Development and Validation of a Dynamic Response Model for a Cold Flow Circulating Fluidized Bed

Abstract Tests were performed in a 0.1-m diameter small circulating fluidized bed (SCFB) and 0.3 m diameter cold flow circulating fluidized bed (CFCFB) riser systems located at the National Energy Technology Laboratory (NETL) to study the effects of riser diameter on the riser hydrodynamics. These tests were performed at solids circulation rates of Gs = 20 and 75 kg/m2 s and superficial gas velocities of Ug = 5.8 and 6.5 m/s using high-density polyethylene (HDPE) pellets with a density of 0.863 g/cm3, particle size range of 600–1400 µm (with a Sauter mean diameter of 871 µm, placing them in the Geldart B classification). Comparisons of riser axial pressure and solids fraction profiles, radial particle velocity profiles, and radial profiles of higher statistical moments and select chaos analysis parameters were considered. The results showed that for a given Ug and Gs, the smaller diameter riser exhibited characteristics associated with more dilute solids flow than that observed in the larger diameter riser. Additionally, the larger diameter riser exhibited a downward flow of solids near the wall under all test conditions, whereas the smaller diameter riser data exhibited little or no indications of solids downflow near the wall. These findings suggest that, from an industrial standpoint, a direct scaleup of small-scale tests cannot readily be accomplished as the solids holdup and the solids velocity profiles in small units (those normally tested in the laboratory) are not similar to those of large units and the performance of large units can therefore not be predicted from small-scale tests.

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Systematic Study of Pressure Fluctuation in the Riser of a Dual Inter-Connected Circulating Fluidized Bed: Using Single and Binary Particle Species

Processes ◽

10.3390/pr7120890 ◽

2019 ◽

Vol 7 (12) ◽

pp. 890 ◽

Cited By ~ 2

Author(s):

Yusif A. Alghamdi ◽

Zhengbiao Peng ◽

Caimao Luo ◽

Zeyad Almutairi ◽

Behdad Moghtaderi ◽

...

Keyword(s):

Fluidized Bed ◽

Pressure Fluctuation ◽

Circulating Fluidized Bed ◽

Pressure Fluctuations ◽

Single Species ◽

Terminal Velocity ◽

Operating Conditions ◽

Cold Flow ◽

Fluidization Regime ◽

Spectrum Density

This study systematically investigates the pressure fluctuation in the riser of a dual interconnected circulating fluidized bed (CFB) representing a 10 kWth cold-flow model (CFM) of a chemical-looping combustion (CLC) system. Specifically, a single-species system (SSS) and a binary-mixtures system (BMS) of particles with different sizes and densities were utilized. The pressure fluctuation was analyzed using the fast Fourier transform (FFT) method. The effect of introducing a second particle, changing the inventory, composition (i.e., 5, 10 to 20 wt.%), particle size ratio, and fluidization velocity were investigated. For typical SSS experiments, the results were similar to those scarcely reported in the literature, where the pressure fluctuation intensity was influenced by varying the initial operating conditions. The pressure fluctuations of BMS were investigated in detail and compared with those obtained from SSS experiments. BMS exhibited different behaviour; it had intense pressure fluctuation in the air reactor and in the riser when compared to SSS experiments. The standard deviation (SD) of the pressure fluctuation was found to be influenced by the fluidization regime and initial operating conditions, while the power spectrum density (PSD) values were more sensitive to the presence of the particles with the higher terminal velocity in the binary mixture.

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