Method and system for efficiently and continuously removing VOC (Volatile Organic Compounds) of polypropylene material in energy-saving manner

Abstract

The invention relates to an efficient and energy-saving system for continuously removing VOC (Volatile Organic Compounds) from a polypropylene material. The system comprises a, a feeding device; the ridge tower sequentially comprises a preheating section, a devolatilization section, a pre-cooling section and a cooling section from top to bottom, a middle rotary valve is arranged between the pre-cooling section and the cooling section, and the preheating section, the devolatilization section and the pre-cooling section are used for conducting preheating, devolatilization and pre-cooling treatment on the PP particles under the action of heated nitrogen; a feeding rotary valve is arranged at the top of the ridge tower, and a discharging rotary valve is arranged at the bottom of the ridge tower; the nitrogen generating device and the heater are respectively used for generating and heating nitrogen so as to provide hot nitrogen required by devolatilization treatment; a heating section fan is arranged between the nitrogen generating device and the heater; d, a cooling section fan is used for further cooling the pre-cooled PP particles; and e, a middle rotary valve and a discharging rotary valve. The VOC in the polypropylene granules is reduced to be less than 50ppm through nitrogen operation, and the odor grade is less than 4.0. Finally, the VOC content in the polypropylene is reduced, meanwhile, the odor grade is reduced, and the quality of the polypropylene resin is improved.

Description

Technical Field

[0001] This invention relates to the field of post-processing technology for polypropylene granules, and more particularly to a method and system for efficient, energy-saving, and sustainable removal of VOCs from polypropylene materials. Background Technology

[0002] Relevant departments have introduced a series of testing methods and standards to regulate in-vehicle air pollution. Examples include GB / T27630-2011 "Guidelines for Evaluating Air Quality in Passenger Cars", HJ / T400-2007 "Sampling and Determination Methods for Volatile Organic Compounds and Aldehydes and Ketones in Vehicles", CQC9205-2014 "Sampling and Determination Methods for Volatile Organic Compounds and Aldehydes and Ketones in the Passenger Cabin of Automobiles", CQC9206-2014 "Evaluation Methods for PM2.5 Detection in Passenger Cars", and CQC9207-2014 "Evaluation Methods for Odor Detection in Passenger Cars".

[0003] Polypropylene meltblown special materials have a strong odor and high VOC content due to various factors during the production process, including catalyst residue, additive decomposition, and resin degradation. Therefore, they cannot be directly used in the production of medical masks. Thus, the VOC release problem of meltblown special materials has become one of the urgent issues to be addressed. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, reduce the VOC content in existing PP products, lower the odor level, and improve product quality, this invention proposes a method and system for continuous and efficient VOC removal from polypropylene, achieving a lower odor level. The principle involves using nitrogen as the heating and degassing medium. Polypropylene granules are heated with nitrogen, during which volatile organic compounds (VOCs) in the polypropylene granules continuously diffuse into the hot nitrogen. Then, the volatile organic compounds (VOCs) are removed from the polypropylene granules through nitrogen dispersion.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] A highly efficient, energy-saving, and sustainable system for removing VOCs from polypropylene materials includes:

[0007] a. A feeding device, which includes a pneumatic conveying device and a feeding hopper, wherein the pneumatic conveying device is used to feed the PP granules to be processed into the feeding hopper and controls the PP granules to enter the ridge tower through a feed rotary valve;

[0008] b. A ridge tower, which includes, from top to bottom, a preheating section, a devolatilization section, a precooling section, and a cooling section. An intermediate rotary valve is provided between the precooling section and the cooling section. The preheating section, devolatilization section, and precooling section are used to preheat, devolatilize, and precool the PP particles under the action of heated nitrogen. The top of the ridge tower is equipped with a feed rotary valve, and the bottom is equipped with a discharge rotary valve.

[0009] c. A nitrogen generator and a heater are used to generate and heat nitrogen, respectively, to provide the hot nitrogen required for the devolatilization process, which is used to heat the PP particles to 105℃~120℃ during the devolatilization process so that the VOCs remaining in the PP particles are desorbed; a heating section fan is provided between the nitrogen generator and the heater.

