CN101486032A - Inertia elutriator for plastic pellets material as well as elutriation technique and use thereof - Google Patents

Abstract

The invention relates to an inertial elutriator for plastic pellets and its elutriation process and application, relating to plastic production. The elutriator includes an elutriation cylinder and an outlet N4. Air inlet N3, convection separation cylinder, air outlet N2, acceleration inner cylinder, acceleration cylinder, cone cylinder, air inlet cylinder, air inlet N5 and feeding cylinder. The upper end of the feed cylinder is inserted into the air intake cylinder at the lower end of the feed port. Two layers of grids are fixed in the elutriation cylinder, the grid inclination angle is 30°～60°, and the spacing is 30～100mm. The length of the accelerating cylinder is 600-1200mm, and its pipe diameter is the same as that of the feeding cylinder, and the effect is best when the length of the convection separating cylinder is 300mm. The best process conditions are: the wind speed of the air inlet N5 is 10-20m/s, the wind speed of the air inlet N3 is 10-15m/s, and the feeding speed of the feeding inlet N1 is less than 800g/s, accelerating the inner cylinder and convection The wind speed in the annulus of the separating cylinder is less than 15m/s. It can remove fine dust in the pellets and greatly reduce the overflow of pellets with the airflow. The comprehensive classification efficiency reaches 97.8%, an increase of 28%.

Description

Inertial elutriator for plastic pellets and its elutriation process and application

technical field

The invention belongs to the production technical field of plastic pellets, and more specifically relates to the improvement and innovation of an inertial elutriator for plastic pellets and its elutriation process and application.

Background technique

Inertial elutriator is a kind of particle classification equipment, which is mainly used for the separation of tiny grains and fiber dust in granular products. Its working principle is: using the speed difference between the gas-solid two-phase in each area, the particles attached to the surface of the particles The fine dust is shed by the shear action of the gas on the solid surface. The airflow suddenly accelerates, decelerates or changes direction, and the airflow boundary layer bypassing the pellet surface needs to be re-established. At this time, the shear force of the airflow on the pellet surface is multiplied. During operation, the solid particles entering the device go through an acceleration and deceleration stage, and under the shearing action of the air flow, the coarse and fine particles are separated, and the finished product particles fall to the silo, and the fine dust is discharged out of the device with the air flow, so as to achieve elutriation cleanliness the goal of. No. 200520030469.6 patent application titled "solid particle separation hopper" is exactly this structure.

For any classification method, in order to obtain a better classification effect, the key is how to improve the dispersibility of the classified materials and choose a suitable separation method.

The existing problems of elutriators are:

(1) The residence time of the pellets in the device is short, and the elutriation is not sufficient. One of the characteristics of existing elutriators is that the processing capacity is large, and the processing capacity that has is 27000kg/h, namely 7.5kg/s. The falling height of the pellets was about 3.5 m. The distance from the feeding area to the cone where the pellets are in contact with the gas is about 2.0m, and the contact time is only about 2s. During this period, the pellets first flow in parallel with the gas, and then turn into a countercurrent flow. After entering the circulation area, the gas blows horizontally through the vertically falling solid phase flow. There is still a small amount of dust attached to the surface of the particles in the material.

(2) A small amount of pellets are carried out in the outlet air. In the convection zone, after the downdraft meets the updraft, it turns into a lateral flow and directly flows out of the device. Since the outlet has no shielding measures, when the particles close to the side wall meet the local high-speed lateral airflow, they will enter the annular exhaust chamber with the airflow, and be discharged out of the device together with the gas and fine dust, resulting in material leakage.

The flow field of the traditional elutriator mainly has three problems: the radial velocity gradient of the air flow in the acceleration section is too large, which will lead to uneven acceleration of the pellets; the area above and below the sleeve in the convection section is connected to the annular gap, so that Part of the gas in the gas-solid two-phase flow from the feeding section will suddenly turn into a lateral flow in the area above the upper end of the sleeve and enter the annulus. Turning to lateral flow into the annulus, the radial velocity of the two streams of fluid diverted from top to bottom will take out part of the large particles entering the convection section; fine dust is still attached to the granular products after elutriation, resulting in poor product quality Up to standard.

