Behavior of particles and bubbles around immersed tubes in a fluidized bed at high temperature and pressure: a DEM simulation

Abstract

Numerical simulations were carried out to investigate the behavior of particles and bubbles around immersed tubes in a two-dimensional fluidized bed at elevated pressures. Bed temperature was kept constant at 850°C and bed pressure was varied from 0.1 to 1.2 MPa. The particle–tube impact velocity and impact angle, the number of particle–tube impacts and the bed voidage around tubes in a staggered tube bank were calculated. It was found that the bed expansion height increased with the increasing pressure both at constant u 0/ u mf and u 0− u mf. Under elevated pressure, 1.2 MPa, the bubble frequency was about 4–8 Hz which was slightly higher than 2–4 Hz for the ambient condition, and the time-averaged velocity of particle–tube impacts at tube bottom area was also higher than that under the ambient pressure. The average particle–tube impact velocity showed its maximum at 10–70° from the tube bottom. The time average of bed voidage around a tube increased with the increasing pressure. The distributions of bed voidage and particle–tube impact velocity around a tube were asymmetrical, which may be due to the local bubble habits. The tube erosion rate was predicted to be 7.9–19.4 μm/1000 h and the maximum erosion occurred at ambient pressure because of the large amount of particle–tube impacts.