 51 and a multi-stage nitrogen distributor 52. The multi-stage nitrogen heater 51 is used to heat the fresh nitrogen to the required temperature (the temperature is lower than the Vicat softening point temperature of the polyolefin resin), and the multi-stage nitrogen distributor 52 (using a cross beam structure or an inverted cone structure) is used to evenly disperse the multi-stage hot nitrogen into the high-temperature degassing chamber 1. The multi-stage hot nitrogen (the number of injection stages is two to five) comes into counter-current contact with the polyolefin resin powder after the first stage of degassing, which can perform multi-stage degassing on the polyolefin resin powder after the first stage of degassing, further reducing the VOC content in the polyolefin resin powder after the first stage of degassing.

[0036] Heater 11: Installed on the outer wall of the high-temperature degassing chamber 1, in the form of a coil, a half-pipe, or an electric heating belt, heating the high-temperature degassing chamber 1 with heating media such as steam, hot water, or hot oil to maintain the high-temperature environment inside the high-temperature degassing chamber 1 and promote VOC desorption; the temperature of the heating medium must be lower than the Vicat softening point temperature of the polyolefin resin, and the heating medium is equipped with a temperature display and alarm function to prevent the polyolefin resin powder in the high-temperature degassing chamber 1 from softening due to excessively high heating medium temperature.

[0037] At the same time, the various components work synergistically to improve the VOC removal effect in polyolefin resin powder. The specific synergistic process is as follows: The high-temperature degassing chamber 1 serves as the core reaction space. By allowing the polyolefin resin powder to flow from the top to the bottom of the high-temperature degassing chamber 1 in the form of a plunger flow, the residence time of the polyolefin resin powder in the high-temperature degassing chamber 1 is guaranteed. The heater 11 on the outer wall of the high-temperature degassing chamber 1 heats the high-temperature degassing chamber 1, maintaining the high-temperature environment inside the high-temperature degassing chamber 1, and providing the basic conditions for VOC desorption. The hot nitrogen (both at temperatures below the Vicat softening point of the polyolefin resin) supplied by the primary nitrogen supply circuit 4 and the multi-stage nitrogen supply circuit 5 comes into countercurrent contact with the polyolefin resin powder in the high-temperature degassing chamber 1, utilizing the carrying effect of the high-temperature nitrogen to remove VOCs from the polyolefin resin powder. The primary nitrogen supply preferentially uses nitrogen recovered by the tail gas recovery unit 3 as the gas source to achieve nitrogen circulation, reduce costs, and the primary hot nitrogen containing polar media can simultaneously deactivate the catalysts and co-catalysts contained in the polyolefin resin powder. The multi-stage nitrogen supply uses fresh nitrogen, which is injected in stages from the second to the fifth stage, and combined with the phase balance principle to further reduce the VOC content in the polyolefin resin powder after primary removal, avoiding flow short circuits in the polyolefin resin powder in the high-temperature degassing chamber 1.

[0038] The primary nitrogen distributor 42 and the multi-stage nitrogen distributor 52 (cross-beam structure or inverted cone structure) ensure that hot nitrogen is evenly dispersed in the high-temperature degassing chamber 1, making full contact with the polyolefin resin powder in the high-temperature degassing chamber 1. At the same time, it avoids the problem of uneven nitrogen distribution caused by polyolefin resin powder clogging the distributor, thus enhancing mass transfer efficiency. Filter 2 filters the gas discharged from the top of the high-temperature degassing chamber 1, preventing polyolefin resin powder particles from entering the tail gas recovery unit 3. This ensures that the tail gas recovery unit 3 effectively recovers the nitrogen, unreacted monomers, and solvents filtered by filter 2. The recovered nitrogen is then fed back into the primary nitrogen supply circuit 4 as the primary nitrogen source, forming a nitrogen circulation system.