In short, in the traditional production of plastic pellets such as polyethylene, due to the complexity of gas-solid two-phase flow and the lack of experiments, the elutriation method and structural design of inertial elutriators are still not reasonable enough. Therefore, plastic dust is entrained in the product pellets, which not only affects product quality but also affects market sales. At the same time, a small amount of granular material overflows with the airflow, causing material loss. The main reason for the above problems is that the current inertial pellet elutriators do not elutriate and clean the fine dust in the pellets. These problems need to be solved urgently.

Contents of the invention

The object of the present invention is to overcome the above-mentioned shortcomings and deficiencies, and to provide a plastic pellet inertial elutriator and its elutriation process and application. According to the movement law of particles in the elutriation flow field and its influencing factors, it uses the periodic change of the relative velocity of the gas-solid two-phase to strengthen the elutriation process, and then strengthens the shearing effect of the airflow on the particle surface and the airflow turbulence of the elutriation cylinder. movement, suppressing the harmful circulating vortex. Therefore, the mechanical structure and turbulent flow field structure in the elutriator are improved, and optimized process parameters are provided to remove plastic fine dust in the pellets and improve the separation efficiency of the elutriator. At the same time, the overflow of pellets with the airflow is greatly reduced, and the pollution of the environment is greatly reduced. It can be widely used in the classification and elutriation of coarse and fine particles in the production of plastic pellets.

In order to achieve the above purpose, the present invention includes an elutriation cylinder, an air inlet N3 installed in the middle of the elutriation cylinder, a feed inlet and an air outlet. The bottom of the elutriation cylinder is a cone, and the bottom of the cone is provided with a discharge port N4. The air inlet N3 is welded on the middle side of the elutriation cylinder. The upper part of the elutriation cylinder is a cone with reduced diameter, and the top of the cone is welded with a convection separation cylinder. The diameter of the convective separation cylinder is smaller than that of the elutriation cylinder. The middle side of the convection separation cylinder is welded with an air outlet N2. An acceleration inner cylinder is welded in the middle of the top of the convection separation cylinder, and most of the acceleration inner cylinder is inserted into the convection separation cylinder to leave an annular gap and its upper end is higher than the upper end of the convection separation cylinder. The top of the acceleration inner cylinder is welded with the acceleration cylinder. The top of the acceleration tube is welded with a small cone, and the upper end of the small cone is welded with an air intake tube. The upper side of the air intake cylinder is welded with an air inlet N5, and the feeding cylinder inserted into the air intake cylinder is welded along the middle of the air intake cylinder with an annular gap between them. The upper end of the feeding cylinder is the feeding port N1.

The acceleration inner cylinder is long tapered, its upper end is connected with the acceleration cylinder and has the same diameter, and then the caliber gradually expands. After connecting the accelerating cylinder and the accelerating inner cylinder with gradually expanding diameter, the short-circuit flow and dead vortex in the annulus at the top of the convection section are effectively eliminated, the mutual disturbance of the opposing airflow is avoided, and it is more conducive to the dispersion of materials.

The upper part of the elutriation cylinder is fixed with two layers of grids. The inclination angle of the grid is 30°～60°, and the pitch is 30～100mm. These unique internal component designs make the gas phase flow field more uniform and regular, increase the shearing effect of the air flow on the pellets, and prolong the residence time. At the same time, when the pellets reach the grid, they will collide with the grid and slide down. Almost all the particles are in contact with the metal grid, and the metal grid can eliminate the static electricity generated by the friction between the pellets. The advantage of eliminating static electricity is that the pellets with static electricity enter the silo and packaging system and cause fire and other dangers. The LDPE device of a certain factory has learned lessons in this regard. After eliminating static electricity, the safety of the system is greatly improved; pellets Static electricity will attract the dust with the opposite charge, making it difficult for the dust to leave the surface of the pellets, resulting in poor washing effect. After the static electricity is eliminated, together with the bouncing and shaking of the pellets after colliding with the grid, the elutriation effect can be greatly improved. In short, adding grilles not only eliminates potential safety hazards but also greatly improves the overall classification efficiency.

