Use of pressure to mitigate gas bypassing in fluidized beds of FCC catalyst particles

• Gas bypassing occurred in a 3.7 m tall fluidized bed of FCC catalyst particles.
• Pressure fluctuations and local bubble void fraction can diagnose gas bypassing.
• Operating at a freeboard pressure of 100 to 140 kPag stopped the gas bypassing.

Deep gas fluidized beds of low-fines fluid catalytic cracking (FCC) catalyst particles can have severe gas maldistribution due to gas bypassing. Tests were conducted in a 0.6-m-diameter unit using 3.2% and 4% fines less than 44 μm FCC catalyst particles to determine the influence of system pressure on gas bypassing in a fluidized bed of 3.66 m static bed height. The freeboard pressure was varied up to 207 kPag (30 psig). Differential pressure fluctuations were measured at four locations around the column, bubble void fraction was measured at two opposite locations close to the column wall, and radial bubble void fraction profiles were measured at axial elevations of 0.9 and 1.52 m. At no or low pressures, gas bypassing was present in the bed. With gas bypassing, differential pressure fluctuation intensities were significantly different around the column, significantly higher bubble void fractions were measured close to the inner wall on one side of the column than on the opposite side, and the radial bubble void fraction profiles were not symmetrical about the column axis. Increasing the system pressure weakened the intensity of gas bypassing. Gas bypassing disappeared at a freeboard pressure of about 100 to 140 kPag (15 to 20 psig).

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