[0039] Temperature control for all components (including the internal temperature of the high-temperature degassing chamber 1, the heating medium temperature of heater 11, the primary hot nitrogen temperature, and the multi-stage hot nitrogen temperature) must be kept below the Vicat softening point temperature of the polyolefin resin. This prevents the polyolefin resin powder in the high-temperature degassing chamber 1 from softening and clumping, ensuring smooth flow of the polyolefin resin powder and stable degassing process. Through the synergistic effect of these components, the odor level of the final polyolefin product can be controlled to around level 3, achieving an effect similar to VOC removal via steam, while reducing steam consumption and wastewater generation.

[0040] Figure 2 This is a schematic flowchart of a method for removing VOCs from polyolefin resin powder, provided in an embodiment of this application.

[0041] Based on a general inventive concept, such as Figure 2As shown, this application provides a method for removing VOCs from polyolefin resin powder. The method is adapted to the system of any embodiment of the first aspect, and includes: S1. Polyolefin resin powder from the reaction unit enters the high-temperature degassing chamber 1 from the top and flows downward in the form of a plunger flow within the high-temperature degassing chamber 1; unreacted monomers and solvents are adsorbed on the surface and in the internal pores of the polyolefin resin powder. S2. First-stage hot nitrogen gas is introduced into the high-temperature degassing chamber 1 through the distributor at the top of the chamber. The first-stage hot nitrogen gas comes into counter-current contact with the downward-flowing polyolefin resin powder to perform first-stage degassing. S3. Multi-stage hot nitrogen gas is introduced into the high-temperature degassing chamber 1 from the bottom or lower distributor. The multi-stage hot nitrogen gas comes into counter-current contact with the polyolefin resin powder after primary degassing to perform multi-stage degassing. The number of stages of the multi-stage hot nitrogen gas is two or more.

[0042] In some embodiments, the residence time of the polyolefin resin powder in the high-temperature degassing chamber 1 is 1 to 6 hours.

[0043] In some embodiments, the temperature of the primary hot nitrogen, the temperature of the multi-stage hot nitrogen, and the internal temperature of the high-temperature degassing chamber 1 are all lower than the Vicat softening point temperature of the polyolefin resin powder.

[0044] In some embodiments, the primary hot nitrogen gas contains a polar medium, such as water or alcohol, used for deactivating the catalyst and co-catalyst.

[0045] In some embodiments, the ratio of the flow rate V1 of the primary hot nitrogen to the flow rate M of the polyolefin resin powder, V1:M, is (5-40):1; the ratio of the total flow rate V2 of the multi-stage hot nitrogen to the flow rate M of the polyolefin resin powder, V2:M, is (1-10):1; wherein, if the units of V1 and V2 are both Nm 3 If M is / h, then the unit of M is t / h.

[0046] It should be noted that the flow rate V1 of the primary hot nitrogen and the flow rate M of the polyolefin resin powder are set to a ratio of (5~40):1. This range can provide sufficient primary hot nitrogen for the primary degassing process of the polyolefin resin powder, ensuring that the primary hot nitrogen and the polyolefin resin powder that has just entered the high-temperature degassing chamber 1 and has adsorbed a large amount of unreacted monomers and solvents on its surface and in its internal pores are in full counter-current contact. Through the carrying effect of the primary hot nitrogen, most of the VOCs contained in the polyolefin resin powder are efficiently removed, laying a good foundation for the subsequent multi-stage degassing of the polyolefin resin powder. At the same time, it ensures that the polyolefin resin powder in the high-temperature degassing chamber 1 maintains a stable plunger flow state, avoiding insufficient degassing of the polyolefin resin powder due to insufficient primary hot nitrogen, or increased energy consumption of the primary nitrogen heater 41 due to excessive primary hot nitrogen.

