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Deep bubbling fluidized beds have some advantages that make them attractive for industrial applications. Using different powders, this paper investigates the bubbling behavior in deep beds. The results show that bubbles grow faster in the bed of angular/rough particles than in that of round/smooth particles and that the rate of bubble growth increases with increase in the particle size. With an increase in the bed height, the changes in the bubble diameter and solids distribution decrease within the bubbling regime but may vary within the slugging regime due to the chaotic behavior of slug flows. The bubble frequency increases with an increase in the gas velocity only when the bubble diameter is below a certain threshold value; for larger bubbles, the bubble frequency is lower. The maximum bubble frequency indicates the onset of slugging. Correlations for predicting the maximum bubble/slugging frequency averaged over the bed height and the corresponding bubble diameter are proposed.

This paper focuses on the experimental demonstration of a three-stage GST (gas switching technology) process (fuel, steam/CO 2 , and air stages) for syngas production from methane in the fuel stage and H 2 /CO production in the steam/CO 2 stage using a lanthanum-based oxygen carrier (La 0.85 Sr 0.15 Fe 0.95 Al 0.05 O 3 ). Experiments were performed at temperatures between 750–950 °C and pressures up to 5 bar. The results show that the oxygen carrier exhibits high selectivity to oxidizing methane to syngas at the fuel stage with improved process performance with increasing temperature although carbon deposition could not be avoided. Co-feeding CO 2 with CH 4 at the fuel stage reduced carbon deposition significantly, thus reducing the syngas H 2 /CO molar ratio from 3.75 to 1 (at CO 2 /CH 4 ratio of 1 at 950 °C and 1 bar). The reduced carbon deposition has maximized the purity of the H 2 produced in the consecutive steam stage thus increasing the process attractiveness for the combined production of syngas and pure hydrogen. Interestingly, the cofeeding of CO 2 with CH 4 at the fuel stage showed a stable syngas production over 12 hours continuously and maintained the H 2 /CO ratio at almost unity, suggesting that the oxygen carrier was exposed to simultaneous partial oxidation of CH 4 with the lattice oxygen which was restored instantly by the incoming CO 2 . Furthermore, the addition of steam to the fuel stage could tune up the H 2 /CO ratio beyond 3 without carbon deposition at H 2 O/CH 4 ratio of 1 at 950 °C and 1 bar; making the syngas from gas switching partial oxidation suitable for different downstream processes, for example, gas-to-liquid processes. The process was also demonstrated at higher pressures with over 70% fuel conversion achieved at 5 bar and 950 °C.

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