DEM-MBD coupling simulation model for screening sticky and wet particles using a relaxation screen

Abstract

The present invention discloses a DEM-MBD coupling simulation model for screening sticky and wet particles using a loose screen. The simulation model is a model that couples the motion trajectory of the screen with the characteristics of the sticky and wet particles. The screen includes five screens connected in sequence: screen one, screen two, screen three, screen four and screen five, and the motion phases of two adjacent screens differ by 180°. The velocity distribution and motion trajectory of the sticky and wet particles during the screening process are simulated. The results show that the loose screen can provide a high speed for the deagglomeration of agglomerated particles and the separation of sticky particles from the screen plate. Therefore, the loose screen can successfully screen the sticky and wet organic fertilizer particles and obtain organic fertilizers in an easily absorbable range.

Description

Technical Field

[0001] The invention belongs to the technical field of screening, and in particular relates to a DEM-MBD coupling simulation model for screening sticky and wet particles by using a relaxation screen. Background Art

[0002] Wet particles have the characteristics of high moisture content and easy adhesion, which are prone to problems such as sticky holes and blocked holes, making the screening process difficult. The loose screen is an effective screening method for wet particles, which is suitable for the screening of wet organic fertilizers, wet coal, wet garbage and other wet particles. However, most of the previous studies were on the screening of dry particles, or only optimized parameters were obtained through experiments. Zhao et al. screened dry garbage particles through experiments and analyzed the effects of different shear spring stiffness on the screening efficiency of the loose screen. The results showed that when the shear spring stiffness was 11440kN / m, the screening efficiency reached 97.07%. Chen et al. established a loose screen model, observed the motion trajectory of a single dry particle, and studied the effect of screen acceleration on particle motion and screening efficiency. Yu et al. screened wet coal particles through experiments. The results showed that the loose screen screening gave the wet coal particles a great impact force, loosened the wet coal particles and avoided blocking holes, so that the screening efficiency reached 85.41%. Yu et al. screened iron ore particles through experiments and analyzed the influence of changes in the dynamic response of the relaxation screen on the screening efficiency. The results showed that the screening efficiency was the highest in the near anti-resonance region. However, only a few scholars have conducted simulation research on the screening of sticky and wet particles by relaxation screens. Cao Rong et al. established a relaxation screen screening model for sticky and wet particles through simulation, and simulated the movement of the screen by an approximate flexibility method. The results showed that changing the screen surface morphology can increase the crushing rate of wet coal agglomerates and improve the screening efficiency. Yu et al. conducted simulation research on the screening of sticky and wet particles by relaxation screens. The results showed that the agglomerated sticky and wet particles were deagglomerated and the problem of screen hole blockage was solved. However, the models used in these two documents cannot simulate the hyperelastic characteristics of the relaxation screen (especially when the tension of the screen is positive), nor can they calculate the influence of particle gravity on the deformation of the screen, so they are not consistent with the actual working conditions. Summary of the invention

[0003] In order to solve the above problems, the present invention proposes a DEM-MBD coupling simulation model for screening sticky and wet particles using a relaxation screen.

[0004] The DEM-MBD coupling simulation model for screening sticky and wet particles using a relaxation screen of the present invention is a model that couples the motion trajectory of the screen with the characteristics of the sticky and wet particles, including five screens connected in sequence: screen one, screen two, screen three, screen four and screen five, the motion phases of two adjacent screens differ by 180°, and two adjacent screens share a kinematic pair. The driving equation D1 of the kinematic pair displacement at screen one, screen three and screen five is:

[0005]

[0006] Where n is the rotation speed, r / min; e is the eccentricity, mm; △l is the tension, mm; t is the time, s.

[0007] The driving equation D2 for the displacement of the kinematic pair of the second and fourth screens is:

[0008]

[0009] Where n is the rotation speed, r / min; e is the eccentricity, mm; △l is the tension, mm; t is the time, s.

[0010] The simulation model further includes sticky particles, and the surface energy W of the sticky particles is:

[0011] W=γ1+γ2-γ 12

[0012] Where γ1 is the surface energy of particle 1, J / m 2 ; γ2 is the surface energy of particle 2, J / m 2 ; γ 12 is the surface energy between particle 1 and particle 2, J / m 2 .

