The report gives results of the operation of a 17-MW Chemically Active Fluid Bed (CAFB) demonstration unit, retrofitted to a natural gas boiler. The CAFB process gasifies high-sulfur, high-metals-content liquid and solid fuels. Residual oil, lignite, and bituminous coal were gasified separately or together between November 1979 and June 1981. Design and operational areas where upgrading would be beneficial were identified. Continuous monitors were used to measure boiler flue gas emissions of SO2, NOx, CO, oxygen, CO2, and opacity. Periodic manual emission tests were conducted for particulate, SO2, and Nox, using EPA reference methods. Emissions of these three criteria pollutants were generally lower than New Source Performance Standards for utility boilers, although occasionally excessive particulate and SO2 emissions were observed. NOx emissions were consistently lower than those from natural gas combustion. Results of detailed chemical analyses and biological assays are reported.