Residence times in fluidized beds with secondary gas injection

• Published in: Powder technology 2008-01, Vol.180 (3), p.321-331
• Main Authors: Christensen, D., Nijenhuis, J., van Ommen, J.R., Coppens, M.-O.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; Experimental method; Fluidization; Fluidized bed; Fractal injector; Heat and mass transfer. Packings, plates; Miscellaneous; Reactors; Residence time distribution; Secondary injection; Solid-solid systems
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2007.02.021

Experiments were carried out to determine the effects of secondary gas injection on the gas residence time and macromixing characteristics in a bubbling fluidized bed. Primary gas is introduced via a bottom distributor plate, while secondary gas is introduced via a fractal injector submerged in the bed. Results indicate that the average residence time decreases only slightly. Calculated overall reactor Péclet numbers indicate that the gas experiences less back-mixing with secondary gas injection. The bubble size was observed to decrease by up to 70%, indicating improved gas–solid contact. Taking this improved contact and plug flow behavior into account, the conversion in a fluidized bed with secondary gas injection is expected to increase significantly, particularly for mass-transfer limited reactions. Experiments were carried out to determine the effects of secondary gas injection, via a fractal injector, on the gas residence time and macromixing characteristics in a bubbling fluidized bed. Results indicate that the average residence time decreases only slightly, while the gas experiences less back mixing. Since the bubble size also decreases significantly, it is expected that conversion should improve. [Display omitted]