The Investigation of Solids Velocity in the Circulating Fluidized Beds
Date Issued
2008
Date
2008
Author(s)
Wang, Chi-En
Abstract
The local time-mean particle velocity profile in the different flow regimes and solid circulation rate was acquired by optical fiber probes which detected at the different axial and radial positions in a 0.108 m i.d., 5.75 m high with 0.108 m i.d., 5.75 m high expanded-top circulating fluidized bed for FCC catalyst (dp=78 microns, particle density =1880 kg/m3). Upstream and downstream light signals which reflect from particles were received by optical fiber probes and were used to compute delay time by cross-correlation function. Then the local time- mean particle velocity can be acquired by statistics. The results show that the local time-mean particle velocity was always the maximum value in the central region of the riser, then decreased toward the wall, even became negative value at the wall. It means particles move upward in the central region of the riser and a downward particle movement exists near the wall. When operated in the bubbling fluidized bed and the turbulent fluidized bed, the time-mean particle velocity decreased with measuring height. When operated in the fast fluidized bed and core-annulus dilute phase flow and the flow regime which between the turbulent fluidized bed and the fast fluidized bed, the time-mean particle velocity increased with measuring height. When measuring height was fixed at 35 cm and 55 cm and increased the superficial gas velocity, the time-mean particle velocity first increased with the superficial gas velocity, then decreased in the flow regime which between the turbulent fluidized bed and the fast fluidized bed, and finally the time-mean particle velocity increased with the superficial gas velocity again. When measuring height fixed at 75 cm and increased the superficial gas velocity, the time-mean particle velocity first increased with the superficial gas velocity, then decreased in the core-annulus dilute phase flow. And when measuring height was fixed at 115 cm and increased the superficial gas velocity, the time-mean particle velocity was increased with the superficial gas velocity.
Subjects
particle velocity profile
optical fiber probes
circulating fluidized bed
Type
thesis
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