Evaluation of the potential of non-woody invasive plant biomass for electricity generation

[摘要] ENGLISH ABSTRACT: Invasive alien plants (IAPs) threaten the existence of plant and animal biodiversity as they cause destruction to the natural habitats they invade. In South Africa the Natural Resource Management (NRM) programme clears these plants. In efforts to add value to the clearing operation, the NRM Programme's objective is to utilise the cleared IAP biomass for economic purposes, thereby contributing to the sustainable management and control of invasive species.The objectives of this study were to assess the potential and the economic viability to supply non-woody IAP biomass for electricity generation.The study was conducted on biomass samples from 13 common non-woody IAPs in South Africa namely: Arundo donax (Giant reed), Lantana camara (Lantana), Pontederia cordata (Pickerel weed), Ricinus communis (Castor-oil plant), Opuntia ficus-indica (Sweet prickly pear), Solanum mauritianum (Bugweed), Atriplex nummunlaria (Saltbush), Cestrum laevigatum (Inkberry), Senna didymobotrya (PB Cassia), Chromoleana odorata (Chromoleana), Eichhornia crassipes (Water hyacinth), Cerus jamacaru (Queen of the night) and the Agave sisilana (Sisal plant). Properties, such as density, moisture content, calorific value, ash content and volatile content, elemental composition as well as processability and estimated drying time were determined in order to assess the suitability of the biomass for different thermo-chemical conversion techniques (combustion, gasification and pyrolysis). This study only assessed the potential of non-woody IAPs for electricity generation, with the main focus on thermochemical conversion. Although some of the species might be suitable for bio-chemical conversion, a detailed overview of biochemical pathways is beyond the scope of this study.The second part of the study examined the economic and financial perspective of the biomass supply to generate electricity, in which the harvesting, chipping and transport costs of the biomass were considered.The results of this study showed that non-woody invasive biomass has the potential to be used as feedstock for electricity generation through combustion. None of the species were found to be suitable for gasification or pyrolysis due to their high silica, chlorine and ash content. Sweet prickly pear, Water hyacinth, Queen of the night, Sisal, Pickerel weed and the Castor-oil plant had a too high moisture content and would be best suited for energy production through biochemical conversion pathways. The total average cost to harvest and transport non-woody IAP chips to an energy plant was R33/GJ, which is approx. 50% more expensive than other biomass feedstocks (Forestry residues and woody IAPs).Overall when taking physical, chemical and financial aspects into consideration Giant reed, Saltbush, and Chromoleana were the best species to be utilised as feedstock. However, without a 'fuel cost subsidy from the NRM programme, the harvesting of non-woody alien invasive species for energy production is unlikely to be financially viable.

[发布机构] Stellenbosch University