Chipping operations and chip quality from mixed hardwood forests for bioenergy

Abstract

A mechanized 1 harvesting system combined with whole-tree chipping was investigated on two harvesting sites in central and eastern Ohio, USA. Production and machine rate data of the operations were collected through time-motion studies, with chipping sub-tasks (elements) defined as: feeding, chipping, and loading. Chipping cycles averaged 21.5 min to produce 13.3 dry (21.3 green) tonnes per truckload, providing an hourly rate of 37.3 dry tonnes per productive machine hour (PMH), excluding delays. Total cycle time including truck delivery averaged 183 min, resulting in an hourly production rate of 4.4 dry tonnes/PMH delivered. The complete harvesting system included one feller-buncher, two grapple skidders, and a chipper. Harvesting cost ranged from (USD) $22.2 to $27.8/dry tonne, at the landing. Trucking cost was $0.48/dry tonne/km for the average hauling distance of 78 km. The total delivered cost amounted to $59.9–$65.5 per dry tonne. Chips were sampled from the operations and characterized to evaluate their quality as a bioenergy fuel, according to ANSI Standard AD17225–4:2014 Solid Biofuels. Results of chip properties indicated 37.5% green moisture (i.e. water mass fraction), 0.212 g/cm3 bulk density, 10.5% bark content, 0.49% ash, and 18.59 MJ/Kg calorific heating value. Size distribution of wood chips was categorized into small (3–<16 mm) 46%, medium (16–<45 mm) 45%, and large (45–63 mm) 3%, respectively. Fines (<3 mm) composed less than 1% while 4.5% were oversize (>63 mm). These whole-tree chips were found to meet the requirements of the highest grade (A1) of the U.S. wood chip fuel quality standard for bioenergy applications.