Modeling on the pyrolysis of particles of low-rank coal and CaO mixture

Abstract

Pyrolysis of low-rank coal at the presence of CaO can result in uniform mixture of residual char and CaO, which can further produce calcium carbide for providing alternative way of ethyne production. Large mixture (i.e. with the addition of CaO) coal particle at centimeter-scale is usually used in such industrial pyrolysis process, for which intraparticle phenomena and pyrolysis behaviors remain largely unknown. The pyrolysis process of a centimeter-scaled mixture coal particle in ellipsoidal shape was studied with a model coupling pyrolysis kinetics and intraparticle transport phenomena. The model was validated against experimental data from both the literature and the present experiments. It was demonstrated that the addition of CaO into the coal particle can promote coal pyrolysis. Quantitative results regarding the effect of particle properties show that smaller particle size can promote the whole pyrolysis process while larger porosity is favorable for the timely removal of volatile from the particle. As for the effect of operating conditions, higher operating temperature and higher purge rate of nitrogen can promote particle heating, and therefore beneficial for the pyrolysis process. Considering pyrolysis efficiency, energy consumption and process complexity, the mixture coal particle with the size of a = 40 mm, b = 29 mm and c = 20 mm in ellipsoidal shape and the porosity of 0.07 at the operating temperature of 923 K and nitrogen purge rate of 0.1 m/s was appropriate for the potential industrial pyrolysis process. The present simulation results on the effect of particle properties and operating conditions could help to provide a simple, quick method of selecting proper particle properties and operating conditions for the industrial application of low-rank coal through pyrolysis with the addition of CaO.