Sorbent characterization for circulating fluidized bed scrubbers

Harmful sulfur dioxide (SO2) emissions from power plants have increasingly been restricted since the 1970’s. Circulating fluidized bed (CFB) scrubber is a dry flue gas desulfurization method of absorbing SO2 out of the flue gas with sorbent. In current commercial plants, the used sorbent is commercial or on-site hydrated calcium hydroxide. The CFB scrubber process is characterized by a close but adequate approach to the flue gas saturation temperature that is achieved by spraying water to the absorber followed by a particulate control device. Very high SO2 removal is achieved along with a dry byproduct that is continuously recirculated back to the absorber for enhanced sorbent utilization. The aim of this work is to develop a method that would characterize the reactivity of sorbents used in CFB scrubbers and to conclude how different process parameters and sorbent properties affect the sulfur absorption. The developed characterization method is based on a fixed bed of sorbent and inert silica sand, through which an SO2 containing gas mixture is led. The reaction occurs in the bed and the SO2 concentration in the outlet as a function of time, a breakthrough curve, is obtained from the analyzer. Reactivity of the sorbents are evaluated by the absorbed sulfur amount. Results suggest that out of process parameters, lower SO2 concentration, lower temperature and higher moisture content enhance the desulfurization. Between different sorbents, specific surface area seems to be the most significant parameter. Large surface area linearly leads to more efficient desulfurization. Overall, the solid conversion levels in the tests were very low creating uncertainty to the validity of the results. New desing is being planned to overcome the problems of the device.