Study of the magnesium dust cloud hot surface ignition characteristics in the Godbert-Greenwald furnace

Magnesium dust cloud hot surface ignition characteristics in the Godbert-Greenwald (G-G) furnace are simulated. CFD models and algorithms selected for the simulation are validated through comparison between simulated dust cloud critical ignition temperature (CIT) results and experimental dust cloud minimum ignition temperature (MIT) data. The magnesium dust cloud ignition process in the G-G furnace mainly characterizes three stages: dust dispersion and cloud formation, dust cloud deposition and heat accumulation, and dust cloud thermal runaway. Particle size increase shortens particle residence time in the furnace and lifts the particle-gas thermal resistance, leading to more significant delays between particle ignition and gas flame formation for larger particle sizes over 100 μm. Under the marginal super-critical ignition state as the furnace heating temperature just reaches the CIT level, if the CIT of a specific particle sized dust cloud is higher than the MIT of the same sized single magnesium particle (MITP), the dust cloud ignition mainly characterizes an individual particle ignition driven mode, otherwise governed by a collective particle heating driven mode. The simulated magnesium dust cloud CIT stays rather stable under lower dust dispersion pressures (P_dis) below 2 kPa, but shows a clearer increasing trend as P_dis further rises.