[0013] The normal elastic contact force F of the sticky particle JKR for:

[0014]

[0015] Where W is the surface energy, J / m 2 ; a0 is the contact surface radius after considering cohesion, mm; R * is the equivalent contact radius, mm; E * is the equivalent elastic modulus, N / m 2 .

[0016] The sieves 1, 2, 3, 4 and 5 are all cuboids of 250 mm×150 mm×5 mm, the size of the sieve holes of each sieve is 15 mm×5 mm, and the spacing between different sieve holes is 5 mm.

[0017] The e is 6 mm and Δl is 4 mm.

[0018] The Hertz-Mindlin model is used to characterize the relationship between the sticky particles and the screen.

[0019] The kinematic pair refers to a crank-connecting rod mechanism.

[0020] The factors affecting the simulation model are surface energy, rotation speed, tension and feed amount.

[0021] The beneficial effect of the present invention is that the DEM-MFBD coupling simulation model of the present invention for screening sticky and wet particles using a relaxation screen simulates the velocity distribution and motion trajectory of the sticky and wet particles during the screening process. The results show that the relaxation screen can provide a high speed for the deagglomeration of agglomerated particles and the separation of sticky particles from the screen plate. Therefore, the relaxation screen can successfully screen sticky and wet organic fertilizer particles to obtain organic fertilizers in an easily absorbable range. With the increase of surface energy, both flow and screening efficiency decrease. With the increase of rotation speed, both increase first and then decrease slightly. With the increase of tension content, both show an upward trend at low rotation speed and a downward trend at high rotation speed. With the increase of feed amount, the screening efficiency decreases, and the total flow rate increases first and then decreases. By adjusting the rotation speed, tension, and feed amount, the relaxation screen can also be used to screen other sticky and wet particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the particle deformation surface considering cohesion.

[0023] Figure 2 This is the schematic diagram of DEM-MFBD coupling simulation.

[0024] Figure 3 It is a finite element model of multiple screens.

[0025] Figure 4 It is a simulation model of relaxation screen screening.

[0026] Figure 5 It is a model comparison verification of the sieve.

[0027] Figure 6 These are the theoretical, simulation and test values ​​of the displacement of a single screen.

[0028] Figure 7 is the particle velocity distribution.

[0029] Figure 8 It is the particle distribution at different times within a single cycle.

[0030] Fig. 9 is a schematic diagram of particle trajectories.

[0031] Fig.10 is the particle distribution at different surface energies.

[0032] Fig.11 It is the evaluation index of different surface energies.

[0033] Fig.12 It is the particle distribution at different rotation speeds.

[0034] Fig.13 These are the evaluation indicators when the rotation speed is not passed.

[0035] Fig.14 It is the particle distribution at different tension amounts at a speed of 200r / min.

[0036] Fig.15 These are the evaluation indicators at different tension levels at a speed of 200r / min.

[0037] Fig.16 It is the particle distribution at different tension amounts at a speed of 320r / min.

[0038] Fig.17 These are the evaluation indicators at different tension levels at a speed of 320r / min.

[0039] Fig.18 It is the particle distribution at different feed amounts.

[0040] Fig.19 These are the evaluation indicators when the feed volume is not passed.

[0041] Fig. 20 It is a test prototype of the relaxation screen.

[0042] Fig.21 It is the working flow chart of the test prototype of the relaxation screen. DETAILED DESCRIPTION

[0043] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0044] 1. Setting of sticky particles

[0045] According to the mesh size of the sieve (the mesh size is 15mm×5mm, that is, the shortest side is 5mm), the sticky particles can be divided into small particles and large particles. Small particles refer to particles with a particle size smaller than the shortest side length of the mesh, that is, particles with a particle size of 2mm and 4mm. As long as there are enough opportunities to contact the mesh, small particles are very easy to pass through the sieve; large particles refer to particles with a particle size larger than the shortest side length of the mesh, that is, particles of 6mm and 10mm. Due to their own size, large particles are not only impossible to pass through the sieve, but may also block the mesh and affect the passing of small particles.

