Abstract
One of the most widely used processes for municipal solid waste disposal in several industrialized countries is the thermal treatment with energy recovery, but an important issue related to Municipal Solid Waste Incinerators (MSWI) is the emission into the atmosphere of airborne pollutants. Among these, acid gases (hydrochloric acid, sulphur dioxide and hydrofluoric acid) are of particular concern due to their high potential impact on humans and on the environment (effects due to long term exposure, acid rains, etc. are documented). In the present study, a previously developed operational model was used to perform an economic optimization of operating conditions of an existing waste-to-energy plant, using measured process data. The analysed system consists of a two-stage treatment, where dry powder of calcium hydroxide and sodium bicarbonate are used in the first and in the second stage respectively. Since the composition of the flue gas can vary significantly in a MSWI, a set of simulations was carried out considering the operating conditions of some representative operational periods. The model was then adapted to simulate the performance of the reference plant when using the same reactant in both stages. The considered alternatives were a double stage with calcium hydroxide and a system with bicarbonate in both stages. Finally, a comparison between these systems is presented, analysing reactant costs, disposal costs and overall operational costs.
