Medium Temperature Desulfurization for Oxyfuel and Regenerative Calcium Cycle

Desulfurization at medium temperature was investigated with focus on impacts of temperature and CO2 concentration under Oxyfuel firing and Regenerative Calcium Cycle (RCC) conditions. Investigation started with thermodynamic analysis and ThermoGravimetric Analysis (TGA). Tests were then conducted by a bench-scale fixed-bed type reactor, using a synthetic gas mixture. Various parameters were evaluated. The envelope covered temperature variation of 150-450 °C, CO2 concentrations in the gas stream up to 60% and water concentrations between 0 to 25%. These tests were done having SO2 concentrations in the gas of 2000 ppm SO2. Furthermore different types of lime samples were screened.It was found that CO2 had strong impact on medium temperature desulfurization. Capture of CO2 by the lime was enhanced by increasing temperature. CO2 competed with SO2 and the relative extent to react with lime varied with temperature. Rate of reaction increased with temperature, the capacity of lime-to-SO2 and lime-to-CO2 increased as well. Optimum temperature windows were searched and will be discussed.Based on the tests results, scenarios of desulfurization options at medium temperature range for Oxy and RCC are evaluated, and will be discussed in details.The testing results show issues related to high concentration of CO2 under the Oxy conditions at temperature over 250 °C. Though capacity of lime for SO2 increases with temperature, the amount is limited due to reaction with CO2 at high concentration. Desulfurization at medium temperature range, 250 - 450 °C, should be aiming at moderate SO2 removal, and the reuse of the spent reagent is considered in the downstream wet desulfurization process.With about 10% CO2, in the RCC conditions, it is more optimistic to remove SO2 in the medium temperature range. Optimum temperature range is discussed for achieving moderate SO2 removal. Reuse of the spent reagent is considered in the downstream wet desulfurization process