Investigation of mixing behaviors in a spouted bed with different density particles using discrete element method

CFD and statistical approach to optimize the average air velocity and air volume fraction in an inert-particles spouted-bed reactor (IPSBR) system

Inert-particles spouted bed reactor (IPSBR) is characterized by intense mixing generated by the circular motion of the inert particles. The operating parameters play an important role in the performance of the IPSBR system, and therefore, parameter optimization is critical for the design and scale-up of this gas–liquid contact system. Computational fluid dynamics (CFD) provides detailed modeling of the system hydrodynamics, enabling the determination of the operating conditions that optimize the performance of this contact system. The present work optimizes the main IPSBR operating parameters, which include a feed-gas velocity in the range 0.5–1.5 m/s, orifice diameter in the range 0.001–0.005 m, gas head in the range 0.15–0.35 m, mixing-particle diameter in the range 0.009–0.0225 m, and mixing-particle to reactor volume fraction in the range 2.0–10.0 vol % (which represents 0.01–0.1 kg of mixing particles loading). The effects of these parameters on the average air velocity and average air volume fraction in the upper, middle, and conical regions of the reactor were studied. The specific distance for each region has been measured from the orifice point to be 50 mm for the conical region, 350 mm for the middle region and 550 mm for the upper rejoin. The selected factors were optimized to obtain the minimum air velocity distribution (maximum gas residence time) and the maximum air volume fraction (maximum interfacial area concentration) because these conditions will increase the gas holdup, the gas–liquid contact area, and the mass transfer coefficient among phases. Response surface methodology (RSM) was used to determine the optimum operating conditions. The regression analysis showed an excellent fit of the experimental data to a second-order polynomial model. The interaction between the process variables was evaluated using the obtained three-dimensional surface plots. The analysis revealed that under the optimized parameters of a feed-gas velocity of 1.5 m/s, orifice diameter of 0.001 m, gas head of 0.164 m, mixing-particle diameter of 0.0225 m, and mixing-particle loading of 0.02 kg, the minimum average air velocity and highest air volume fraction were observed throughout the reactor.

Effects of temperature and particle size on biomass torrefaction in a slot-rectangular spouted bed reactor

Sawdust particles of different sizes (0.25-0.5, 0.5-1.0 and 1.0-2.0mm) were torrefied in a continuous slot-rectangular spouted bed reactor. The effects of particle size and temperature were investigated on the properties of the torrefied product, such as proximate analysis, ultimate analysis, HHV, skeletal density, and energy yield. Temperature was the most important variable in the torrefaction process. Increasing the particle size led to more weight loss of sawdust and increased mass of the torrefied product remaining in the reactor. The ash content evolution of the torrefied product showed that its properties approached a steady state within 20min. The reduction in Sauter mean particles size was up to 20.3% and 28.2% for 0.25-0.5mm and 0.5-1.0mm sawdust, respectively.