Advanced fluidized bed combustion sorbent reactivation technology

A new technique for simultaneous grinding and hydrating of fluidized bed combustion (FBC) bottom ash has been developed. This method has been shown to be effective in hydrating the CaO component of the ash, so that the sorbent is reactivated. Careful control of water levels is required to prevent energy demand increases for grinding. No problems associated with the potentially exothermic reaction of water with FBC bottom ash have been observed during grinding. When excess water (over that required by hydration) is used, the resulting material is a slurry and, while quantitative conversion of CaO in the solids is achieved, using the slurry for the sorbent would require a redesign of the limestone feed system. Therefore, coal or unreacted ash is added to the mixture after grinding. The resulting dry product contains the spent bed material in a completely hydrated form. The reactivated ash produced has been evaluated for sulfur capture using thermogravimetric analysis and a CFBC pilot plant. Conversion rates of almost 100% are achieved for ash after grinding hydration. An industrial demonstration of the technology has supported its viability with no decrease in sulfur capture, while limestone requirements decreased by 18%. The economic implications of the industrial applicability of the technology are outlined in a case study using the Point Aconi CFBC unit. Decreased limestone usage is calculated to net savings in the order of $500000/year. The project is calculated to have an equity payback of less than 1 year.