Classification performance of model coal mill classifiers with swirling and non-swirling inlets

doi:10.1016/j.cjche.2019.12.002

Abstract

Abstract: The classification performance of model coal mill classifiers with different bottom incoming flow inlets was experimentally and numerically studied. The flow field adjacent to two neighboring impeller blades was measured using the particle image velocimetry technique. The results showed that the flow field adjacent to two neighboring blades with the swirling inlet was significantly different from that with the non-swirling inlet. With the swirling inlet, there was a vortex located between two neighboring blades, while with the nonswirling inlet, the vortex was attached to the blade tip. The vorticity of the vortex with the non-swirling inlet was much lower than that with the swirling inlet. The classifier with the non-swirling inlet demonstrated a larger cut size than that with the swirling inlet when the impeller was stationary (~0 r·min^-1). As the impeller rotational speed increased, the cut size of the cases with non-swirling and swirling inlets both decreased, and the one with the non-swirling inlet decreased more dramatically. The values of the cut size of the two classifiers were close to each other at a high impeller rotational speed (≥120 r·min^-1). The overall separation efficiency of the classifier with the non-swirling inlet was lower than that with the swirling inlet, and monotonically increased as the impeller rotational speed increased. With the swirling inlet, the overall separation efficiency first increased with the impeller rotational speed and then decreased when the rotational speed was above 120 r·min^-1, and the variation trend of the separation efficiency was more moderate. As the initial particle concentration increased, the cut sizes of both swirling and non-swirling inlet cases decreased first and then barely changed. At a low initial particle concentration (<0.04 kg·m^-3), the classifier with the swirling inlet had a larger cut size than that with the non-swirling inlet.

Key words: Coal mill classifier, Cut size, Non-swirling inlet, Particle image velocimetry, Impeller rotational speed

摘要： The classification performance of model coal mill classifiers with different bottom incoming flow inlets was experimentally and numerically studied. The flow field adjacent to two neighboring impeller blades was measured using the particle image velocimetry technique. The results showed that the flow field adjacent to two neighboring blades with the swirling inlet was significantly different from that with the non-swirling inlet. With the swirling inlet, there was a vortex located between two neighboring blades, while with the nonswirling inlet, the vortex was attached to the blade tip. The vorticity of the vortex with the non-swirling inlet was much lower than that with the swirling inlet. The classifier with the non-swirling inlet demonstrated a larger cut size than that with the swirling inlet when the impeller was stationary (~0 r·min^-1). As the impeller rotational speed increased, the cut size of the cases with non-swirling and swirling inlets both decreased, and the one with the non-swirling inlet decreased more dramatically. The values of the cut size of the two classifiers were close to each other at a high impeller rotational speed (≥120 r·min^-1). The overall separation efficiency of the classifier with the non-swirling inlet was lower than that with the swirling inlet, and monotonically increased as the impeller rotational speed increased. With the swirling inlet, the overall separation efficiency first increased with the impeller rotational speed and then decreased when the rotational speed was above 120 r·min^-1, and the variation trend of the separation efficiency was more moderate. As the initial particle concentration increased, the cut sizes of both swirling and non-swirling inlet cases decreased first and then barely changed. At a low initial particle concentration (<0.04 kg·m^-3), the classifier with the swirling inlet had a larger cut size than that with the non-swirling inlet.

关键词: Coal mill classifier, Cut size, Non-swirling inlet, Particle image velocimetry, Impeller rotational speed

Lele Feng, Hai Zhang, Lilin Hu, Yang Zhang, Yuxin Wu, Yuzhao Wang, Hairui Yang. Classification performance of model coal mill classifiers with swirling and non-swirling inlets[J]. Chinese Journal of Chemical Engineering, 2020, 28(3): 777-784.

