Numerical study in the pressure effects on coal catalytic hydrogasification in the bubbling fluidized bed

Pressurized fluidized bed coal catalytic hydrogasification is a promising coal-to-SNG technology. Its scale-up faces some challenges, such as hot-spot controlling, particle-size selection, and char residue discharging. Pressure is recognized as a critical influencing factor. In order to reveal the pressure effects, numerical simulations are carried out at different pressures (1 MPa, 2 MPa, 3 MPa, and 4 MPa), and last for the whole residence time by using the validated MP-PIC model. The pressure effects are carefully analyzed in terms of bubble size, bed temperature, global conversion, particle-scale dynamics, and individual reactivity. Results show that elevated pressure contributes to the generation of small bubbles, and the reaction is intensified at the place where small bubbles accumulate. But pressure over 3 MPa should be avoided, otherwise, the hot spot of 1400 K will occur. Then pressure selection is suggested as a compromise between reaction intensification and avoiding the hot spot. Based on different pressure results, the particle size distribution for the current process is also suggested in the range between 50 mu m and 350 mu m. Finally, the optimal interrelationship between pressure, particle size, and gas velocity is found, which provides useful guidance for the scale-up of the CCHG reactor.