The length of the acceleration cylinder is 600-1200mm, and its pipe diameter is the same as that of the feeding cylinder, and the length of the convection separation cylinder is 200-500mm. This size range works best.

According to the above-mentioned elutriation process of the inertial elutriator for plastic pellets, the wind speed of the upper air inlet N5 is 10-20m/s, the wind speed of the lower air inlet N3 is 10-15m/s, and the feed of the feed inlet N1 The speed is less than 800g/s. The wind speed in the annulus of the acceleration inner cylinder and the convection separation cylinder is less than 15m/s.

The above process conditions are extremely reasonable, which prolongs the processing time and makes the material have obvious luster. The biggest advantage is reflected in the treatment of attached dust, which is clean and dust-free.

The elutriator and its elutriation process are used in the production of plastic granules and other granules to separate the coarse and fine particles, and the clean finished granules fall to the silo, and the tiny grains and fiber dust are discharged out of the device with the airflow.

According to the movement law of the particles in the elutriation flow field and its influencing factors, the present invention utilizes the periodical change of the relative velocity of the gas-solid two-phase to strengthen the elutriation process, thereby strengthening the shearing effect of the air flow on the surface of the particles and the air flow of the elutriation cylinder Turbulence, suppression of harmful circulating vortices. Therefore, the mechanical structure and turbulent flow field structure in the elutriator are improved, and optimized process parameters are provided to remove plastic fine dust in the pellets and improve the separation efficiency of the elutriator. At the same time, the overflow of pellets with the airflow is greatly reduced, and the pollution of the environment is greatly reduced. It can be widely used in the production classification and cleaning of various plastic pellets and other pellets.

Description of drawings

Fig. 1 is a schematic cross-sectional view of the structure of the elutriator of the present invention.

Figure 2 is a schematic diagram of the grid.

Detailed ways

Example 1. An inertial elutriator for polyethylene pellets, as shown in Figures 1 to 2.

It includes an elutriation cylinder 1, an air inlet N3 installed in the middle of the elutriation cylinder 1, a feed inlet N1 and an air outlet N2. The bottom of the elutriation cylinder 1 is a cone 2, and the bottom of the cone 2 is provided with a discharge port N4. The air inlet N3 is welded on the middle side of the elutriation cylinder 1 . The upper part of the elutriation cylinder 1 is a cone 3 with a reduced diameter, and a convection separation cylinder 4 is welded to the top of the cone 3 . The diameter of the convective separation cylinder 4 is smaller than that of the elutriation cylinder 1 . An air outlet N2 is welded on the side of the middle part of the convection separation cylinder 4 . The middle of the top of the convection separation cylinder 4 is welded with an acceleration inner cylinder 5, and most of the acceleration inner cylinder 5 is inserted into the convection separation cylinder 4 to leave an annular gap 6 and its upper end is higher than the convection separation cylinder 4 upper ends. The top end of the acceleration inner tube 5 is welded with the acceleration tube 7 . The top of the acceleration tube 7 is welded with a small cone 8, and the upper end of the small cone 8 is welded with an air intake tube 9. The upper side of the intake cylinder 9 is welded with an air inlet N5, and the feed cylinder 10 inserted in the intake cylinder 9 is welded along the middle of the intake cylinder 9, leaving an annular gap between the two. The upper end of the feeding barrel 10 is a feed inlet N1.

