Soot sludge is formed in the production of formic acid. Currently, this waste is combusted together with heavy fuel oil in a boiler. The current theoretical lower heating value of the sludge is -23.8 MJ/kg(d.b). Drying of sludge increases the heating value, and decreases oil use. Drying of pure sludge in a fixed bed is impossible in practice and therefore sawdust is mixed with it before drying. This study aims to fill the gap in knowledge about soot sludge and sawdust drying by studying its drying kinetics experimentally in a fixed bed. The influence of drying on fuel oil consumption is also preliminarily evaluated. Drying curves were determined for bed heights of 100, 200 and 300 mm, inlet air temperatures of 40, 80 and 100 degrees C, and air velocities of 0.75 and 0.9 m/s. According to the results, the optimal mixture ratio of soot sludge and sawdust is 50%(soot) (sludge) 50%(sawdust) (vol.%), with an air velocity of 0.75 m/s and a bed height of 200 mm. Oil savings of 104 MJ/kg(dry,) (soot sludge) are achieved when the mixture is dried to the final moisture content of 40%. (C) 2015 Elsevier B.V. All rights reserved.