CEE April-June 2012

tapered rollers {Figure 3). The design permits changing of the grinding table, nozzle ring and rollers without significant conversion work. The feed material is fed centrally onto the grinding table via the grit funnel of the classifier. The grit discharge system was designed in such a way that tests can be performed either with or without an external circuit without major conversion work. The specific grinding pressure can be varied from1 00 kN/m 2 to 1OOOkN/m 2 . The hydraulic system is equipped with two gas pressure accumulators. Table 1 provides an overview of the mill's geometrical dimensions. Table-1 Geometric Characteristic data for the VRM2 Mean roller circle diameter Drw 156 mm Grinding plate diameter Dr 200mm Mean grinding roller Dwm 133 mm diameter Number of grinding rollers m,z 2 Orifice height h variable Grinding-gap width s 0 - 15 mm Grinding roller inclination 15° Inclination of grinding track y oo Setting measurement parameters; control/regulation The measurement parameters of this mill were set to enable the recording of a comprehensive profile of the mill in various operating states. Five relative-pressure sensors and four temperature sensors were incorporated to permit the plotting of a pressure and temperature profile (Figure 4). The mechanical power applied to the grind ing table is measured by means of a torque measurement shaft. All operating data are recorded automatically, in machine-readable form, and stored on a memory card. The machine is controlled by means of a panel featuring touch-screen control, thus permitting easy operation combined with great flexibi lity for the user. Where the external circuit is used , the mass flow is measured directly in the grit recirculation by means of a mechanically isolated impact weigher. The system fan and the feed system can be controlled, on the one hand , by selecting a fixed speed , and also fully automatically, by means of a PID controller. System air rate can thus be adjusted to a constant volumetric flow, or feed adjusted to a mass flow or a target pressure drop across the mill. Cross-flow rotary- cage classifieree The mill was combined with the CTM0014V cross-flow rotary-cage classifier developed in house (Figure 5) . The classifier has a classifier wheel Measuring positions VRM2 CE ft'ii'~G M Mus flow lk&/hl M Torque [Nm] n Spefd [rpml p Relative pressure [bar] T Tempe<ature rCJ V Volume flow (m'lhl ~ Svstem flow sheet slmofifled sensor svstem 26