Comparison of the performance of liquid–gas injection nozzles in a gas–solid fluidized bed

It is often necessary to inject a liquid in fluidized bed reactors, such as fluid cokers, fluid catalytic crackers and gas-phase polymerization reactors. A more uniform dispersion of the injected liquid over the bed solids minimizes agglomeration, and prevents mass and heat transfer limitations, resulting in improved reactor operability and increased yields of desired products. The quality of the injection can be significantly affected by nozzle design and by several operating parameters. The goal of the current study was to compare several gas-assisted liquid injection nozzles under a variety of operating conditions. The nozzles sprayed water atomized with air into a bed of silica sand particles fluidized with air. The quality of the jet-bed interaction associated with each experiment was characterized using a conductive probe method, which uses the measured electrical conductance of the bed. It has been found that the bed conductance increases as the liquid becomes more uniformly dispersed throughout the fluidized bed. The droplet size of the injected spray was also measured in open air using a laser scattering system. In all tests, the liquid flowrate was held constant, while the atomization gas flowrate was varied. It was found that different nozzles displayed their best performance at different gas flowrates. Large droplets tended to negatively impact the spread of liquid throughout the bed, especially when they were larger than the fluidized particles. Large fluctuations in the water flowrate tended to decrease the performance of the nozzles. Multi-linear regression was used to correlate the nozzle performance to various nozzle parameters.