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Fig. 11 Development of σ with respect to different d(u in ) and normalization respective to σ in the
constant optimal case (a), optimal time-varying influx rate u in (b), optimal solution at final time
together with the PSD of external nuclei q in,3 (c) and surface plot of the optimal solution (d)
fractions by two screens: The large fraction which is milled and fed back to the FBSG
module, the product which is collected and the fine fraction which is also fed back to
the FBSG module. An initial PSD q 0 with a mean particle size of 2 mm and with an
RSD of approximately 20 % is considered. At final time t f = 70 min, the goal is is
to find a proper time-dependent milling power P such that simultaneously the mass
of the total product with PSD q tot cumulated over time is maximized and the energy
consumption of the mill is minimized.
For screen 1 and screen 2, respectively, grade efficiency functions 1 , , 2 according
to the model of Molerus and Hoffmann (cf. [56]) with cut size x cut,1 = 7 mm and