| This investigation was conducted to determine if greater amounts of SO{dollar}sb2{dollar} can be removed by naturally occurring sorbents from coal-fired, atmospheric, fluidized-bed combustors if a greater understanding of the calcination process during simultaneous calcination and sulfation is ascertained.; A bench-scale, fluidized-bed reactor, ca. 68 in{dollar}sp3{dollar} (1,114 cm{dollar}sp3){dollar} of total volume, 1.5 inI.D., utilizing 100 mesh U.S. Standard Sieve stainless steel screens for a frit, was successfully operated and found to be capable of producing the necessary, repeatable data for addressing the hypothesis. Electronic mass flow meters were used to deliver a synthetic gas mixture consisting of N{dollar}rmsb2, Osb2, COsb2,{dollar} and SO{dollar}sb2.{dollar} On-line gas analyzers were used to measure the real-time effluent concentrations of the latter three species. Gas compositions usually consisted of 4 vol% O{dollar}sb2{dollar}; 2,000 vppm SO{dollar}sb2{dollar}; 0-40 vol% CO{dollar}sb2{dollar}; and the balance N{dollar}sb2.{dollar} Three limestones with particles sizes ranging from 150 to 1,000 {dollar}mu{dollar}m were used along with sized quartz for bed material. All experiments were performed at atmospheric pressure with temperatures generally ranging from 850 to 900{dollar}spcirc{dollar}C.; Calcination and sulfation occur simultaneously with respect to time and both the sulfation rate and calcium utilization generally increase with increasing calcination rates. CO{dollar}sb2{dollar}-induced sintering decreases the calcine surface area while simultaneously increasing the mean diameter pore size; the significant reduction in developed surface area negates any perceived benefit of larger mean diameter pores for increased sorbent performance. Additionally, the use of elevated concentrations of CO{dollar}sb2{dollar} in an attempt to minimize the development of an impermeable CaSO{dollar}sb4{dollar} rim via the slow release of CO{dollar}sb2{dollar} through the porous solid is generally not a viable method for increasing the sorbent performance (sulfation rate and calcium utilization) since intra-particle, thermally-induced fractures provide access paths for CaO located towards the center of the particle--negating the benefits of larger pores and the slow "percolation" of CO{dollar}sb2{dollar} through the porous matrix. The calcination process was successfully modeled wherein intra-particle partial pressures of CO{dollar}sb2{dollar} and extents of calcination are quantified. |
