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

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 degreesC 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(o)/u(mf) and u(o)-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 degrees 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 mum/1000 h and the maximum erosion occurred at ambient pressure because of the large amount of particle-tube impacts. (C) 2000 Elsevier Science Ltd. All rights reserved.