[0010] d. Cooling section fan, used to introduce ambient air into the cooling section of the ridge tower to further cool the pre-cooled PP granules;

[0011] e. The intermediate rotary valve and the discharge rotary valve are used to control the flow of PP particles in the ridge tower and the discharge from the ridge tower, respectively.

[0012] According to a specific embodiment of the present invention, the system further includes a packaging machine for receiving and packaging PP granules discharged from the roof tower.

[0013] According to a specific embodiment of the present invention, a nitrogen circulation pipeline is provided between the preheating section and the precooling section, so that after the hot nitrogen heats the PP particles in the preheating section, the temperature decreases, and then it enters the precooling section through the circulating fan, contacts the devolatilized PP particles for precooling, and reduces the temperature of the PP particles to below 105°C, and is then reheated and circulated back to the preheating section.

[0014] According to a specific embodiment of the present invention, the PP particles are heated to a temperature of 80°C to 90°C in the preheating section, to a temperature of 105°C to 120°C in the devolatilization section, preferably 110°C to 120°C, more preferably 115°C to 120°C, cooled to a temperature of 95°C to 100°C in the precooling section, and cooled to a temperature of 50°C ± 5°C in the cooling section.

[0015] According to a specific embodiment of the present invention, the PP particle filling rate in the ridge tower is between 75% and 85%; the total devolatilization time of the PP particles in the ridge tower is 2h to 3h, preferably 2.5h to 3h.

[0016] According to a specific embodiment of the present invention, the system further includes an air filter disposed before the cooling section fan to filter the air entering the cooling section and prevent impurities from contaminating the PP particles.

[0017] According to a specific embodiment of the present invention, a cyclone separator and a fine powder storage area are provided on the side of the roof tower. The devolatilization tail gas generated during the devolatilization process is separated into solid and gas by the cyclone separator. The solid enters the fine powder storage area and is discharged through the powder rotary valve at the bottom of the fine powder storage area, while the gas enters the tail gas discharge pipe. The devolatilization tail gas contains nitrogen, VOCs and mixed fine powder.

[0018] According to a specific embodiment of the present invention, the nitrogen generating device is a nitrogen generator used to separate nitrogen from compressed air.

[0019] According to a specific embodiment of the present invention, the system further includes a nitrogen filter disposed before the heater for filtering nitrogen entering the deashing section to prevent impurities from contaminating the PP particles.

[0020] According to a specific embodiment of the present invention, a hopper is provided between the feeding hopper and the feeding rotary valve, and the feeding hopper and the hopper are used to temporarily store and transport PP particles to be processed.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention utilizes a nitrogen circulation pipeline to ensure sufficient heat exchange between newly added cold PP granules and the relatively hot circulating nitrogen, guaranteeing the preheating function of the PP granules. After heat exchange, the nitrogen temperature decreases and enters the pre-cooling section of the device through the circulation system. Here, the cooler nitrogen can exchange heat with the hotter PP granules, ensuring the temperature of the PP granules decreases while simultaneously raising the nitrogen temperature, thus continuing the cycle. This circulating nitrogen system of the invention not only significantly reduces nitrogen consumption and greatly increases heat transfer efficiency, but also ensures that the temperature of the PP granules drops below 100°C after cooling in the pre-cooling section. Research shows that polypropylene (PP) granules are prone to oxidation when in contact with air at temperatures exceeding 100°C, generating new VOCs and leading to higher test results for the PP granules. This invention uses a nitrogen circulation system to cool the PP granules to a "safe temperature" where oxidation is less likely, before using air for complete cooling. This significantly reduces nitrogen consumption, saving energy and reducing emissions, while also ensuring that the VOC coefficient and odor of the polypropylene product do not increase. The resulting polypropylene product has a VOC level of up to 40 ppm and an odor rating of 4.0 or below.

