Effect of Processing Conditions on the Constant-Volume Carbonization of Biomass

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