[0046] Table 1 Particle size distribution of simulated wet particles

[0047]

[0048] Next, the setting of the sticky organic fertilizer particle model is explained. In order to simulate the sticky state between the sticky organic fertilizer particles, the Hertz-Mindlin with JKR contact model is introduced to define the contact between the particles. Figure 1 The particle deformation surface considering cohesion in this model, R1, R2 are the radii of particle 1 and particle 2 respectively. a is the contact radius between particles, a0 is the contact surface radius after considering cohesion, R * is the equivalent contact radius, δ n is the overlap amount. Due to the cohesive force, the contact radius of the two particles increases from a to a0.

[0049] Assume the surface energy between the sticky organic fertilizer particles is W, J / m 2 , we can get formula (1):

[0050] W=γ1+γ2-γ 12 (1)

[0051] Where γ1 is the surface energy of particle 1, J / m 2 ; γ2 is the surface energy of particle 2, J / m 2 ; γ 12 is the surface energy between particle 1 and particle 2, J / m 2 When the materials of the two particles are the same, the surface energy γ 12 = 0, that is, γ1 = γ2 = γ, and W = 2γ. Due to the influence of surface energy on the movement of sticky particles, the normal elastic contact force F JKR (N) is calculated based on the Johnson-Kendall-Roberts theory by formula (2):

[0052]

[0053] Where E * is the equivalent elastic modulus (N / m 2 ).

[0054] In addition, the Hertz-Mindlin (no-slip) contact model is used to characterize the contact properties between the sticky organic fertilizer particles and the screen. Among them, the restitution coefficient, static friction coefficient and dynamic friction coefficient between the particles are 0.35, 0.55 and 0.13, respectively, and the restitution coefficient, static friction coefficient and dynamic friction coefficient between the particles and the screen are 0.4, 0.4 and 0.35, respectively. The sticky organic fertilizer particles after drum granulation are generally spherical particles. According to the grading, four particle sizes of 2, 4, 6 and 10 mm are set, and their mass accounts for 15, 20, 40 and 25%, respectively. The Poisson's ratio of the particles is 0.1 and the density is 1100kg / m 3 , the shear modulus is 5.5MPa.

[0055] 2. DEM-MFBD coupling model

[0056] The discrete element software EDEM can simulate the movement of organic fertilizer sticky particles and the movement of geometric bodies. However, due to the limitations of the software itself, it cannot simulate the large deflection deformation of the fluted screen mesh. The multi-body dynamics software RecurDyn can simulate the large deformation of the fluted screen mesh. Therefore, giving full play to the respective advantages of EDEM and RecurDyn and realizing the discrete element and multi-flexible system dynamics coupling simulation (DEM-MFBD coupling simulation) through the interface between the software is a good method to study the screening of organic fertilizer sticky particles by the fluted screen. The principle of DEM-MFBD coupling simulation of fluted screen screening is as follows Figure 2 As shown in the figure, when performing coupled calculations, RecurDyn transmits the position and velocity of the screen to EDEM. EDEM calculates the force and torque exerted by the particles on the screen and returns them to RecurDyn. In the next time step, RecurDyn calculates the new position and velocity of each point on the screen based on the new load information and its driver program, and then transmits data in a cyclic interactive manner, thus realizing bidirectional coupled calculations.

[0057] Compared with the previous simulation of the relaxation screen, the DEM-MFBD coupling simulation can not only calculate the hyperelastic characteristics of the polyurethane mesh of the relaxation screen, but also realize the calculation of the reaction force of the particles on the screen on the screen. The following is an explanation of the setting of the DEM-MFBD coupling model for relaxation screen screening.

[0058] 3. Screen geometry parameters

[0059] The mesh is a 250mm×150mm×5mm cuboid in geometric shape, with mesh holes of 15mm×5mm and a spacing of 5mm between different mesh holes. The 3D mesh model of the mesh is meshed using the Mesh module in RecurDyn. After meshing, each mesh has 15453 nodes, 7828 Solid8 meshes and 4 Solid4 meshes. The specific meshing results are as follows: Figure 3 shown.

