Device and method for removing VOC from polypropylene and reducing odor level by steam method

Abstract

The present invention relates to a device and method for removing VOC from polypropylene and reducing the odor level by steam method, the device comprising: a cyclone separator for separating polypropylene particles from an upstream air delivery system from a conveying gas; a preheating tower connected to the discharge port of the cyclone separator, a first steam inlet provided on the preheating tower body, and a tail gas outlet provided on the top of the preheating tower; a devolatilization tower connected to the discharge port of the preheating tower, a second steam inlet provided on the devolatilization tower body, and a steam outlet provided on the top of the tower, the steam outlet being connected to the first steam inlet. By utilizing the characteristics of low boiling point of water and weak interaction force with non-polar polypropylene molecules, a complete set of technology for removing VOC from polypropylene particles and reducing the odor level by steam method has been developed.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene processing, and in particular to a device and method for removing VOC from polypropylene and reducing odor level by steam method. Background Art

[0002] Polypropylene has developed rapidly abroad due to its excellent comprehensive performance and low production cost. Among the five major synthetic resins used in plastics in the world, the output of polypropylene accounts for about 1 / 4. From a global perspective, the per capita consumption of polypropylene is about 9-10kg, and the per capita consumption of polypropylene in developed countries is 20-32kg. The production, processing, storage and transportation of polypropylene will lead to the generation of volatile organic compounds (VOC). According to the US International Technology Evaluation Center, VOC is one of the most important threats to human health in modern society. The quality of air is directly related to people's health. The harm of VOC pollution to people's health has attracted the attention of the country, manufacturers and consumers.

[0003] In response to this situation, some well-known foreign companies and research institutions have conducted research on low-VOC polypropylene to varying degrees and have made some progress. In the field of polypropylene processing, the main measures to reduce the VOC and odor of polypropylene are: (1) Screening and using more effective stability additives. For example, the use of additive systems that have good compatibility with polypropylene or have synergistic effects can effectively reduce the VOC and odor of polypropylene because stability can be achieved at a lower addition amount. (2) Optimizing the processing technology. Using high-temperature extrusion granulation, using vacuum during the extrusion process, and high-temperature baking and drying of the prepared particles can all remove residues in polypropylene to a certain extent. (3) Adding components that have a good adsorption effect on low-molecular residues. Studies have found that adding a certain amount of inorganic porous materials such as volcanic ash and zeolite molecular sieves can also eliminate VOCs in polypropylene, although the effect is greatly affected by the specific surface area, pore structure, surface structure, pore size, and pore size distribution of such substances.

[0004] In view of the increasing requirements of users for food hygiene and health safety, the existing foreign advanced technology cannot completely solve the VOC and odor problems of polypropylene products. Therefore, the development of VOC removal technology for polypropylene products is an inevitable trend. Summary of the invention

[0005] One of the purposes of the present invention is to provide a device for removing VOC from polypropylene and reducing the odor level by steam. The device can efficiently remove the VOC content in polypropylene materials, reduce its odor level, improve the quality of polypropylene materials, and improve the overall quality of the domestic polypropylene production industry.

[0006] One of the purposes of the present invention is to provide a method for removing VOC from polypropylene and reducing the odor level by steam. The method is based on the above-mentioned device for efficiently removing VOC from polypropylene and reducing the odor level by steam. The principle is to use low-pressure (0-0.15MPa.g, where MPa.g refers to the pressure expressed by gauge pressure) saturated steam as the heating and degassing medium in view of the high VOC content, strong odor and low softening point of polypropylene materials.

[0007] To achieve the above object, the present invention provides a device for removing VOC from polypropylene and reducing the odor level by steam, which comprises:

[0008] A cyclone separator for separating polypropylene particles from the conveying gas from the upstream air conveying system;

[0009] A preheating tower is connected to the discharge port of the cyclone separator, a first steam inlet is provided on the tower body of the preheating tower, and a tail gas outlet is provided on the top of the preheating tower;

[0010] The devolatilization tower is connected with the discharge port of the preheating tower. A second steam inlet is arranged on the tower body of the devolatilization tower, and a steam outlet is arranged on the tower top. The steam outlet is connected with the first steam inlet.

[0011] The device for removing VOC from polypropylene and reducing odor level by steam method of the present invention further comprises:

[0012] A cooling tank is connected to the discharge port of the devolatilization tower, and a cooling water inlet is provided on the cooling tank;

[0013] A particle centrifugal dryer is connected to the discharge port of the cooling tank;

[0014] A vibrating screen connected to a discharge port of a particle centrifugal dryer;

[0015] A feeding hopper, located below the vibrating screen;

[0016] The filter cooler is connected to the particle centrifugal dryer and the devolatilization tower.

[0017] The device for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises: a first rotary valve and a second rotary valve connected in series are arranged between the cyclone separator and the preheating tower; a third rotary valve is arranged between the preheating tower and the devolatilization tower; a fourth rotary valve and a fifth rotary valve connected in series are arranged between the devolatilization tower and the cooling tank, an exhaust port is arranged between the fourth rotary valve and the fifth rotary valve, and a third steam inlet is also arranged on the preheating tower, and the third steam inlet is communicated with the exhaust port.