[0047] The total flow rate V2 of the multi-stage hot nitrogen and the flow rate M of the polyolefin resin powder are set to a ratio of (1~10):1. This range can provide a suitable amount of fresh hot nitrogen for the multi-stage degassing process of the polyolefin resin powder after the first-stage degassing. This allows the multi-stage hot nitrogen to continuously contact the polyolefin resin powder, which has already had most of the VOCs removed, in a counter-current manner, further removing the residual VOCs in the polyolefin resin powder. This achieves the goal of deep VOC removal from the polyolefin resin powder, ensuring that the VOC content of the final polyolefin resin powder meets the standards. At the same time, it avoids the effect of deep VOC removal from the polyolefin resin powder due to insufficient fresh hot nitrogen, or the waste of fresh nitrogen resources and the increase in the processing load of the tail gas recovery unit 3 due to excessive fresh hot nitrogen.

[0048] In summary, this application adopts the following measures to improve the VOC removal effect in polyolefin resin powder: (1) To enhance the degassing effect, the residence time of polyolefin resin powder in the high-temperature degassing chamber needs to be set according to the VOC medium being removed. Usually, the residence time of polyolefin resin powder in the high-temperature degassing chamber needs to be set between 1 and 6 hours. For the minimum residence time requirement of polyolefin resin powder set for a specific device, when the actual residence time of polyolefin resin powder in the high-temperature degassing chamber is less than the minimum residence time set for the specific device, a corresponding alarm device needs to be set to remind the operator to adjust the conveying rate of polyolefin resin powder or the operating parameters of the high-temperature degassing chamber in a timely manner.

[0049] (2) To enhance the degassing effect, the outer wall of the high-temperature degassing chamber is equipped with an outer shell heating device. The outer shell heating device can be in the form of a heating coil or an electric heating tape. The heating medium can be steam, hot water, or hot oil. In order to avoid the polyolefin resin powder in the high-temperature degassing chamber from softening due to excessively high heating medium temperature, the temperature of the heating medium is required to be lower than the Vicat softening point temperature of the polyolefin resin. Therefore, a temperature display device and a temperature alarm device should be installed on the heating medium conveying pipeline or heating device to ensure that the heating medium has temperature display and alarm functions.

[0050] (3) In order to enhance the degassing effect, the nitrogen gas at each stage entering the high temperature degassing chamber needs to be heated to the required high temperature by the heater. The temperature of the nitrogen gas after heating at each stage should be lower than the Vicat softening point temperature of the polyolefin resin.

[0051] (4) To enhance the degassing effect and save nitrogen, the primary nitrogen entering the high-temperature degassing chamber is preferably nitrogen recovered by the tail gas recovery device, and the insufficient part is supplemented by fresh nitrogen as the source of primary nitrogen. To deactivate the catalyst and co-catalyst contained in the polyolefin resin powder, a small amount of polar medium is added to the primary nitrogen in a set ratio. The polar medium is water or alcohol.

[0052] (5) To enhance the degassing effect, the nitrogen gas entering the high-temperature degassing chamber is fresh nitrogen gas in stages 2 to 5. The fresh nitrogen gas is heated by the corresponding multi-stage nitrogen heater before entering the high-temperature degassing chamber. The temperature of the nitrogen gas after heating stages 2 to 5 is required to be lower than the Vicat softening point temperature of the polyolefin resin.

[0053] (6) To enhance the degassing effect, each stage of nitrogen entering the high-temperature degassing chamber is equipped with a dedicated nitrogen distributor. The dedicated nitrogen distributor facilitates the uniform dispersion of nitrogen at each stage within the high-temperature degassing chamber and ensures full contact with the polyolefin resin powder inside. Simultaneously, the dedicated nitrogen distributor must have an anti-clogging structure to prevent the polyolefin resin powder in the high-temperature degassing chamber from clogging the nitrogen distributor, thus avoiding uneven distribution of nitrogen within the chamber.

[0054] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0055] Example 1 Taking the degassing design of polypropylene powder in a polypropylene plant as an example, a case study of high-temperature degassing of polypropylene powder is provided, as follows: Polypropylene powder (temperature approximately 80°C) transported from the upstream low-pressure separator enters the high-temperature degassing chamber 1. The surface and internal pores of the polypropylene powder entering the high-temperature degassing chamber 1 contain 2% unreacted monomers (propylene and ethylene). The polypropylene powder flows from the top to the bottom of the high-temperature degassing chamber 1 in a plunger flow manner. The residence time of the polypropylene powder in the high-temperature degassing chamber 1 is controlled by adjusting the normal material level, maintaining it at 3 hours. The Vicat softening point temperature of conventional polypropylene grades is 140–150°C.

