Design of entrained-flow and moving-, packed-, and fluidized-bed sorption systems: Grain-model kinetics for hot coal-gas desulfurization with limestone

Concentration profiles in several configurations of sorption systems (moving, packed, and fluidized beds and entrained-flow) were determined using the grain and the unreacted shrinking core model for the description of the gas-solid reaction kinetics. General equations for the design and analysis of all these reactor configurations are given, and simple analytical solutions are proposed. The behavior of these reactors can be expressed as a function of only four parameters: the size of the sorbent pellet and the Peclet, Sherwood (or Blot), and Damkohler numbers. These general equations were then applied to the lime(stone)/H2S systems. Using limestone particles with diameters on the order of 100 mu m for entrained-flow and with diameters on the order of 1 mm for the other configurations, it was found that H2S could be removed from the hot coal gas to near its equilibrium value with more than 75% sorbent utilization and with reasonable bed depth (about 1 m, or 1-s contact time for entrained-flow) when the reactor temperature is maintained 25-50 degrees C above the calcination temperature of the calcium carbonate.