Desulfurization Characteristics of Fuel-Born Alkali and Alkali Earth Metal Compounds in Coal Ashes from Lab-Scale Experiment to Real-Scale Monitoring of CFBC and PC Boiler

Previous research findings and experiential accounts have provided evidence that specific components of coal ash play a catalytic role in the dry desulfurization of flue gas such that their contributions need to be considered for determining the optimal amount of desulfurizing agent such as limestone. The purpose of this study was to quantify the desulfurization characteristics of coal ash in a 500 MW pulverized coal combustion (PC) boiler as well as a 1000 MW circulating fluidized bed combustion (CFBC) boiler. In parallel with a year-long data collection of coal blends and emission characteristics, a series of temperature-controlled fixed bed (lab scale) experiments were conducted for 11 individual (but representative) coal samples. The results indicated that desulfurization by fly ashes appeared to proceed roughly in proportion to the total alkali (TA) contents of the ash, which were consistent with our preliminary test result of the CFBC boiler. In the PC boiler, however, the desulfurization reaction seemed to be very kinetically limited, apparently deactivating the TA components. We developed a practical equation for a priori prediction of SO2 concentration based on the sulfur content of coal blends.