Optimization of the Economic and Environmental Profile of HCl Removal in a Municipal Solid Waste Incinerator through Historical Data Analysis

Abstract

In order to comply with increasingly ambitious environmental regulations, the best available techniques for the abatement of several airborne pollutants are often based on multi-stage treatment processes. Treatment of hydrogen chloride (HCl), a typical fuel-related pollutant from the combustion of waste or biomass, is such a case. In the multi-stage configuration, while the overall required removal of pollutants is fixed, there are degrees of freedom in the repartition of the removal between stages, leaving room for process optimization. The present study offers an approach to the optimization of HCl removal, applied to a Municipal Solid Waste Incinerator (MSWI) equipped with a two-stage HCl abatement system based on the respective injection of hydrated lime and sodium bicarbonate. Historical plant data of the operation of the system for a reference year were collected and processed, in order to calibrate a semi-empirical model for the description of the two HCl treatment stages. The specific features of the two reactant systems, i.e. i) the temperature dependence of lime reactivity in the 1st stage and ii) the role of the bicarbonate cake on the fabric filter in the 2nd stage, were taken into account in the modelling. Process operation was then simulated by means of the calibrated and validated model, thus showing the advantage in terms of cost savings (-15 % annual operating costs) and avoided environmental impacts (-21 % annual generation of process residues) of operating the system at its optimum compared to the recorded process performance. The optimal repartition of removal between stages was found to depend on operating temperature and inlet HCl concentration.