A regenerable calcium-based core-in-shell sorbent for desulfurizing hot coal gas

A regenerable calcium-based sorbent was prepared by pelletizing either powdered limestone or calcium sulfate hemihydrate and then coating the pellets with an optimum mixture of powdered alumina and limestone. The pellets were subsequently calcined and treated at high temperature to produce pellets with a calcium oxide core surrounded by a strong, inert porous shell. The crushing strength of the core-in-shell pellets was directly proportional to the shell thickness. The performance characteristics of the sorbent were determined by employing a thermogravimetric analysis system to measure the rate of reaction of individual pellets with small concentrations of H2S at high temperature. The reaction was rapid and directly proportional to H2S concentration. The reaction rate was not affected greatly by the thickness of the Pellet shell or by temperature in the range of 840-920 degreesC. However, the rate was more rapid for hemihydrate-based pellets than for limestone-based pellets. The hemihydrate-based pellets also had the advantage of withstanding repeated loading and regeneration without suffering a significant loss of reactivity, whereas the limestone-based pellets did suffer markedly.