Some call bio-oil the poor relation of biofuels. There is no established market for it, and until recently there has been little advocacy on its behalf.
That may be about to change. Major oil companies are now working to develop bio-oil from cellulosic materials such as corn stalks, stems, leaves and other nonfood agricultural residues, as well as hardy grasses. ConocoPhillips recently entered into a research partnership with Iowa State University (ISU) and the National Renewable Energy Laboratory to evaluate the economics of numerous approaches to making advanced biofuels, including bio-oil.
"Right now, bio-oil can be used as boiler fuel and even burned in some kinds of gas turbines,” says Robert C. Brown, director of the Bioeconomy Institute at ISU and leader of the collaborative research. However, with further upgrading, bio-oil is suitable as a transportation fuel and could help displace petroleum products, he says.
"This research collaboration brings together the complementary strengths of a major energy company, a national energy laboratory and a land-grant university to advance these technologies and move them closer to the marketplace,” Brown adds.
Bio-oil is produced by a thermal conversion process called pyrolysis, which heats biomass particles in an oxygen-free environment to a carefully controlled temperature and then quickly cools the volatile materials formed during the reaction. This process creates three products: char, gas and an energy-rich liquid called bio-oil. Pyrolysis, based on the idea of the chemical decomposition of organic materials by applying heat, has been a common tool in the waste management industry for some time.
Bio-oil can be burned to produce heat and electricity or converted into transportation fuel at petroleum refineries. Bio-oil has about 40% of the heating value of diesel but can be used directly in diesel engines or gas turbines. It has a higher viscosity than diesel, so it must be pre-heated to lower the viscosity. Many see bio-oil as an intermediary to a number of higher-value chemicals, pharmaceuticals and food additives.
While initial biomass sources for bio-oil will likely be wood waste and cellulosic plant materials, researchers at Virginia Tech are developing a pyrolysis unit with the hopes to create bio-oil from poultry waste. Foster Agblevor, Virginia Tech associate professor of biological systems engineering, says that there is more than 5.6 million tons of poultry litter produced each year in the U.S., causing huge amounts of potentially dangerous waste with limited means of disposal.
Agblevor says that the current portable pyrolysis units are designed to heat the poultry litter until it vaporizes. The vapor is then condensed to produce bio-oil and a slow release fertilizer that is recovered from the reactor. The remaining gas can be used to operate the pyrolysis unit, making it a self-sufficient system.
If Agblevor can offer transportable pyrolysis units, farmers may not only be able to get rid of litter diseases but also create a new revenue source in the form of renewable energy.
"The type of poultry litter used will affect the amount and quality of the bio-oil produced and ultimately impact the producer's profitability,” Agblevor says. "Finding the right set of conditions for the poultry litter is key to the adaptation of this technology.”
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- November 2008