Acid Gas Removal Unit in Waste-to-energy Plants: Data-driven Models for Advanced Control

Flue gas cleaning is a crucial step in waste-to-energy (WtE) plants that process municipal solid waste. This paper analyzes the acid gas removal line of an Italian WtE plant, based on the injection of dry alkaline solid sorbents (calcium hydroxide Ca(OH)2 and sodium bicarbonate NaHCO3) for the abatement of hydrogen chloride, HCl. The aim of the study is to develop different data-driven models for the description of the acid gas treatment process with the final goal of implementing them in model-based controllers for optimizing the feed rate of alkaline reactants thus minimizing solid waste production. System identification and validation techniques have been applied to process data. Different input-output and state-space models are identified by optimizing related model orders and validated on different routine data. The comparison of two system structures (sequential and holistic) evidenced the importance of measuring additional internal variables to maintain low system orders and delays. Anyway, results appear reliable and promising for control purposes, making different modeling approaches and control structures possible.