Self-Energized Pyrolysis Process for Sustainable Biochar Production

Abstract

Biochar has sparked interest as a strategy for carbon capture and sequestration to offset carbon dioxide emissions, along with its various applications such as soil amendment, filler, catalyst, food/feed additive, or adsorbent. This interest is not merely a media-driven opportunity, but also stems from the ample availability of residual biomass and organic waste that can be transformed and integrated into production chains to reduce their environmental footprint. However, this interest attracts the adoption of production technologies that, while meeting the goal of carrying out the pyrolysis process, need to be environmentally sustainable. In this paper, a model based on laboratory-scale experimentation results is proposed and three fundamental stages of the industrial pyrolysis process for the sole production of biochar are explored: drying, pyrolysis itself, and the combustion of gases and vapors as an energy source. In this scenario, the production of pyrolysis liquids is avoided, eliminating the need for condensation equipment, reducing operating costs, and preventing handling problems and potential contamination of the biochar. Three types of biomasses were used experimentally to evaluate the yields and characteristics of the pyrolysis products: cocoa bean shells, white spruce bark, and poplar bark. Cocoa bean shells were then selected to investigate the sensitivity of the main model parameters. The study demonstrates that the combustion of gases and vapors produced during the pyrolysis process of dried feedstocks generates sufficient energy to sustain the process itself. The efficiency of the combustion process, the heat transfer to the pyrolysis reactor, and the input moisture of the biomass feedstock represent the critical parameters affecting the thermal sustainability of the process.