Hydrogen Chloride Removal from Flue Gas by Low-Temperature Reaction with Calcium Hydroxide

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)2and 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.