[0060] In order to make the created screen model simulate the relaxation motion of the screen and make the motion phase of adjacent screens differ by 180°, it is also necessary to add a drive at both ends of the screen, that is, apply a translational motion pair at the nodes at both ends of each screen and add a drive function. The finite element model of multiple screens after the drive is applied is as follows: Figure 3 As shown, the driving equation D1 of the displacement of the kinematic pair at screen one, screen three and screen five is:

[0061]

[0062] Where n is the rotation speed, r / min; e is the eccentricity, mm; △l is the tension, mm; t is the time, s.

[0063] The driving equation D2 for the displacement of the kinematic pair of the second and fourth screens is:

[0064]

[0065] Where n is the rotation speed, r / min; e is the eccentricity, mm; △l is the tension, mm; t is the time, s.

[0066] like Figure 4 As shown in the figure, in order to facilitate the collection of simulation data of sticky organic fertilizer particles, the under-screen area is evenly divided into 5 sub-areas (numbered 1-5), and a separate drop area (numbered 6) is set. The particle factory is a Φ100mm×140mm cylinder, and different screens are connected by synchronously moving partitions to prevent particles from falling between the screens.

[0067] In order to ensure the reliability of the screen simulation, the simulation model was verified based on the experiment and the classic elastic pressure bar model. The experimental values ​​of the screen centerline displacement under different displacements at both ends of a single screen, the elastic pressure bar theoretical values ​​and the simulation values ​​were compared. Figure 5 As shown. Figure 6 From the comparison results, it can be seen that with the increase of the movement of the two ends of the screen, the theoretical displacement, simulation displacement and experimental displacement of each point of the screen gradually increase, and the change amplitudes of the three are similar, which verifies the reliability of the screen model.

[0068] 4. Screening process analysis

[0069] 4.1 Particle speed

[0070] Firstly, the screening process is analyzed. The simulation conditions of the research object are spindle speed 280r / min, feed volume 20kg / min and surface energy 0.3J / m 2 , the analysis time point is 8s. Figure 7 As shown in the particle velocity distribution, the particles fall freely from the particle factory under the action of gravity, and the particle velocity increases continuously during this period. Since the adjacent screens move in a strictly half-cycle difference, the particle motion patterns on screens 1, 3 and 5 are similar, and the particle motion patterns on screens 2 and 4 are similar, so only the particles on screens 2 and 3 are analyzed below. Figure 7As can be seen in a, the movement of the screen causes the particles to deagglomerate, and some small particles close to the screen holes pass through the screen, while the vast majority of particles are thrown from the moving screen 2 to the screen 3. The closer the particles are to the middle of the screen, the greater the amplitude of their ejection, while the particles close to the edge of the screen can no longer be ejected, and they condense and accumulate near the junction of the two screens (such as Figure 7 b) This is because the maximum velocity of particles at the edge of the screen is always low, and the movement of the screen at the edge cannot cause the agglomerated particles to deagglomerate and accumulate. Figure 7 As can be seen from Figure c, the movement states of the particles on screen 3 can be roughly divided into two types: falling and waiting to be ejected. Some of the falling particles will fall on screen 3 for further screening, while the other part will fall on screen 4 for screening. Most of the particles waiting to be ejected are located in the middle and upper part of the screen. Although these particles are in direct contact with the screen, they are not completely screened due to inappropriate particle landing points or too large particle sizes. These particles will be ejected from the screen along the upper side for the next screening.

[0071] 4.2 Particle distribution

[0072] Figure 8 is the distribution change of the sticky particles on the screen 3 in one cycle, Figure 8 It can be seen from a that at 7.525s, the screen is in the most relaxed state and is in a bow shape under the reaction force of the sticky particles, and some small particles close to the screen holes pass through the screen. Figure 8 From b, we can see that at 7.675s, the stretched screen ejects the sticky particles, the particles begin to deagglomerate and the small particles close to the screen holes continue to pass through the screen. Figure 8 c shows that at 7.7s, the screen begins to return to a relaxed state, and the ejected particles begin to fall after reaching the highest point. At this time, the deagglomeration process of the sticky and wet particles ends, and the deagglomerated particles gradually separate into layers. Figure 8 It can be seen from the figure that at 7.75s, the deagglomerated particles fall back onto the screen, and the small particles close to the screen holes have a chance to pass through the screen. After that, the screen returns to its most relaxed state, and a new screening cycle begins again. After multiple screens and multiple screening cycles, the sticky and wet particles are screened.

