SteamBioAfrica

The biofuel production potentials for encroacher and invasive bush biomass species found in Southern Africa were assessed using different valorization routes. Theoretical models were employed to calculate the biofuel yields. The gasification-catalytic route produced highest ethanol yields (450–488 L/t) while the lowest values were from enzymatic/acid hydrolysis-to-fermentation route. Blue gum gave the highest ethanol yields. Biodiesel and naphtha yields produced through Fischer-Tropsch synthesis were highest for blue gum (196 L/t) and lowest for Acacia raficiens (176 L/t). The highest biogas and biomethane potential of 458 L/kg.VS and 229 L/kg.VS respectively were obtained from black wattle while the respective lower values (270 L/kg.VS and 132 L/kg.VS) were recorded for blue gum. Senegalia mellifera gave the highest torrefied biofuel energy and mass yields at 0.92 and 0.97 respectively while black wattle had the lowest mass and energy yields at 0.75 and 0.83 respectively. From an energy yield basis, the acid hydrolysis-fermentation route yielded an average of 3.69 GJ/t of biomass while the highest yields came from the gasification-catalytic conversion route which was 9.7 GJ/t. The average energy yield variations across biomass species ranged 5.11–6.19 GJ/t which is around 30 % of the raw biomass' calorific value. These early results provide insights towards the best pairing of appropriate biomass species and energy conversion route. Further evaluations of these biomass-valorization technology pairing to unpack process efficiencies, cost and kinetics are required using real process experiments instead of using theoretical models. These additional tests should include sustainability assessment to guide future commercialization decisions.

A number of biomass processing plants that use torrefaction technology are coming up globally as this technology advances from several years of pilot and laboratory research studies to commercialization. However, continued and sustainable growth of biomass torrefaction industry hinges on the accessibility to critical technology information by decision makers especially on process efficiency measurement. This study attempts to organize and put together critical process efficiency measurement information about torrefaction technologies and later zeroes on one specific torrefaction technology called the superheated steam (SHS) torrefaction technology. The study focusses on different torrefaction technologies' applicability to processing bush encroacher and invasive bush species commonly found in Southern Africa. The study includes (a) a brief and general review of torrefaction processing plant performance metrics (b) a collection of plant and product performance information pertaining to a case study that employed SHS torrefaction technology on encroacher and invasive bush species of Southern Africa. The main objective of this study is to disseminate knowledge that can be useful in advancing SHS torrefaction technology towards addressing bush encroachment related issues, while fighting climate change through the production of renewable solid biofuels and biochemicals from these bushy woods. The review established that SHS torrefaction of Southern African encroacher and invasive bushes is technically feasible although additional optimization studies are required to prove commercial viability and improve competitiveness of the technology over fossil based processes and products.