Development and Evaluation of Continuous Biomass Torrefaction and Densification Process for Commercial Briquette Production

Successful use of energy dense torrefied biomass to produce drop-in coal replacement fuel has proved difficult for two reasons: 1) overheating of dies during densification, and 2) inability to produce water-resistant pellets. As a result, most torrefaction companies use a binder to reduce the die friction and/or to make densified product water resistant. Also, the majority of torrefaction companies use clean wood chips or sawdust as feedstock, adding to production costs. In Phase I research HM3 Energy had encouraging results producing sturdy, somewhat water-resistant briquettes on commercial densification equipment with batch-torrefied juniper forest waste. Die temperature control was tested and an inexpensive post-conditioning process that doesn't use binders was implemented. The briquettes performed well in 6' drop tests after 24-hour water soaks.Economical and reliable torrefaction and densification are key to commercial briquette production. We have designed a bigger 500 lbs./hour mass flow torrefier for easy scale up. It will be installed at a new demonstration facility with other key pieces of commercial size or easily scalable commercial design. During Phase II we will link together these key parts of our technology: torrefaction, densification and post-densification conditioning into one continuous operation to determine effects on torrefier residence time and temperature, die temperature control and post-densification conditioning, to consistently produce truly hard and water resistant briquettes. The briquettes will be test burned at a pulverized coal combustion facility which models the operation of large pulverized coal power plants. We will also determine uniform hot gas distribution across the bed for scale up of the torrefier to 2 tons/hour. Success could lead to significant production cost savings necessary to make torrefied biomass a viable drop-in coal replacement fuel.