Full Scale Assessment of the Influence of a Precessing Jet of Air on the Performance of Pulverised Coal Flame in a Cement Kiln

摘要

The first full-scale assessment of the performance of precessing jet nozzles when firing pulverised fuel, the "Solid Fuel Gyro-Therm~(TM)" (SFGT), is reported. The trials were undertaken in the 3000 tpd rotary kiln of Ash Grove Cement, Durkee, Oregon. The burner comprised an annular stream of indirect-fired pulverised coal, two co-annular streams of axial air, and a central precessing jet air nozzle. This design allowed the burner to be configured either as a SFGT or the benchmark "High Momentum" burner, simply by adjusting valves. The benchmark burner had been optimised using physical modelling to have a Craya Curtet parameter of 2.2. The same total mass of "primary" air was introduced through the burner in both configurations. The results showed that the introduction of air through the Precessing Jet nozzle resulted in a dramatic shift in the heat flux profile toward the front of the kiln. This shift is quantified by shell temperature profiles and pyrometer measurements of the bed temperature. Consistent with this shift in heat flux was a reduction in fuel usage by around 4%, based on the average of all test periods, and by about 5% based on short-term comparisons under comparable operating conditions. Quantification of the difference in NO emissions was hampered by differences in the average excess air across the various trial periods. Hence, while the average NO concentration was comparable with the two burners, this is not considered to be a representative comparison. A comparison based on the most similar periods of 6 hour operation revealed a 27% reduction in NO emissions with the SFGT.