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Wood biomass is turned into industrial fuel through chipping. The efficiency of chipping depends on many factors, including chipper knife wear. Chipper knife wear was determined through a long-term follow-up study, conducted at a waste wood recycling yard. Knife wear determined a sharp drop of productivity (>20%) and a severe decay in product quality. Dry sharpening with a grinder mitigated this effect, but it could not replace proper wet sharpening. Increasing the frequency of wet sharpening sessions determined a moderate increase of knife depreciation cost, but it could drastically enhance machine performance and reduce biomass processing cost. Since benefits largely exceed costs, increasing the frequency of wet sharpening sessions may be an effective measure for reducing overall chipping cost. If the main goal of a chipper operator is to increase productivity and/or decrease fuel consumption, then managing knife wear should be a primary target. (C) 2014 Elsevier Ltd. All rights reserved.

The study tested the use of a trommel screen originally designed for compost materials to reject oversize particles from hog fuel, processed from several sources and by two different comminution devices. The experiment consisted in screening material previously comminuted by a convertible crusher, designed to use both hammers and knives. Three different feedstock types were used, and namely: discarded pallets, logs and branches from park maintenance. Each feedstock type came in two different qualities, depending on the tool used for comminution, i.e. hammers or knives. Trommel screen productivity varied between 4.2 t h-1, and 5.2 t h-1 of oven dry material. Screening hog fuel derived from pallets was 30% and 40% less productive than screening fuel derived from logs and branches, respectively. Screening cost varied from 16.2 EUR t-1 dry material in the case of branches, to 19.9 EUR t-1 oven dry material for pallets. Screening allowed an increase of fuel quality only when applied to pallet-derived hog fuel.

A commercial drum chipper was fed alternately and piecewise with poplar stems and poplar tops, in order to determine the effect of piece size and tree part on machine performance. Chipping stems required most of the available power (231 kW) delivered by the tractor, whereas chipping tops took about half that much. However, productivity was twice as high with stems, compared to tops (i.e. 25 and 11 t h-1 of oven dry wood, respectively). As a consequence, specific fuel consumption per unit product was 15% lower with stems, compared to tops - i.e. 0.61 and 0.72 L m-3, respectively. Mean feeding speed was 0.37 m s-1 for stems and 0.41 m s-1 for tops, but the difference was not significant (p = 0.1677). Productivity and fuel consumption were strongly related to piece size, but tree part had its own additional effect, independent from size and possibly related to form. When chipping tops it is advisable to feed more pieces at a time, in order to partly compensate for the effect of piece size. Operators expecting to chip primarily small-size materials may acquire special chipper versions with wider drums and additional side rollers, for smoother mass feeding. oThe same chipper was tested with poplar stems and tops.oChipping stems resulted in higher productivity and lower fuel consumption.oChipping stems required most of the available tractor power.oChip particle size distribution was about the same for both feedstocks. © 2013 Elsevier Ltd.

In Italy, olive tree groves may offer up to a million tonnes of dry biomass per year as pruning residue. Searching for a cost-effective way to tap this potential, the authors tested a new machine, capable of recovering pruning residue at the same time as pruning. The pre-commercial prototype was tested on four different plots and compared to a simpler tractorbase mechanical pruning unit. The authors conducted detailed time-studies in order to determine machine productivity and residue recovery cost. The integrated machine can treat between 0.2 and 0.6 ha h(-1), producing between 0.33 and 1.03 tonnes of fresh residue hour(-1). Its integrated residue recovery function does not slow the pruning, which actually proceeds faster than with the tractor-base unit, due to the more efficient multiple-disc cutting bar. The marginal cost of residue recovery hovers around 40-45 (sic) fresh tonne(-1). However, the new machine must not be considered just as a biomass harvester, but rather as a mechanical pruning unit with an integrated biomass recovery function. Its main benefit derives from the capacity of performing a very effective mechanical pruning, and the residue recovery function is a secondary benefit yet unavailable on standard pruning machines. Its deployment must be seen in the context of a general effort to modernize olive grove management and to develop an integrated biomass production system, rather than as a further attempt to build a specialised biomass supply chain.

