Effect Of Microwave Coupling And Ultrasonic Modification On Pulverized Coal Combustion Properties

Difficulty in improving combustion performance of pulverized coal is considered a major factor in limiting injection amount of pulverized coal in blast furnace. For this purpose, improving combustion performance of pulverized coal at raceway has become an essential and critical part in increasing injection ratio in blast furnace. In this paper,microwave-ultrasonic coupling co-processing in the external field is utilized in modification of pulverized coal injection in blast furnace, a comprehensive study has been conducted on combustion performance of modified pulverized coal by making use of lab-made burner, laser particle size analyzer, scanning electron microscope and other measures for analysis and testing, techniques have been established for coupling co-processing of pulverized coal in external field, based on which the role and rules of coupling in external field in improving combustion performance of pulverized coal have been further discussed, thus the following conclusion has been reached:(1) Microwave-treated bituminous coal and anthracite were observed with an increase in combustion ratio as microwave radiation duration elapses prior to the best radiation time is reached while with rapid decrease along with the radiation duration after the peak is reached. Bituminous coal boasted the optimum microwave modification power of 132 W and optimum modification time of 60 s while anthracite had the optimum microwave modification power of 132 W and optimum modification time of 30 s.(2) Substantial change was found in combustion ratio of bituminous coal and anthracite which were co-processed in external ultrasonic-microwave coupling field in different conditions, that is, the combustion ratio increased distinctly with duration of coupling modification. When the duration became longer than 10 min, the curve showed a tendency toward stabilization, which indicated high-power ultrasonic wave had allowed combustion ratio of the pulverized coal to improve greatly within certain amount of time, yet the ratio approached to stabilization as time elapsed. In the testing conditions, optimum ultrasonic wave radiation could be achieved when the power was350 W and radiation duration was 10 min.(3) The ultrasonic-microwave coupling has changed size distribution of the bituminous coal and anthracite, particularly, size of microwave-treated pulverized coal decreased somewhat and that of ultrasonic-microwave co-processed pulverized coal further decreased. In the test, pulverized coal of the coupled bituminous coal and anthracite experienced a decrease in maximum particle size range and the average particle size, and combustion ratio of the pulverized coal was improved as a result of finer particle size.(4) The coupled bituminous coal and anthracite were found identical with each other in microstructure change trend. Compared with the untreated pulverized coal, the microwave-treated one appeared in smaller particle size and the coupled one in thebiggest particle size change. Particle size distributions of the two pulverized coals treated in different ways also showed that, the coupled pulverized coal could be seen in a smaller particle size than the microwave-treated one and untreated one. The coupling treatment could achieve a more even size distribution and a higher percentage of fine particles.