By initiating chain reactions that consume NOx, CHi radicals play an important role in natural gas reburning. In conventional reburning, most of the methane is consumed in reactions with oxygen to form CO, and does not produce CHi radicals as intermediate products, which limits NO reduction efficiency. Activating natural gas externally to the boiler may generate a mixture of CHi radicals by passing CH4 through a discharge before injection into the reburning zone. Five activation technologies are reviewed: microwave heating and discharge plasmas, electron beam irradiation-induced plasmas, corona discharge induced plasmas, and thermal plasmas. Wall, cyclone and tangentially fired boilers were considered in the economic assessment. From preliminary capital and operating cost estimates, pulse corona and electron beam techniques appear to be the most promising activation techniques.