Numerical simulation of the complex thermal processes in a vortexing precalciner

Abstract To reveal the coupling process of coal combustion and calcium carbonate (CaCO 3 ) decomposition, an actual vortexing precalciner was numerically simulated. Precalciners are used to pre-decompose the raw meal (mainly CaCO 3 ) in a suspended condition. The flow pattern of a mixed stream of tertiary air and flue gas was displayed, the coal combustion characteristics in the precalciner were analyzed, and the coupling mechanism of the coal combustion and raw-meal decomposition was explored. The predicted burn-off rate of the pulverized coal stream was 98%, and the decomposition rate of the CaCO 3 was 93%, in accordance with actual engineering data. The results show that the interaction of the transverse rotating tertiary air and the vertically spouting flue gas causes a spirally rising gas-flow field. The pulverized coal stream starts to burn when injected into the prechamber, and burns rapidly when rising into the cone section and the column section above the prechamber, forming a violent combustion region where the CaCO 3 decomposes rapidly. Then, when the pulverized-coal and raw-meal streams spirally rise along the precalciner, the char burning rate reduces gradually and the CaCO 3 decomposition rate decreases until the coal-combustion reaction and the CaCO 3 decomposition end. The results obtained in this study not only provide important theoretical guidance for optimizing the precalciner’s operation parameters, but also lay a foundation for further research about this type of precalciner, e.g., the staged and refuse-derived fuel combustion processes, to save energy and reduce emissions.