High-speed processing of woody stems with a flail hammer shredder

摘要

Willow and other woody crops could become an important source ofbioenergy, but harvesting and transportation remain difficult or expensive. A recently developed cutter-shredder-baler successfully harvested willow over small areas at reasonable cost. However, the shredder used flail hammers that required a high power input; the hammers were quite aggressive and were the source of losses during harvest. To improve and optimize the shredding process, a laboratory-scale flail hammer type shredder was designed and built. The main rotor was 1020 mm in length and 210 mm in diameter. It could be operated at rotary speeds between 1320 and 2390 rpm. Hammers of 1.7 kg were hinged to the rotor to test various levels of shredding. Other controllable parameters included: the space between the hammer and the hood, the position of a counter-knife and the rate of crop flow by adjusting the feeding conveyor speed or the willow mass processed. A data acquisition system measured continuously power and rotary speed. After shredding, the conditioned stems were sorted in five classes according to length: 0-250 mm, 250-500 mm, 500-750 mm, 750-1000 mm, and over 1000 mm. Results indicate that shredding energy averaged 3.1 kJ/kg on a dry matter (DM) basis of processed willow. High rotary speed (2390 rpm) produced the largest quantity of small particles (up to 58% less than 250 mm) and also the highest level of loss during processing (up to 17%). A low flail rotary speed and a wide spacing between the flails and the hood resulted in acceptable stem processing for subsequent baling while reducing energy requirement and DM loss.