An experimental investigation of the mass transfer mechanisms in sulfur dioxide absorption in lime solutions

An experimental investigation was conducted to study the mass-transfer mechanisms in SO{dollar}sb2{dollar} absorption in lime solutions at gas temperatures ranging from 24{dollar}spcirc{dollar}C to 114{dollar}spcirc{dollar}C. The experiments were performed using a wetted-wall column apparatus with SO{dollar}sb2{dollar} concentrations ranging from 1800 ppm to 7350 ppm, calcium concentrations of 2.82 {dollar}times{dollar} 10{dollar}sp{lcub}-6{rcub}{dollar} gmol/cm{dollar}sp3{dollar} to 1.25 {dollar}times{dollar} 10{dollar}sp{lcub}-5{rcub}{dollar} gmol/cm{dollar}sp3{dollar}, and column heights of 14 cm to 29 cm.; The inlet SO{dollar}sb2{dollar} concentration had a significant effect on the rate of SO{dollar}sb2{dollar} absorption, with the average absorption flux increasing with increasing SO{dollar}sb2{dollar} gas concentration. Increasing gas temperature did not significantly affect the rate of SO{dollar}sb2{dollar} absorption. The presence of lime in solution enhanced the average SO{dollar}sb2{dollar} absorption flux and appeared to maintain the SO{dollar}sb2{dollar} absorption capacity of the liquid, thereby negating the effect of decreasing SO{dollar}sb2{dollar} solubility in water with increasing temperature. Slight increases in both the system's gas-phase resistances and enhancement factors were observed with increasing gas temperature.; Under the conditions studied, the mass-transfer resistance in the SO{dollar}sb2{dollar}-lime solution system was predominantly liquid-phase controlled, with observed gas-phase resistances ranging up to 42% of the total. Comparison to literature data shows that the system mass-transfer mechanism can be dominated by either the gas-phase resistance or the liquid-phase resistance, depending upon the gas-liquid contact times. Thus, results from this research support the need to incorporate both gas- and liquid-phase mass-transfer resistances when modeling the absorption of SO{dollar}sb2{dollar} in lime solutions and lime slurries, such as that occurring in the constant rate drying stage of the spray drying flue gas desulfurization process.