Bio-FLASHCHAIN® theory for rapid devolatilization of biomass. 8. Validations for hardwoods

Abstract

This study redevelops and validates a reaction mechanism called bio-FLASHCHAIN® (bio-FC™) to simulate the rapid primary devolatilization of any hardwood at any operating conditions. It presents evaluations with test measurements on 30 hardwood samples at temperatures from 300 to 1400°C; heating rates from 1 to 7200°C/s; contact times to 1800 s; and pressures from 0.01 to 0.13 MPa. Collectively, the test data cover the yields and elemental compositions of oils and char and the yields of CO, CO2, and H2O, but largely exclude light oxygenated gases and H2. Bio-FC™ accurately simulates complete product distributions for a broad selection of hardwoods with widely variable compositions, major component percentages, and AAEM levels, and correctly depicts how variations in heating rate, temperature, contact time, and pressure shift these distributions. This is the first time a reaction mechanism has displayed all these capabilities. The only persistent flaw in the data evaluations is that simulated H-contents of oils are low by approximately 1 wt%. Proximate and ultimate analyses, the percentages of cellulose, hemicellulose, and lignin, and AAEM loadings are required input. Nearly all kinetic parameters were specified directly from previous validations of the submechanisms for mineral-free and AAEM-loaded cellulose, hemicelluloses, and lignins. Cellulose devolatilization invokes both spontaneous and catalytic reaction channels but only spontaneous channels are activated for hemicellulose and lignin because AAEM loadings in hardwoods are moderate. According to bio-FC™, the distinctive devolatilization behavior of particular wood samples is due to acute sensitivities to both heating rate and AAEM loading in the cellulose-derived yields of oils and char, whereas compositions of oils and chars are most sensitive to cellulose percentages in woods. These dependences obscure the relations among cellulose percentages in whole woods and the contributions that cellulose makes to devolatilization products of whole woods, which vary widely among hardwoods. Sensitivities to variations in heating rate and AAEM loading are much weaker in hemicelluloses and lignins.