Thermodynamic behaviour of sodium and calcium based sorbents in the emission control of waste incinerators.

The dry treatment of flue gas produced by incineration processes is discussed thermodynamically. The study investigates the theoretical limits achieved by sodium and calcium based sorbents in the removal of the pollutant species HCl, NOx and SO2. Calculations were performed varying the temperature and the molar ratio between the amount of the injected alkaline sorbent and the content of the pollutant gaseous species in the flue gas. Results show that sodium cation based sorbents are more efficient than calcium based ones in the whole investigated temperature range (100-600 degrees C). The higher effectiveness of sodium based sorbents is particularly remarkable towards hydrogen chloride, whose concentration can always be reduced below the values set by the environmental regulations. Possible improvements in the treatment efficiency of combustion fumes obtainable with sodium based sorbents can be mainly summarised in a lower concentration of HCl in the treated gas and in a partial reduction of NOx concentration.