Simultaneous hydration/carbonation of FBC ash by low-frequency sonication

Simultaneous hydration and carbonation of ash from fluidized bed combustion was studied using a new sonication technology. Enhanced carbonation of the ash by CO2 was achieved at ambient temperature by use of a sonic generator with low frequency (100-500 Hz). At lower sonic intensity, the product was mainly Ca(OH)2 whereas at higher intensity the product was primarily CaCO3. Results of a simulation, assuming that the CaCO3 is formed from Ca(OH)2, described the observed time dependence for Ca(OH)2 and CaCO3 conversion well. The hydrated/carbonated ash was tested as sulphur sorbent and the sulphation activity of the ash increased with increasing CaCO3 content. This result can be attributed to the larger molar volume of CaCO3 compared to that of Ca(OH)2, which resulted in larger porosity and specific surface area of the particles upon thermal decomposition.