References

[1] O. Williams, G. Newbolt, C. Eastwick, Influence of mill type on densified biomass comminution, Appl. Energy 182(2016) 219-231.
[2] M. Bilen, S. Kizgut, Modeling of unburned carbon in fly ash and importance of size parameters, Fuel Process. Technol. 143(2016) 7-17.
[3] M. Bilen, S. Kizgut, Prediction of unburned carbon in bottom ash in terms of moisture content and sieve analysis of coal, Fuel Process. Technol. 138(2015) 236-242.
[4] J.L. Ferrin, L. Saavedra, Distribution of the coal flow in the mill-duct system of the as pontes power plant using CFD modeling, Fuel Process. Technol. 106(2013) 84-94.
[5] H. Li, Y. He, F. Shi, Performance of the static air classifier in a vertical spindle mill, Fuel 177(2016) 8-14.
[6] J.J. Parham, W.J. Easson, Flow visualisation and velocity measurements in a vertical spindle coal mill static classifier, Fuel 82(15-17) (2003) 2115-2123.
[7] H. Lee, M.S. Klima, P. Saylor, Evaluation of a laboratory rod mill when grinding bituminous coal, Fuel 92(1) (2012) 116-121.
[8] S. Ataş, U. Tekir, M.A. Paksoy, Numerical and experimental analysis of pulverized coal mill classifier performance in the Soma B power plant, Fuel Process. Technol. 126(2014) 441-452.
[9] T. Kojovic, F. Shi, M. Brennan, Modelling of vertical spindle mills. Part 2:Integrated models for E-mill, MPS and CKP mills, Fuel 143(2015) 602-611.
[10] F. Shi, T. Kojovic, M. Brennan, Modelling of vertical spindle mills. Part 1:Sub-models for comminution and classification, Fuel 143(2015) 595-601.
[11] C. Hosten, B. Fidan, An industrial comparative study of cement clinker grinding systems regarding the specific energy consumption and cement properties, Powder Technol. 221(2012) 183-188.
[12] A. Trubetskaya, Y. Poyraz, R. Weber, Secondary comminution of wood pellets in power plant and laboratory-scale mills, Fuel Process. Technol. 160(2017) 216-227.
[13] K.S. Bhambare, Z. Ma, P. Lu, CFD modeling of MPS coal mill with moisture evaporation, Fuel Process. Technol. 91(5) (2010) 566-571.
[14] W.N. Xie, Y.Q. He, Y.H. Zhang, Simulation study of the energy-size reduction of MPS vertical spindle pulverizer, Fuel 139(2015) 180-189.
[15] J. Blondeau, R. Kock, J. Mertens, Online monitoring of coal particle size and flow distribution in coal-fired power plants:Dynamic effects of a varying mill classifier speed, Appl. Therm. Eng. 98(2016) 449-454.
[16] R. Guizani, I. Mokni, H. Mhiri, CFD modeling and analysis of the fish-hook effect on the rotor separator's efficiency, Powder Technol. 264(2014) 149-157.
[17] L. Gao, Y. Yu, J. Liu, Study on the cut size of a turbo air classifier, Powder Technol. 237(2013) 520-528.
[18] L. Karunakumari, C. Eswaraiah, S. Jayanti, Experimental and numerical study of a rotating wheel air classifier, AIChE J. 51(2005) 776-790.
[19] Q. Huang, J. Liu, Y. Yu, Turbo air classifier guide vane improvement and inner flow field numerical simulation, Powder Technol. 226(2012) 10-15.
[20] Q.L. Yang, J.X. Liu, Analysis of flow field in turbo air classifier and improvement of rotor cage structure, Chemical Engineering (China) 1(2010) 0-22.
[21] L. Guo, J. Liu, S. Liu, Velocity measurements and flow field characteristic analyses in a turbo air classifier, Powder Technol. 178(2007) 10-16.
[22] Y. Feng, J. Liu, S. Liu, Effects of operating parameters on flow field in a turbo air classifier, Mineral Engineering 21(2008) 598-604.
[23] W. Xing, Y. Wang, Y. Zhang, Experimental study on velocity field between two adjacent blades and gas-solid separation of a turbo air classifier, Powder Technol. 286(2015) 240-245.
[24] R. Liu, J. Liu, Y. Yu, Effects of axial inclined guide vanes on a turbo air classifier, Powder Technol. 280(2015) 1-9.
[25] L. Afolabi, A. Aroussi, N.M. Isa, Numerical modelling of the carrier gas phase in a laboratory-scale coal classifier model, Fuel Process. Technol. 92(3) (2011) 556-562.
[26] R. Vuthaluru, O. Kruger, M. Abhishek, Investigation of wear pattern in a complex coal pulveriser using CFD modeling, Fuel Process. Technol. 87(2006) 687-694.
[27] M. Kozic, S. Ristic, B. Katavic, Redesign of impact plates of ventilation mill based on 3D numerical simulation of multiphase flow around a grinding wheel, Fuel Process. Technol. 106(2013) 555-568.
[28] P. Toneva, P. Epple, M. Breuer, Grinding in an air classifier mill-Part I:Characterization of the one-phase flow, Powder Technol. 211(2011) 19-27.
[29] K.V. Shah, R. Vuthaluru, H.B. Vuthaluru, CFD based investigations into optimization of coal pulveriser performance:Effect of classifier vane settings, Fuel Process. Technol. 90(9) (2009) 1135-1141.
[30] P. Toneva, K.E. Wirth, W. Peukert, Grinding in an air classifier mill-Part II:Characterization of the two-phase flow, Powder Technol. 211(1) (2011) 28-37.
[31] H.B. Vuthaluru, V.K. Pareek, R. Vuthaluru, Multiphase flow simulation of a simplified coal pulveriser, Fuel Process. Technol. 86(11) (2005) 1195-1205.
[32] A. Morsi, A.J. Alexander, An investigation of particle trajectories in two-phase flow systems, J. Fluid Mech. 55(2) (1972) 193-208.