A series of experiments were conducted in the 0.3-meter diameter, 15.45-m high cold flow circulating fluid bed (CFB) test facility at the National Energy Technology Laboratory (NETL) of the U. S. Department of Energy. Operation of the CFB demonstrated that high density conditions can be achieved throughout the entire riser with sufficiently high solid fluxes in a riser taller than what has been previously reported in the literature. Tests were conducted on Geldart type B, 60 μm diameter, glass beads at two different gas velocities (5.1 and 7.8 m/s). The riser’s axial solids fraction profile provided distinct characteristics that enabled us to differentiate between dense suspension upflow (DSU) and core annular flow regimes. The apparent solids holdup in the riser exceeded 7% when operating in DSU. A fiber optic probe was used to measure particle velocities near the wall 8.5 m above the solids entry. These measurements did not always record upward particle velocities when in DSU conditions. A number of possible reasons are identified and discussed. Solid fluxes greater than 250 kg/m2-s for 5.1 m/s and 350 kg/m2-s at 7.8 m/s appeared to be sufficient to achieve DSU conditions. The trend in the measured particle velocities near the wall was also consistent with these transitions. The transition from core annular conditions to DSU operations depended upon both gas velocity and solids flux and was in good agreement with an existing correlation found in the literature.

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