[0018] The device for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises a particle conveying pump between the cooling tank and the particle centrifugal dryer for conveying a mixture of polypropylene particle material and water.

[0019] The device for removing VOC from polypropylene and reducing odor level by steam method of the present invention comprises an exhaust port and an air suction port on the particle centrifugal dryer, and the exhaust port is connected to a centrifugal fan.

[0020] The device for removing VOC from polypropylene and reducing the odor level by steam method of the present invention, wherein the bottoms of the preheating tower and the devolatilization tower are both provided with steam condensate outlets, and the steam condensate outlets are both installed with Johnson nets, and the aperture of the Johnson nets is less than 0.5 mm;

[0021] The device for removing VOC from polypropylene and reducing the odor level by steam method of the present invention, wherein the preheating tower and the devolatilization tower are both provided with a weighing control system, the weighing control system of the preheating tower is connected to the third rotary valve, and the weighing control system of the devolatilization tower is connected to the fourth rotary valve.

[0022] The device for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises a start-up water replenishment port on the cooling tank and an agitator in the cooling tank.

[0023] The device for removing VOC from polypropylene and reducing the odor level by steam method described in the present invention comprises three or more layers of steam distributors in the preheating tower, a rake is provided at the bottom of the preheating tower, the rake is connected to a motor and performs circular motion in the vertical direction under the drive of the motor.

[0024] The device for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises three or more layers of steam distributors in the devolatilization tower, a rake is provided at the bottom of the devolatilization tower, the rake is connected to a motor and performs circular motion in the vertical direction under the drive of the motor.

[0025] The device for removing VOC from polypropylene and reducing the odor level by steam method described in the present invention, wherein the vibrating screen is equipped with a double-layer screen, and the vibrating screen is provided with a particle inlet, a particle outlet, a fine powder outlet and a large particle outlet, and the particle outlet is connected to the feeding hopper.

[0026] To achieve the above object, the present invention also provides a method for removing VOC from polypropylene and reducing the odor level by steam, using the above-mentioned device, comprising the following steps:

[0027] Feeding: The polypropylene particles from the upstream are transported to the cyclone separator through the upstream pneumatic conveying system for gas-solid separation, and the separated solid polypropylene particles are transported to the preheating tower;

[0028] Degassing: The polypropylene particles fill the preheating tower and flow from top to bottom. Hot steam is introduced into the preheating tower to contact with the polypropylene particles. The material is preheated and then transported to the devolatilization tower. Low-pressure steam is introduced into the devolatilization tower. The polypropylene particles contact with the low-pressure steam in the devolatilization tower to further increase the temperature and perform constant-temperature devolatilization. The removed VOC is discharged with the uncondensed steam and enters the preheating tower to preheat the material.

[0029] The method for removing VOC from polypropylene and reducing the odor level by steam method of the present invention further comprises the following steps:

[0030] Particle cooling and transportation: The devolatilized polypropylene particles enter the cooling tank for cooling;

[0031] Drying and screening: The cooled polypropylene particles are dried in a particle centrifugal dryer, and then sent to a vibrating screen for screening. The qualified polypropylene particles are sent to a feeding hopper;

[0032] Water treatment: Filter and treat the process water containing fine powder discharged from the devolatilization tower and particle centrifugal dryer.

[0033] The method for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises the following steps: the temperature of the hot steam introduced into the preheating tower is 100-105°C, the material is preheated to 80-105°C, and after staying for 20-40 minutes, it is input into the devolatilization tower, and the pressure in the preheating tower is 7.8-25 kPa.

[0034] The method for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises the following steps: the temperature of the steam introduced into the devolatilization tower is 106-127°C, the polypropylene particles are heated to 106-125°C and then subjected to constant temperature devolatilization, the devolatilization time is 1-4 hours, preferably 1.2-3 hours, and the pressure in the devolatilization tower is 25-150 kPa, preferably 80-110 kPa.

[0035] The method for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises cooling the polypropylene particles to 60-80° C. in a cooling tank.

[0036] The method for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises the following steps:

[0037] The polypropylene particles from the upstream are transported to the cyclone separator through the upstream pneumatic conveying system for gas-solid separation. The separated solid-phase polypropylene particles are locked with air through the first rotary valve and the second rotary valve and transported to the preheating tower.

