The goal of the U.S. Department of Energy (DOE) Clean Coal Technology (CCT) program is to furnish the energy marketplace with a number of advanced, more efficient, and environmentally responsible coal utilization technologies through demonstration projects. These projects seek to establish the commercial feasibility of the most promising advanced coal technologies that have developed beyond the proof-of-concept stage. This document serves as a DOE post-project assessment of a project selected in CCT Round 2. The project is described in the report ''Demonstration of Selective Catalytic Reduction (SCR) Technology for the Control of Nitrogen Oxide (NO(subscript x)) Emissions from High-Sulfur, Coal-Fired Boilers'' (Southern Company Services 1990). In June 1990, Southern Company Services (Southern) entered into a cooperative agreement to conduct the study. Southern was a cofunder and served as the host at Gulf Power Company's Plant Crist. Other participants and cofunders were EPRI (formerly the Electric Power Research Institute) and Ontario Hydro. DOE provided 40 percent of the total project cost of $23 million. The long-term operation phase of the demonstration was started in July 1993 and was completed in July 1995. This independent evaluation is based primarily on information from Southern's Final Report (Southern Company Services 1996). The SCR process consists of injecting ammonia (NH3) into boiler flue gas and passing the 3 flue gas through a catalyst bed where the NO(subscript x) and NH3 react to form nitrogen and water vapor. The objectives of the demonstration project were to investigate: Performance of a wide variety of SCR catalyst compositions, geometries, and manufacturing methods at typical U.S. high-sulfur coal-fired utility operating conditions; Catalyst resistance to poisoning by trace metal species present in U.S. coals but not present, or present at much lower concentrations, in fuels from other countries; and Effects on the balance-of-plant equipment from sulfur compounds formed by reactions between sulfur dioxide (SO2), sulfur trioxide (SO3), and NH3 (e.g., plugging and corrosion of downstream equipment). The Clean Air Act, initially promulgated in 1970, established New Source Performance Standards (NSPS) for emissions of SO2, NO(subscript x), and particulates, among other pollutants, from stationary coal-fired power plants. These regulations were made more stringent in the Clean Air Act Amendments (CAAA) of 1990. The SCR process is one way to meet the NO(subscript x) emissions requirements of the CAAA.