Cement, Energy and Environment

In-depth studies in BM with a variable-speed electric drive (within 0 to 1.4 ncr) in the field of parameters "rotational speed - grinding bodies fill factor" were conducted on the 2 x1 0.5 m mill at the Belgorod Cement plant, Russia. The three operating conditions obtained (Figures 1 and 2), besides having a practical significance, are theoretically interesting because they explain the effectiveness of different mill rotational speeds (n>n rated; n = nrated = 0.76 ncr; n<nrated), thus having reconciled their many supporters and opponents. The data in Figures 1 and 2 results in the following conclusions: • A bigger ball charge requires a lower mill rotational speed . • To ensure maximum productivity at specified grinding fineness and minimal electric power consumption, it is necessary that <p =0.36 and nopt =0.65ncr· • This operating condition can be implemented only with variable-speed electric drive, allowing one to not only find the optimal operating condition, but also to adjust the static characteristic drift in time with an automatic control system. • The speed conditions n =0.76 ncr (<p =0.32) and especially n = 0.9 ncr (<p =0.28) are false optimums because the actual ball fill is at a lower level and limited by the power and rotational speed of the non-controlled electric drive. • The regularities obtained are universal for any standard size mills. These results and conclusions are in full agreement with those of Dr. Beke Bela who analytically confirmed the full agreement of dependencies (Figures 1 and 2) by comparing the authors' results with those of Italian researchers obtained J5 ~ ' independently at the Guidonia Cement plant in Rome on three 4.8 x 15.4 m mills with a variable-speed grearless 6000 kW electric drive. The control range of these mills is within 0.66 n cr to 0.79 n cr. i.e. only 13 per cent. t- ~ J ./ r- 30 ·- - · 21J 50 -- J! - IJ r- - ·- (/ ~ ld -- - If_ -· - J "-ff"J ~ r- r-- - - - __ ..._. 60 70 80 Figure 2. Electric power consumption y vs. ball fill factor (<pl = 0.28; <p2 = 0.32; q>3 = 0.36) and mill rotational speed n. q> 0,36 0,32 - - ., CIS CICS 00, = = = 0 . 0 -~ . ., . ., ·- ·- ' "0 "0 "0 "0 ..s::: ~ CICS (.) 0,28 0 4 8 12 16 t, day Figure 3. Grinding bodies wear vs. operating time. 15