[0038] The polypropylene particles in the preheating tower fill the tower body and flow from top to bottom, contacting with hot steam, and are discharged from the bottom outlet of the tower after being preheated, and sent to the devolatilization tower through the third rotary valve. The VOC-containing steam discharged from the top of the preheating tower is sent to the tail gas treatment section for incineration or mixed with nitrogen for cooling and then discharged to the flare system;

[0039] Low-pressure steam is introduced into the devolatilization tower, and the polypropylene particles are accumulated in the devolatilization tower in a dense phase moving bed and move slowly from top to bottom. They are further heated up by contact with the low-pressure steam and devolatilize at a constant temperature. The excess steam is continuously discharged to the preheating tower through the pressure regulating valve at the top of the devolatilization tower, and the condensate in the devolatilization tower and the preheating tower during startup and operation is discharged from the system;

[0040] The weighing control system of the preheating tower transmits the weight signal of the preheating tower to the speed change device of the third rotary valve, and controls the discharge speed of the preheating tower by controlling the rotation speed, so that the total amount of material in the preheating tower remains constant. The weighing control system of the devolatilization tower transmits the weight signal of the devolatilization tower to the speed change device of the fourth rotary valve, and controls the discharge speed of the devolatilization tower by controlling the rotation speed, so that the total amount of material in the devolatilization tower remains constant.

[0041] The devolatilized polypropylene particles are discharged through the fourth rotary valve and the fifth rotary valve to lock the steam and then enter the cooling tank. The agitator provided in the cooling tank ensures that the particles are evenly mixed with water and are discharged from the discharge port of the cooling tank after cooling. They are then sent to the particle centrifugal dryer through the particle conveying pump for drying and dehydration.

[0042] The polypropylene particles enter the particle centrifugal dryer for drying. Under the suction action of the centrifugal fan, the internal wet air is discharged to further reduce the water content of the particles.

[0043] The dried polypropylene particles are conveyed to the vibrating screen, and the particles are separated from the fine powder and large particles through two layers of screens, and discharged from the equipment through their respective discharge ports, and the particles are conveyed to the feeding hopper;

[0044] The process water containing fine powder discharged from the devolatilizer and particle centrifugal dryer is filtered and treated.

[0045] Beneficial effects of the present invention:

[0046] (1) Using low-pressure steam as the VOC removal medium

[0047] Combining the characteristics of the distribution of amorphous and crystalline regions of polypropylene resin changing with temperature, and taking advantage of the low boiling point of water and the weak interaction between water and non-polar polypropylene molecules, a set of technologies for removing VOC from polypropylene particles and reducing odor levels by steam has been developed. Steam can accelerate the thermal movement of polymer chains in the amorphous and transitional regions of polypropylene particles, promote the enrichment of small molecular VOCs wrapped in the amorphous and transitional regions, and then precipitate VOC molecules under the driving force of concentration difference. At the same time, saturated water vapor has large latent heat and good heat transfer effect. Under sufficient heating conditions, it is also conducive to the diffusion and precipitation of VOCs. The pressure of low-pressure saturated steam is 25-150kPa.g. The steam temperature within this pressure range can achieve the ideal purpose of deep removal of VOCs from materials; if the steam pressure continues to increase, on the one hand, it is not conducive to the escape of VOCs in the material, and on the other hand, the steam temperature increases with the pressure. Too high a temperature will cause the polypropylene particles to soften and deform, and the yellow index to rise.

[0048] (2) Use a preheating tower and a devolatile tower in series to remove VOC

[0049] Its advantages are:

[0050] A: If a single-stage devolatilization tower is used, after the material enters the tower, most of the steam is used to heat the material for condensation, and a small amount of steam is discharged with VOC gas. The amount of steam passing through the material layer is small, and the steam does not carry VOC sufficiently, which will inevitably lead to unsatisfactory VOC removal effect.

[0051] B: Double tower operation is adopted. The purpose of the devolatilization tower is to allow the steam to fully contact the material and carry VOC out of the discharge equipment, and the purpose of the preheating tower is to heat the material. After the steam is introduced into the devolatilization tower, since the material has been preheated, only a small amount of steam condenses, and most of the steam passes through the material layer and carries VOC out of the devolatilization tower and enters the preheating tower to heat the material. The operating pressure of the devolatilization tower is about 25~150kPa.g, and the operating pressure of the preheating tower is about 7.8~25kPa.g. Finally, the exhaust steam carrying VOC is discharged from the preheating tower, and the discharge temperature is low, which realizes the cascade utilization of steam and effectively reduces the steam energy loss.

[0052] C: The upstream of the preheating tower is the air delivery system feed rotary valve. Reducing the operating pressure of the preheating tower can reduce the operating pressure of the rotary valve, thereby reducing the difficulty of the rotary valve design, better achieving system sealing and reducing steam loss.

[0053] D: When the material is discharged from the bottom of the devolatilization tower, it will carry a small amount of steam. Introducing this part of steam into the preheating tower can realize the secondary utilization of steam and further reduce heat loss.

[0054] (2) Hydraulic conveying of solid particles

[0055] The particles after VOC removal are transported by hydraulic power, which can prevent contact with oxygen, make the system safer, and avoid the contact between hot materials and air to produce new VOC. The solid-liquid mixture is transported by a vortex pump or a Tesla pump. A vortex pump or a Tesla pump is a type of pump suitable for transporting materials containing solid particles. It uses a vortex impeller with a semi-open or open structure and is placed on one side of the volute. The volute flow channel in front of the impeller is free of any obstruction, so it can transport fluids with various solids without clogging and has good passing performance.

