Comparing the Performance of Recirculating Cyclones Applied to the Dry Scrubbing of Gaseous HCl with Hydrated Lime

Recirculating cyclone systems, combining a numerically optimized reverse flow gas cyclone (RS_VHE geometry) with a straight-through cyclone concentrator, were employed as reaction chambers for the dry scrubbing of gaseous hydrogen chloride with solid hydrated lime particles. The performance of this technology was tested at laboratory scale with two differently sized RS_VHE cyclones (0.020 and 0.026 m internal diameter) coupled to the same recirculator of 0.020 m internal diameter. The experimental conditions were the following: reaction temperature approximate to 326 K, gas flow rate approximate to 2.9 x 10(-4) m(3).s(-1) at STP, and relative humidity of the gas 8.5%. The experimental variables were the solids feed rate [(1.0-9.2) x 10(-7) kg.s(-1)] and HCl concentration in the inlet gas [(0.35-2.8) x 10(-2) mol.m(-3)], giving different values for the ratio between the amount of fresh hydrated lime and HCl feed at the inlet of the recirculating cyclone systems (R) and that corresponding to the stoichiometric quantity (SR). The acid removal efficiencies ranged from 10 to 96%, and the best performances were obtained for high values of the ratio R/SR. Increasing the cyclone diameter while maintaining cyclone geometry improved the performance of the acid gas removal as well as the solid reactant conversion, but the average particle collection efficiency was lowered from (98.0 +/- 0.7)% to (89.3 +/- 1.7)%.