Gavin P. Towler

Thermodynamic analysis of a fluidized-bed combustor

Abstract A paper previously published in this journal (Thermochim. Acta, 75 (1984) 9) analyzed the thermodynamics of reactions involved in the capture of sulfur by calcium carbonate in fluidized-bed combustors. It is shown here that the earlier paper contained several fundamental errors, and consequently many of the results presented were incorrect. For this work a model of the system was developed that allowed for investigation of a wider range of temperatures and pressures and included the effect of vapor-phase non-ideality. Using this model a corrected thermodynamic analysis was performed and the scope of the previous study was extended to cover a range of operating conditions. The analysis shows that sulfur capture is primarily by reaction of SO2 with CaO formed from calcined limestone. For typical fluidized-bed combustor conditions of 850°C, 1 atm, sulfur is removed to a level of 0.003 ppm, while at pressures typical of pressurized fluidized-bed combustors (20 atm) the equilibrium sulfur concentration in the gas phase is 0.0003 ppm. There are pitfalls in applying the results of equilibrium predictions to actual performance.