MATHEMATICAL-MODEL OF CHALCOCITE PARTICLE COMBUSTION

A mathematical model has been developed to simulate the combustion of a single chalcocite particle (particle diameter between 10 and 100 mic rons) in air, oxygen, and oxygen-SO, mixtures, Neglecting temperature and composition gradients within the particle, the model computes the thermal and compositional changes of the particle as a function of tim e. Five chemical reactions were considered to describe the chemical in teraction between the gas and particle and within the particle, Copper vaporization below the boiling point was calculated by a balance betw een the vaporization rate (characterized by the Langmuir-Knudsen equat ion) and mass transfer from the surface of the particle. The model cal culations were verified by comparison with published mass loss data ob tained in a stagnant gas reactor. The model revealed that for particle s combusting in oxygen, copper vaporization below the boiling point do es not limit particle temperature, and particles of all sizes between 20 and 100 microns can readily reach the boiling point of copper (2836 K). Thus, the particle explosions observed in an earlier study are li kely due to copper boiling within a combusting particle. Calculations of particle combustion in air showed that only small (<20-micron diame ter) particles would be capable of exploding, which agreed generally w ith earlier observations. Consequently, in a commercial flash-converti ng furnace, careful control of particle size and oxygen atmosphere mus t be maintained to minimize particle explosions and concomitant dust f ormation.