[0073] 4.3 Particle Trajectory

[0074] The trajectories of particles with different sizes are analyzed. Fig. 9It can be seen that during the screening process, when the landing point of small particles is appropriate, they can pass through the screen directly (particle 1). Some small particles will change their original movement trajectory due to collision with other particles or the screen, thereby passing through the screen (particle 2). Some particles will gradually slide to the top of the screen hole during the screening process and pass through the screen (particle 3). Although some particles have multiple contacts with the screen, they fail to pass through the screen due to inappropriate landing points (particle 4) or too large particle size (particle 5), and are finally transferred to the discharge port for discharge.

[0075] 5. Analysis of influencing factors

[0076] 5.1 Effect of surface energy

[0077] When the speed is 240r / min and the feed rate is 30kg / min, the influence of surface energy on mass flow rate and screening efficiency is as follows: Fig.10 and Fig.11 When the surface energy is less than 0.6 J / m 2 When the surface energy is 0.3 J / m 2 When the surface energy increases to 0.6 J / m 2 The mass flow of particles under screen 1 and screen 2 is greatly reduced. When the surface energy is greater than 0.6 J / m 2 When the cohesion between particles increases, the maximum speed given by the screen to the particles is no longer able to break the cohesion between the particles. At this time, the particles containing large particles not only cannot pass through the screen, but also block the screen holes and prevent small particles from passing through the screen. Therefore, the surface energy is 0.9 and 1.2 J / m 2 The total mass flow rate was reduced to 9.1 and 7 kg / min respectively, and the screening efficiency was lower than 67% and 55% respectively.

[0078] 5.2 Effect of rotation speed

[0079] When the feed rate is 20kg / min and the surface energy is 0.3J / m 2 When the rotation speed affects the mass flow rate and screening efficiency, Fig.12 and Fig.13As shown. As can be seen from the figure, with the increase of the speed, the total mass flow rate and the screening efficiency first increase and then gradually decrease, and reach the maximum at 240r / min. Among them, when the speed is 160r / min, the mass flow rate under screen one and screen two is much lower than the mass flow rate at other speeds. This is because the screen at this speed cannot give the particles a large enough speed for deaggregation. As the speed increases to 200r / min, the mass flow rate under screen one and screen two increases, and the total mass flow rate and screening efficiency increase from 3.4kg / min and 48% to 6.81kg / min and 98%. Obviously, the speed at this time can make the particles deaggregate. As the speed continues to increase to 280r / min, although the particles can be easily deaggregated, the particle speed is too large at this time, so that more small particles are not fully screened and are transported to the blanking port and discharged by mistake, thereby reducing the screening efficiency. Considering the screening efficiency and the total mass flow rate, the speed should be selected between 200r / min-320r / min.

[0080] 5.3 Effect of tension

[0081] The above article has studied the effect of speed on the screening of sticky organic fertilizer particles by the relaxation screen, and determined the appropriate speed range to be 200r / min-320r / min based on the screening efficiency. Next, the study of tension will be carried out at the lowest and highest speeds within this range. First, the speed is 200r / min, the feed rate is 20kg / min, and the surface energy is 0.3J / m 2 The influence of tension on the total mass flow rate and screening efficiency was investigated under the conditions of . Fig.14 is the particle distribution at different tensions, Fig.15 These are the evaluation indicators at different tension levels.

[0082] When the tension increases from -2mm to 4mm, the maximum speed increases from 0.694m / s to 0.845m / s ( Fig.15 a), the particle speed along the screen increases from 0.05m / s-0.054m / s to 0.101m / s-0.17m / s ( Fig.15 b), the average residence time of the particles above the sieve and below the sieve decreased from 20.964s and 14.303s to 9.098s and 2.248s ( Fig.15 c). In other words, the maximum velocity of the particles increased by 20%, the velocity of the particles along the screen increased by 2.02-3.14 times, and the average residence time of the particles on the screen and the particles under the screen decreased by 56.6% and 84.3%. At the same time, the accumulated mass of the particles on each screen gradually decreased from 1.068kg-1.561kg to 0.329kg-0.469kg, with a decrease of 58.3% and 69.9% respectively ( Fig.15 d).