The acceleration inner cylinder 5 is long tapered, and its upper end is connected with the acceleration cylinder 7 and has the same diameter, and then the diameter gradually expands. After connecting the acceleration cylinder 7 and the acceleration inner cylinder 5 with a gradually expanding diameter, the short-circuit flow and dead vortex in the annular gap at the top of the convection section are effectively eliminated, the mutual disturbance of the opposing airflow is avoided, and it is more conducive to the dispersion of materials. Two layers of grids 11 are fixed on the upper part of the elutriation cylinder 1 . The inclination angle of the grid 11 is 45°, and the pitch is 50mm. The length of the acceleration cylinder 7 is 800mm, and its pipe diameter is the same as that of the feeding cylinder 10, and the length of the convection separation cylinder 4 is 300mm.

As shown in Figure 1, through the optimization of feeding section, acceleration section I and acceleration section II, convection separation section and elutriation section, the effect is obvious. After connecting the acceleration section and the inner cylinder with gradually expanding diameter, the short-circuit flow and dead vortex in the annulus at the top of the convection section are effectively eliminated, the mutual disturbance of the opposing airflow is avoided, and it is more conducive to the dispersion of materials. By adjusting the length and diameter of the separation section, the shear force of the airflow on the particles is increased, and the residence time of the particles is increased. In the elutriation area, by moving the intake position downward and adding two layers of grills, the airflow in this area is more uniform and regular, and the effect of grille diversion and rectification is obvious, which strengthens the elutriation effect of the airflow on the pellets.

The structure of the elutriator is shown in Figure 1. Pellets are fed from N1 and fall by gravity. In the lower part of the feeding section, the gas that is accelerated by the gas entering the annulus of the feeding section from N5 flows downward through the accelerating section and flows into the convective separation section. In the convection section, the particles and gas flowing downward meet the rising air flow from the N3 inlet of the circulation area, and the two air flows turn to flow upward. Most of the fine dust attached to the surface of the particles breaks away from the surface of the particles and enters the gas phase in this area. , is taken out of the device by the gas exhausted from N2. The pellets continue to fall by gravity and inertia, and flow countercurrently with the updraft in the lower section of the convection zone, and the fine dust on the surface of the pellets is further elutriated and then falls into the circulation zone. In the circulation zone, the gas entered by N3 traverses through the continuously falling pellets, part of which turns upward and enters the convection zone, and part of it turns downward. Driven by the high-speed airflow injected by the air nozzle, a circular flow is formed, and the pellets are elutriated again, and the clean pellets fall into the cone, and are sent out of the device from N4 by the conveyor.

In fact, there is a speed difference between the gas and solid phases in each zone, and the fine dust attached to the surface of the pellets is shed by the shear of the gas on the solid surface. The shear force F _d can be approximated by the Orson correction formula of Stokes formula:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}\frac{{\mathrm{<span\; class="notranslate">\; \&rho;<figure-callout\; id="2"\; label="u"\; filenames="A200810249628E00101.png"\; state="\{\{state\}\}">u</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}$

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; twenty\; four</span>}}{\mathrm{<span\; class="notranslate">\; Re</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 8</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; )</span>$

In the formula: u is the slip velocity between gas and solid, D is the particle diameter, and Re is the gas phase Reynolds number.

The greater the relative velocity of the gas-solid two-phase, the greater the shear force on the surface of the pellets, which is more conducive to the falling off of the fine dust from the surface of the pellets. However, the airflow suddenly accelerates, decelerates or changes direction, and the airflow boundary layer bypassing the surface of the pellets needs to be re-established. At this time, the shear force of the airflow on the surface of the pellets can be doubled, which is more conducive to the elutriation of fine dust. During operation, the solid particles entering the device keep falling, while the airflow is constantly changing direction and speed, so as to achieve the purpose of elutriation and cleaning.

The influence of the pipe diameter and length of the acceleration section on the flow field is as follows: classified according to the grading force field, the elutriator is an inertial separation device, and the pellets need to be accelerated to a certain speed to obtain sufficient inertial force. The role of the acceleration section is very critical. The diameter of the acceleration section is large, and the dispersibility of the particles is good, but the gas velocity is too low, which will cause the particles to not get enough speed, and vice versa. The present invention therefore designs a reasonable size of the acceleration section.

