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

[摘要] ENGLISH ABSTRACT: This study is aimed at testing the possibility of using woody biomass from three invasivewoody vegetation types (Spider Gum, Myrtle and Acacia) for production of bioenergy in theCape Agulhas Plain. Physical recoverability of the woody biomass was studied by means ofa semi-mechanized harvesting system to evaluate potential productivity, operational costsand 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 usingactivity sampling and time study techniques. Activity sampling was applied on manual andmotor-manual harvesting in order to record harvesting time and standard time studytechniques were used to obtain time data for extraction, chipping and road transportoperations.Findings revealed benefits associated with the utilisation of invasive woody vegetation asenergy feedstock. Therefore, the problem of exotic tree species can be dealt with bytransforming them into energy feedstock, thus minimising the effect of invasive plants. Atthe same time essential biomass energy can be produced, while some of the cost ofproduction could be offset by the benefits accruing from the biomass energy.The Acacia site, characterized by larger mature dense trees, had the highest amount ofharvested biomass compared to the rest of the vegetation types (i.e. Myrtle and SpiderGum).The overall system productivity was found to be significantly influenced by a low equipmentutilisation rate, estimated at 50%. This resulted in low production rates in general. The lowsupply rate of material to the chipper by the three-wheeled loader (1.5 – 5.3 oven-dry tonneper 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 ODTPMH-1 at the harvesting sites. This resulted in a significant energy balance of 463 GJbetween output and input energy of the system. The overall total supply chain system costsbased various road transport distances of species ranged from R 322.77 ODT-1 to R 689.76ODT-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 410ODT-1), biomass recoverability in this field trial had a higher total system cost due to lowproductivity, resulting from the low equipment utilisation rate applied.

[发布机构] Stellenbosch University