Low-rank steam coal is an important coal resource, but has high water and ash content, which needs to be separated to improve its quality and calorific value. In this paper, the process of screening using a flip-flow screen and density separator using a shallow groove dense-medium separator for steam coal was proposed and applied to the Lijiahao coal preparation plant. Kinematics of the screen box and the surface of the flip-flow screen were investigated using an acceleration and laser displacement measurement and analysis system. The mechanism of the flip-flow screen to overcome aperture blocking and to enhance the screening performance for moist and fine coal was discussed. The results from an industrial experiment when screening at 3 mm showed that the screening efficiency was 82.51%, while the total misplaced materials were 5.91%. The commercial separation of a wide size range of coal using a shallow groove dense-medium separator was analyzed. The results showed that the system exhibited satisfactory separation performance for 100–3 mm coal, whereas the corresponding E_p value was found to be 0.06 g/cm³. Compared with the 6 mm separation system, the yield of clean coal increased by 8.50%, which remarkably increased the economic benefits for the company.

Screening is an indispensable unit operation that is used extensively in many industries to separate particulate materials into different size fractions. A banana screen has high screening efficiency and is widely used for coal classification. In this study, the kinematic characteristics and velocity distribution of the banana screen surface during equal-thickness screening were investigated. High-speed dynamic test system results showed that the migration velocity and distance of different screen surface stages increase with running time from point 1 to point 5. Based on the experimental data and Box–Behnken response surface methodology results, the best screening effect occurred when the angle of eccentric blockψ was 100°, the excitation frequency f was 34 Hz and the feed rate Q was 3 kg/s. Furthermore, the sequence of influencing degree of various factors on screening efficiency η followed the order: f > ψ > Q. The actual screening efficiency was 92.993% when the operating conditions wereψ = 103°, f = 32 Hz, and Q = 3.5 kg/s, indicating a satisfactory screening performance of coal using a banana screen.

Multi-stage variable inclination equal-thickness screen (MSVIETS) is widely used in separating coal and mineral particles because of its large production capacity and good screening performance. In this study, the influence law of different operating parameters on the kinematic characteristics of infeed and outfeed ends surface and particles was investigated by using a high-speed camera analysis system. The spatial–temporal evolution process of screen surface and particles was revealed by Image-Pro Plus software. Screening experiments were used to verify the spatial and temporal distribution properties of the material. The operational parameters F_t, f and q all had a significant influence on the displacement. The displacement of the screen surface and particles at the infeed and outfeed ends during load operation increased to above 20 mm compared with that no load. The motion speed under load conditions was approximately five times higher than that under no load, which indicated that there was an energy transfer between the screen surface and particles. At T = 7.5 s, the overlap coefficient R-value was the largest according to image analysis software co-location analysis. This valued indicated the greatest effective utilization area of the screen surface. When the operating parameters were F_t = 6.43 kN, f = 34 Hz and q = 3 kg/s, the screening efficiency reached a maximum value at 94.41%. The total mismatched materials had a minimum value of 1.98%.

Elastic screening methods are widely used in the classification of moist coal as they can overcome the problem of aperture blockage. However, the use of an equally inclined screen surface with balanced excitation facilitates material accumulation, worsening the screening performance. Here, a disequilibrium excitation structure was proposed to solve the accumulation problem, and its synchronization process was studied using a high-speed camera system. The spatial motion of the rigid-flex elastic screen surface along material flow direction was reconstructed using a vibration test system. The influence of disequilibrium excitation force coefficient (F_de) and relative vibration motor shaft span (l_vms) on the screening performance of moist coal was investigated. The results showed that the phase difference between the two eccentric rotors gradually decreased to 0 under the coupling effect of the electromechanical system, achieving synchronous stable operation. The spatial trajectories of different parts of the rigid-flex elastic screen surface were close to ellipsoidal, with the long axis of the ellipse decreasing along the direction of material flow. The screening efficiency showed a maximum and the total misplaced materials showed a minimum with increasing F_de and l_vms. The optimum screening efficiency of 86.35% and the corresponding total misplaced materials of 5.03% were achieved at F_de = 1.15 and l_vms = 40%. Compared to the equilibrium excitation structure, the elastic screening process was enhanced by the use of disequilibrium excitation, with the screening efficiency increasing by 3.20%.

Equal-thickness screening is a critical part of mineral processing; recently, the multistage variable-inclination equal-thickness screen (MSVIETS) has been utilized in the mining industry across the world. In this work, a model of the collision mechanics between particles and the multistage variable-inclination screen surface was established. The maximum collision force (F _max) was found to be closely related to amplitude, frequency, screen surface inclination, and number of stages. The time-frequency response characteristics of multistage (3-, 4-, and 5-STAGE) screen surfaces were studied by the vibration test analysis system. The permeation screen distribution law of grain groups on the screen surface was revealed. The obtained results show the best screening performance can be obtained from the 5-STAGE scheme with a screening efficiency of higher than 95% and total mismatch content of less than 2%. The synergistic mechanism between two of the parameters was revealed by Box-Behnken response surface methodology (BBRSM). Then, the correlation between the screening evaluation index and the multiple parameters was obtained, and the significant order of the parameters influencing the screening evaluation index was F _t > f > n.