Characterization of steam reactivation mechanisms in limestones and spent calcium sorbents

Three limestones and three spent calcium sorbents with differing sulfation patterns were subjected to sulfation and steam hydration at 250 and 450 deg reesC in an effort to identify the optimum conditions for increasing their ability to capture sulfur. Visual and chemical investigations of the hydrat ed and resulfated samples using a scanning electron microscope indicate tha t the sulfation pattern controls whether or not a Limestone can be reactiva ted significantly using steam. The increasing calcium utilization with decr easing hydration temperature results from fracturing during both hydration and de-hydration. Spent sorbents were harder to reactivate than pure limest ones. Only low temperature (250 degreesC) steam hydration led to an increas e in utilization for two of the spent sorbents. Problems reactivating the s pent sorbent may be related to the higher temperatures encountered in the b oilers in which they were produced compared to the Limestones prepared in t he laboratory. The sulfation 'history' of the spent sorbents, as well as re actions between the limestone and the coal (both the organic and inorganic fractions), may also contribute in reducing the response to hydration of sp ent sorbents. (C) 2001 Elsevier Science Ltd. All rights reserved.