The use of sodium bicarbonate (NaHCO 3) as a solid reactant for the removal of acid pollutants in industrial flue gas streams is a simple and effective process solution. Nonetheless, despite its technological maturity, the industrial application of NaHCO 3-based flue gas treatment is still highly empirical. A better knowledge of the heterogeneous reaction process could allow process optimization, resulting in a reduction both in the consumption of reactants and in the generation of solid waste products. In the present study, the reactivity of NaHCO 3 toward HCl and SO 2 was investigated in the temperature range between 120 and 300°C. The key role of thermal activation in determining the reactivity of the sorbent was confirmed. The choice of the optimal temperature for acid gas sorption results from a trade-off: higher temperatures increase the reaction kinetics, but induce the sintering of the activated sodium carbonate. The occurrence of sintering is particularly detrimental for high removal efficiency toward SO 2 , possibly due to the role of the sodium sulfite layer originated by SO 2 sorption. As a consequence, the optimal operating temperature resulted as 150°C for SO 2 and 210°C for HCl. The choice of operating temperature in industrial dry sorbent injection units for acid gas abatement is discussed in view of the present findings.

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Municipal solid waste incineration (MSWI) is a method of waste valorization whose overall sustainability depends on the effective removal of the gaseous contaminants generated. Hydrogen chloride (HCl) is a typical pollutant formed in waste combustion. Dry processes based on its reaction with basic powders such as calcium hydroxide are among the state-of-the-art best available technologies for MSWI flue gas treatment. An experimental investigation of the heterogeneous reaction process between hydrogen chloride and calcium hydroxide in the temperature range between 120 and 180 °C was carried out. A laboratory-scale fixed bed reactor connected to a Fourier transfrom infrared (FTIR) spectrometer was used for the online continuous monitoring of HCl conversion. Solid reaction products were characterized using thermogravimetric analysis and X-ray diffractometry. The experimental data collected were used to validate a fundamental kinetic model for the description of the gas–solid reaction between Ca­(OH)2 and HCl. A sensitivity analysis was carried out to assess the importance of the different temperature-dependent parameters in the model. The results allow an improved understanding of the heterogeneous reaction process that is applied in acid gas dry removal processes.

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