[0083] When the tension is -2 mm, the speed of the screen is low, and the maximum speed of the particles is not enough to break the bond (5a). In addition, since the screen cannot be fully unfolded under this tension, the screen will always appear like this under the gravity of the particles on the screen and the weight of the screen. Fig.14 The catenary shape shown in a makes it easy for particles to accumulate on the screen and even cause the phenomenon of ore-carrying. Since the particles will agglomerate after accumulation, which will seriously hinder the movement of particles on the screen, the speed of particles along the screen is low, that is, less than 0.05m / s, which makes the average residence time of particles longer ( Fig.15 b, c). Under this tension, the particle layer is the thickest, the accumulation mass of the particles on the screen is the largest and far higher than the data of the other three simulation groups, and a large number of small particles are accumulated in the middle of the particle layer ( Fig.15 d, Fig.14 a), which seriously hinders the penetration of small particles. Therefore, the total mass flow rate and screening efficiency of the particles under the screen are only 3.4 kg / min and 47.96% ( Fig.15 f). When the tension is 0 mm, the stacking mass of the particles on the screen decreases ( Fig.15 d), the chances of small particles passing through the screen increase, so the total mass flow rate of particles under the screen and the screening efficiency increase ( Fig.15 f).

[0084] As the tension continues to increase, the elastic characteristics of the screen are gradually reflected. When the tension is 2mm and 4mm, the increase in the acceleration of the screen helps the particles to be thrown up, deaggregated and screened. At this time, the maximum speed of the particles can break the bond and deaggregate the bonded particles ( Fig.15 a), the speed of particles along the screen increases, and the average residence time of particles decreases accordingly, so particles are not easy to accumulate, that is, the accumulation mass of particles on the screen gradually decreases ( Fig.15 bd), the screening efficiency is as high as 95% or more ( Fig.15 f).

[0085] It is worth noting that when the tension is 4 mm, the screen is stretched to a greater extent, and the elastic properties of the polyurethane screen have been fully reflected. At this time, the acceleration of the screen is large, and the particles have a large speed and a short average residence time ( Fig.15 ac), so the particles on the sieve are difficult to accumulate and agglomerate ( Fig.15 d, Fig.14 d), which also allows up to 98.31% of small particles to pass through the sieve ( Fig.15 f).

[0086] Keeping other parameters unchanged, the influence of tension on total mass flow rate and screening efficiency was studied at a rotation speed of 320 r / min. Fig.17 are the evaluation indicators at different tension levels, Fig.16 Particle distribution at different tension levels.

[0087] When the tension increases from -2 mm to 2 mm, the maximum velocity of the particles increases from 1.607 m / s to 1.913 m / s ( Fig.17 a), the particle speed along the screen increases from 0.110m / s-0.234m / s to 0.203m / s-0.424m / s ( Fig.17 b), the average residence time of the particles above the sieve and below the sieve decreased from 5.997s-1.415s to 3.050s-1.035s respectively ( Fig.17 c), that is, the maximum velocity of the particles increased by 19%, the velocity of the particles along the screen increased by 81%-85%, and the average residence time of the particles on the screen and the particles under the screen decreased by 49% and 27%, respectively. As the tension continued to increase from 2mm to 4mm, the maximum velocity of the particles and the velocity along the screen no longer increased or increased insignificantly ( Fig.17 a, b), and the average residence time of the particles above the sieve and below the sieve did not change significantly ( Fig.17 c).

[0088] In addition, compared Fig.15 a, b and Fig.17 It can be seen from a and b that no matter what value the tension takes from -2mm to 4mm, the maximum speed of the particles on the screen at a speed of 320r / min (greater than 1.607m / s) is significantly higher than the maximum speed of the particles on the screen at a speed of 200r / min (less than 0.845m / s), and the speed of the particles on the screen along the screen (0.110m / s-0.440m / s) is higher than the speed of the particles on the screen along the screen at 200r / min (0.035m / s-0.170m / s). The average speed of the particles on the screen and the particles under the screen is The residence time (2.881s-5.997s, 0.86s-1.415s) is lower than the average residence time of the particles on the screen and the particles under the screen at a speed of 200r / min (9.098s-20.964s, 2.248s-14.303s), which makes the particle accumulation mass on each screen at a speed of 320r / min (0.076kg-0.445kg) lower than the particle accumulation mass on each screen at a speed of 200r / min (0.329kg-1.561kg) ( Fig.15 d and Fig.17d). In summary, at a rotation speed of 320 r / min, the maximum speed of the particles can easily break the adhesion between the particles. Because the speed of the particles along the screen is relatively high, the average residence time of the particles on the screen and the particles under the screen is relatively short, thus avoiding the accumulation of particles ( Fig.16 ad). Therefore, the total mass flow rate and screening efficiency of the particles at a speed of 320r / min are relatively high, and the total mass flow rate and screening efficiency are higher than 6.2kg / min and 88% respectively ( Fig.17 e, f).

