TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The fuel system comprises: a mixture of at least two different fossil regular fuels comprising brown coal, black coal and/or anthracite, and at least one biogenic carbon donor comprising biomass; a refinement product, which is coke, petroleum coke, brown coal coke or charcoal; and a fraction of biogenic carbon carriers of at least 20 wt.%. Preferred Components: The biogenic carbon donor is at least one regrowable raw material comprising wood, natural fiber, vegetable oils, alcohol, sugar, starch, dried vegetables or cereals. The content of fossil carbon compared to fossil fuel is reduced by at least 11% concerning the calorific value, with the percentage of fossil carbon being put in relation to the calorific value for calculating the content of fossil carbon. The first regular fuel is anthracite or lean coal, comprising a volatile water and ash-free fraction (waf) of less than or equal to 10 wt.% The second regular fuel is forge coal, fat coal, gas coal, long-flame coal, bituminous coal, pre-dried black lignite or pre-dried dull brown coal, comprising a volatile water and ash-free fraction(waf) of 10 less than or equal to 40 wt.%. Preferred Process: In the process: at least 20 wt.% of biogenic carbon carrier is mixed in step (c); a substantially solid biomass, preferably wood, wood pellets, wood chips, natural fibers, cereals, sugar or dried vegetables are mixed as a biogenic carbon carrier. The substantially solid biomass before mixing is impregnated with a substantially liquid biogenic carbon carrier, preferably vegetable oil, vegetable fat and/or alcohol, and prior to mixing the biogenic carbon carrier, the refinement product is mixed to the mixture obtained in step (b). The substantially dust or powder-like substrate, preferably saw dust, legume shred or coal dust are mixed to the mixture obtained in step (b) and/or (c). EXAMPLE - Low volatile anthracite coal (33 wt.%) was mixed with a medium volatile fat coal (33 wt.%) in a mixing drum, until a homogeneous mixture was obtained. Wood pellets (33 wt.%) were added in the mixing drum to the obtained mixture and mixed until a substantially homogeneous mixture was obtained. The obtained mixture showed water (7 wt.%), ash (9.8 wt.%), a volatile material fraction (34.89 wt.%), sulfur (0.86 wt.%) and a total carbon content of 61.37 wt.%, with 46.03 wt.% of the total carbon content of 61.37 wt.% (being fossil carbon (46.03 wt.%) and biogenic carbon (15.33 wt.%) to give a mixture showing a fuel value of 23865 J/g and a calorific value of 5462 cal/g.