Forest understory is an under-utilized woody biomass totaling about 300 million dry tons in the southeastern U.S. alone. One percent recovery of this potential source of energy amounts to about 25 billion Btu per year. Traditional forest management practices require controlled understory burning. To recover the understory as an economical fuel, this raw biomass must be processed to overcome its inherent problems, such as, low bulk density, low energy density, and poor handling traits during transportation and long-term storage. To this end, a hybrid torrefaction process is proposed to convert the forest understory to a & quot;universal fuel & quot; with desirable properties. This woody biomass intensification approach facilitates Forest Understory Energy Logistics (FUEL) from the grass root of the supply chain for a wide range of biomass energy applications. The goal of this project is to design, construct and test a bench-scale FUEL system that is effective, robust and scalable for practical applications. The FUEL system relies on a primary conversion vessel supported by a number of auxiliary unit operations. This integrated system involves several reaction steps under continuous-flow processing, semi-automated conditions. To feed this system, a variety of woody species is harvested via baling machines, and then shredded and homogenized by comminuting devices. Raw, shredded biomass enters the top of the primary vessel and into the drying zone. The dried biomass proceeds down to the torrefaction zone where the bonded water and 1/3 of the biomass will be thermally driven off as volatile gases. At the base of the torrefaction zone, the greater portion of the feedstock will be removed as torrefied stock (BioCoal) and delivered to pellet-making machines. This pelletized BioCoal retains 90% of the original energy, but in a more dense and durable form with an intensification factor of about 3. Beneath the torrefaction zone is the pyrolysis zone, where a lesser portion of the feedstock is subjected to even higher temperatures. SynGas, bio-oils and other refinable products are produced. In the combustion zone, the last remaining volatile components are driven off and combusted. The remaining char is directed to the reduction zone where ashes are filtered off and the BioChar removed from the vessel and quenched. The inputs to the FUEL system are comminuted woody biomass and air. There are several output products BioCoal, SynGas, BioChar and Ash. The entire process is driven by about 1/10th of the energy in the incoming biomass. The conditions of each process step need to be optimized for ideal distribution of these products in connection with intended applications. The correlations of the physical and chemical characteristics of the woody biomass feedstock with the reactor design and operating conditions will be determined to adequately establish cost/benefit ratios. At the completion of the project, the performance of the proposed the FUEL system will be demonstrated to show marked improvement in biomass specifications and cost benefits throughout the supply chain.