[0089] When the tension is -2 mm and 0 mm, the lower particle speed along the screen allows the particles to stay on the screen for a long enough time to be screened ( Fig.17 b, c). Especially when the tension is -2mm, the particles have more chances to pass through the screen because they are in contact with the screen for a longer time. At this time, the screening efficiency is above 98% ( Fig.17 f). When the tension is 2mm and 4mm, the particle speed is high ( Fig.17 b) The particles on the screen will be thrown to a high height and a long distance, and stay on the screen for a short time, so some small particles are not fully screened and are sent to the drop port ( Fig.17 c, Fig.16 c, d), which in turn causes a decrease in screening efficiency ( Fig.17 f).

[0090] In summary, when the speed is 200r / min and negative tension is used, the maximum speed of the particles cannot break the bond, and the bonded particles will seriously hinder the movement of the particle flow on the screen. Therefore, the speed of the particles along the screen is low, the residence time is long, and the particles on the screen will be seriously accumulated, and the total mass flow and screening efficiency will be greatly reduced. At this time, the use of positive tension is conducive to breaking the particle bond, thereby increasing the total mass flow and screening efficiency. When the speed is 320r / min, regardless of whether the tension is positive or negative, the maximum speed of the particles can always break the bond between the particles, so that the total mass flow and screening efficiency are at a high level. Taking both situations into consideration, the optimal tension is determined to be 4mm.

[0091] 5.4 Effect of feed amount

[0092] When the speed is 240r / min and the surface energy is 0.3J / m 2 When the feed rate affects the mass flow rate and screening efficiency, Fig.18 , Fig.19As shown. As can be seen from the figure, with the increase of feed amount, the screening efficiency gradually decreases, while the total mass flow rate increases first and then decreases. When the feed amount is between 20-30kg / min, small particles can quickly pass through the sieve holes, and the screening efficiency exceeds 98% at this time. This is because the accumulation layer is thin at this time, and the speed given to the particles by the screen is sufficient to break the agglomeration between the particles, thereby deagglomerating the agglomerated particles. Among them, when the feed amount is 20kg / min, the mass flow rate of particles under screens one to five decreases significantly to near zero in turn. When the feed amount is increased to 30kg / min, the mass flow rate of particles under screens two to five still decreases significantly to near zero in turn, which shows that there is a large room for improvement in the total mass flow rate. When the feed amount increases to 40kg / min, although the screening efficiency decreases, it is still as high as 95%. At the same time, the mass flow rate under screens three to five increases significantly. When the feed rate is greater than or equal to 50kg / min, the particles are difficult to deagglomerate due to the thick particle layer, which makes it difficult for small particles to pass through the screen, and the screening efficiency drops to 78.6% and 62.8% respectively. In order to ensure high screening efficiency and obtain the largest possible total mass flow rate, the feed rate should be 40kg / min.

[0093] 6. Screening test

[0094] The test prototype of the relaxation screen mainly includes a frame, four screens (taking four screens as an example), a crank connecting rod mechanism, an eccentric mechanism, a belt, a motor, a speed regulator and a feed inlet, etc. Fig. 20 As shown. A crank-connecting rod mechanism is connected to the middle position of two adjacent screens, so that the phase difference between the two adjacent screens is 180°. The crank-connecting rod mechanism is connected to the eccentric mechanism, and the eccentric mechanism is connected to the motor through a belt. The motor transmits the torque to the eccentric mechanism through the belt, and the eccentric mechanism drives the connecting rod mechanism to swing back and forth in a small amplitude. Since the swing angle is small, it can be regarded as a reciprocating linear motion. One end of the screen is fixed to the frame, and the other end is fixed to the connecting rod mechanism, so that when the reciprocating motion is realized, the adjacent screens make a relaxation motion with a phase difference of 180°. The screen is made of polyurethane material, and the size of each screen is 250mm×150mm×5mm, the size of the screen hole is 15mm×5mm, and the spacing between the screen holes is 5mm. Set the screen tension to 4mm, the eccentricity to 6mm, and adjust the motor speed through the speed regulator, and manually adjust the feed amount for feeding.