[0056] The outer wall of the high-temperature degassing chamber 1 is equipped with a heater 11. The heater 11 on the outer wall of the high-temperature degassing chamber 1 is in the form of a coil, and the heater 11 on the outer wall of the high-temperature degassing chamber 1 uses low-pressure steam as the heating medium. The heater 11 on the outer wall of the high-temperature degassing chamber 1 is used to maintain the temperature inside the high-temperature degassing chamber 1 (the temperature inside the high-temperature degassing chamber 1 is lower than the Vicat softening point temperature of polypropylene).

[0057] The inlet of the primary nitrogen supply circuit 4 is connected to the nitrogen recovery outlet of the tail gas recovery unit 3 and a fresh nitrogen source. The nitrogen supplied by the primary nitrogen supply circuit 4 is a mixture of nitrogen recovered by the tail gas recovery unit 3 and fresh nitrogen. The primary nitrogen supply circuit 4 preferentially uses the nitrogen recovered by the tail gas recovery unit 3. When the amount of nitrogen recovered by the tail gas recovery unit 3 is insufficient, it is supplemented by fresh nitrogen. The nitrogen supplied by the primary nitrogen supply circuit 4 is heated by the primary nitrogen heater 41 to become primary hot nitrogen. Polar medium (water vapor, the volume of which is 0.2% to 1% of the total volume of primary hot nitrogen) is added to the primary hot nitrogen to contain the polymerization catalyst and TEAL contained in the deactivated polypropylene powder. The primary hot nitrogen is transported to the upper middle part of the high temperature degassing chamber 1 through the primary nitrogen distributor 42. The primary hot nitrogen comes into countercurrent contact with the downward flowing polypropylene powder to perform primary degassing of the polypropylene powder. The content (wt) of unreacted monomers in the polypropylene powder after primary degassing is 100~300ppm.

[0058] The inlet of the multi-stage nitrogen supply circuit 5 (with two to three injection stages) is connected to a fresh nitrogen source. The fresh nitrogen supplied by the multi-stage nitrogen supply circuit 5 is heated into multi-stage hot nitrogen by the multi-stage nitrogen heater 51. The multi-stage hot nitrogen is delivered to the bottom or lower part of the high-temperature degassing chamber 1 through the multi-stage nitrogen distributor 52. The multi-stage hot nitrogen comes into counter-current contact with the polypropylene powder after the first stage of degassing to perform multi-stage degassing on the polypropylene powder after the first stage of degassing. The content (wt) of unreacted monomers in the polypropylene powder after multi-stage degassing is 50~200ppm, and the odor level of the polypropylene powder is level 3. To enhance the degassing effect, the high-temperature degassing chamber 1 is equipped with two contraction sections. The first-stage nitrogen distributor 42 and the multi-stage nitrogen distributor 52 are both integrated inside the high-temperature degassing chamber 1.

[0059] The gas discharged from the top of the high-temperature degassing chamber 1 (containing nitrogen, unreacted monomer propylene, and ethylene) is first filtered by filter 2. Filter 2 removes polypropylene powder particles entrained in the gas discharged from the top of the high-temperature degassing chamber 1. The gas filtered by filter 2 then enters the tail gas recovery unit 3. The tail gas recovery unit 3 recovers the nitrogen, unreacted monomer propylene, and ethylene from the gas filtered by filter 2. The nitrogen recovered by the tail gas recovery unit 3 is returned to the inlet of the primary nitrogen supply circuit 4 as a circulating gas source for primary nitrogen.

