A method for manufacturing biomass based fuel configured to reduce chemical and/or mechanical effects of flue gas on heat transfer surfaces is described. The method comprises providing biomass and steam into a reactor; maintaining said biomass and said steam simultaneously in the reactor, in a pressure of at least 10 bar(a) and at a temperature from 180° C. to 250° C. for at least 2 minutes; and decreasing the pressure in the reactor and/or conveying biomass out of the reactor such that the pressure of the environment of the biomass decreases below 5 bar(a), to produce steam-exploded biomass. The method further comprises adding some combustion additive to the biomass and/or the steam-exploded biomass.