Calcium Reclamation and Synthesis of PCC For Acid Gas Control in Flue Gas

Abstract

Fossil fuels currently play an invaluable role; accounting for over 80 % of the world's energy needs. The combustion of these fuels, however, generates the majority of anthropogenic acid gases, such as SO2 and CO2. Thus, reducing emissions from fossil fuel conversion systems and stabilizing current levels of major pollutants in the atmosphere are essential to ensure the continued use of inexpensive fossil fuels while maintaining the delicate equilibrium in the environment. The increased number of natural disasters and the passage of major political programs, like the Clear Skies Act of 2003 and the Clean Air Act of 1990, highlight this need. Post-combustion removal of SO2 in flue gas can be achieved by contacting acidic SO2 with alkaline sorbents such as limestone (CaCO3), lime (CaO), and hydrated lime (Ca(OH)2). The conventional flue gas desulfurization (FGD) processes are broadly classified as wet and dry processes and their overall conversions are about 90 % and 60 %, respectively. Considering the large quantity of Ca-bearing sorbents needed for FGD processes, the reclamation of unused Ca in these wastes is an attractive solution for improving the overall process economics. In this project, various calcium sources are used to synthesize precipitated calcium carbonate (PCC) that has optimal morphological properties for both SO2 and CO2 capture from flue gas. First, different industrial wastes, Ca(OH)2, and CaCO3 are procured and characterized for their Ca content. Various chelating agents are then used to promote the dissolution of solid samples. Based on the results of the calcium leaching tests, a common chelating agent, IDA, is selected for the subsequent investigation of PCC synthesis. It is found that IDA promotes the dissolution of Ca-bearing solids, while it does not interfere with the subsequent precipitation of PCC process. Finally, the effectiveness of PCC, produced with IDA, on SO2 capture and CO2 separation is investigated using a multi-gas thermal gravimetric analyzer.