Study on Energy Recovery and Anhydrite Production from Elemental Sulfur

Abstract

An industrial-scale model was developed for production of anhydrite (CaSO4) via oxidation of elemental sulfur (S) with calcite (CaCO3), and potential electrical generation. In the proposed system, sulfur is first oxidized in a combustion chamber to form sulfur dioxide (SO2) at high temperature and pressure, and expanded in a turbine to produce electrical power. Then, the SO2 is converted to CaSO4 through a Flue Gas Desulfurization (FGD) boiler. Further energy is recovered from the flue gas through a Heat Recovery Steam Generator (HRSG). In this study, three cases were elaborated, with the best resulting in a predicted power production of 531 MW from a flow of sulfur at 72 kg/s. The corresponding CO2 emissions are 0.675 kg/kWh, less than a new coal-fired plant’s emissions of 0.762 kg/kWh. Experimental studies were undertaken to test for the sulfur conversion to anhydrite in two different lab-scale reactor systems. In the first, sulfur was gasified in an evaporator, and the resulting gas was flowed to a reactor containing calcite, similarly to a FGD system. In the second, sulfur and calcite were inserted in the same vessel to test for direct reaction. Using thermogravimetric and x-ray diffraction tests, it was found that the sulfation percentage increased as a function of temperature from 600 to 800 ⁰C, and was close in value at 800 and 900 ⁰C. The increase of temperature resulted in calcination of calcite to lime (CaO), which reacts better with sulfur; however, when reaching 900 ⁰C, sintering may have occurred, resulting in obstruction of further conversion. Molar ratios of S-CaCO3 of 0.5 showed a better conversion of sulfur (at 700, 800 and 900 ⁰C) than when the reactants were equimolar. Using pure oxygen instead of air almost always showed a higher conversion for all temperatures and reactant ratios.