| OCR Text |
Show mill for a given mill and coal. It is a very difficult task to measure these variables in the mill and to quantify as a function of mill size and operating condi tions for a given coal. It is noted, however, that an identical size distribution is obtained for a constant value of S1W/F' in eqn.(8). Therefore, computations were performed for various values of F' using S1W and b1j values determined in the batch ring-roller mill, and c 1 and S1 values evaluated for test mills. Comparing the computed product size distributions wi th the test resul t, therefore, one can estimate the values of F', followed by 0 and, therefore, the scale factor k from the simulation(i.e. the batch roller mill) to the bench- and pilotscale mills. (13) A series of test results were thus analyzed and the scale factor k was then obtained as a function of the make-up feed rate to the circuit and mill conditions. k/k m= l-exp( -0/ 0 m) (14) where k is the maximum scale factor from the batch mill to a given m mill and Q is the characteristic value of the mill out~ut rate at k/k =0. 632 ~ The maximum scale factor k is defined by3 . m m k m =M(J)D I ( MmD ) b ate h ( 15) where M is the crushing load, ill the rotational speed of mill and D the mean race diameter of mill. Furthermore, Q is related to m type of coal and km• ( 16 ) where aois the constant defined by eqn.(4) a 3 and n3 are descriptive parameters. Figure 8 shows the variation of scale factors with the make-up feed rate the mill circui t plotted according to eqn. (14). The dependence of Q on mill conditions and the type of coal is shown in Fiaure 9. m ~ o +J o co '+- a,..... 1.0...------------------, 0.8 o (m) 6 0.17 o 0.61 :::J I 0.6 :u~ - E co.::,t. ~" 0.4 o (m) Coal 0.17 0.61 E .::,t. Q).::,t. ........ .;>:; co a; a: 8 A 6. C • 0 o • 0 0.2 E a o 10-3 ....... _-"-_ ......... I10....1 ..................... _---A o 1 2 3 0.1 Relative make- up feed rate O/Om (- ) ao (mm-') Fig.8 Variation on k with 0 Fig.9 Dependence of Qm/km on ao 6 |
