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

Melane, Mandlakazi (2016-12)

Thesis (MScFor)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANSE OPSOMMING: Indringerplante bedreig die voortbestaan van plant en dier biodiversiteit omdat hulle natuurlike habitate indring en vernietig. In Suid Afrika word hierdie plante verwyder deur die Natuurlike Hulpbron Bestuur (NHB) program. In pogings om waarde toe te voeg tot skoonmaakoperasies het die NHB program ‘n doelwit om die verwyderde indringer biomassa te gebruik vir ekonomiese doeleindes. Hierdie doelwit dra by tot die volhoubare bestuur en kontrole oor indringerplante. Die doelwitte van hierdie studie was om die potensiaal en ekonomiese volhoubaarheid van die voorsiening van nie-houdagtig indringerplante vir elektrisiteitsopwekking te ondersoek. Die studie is uitgevoer op biomassa mosters van 13 van die mees algemene nie-houdagtige indringerplante in Suid Afrika, genaamd: Arundo donax (Spaansriet), Lantana camara (Lantana), Pontederia cordata (Jongsnoekkruid), Ricinus communis (Kasterolieplant), Opuntia ficus-indica (Soet turksvy), Solanum mauritianum (Luisboom), Atriplex nummunlaria (Soutbos), Cestrum laevigatum (Inkbessie), Senna didymobotrya (Grondboontjiebotterkassia), Chromoleana odorata (Parafienbos), Eichhornia crassipes (Waterhiasint), Cerus jamacaru (Nagblom) and the Agave sisilana (Sisalplant). Eienskappe soos digtheid, voginhoud, kalorifiesewaarde, as-inhoud, vlugtigheidsinhoud, elementsamestelling sowel as verwerkbaarheid en droogtyd is bepaal om sodoende die geskiktheid van die biomassa vir verskillende termo-chemiese omsettings metodes te bepaal (verbranding, gassifikasie en pirolise). Die studie het slegs die potensiaal van nie-houtagtige indringerplante vir elektrisiteitsopwekking ondersoek met die hoof fokus op termo-chemiese omsetting. Alhoewel sommige van die spesies geskik mag wees vir bio-chemiese omsetting is ‘n gedetaileerde oorsig van die bio-chemiese prosesse buite die bestek van die studie. Die tweede deel van die studie ondersoek die ekonomiese en finansiele perspektief van biomasa voorsiening om elektrisitiet op te wek. Dit sluit in die ontginning, versnippering en vervoerkostes van die biomassa. Die resultate van die studie wys dat nie-houdagtige indringer biomassa die potensiaal het om as roumateriaal gebruik te word vir elektrisiteits generasie deur verbranding. Geen van die spesies was geskik vir gassifasie of pirolisie weens hoë silica, chloor en as inhoud. Soet turksvy, Waterhiasint, Nagblom, Sisal, Jongsnoekkruid en die Kasterolieplant het ‘n te hoë voginhoud en sal mees geskik wees vir bio-chemise opsettings metodes. Die totale gemiddelde koste van ontginning en vervoer van nie-houdagtige indringerplante tot by die energie aanleg was R 33/GJ, wat nagenoeg 50% duurder is as ander biomass roumateriaal (Bosbou residu en houtagtige indringerplante). Ontginning en vervoerkostes vergelyk ongunstig met die van biomassa roumateriaal tipes soos bosbou afval en houdagtige indringerplante. Wanneer die fisiese, chemiese en finansiele aspekte oorweeg word is Spaansriet, Soutbos en Parafienbos die beste spesies vir bio-energie roumateriaal. Sonder ‘n brandstof subsidie vanaf die NHB program is die ontginning van nie-houdagtige indringerspesies vir energie produksie nie finansieel haalbaar nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100116
This item appears in the following collections: