MSWI flue gas two-stage dry treatment: Modeling and simulation

Power generation from Municipal Solid Waste incineration is widespread used as a technology for solid waste treatment and energy recovery. One of the main impacts of these plants is the continuous emission of pollutants into the atmosphere. Another issue to be addressed is the generation of solid or liquid residues from flue-gas cleaning, depending on the flue-gas treatment process. Among the substances produced during thermal incineration, acid gases are of particular interest because of their environmental impact. One of the most promising combination of Best Available Technologies for an enhanced removal efficiency of acid gases is the two-stage dry treatment. In the analysed process, solid powder of calcium hydroxide (slaked lime) is used in the first stage while in the second one sodium bicarbonate (more effective) is injected, allowing the decrease of pollutants concentration until the design values. In the present study an operational model (based on the ratio of reactant rate to stoichiometric rate) is proposed to fit literature data concerning the performance of the process considered. The implementation of the model in a simulation software has allowed describing the design conditions of a typical Municipal Solid Waste Incinerator (MSWI). Other simulations were carried out with the aim of reducing solid products formed by flue gas treatment without decreasing the removal efficiency. The model was also used to assess the possible cost optimization by the identification of optimal reactant feed rates.