[0056] (3) Use a particle dryer + vibrating screen to dry the material

[0057] The particle centrifugal dryer is a device specially used to remove water droplets attached to the surface of particles. Working together with the vibrating screen, it can reduce the moisture content of particles to ≤5‰, meeting the product technical requirements.

[0058] (4) Tail gas emission process after devolatilization

[0059] The VOC-containing steam discharged from the preheating tower cannot be discharged directly to the flare. If the tail gas is condensed through a heat exchanger, a higher concentration of VOC gas will be formed. This gas is used as the second release source. It is necessary to divide the explosion-proof area in the engineering design, and the safety design of the entire system needs to be improved. For this reason, nitrogen is added before the tail gas is condensed and then cooled. In this way, nitrogen is used to replace steam to avoid the generation of dangerous gases. At the same time, the replaced tail gas can be directly discharged to the flare system, which is simple in process and highly safe.

[0060] (5) Compared with the existing polypropylene particle fine powder removal cooling process, the filter cooler has the following advantages: fine powder filtration and process water cooling are achieved in one device, replacing the traditional polypropylene fine powder filtration equipment and process water cooling equipment, and filtering thoroughly, avoiding the possibility of fine powder entering the cooling equipment and not clogging the heat exchange equipment. It occupies a small area, and the purified water after filtration and cooling can flow to the water-using equipment by high head difference, without the need for water pump transportation.

[0061] (6) Compared with the method described in the patent "System for deep removal of VOC and drying of polypropylene materials" (patent number 2020209583124), the present invention is not only suitable for intermittent working conditions, but is more suitable for continuous working conditions, and can be used to process large quantities of polypropylene materials with simple operation. The method described in Chinese patent 2020209583124 is only suitable for small-batch production processes under intermittent working conditions.

[0062] (7) Through the method of the present invention, the polypropylene processing capacity is 0.1 to 50 tons / hour, or even larger. The VOC content of the polypropylene material to be processed is greater than 300 ppm, and the VOC of the treated polypropylene material is less than 60 ppm, and the VOC can be further reduced to below 20 ppm, meeting the product technical requirements.

[0063] (8) The investment and operation costs of the device are low, and the product quality is greatly improved, which can meet the requirements of the EU standard for automotive materials (VOC ≤ 80ppm). BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a schematic structural diagram of a device for removing VOC from polypropylene and reducing odor levels using a steam method according to an embodiment of the present invention;

[0065] Figure 2 The present invention is a flowchart of a method for removing VOC from polypropylene and reducing odor levels by steam method according to an embodiment of the present invention.

[0066] Reference numerals:

[0067] 1. Cyclone separator, 2-1. First rotary valve, 2-2. Second rotary valve, 3. Preheating tower, 4. Third rotary valve, 5. Devolatilization tower, 6. Fourth rotary valve, 7. Fifth rotary valve, 8. Cooling tank, 9. Particle conveying pump, 10. Particle centrifugal dryer, 11. Centrifugal fan, 12. Vibrating screen, 13. Feeding hopper, 14. Filter cooler; DETAILED DESCRIPTION

[0068] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0069] refer to Figure 1 A device for removing VOC from polypropylene and reducing the odor level by steam method, comprising: a cyclone separator 1, used to separate polypropylene particles from an upstream air delivery system from conveying air; the cyclone separator 1 comprises a feed port, an exhaust port and a discharge port, the feed port is connected to the air delivery system through a pipeline, and the exhaust port discharges the conveying air to a downstream dust removal device; a preheating tower 3, which is connected to the discharge port of the cyclone separator 1, a first steam inlet is provided on the tower body of the preheating tower 3, and a tail gas outlet is provided on the top of the preheating tower 3; a devolatilization tower 5, which is connected to the discharge port of the preheating tower 3, a second steam inlet is provided on the tower body of the devolatilization tower 5, and a steam outlet is provided on the top of the tower, and the steam outlet is connected to the first steam inlet.

[0070] When used specifically, the polypropylene particles from the upstream are transported to the cyclone separator 1 through the upstream pneumatic conveying system for gas-solid separation, and the separated solid-phase polypropylene particles are transported to the preheating tower 3; the polypropylene particles fill the preheating tower 3 and flow from top to bottom, and hot steam is introduced into the preheating tower 3 to contact with the polypropylene particles. The material is preheated and then transported to the devolatilization tower 5; low-pressure steam is introduced into the devolatilization tower 5, and the polypropylene particles are further heated by contacting with the low-pressure steam in the devolatilization tower 5 and devolatilization is performed at a constant temperature, and the removed VOC is discharged with the uncondensed steam and enters the preheating tower 3 to preheat the material.

[0071] As a preferred embodiment, it also includes: a cooling tank 8, which is connected to the discharge port of the devolatilization tower 5, and the cooling tank 8 is provided with a cooling water inlet; a particle centrifugal dryer 10, which is connected to the discharge port of the cooling tank 8; a vibrating screen 12, which is connected to the discharge port of the particle centrifugal dryer 10; a feeding hopper 13, which is located below the vibrating screen 12, whose inlet is connected to the discharge port of the vibrating screen 12 through a pipeline, and whose outlet is connected to the downstream air delivery system; a filter cooler 14, which is connected to the particle centrifugal dryer 10 and the devolatilization tower 5.