The impact of the structure of the convection section on the flow field is as follows: the convection section is divided into the inner cylinder space and the annular gap. The wall keeps the two air streams from disturbing each other. At the same time, the convection section has the effect of expanding pressure, which reduces the velocity of the downdraft airflow and increases the static pressure. The present invention therefore devises a novel structure that can simultaneously meet the requirements of isolated airflow and diffusion.

The influence of the pipe diameter and length of the separation section on the flow field is as follows: the upper and lower intake air collides in the separation section, and most of the fine dust is also separated in the separation section. The action time of gas-solid two-phase. The present invention is therefore designed with appropriate dimensions.

The influence of the internal structure of the elutriation area on the flow field is as follows: the elutriation area has a large space, the gas velocity in the lower part is high, there are large and small vortices, the flow pattern is basically a weak swirl, and the particles passing through this area are repeatedly elutriated , the fine dust attached to the particles is separated, the large vortex lifts up the fine dust, and is discharged out of the device with the updraft. The internal component (grid) designed by the invention can suppress the harmful backflow vortex and prolong the residence time of the particles.

By adjusting the length and diameter of the separation section, the present invention increases the shear force of the airflow on the particles and increases the residence time of the particles; The airflow is more uniform and regular, and the diversion and rectification effect is obvious, which strengthens the elutriation effect of the airflow on the pellets.

This embodiment has the following advantages: an internal member (acceleration inner cylinder 5) is added in the convection section, eliminating the short-circuit flow near the outlet and preventing the pellets from escaping. By shortening the acceleration section and lengthening the convection section, the residence time of the pellets is increased, and the shearing effect of the airflow on the surface of the pellets is strengthened. Adding a grid in the elutriation area regulates the flow field, eliminates electrostatic adsorption, and at the same time makes the dust on the surface of the pellets vibrate and detach, which promotes the separation of fine dust.

Table 1 and Table 2 below are the performance test results of the traditional inertial elutriator and this embodiment, respectively.

Table 1. Classification performance experiment results of traditional elutriators

Table 2. The results of the experiment on the classification performance of the elutriator in this embodiment

The above experimental data show that the comprehensive classification efficiency of the elutriator in this embodiment reaches 97.8%, which is about 28% higher than that of the traditional elutriator. The data of working conditions 1 and 2 show that this is mainly due to the low separation efficiency of large particles, but the separation efficiency of working condition 3 is relatively high for large particles, and the separation efficiency of fine dust can also meet the requirements of industrial production . Working conditions are different operating conditions.

Example 2. An inertial elutriator for polyethylene pellets. The inclination angle of the grid is 30°, and the pitch is 100mm. The length of the acceleration cylinder is 600mm, and its pipe diameter is the same as that of the feeding cylinder, and the length of the convection separation cylinder is 500mm. All the other are with embodiment 1.

Example 3. An inertial elutriator for polyethylene pellets. The inclination angle of the grid is 60°, and the spacing is 30mm. The length of the acceleration cylinder is 1200mm, and its pipe diameter is the same as that of the feeding cylinder, and the length of the convection separation cylinder is 200mm. All the other are with embodiment 1.

Examples 2 and 3 can remove the fine dust in the pellets, greatly reduce the overflow of the pellets with the airflow, and have high comprehensive classification efficiency. It can be widely used in the production classification and cleaning of various plastic pellets and other pellets.

Example 4. The invention discloses an elutriation process of an inertial elutriator for plastic granules. The wind speed of the upper air inlet N5 is 15m/s, the wind speed of the lower air inlet N3 is 13m/s, and the feed speed of the feed inlet N1 is less than 800g/s. The wind speed in the annulus of the acceleration inner cylinder and the convection separation cylinder is less than 15m/s. When the air velocity in the annular gap is lower than 15m/s, the separation time of the material can be prolonged, and the effect is very good. The operation process mainly includes the intake air volume and feeding speed of the upper and lower air inlets.

