Recirculation of NOx and SOx Scrubber Effluent to an Industrial Grate Fired MSW Boiler - Influence on Combustion Performance, Deposition Behavior, and Flue Gas Composition

Journal article, 2022

The concept of scrubber effluent recirculation has recently received attention in connection to NOx emission control. Here, we present data from an industrial-scale MSW-fired plant, where effluent from a combined NOx and SOx scrubber was recirculated and injected into a grate-fired boiler. The combustion characteristics were carefully studied during the injections to observe the potential effects on burnout and flue gas composition. In addition, deposition measurements were performed to observe effects on growth rate and chemical composition of deposits, which are critical factors for any solid fuel-fired heat and power plant. The recirculation of the nitrogen-rich waste streams was performed via pre-existing liquid injection equipment, and the results show that the N-containing compounds in the scrubber effluent were efficaciously reduced to inert nitrogen gas. Furthermore, the recirculation of the scrubber effluent may reduce ammonia demand for selective non-catalytic reduction systems by inhibiting the formation of ammonium chloride. Sulfur and alkali components in the effluent increased the deposition growth rate and also changed the chemical composition of the deposits. Understanding how the local conditions at the injection point influence the distribution and speciation of the injected compounds is essential for a successful recirculation strategy.