[0072] As a preferred embodiment, a first rotary valve 2-1 and a second rotary valve 2-2 are provided in series between the cyclone separator 1 and the preheating tower 3; a third rotary valve 4 is provided between the preheating tower 3 and the devolatilization tower 5, and the third rotary valve 4 connects the discharge port of the preheating tower 3 and the feed port of the devolatilization tower 5, and its function is to lock steam and solid particle transportation, prevent a large amount of steam in the devolatilization tower 5 from entering the preheating tower 3 through the third rotary valve 4, and at the same time transport the particle material into the downstream devolatilization tower 5; a fourth rotary valve 6 and a fifth rotary valve 7 are provided in series between the devolatilization tower 5 and the cooling tank 8, and a two-stage rotary valve (fourth rotary valve 6, fifth rotary valve 7) is used in series, and its function is to lock steam and solid particle transportation, prevent steam in the devolatilization tower 5 upstream of the fourth rotary valve 6 from entering the downstream cooling tank 8, and at the same time transport the polypropylene material downstream. The inlet of the fourth rotary valve 6 is connected to the discharge port of the devolatilization tower 5, and the outlet of the fifth rotary valve 7 is connected to the feed port of the downstream cooling tank 8. An exhaust port is provided between the fourth rotary valve 6 and the fifth rotary valve 7, and its function is to discharge a small amount of steam carried during the material conveying process. A third steam inlet is also provided on the preheating tower 3, and the third steam inlet is communicated with the exhaust port.

[0073] A two-stage rotary valve (first rotary valve 2-1, second rotary valve 2-2) is used in series between the cyclone separator 1 and the preheating tower 3, which is used to lock steam and solid particle transportation, prevent steam in the preheating tower 3 downstream of the rotary valve from entering the cyclone separator 1, and transport the polypropylene material downstream. The inlet of the first rotary valve 2-1 is connected to the discharge port of the cyclone separator 1, and the outlet of the second rotary valve 2-2 is connected to the feed port of the downstream preheating tower 3.

[0074] The discharge port of the preheating tower 3 is connected to the downstream third rotary valve 4, and the tower is designed with three or more layers of steam distributors. The polypropylene material is filled in the preheating tower. The preheating tower 3 is provided with two steam inlets, the first steam inlet and the third steam inlet. The first steam inlet is connected to the steam outlet from the downstream devolatilization tower 5 through a pipeline, and the third steam inlet is connected to the exhaust port between the fourth rotary valve 6 and the fifth rotary valve 7 through a pipeline. Steam enters the steam distributor of the preheating tower 3 from the steam inlet on the preheating tower 3 body, and is evenly dispersed in the tower to directly contact and exchange heat with polypropylene particles. A rake is provided at the bottom of the preheating tower 3, and a motor is used to drive the rake to perform circular motion in a vertical reverse direction to prevent polypropylene particles from bridging at the discharge port at the bottom of the tower, and at the same time help the particle material to discharge smoothly. A steam condensate outlet is provided at the bottom of the preheating tower 3, and the steam condensate outlet is installed with a Johnson net (aperture <0.5mm), which is used to discharge the steam condensate after steam heat exchange condensation from the preheating tower 3 and prevent the particle material from being discharged. A tail gas outlet is provided at the top of the preheating tower, and the tail gas outlet discharges a small amount of steam carrying VOC out of the system.

[0075] The discharge port of the devolatilization tower 5 is connected to the fourth rotary valve 6, and the interior of the tower is designed with three or more layers of steam distributors. The polypropylene material is filled in the devolatilization tower 5. A steam inlet is arranged on the tower body of the devolatilization tower 5. The steam inlet is connected to the low-pressure steam from the public engineering system through a pipeline. The steam enters the steam distributor in the tower from the steam inlet on the tower body of the devolatilization tower 5, and is evenly dispersed in the tower to directly contact and exchange heat with the polypropylene particles. A rake is arranged at the bottom of the devolatilization tower 5. The motor drives the rake to perform circular motion in the vertical reverse direction to prevent the polypropylene particles from bridging at the discharge port at the bottom of the tower, and at the same time helps the particle material to be discharged smoothly. A steam outlet is arranged at the top of the devolatilization tower, and most of the uncondensed steam is discharged from the steam outlet and connected to the steam inlet of the preheating tower 3 through a pipeline. A steam condensate outlet is arranged at the bottom of the devolatilization tower 5, and the steam condensate outlet is installed with a Johnson net (aperture <0.5mm), which is used to discharge the steam condensate after steam condensation out of the devolatilization tower 5 and prevent the particle material from being discharged.

[0076] The inlet of the cooling tank 8 is connected to the outlet of the fifth rotary valve 7 through a pipeline. The cooling tank 8 is provided with a cooling process water inlet, which is connected to the process water outlet from the filter cooler 14 through a pipeline. The process water and the particulate material enter the cooling tank 8 and are evenly mixed under the action of the agitator, and are discharged through the outlet of the cooling tank 8. At the same time, the top of the cooling tank 8 is also provided with a start-up water replenishment port for replenishing cooling water during start-up.

