Visualization of water vapour flow in a packed bed adsorber by near-infrared diffused transmittance tomography

Abstract

This work presents a procedure based on spatially-resolved near-infrared imaging, in order to observe temperature and composition maps in gas-solid packed beds subjected to effects of aspect ratio and non-isothermal conditions. The technique was applied to the water vapour flow in a packed bed adsorber of low aspect ratio, filled with silica gel, using a tuneable diode laser, focal planar array detector and tomographic reconstruction. The 2D projected images from parallel scanning permitted data to be retrieved from the packing and above the packing sections of 12.0 Â 12.0 Â 18.2 mm 3 at a volume-resolution of 0.15 Â 0.15 Â 0.026 mm 3 and a time-resolution of less than 3 min. The technique revealed uneven temperature and composition maps in the core packed bed and in the vicinity of the wall due to flow maldistribution. In addition, the heat uptake from the packed bed and local crossmixing were experimentally ascertained by local profiles of the water vapour composition and temperature under various aspect ratios and feed flow rates. The relative deviations in temperature and compositions were 11.1% and 9.3%, respectively. The deviation in composition, which covers the packing and above the packing sections, was slightly higher than the deviation of 8% obtained up-todate but was limited to the exit of a packed bed adsorber.

Experimental investigations into the adsorption enhancement in packed beds using Z-Annular flow configuration

“…In this zone a maximum temperature of about 57.1°C was recorded. The zone of mass transfer then increased with time in the direction of the moist airflow and this was observed with the subsequent increase in temperatures of MTZ2 and MTZ3 respectively, a phenomenon consistent with findings by Nic An tSaoir et al 31 . Here the maximum achieved for MTZ2 was about 45°C and about 40°C for MTZ3 before they both declined to relative steady state temperatures.…”

Screening wall effects of a thin fluidized bed by near-infrared imaging

“…A present extension of the technique is under development for tomographic measurements of gaseous flow inside the reactor using NIR diffuse transmittance by a fine bandwidth laser source [29]. 3D visualization of cross-sectional profiles of water vapour and temperature but also of other species such as hydrocarbons and common gases will benefit in situ investigations of gaseous flows and anisotropic dispersions inside catalytic reactors.…”

“…The extension to multiple species detection such as common gases CO, CO 2 and NO x , which are known to exhibit low absorption coefficients compared to water, is ongoing by adapting cavity enhanced absorption spectroscopy technique to a 2D design that would promote the optical path and make the technique sensitive to low compositions of low absorbing gases [29]; (2) Wall transparency and deflection were taken into account by using a highly transparent glass of small thickness. Larger thicknesses that would be convenient to higher pressure flow require the additional design of the ray geometry to be taken into account; and (3) instead of the affordable broadband light, a polarised light with large tuneability range would reach more stability, higher signal to noise ratio and detection limits of water vapour.…”

Evolution and Enabling Capabilities of Spatially Resolved Techniques for the Characterization of Heterogeneously Catalyzed Reactions

“…Nic an tSaoir et al , developed a spatially resolved technique called near-infrared diffused transmittance tomography (NIRDTT) to obtain 2D and 3D temperature and flow composition profiles of water vapor within fluidized and packed bed reactors (Figure ). This significant advance in tomography has been attributed to advances in high-speed electronics and improved fiber optic technologies.…”