SBIR-STTR Award

Unlike raw wood pellets, energy dense torrefied biomass pellets or briquettes share important traits with coal which make them a promising alternative clean fuel to use directly in coal plants. They are brittle (not fibrous, like raw pellets), so they can be pulverized just like coal before being fed into the coal boiler. They also have similar BTU content to coal and are water resistant, so they can be shipped and stored without cover, which means they don’t require the very expensive plant modifications necessary to burn raw wood pellets. However, economical densification of torrefied biomass without the use of a binder has proven to be the most challenging part of the torrefaction process world-wide, stagnating commercialization of this promising solid biofuel industry. The goal of this research is to successfully design a reliable, economical commercial densification system that consistently produces sturdy, water resistant briquettes without the use of binders. Low-cost forest waste residue will be used as feedstock. If successful, in the long term this technology could provide a commercial market for forest residue as feed stock for production of torrefied biomass fuel and greatly reduce costs incurred in forest and rangeland restoration efforts. When carbon neutral torrefied biomass briquettes replace coal, the negative effects of coal-fired power plant emissions such as carbon dioxide, sulfur dioxide, nitrogen oxides, mercury and other toxic metals present in the coal and coal ash will be mitigated. As feed stock for its creation of solid biomass fuel, HM3 Energy’s torrefaction technology uses renewable and sustainable forest waste, which can be obtained from undesirable species (such as western Juniper) present in semi-arid regions and through forest thinning and removal of accumulated forest debris. At this time, these juniper slash piles are usually burned in place. In its NIFA SBIR Phase 2 research (OREW-2011-02347), HM3 Energy demonstrated successful densification of torrefied pine and juniper forest residue on commercially available equipment using some crude modifications. The briquettes so produced were sturdy and water resistant, but not uniformly so. This project builds upon the knowledge acquired during that research to complete our technology development so that economical, trouble-free, and continuous densification of quality briquettes can occur using the same commercial equipment with optimized modifications. Using western juniper forest waste as feedstock, we will develop, test and optimize conditioning of the biomass and briquetting die to ensure proper continuous densification. This includes proper size reduction and moisture level of the torrefied biomass feed stock as well as temperature and pressure of the die.

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.