Evaluation of Asparagus Fern and Rhizome Residues as Bio-Energy Source

Development of renewable energy has been expected instead of oil in the world. Biomass has attracted attention as source of renewable energy. Asparagus is harvested except spring from the commercial demand in Japan. When asparagus is harvested from late autumn and early spring in greenhouse, it is necessary to heat both in bed and inside greenhouse after transplanting of rootstocks. Usually, yellow-colored ferns are removed in autumn. Besides, rhizome (rootstocks) become residue after harvest in the greenhouse production. We tried to make pellets from yellow-colored ferns and rhizome and energy generation was evaluated. Yellow colored ferns and rhizomes were collected from IACT field and rootstocks were obtained from 1-year-old plants on 13 November 2008. After drying, ferns and rhizomes were smashed. Dried fern could be smashed smoothly, however, rhizomes were sticky. For pellet formation, water content was important. In yellow-colored fern, pellet formation succeeded when water content was 14%. In dried rhizomes, pellet formation was not carried out at 13% water content and pellet was formed at 6.6% water content. Physical characteristics of fern-pellets and rhizome-pellets were measured and combustion test was performed by heater for woody pellet. Ash content was 5.4% in fern and 23.6% in rhizome, and they were obviously higher than that in wood, less than 1%. Continuous combustion was not performed because of high ash content in both materials. Energy generation values were 18.6 MJ/kg in fern-pellets and 15.7 MJ/kg in rhizome-pellets. These values were a little small compared with that of woody pellet, 20.1 MJ/kg. Asparagus production system in greenhouse with warming by biomass energy will be examined in Hokkaido University.