[0077] The particle centrifugal dryer 10 is a device specially used to remove water droplets attached to the surface of particles. It mainly uses the centrifugal force field and the bouncing impact of particles for dehydration. Under the action of centrifugal force, the water droplets flow from the screen holes into the annular water channel between the cylinder and the screen, and then are discharged from the drain port into the downstream filter cooler 14. At the same time, in order to increase the drying effect, the equipment is provided with an exhaust port and an air suction port. The air suction port is provided with a dust removal screen to prevent impurities from entering the dryer with the air. The exhaust port is connected to the centrifugal fan 11 through a pipeline. Under the suction action of the centrifugal fan 11, the internal humid air is discharged to further reduce the water content of the particles. The particle centrifugal dryer 10 is also provided with a particle outlet.

[0078] The function of the vibrating screen 12 is to separate a small amount of fine powder carried in the granular material through vibration screening. A double-layer screen is installed in the vibrating screen 12, and the mesh number of the screen can be selected according to the specific situation, for example, it can be 4 mesh and 8 mesh. The vibrating screen 12 is respectively provided with a particle inlet, a particle outlet, a fine powder outlet and a large particle outlet. The particle inlet is connected to the particle outlet of the particle dryer 10 through a pipeline, the particle outlet is connected to the feeding hopper 13 through a pipeline, and the fine powder outlet discharges the screened fine powder out of the vibrating screen 12. The large particle outlet is used to discharge abnormal large particle size particles brought into the vibrating screen 12 out of the vibrating screen 12.

[0079] The filter cooler 14 is used to separate the fine powder generated during the devolatilization and drying process of the system from the process water and to cool the process water at the same time.

[0080] As a preferred embodiment, a particle delivery pump 9 is provided between the cooling tank 8 and the particle centrifugal dryer 10 for delivering a mixture of polypropylene particle material and water. The discharge port of the cooling tank 8 is connected to the particle delivery pump 9 through a pipeline. The outlet of the particle delivery pump 9 is connected to the inlet of the particle centrifugal dryer 10. The delivery pump can be a vortex pump or a Tesla pump. No specific specification is made, as long as the material delivery can be achieved. Specifically, products of Dalian Haite Pump Co., Ltd., Kunming Jiahe Technology Co., Ltd., and Shanghai Denai Pump Co., Ltd. can be selected.

[0081] As a preferred embodiment, the preheating tower 3 and the devolatilization tower 5 are both provided with a weighing control system. The weighing control system of the preheating tower 3 is connected to the third rotary valve 4 , and the weighing control system of the devolatilization tower 5 is connected to the fourth rotary valve 6 .

[0082] Please refer to Figure 2 The method for removing VOC from polypropylene and reducing the odor level by steam method of the present invention comprises the following steps:

[0083] (1) Feeding process: The polypropylene particles from the upstream are transported to the cyclone separator 1 through the upstream pneumatic conveying system for gas-solid separation. The separated solid-phase polypropylene particles are locked with air through the first rotary valve 2-1 and the second rotary valve 2-2 and transported to the preheating tower 3;

[0084] (2) Degassing process: The polypropylene particles fill the preheating tower 3 and flow from top to bottom, directly contacting with steam at a temperature of about 100-105°C from the devolatilization tower 5. The material is preheated to about 100°C and then discharged from the bottom outlet of the tower, contacting with the polypropylene particles. The material is preheated and transported to the devolatilization tower 5; 106-127°C steam is introduced into the devolatilization tower 5, and the material is directly in contact with the steam in the tower and further heated to nearly 120°C for constant temperature devolatilization. The polypropylene particles are accumulated in the tower in a dense phase moving bed and move slowly from top to bottom to ensure a certain residence time. The residence time in the preheating tower 3 is about 30 minutes, and the residence time in the devolatilization tower 5 is about 1-4 hours, and the optimal residence time is 1.2-3 hours. The control pressure in the devolatilization tower 5 is about 25-150 kPa.g, and the optimal control pressure is 80-110 kPa.g. The excess steam is continuously discharged to the preheating tower 3 through the tower top pressure regulating valve. The control pressure of the preheating tower 3 is about 7.8-25 kPa.g. The steam condensate outlet at the bottom of the preheating tower 3 and the devolatilization tower 5 can discharge the condensate in the tower during startup and operation.

[0085] The VOC-containing steam discharged from the top of the preheating tower 3 can be sent to the tail gas treatment section for incineration, or mixed with nitrogen and cooled before being discharged to the flare system.

[0086] The preheating tower 3 and the devolatilization tower 5 are equipped with a weighing control system, through which the weight signals of the preheating tower 3 and the devolatilization tower 5 are transmitted in real time to the speed change devices of the third rotary valve 4 and the fourth rotary valve 6 at the bottom of the corresponding tower, and the rotation speed of the rotary valve is controlled, thereby controlling the discharge speed of the preheating tower 3 and the devolatilization tower 5, so that the total amount of material in the tower is kept constant.

