An experimental study on the effect of particle geometry on drag and flow behaviors in a packed fluidized bed
Gasification offers a promising solution to producing fuels effectively in the coming years by providing a low-cost energy system, clean environmental performance, and reliability. Feedstock is prepared and fed to a gasifier in either a dry form or as slurry (mixed with water). One application of this technology uses heat, pressure, and steam to convert feedstock into a gaseous mixture, composed primarily of carbon monoxide (CO) and hydrogen (H2 ), named as syngas. Several technical and commercial issues were identified by the Nation Energy Technology Laboratory (NETL) in 2006 Multiphase workshop. US Department of Energy (DOE) is now focusing on attaining a significant development in the design and operation of multiphase flow devices. They postulated different short-term, long term research goals to modify and develop these device performances by the year 2015. Despite previous efforts to develop the fundamentals of flow field in a fluidized bed reactor, most of them are based on spherical particles whereas actual beds are operated on non-spherical particles. Hence, this thesis focuses on presenting the hydrodynamic analysis of a packed fluidized bed operated with both spherical and non-spherical particles to generate fundamental idea useful for designing the non-spherical particle based fluidized bed reactor. For this purpose, gas phase analysis and particle scale motion analysis were performed in this study. Pressure fluctuations and high speed imaging analysis were utilized to characterize the bed behavior in semi-dilute flow (less than 4% in this work). To present the effect of bed diameters on fluidization behavior, a plexiglass tube with 3.8 cm outside diameter and a quartz tube with 12 cm outside diameter were employed. Pressure fluctuations at different bed heights were also analyzed. Borosilicate spherical glass beads with a 1mm diameter and crushed non-spherical particles with diameters between 150 to 2000 &mgr;m were used for the experimental analysis. This thesis also presents a method to analyze the particle sphericity, particle size distribution, and particle characterization. Mapping of several bed pressure drops with superficial gas velocity across the bed are presented showing the minimum fluidization, full fluidization, and terminal velocity. MatPIV analysis of high speed images, captured at 500 frames per second, and PIV analysis with 62 Hz CCD camera and 5 Amp laser showing the flow field vectors, magnitude of velocity, vorticity for both spherical and non-spherical particles, are also presented to characterize the bed behavior at particle scale motion. The pressure fluctuations with spherical particles show more uniform behavior with spherical particles than the non-spherical particles and the increased bed height produce more uniform pressure fluctuation response. Drag coefficient analysis for non-spherical particle diameters between 500 to 600 micron, 600 to 710 micron,710 to 850 micron, 850 to 1180 micron and 1180 to 2000 micron were conducted in this work to generate a fundamental idea regarding the required uplifting drag force for fluidizing the particles in a packed bed.
Rahman, Md Mahamudur, "An experimental study on the effect of particle geometry on drag and flow behaviors in a packed fluidized bed" (2011). ETD Collection for University of Texas, El Paso. AAI1498313.