Effects of grate size on grinding productivity, fuel consumption, and particle size distribution

Matching the right feedstock quality to a biomass conversion technology effectively facilitates the energy conversion process and improves the economic feasibility of forest biomass for energy production. In this study, we conducted a controlled experiment on a horizontal grinder to evaluate the effect of three different grate size combinations on grinding productivity, fuel consumption, and particle size distribution for two different biomass types (mixed conifer slash and hardwood whole trees). Mixed conifer slash resulted in higher grinding productivity (39.0 to 45.1 bone dry US tons/h) and a lower fuel consumption rate (0.57 to 0.90 gal/h) than hardwood whole trees. Small grate size configurations (2-, 3-, and 3-in. holes) in the grinder had low grinding productivity and higher fuel consumption rates compared with large grate size configurations (3-, 4-, and 4-in. holes). High grinding productivity and low fuel consumption rates were accomplished by using a new anvil type that is manufactured with holes in the plate. The study also showed that production of small feedstock particles (length,<2 in.) from logging slash was operationally feasible by using small grates and a newly designed anvil. Additional research is needed to further control oversized materials and improve our knowledge about the effect of moisture content on grinding productivity, especially with a wide range of grate size combinations.