The Authors tested a complete new system for recovering wood fuel from the termination of depleted orchards. This operation can generate between 25 and 80 fresh t ha?¹, that can be directed to the growing bioenergy sector. The new system is based on highly-mobile low-investment general-purpose equipment, which allows containing operational cost and speeding relocation between work sites. The new residue collection system is quite flexible, and achieves cost-effective recovery on relatively small fields, often smaller than 1 ha. Under the conditions of the study, trees are cut, chipped and delivered at a cost between 35 and 40 EUR t?¹ (40% water mass fraction), provided that fields are within a 20 km distance from the biomass plant. Use of a standard drum chipper results in a better product quality than if a grinders is used, as is the case for conventional orchard removal operations. Feeding the chipper with a separate loader allows a significant cost reduction, provided that the field offers at least 25 t of fresh wood. In the future, use of remote controls and electronic tethers may allow a further cost reduction, which is estimated at 15%.

The authors tested a 409kW forager turned into an industrial chipper through a special conversion kit. Conversion was temporary, and the forager could be returned to its original occupation with one day of work. The converted forager proved as effective as a dedicated chipper of the same power. Net chipping productivity varied between 25 and 33greenth-1. Productivity was highest with poplar tops and lowest with pine tops. Fuel consumption ranged from 1.6 to 1.8lgreent-1. Fuel consumption did not change with tree species, but increased significantly with knife wear. Temporary conversion allowed a better depreciation of the invested capital and resulted in a 25% reduction of unit chipping cost. The converted forager proved an ideal solution wherever the production of wood chips was a complementary business within the scope of a larger agricultural economy. In technical terms, this machine offered the combined advantages of road-capability and good off-road mobility, allowing low-cost independent relocation and effective in-field chipping. © 2013 Elsevier Ltd.

The Authors surveyed 6 industrial chipping operations for a whole work year, collecting data about machine usage, product output, fuel consumption and chipper knife wear. Despite the challenging work conditions offered by mountain operations, industrial chipping contractors manage to achieve a high machine use, ranging from 500 to over 2,500 h year(-1). Product output varies between 18,000 and over 120,000 m(3) loose chips per year. In order to acquire enough jobs, operators may travel between 1,500 to over 20,000 km in a year. Industrial chipping contractors adopt different operational strategies to achieve their production targets, and they equip accordingly. Some operators prefer to tap smaller local areas and opt for smaller tractor-powered chippers, which are less powerful and productive than larger independent-engine units, but cheaper and capable of negotiating low-standard forest roads. Others prefer to explore larger areas and achieve higher product outputs, and they opt for larger independent-engine chippers, often mounted on trucks. Long term productivity varies with machine type: tractor-powered units produce between 40 and 50 m3 loose chips per hour, whereas larger independent-engine chippers produce between 60 and 90 m3 loose chips per hour. Specific fuel consumption is about 0.5 L diesel per m3 loose chips, regardless of chipper type. A sharp knife set can process between 200 and 1,500 m3 loose chips before getting dull. Disposable knives last longer and are cheaper to manage than standard re-usable knives. (C) 2014 Elsevier Ltd. All rights reserved.

The termination of a fruit orchard generates a considerable amount of residues that can be used as fuel in biomass-fired power plants. Various studies have explored the separate collection of the above-ground tree portion and the rootstock. The present work analyses the potential of complete-tree harvesting (aboveground biomass and rootstock) from a depleted peach orchard and compares this technique with the collection of the aboveground biomass (pruning residues and stems) only. Complete trees were extracted and piled, then ground into chunks and cleaned to reduce contamination with dirt and stones. As an alternative, trees were cut, stacked and chipped, leaving the rootstocks in the ground for later disposal. Extracting complete trees and piling them at the field's edge proceeded at a pace of ca. 1 ha day-1. Grinding and cleaning allowed reducing soil contamination by 10-15%. The study showed that complete-tree harvesting is a viable approach to containing the costs of biomass recovery from depleted orchards. Supply chain efficiency is maximized by including biomass compaction during the loading of trucks.