Ignition of large size coal in a gas-phase temperature adjustable concentrating photothermal reactor: The influence of volumetric reactions

Ignition of large size coal was the basis of the design and application of Fluidized Bed (FB) and Circulating Fluidized Bed (CFB) combustion technologies. The strongly coupled gas-phase and solid-phase temperature fields in existing experimental apparatus provoked obstacles for the determination of the influence of volumetric reactions on large size coal ignition. In this study, a gas-phase temperature adjustable concentrating photothermal reactor (GTA-CPR) was developed, and the gas-phase temperature could be effectively regulated by the preheated gas flow while the solid-phase temperature was determined by the irradiation voltage. 25 experimental conditions corresponded to 5 levels of solid-phase temperatures with 5 levels of gas-phase temperatures. Enhanced volumetric reactions (by higher gas-phase temperature) led to significant decrease in ignition delay (≥50%) and prolongation of flame duration (≥1.1 times). Real-time CH4 concentration in volumetric reaction boundary was detected with Mass Spectrometry (MS), which exhibited double peaks. The first CH4 peak height decreased dramatically while the second CH4 peak height increased with the gas-phase temperature, indicating the advanced ignition and enhanced volumetric reactions. Ultimately, an ignition delay prediction model was proposed through Backward induction and the indispensable importance of volumetric reactions to coal ignition was evidenced.