Joseph S. Mei

Improvement in Precision, Accuracy, and Efficiency in Standardizing the Characterization of Granular Materials

Useful prediction of the kinematics, dynamics, and chemistry of a system relies on precision and accuracy in the quantification of component properties, operating mechanisms, and collected data. In an attempt to emphasize, rather than gloss over, the benefit of proper characterization to fundamental investigations of multiphase systems incorporating solid particles, a set of procedures were developed and implemented for the purpose of providing a revised methodology having the desirable attributes of reduced uncertainty, expanded relevance and detail, and higher throughput. Better, faster, cheaper characterization of multiphase systems result. Methodologies are presented to characterize particle size, shape, size distribution, density (particle, skeletal and bulk), minimum fluidization velocity, void fraction, particle porosity, and assignment within the Geldart Classification. A novel form of the Ergun equation was used to determine the bulk void fractions and particle density. Accuracy of properties-characterization methodology was validated on materials of known properties prior to testing materials of unknown properties. Several of the standard present-day techniques were scrutinized and improved upon where appropriate. Validity, accuracy, and repeatability were assessed for the procedures presented and deemed higher than present-day techniques. A database of over seventy materials has been developed to assist in model validation efforts and future desig

Gas velocity distribution in a circular circulating fluidized bed riser

Abstract An experimental study of gas velocity distribution in the riser of a circulating fluidized bed was carried out in a cold flow Plexiglas model. The gas velocity distribution is essential not only for design and scale-up but also for optimization of circulating fluidized bed reactors for fossil energy applications. Tests were conducted in a circulating fluidized bed riser with a diameter of 200 mm and a height of 5.5 m. The experimental results showed that the local gas velocity varied with radial position, elevation, solids circulation rate, superficial velocity and particle size. The particle circulation rates were found to have a significant influence on the gas velocity profiles. An empirical relationship for gas velocity distribution in the circulating fluidized bed riser was obtained based on the particle circulation rate, superficial velocity, and particle diameter.

The Mapping of Flow Regimes for a Light Material: Cork

A series of experiments was conducted in the 0.3-meter diameter circulating fluidized bed test facility at the U.S. Department of Energy’s National Energy Technology Laboratory (NETL). Cork, the bed material used in this study, is a coarse, light material, with a particle density of 189 kg/m3 and a mean diameter of 1007 μm. Fluidizing this material in ambient air provides approximately the same gas to solids density ratio as coal and coal char in a pressurized gasifier. Furthermore, the density ratio 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. The purpose of this study is to generate reliable data to validate the mathematical models currently under development at NETL. Using such coarse, light material can greatly facilitate the computation of these mathematical models. This paper presents and discusses data for the operating flow regimes of dilute-phase, fast-fluidization, and 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 ΔP/ ΔL-Gs-Ug plot. The coarse cork particles exhibited different behavior than the measurements on heavier materials found in published literature, such as alumina, sand, FCC, and silica gel. Stable operation can be obtained at a fixed riser gas velocity that is higher than the transport velocity (e.g. at Ug = 3.2 m/sec), even though the riser is operating within the fast fluidization flow regime. Depending upon the solid 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, and solid fractions in the upper-dilute and the lower-dense regions of a fast fluidization flow regime. Comparisons of measured data show rather poor agreement with these empirical correlations. Xu et al. (2000) have observed this lack of agreement in their study of the effect of bed diameter on the saturation carrying capacity. The basis of empirical correlations depends on bed diameter and particle type, and are generally not well understood.Copyright

Hydrodynamics of a Transport Reactor Operating in Dense Suspension Upflow Conditions for Coal Combustion Applications

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.Copyright