[0060] Example 2 Taking the degassing design of polyethylene powder in a polyethylene plant as an example, an implementation case of high-temperature degassing of polyethylene powder is provided, as detailed below: Polyethylene powder (temperature approximately 85–110°C) transported from the upstream low-pressure separator enters the high-temperature degassing chamber 1. The surface and internal pores of the polyethylene powder entering the high-temperature degassing chamber 1 are adsorbed with approximately 0.5% unreacted monomers (ethylene, butene-1, or hexene-1). The polyethylene powder flows from the top to the bottom of the high-temperature degassing chamber 1 in the form of a plunger flow. The residence time of the polyethylene powder in the high-temperature degassing chamber 1 is controlled by adjusting the normal material level of the high-temperature degassing chamber 1, so that the residence time of the polyethylene powder in the high-temperature degassing chamber 1 is maintained at approximately 6 hours. The Vicat softening point temperature of conventional grades of polyethylene is 120–150°C.

[0061] The outer wall of the high-temperature degassing chamber 1 is equipped with a heater 11. The heater 11 on the outer wall of the high-temperature degassing chamber 1 is adapted to hot water heating (such as coil or half-pipe type), and the heater 11 on the outer wall of the high-temperature degassing chamber 1 uses hot water as the heating medium. The heater 11 on the outer wall of the high-temperature degassing chamber 1 is used to maintain the temperature inside the high-temperature degassing chamber 1 (the temperature inside the high-temperature degassing chamber 1 is lower than the Vicat softening point temperature of polyethylene).

[0062] The inlet of the primary nitrogen supply circuit 4 is connected to the nitrogen recovery outlet of the tail gas recovery unit 3 and a fresh nitrogen source. The nitrogen supplied by the primary nitrogen supply circuit 4 is a mixture of nitrogen recovered by the tail gas recovery unit 3 and fresh nitrogen. The primary nitrogen supply circuit 4 preferentially uses the nitrogen recovered by the tail gas recovery unit 3. When the amount of nitrogen recovered by the tail gas recovery unit 3 is insufficient, it is supplemented by fresh nitrogen. The nitrogen supplied by the primary nitrogen supply circuit 4 is heated by the primary nitrogen heater 41 to become primary hot nitrogen. A small amount of polar medium (water vapor, the volume of which is 0.2% to 1% of the total volume of the primary hot nitrogen) is added to the primary hot nitrogen to contain the polymerization catalyst and TEAL contained in the deactivated polyethylene powder. The primary hot nitrogen is transported to the upper middle part of the high temperature degassing chamber 1 through the primary nitrogen distributor 42. The primary hot nitrogen comes into countercurrent contact with the downward flowing polyethylene powder to perform primary degassing of the polyethylene powder. The content (wt) of unreacted monomers in the polyethylene powder after primary degassing is 100~300ppm.

[0063] The inlet of the multi-stage nitrogen supply circuit 5 (with two to three injection stages) is connected to a fresh nitrogen source. The fresh nitrogen supplied by the multi-stage nitrogen supply circuit 5 is heated into multi-stage hot nitrogen by the multi-stage nitrogen heater 51. The multi-stage hot nitrogen is delivered to the bottom or lower part of the high-temperature degassing chamber 1 through the multi-stage nitrogen distributor 52. The multi-stage hot nitrogen comes into counter-current contact with the polyethylene powder after the first stage of degassing to perform multi-stage degassing on the polyethylene powder after the first stage of degassing. The content (wt) of unreacted monomers in the polyethylene powder after multi-stage degassing is 50~200ppm, and the odor level of the polyethylene powder is less than level 3. To enhance the degassing effect, the high-temperature degassing chamber 1 is equipped with two contraction sections. The first-stage nitrogen distributor 42 and the multi-stage nitrogen distributor 52 are both integrated inside the high-temperature degassing chamber 1.

