We have developed new technologies to improve particle classification performance of vertical roller mills using a rotary nozzle ring with reverse swirling flow and a louver separator. A rotary nozzle and a louver are installed in primary and secondary classification sections of the mill, respectively. A series of tests using a pilot scale mill showed that these technologies reduce the fraction of coarse particles, power consumption of the mill and mill differential pressure. For an industrial scale-up, we conducted a demonstration test using a vertical roller mill equipped in a 700MW thermal power plant consisting of a pulverized coal firing boiler and six mills with approx. 70t/h nominal grinding capacity in each. In this paper, we discuss demonstration test results on the viewpoint of decreasing coarse particle fractions, power consumption and mill differential pressure. Under normal operating conditions, the coarse particle fraction in pulverized coal was reduced more than 50%, power consumption was reduced 7% and differential pressure was reduced approx. 50%. Additionally, power consumption was reduced approx. 15% under high coal feed conditions. We confirmed that these new technologies effectively improved performance in higher mill loading rates. These results provide a prospect of upgrading the plant performance, especially in reducing unburned carbon in fly ash and power consumption of auxiliary equipment.
Effects of Blade Parameters on the Flow Field and Classification Performance of the Vertical Roller Mill via Numerical Investigations
