Impact of densification process on unprocessed biomass and post-hydrothermal carbonization

Abstract

The pulp and paper industry use biomass residues, such as paper sludge and bark as fuel to provide energy for their plants. However, issues such as high-water content or low heating value limit the amount of energy that can be utilized. Processes to improve heat generation include biomass densification, which facilitates transportation and handling and can increase energy yield. However, the technical feasibility of briquetting is a function of the feedstock and preprocessing. This study introduces a novel approach to briquette production from biomass residues by utilizing wet biomass with water as a natural binder, contrasting with conventional methods that require forced drying and/or the addition of binders. The objective of this research was to investigate the impact of briquetting both unprocessed biomass and post-hydrothermal carbonization. The study focused on manufacturing briquettes derived from different sources, including bark (Balsam fir), paper sludge, and hydrochar of paper sludge. The feedstock was characterized for ash content and higher heating value. Biomass particle size (range), moisture content (range), process temperature (range), process pressure (range), and process residence time (range) were varied in briquetting experiments to determine conditions to produce high-quality briquettes with minimal energy input. Moisture content as high a 50 wt% in feedstock produced technically feasible briquettes, with appropriate physical-mechanical properties (durability, volumetric expansion and apparent density), and energetic potential (calorific value). The addition of heat (pressing temperature of 150 °C) during the pressing process resulted in briquettes with enhanced physical-mechanical, and energetic properties, surpassing those produced at room temperature. Further tests with additional steps in the production process are required to meet commercialization standards in Canada, but the treatments conducted in this study effectively improved the energy potential of biomass for internal industrial energy gains.