Requirements for very high power electron beam systems for utility stack gas treatment

Energetic electrons in gas cause the formation of very reactive free radicals, ions, and excited-state molecules. These can react either with each other, or with oxygen and water in the system, or with some intentionally added chemical component and, thereby, produce removable compounds. Fuel economies and an increasing global interest in improving the environment, have resulted in a resurgence of interest in using very high power electron beam systems to reduce stack gas pollutants (SO2, NOsub(x), etc.), a process examined at low power levels in the last decade at JAERI. Increasing industrial demands for large width (greater than 2 meters), high dose rate (1 megarad at 1500 meters/minute) electron processors has led to significant advances in high power systems over the past several years. Selfshielded systems capable of up to 1000 mA at 300 kV are now in commercial use. The total electron beam requirements for fossil fuel fired power plants with generating capacities below 500 MWe can be met by a reasonable number of these state-of-the-art 300 kilowatt modules. Electron beam modules with power levels approaching 1 megawatt may ultimately be necessary to provide economy of scale for generating capacities higher than this, unless significant breakthroughs are made in enhancing the formation of stable removable compounds. This paper presents some of the results from the 300 kV, 180 kW electron beam pilot installation in Karlsruhe, West Germany along with a description of the state-of-the-art 300 kW electron processors. The requirements for very high power electron beam systems approaching 1 MW are discussed and some ideas for optimizing total electron beam system costs through the enhanced formation of stable removable compounds described. (author)