| The utilization of low-grade fuels in cement rotary kiln has some difficulties. The combustion characteristics of low-grade fuelsneed further investigation, and it is still not clear about temperature distribution particularly clinkering zone in kiln. Furthermore, current multi-channel burners have too many air-paths and the outlet wind speed velocity is too high. So the principal research work has been developed in four aspects as follows:Firstly, thermogravimetry was applied to analyze the static combustion characteristics of different quality fuels, and a new method based on multiple scan methods was put forward to deduce the kinetic triplet. From the combustion characteristics point of view, bituminous coals are the best, lean coals and anthracites are the second, stone coals are the worst. The lignite is very good at ignition and steady combustion features, but worse in the late burn-out phase. The results show that the combustion of bituminous coals and lignite is controlled by the three dimensional diffusion model (cylindrical symmetry), and of lean coals, anthracites and stone coals is in according with the randomly nucleating and nucleus growth model. Judged from coal rank, combustion characteristics and kinetic analyzing results, the stone coal should be classed as a high rank and maggy anthracite coal.Secondly, the dynamic combustion characteristics of low-grade fuels were investigated by subsiding furnace which could simulate kiln condition, and a new method based on the derivative of the differential thermal theory was advanced to confirm the igniting point. The results indicate that properly decreasing the excess air factor, reducing the particle diameter, raising the volatile matter and caloric value, and enhancing the temperature of furnace wall and the secondary air is propitious to the ignition and burnout characteristics.Thirdly, a physical modelling test facility was constructed to explore the impact of burner exit configuration on flow field and mixing intensity, and a new type of burner with gear axial air outlet was originated. The results demonstrate that raising the angel of whirl blade (AWB) can intensify the mixture between the primary and secondary air, but is not always good for external recirculation zone (ERZ). The divergent outlet is beneficial to both the formation of internal recirculation zone (IRZ) and the expansion of ERZ, however, it will weaken the jet stiffness and the mixing intensity. The gear configuration of axial air channel not only benefits IRZ and ERZ, but also strengthens mixing intensity as a whole.Fourthly, the effect of burner operating parameters on the combustion of low-grade fuels in entire kiln was studied systematically through the computer-aided test (CAT). From the results obtained, it is a better operating mode that AWB is 45°, the ratio of axial flow to swirl is 3:1, and the excess air ratio is 1.2. It can form the modest IRZ and ERZ and ensure the favorable high temperature zone distribution. Furthermore, it can avoid local hyper-thermal zone and at the same time insure complete combustion. So it is practicable to utilize low-grade fuels such as anthracites by three channel burner in satisfactory operating condition.Lastly, the application of different quality fuels in cement rotary kiln was discussed, and the performance indexes of clinkering system were investigated when low-grade fuels were used.
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