Environmental assessment of combined acid gas emission control with alternative dry sorbent injection systems

In a holistic approach to environmental protection, the optimisation of end-of-pipe technologies for air pollution control has to take into account not only process performance but also indirect impacts related to the production of reactants and the disposal of by-products. In this perspective, a thorough environmental assessment of the life cycle impacts associated with the adoption of alternative technologies is a useful tool for the selection of an all-round environmentally sound solution. In the present study, a comparative analysis is carried out to evaluate the overall environmental footprint of two alternative dry sorbent injection configurations for acid gas removal in waste-to-energy plants, adopting a life cycle viewpoint to consider the related supply and disposal chains. A previously developed operational model is employed to quantify the streams of reactants and residues associated with acid gas emission control for the two alternatives, which are functions of the reactivity of the different sorbents towards three acid pollutants (HCl, SO2, HF). In particular, HF, which is usually present in considerably lower concentrations than HCl and SO2 in flue gases, is generally neglected in process optimisation studies, but it is particularly harmful for both human health and ecological integrity. Here its removal is taken into account in order to include the related impacts in the environmental assessment.