| The effective lower size limit for separation is relatively high for dense medium hydrocyclones of large diameter, while the recovery of+0.25mm particles is relatively low in flotation. Thus three-stage classification and separation mode with independent coarse coal recovery system is widely accepted by coal preparation plants. Developing new coarse coal separators will drive the development of coarse coal separation technique.Based on water-only cyclones, borrowing the idea of the flow hindering plate in Levis hydraulic classifier to produce upward flow, a new complicated cone (CC) structure producing hydraulic jump was developed. From top to bottom, the CC structure includes the first negative cone, the second adverse positive cone, and the third negative cone, forming a discontinuous cone structure. Since the incorporation of the second adverse positive cone shortens the total height of the CC structure, making the cyclone much like a column configuration, this new developed cyclone was named as Cyclone Column Separator (CCS) with a complicated cone producing hydraulic jump for coal slime, and has been licensed as an invention patent. The aim of the development of the cone structure is to increase the separation sharpness.Taking coal slime as a separation object, experiments concerning the effect of the structure and operating parameters of Φ150mm CCS on separation were carried out, and optimized CCS cone structure and proper operation conditions were determined. Employing Fluent6.3.26, the effect of the structure and operating parameters on the flow field inside CCS was also studied. On the basis of the above studies, the CCS was scaled up to Φ700mm and successfully applied in the coarse coal separation practice. The main conclusions include:(1) The comparison of the separation performance of CCS with that of water-only cyclones of various cone angles was carried out. The design philosophy of CC producing hydraulic jump was proved to be much superior to the traditional water-only cyclones, showing higher separation sharpness than water-only cyclones of various cone angles. By adding an adverse positive cone in the single cone of90°, the separation was strengthened, and the loss of low density coarse particles decreased significantly. It has a separation density much close to that of water-only cyclone of110°. The probable error for+lmm and0.5-1mm can reach0.058and0.083, respectively.(2) The effect of the position (H), the angle (α2), and the length (L) of the second positive cone on the separation performance of CCS was researched, and the influence of each parameter on the separation was determined employing of the surface analysis. The results show that the significance of the influence of each parameter is:L>α2>H. With the increasing of the cone length, the coarse clean coal ash, tailing coal ash, and the clean coal yield all increased, with decreased separation efficiency. With the increasing of the second positive cone angle, the coarse clean coal ash, tailing coal ash, and the clean coal yield all increased, with the separation efficiency decreased slightly. With the upward movement of the second positive cone position, the coarse clean coal ash, tailing coal ash, and the clean coal yield all decreased, with the separation efficiency increased slightly.(3) The effect of the angle of both the first and the third negative cone(α1and α3) on the separation performance of CCS was researched. Employing variance analysis, it was determined that the influence of the angle of the third negative cone is more significant than that of the first negative cone. With the increasing of the third negative cone angle, the clean coal ash, tailing coal ash, and the clean coal yield all decreased significantly, and when the third negative cone angle was130°, the tailings ash was relatively low and the separation is poor. The influence of the first negative cone angle on the clean coal ash, tailing coal ash, and the clean coal yield were not significant.(4) The effect of the apex diameter, overflow diameter, length of the vortex finder, feeding pressure and feeding concentration on the separation performance of CCS was researched. The results show that with the increasing of the overflow diameter and the decreasing of the apex diameter, the coarse clean coal ash, tailing coal ash, and the clean coal yield all increased. With the deepening of the length of the vortex finder, the coarse clean coal yield, the clean coal ash, and the tailing coal ash all increased, but at relatively deep length of the vortex finder, the separation effect of fine particles became worse. So the proper length of the vortex finder into the cylinder was about150mm. With the increasing of the feeding pressure, the clean coal ash, tailing coal ash, and the clean coal yield all increased slightly, with separation efficiency slightly decreased. The feeding pressure should be controlled to be at0.08-0.15MPa. The increasing of the feeding concentration increased the overflow ash, decreased the ash content of the fine particles in the underflow, but has no significant influence on the ash content of the coarse particles in the underflow, decreasing the separation efficiency. The feeding concentration should be controlled below160g/L.(5) Mathematical models for partition curves involving four parameters were constructed based on the generalized skew normal distribution, and proved to have relatively high fitting goodness and adaptability. The separation density δp and probable error Ep can represent the left and right position and the steepness of the medium of the curves, respectively. In addition, skewness coefficient κ and kurtosis coefficient K showed perfect indication for the symmetry and the shape of the both ends of the partition curves, respectively. A positive skewness coefficient means a left-skewed partition curve, indicating higher losses of low density materials. On the contrary, a negative skewness coefficient means a right-skewed partition curve, indicating more serious contaminant of high density materials. Higher kurtosis coefficient means greater separation sharpness.(6) Employing the developed mathematical models of generalized skew normal distribution for partition curves involving four parameters, the separation performance of water-only cyclones with different cone angles as well as CCSs with different cone structure was quantitatively assessed. The results show that CCS has higher separation sharpness than various water-only cyclones of different cone angles. The separation density almost did not change but the separation sharpness increased slightly when the length of the second positive cone changed from short to medium. For the longest cone length, the partition curve moved right significantly and the separation density increased significantly, while the separation sharpness decreased. The angle of the second positive cone has certain influence on the separation density and sharpness. The separation density of20°cone is significantly higher than that of15°cone, and the separation density of15°cone is only slightly lower than that of10°cone. The CCS with15°cone angle has the steepest partition curve and presents the highest separation sharpness. The upper position of the second positive cone increases the separation density slightly, while the medium position presents a slightly higher sharpness. When the first and the third cone angles are both90°, the length and the angle of the second positive cone are15mm and15°, respectively, the position of second cone is30mm, the probable error of broad size fraction can reach0.114, presenting highest separation sharpness.(7) Employing Fluent software, the difference of the flow field inside the CCS and the water-only cyclones of different cone angles, as well as the influence of the structural and operating parameters on the field characteristics of CCS was studied by the combination of RSM turbulence model and MIXTURE multi-phase model. The results show that the locus of zero vertical velocity (LZVV) in CCS was broken into two parts by the second positive cone. Compared with water-only cyclones with single cone structure, the diameter of LZVV was clearly enlarged, and the axial velocity near the connection of the cylinder and the cone at30to50mm radial positions was increased, both of which resulted in the increase of separation density. In addition, the turbulence intensity inside the cone of CCS is significantly lower than that inside water-only cyclones with single cone, allowing more stable separation and resulting in higher separation sharpness.(8) CCS of Φ700mm was designed and applied in the coarse coal separation practice in Shaqu Coal Preparation Plant. After equipment debugging, the feeding pressure was determined to be150KPa, and the length of the vortex finder650mm. Industrial effect assessment results show that the clean coal ash of+0.25mm is8.31%, the tailings ash is49.21%, the separation recovery efficiency is94.45%. The probable error of+1mm and0.5-1mm are0.056and0.115, respectively, indicating good separation effect. |
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