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RESEARCH PAPERS

Flow Regime Study of a Light Material in an Industrial Scale Cold Flow Circulating Fluidized Bed

[+] Author and Article Information
Joseph S. Mei, Lawrence J. Shadle

 National Energy Technology Laboratory, U.S. Department of Energy, 3601 Collins Ferry Rd., Morgantown, WV 26507-0880

Esmail R. Monazam

 REM Engineering, 3566 Collins Ferry Rd., Morgantown, WV 26505

J. Energy Resour. Technol 128(2), 129-134 (Mar 22, 2006) (6 pages) doi:10.1115/1.2199566 History: Received June 14, 2004; Revised March 22, 2006

A series of experiments was conducted in the 0.3meter diameter circulating fluidized bed test facility at the National Energy Technology Laboratory (NETL) of the U. S. Department of Energy. The particle used in this study was a coarse, light material, cork, which has a particle density of 189kgm3 and a mean diameter of 812μm. Fluidizing this material in ambient air approximates the same gas-solids density ratio as coal and coal char in a pressurized gasifier. The purpose of this study is twofold. First, this study is to provide a better understanding on the fundamentals of flow regimes and their transitions. The second purpose of this study is to generate reliable data to validate the mathematical models, which are currently under development at NETL. Utilization of such coarse, light material can greatly facilitate the computation of these mathematical models. Furthermore, the ratio of density of cork to air under ambient conditions is similar to the density ratio of coal to gas at the gasification and pressurized fluidized bed combustion environment. This paper presents and discusses the data, which covered operating flow regime from dilute phase, fast fluidization, and to dense phase transport by varying the solid flux, Gs at a constant gas velocity, Ug. Data are presented by mapping the flow regime for coarse cork particles in a ΔPΔLGsUg plot. The coarse cork particles exhibited different behavior than the published literature measurements on heavier materials such as alumina, sand, FCC, silica gel, etc. A stable operation can be obtained at a fixed riser gas velocity higher than the transport velocity, e.g., at Ug=3.2ms, even though the riser is operated within the fast fluidization flow regime. Depending upon the solids influx, the riser can also be operated at dilute phase or dense phase flow regimes. Experimental data were compared to empirical correlations in published literature for flow regime boundaries as well as solids fractions in the upper dilute and the lower dense regions for fast fluidization flow regime. Comparisons of measured data with these empirical correlations show rather poor agreements. These discrepancies, however, are not surprising since the correlations for these transitions were derived from experimental data of comparative heavier materials such as sands, FCC, iron ore, alumina, etc.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical size distribution of cork bed material

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Figure 2

Schematic of CFB test unit indicating gas-solids separation and aeration location

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Figure 3

Riser incremental pressure profile for duplicate tests

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Figure 4

Local pressure drop as a function of inlet solid flux at various riser gas velocities (after Yerushalmi and Cankurt, 1979)

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Figure 5

Pressure drop across the entire length of the riser as a function of inlet solid flux at various riser gas velocities

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Figure 6

Pressure drop across the entire length of the riser as a function of inlet solid flux at riser gas velocity of Ug=3.2m∕s

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Figure 7

(a) Solids fraction axial profiles for the dilute-phase flow regime at a riser gas velocity of Ug=3.2m∕s. (b) Solids fraction axial profiles for the fast fluidization flow regime at a riser gas velocity of Ug=3.2m∕s. (c) Solids fraction axial profiles for the dense-phase flow regime at a riser gas velocity of Ug=3.2m∕s.

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Figure 8

Flow regime and regime boundaries for cork particles at riser gas velocity of Ug=3.2m∕s

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Figure 9

Average solids fraction in the upper dilute and the lower dense regions of a riser at a gas velocity of Ug=3.2m∕s

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Figure 10

(a) Average solid fraction in the bottom dense region of a riser at gas velocity of Ug=3.2m∕s. (b) Average solid solid fraction in the upper dilute region of a riser at gas velocity of Ug=3.2m∕s.

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