Harvesting of invasive woody vegetation (Eucalyptus lehmanii, Leptospermum laevigatum, Acacia cyclops) as energy feedstock in the Cape Agulhas Plain of South Africa

Kitenge, Emile Museu (Stellenbosch : Stellenbosch University, 2011-12)

Thesis (MFor)--Stellenbosch University, 2011.

Thesis

ENGLISH ABSTRACT: This study is aimed at testing the possibility of using woody biomass from three invasive woody vegetation types (Spider Gum, Myrtle and Acacia) for production of bioenergy in the Cape Agulhas Plain. Physical recoverability of the woody biomass was studied by means of a semi-mechanized harvesting system to evaluate potential productivity, operational costs and the estimated yield energy gain. The system consisted of five components: manual harvesting, motor-manual harvesting, extraction, chipping and road transport. Data on the system productivity was obtained using activity sampling and time study techniques. Activity sampling was applied on manual and motor-manual harvesting in order to record harvesting time and standard time study techniques were used to obtain time data for extraction, chipping and road transport operations. Findings revealed benefits associated with the utilisation of invasive woody vegetation as energy feedstock. Therefore, the problem of exotic tree species can be dealt with by transforming them into energy feedstock, thus minimising the effect of invasive plants. At the same time essential biomass energy can be produced, while some of the cost of production could be offset by the benefits accruing from the biomass energy. The Acacia site, characterized by larger mature dense trees, had the highest amount of harvested biomass compared to the rest of the vegetation types (i.e. Myrtle and Spider Gum). The overall system productivity was found to be significantly influenced by a low equipment utilisation rate, estimated at 50%. This resulted in low production rates in general. The low supply rate of material to the chipper by the three-wheeled loader (1.5 – 5.3 oven-dry tonne per production machine hour) was found to be a major constraint in the chipping process, especially when considering that the chipper is potentially capable of chipping 4 – 9.4 ODT PMH-1 at the harvesting sites. This resulted in a significant energy balance of 463 GJ between output and input energy of the system. The overall total supply chain system costs based various road transport distances of species ranged from R 322.77 ODT-1 to R 689.76 ODT-1 with an average of R 509 ODT-1. This was found to be costly compare to the case where high machine utilisation rate and optimal productivity are used (average of R 410 ODT-1), biomass recoverability in this field trial had a higher total system cost due to low productivity, resulting from the low equipment utilisation rate applied.

AFRIKAANSE OPSOMMING: Hierdie studie was gemik daarop om die moontlikheid van die gebruik van houtagtige biomassa, afkomstig van uitheemse plantegroei (Bloekom, Mirte en Akasias) op die Agulhasvlakte vir bio-energie te ondersoek. Potensiële produktiwiteit, bedryfskostes en die geskatte energie opbrengs toename is gebruik, om die fisiese opbrengs van houtagtige biomassa van ʼn semi-gemeganiseerde ontginningstelsel te evalueer. Die stelsel het uit vyf komponente bestaan: Handontginning, motor-handontginning, uitsleep, verspandering en padvervoer. Data oor die stelselproduktiwiteit is uit tydstudie en aktiwiteit steekproewe verkry. Aktiwiteit steekproewe is toegepas op hand- en motorhandontgining om ontginingstyd te verkry, terwyl tydstudie standaardtegnieke gebruik is om tyd data vir uitsleep, verspandering en padvervoer werksaamhede te verkry. Bevindings het die voordele met bettrekking tot die gebruik van uitheemse plantegroei as energiebron bevestig. Die uitdaging rondom die verspreiding van uitheemse plantegroei kan dus aangespreek word deur dit as energiebron te benut. Die produksiekoste vir die toegang tot die bruikbare biomassa kan moontlik voorsien word uit die voordele van die gebruik van die energie wat uit die benutting van die biomassa verkry word. Die groter meer volwasse en digte Akasia opstand het die meeste ontginde biomassa gelewer vergeleke met die ander opstande in die studie (d.i. Mirte en Bloekom). Die stelselproduktiwiteit is beduidend beïnvloed deur die lae toerustinggebruik wat minder as 50% beloop het. Dit het ook laer produksievermoë in die algemeen tot gevolg gehad. In die verspandering werksaamheid blyk die lae invoer tempo (1.5 – 5.3 oonddroog ton per produktiewe masjienuur) van die driewiellaaier die beperking op die proses te wees, veral as in ag geneem word dat die verspandering teen 4-9.4 ODT PMH-1 kan geskied. Die resultaat was ʼn beduidende energie balans van 463 GJ tussen uitset- en invoerenergie van die stelsel. Die totale toevoerketting kostes gegrond op verskeie padvervoer afstande van die spesies was tussen R 322.77 ODT-1 tot R 689.76 ODT-1, met ʼn gemiddelde rondom R 509 ODT-1. Die resultaat is duur gevind in vergeleke met gevalle waar hoë masjiengebruik en optimale produktiwiteit (gemiddeld van R 410 ODT-1), moontlik was. Die biomassaherwinning in die studie het ʼn hoër totale stelselkoste gehad veroorsaak deur lae produktiwiteit, wat verwant is aan die laer toerusting gebruikstempo wat verkry is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/17873
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