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Description
The energy utilisation of shrub biomass requires specialised machinery adapted to shrubland conditions, enabling efficient harvesting and collection in cost-effective formats suitable for energy production. Proper handling is essential to minimise soil contamination and ensure the production of high-quality biofuels. Current harvesting technologies integrate clearing and biomass collection into a single operation, producing either baled or mulched material, each associated with distinct logistical requirements within the biomass supply chain.
This study presents a comparative analysis of mechanised shrub biomass harvesting using two different machines associated with different logistics systems: a López Garrido TBA-2300 harvester-mulcher and a Biobaler WB55 harvester-baler. The techno-economic evaluation was conducted in a natural mountain shrubland dominated by rockrose (Cistus laurifolius L.) in Soria (Spain). This species commonly occurs in association with oak, pine and holm oak forests on acidic or decalcified calcareous soils. In the Iberian Peninsula, rockrose occupies 51,377 ha as a dominant species and 680,856 ha as a secondary species (San Miguel et al., 2004; Montero et al., 2020), extending across wide areas of the central-northern, eastern and southern regions.
The López Garrido TBA 2300 harvester-mulcher, powered by a 200 hp forest-adapted tractor equipped with a reverse driving position, is driven by the power take-off and hydraulic system and has a working width of 2.3 m. Biomass is shredded by mobile hammers and conveyed by a screw and turbine into a 5 m³ front container for temporary storage. In contrast, the Biobaler WB55 performs shrub cutting, collection and baling in a single operation with a similar working width (2.3 m). The harvested biomass is compacted into cylindrical bales (Ø 1.2 m), automatically tied and discharged at the rear, facilitating handling, transport and storage.
The mechanised harvesting trial was designed to assess weight productivity (tWM/PMH, tonnes of wet matter per productive machine hour), area productivity (ha/PMH), operational costs (€/tWM) and harvesting efficiency (CE, %), defined as the ratio between collected biomass and the biomass available prior to harvesting. Operational times were recorded using the Valtra Connect telemetry system installed in the tractor, allowing remote monitoring of productive working hours, travelling speed, fuel and additive consumption, and spatial tracking of the operated areas.
Under similar stand conditions, the harvester-mulcher achieved significantly better performance than the harvester-baler. Biomass recovery reached 3.9 tWM/ha compared with 1.3 tWM/ha, while productivity was 1.4 versus 0.5 tWM/PMH. Harvesting efficiency was also higher (82% compared with 52%). These differences translated into substantially lower collection costs, with biomass harvested using the harvester-mulcher costing 48 €/tWM compared with 192 €/tWM for the baler, and productive hourly costs being 22% lower (82 €/PMH versus 105 €/PMH).
For biofuel production, the material was ground using a 30 mm screen and sieved through a 2 mm mesh to reduce fines. The resulting hog fuel was classified as class I1 according to ISO 17225-9. Rockrose represents a low-cost solid fuel characterised by low emissions of NOx, SO₂, HCl and minimal slagging, but its high ash content makes it more suitable for industrial than residential applications.
| Keywords | Harvester-baler; Harvester-mulcher; Scrub; Biomass |
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