Abstract
The effects of processing conditions (closed versus open reactor, pressure, temperature, soaking time, biomass loading, heating rate, and fuel particle size) on product yields and char properties from constant-volume carbonization are reported. Increasing the pretest, inert-gas, system pressure from 0 to 2.17 MPa did not significantly affect product yields or char proximate analysis results. Increasing the reaction time from 30 to 190 min and the temperature in the 300–550 °C range improved fixed-carbon contents and reduced volatile matter while maintaining or slightly increasing the fixed-carbon yields. In contrast to flash carbonization or traditional carbonization observations where larger particles produce beneficial effects, constant-volume carbonization produced equal or higher fixed-carbon contents and yields from smaller biomass particles. This offers possibilities that smaller-sized, lower-grade biomass can be used to produce high, fixed-carbon yield charcoal. Under certain processing conditions, the particulate biomass underwent a transient plastic phase transition that produced a single solid piece of final char. The roles of processing conditions in the formation of this transient plastic phase are also discussed.