Optimizing processing parameters for biochar production : Quality and process management

Abstract

With the environment and climate conditions changing, it is obvious how anthropogenic factors have contributed to climate change ever since the industrialization period started. The need for applying green engineering and technology and modifying modern technology into more sustainable solutions is significant. In recent years pyrolysis has emerged as a sustainable technology for turning biomass and biowaste into carbonaceous products, also called biochar, with applications in multiple industries as the replacement for non-renewable materials.

This thesis was implemented in a research project funded by Business Finland. The need for a quality management system, documenting critical measurement points, improving quality of the final product and increasing knowledge regarding the quality affecting factors were the reasons this thesis was done for Carbofex Oy. To support the thesis there were four research questions. First question was how biochar quality is affected by changing parameters, specifically regarding PAH concentration. Second question was how reactor type and feedstock affect yield. Third question was what industries could benefit from biochar and how are they applied. And the last question was how polycyclic aromatic hydrocarbon (PAH) concentration could be minimized in biochar. To answer these questions a literature review and scientific experiments were conducted. The thesis started with a literature review of the theory behind pyrolysis, pyrolysis chemistry and biomass selection and classification. The focus of the thesis was on the different biochar production methods, application areas and biochar’s requirements on those applications and different reactor types for slow and intermediate pyrolysis were also reviewed and compared.

The experimental part of the thesis focused on the contribution of different process parameters to the PAH concentration in the final product. Selected parameters were chosen based on the literature review and previous knowledge of the process and they were compared to the PAH results from a certified laboratory. Feedstock and biochar moisture were also tracked but other parameter values were extracted from the process system data history during test runs. PAH results were analyzed from January 2024 to July 2024 and the data was exported to Excel for visual analysis.

The results of the analysis showed that there was no significant correlation between any of the selected parameters. While there was no expected correlation between most of the parameters, there was expectations that there would be a direct correlation between post pyrolytic temperature and possibly pressure difference inside the reactor. The most significant use was that in the light of new information, other goals of the manufacturing process can be safely optimized without risking PAH threshold values.

The thesis also highlighted the need for thorough systematic inspections more often to ensure process stability and proper extraction of gases. A quality manual is created from the contents of this thesis which will be used to improve the biochar manufacturing automation and production operation. Analysis tool for PAH analysis will be used to detect trend in the future. From the findings of this thesis work, in a larger scale research, the focus will be on a single parameter at a time to avoid multiple parameters having dual effect.