Flow of High Solids Density Suspensions in an 18 m High Circulating Fluidized Bed

Abstract

The detailed distributions of solids holdup in an 18 m high-density circulating fluidized bed are mapped under various operating conditions with fluid catalytic cracking particles. Solids flux (G s) is as high as 1000 kg/(m2 s) when the superficial gas velocity (U g) ranges from 5 to 9 m/s and high-density operation is achieved. For axial distribution, solids holdup decreases exponentially along the riser with a solids holdup up to 0.17 at the riser exist, indicating the high-density operation has been achieved when G s > 800 kg/(m2 s). For radial distribution, a parabolic radial profile at high-density conditions also replaces the “core-annual” flow structure at low-density conditions. Particles can be accelerated to the axial height of 12 m under G s > 800 kg/(m2 s). Both increasing U g and/or decreasing G s can enhance flow development at high-density conditions. The solids-to-air ratio is almost the same at about 70 when high-density operations are achieved.

Particle Velocity Distribution and Its Prediction in a 14 m Two-Dimensional Circulating Fluidized Bed Riser

“…More details of this unit can be found in the previous work. 35 The 2-D CFB system is usually thought as a slice cut for the three-dimensional flow field with a narrow gap between two flat transparent walls. One of the advantages is that the 2-D CFB can be used to provide a visual study for the identification of mesoscale solids flow.…”

“…More detailed information about the optical fiber probe is given elsewhere. 35 The particle velocity can be determined by…”

“…All components of this unit, except the storage tank, are made of acrylic material for convenience of flow observation. More details of this unit can be found in the previous work . The 2-D CFB system is usually thought as a slice cut for the three-dimensional flow field with a narrow gap between two flat transparent walls.…”

“…22,23 While a large number of papers have quantitatively reported on the hydrodynamics, 6,14,24−34 few of them deal with ε s and/or V p under HF or HD conditions, especially for the quantitative discretion of V p distribution. 9,35 Information of particle velocity can reflect solids resident time, gas−solids interaction, and contacting and mixing behavior. 36 Thus, quantitative studies on V p can be used to estimate the gas−solids conversion which depends on the reaction rate and the residence time in the reactor.…”

“…As is known, two of the key hydrodynamic parameters, solids holdup (ε s ) and particle velocity ( V p ) for CFB systems, can be used to describe the flow characteristics to better understand heat transfer, mass transfer, and gas–solids contacting efficiency in the CFB reactors. , These two parameters are also the basis for commercial CFB reactor modelling, optimization, and design. From a modelling point of view, proper quantification of ε s and V p is crucial for obtaining good numerical results. , While a large number of papers have quantitatively reported on the hydrodynamics, ,,− few of them deal with ε s and/or V p under HF or HD conditions, especially for the quantitative discretion of V p distribution. , Information of particle velocity can reflect solids resident time, gas–solids interaction, and contacting and mixing behavior . Thus, quantitative studies on V p can be used to estimate the gas–solids conversion which depends on the reaction rate and the residence time in the reactor .…”