Reutilization of MgO Byproducts from the Calcination of Natural Magnesite in Dry Desulfurization: A Closed-Loop Process

Abstract

Dry desulfurization is an attractive alternative to wet flue gas desulfurization (WFGD) because it avoids wastewater management and requires less energy inputs and lower operation costs. In this research, the byproducts from a process generating the SO2 emissions were tested for dry desulfurization. Thus, the same byproducts from the calcination of natural magnesite (two cyclone dusts from the air pollution control system, LG-MgO and LG-D, and one fraction obtained after calcination, LG-F) that were already studied in a WFGD were assessed in a dry desulfurization process. The byproducts were tested raw and modified by two hydration methods and in semi-dry conditions. The SO2 sorption performance was evaluated by means of breakthrough curves (parts per million of SO2 at the outlet versus time) and desulfurization potential (liters of SO2 adsorbed per kilogram of byproduct). Accordingly, the byproducts showed good performance with respect the lime used as adsorbent in conventional dry flue gas desulfurization (FGD). The breakthrough curves showed that the process was characterized by a first stage controlled by the surface reaction rate and a subsequent product layer diffusion-controlled stage. During the former, the three MgO byproducts showed the same behavior, although those with a high CaO content presented an enhancement of the latter mechanism. The dust material LG-MgO presented the best desulfurization potential, up to 25.2 L kg–1, while LG-D and LG-F achieved 16.5 and 15.9 L kg–1 respectively. The modification of the byproducts significantly improved the adsorption capacity, especially for LG-MgO in semi-dry conditions, to up to 35.0 L kg–1. The use of these byproducts in a dry process avoids generating wastewater effluents and allows us to obtain a solid mixture basically made of magnesium and calcium sulfite, which could be further recovered or reutilized. This is, to the knowledge of the authors, the first study considering a closed-loop dry desulfurization process.