CONSOLIDATION MECHANISMS STUDY OF BIOCHAR AND DOUGLAS FIR SLASH DURING PELLETIZATION

Hanwen Zhang

Biochar derived from pyrolysis of biomass has been proved to be effective to improve the soil quality, conserve water, sequester carbon and produce renewable energy. Limitations occur in the transportation and handling of the high carbon material as biochar is in particulate form and has low bulk density. Attempts to overcome these challenges led to an increasing interest into the biomass densification technologies such as pelletization and briquetting, the present study investigated the consolidation mechanism of biochar and Douglas fir slash (stem and leaf materials) during pelletization from several aspects. The single pelleter unit was utilized to perform the compaction and extrusion tests on biochar and Douglas fir slash grinds, Analysis of variance showed that biochar had a significant effect (P<0.05) on both of the compaction and extrusion energy consumption, which increased with higher biochar content. Process temperature significantly influenced the compaction energy consumption, which increased with higher temperature in the range from 80 to 140oC. Results also showed that stem and leaf materials had a significant influences on the compaction process but minimal influences on the extrusion process. To understand how the friction between the biomass particles and the die surface wall behaves during the compression, an external load cell was set up at the bottom of the single pelleter unit to measure the die wall friction during compaction. Results showed that biochar consumed a higher frictional energy followed by stem and leaf materials during the compaction process, findings also showed that the compression behavior of the binary and ternary mixtures is acted as the intermediate materials between those plain mixture components. The pressure and relative density derived from compression curves were then incorporated into several widely used compaction models. Results demonstrated that Kawakita provides the best fitting for both of the sinlge components and binary mixtures, the model constants showed that biochar compact had the highest failure strength. The fourth study compared the specific energy consumption of biomass pelletization between the single pelleter unit and industrial pellet mill, the influences of the binder and lubricant addition on the pellet output and durability were also examined.

CONSOLIDATION MECHANISMS STUDY OF BIOCHAR AND DOUGLAS FIR SLASH DURING PELLETIZATION

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