A base case process design for the pyrolysis of pinedust and Acacia tortilis residues was rated unsustainable due to the use of a fossil-based, high-cost energy source; the absence of energy integration and low yields of the targeted dry oil. Incremental improvements were made using a logical matrix based on demonstrated best practices from literature, including the use of a fast pyrolysis regime to increase bio-oil quality and yield. More sustainable sources of energy such as the use of char by-products in a self-energizing system or the use of concentrated solar were proposed. Integrating such improvements will improve the techno-economic outlook of the project by lowering the production cost of the pyrolysis oil while reducing the ecological impact of the process. We assumed the technical feasibility of utilizing the bio-oil as a substitute for fuel oils in slow engines, which has been theoretically proven and partially demonstrated. The logical matrix led to sustainable conceptual models for a pyrolysis system that can supply bio-oil for use in a heavy fuel oil power generator. Bio-oil would be a cost-effective solution for substituting fuel oil, which is facing stiffer regulatory restrictions due to its high sulphur and black carbon emissions.