Gas recycling in fluidized bed to avoid defluidization for reactions accompanied by decrease in the number of moles

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2013-01, Vol.215-216 (15), p.671-677
• Main Authors: Kai, Takami, Matsumura, Akihiro, Sezutsu, Koki, Nakazato, Tsutomu, Nakajima, Mitsuyuki
• Format: Article
• Language: English
• Subjects: chemical engineering; Chemical reactors; Defluidization; Fluidization; Fluidized bed; fluidized beds; Gas recycle; recycling
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2012.10.066

► Defluidization occurs when reactions are accompanied by a mole number decrease. ► Two operation modes of gas recycling were studied to establish stable operations. ► Defluidization zone is correlated by two parameters based on experimental data. ► A reactor model considers a decrease in the number of moles is used. ► The required recycle ratio is within the acceptable range for industrial operations. A gas recycling method for establishing stable operations of a fluidized catalyst bed is studied in order to perform reactions accompanied by a decrease in the number of moles. Two operation modes using gas recycling are evaluated to prevent defluidization and establish stable operation. For the first operation mode, because the influence of the decrease in the number of moles on the fluidization quality is reduced by adding a dilute gas to the feed, the reactor is operated with high conversion and a part of the outlet gas is recycled to the reactor inlet. The fluidization quality is also improved by decreasing the reaction rate. Therefore, for the second mode, the reactor is operated with low conversion, and the unreacted components in the outlet gas are separated from the product gas and recycled to the reactor inlet. It is possible to increase the overall conversion to a high level by gas recycling. Experimental data in previous studies and a fluidized-bed-reactor model that considers the decrease in the number of moles are used in order to determine the required recycle ratio and reaction rate constant for establishing a stable operation. Even when a reaction is accompanied by a 50% decrease in the number of moles, the required recycle ratio is below 9 for the recycle mode without separation and below 5.5 for the recycle mode with separation.