Thermochemical energy utilization of biomass in Rwanda - a screening of potential feedstocks

Sammanfattning: Traditional bioenergy practices in sub-Saharan Africa involve collecting natural forest wood and burning it in simple fireplaces for household cooking. This is actually still very common, especially in rural areas. The situation is unfortunately connected to health issues, inequality and natural forest degradation and deforestation. To alleviate these problems, agricultural residues and agroforestry trees can be used as feedstocks in more efficient and less polluting cooking solutions and local electricity production, via thermochemical conversion processes. However, the feedstock availability and suitability for such processes needs to be better mapped, evaluated and understood. With a focus on Rwanda, the aim of this study was therefore to investigate the potential feedstock for thermochemical energy utilization of agricultural residues and woody biomass produced in agroforestry settings.Interviews with 14 agro-processing companies were conducted, which provided data for the available amounts of a range of different potential biomass fuels based on agricultural residues, such as cassava peels, coffee husks, coffee pulps, maize cobs, maize screening, rice husk and sugarcane bagasse. This data was then applied to estimate the total residue quantities available in Rwanda. 23 biomass samples, both agricultural residues and woody biomass, were also collected and characterized in the laboratory by means of a so called proximate analysis, i.e. moisture, ash content, volatile matter and fixed carbon.Based on this study, it was clear that there are significant amounts of agricultural residues produced and handled in Rwanda. Cassava peels and maize cobs were estimatedly abundant, with sugarcane bagasse and rice husk also being available in large quantities. Depending on the application, moderate to strong seasonalities of some residues, such as maize cobs, can be challenging. Another circumstance of great relevance here is that a vast majority of the agricultural residues assessed in this work already seemed to be utilized for different purposes, such as fuel for heating or cooking.Regarding fuel properties and quality, related to ash, volatile matter and fixed carbon content, many of the feedstocks investigated indicated good suitability in some kind of thermochemical conversion process. However, high moisture contents may need to be addressed in some cases to avoid low process efficiencies, such as for maize cobs, sugarcane bagasse and fresh agroforestry trees.