[0023] After VOC removal treatment, the polypropylene material is as follows:

[0024] (1) The VOC content in the final packaged polypropylene material is lower than that in the untreated polypropylene material, and can be as low as 15 ppm, which is far lower than the VOC content of the raw polypropylene material.

[0025] (2) It has good reaction continuity and can be used continuously for a long time.

[0026] (3) The heating and pre-cooling of PP particles after entering the roof tower effectively utilizes circulating nitrogen, greatly reducing the amount of nitrogen used, and avoiding the oxidation of PP particles by direct contact with air at high temperatures to generate new VOCs.

[0027] (4) The equipment has low investment and operating costs, and has a high effect on product quality improvement. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a system for the efficient, energy-saving, and sustainable removal of VOCs from polypropylene materials. Detailed Implementation

[0029] Combined with appendix Figure 1 A highly efficient, energy-saving, and sustainable system for removing VOCs from polypropylene materials, comprising:

[0030] a. A feeding device, comprising a pneumatic conveying device and a feeding hopper (S-1101), wherein the pneumatic conveying device is used to feed the PP granules to be processed into the feeding hopper (S-1101), and controls the PP granules to enter the ridge tower (T-1101) through a feed rotary valve (X-1101); specifically, the pneumatic conveying device is a vacuum feeding blower (C-1101);

[0031] b. Ridge tower (T-1101), which includes, from top to bottom, a preheating section, a devolatilization section, a precooling section, and a cooling section. An intermediate rotary valve (X-1102) is provided between the precooling section and the cooling section. The preheating section, devolatilization section, and precooling section are used to preheat, devolatilize, and precool the PP particles under the action of heated nitrogen. The top of the ridge tower (T-1101) is provided with a feed rotary valve (X-1101), and the bottom is provided with a discharge rotary valve (X-1103).

[0032] c. A nitrogen generator and a heater (E-1101) are used to generate and heat nitrogen, respectively, to provide the hot nitrogen required for the devolatilization process, which is used to heat the PP particles to 105℃~120℃ during the devolatilization process so that the VOCs remaining in the PP particles are desorbed; a heating section fan (C-1102) is provided between the nitrogen generator and the heater (E-1101);

[0033] d. Cooling section fan (C-1104) is used to introduce ambient air into the cooling section of the ridge tower (T-1101) to further cool the pre-cooled PP granules;

[0034] e. The intermediate rotary valve (X-1102) and the discharge rotary valve (X-1103) are used to control the flow of PP particles in the ridge tower (T-1101) and the discharge from the ridge tower (T-1101), respectively.

[0035] In the above system, a nitrogen circulation pipe is provided between the preheating section and the precooling section. This allows the hot nitrogen to heat the PP particles in the preheating section, lowering their temperature before passing through a circulating fan (C-1103) into the precooling section. There, it contacts the devolatilized PP particles for precooling, reducing their temperature to below 105°C. The particles are then reheated and circulated back to the preheating section. The PP particles are heated to 80°C–90°C in the preheating section, to 105°C–120°C (preferably 110°C–120°C, more preferably 115°C–120°C) in the devolatilization section, and cooled to 95°C–100°C in the precooling section. Finally, they are cooled to 50°C ± 5°C in the cooling section. After being heated by nitrogen in the preheating section, the PP granules enter the devolatilization section, where they are further heated by nitrogen in the heater (E-1101) to the target devolatilization temperature. During this process, the PP granules move downwards along the ridge tower (T-1101) in a plug flow, undergoing devolatilization until they enter the precooling section of the ridge tower (T-1101). Upon entering the precooling section, the PP granules come into contact with the cooler circulating nitrogen, undergoing precooling to 95℃~100℃. Afterward, the PP granules leave the precooling section and are conveyed through an intermediate transfer valve into the cooling section. In the cooling section, the PP granules come into contact with ambient temperature air conveyed by the cooling section fan (C-1104) and are cooled to 50℃±5℃. Finally, the PP granules are discharged from the ridge tower (T-1101) and conveyed to the packaging machine (T-1103) by the discharge rotary valve (X-1103).

