Analysis of a dry flue gas cleaning process with steam activation

Dry Flue gas cleaning is a process aimed at the reduction of acid gases, such as SO2 and HCl, in order to limit the environmental impact of, e.g., waste to energy plants. A dry flue gas cleaning process involves injecting fresh and partly spent though reactivated solid particles, such as hydrated lime, into the flue gas stream, that react with the acid gases. The resulting products of the reaction are solid inert particles that are captured using a bag house filter. This type of process has some limitations in terms of removal efficiency and cannot be operated below a certain temperature threshold, which in turn limits the heat recovery capacity of such a plant. The solid products of this process have been studied for decades, but doubts about the main reaction pathways persist, in particular for processes that involve more than one acid gas and that are mixed with fly ash. A dry flue gas cleaning process with steam activation is investigated, tests were performed at a pilot plant, to simulate the conditions of a real process. The tests performed showed that steam injection is indeed feasible and can be used instead of liquid water injection. The analyses of the solid product, highlighted the presence of different substances but also a discrepancy between online and offline analysis was detected, and the reasons are still to be investigated.