[0095] As shown in 21, the high viscosity organic fertilizer particles flow from the feed port to the screen 1, and then are thrown up, deagglomerated, collided and screened under the action of the screen, wherein most of the particles fall into the storage bag under the screen, and a few particles flow to the drop port, and the particles on the screens 1 and 2 are significantly more than those on the screens 3 and 4. In short, the relaxation screen can achieve the screening of high viscosity organic fertilizer particles.

[0096] (1) The sticky organic fertilizer particles were successfully screened out using a relaxation screen, and organic fertilizer particles within the easily absorbable range were obtained, which is beneficial to increase fertilizer absorption, reduce fertilizer utilization rate, and improve the soil environment.

[0097] (2) With the successful screening of high-moisture and high-viscosity organic fertilizer particles, the loose-type screen has become an effective solution for screening sticky and wet particles. By adjusting the screening variables, the loose-type screen can also be used to screen other sticky and wet particles, such as wet coal, wet garbage, pulp, etc.

[0098] (3) By using the DEM-MBD coupling model, not only can complex motions be performed and many particles can be generated, but also collisions between particles and impacts between particles and the screen plate can be realized. Therefore, the DEM-MBD coupling model can be used to simulate sand excavation, seeding, material transportation, particle screening, etc.

[0099] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0100] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A DEM-MBD coupled simulation model for screening sticky and wet particles using a relaxation screen, characterized in that: The simulation model is a model that couples the motion trajectory of the screen with the characteristics of the sticky particles, including five screens connected in sequence: screen one, screen two, screen three, screen four and screen five. The motion phases of two adjacent screens differ by 180°, and two adjacent screens share a kinematic pair. The driving displacement equation D1 of the kinematic pairs at screen one, screen three and screen five is: In the formula, n is the speed, r / min; e is the eccentricity, mm; △l is the tension, mm; t is the time, s; The driving displacement equation D2 of the kinematic pair of the screen 2 and the screen 4 is: In the formula, n is the speed, r / min; e is the eccentricity, mm; △l is the tension, mm; t is the time, s; The sieves 1, 2, 3, 4 and 5 are all cuboids of 250 mm × 150 mm × 5 mm, the size of the sieve holes of each sieve is 15 mm × 5 mm, and the spacing between different sieve holes is 5 mm; The factors affecting the simulation model are surface energy, rotation speed, tension and feed amount.

2. The DEM-MBD coupled simulation model for screening sticky and wet particles using a relaxation screen according to claim 1, characterized in that: The simulation model further includes sticky particles, and the surface energy W of the sticky particles is: W=γ1+γ2-γ 12 Where γ1 is the surface energy of particle 1, J / m 2 ; γ2 is the surface energy of particle 2, J / m 2 ; γ 12 is the surface energy between particle 1 and particle 2, J / m 2 .

3. The DEM-MBD coupled simulation model for screening wet particles using a relaxation screen according to claim 2, characterized in that: The normal elastic contact force F of the sticky particle JKR for: Where W is the surface energy, J / m 2 ; a0 is the contact surface radius after considering cohesion, mm; R * is the equivalent contact radius, mm; E * is the equivalent elastic modulus, N / m 2 .

4. The DEM-MBD coupled simulation model for screening sticky and wet particles using a relaxation screen according to claim 3, characterized in that: The Hertz-Mindlin model is used to characterize the relationship between the sticky particles and the screen.

5. The DEM-MBD coupled simulation model for screening sticky and wet particles using a relaxation screen according to claim 1, characterized in that: The kinematic pair refers to a crank-connecting rod mechanism.

Images