•A method to calculate the onset velocity of liquid–solid fluidized bed was proposed by simulation.•Onset velocity was determined by the fitted particle mean residence time vs. liquid velocity lines.•Collisional parameters did not affect mean residence time and onset velocity.•Humps and trailing on residence time distribution curves originated in particle-scale behavior.Until now, the onset velocity of circulating fluidization in liquid–solid fluidized beds has been defined by the turning point of the time required to empty a bed of particles as a function of the superficial liquid velocity, and is reported to be only dependent on the liquid and particle properties. This study presents a new approach to calculate the onset velocity using CFD–DEM simulation of the particle residence time distribution (RTD). The onset velocity is identified from the intersection of the fitted lines of the particle mean residence time as a function of superficial liquid velocity. Our results are in reasonable agreement with experimental data. The simulation indicates that the onset velocity is influenced by the density and size of particles and weakly affected by riser height and diameter. A power-law function is proposed to correlate the mean particle residence time with the superficial liquid velocity. The collisional parameters have a minor effect on the mean residence time of particles and the onset velocity, but influence the particle RTD, showing some humps and trailing. The particle RTD is found to be related to the particle trajectories, which may indicate the complex flow structure and underlying mechanisms of the particle RTD.

In order to reduce the emission of CO2, a thermodynamic and experimental investigation has been carried out to develop a new process for converting barium sulfate to barium sulfide involving elemental sulfur. In this improved process, the starting raw material barium sulfate was reduced by elemental sulfur to produce barium sulfide. The results indicated that the main products of BaSO4–S reaction produces were solid barium sulfide and sulfur dioxide, which could be used for producing sulfuric acid. Thermodynamic analyses showed that the reaction of the barium sulfate decomposition by sulfur was a complicated gas–solid reaction process with rising temperature. By simulation, the barium sulfate decomposition began at about 675 K and was completed at 1800 K. The thermodynamic and experimental results indicated that the rising reaction temperature and the increasing sulfur partial pressure contributed to reaction process. The decomposition temperatures of barium sulfate obtained by experiments were in a reasonable consistency with the simulation results, although they were a little higher than that obtained by simulation, due to the limited reaction time.