A Liquid Torrefication Process for Producing a Storable, Energy-Dense Fuel From Biomass Feedstock

This paper discusses a novel process for creating torrefied wood pellets by using a liquid torrefication process. Torrefication is a type of pyrolysis process originally developed for converting wood to an energy-dense material with properties similar to coal that would be more compact and practical to ship long distances and store outdoors. Torrefied wood has been used in specialized metallurgy and other industrial applications, but wide-scale utilization of torrefication for biofuel production has not been commercialized. Virtually all of the processing methods used in the past involve exposing biomass to hot, inert gas in an oxygen free environment; this gas-phase torrefication has a number of drawbacks, including a net-negative overall energy balance; generation of polluted gas that is difficult to treat or control; safety issues associated with the intrusion of oxygen into the inert gas; large equipment size and associated initial capital cost; operating cost; and manufacture of a nonuniform product. This paper discusses a technique that uses a heat treatment fluid in lieu of an inert gas which has numerous advantages over gas-phase torrefication and resolves many of the problems resulting from the commercial application of gasphase torrefication. This process for converting biomass to biofuel using a liquid-phase torrefication process is being developed under the trade name CNFbiofuel™ where CNF is an acronym for Carbon Neutral Fuel. The CNF Biofuel process has been developed on a small scale and results of preliminary testing are presented. Measurements of the energy content for the proposed biofuel process indicate an 18% increase in energy content for torrefied versus untreated wood pellets. Furthermore, the energy density measurements of these treated samples were also consistently higher than the untreated samples. Measurements have also been performed in order to measure the hydrophobic ability of the treated pellets and the results indicate that saturation with water has only a small effect on energy content. The heating value was determined to be reduced by only 2.2% on average after soaking in water for six hours and then being allowed to dry for 12 hours. The potential advantages of liquid-phase torrefication over any currently available gas-phase process are discussed.