[0036] In the above system, to prevent nitrogen short-circuiting during VOC removal, PP particles in the ridge tower (T-1101) are added to a specified position, ensuring a PP particle filling rate of 75-85% within the ridge tower (T-1101). Before feeding, the nitrogen generator is turned on, and the heating section fan (C-1102) is started to send room-temperature nitrogen into the heater (E-1101) for heating. The temperature after nitrogen heating can be finely adjusted according to the different grades of PP particles, approximately 110℃-125℃. After heating, the nitrogen enters the ridge tower (T-1101) to heat the entire tower and purge the air from the tower. Once the PP particles enter the ridge tower (T-1101), the hot nitrogen heats the PP particles, raising them to the devolatilization temperature, maximizing the devolatilization effect and ensuring the integrity of other properties. The total devolatilization time of PP granules in the ridge tower (T-1101) is 2-3 hours, preferably 2.5-3 hours. Once the PP granules in the ridge tower (T-1101) reach the specified level, the intermediate rotary valve (X-1102) can be opened to begin feeding. By adjusting the rotation speeds of the feed rotary valve (X-1101) and the intermediate rotary valve (X-1102), the residence time and level of the PP granules in the ridge tower (T-1101) are ensured.

[0037] In the above system, a cyclone separator and a fine powder storage area are provided on the side of the roof tower (T-1101). The devolatilization tail gas generated during the devolatilization process is separated into solid and gas by the cyclone separator. The solid enters the fine powder storage area and is discharged through the powder rotary valve (X-1104) at the bottom of the fine powder storage area, while the gas enters the tail gas discharge pipe. The devolatilization tail gas contains nitrogen, VOCs and mixed fine powder.

[0038] In the above system, the nitrogen generator is a nitrogen generator (T-1102) used to separate nitrogen from compressed air. This compressed air is provided by a compressor (C-1105), which, during operation, efficiently compresses air from its natural state, converting it into compressed air with a higher pressure, thus providing a stable source of raw materials for the nitrogen generator (T-1102).

[0039] In the above system, a hopper (V-1101) is provided between the feeding hopper (S-1101) and the feed rotary valve (X-1101). The feeding hopper (S-1101) and the hopper (V-1101) are used to temporarily store and transport the PP granules to be processed. The cooling section fan (C-1104), the heating section fan (C-1102), and the circulating fan (C-1103) are used to ensure that circulating nitrogen, heated nitrogen, and air can smoothly enter the roof tower (T-1101) to control the temperature of the PP granules.

[0040] Preferably, the system further includes a nitrogen filter (F-1101A / B), which is installed before the heater (E-1101) to filter the nitrogen entering the deashing section and prevent impurities from contaminating the PP particles. To improve the filtration effect, multiple nitrogen filters (F-1101A / B) can be connected in parallel.

[0041] Preferably, the system further includes an air filter (F-1102A / B), which is installed before the cooling section fan (C-1104) to filter the air entering the cooling section and prevent impurities from contaminating the PP particles. To improve the filtration effect, multiple air filters (F-1102A / B) can be connected in parallel.

[0042] Optionally, the system also includes a packaging machine (T-1103) for receiving and packaging the PP granules discharged from the roof tower (T-1101). If the packaging machine (T-1103) needs maintenance or replacement, the cooled PP granules can be temporarily placed into a temporary PP granule buffer tank.

