Ca-rich Ca-Al-oxide, high-temperature-stable sorbents prepared from hydrotalcite precursors: synthesis, characterization, and CO2 capture capacity.

We present the design and synthesis of Ca-rich Ca-Al-O oxides, with Ca(2+)/Al(3+) ratios of 1:1, 3:1, 5:1, and 7:1, which were prepared by hydrothermal decomposition of coprecipitated hydrotalcite-like Ca-Al-CO(3) precursors, for high-temperature CO(2) adsorption at 500-700 °C. In situ X-ray diffraction measurements indicate that the coprecipitated, Ca-rich, hydrotalcite-like powders with Ca(2+)/Al(3+) ratios of 5:1 and 7:1 contained Ca(OH)(2) and layered double hydroxide (LDH) phases. Upon annealing, LDH was first destroyed at approximately 200 °C to form an amorphous matrix, and then at 450-550 °C, the Ca(OH)(2) phase was converted into a CaO matrix with incorporated Al(3+) to form a homogeneous solid solution without a disrupted lattice structure. CaO nanocrystals were grown by thermal treatment of the weakly crystalline Ca-Al-O oxide matrix. Thermogravimetric analysis indicates that a CO(2) adsorption capacity of approximately 51 wt. % can be obtained from Ca-rich Ca-Al-O oxides prepared by calcination of 7:1 Ca-Al-CO(3) LDH phases at 600-700 °C. Furthermore, a relatively high CO(2) capture capability can be achieved, even with gas flows containing very low CO(2) concentrations (CO(2)/N(2) = 10 %). Approximately 95.6 % of the initial CO(2) adsorption capacity of the adsorbent is retained after 30 cycles of carbonation-calcination. TEM analysis indicates that carbonation-promoted CaCO(3) formation in the Ca-Al-O oxide matrix at 600 °C, but a subsequent desorption in N(2) at 700 °C, caused the formation CaO nanocrystals of approximately 10 nm. The CaO nanocrystals are widely distributed in the weakly crystalline Ca-Al-O oxide matrix and are present during the carbonation-calcination cycles. This demonstrates that Ca-Al-O sorbents that developed through the synthesis and calcination of Ca-rich Ca-Al LDH phases are suitable for long-term cyclic operation in severe temperature environments.

Filtration of dust particulates with a moving granular bed filter.

The goal of this study was to evaluate the performance of a moving granular bed filter designed for cold test to filter coal particulates. A series of experiments were carried out at room temperature to demonstrate the collection efficiency of this method of filtration technology (i.e., the moving granular bed filter) at different filtration superficial velocities and mass flow rates of filter granules but with a fixed inlet dust concentration. The dynamic characteristics of the filter system were evaluated by measuring variations in the outlet concentration and size distribution of dust particulates. The collection mechanisms of the filter granules in the moving granular bed filter were also studied. Experimental results showed that the collection efficiency could be enhanced by using a filtration superficial velocity of 30 cm/s and mass flow rate of 450 g/min. The results of this study indicate this type of method could be useful for application in different cross-flow filter systems for gas cleanup. The focus in the current study is essentially the development of a moving granular bed filter that could be applied in a high-temperature environment. The results are expected to serve as the basis for future research.