[0087] (3) Particle cooling and conveying process: After devolatilization, the polypropylene pellets are discharged through the fourth rotary valve 6 and the fifth rotary valve 7 to lock the steam and enter the cooling tank 8. The cooling process water from the filter cooler 14 also enters the cooling tank 8 by gravity. The cooling tank 8 is equipped with an agitator to ensure that the pellets and water are evenly mixed and cooled to 60-80°C before being discharged from the outlet of the cooling tank 8 and sent to the pellet centrifugal dryer 10 for drying and dehydration through the pellet conveying pump 9.

[0088] (4) Drying and screening process: When the particles enter the particle centrifugal dryer 10 and contact the inclined segmented blades, they are thrown up in a spiral, forming a sawtooth irregular motion trajectory between the rotor and the screen. At the same time, the particles jump and collide in the space between the screen and the rotor at a certain frequency. Under the action of centrifugal force, the escaped water droplets flow from the screen holes into the annular water channel between the cylinder and the screen, and then are discharged from the drain port into the downstream filter cooler 14. At the same time, in order to increase the drying effect, the equipment is provided with an exhaust port and an air suction port. The exhaust port is connected to the centrifugal fan 11 through a pipeline. Under the suction action of the centrifugal fan 11, the internal humid air is discharged to further reduce the water content of the particles. The hot polypropylene particle material enters the feed port of the vibrating screen 12 evenly from the discharge port of the particle centrifugal dryer 10. Under the excitation force of the vibration motor, it jumps and screens toward the discharge port. The particle material is separated from the fine powder and large particles through two layers of screens and discharged from the equipment through their respective discharge ports. The material is further cooled and dried in the vibrating screen 12, and its own heat is used to further dry the moisture, and the moisture content of the final discharged material is ≤5‰. The qualified polypropylene granules after screening are discharged from the discharge port of the vibrating screen 12 into the feeding hopper 13, and are sent to the homogenization silo through the downstream air delivery system.

[0089] The process water discharged from the drain port of the particle centrifugal dryer 10 enters the filter cooler 14 to separate the conveying water and dust. The filter cooler 14 is designed with two chambers, one of which is a slender water purification chamber with a heat exchanger designed at the bottom, and the other chamber is a fine powder discharge chamber. The process water entering the filter cooler 14 from the particle centrifugal dryer 10 falls into the water purification chamber. The density difference between fine powder and water is used to cause the fine powder to suspend on the water surface and overflow to the fine powder discharge chamber. The dust-containing water in the fine powder discharge chamber is discharged from the equipment. The process water without fine powder in the water purification chamber is returned to the cooling water tank 8 by gravity flow to mix with the particle material and be recycled.

[0090] The present invention discloses a system and method for efficiently removing VOC from polypropylene and reducing the odor level by steam method. The raw material processed is gas phase polypropylene material, and the system and method are also applicable to granular polypropylene materials produced by other processes and methods.

[0091] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for removing VOC from polypropylene and reducing odor level by steam, characterized in that: A device for removing VOC and reducing odor levels in polypropylene using a steam method, the device comprising: A cyclone separator for separating polypropylene particles from the conveying gas from the upstream air conveying system; A preheating tower is connected to the discharge port of the cyclone separator, a first steam inlet is provided on the tower body of the preheating tower, and a tail gas outlet is provided on the top of the preheating tower; A devolatilization tower is connected to the discharge port of the preheating tower, a second steam inlet is provided on the tower body of the devolatilization tower, and a steam outlet is provided on the tower top, and the steam outlet is connected to the first steam inlet; A cooling tank is connected to the discharge port of the devolatilization tower, and a cooling water inlet is provided on the cooling tank; A particle centrifugal dryer is connected to the discharge port of the cooling tank; A vibrating screen connected to a discharge port of a particle centrifugal dryer; A feeding hopper, located below the vibrating screen; A filter cooler connected to the particle centrifugal dryer and the devolatilization tower; The method comprises the following steps: Feeding: The polypropylene particles from the upstream are transported to the cyclone separator through the upstream pneumatic conveying system for gas-solid separation, and the separated solid polypropylene particles are transported to the preheating tower; Degassing: The polypropylene particles fill the preheating tower and flow from top to bottom. Hot steam at 100-105℃ is introduced into the preheating tower to contact the polypropylene particles. The pressure in the preheating tower is 7.8-25kPa. The material is preheated and then transported to the devolatilization tower. Low-pressure steam at 106-127℃ is introduced into the devolatilization tower. The polypropylene particles are further heated up by contacting the low-pressure steam in the devolatilization tower and devolatilize at a constant temperature. The removed VOC is discharged with the uncondensed steam and enters the preheating tower to preheat the material. The pressure in the devolatilization tower is 25-150kPa. Particle cooling and transportation: The devolatilized polypropylene particles enter the cooling tank for cooling; Drying and screening: The cooled polypropylene particles are dried in a particle centrifugal dryer, and then sent to a vibrating screen for screening. The qualified polypropylene particles are sent to a feeding hopper; Water treatment: Filter and treat the process water containing fine powder discharged from the devolatilization tower and particle centrifugal dryer.

