EXECUTIVE SUMMARY
Vertical risers constitute an important class of reactors for contacting solid particles and gases in the chemical engineering, petroleum refining and power generation industries. In an effort to inform recent models of their fluid dynamics, we employed a unique facility that recycles fluidization gases of adjustable properties.
In that facility, we investigated the effects of gas density, scale and operating conditions while achieving hydrodynamic similarity with generic high-temperature risers operating at pressures of 1 and 8 atm. We interpreted our results in the upper riser using steady, fully-developed momentum balances for the gas and solid phases. The analysis showed that the “atmospheric” and “pressurized” experiments conform to distinct viscous and inertial regimes. It also provided quantitative predictions for the suspension density in the upper riser.
By recording radial profiles of volume fraction and axial gradients of gas pressure, we inferred the shear stress at the wall and found conditions where the solid recirculation produces shear stresses directed along the flow, rather than against Tt.
From a study of solid clusters, we produced a robust correlation for their descending velocity at the wall and concluded that their dynamics in that region is mainly governed by particle interactions.
We also compared our measurements of pressure losses and efficiency of a cyclone operating at high pressure and solid loading with available models. Finally, we developed new process instrumentation to record local values of the solid volume fraction in high-temperature industrial vessels and we produced an exhaustive state-of-the-art review of experimental techniques for dense gas-solid flows.