Thermodynamic Analysis and Exergy Optimisation of Biomass Conversion Systems for Distributed Energy Generation in Rural Nigeria

This study conducts a thermodynamic analysis and exergy-based optimisation of biomass conversion systems for distributed rural energy generation in Nigeria, developing original theoretical contributions to agricultural energy systems engineering in sub-Saharan Africa. Nigeria's rural energy poverty is pervasive, and agricultural biomass residues represent the most abundant and accessible renewable energy resource for distributed generation in farming communities. However, existing biomass energy systems deployed in Nigeria operate at low thermodynamic efficiency due to suboptimal conversion pathway selection, poor system integration, and absence of exergy analysis in system design. This study applies exergy analysis and second law thermodynamics to characterise the irreversibility sources and efficiency ceiling of five biomass conversion pathways, specifically direct combustion, gasification, pyrolysis, anaerobic digestion, and combined heat and power systems, for three representative agricultural biomass feedstocks available in northern and southern Nigeria. A mixed integer nonlinear programming optimisation model is formulated to select optimal conversion pathway combinations and operating conditions that maximise exergetic efficiency for specified rural energy demand profiles across six representative Nigerian rural community archetypes. Findings reveal that integrated gasification-CHP systems achieve exergetic efficiency of 42 to 48 percent, significantly exceeding direct combustion at 12 to 18 percent. Optimal biomass-to-energy pathway combinations differ substantially between northern crop residue-dominated and southern wet organic waste-dominated supply contexts. The study contributes an original exergy optimisation framework for Nigerian rural biomass energy systems and recommends exergy analysis as a standard tool for biomass energy project design.

Keywords: exergy analysis, biomass conversion, rural energy, thermodynamic optimisation, Nigeria.