Numerical simulation of complex thermal decomposition processes in pyrolysis furnace for recycling solid waste Mg(NO3)2.2H2O

Abstract

This study aims to reveal the complex thermal decomposition processes in a pilot-scale pyrolysis furnace for recycling solid waste Mg(NO3)2.2H2O produced in nitric acid leaching process of laterite nickel ore, by using CFD method. Specifically, an integrated mathematical model combining the gas-particle flow and the thermal decomposition reaction as well as the heat, mass transfer between gas and particle was developed based on the Euler-Lagrange method. And then, the developed model was used to study the flow characteristics of the gas and particle and the thermal decomposition processes for Mg(NO3)2.2H2O in the pyrolysis furnace. Furthermore, the effect of operating parameters (gas inlet temperature, mass flow rate and particle size of Mg(NO3)2.2H2O) on the performance of pyrolysis furnace (decomposition rate of Mg(NO3)2.2H2O) was studied. The results show that the developed model is reasonable. Increasing gas inlet temperature, decreasing mass flow rate and particle size of Mg(NO3)2.2H2O can effectively promote the decomposition rate of Mg(NO3)2.2H2O. Under the conditions of gas inlet temperature 1123 K, mass flow rate of Mg(NO3)2.2H2O 200 kg/h, and average particle size of Mg(NO3)2.2H2O 75 µm, the dehydration reaction mainly occurs in the furnace height of 11–8 m, while the denitration reaction mainly occurs in the furnace height of 10.5–1 m. The total decomposition rate of Mg(NO3)2.2H2O is 99.75%.