Example 5. The invention discloses an elutriation process of an inertial elutriator for plastic granules. The wind speed of the upper air inlet N5 is 10m/s, the wind speed of the lower air inlet N3 is 15m/s, and the feed speed of the feed inlet N1 is less than 800g/s. The wind speed in the annulus of the acceleration inner cylinder and the convection separation cylinder is less than 15m/s. When the air velocity in the annular gap is lower than 15m/s, the separation time of the material can be prolonged, and the effect is very good. The operation process mainly includes the intake air volume and feeding speed of the upper and lower air inlets.

Example 6. The invention discloses an elutriation process of an inertial elutriator for plastic granules. The wind speed of the upper air inlet N5 is 20m/s, the wind speed of the lower air inlet N3 is 10m/s, and the feed speed of the feed inlet N1 is less than 800g/s. The wind speed in the annulus of the acceleration inner cylinder and the convection separation cylinder is less than 15m/s. When the air velocity in the annular gap is lower than 15m/s, the separation time of the material can be prolonged, and the effect is very good. The operation process mainly includes the intake air volume and feeding speed of the upper and lower air inlets.

The process conditions of Examples 4-6 make the processed materials have obvious luster, and the biggest advantage is reflected in the treatment of attached dust, which is clean and dust-free. It can be widely used in the production classification and cleaning of various plastic pellets and other pellets.

Claims (8)

1. A plastic pellet inertial elutriator, comprising an elutriating cylinder, an air inlet N3 installed in the middle of the elutriating cylinder, a feed inlet and an air outlet, and the bottom of the elutriating cylinder is a cone , the bottom of the cone has a discharge port N4, which is characterized in that the air inlet N3 is welded on the middle side of the elutriation cylinder, the upper part of the elutriation cylinder is a cone with a reduced diameter, and the top of the cone is welded with convection Separation cylinder, the diameter of the convection separation cylinder is smaller than the elutriation cylinder, the middle side of the convection separation cylinder is welded with an air outlet N2, the top of the convection separation cylinder is welded in the middle of the acceleration inner cylinder, and most of the acceleration inner cylinder is inserted into the convection separation cylinder. There is an annular gap between them and its upper end is higher than the upper end of the convection separation cylinder. The acceleration cylinder is welded in the middle of the top of the acceleration inner cylinder. The top of the acceleration cylinder is welded with a small cone. An air inlet N5 is welded on the side of the upper part, and the feeding cylinder inserted into the air inlet cylinder is welded along the middle of the air inlet cylinder with an annular gap between them, and the upper end of the feeding cylinder is the feeding inlet N1. 2. The inertial elutriator for plastic granules according to claim 1, characterized in that said acceleration inner cylinder is long tapered, its upper end is connected with the acceleration cylinder and has equal diameters, and then the diameter gradually expands. 3. The inertial elutriator for plastic pellets according to claim 1 or 2, characterized in that the upper part of said elutriation cylinder is fixed with two layers of grids. 4. The inertial elutriator for plastic granules according to claim 3, characterized in that the inclination angle of said grid is 30°～60°, and the spacing is 30～100mm. 5. The inertial elutriator for plastic granules according to claim 4, characterized in that the length of said acceleration cylinder is 600-1200mm, the pipe diameter is the same as that of the feeding cylinder, and the length of the convection separation cylinder is 200-500mm. 6. A kind of elutriation process according to the described plastic pellet inertia elutriator of claim 1, it is characterized in that the wind speed of upper air inlet N5 is 10～20m/s, the wind speed of lower air inlet N3 is 10～20m/s. 15m/s, the feed speed of feed port N1 is less than 800g/s. 7. The elutriation process according to claim 6, characterized in that the wind speed in the annulus of the accelerating inner cylinder and the convective separation cylinder is less than 15m/s. 8. A use of the inertial elutriator for plastic pellets according to claim 1, characterized in that it is used in the production of plastic pellets and other pellets to separate coarse and fine particles, and the clean finished pellets fall to the material. The bin, tiny crystal grains and fiber dust are discharged out of the device with the airflow.

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