Study on a separation technology for more efficient utilization of pulverized coals in cement plants

A new separation technology for pulverized coals in cement plants was proposed. Two pulverized coals, NJ and ZZ, were sampled in two cement plants in China. Not only the ash and volatile matter content but also the size of the ash-containing particles and of those from which volatiles have to evolve have been determined with a float–sink method and a laser particle size analyzer. As the coal needed in a kiln and in a calciner is usually at a ratio of 4:6 in calorific value, the pulverized coals can be separated at 60 µm and 50 µm for NJ and ZZ samples, respectively. It was found that the ash content (air dry base) of the coarser part of NJ sample was 23.51%, in contrast to 34.72% before separation. Similarly, the ash content (air dry base) of the coarser part of ZZ sample was 13.86%, in contrast to 19.50% before separation. The coarser part of the coals is proposed to burn in a kiln while the finer part in a calciner. It was found from combustion simulation that the flames in a kiln are improved while the temperature profiles in a calciner change little. It is expected that the energy efficiency and cement quality will both be improved with this separation technique. Expected economical benefit and possible problems were discussed.