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Modern coal power plants that employ an IGCC system provide an efficient means for power generation. However, toxic and extremely corrosive sulfurous gases produced in a coal gasifier need to be removed from the hot gas prior to combustion in gas turbines. Due to stringent environmental laws, a regenerable sorbent that can remove the unwanted gases at high temperature (e.g. 1170 K) is preferred. In this work, composite sorbents consisting of a limestone core and a cement shell were prepared by pelletizing the powdered materials. In some cases limestone was also incorporated in the shell. The sorbents were characterized by measuring their crushing strength and their adsorption capacity when exposed to H2S gas at high temperature. Several different hydraulic cements were tested including Type I, Type III, and Type IV Portland cements and CA-14 calcium aluminate cement. Other factors investigated included the shell thickness, concentration of limestone in the shell, and pelletization time. The results showed that formulations containing high concentrations of limestone in the shell had higher absorption capacities but at the expense of pellet strength. Longer pelletization times improved pellet strength. The best overall results were achieved when CA-14 cement was incorporated in the shell. While a foundation was laid for sorbents based on the core-in-shell pellet concept, further development is essential and is underway. |
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