[0064] The gas discharged from the top of the high-temperature degassing chamber 1 (containing nitrogen, unreacted monomer ethylene, butene-1 or hexene-1) first passes through filter 2 for filtration. Filter 2 removes polyethylene powder particles entrained in the gas discharged from the top of the high-temperature degassing chamber 1. The gas filtered by filter 2 then enters the tail gas recovery unit 3. The tail gas recovery unit 3 recovers the nitrogen, unreacted monomer ethylene, butene-1 or hexene-1 from the gas filtered by filter 2. The nitrogen recovered by the tail gas recovery unit 3 is returned to the inlet of the primary nitrogen supply circuit 4 as a circulating gas source for primary nitrogen.

[0065] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: In this embodiment, a system and adaptation method for VOC removal from polyolefin resin powder are rationally designed. A high-temperature degassing chamber is designed as the core reaction space, allowing the polyolefin resin powder to flow in a plunger flow manner within the chamber, maintaining a residence time of 1–6 hours. Simultaneously, primary hot nitrogen from a primary nitrogen supply circuit and multi-stage hot nitrogen from a multi-stage nitrogen supply circuit (injection stages ranging from two to five) are provided, contacting the polyolefin resin powder in the high-temperature degassing chamber in counter-current directions. The primary hot nitrogen efficiently removes most of the VOCs contained in the polyolefin resin powder, while the multi-stage hot nitrogen further removes residual VOCs, ultimately controlling the odor level of the polyolefin product to around level 3, achieving an effect similar to steam-based VOC removal. In addition, this application sets up an alarm device for the residence time of polyolefin resin powder in the high-temperature degassing chamber to ensure that the residence time of polyolefin resin powder meets the VOC removal requirements and avoid incomplete VOC removal due to insufficient residence time of polyolefin resin powder in the high-temperature degassing chamber.

[0066] In this embodiment, the primary nitrogen supply circuit preferentially uses nitrogen recovered by the tail gas recovery unit as the primary nitrogen source. Only when the amount of nitrogen recovered by the tail gas recovery unit is insufficient is fresh nitrogen used to supplement the primary nitrogen source. This design significantly reduces the consumption of fresh nitrogen. Simultaneously, the heating medium temperature of the heater on the outer wall of the high-temperature degassing chamber, the primary hot nitrogen temperature, and the multi-stage hot nitrogen temperature are all strictly controlled within a range below the Vicat softening point of the polyolefin resin. This temperature control prevents the polyolefin resin powder in the high-temperature degassing chamber from softening and also prevents additional energy consumption due to excessively high temperatures. Furthermore, the entire process of VOC removal from the polyolefin resin powder does not rely on large amounts of steam, further reducing the overall energy consumption of the system.

[0067] In this embodiment, both the primary nitrogen distributor and the multi-stage nitrogen distributor adopt a crossbeam structure or an inverted cone structure. Both types of distributors are designed to prevent clogging by polyolefin resin powder, thus avoiding blockage and ensuring uniform dispersion of hot nitrogen at each stage within the high-temperature degassing chamber. This ensures sufficient contact between the hot nitrogen and the polyolefin resin powder, while also preventing flow short-circuiting. Furthermore, a temperature display and alarm device are installed on the heating medium's delivery pipeline or heating equipment to monitor the heating medium temperature in real time. This prevents the polyolefin resin powder in the high-temperature degassing chamber from softening and clumping due to excessively high temperatures, ensuring smooth flow of the powder and stable VOC degassing.

[0068] In this embodiment, the exhaust gas recovery unit can recover unreacted monomers and solvents discharged from the high-temperature degassing chamber after filtration, realizing resource recycling of unreacted monomers and solvents and reducing resource waste. Simultaneously, the entire process of VOC removal from polyolefin resin powder does not consume large amounts of steam, thus avoiding the generation of large amounts of wastewater and preventing environmental pollution caused by wastewater discharge, meeting environmental protection requirements.

