SULFUR-DIOXIDE CAPTURE UNDER PFBC CONDITIONS - THE INFLUENCE OF SORBENT PARTICLE STRUCTURE

An unreacted shrinking core model with variable effective diffusivity was applied to sulfation test data from a pressurised thermogravimetri c apparatus (P-TGA) for various limestone and dolomite samples. The pa rticle size was 250-300 mu m for all sorbents. The tests were carried out under conditions typical for a pressurised fluidised bed combustor , i.e. 850 or 950 degrees C, 1.5 MPa. Under these conditions the limes tone remains uncalcined. whilst the dolomite is half-calcined. The sor bents were characterised by chemical composition analysis, particle de nsity measurement, mercury porosimetry and BET internal surface measur ement. A key parameter in this study is the conversion-dependent Thiel e parameter, which reveals a shift in rate-determining mechanism durin g the sorbents' sulfation. The extended model allows the effect of par ticle structure on the reaction rate constant and the product layer di ffusivity to be evaluated. Estimates for the apparent activation energ y of the kinetics and the product layer diffusion can also be given, b ased on data from two temperatures. (C) 1998 Elsevier Science Ltd. All rights reserved.