Session: 10-01 Hydrogen Energy, Alternative Fuels, Bioenergy, and Biofuels

Paper Number: 117026

117026 - Sensitivity Analysis of Process Conditions for Molten Salt Torrefaction 

Biomass torrefaction is a thermochemical treatment that improves the fuel and soil amendment properties of lignocellulosic material. Prior research on torrefaction has focused on torrefaction methods in which the treatment occurs in an inert, gaseous environment. Recently, thermochemical treatment of biomass in molten salts has been explored as a way to improve heat transfer to the biomass and catalyze the reaction. While the effect of the various process conditions that influence torrefaction, such as temperature, residence time, and particle size, have been studied for torrefaction in an inert, gaseous environment, the effect of the process conditions on torrefaction in molten salt is not as well studied.  As such, the present study investigates the sensitivity of process conditions on the resulting torrefied biomass characteristics for molten salt torrefaction. The molten salt consists of a binary blend of lithium and potassium nitrate. A Plackett-Burman screening design of experiments is used to investigate six process conditions: temperature, residence time, particle size, sweep gas composition, lithium content, and salt-to-biomass ratio. The resulting torrefied biomass was analyzed to quantify key biomass metrics for fuel and soil applications. The biomass metrics considered include fixed carbon content, higher heating value, chemical composition, pH, and mass yield. The relative importance of the process conditions on the metrics was calculated using a sensitivity analysis. The sensitivity analysis revealed that temperature and residence time are the two most dominant process conditions on all metrics except pH. The pH is highly sensitive to lithium content and insensitive to temperature. Particle size and lithium content are moderately influential on torrefaction severity across all metrics other than pH. Most metrics respond similarly to the process conditions except pH. Salt-to-biomass ratio and sweep gas are generally the least impactful process conditions for all metrics. The results can be used to help identify process conditions to achieve the desired qualities in the torrefied biomass.

Presenting Author: Lee Kohlin North Dakota State University

Presenting Author Biography: Student pursuing a Masters degree in Mechanical Engineering at North Dakota State University. Received Bachelors in Mechanical Engineering in spring 2022 from North Dakota State University. Research assistant, researching biomass torrefaction in molten salts.