[0043] An embodiment of the present invention also provides a method for efficient, energy-saving, and sustainable removal of VOCs from polypropylene materials using the above-described system, comprising the following steps:

[0044] S1. Use a pneumatic conveying device to pneumatically convey PP granules into the feeding hopper (S-1101);

[0045] S2. Feed PP granules from the feed hopper (S-1101) into the feed hopper (V-1101);

[0046] S3. Control the opening of the feed rotary valve (X-1101) so that PP particles enter the roof tower (T-1101) through the feed rotary valve (X-1101);

[0047] S4. Start the compressor (C-1105) to compress air into the nitrogen generator (T-1102) to produce nitrogen;

[0048] S5. Use the heating section fan (C-1102) to send nitrogen to the nitrogen filter (F-1101A / B) for filtration, and then heat it through the heater (E-1101);

[0049] S6. The heated nitrogen gas is introduced into the roof tower (T-1101) to contact the PP particles, raise the temperature and remove VOCs;

[0050] S7. The exhaust gas after VOC removal is introduced into the cyclone separator on the side of the roof tower (T-1101) to separate the nitrogen containing VOC and the fine powder carried out.

[0051] S8. The separated fine powder is stored in the fine powder storage position on the side of the ridge tower (T-1101), and the fine powder is discharged by periodically opening and closing the powder rotary valve (X-1104);

[0052] S9. The nitrogen gas containing VOCs is discharged into a flare for combustion treatment;

[0053] S10. Turn on the circulating fan (C-1103) to allow nitrogen gas at different temperatures to exchange heat with PP particles at different temperatures in the roof tower (T-1101). After the PP particles are de-VOCed in the devolatilization section of the roof tower (T-1101), they are pre-cooled to 95℃~100℃ and enter the cooling section of the roof tower (T-1101) through the intermediate rotary valve (X-1102).

[0054] S11. Turn on the cooling section fan (C-1104) to allow room temperature air to enter the roof tower (T-1101) cooling section after being filtered by the air filter (F-1102A / B), and come into contact with the PP particles, so that the temperature of the PP particles drops to 50℃±5℃.

[0055] S12. Discharge the cooled PP granules through the discharge rotary valve (X-1103).

[0056] It should be noted that the steps in the method provided by the present invention can be implemented using corresponding devices in the system. Those skilled in the art can refer to the technical solution of the system to implement the steps of the method. That is, the embodiments in the system can be understood as preferred examples of the method, and will not be elaborated here.

[0057] In Example 1, the raw materials used, Jinchang Company Automotive Special Material 1 and Jinchang Company Automotive Special Material 2, are various grades and properties of polypropylene materials produced through extrusion granulation. The purpose is to perform deep VOC removal treatment on the granulated polypropylene (PP) to achieve the following according to standard VDA-277: total volatile matter <0.15%, VOC <50ppm; and according to standard PV3900-2000, an odor rating of less than 4.0.

[0058] Example 1

[0059] Test results of this patented device from Shanghai Jinchang

[0060] Sample Name VOCs (ug / g) Jinchang Company Automotive Special Material 1 - Raw Material 61.5 Jinchang Company's automotive-grade material 1-120℃-2H 40.4 Jinchang Company's automotive special material 1-120℃-3H 34.1 Jinchang Company Automotive Special Material 2 - Raw Material 13.7 Jinchang Company's automotive-grade material 2-110℃-2H 8.3 Jinchang Company's automotive-grade material 2-110℃-3H 7.17

Claims

1. A system for efficient, energy-saving, and sustainable removal of VOCs from polypropylene materials, characterized in that, include: a. A feeding device, which includes a pneumatic conveying device and a feeding hopper, wherein the pneumatic conveying device is used to feed the PP granules to be processed into the feeding hopper and controls the PP granules to enter the ridge tower through a feed rotary valve; b. A ridge tower, which includes, from top to bottom, a preheating section, a devolatilization section, a precooling section, and a cooling section. An intermediate rotary valve is provided between the precooling section and the cooling section. The preheating section, devolatilization section, and precooling section are used to preheat, devolatilize, and precool the PP particles under the action of heated nitrogen. The top of the ridge tower is equipped with a feed rotary valve, and the bottom is equipped with a discharge rotary valve. c. A nitrogen generator and a heater are used to generate and heat nitrogen, respectively, to provide the hot nitrogen required for the devolatilization process, which is used to heat the PP particles to 105℃~120℃ during the devolatilization process so that the VOCs remaining in the PP particles are desorbed; a heating section fan is provided between the nitrogen generator and the heater. d. Cooling section fan, used to introduce ambient air into the cooling section of the ridge tower to further cool the pre-cooled PP granules; e. The intermediate rotary valve and the discharge rotary valve are used to control the flow of PP particles in the ridge tower and the discharge from the ridge tower, respectively.

