TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: In the composition, SRF-material is present in an amount of at least 50 (preferably at least 75, especially at least 90) wt.% based on the dry weight of the starting composition. The starting composition comprises biomass in an amount of 30-80 wt.% based on the dry weight of the starting composition; plastics in an amount of 10-70 wt.% based on the dry weight of the starting composition; water in an amount of 10-20 (preferably 12-17) wt.% based on the total weight of the starting composition; and contaminants in an amount of maximum 5 (preferably maximum 2) wt.% based on the dry weight of the starting composition. Preferred Method: The heating is carried out in a rotating drum. The heating takes place gradually until a mass temperature of 260-360degreesC is reached. The residence time of the starting composition at a temperature of 150-360degreesC is less than 100 minutes (preferably less than 45 minutes, especially 10-30 minutes). The size reduction is carried out by crushing the solid fuel (preferably by using a roller construction and/or jaw crusher). The separation is carried out by screening, where preferably aluminum is separated as the at least one metal. In method (P1), the solid fuel is washed immediately after the torrefaction of the starting composition, while the mass temperature of the torrefied solid fuel is 150 to 360degreesC. In method (P1), the solvent is heated to temperature of 30 to 100 (preferably 60 to 80)degreesC before being used for washing the solid fuel. The method (P1) involves an additional step of washing which is carried out on the washed solid fuel. In method (P1), the solid fuel is quenched with the solvent immediately after the torrefaction of the starting composition, after which the solid fuel moistened with solvent is washed with additional solvent in counter-flow. The method (P1) involves an additional step after the washing of the solid fuel with the solvent, where the additional step includes drying of the solid fuel moistened with solvent; and an additional step of reducing the solid fuel to a particle size of 0.5-5 mm, where the reducing step is carried out prior to the washing of the solid fuel with the solvent. Preferred Components: The solvent is an aqueous solvent (preferably water or an aqueous solution of at least one compound that increase the water-solubility of the chlorine compounds). Preferred Fuel: The solid fuel comprises torrefied biomass in an amount of 40-90 wt.% based on the dry weight of the solid fuel; torrefied plastics in an amount of 10-60 wt.% based on the dry weight of the solid fuel, where at least a part (preferably at least 40 wt.%, especially at least 60 wt.%) of the torrefied biomass is embedded in the torrefied plastics; contaminants in an amount of maximum 5 (preferably maximum 3) wt.% based on the dry weight of the solid fuel; water in an amount of less than 5 (preferably less than 3) wt.% based on the total weight of the solid fuel; and metals in an amount of maximum 0.5 (preferably maximum 0.3, especially maximum 0.2, particularly maximum 0.1) wt.% based on the dry weight of the purified solid fuel. EXAMPLE - A starting composition was prepared by mixing secondary recovered fuel (SRF) (100 wt.%) consisting of biomass (60 wt.%) and plastics (38 wt.%) and contamination (2 wt.% based on dry matter) and a biomass of the type B-wood. The starting material was treated in a rotating drum at a temperature profile, while the starting material was heated to 330degreesC for 45 minutes to form a solid fuel (test). Control solid fuel was prepared by using non-torrefied biomass that could not be crushed. The obtained test/control fuel products were assessed for a number of properties such as granulation, quantity of fine dust, combustion behavior, CO2 reduction, suitability as bulk goods, dust formation during crushing, percentage of volatile compounds in the solid fuel and low calorie value (LCV). The results for test/control fuels were: granulation = very good/very bad, quantity of fine dust = very good/very bad, combustion behavior = very good/moderate, CO2 reduction = good/good, suitability as bulk goods = very good/very bad, dust formation during crushing = very good/not applicable, percentage of volatile compounds in the solid fuel = good/moderate and LCV = very good/moderate respectively. The results showed that the test solid fuel with increasing proportion of SRF in the starting composition gave better results regarding granulation, quantity of fine dust, combustion behavior, suitability as bulk goods, dust formation during crushing without the properties regarding CO2 reduction and percentage of volatile compounds deteriorating excessively.