In Waste-to-Energy (WtE) plants, combustion gas containing HCl and SO2 typically provokes boiler fouling and corrosion, and large consumption of chemicals to meet legal emission standards. HCl and SO2 concentrations in the combustion gas obviously depend on the Cl/S ratio in the incoming waste. However, industrial WtE experiences indicate that conditions established by process control also impact the generation of HCl and SO2 during grate combustion. The latter is studied in the present work through in-depth analysis of industrial WtE process data spanning four years of plant operation. To the authors' knowledge, a similar study was never conducted before. The results suggest that HCl in the combustion gas is strongly influenced by the overall air-to-waste ratio imposed to the (entire) furnace. Findings regarding SO2 rather highlight the significance of conditions established in the waste layer on the grate, i.e., layer thickness and flow rate of primary air. The extent of moisture in the waste seems to enhance these patterns. Whereas state-of-the-art combustion control in WtE plants still only targets the stability of thermal production, the results from this study support a further extension of the control scope with (inorganic-)thermochemical intelligence for boiler corrosion prevention and emissions stabilization.
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