Recent study of heterogeneous reburning suggests effective NO reduction requires an adequate carbon source and a pool of catalysts that reduces not only NO, but also the reaction intermediate HCN [Chen WY and Tang L. Variables, kinetics and mechanisms of heterogeneous rebuming. AlChE J 2001;47:2781-2797]. The current work demonstrates that ashes from lignite-fired power plants contain these desirable catalytic ingredients. Their reactivity is slightly lower than that of ashes produced in laboratory at lower temperatures, probably due to the formation of crystalline structure. The current work also demonstrates that for the power plants remote from lignite resources, ashes from biomass-fired grate boilers are a remarkably effective and economical substitute. About 85% of NO reduction efficiency appears achievable at a stoichiometric ratio 0.945. The raw-material cost estimates of the mixed-fuel technology suggest that it could be competitive with selective catalytic reduction (SCR). (c) 2006 Elsevier Ltd. All rights reserved.