Breakage and Mass Transport of Coal Particles in Ring-roller Mills

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(2)mixing in a grinding zone can be treated as if the grinding zone were equivalent to a fully-mixed reactor, (3)there is no build-up in classi f ication zones and (4) the steady-state mass transport relation of particles through the mill can be applied to unsteady­state conditions. Raw Coal G (t) Qik (t) j~ td3 F ,. (t) ~ ~ f ik . (t) - td2 Grinding zone Primary Secondary classification classification W(t) F 2 . (t) ~ C i I F (t) ~ \ S i I Q (t) ~ W ik (t) W ik (t) I Pik (t) .. I Qik (t) t dl T . (t) t ik ' (t) t dl ·t d2. td3 : Time Delay T (t) t ik (t) Fig.2 Illustration of model and nomenclature Pulverized Coal The mass balance on coal particles of size interval i and grindabili ty class k in the grinding zone over a short time interval can be expressed as follows. ( 1 ) where Sik(t) is the specific rate of breakage of particles of size class i and grindabili ty class k and b ijk is the primary fragment distribution parameter defined as the fraction of particles of grindability class k just broken from particles of size interval j and grindability class k which appears in size interval i. The change in the hold-up in the mill is given by ( 2 ) The hold-up under steady-state con­ditions can be postulated as follows. W = aF' (3 ) Torque sensor Couplin Pressure frame Spring where F' is the coal flow rate through the grinding zone and a is a proportionality constant. \ . 3.Parameter Estimation 3.1 Breakage Parameters The breakage parameters of var­ious types of coals were measured in a laborator~ batch ring-roller mill(D=O.076m) ) shown in Figure 3 using the one-size-fraction method7 ). 3 Fig.3 A laboratory batch ring-roller mill