For sustainable and sound economic development there is a strong demand for extended clean power production, which is affordable by cost, utilising existing coal based plants and large volumes of renewable biomass and continuously waste streams as well, offering high level of process safety with comprehensive long term management of all residual streams from the operations. However, the utilisation of these fuels entails the risk of severe environmental impact due to the presence in them of polluting compounds, i.e. N, S, Hg, Cl etc. A preventive technique for the revitalization of the solid fuel industry by removing barriers by development of cost effective preventive pre-treatment of low-grade solid fuels (combined renewable biomass, lignite, coal, derived fuels) through application of low temperature carbonisation technology is described in this work. This pre-treatment process is made in downsized reductive environment for removal of hazardous air pollutants (such as nitrogen, sulphur, chlorine, mercury) prior to burning and by using the clean fuel to improve the combustion efficiency as well. The integrated application is primarily for the small-scale power plants less than 50 MW power capacity and CHP co-generation, and medium scale power plants less than 300 MW power capacity as well.