2. The system according to claim 1, characterized in that, A nitrogen circulation pipeline is provided between the preheating section and the precooling section, so that after the hot nitrogen heats the PP particles in the preheating section, the temperature decreases, and then it enters the precooling section through the circulating fan. It comes into contact with the devolatilized PP particles to precool them and lower the temperature of the PP particles to below 105°C. After being reheated, it is circulated back to the preheating section.

3. The system according to claim 2, characterized in that, The PP particles are heated to a temperature of 80℃~90℃ in the preheating section, to a temperature of 105℃~120℃ in the devolatilization section, cooled to a temperature of 95℃~100℃ in the precooling section, and cooled to a temperature of 50℃±5℃ in the cooling section.

4. The system according to claim 1, characterized in that, The PP particle filling rate in the ridge tower is between 75% and 85%; the total devolatilization time of the PP particles in the ridge tower is between 2 and 3 hours.

5. The system according to claim 3, characterized in that, The system also includes an air filter, which is installed before the cooling section fan to filter the air entering the cooling section and prevent impurities from contaminating the PP particles.

6. The system according to claim 1, characterized in that, A cyclone separator and a fine powder storage area are provided on the side of the roof tower. The devolatilization exhaust gas generated during the devolatilization process is separated into solid and gas by the cyclone separator. The solid enters the fine powder storage area and is discharged through the powder rotary valve at the bottom of the fine powder storage area, while the gas enters the exhaust gas outlet. The devolatilization exhaust gas contains nitrogen, VOCs and mixed fine powder.

7. The system according to claim 1, characterized in that, The nitrogen generator is a nitrogen generator used to separate nitrogen from compressed air.

8. The system according to claim 1, characterized in that, The system also includes a nitrogen filter, which is installed before the heater to filter nitrogen entering the deashing section and prevent impurities from contaminating the PP particles.

9. The system according to claim 1, characterized in that, A hopper is provided between the feeding hopper and the feed rotary valve. The feeding hopper and the hopper are used to temporarily store and transport PP particles to be processed.

10. A method for efficient, energy-saving, and sustainable removal of VOCs from polypropylene using the system described in claim 9, comprising the following steps: S1. Use a pneumatic conveying device to pneumatically convey PP granules into the feeding hopper; S2. Feed PP granules from the feed hopper into the feed hopper; S3. Control the opening of the feed rotary valve so that PP particles enter the ridge tower through the feed rotary valve; S4. Start the compressor to force air into the nitrogen generator to produce nitrogen; S5. Use the heating section fan to send nitrogen to the nitrogen filter for filtration, and then heat it through the heater; S6. Heat the nitrogen gas into the roof tower, where it comes into contact with the PP particles, raising the temperature and removing VOCs; S7. The exhaust gas after VOC removal is introduced into the cyclone separator on the side of the roof tower to separate the nitrogen containing VOC and the fine powder carried out. S8. The separated fine powder is stored in the fine powder storage location on the side of the roof tower, and the fine powder is discharged by periodically opening and closing the powder rotary valve; S9. The nitrogen gas containing VOCs is discharged into a flare for combustion treatment; S10. Turn on the circulating fan to allow nitrogen gas at different temperatures to exchange heat with PP particles at different temperatures inside the ridge tower. After the PP particles are de-VOCed in the ridge tower's devolatilization section, they are pre-cooled to 95℃~100℃ and enter the ridge tower's cooling section through the intermediate rotary valve. S11. Turn on the cooling section fan to allow ambient temperature air to enter the roof tower cooling section after being filtered by the air filter, and to come into contact with the PP particles, so that the temperature of the PP particles drops to 50℃±5℃. S12. Discharge the cooled PP granules through the discharge rotary valve.

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