Loop seals in circulating fluidized beds – Review and parametric studies using CPFD simulation

• Published in: Chemical engineering science 2020-12, Vol.227, p.115917, Article 115917
• Main Authors: Bandara, Janitha C., Jayarathna, Chameera, Thapa, Rajan, Nielsen, Henrik K., Moldestad, Britt M.E., Eikeland, Marianne S.
• Format: Article
• Language: English
• Subjects: Circulating fluidized bed; CPFD; Loop seal; Rate of particle circulation
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2020.115917

[Display omitted] •Loopseal aeration rate and injection configuration exert a great influence over particle circulation in CFB reactors.•“BC connector” is an interesting CPFD tool to extract a selected section from a complex geometry.•Optimum loop seal aeration was 0.9 Nm3/h resulting in approximate threshold of particle circulation.•Uniform bottom aeration of the loop seal resulted in highest rate of particle circulation. Loop seal is a robust particle recycling technique used in circulating fluidized bed (CFB) reactors. The rate and the location of the loop seal aeration exert a significant impact on the rate of particle circulation (GS). The standpipe balances the cumulative pressure drop across the rest of the CFB by adjusting its particle height or gas-particle slip velocity. Higher fraction of the loop seal aeration naturally flows down to riser. Increased pressure drop in the standpipe results in high rate of particle circulation. Computational-particle-fluid-dynamic (CPFD) code is customized for multiphase flow modelling. The inbuilt tool of “BC connectors” was incorporated to downsize a CFB into a loop seal. The simulation results of GS and system pressures for loop seal showed a perfect match with experimentally validated CFB model. A parametric study for the effects of aeration rate, aeration position and length of the horizontal section was performed using the developed CPFD model of the loop seal. GS increased proportionally with the loop seal aeration, reaching an approximate threshold at 0.9 Nm3/h and beyond that GS did not improve significantly. Uniform aeration from the loop seal bottom realized the highest particle circulation with a 71% increment. The length of the horizontal section of the loop seal exhibited an inverse relationship on the particle circulation.