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Improving Quality and Quantity of Oils Produced from Biomass
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 2007 ASAE Annual Meeting 074150.(doi:10.13031/2013.23505)
Authors: Jason S Midgett, Chandra S Theegala
Keywords: waste treatment, thermochemical conversion, TCC, liquefaction, biomass, renewable energy, bio-oil, dairy manure
The need to decrease our dependence on foreign oil has never been greater. Record high gas prices cost Americans more than just dollars at the pump. Many states are announcing legislation for 25% of total energy to come from renewable sources by the year 2025. No one single alternative energy process exists that will meet this goal. Biomass, however, with its great abundance and high energy potential can lead the way. There are limitations; the high moisture content and low heating values reduce efficiency of energy production through direct burning. Thermochemical conversion (TCC) processes were heavily researched in the 70's with focus mainly in the gasification area. Another technology that emerged during this time was hydrothermal liquefaction (HTL); however, research was limited. Hydrothermal or direct liquefaction is a technique which uses high temperatures and pressures along with a process gas to convert biomass slurries into a higher heating value compound. Prior research suggests that this process is capable of converting 60 percent or more of the volatile solids in a feedstock into a raw oil product; with heating values as high as 80% of petroleum. Preliminary liquefaction or HTL research was conducted on a small batch scale, using a 300ml pressure vessel, equipped with temperature control, agitation, gas inlet and exit valves, a cooling loop system, and pressure transducer for monitoring. The feedstock studied for this paper is not only a large source of biomass, but also creates a significant waste problem. Separated dairy manure collected from the Louisiana State University dairy was dried and homogenized prior to testing. Operating parameters were in the range of 250-350ºC, initial pressure of 2.1MPa, retention time of 15 minutes, 20% total solids, and 0-4 grams of sodium carbonate as catalyst. Heating values as high as 34MJ kg-1 were obtained in 31 wt% yields on an organic basis. Further testing is needed to optimize conditions for maximum conversion to oil.