Engineers at Iowa State University in Ames are testing a new machine that converts biomass to oil and then gas, for conversion to transportation and boiler fuels. The new bio-oil gasifier is part of a next-generation biofuels feasibility research project, funded by state and federal grants of nearly $1.5 million.
The bio-oil gasifier uses a process called pyrolysis — the application of heat without oxygen — that breaks down cellulosic agricultural wastes like corn stalks and wood chips into a thick brown oil. The oil is then sprayed into the gasifier, where the oil is vaporized under heat and pressure to become a synthesis gas made mainly of hydrogen and carbon monoxide. The synthesis gas can then be processed into transportation fuels or the raw material to power steam turbines for electricity.
The bio-oil gasifier has been operating since June and converting bio-oil made from pine wood into synthesis gas. Robert Brown, engineering professor and director of the university’s Bioeconomy Institute, says the bio-oil process short-cuts the process of breaking down biomass feedstocks into sugars for ethanol that has so far eluded a biological solution. “This helps us move toward cellulosic biofuels,” says Brown.
The bio-oil created in the first step by pyrolysis is a denser and liquified version of biomass that is easier to handle and transport than piles of corn stalks or wood chips. Brown says the Iowa State process is similar to nature’s way of breaking down cellulosic biomass, noting, “Nature uses high temperatures to quickly decompose biomass.” Once fully operational the pyrolysis device will produce some 4.5 pounds of biomass oil an hour
Nicholas Creager, a doctoral candidate in mechanical engineering and biorenewable resources and technology, built the reactor that converts the biomass oil into synthesis gas. The reactor is about three feet long and a foot wide and has an insulated stainless steel pipe some six inches in diameter. The pipe is made of silicon carbide and can operate at temperatures exceeding 1,800 degrees Fahrenheit. The reactor itself can contain pressures up to 700 pounds per square inch.
Song-Charng Kong, a mechanical engineering professor is leading development of a computer model that simulates bio-oil gasification. The model will test changes in temperature, pressure, and type of biomass to better understand and improve the gasification process. Another part of the project will develop a virtual reality model of a full-size biofuels plant to visualize and improve a plant before construction crews are ever hired.
“The physics and chemistry will be behind all these models and images,” says Kong. “We can use these models as a tool to understand what will happen as this technology is scaled up.”
Iowa State built the gasifier as part of a two-year, nearly $1 million grant from the U.S. