3D transient CFD study of iron-coke briquettes pyrolysis and quench processes in an optimised gas heat carrier pyrolyser

Iron coke is an emerging alternative material for iron-making blast furnaces. To massively produce iron coke, the industrial-scale gas heat carrier pyrolyser is a suitable reactor, but the present pyrolysis technology requires further improvements to lower energy consumption and CO2 emission. In this study, a transient 3D CFD model is developed to describe the thermochemical behaviours in the industrial-scale pyrolyser. Meanwhile, a DEM model is used to simulate the packing status evolution of ellipsoidal iron-coke hot briquettes in the pyrolyser chamber, which is input as the simulation conditions in the CFD model. The numerical model is validated against the lab-scale and pilot-scale experimental data. The integrated numerical model is then employed to illustrate heating and quenching processes using the recycled pyrolysis gas as the heat carrier. A new concept that utilises recycled pyrolysis gas to quench the hot briquette after pyrolysis inside the chamber is proposed and examined by the numerical model. In addition, the structure optimisation, i.e., adjustment of the gas inlets' layout, is conducted and numerically examined. The simulation results indicate that the present structure of the pyrolyser has some non-uniform temperature zones, such as the upper bed and near-wall areas where the heat is not effectively transferred to the bed like other zones. 10 h of pyrolysis could effectively pyrolysis iron-coke hot briquettes in the chamber, but for the quenching process, 10 h is not able to fully cool down the briquette bed to room temperature. The design of the upper inlet layout could significantly improve the heating and pyrolysis efficiency. It can shorten 14% heating time in comparison with the original lower inlet layout.