2. The method for removing VOC from polypropylene and reducing odor level by steam according to claim 1, characterized in that: A first rotary valve and a second rotary valve connected in series are provided between the cyclone separator and the preheating tower; a third rotary valve is provided between the preheating tower and the devolatilization tower; a fourth rotary valve and a fifth rotary valve connected in series are provided between the devolatilization tower and the cooling tank, an exhaust port is provided between the fourth rotary valve and the fifth rotary valve, and a third steam inlet is also provided on the preheating tower, and the third steam inlet is communicated with the exhaust port.

3. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: A particle conveying pump is arranged between the cooling tank and the particle centrifugal dryer for conveying a mixture of polypropylene particle material and water.

4. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The particle centrifugal dryer is provided with an exhaust port and an air suction port, and the exhaust port is connected to a centrifugal fan.

5. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The bottoms of the preheating tower and the devolatilization tower are both provided with steam condensate outlets, and the steam condensate outlets are both installed with Johnson nets, and the aperture of the Johnson nets is less than 0.5 mm.

6. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The preheating tower and the devolatilization tower are both provided with a weighing control system. The weighing control system of the preheating tower is communicated with the third rotary valve, and the weighing control system of the devolatilization tower is communicated with the fourth rotary valve.

7. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The cooling tank is also provided with a water filling port for starting the machine, and a stirrer is arranged in the cooling tank.

8. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The preheating tower is provided with three or more layers of steam distributors, and the bottom of the preheating tower is provided with a rake, which is connected to a motor and performs circular motion in a vertical direction under the drive of the motor.

9. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The devolatilization tower is provided with three or more layers of steam distributors, and the bottom of the devolatilization tower is provided with a rake, which is connected to a motor and performs circular motion in a vertical direction under the drive of the motor.

10. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The vibrating screen is equipped with a double-layer screen, and is provided with a particle inlet, a particle outlet, a fine powder outlet and a large particle outlet, and the particle outlet is connected to the feeding hopper.

11. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: In the preheating tower, the material is preheated to 80-105°C, and then input into the devolatilization tower after staying for 20-40 minutes.

12. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The polypropylene particles in the devolatilization tower are heated to 106-125°C and then devolatilized at a constant temperature for 1-4 hours.

13. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 12, characterized in that: The pressure inside the deoxidation tower is 80-110 kPa.

14. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The polypropylene particles are cooled to 60-80°C in a cooling tank.

15. The method for removing VOC from polypropylene and reducing odor level by steam method according to claim 1, characterized in that: The following steps are involved: The polypropylene particles from the upstream are transported to the cyclone separator through the upstream pneumatic conveying system for gas-solid separation. The separated solid-phase polypropylene particles are locked with air through the first rotary valve and the second rotary valve and transported to the preheating tower. The polypropylene particles in the preheating tower fill the tower body and flow from top to bottom, contacting with hot steam, and are discharged from the bottom outlet of the tower after being preheated, and sent to the devolatilization tower through the third rotary valve. The VOC-containing steam discharged from the top of the preheating tower is sent to the tail gas treatment section for incineration or mixed with nitrogen for cooling and then discharged to the flare system; Low-pressure steam is introduced into the devolatilization tower, and the polypropylene particles are accumulated in the devolatilization tower in a dense phase moving bed and move slowly from top to bottom. They are further heated up by contact with the low-pressure steam and devolatilize at a constant temperature. The excess steam is continuously discharged to the preheating tower through the pressure regulating valve at the top of the devolatilization tower, and the condensate in the devolatilization tower and the preheating tower during startup and operation is discharged from the system; The weighing control system of the preheating tower transmits the weight signal of the preheating tower to the speed change device of the third rotary valve, and controls the discharge speed of the preheating tower by controlling the rotation speed, so that the total amount of material in the preheating tower remains constant. The weighing control system of the devolatilization tower transmits the weight signal of the devolatilization tower to the speed change device of the fourth rotary valve, and controls the discharge speed of the devolatilization tower by controlling the rotation speed, so that the total amount of material in the devolatilization tower remains constant. The devolatilized polypropylene particles are discharged through the fourth rotary valve and the fifth rotary valve to lock the steam and then enter the cooling tank. The agitator provided in the cooling tank ensures that the particles are evenly mixed with water and are discharged from the discharge port of the cooling tank after cooling. They are then sent to the particle centrifugal dryer through the particle conveying pump for drying and dehydration. The polypropylene particles enter the particle centrifugal dryer for drying. Under the suction action of the centrifugal fan, the internal wet air is discharged to further reduce the water content of the particles. The dried polypropylene particles are conveyed to the vibrating screen, and the particles are separated from the fine powder and large particles through two layers of screens, and discharged from the equipment through their respective discharge ports, and the particles are conveyed to the feeding hopper; The process water containing fine powder discharged from the devolatilizer and particle centrifugal dryer is filtered and treated.

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