[0069] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A system for removing VOCs from polyolefin resin powder, characterized in that, The system includes: A high-temperature degassing chamber (1) is used to contain and transport polyolefin resin powder, which flows from the top to the bottom of the high-temperature degassing chamber (1) in the form of a plunger flow inside the high-temperature degassing chamber (1). A filter (2) is connected to the top of the high-temperature degassing chamber (1) and is used to filter the gas discharged from the top of the high-temperature degassing chamber (1); The exhaust gas recovery unit (3) is connected to the filter (2) and is used to recover nitrogen, unreacted monomers and solvents discharged from the high-temperature degassing chamber (1); A primary nitrogen supply circuit (4) is provided. The inlet end of the primary nitrogen supply circuit (4) is connected to the nitrogen recovery outlet of the tail gas recovery unit (3) and the fresh nitrogen source. The outlet end of the primary nitrogen supply circuit (4) is connected to the upper middle part of the high temperature degassing chamber (1) through a primary nitrogen heater (41) and a primary nitrogen distributor (42) to provide primary hot nitrogen into the high temperature degassing chamber (1). The primary hot nitrogen comes into counter-current contact with the downward flowing polyolefin resin powder to perform primary degassing. A multi-stage nitrogen supply circuit (5) is provided, with its inlet end connected to a fresh nitrogen source and its outlet end connected to the bottom or lower part of the high-temperature degassing chamber (1) via a corresponding multi-stage nitrogen heater (51) and a multi-stage nitrogen distributor (52). This circuit is used to supply multi-stage hot nitrogen to the high-temperature degassing chamber (1), and the multi-stage hot nitrogen is in reverse contact with the polyolefin resin powder after primary degassing to perform multi-stage degassing. The injection stage of the multi-stage nitrogen supply circuit (5) is two or more stages.

2. The system according to claim 1, characterized in that, The number of injection stages in the multi-stage nitrogen supply circuit (5) is two to five.

3. The system according to claim 1, characterized in that, The primary nitrogen distributor (42) and the multi-stage nitrogen distributor (52) adopt a cross beam structure or an inverted cone structure.

4. The system according to claim 1, characterized in that, The outer wall of the high-temperature degassing chamber (1) is equipped with a heater (11).

5. The system according to claim 4, characterized in that, The heater (11) is in the form of a coil, a half-tube, or an electric heating belt.

6. A method for removing VOCs from polyolefin resin powder, characterized in that, The method is adapted to the system according to any one of claims 1 to 5, and the method includes: Polyolefin resin powder from the reaction unit enters the high-temperature degassing chamber from the top and flows downward in the form of a plunger flow within the high-temperature degassing chamber; unreacted monomers and solvents are adsorbed on the surface and in the internal pores of the polyolefin resin powder. Primary hot nitrogen gas is introduced into the high-temperature degassing chamber through a distributor in the upper part of the chamber. The primary hot nitrogen gas comes into counter-current contact with the downward-flowing polyolefin resin powder to perform primary degassing. Multi-stage hot nitrogen gas is introduced into the high-temperature degassing chamber from a distributor at the bottom or lower part of the chamber. The multi-stage hot nitrogen gas comes into counter-current contact with the polyolefin resin powder after primary degassing to perform multi-stage degassing. The multi-stage hot nitrogen gas has two or more stages.

7. The method according to claim 6, characterized in that, The residence time of the polyolefin resin powder in the high-temperature degassing chamber is 1 to 6 hours.

8. The method according to claim 6, characterized in that, The temperatures of the primary hot nitrogen gas, the multi-stage hot nitrogen gas, and the internal temperature of the high-temperature degassing chamber are all lower than the Vicat softening point temperature of the polyolefin resin powder.

9. The method according to claim 6, characterized in that, The primary hot nitrogen gas contains a polar medium, which is water or an alcohol, used to deactivate the catalyst and the co-catalyst.

10. The method according to claim 6, characterized in that, The ratio of the flow rate V1 of the primary hot nitrogen gas to the flow rate M of the polyolefin resin powder, V1:M, is (5-40):

1. The ratio of the total flow rate V2 of the multi-stage hot nitrogen gas to the flow rate M of the polyolefin resin powder, V2:M, is (1~10):

1. Where the units of V1 and V2 are both Nm 3 If M is / h, then the unit of M is t / h.

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