Prediction improvements of ignition characteristics of isolated coal particles with a one-dimensional transient model |
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Authors: | Wantao Yang Bing Liu Hai Zhang Yang Zhang Yuxin WU Junfu Lyu |
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Affiliation: | 1. Key Laboratory for Thermal Science and Power Engineering of Ministry Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China;2. North China Power Engineering Co., Ltd, China Power Engineering Consulting Group, Beijing, China |
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Abstract: | A modified 1-D transient model considering intra-particle thermal conduction is adopted to improve the predictions of the ignition characteristics of isolated coal particles. The study aims at resolving the incorrect prediction on the variation trend of ignition temperature Ti with the change of oxygen concentration XO2, interpreting the contradictory dependencies on coal particle size and furnace temperature and clarifying the conditions when the intra-particle thermal conduction should be considered. The predictions are compared with microgravity data in which the buoyancy effect is minimized. The results reveal that the previous ignition model with transient adiabatic criterion fails to predict the Ti variation with XO2, since it cannot accurately predict Ti and delay time in the low XO2 region. Instead, the ignition model with flammability limit ignition criterion can well predict Ti in a wide range of XO2. Intra-particle thermal conduction causes remarkable temperature differences for large coal particles, and moreover, the variation trends of surface and center temperatures with particle size are very different. The center temperature at ignition drops remarkably with increasing particle size, while the surface temperature barely changes or slightly increases with particle size. At the same particle size, the variation trends of surface and center temperatures with furnace temperature are also opposite. The ignition mode and variation trend of ignition surface temperature with particle size depends on the heating rate and particle size itself. The contradictory experimental results reported by different researchers are attributed to the particle size and temperature measurement location. The conditions necessary to consider the intra-particle thermal conduction are discussed. Lastly, the effect of the intraparticle thermal conduction is shown on an ignition mode diagram. |
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