Carla Nati

Performance and energy efficiency of alternative comminution principles: Chipping versus grinding

Abstract Comminution is a critical process in biomass supply chains and can be conducted with either chippers or grinders. These machines use different work tools(knives and hammers, respectively) and are applied to different feedstock types, but few studies are available on the inherent differences between the two technologies. A versatile grinder, alternatively equipped with hammers and knives, was studied to investigate the effect of tool type on machine productivity, fuel consumption, and product quality.The machine was powered by an agricultural tractor rigged with a flow meter, a torque meter, and shaft revolution meter for determining fuel consumption, power output, and engine speed. Three different feedstock types were processed: discarded pallets, solid logs, and residues from park maintenance, the latter consisting of branches from ornamental tree and shrub species. Depending on feedstock type, the knife configuration was 30–80% (average 50%) more productive than the hammer configuration and required 15–30% (average 24%) less energy per unit of product. Fuel consumption per dry ton was 30–75% (average 52%) higher for the hammer configuration. That held true for all feedstock types. Product quality was better for the knife configuration, except for park maintenance residues. In general, hammers should be limited to product with severe contamination that prevents the efficient use of knives.

Work quality and veneer value recovery of mechanised and manual log-making in Italian poplar plantations

In Italy, poplar plantations represent an important source of wood products, and especially of high-quality veneer logs. These plantations offer favourable conditions to the introduction of forest mechanisation, and especially easy access and industrial management. However, owners fear that mechanised log-making may cause value losses, due to poor length measurement, log surface damage and improper grading. This study compared the performance of manual and mechanised log-making on ten commercial operations, in order to determine the occurrence and the severity of possible value losses due to product degrade. The study found that length measurement errors are smaller for mechanised processing, while the frequency and severity of log surface damage are the same for both treatments. In three cases out of five, mechanised log-making extracted the same value from the stems as manual log-making: in the remaining two, differences were very small and went opposite directions. Significant differences were found between operators, stressing the importance of operator skills and motivation. In fact, the log-making specifications and the pricing structure applied to poplar processing are relatively simple and are unlikely to challenge the ability of personnel and equipment. At present, most Italian poplar growers are unaware of the potential offered by modern technology, whose intelligent use would boost value recovery and decrease harvesting cost. Significant benefits may derive from the introduction of optimised bucking, which may help shifting to a more articulated and rewarding product strategy.

Options for the Mechanized Processing of Hardwood Trees in Mediterranean Forests

Abstract In this study, three different processing options for trees yarded whole at the roadside in a beech thinning operation, typical of the Italian Apennine mountain, were studied. Trees were delimbed, crosscut, and stacked, respectively, by a four- man crew equipped with chainsaws and a hydraulic loader (motor-manual control thesis), by a small stroke harvester head mounted on a light excavator, and by a dedicated 6-wheel harvester. Under the conditions of the study, mechanized processing was less expensive than the motor-manual control thesis, regardless of the specific option. Cost reductions amounted to 27 percent and 38 percent, respectively, for the light processor and the heavy harvester. Annual usage is a crucial factor for the introduction of industrial mechanization: the heavy harvester is preferable to motor-manual processing only when the annual output exceeds 5,000 metric tonnes (t) per year. When this figure grows above 13,000 tonnes per year, it will profitably replace the light processor, not just for monetary gain, but for the inability of the lighter unit to cope with such a heavy workload. On the other hand, the light processor was always less expensive than the motor-manual control, while requiring an additional investment of only (US)

Wood biomass recovery from chestnut orchards: results from a case study

47,000. Therefore, the acquisition of a light processor represents the most viable option, at least for immediate deployment. Its productivity closely matches that of the yarder, allowing for hot-deck (synchronic) operation. All of the options can efficiently process beech trees within the full range of diameters normally obtained from thinning operations, and up to a 30 cm diameter at breast height. As expected, productivity increases with tree size, and even more so for the mechanical units, which normally handle just one or a few trees at a time. Under the conditions of this study, both mechanized options have a potential for bringing processing cost near (US)

Using modified foragers to harvest short-rotation poplar plantations

10 per tonne, which is half the cost of traditional motor- manual processing.

Wood chips size distribution in relation to blade wear and screen use

Sweet chestnut has been for many centuries essential to human diet in large areas of Southern Europe. Its cultivation was abandoned in the last century, but is at present under restoration for socioeconomic reasons, representing also an opportunity for allocating woody residues to the energy sector. A little is known from the literature about sweet chestnut pruning, and the aim of the study was to assess the biomass yield and quality, the productivity and costs of the system as well as its energetic balance between inputs and outputs. The yield of recovered wood material amounted to between 22.3 tonnes of dry matter per hectare (tdw ha−1) and 33.3 tdw ha−1. Time consumption for pruning has been related to trees’ DBH, so detecting a linear relationship, although weak, between tree size and the time spent for maintenance. Productivity expressed as tdw per hour varied according to the site and the operating systems adopted accordingly. Costs for the whole chain, excluding transport to the plant facility amounted to 113 or to 430 € tdw−1 depending on the terrain relief and the presence of an underbrush to be cleaned. Wood chips distribution in size classes provided a material unsuitable for non-industrial due to the percentage of oversize particles, probably due to the high presence of twigs. The energy ratio resulted of 30:1 and 21:1 for the two sites. Transportation had the main impact in terms of energy, followed by extraction and chipping phases.