Wet Route Pellets Production Using Primary Sludge from Kraft Pulp Mill

The substantial expansion of the Brazilian pulp and paper industry in the last years resulted in a significant increase in the solid waste generation. This paper investigates the production of pellets using primary sludge from the effluent treatment plant of a kraft pulp mill, as a fuel for producing energy, using a novel wet route process. The pellet samples were produced in a laboratory pelletizing press, which has a horizontal circular matrix. The samples were characterized by moisture content, high heating value, ash content, dimensions (diameter and length), mechanical durability and fines content. The net heating value and energetic density were also measured. The pellets manufactured with primary sludge were compared to the European standard for non-woody pellets. Pelletization caused a reduction of the moisture content by 37.8 %, and increased the net heating value by 41 % and bulk density by approximately 39 %, which resulted in a 263 % increase in the material's energetic density. Pellet production using a wet route process was appropriate for the primary sludge, and produced pellets with a high mechanical durability (99.3 %) and low fines content (0.062 %), indicating the potential of thermal valorization for incineration in the biomass boiler to produce high-quality steam.