Interactive effects of spray drying characteristics on SO2 capture using limestone sorbent: a response surface methodology study

This study involved an investigation to assess the performance of limestone sorbent for spray dry scrubbing of sulphur dioxide from simulated flue gas using a lab-scale spray dryer. The project comprised of detailed experimental testing utilizing Central Composite Design (CCD) to investigate the influence of spray drying parameters on the removal of SO2 from flue gas. Several experiments were performed to analyse the influence of stoichiometric ratio (0.5 - 2.5), flue gas flowrate (24 - 36 m3/h), and inlet gas temperature (120 - 200 ℃) on SO2 removal efficiency of limestone. A predictive quadratic model was established based on experimental findings to correlate independent variables and the response. The model exhibited a strong fit to the data, indicated by R-squared coefficient of 0.98. The experimental findings revealed that the stoichiometric ratio (SR) had a large impact on the removal efficiency of SO2 in the spray dryer while the flue gas flowrate through the scrubber exhibited minimal influence. The combined effects of the spray drying variables were found to significantly impact the removal efficiency. A high removal efficiency of 70% was achieved when employing a higher stoichiometric ratio (SR=2) and lower temperature (T=140 °C). The lowest removal efficiency was recorded at a high temperature (T=180 °C) coupled with lower stoichiometric ratio (SR=1). The characterization of the dry collected products revealed evidence of desulphurization, manifesting in the formation of hannebachite (Ca2SO3.2H2O) and unreacted sorbent.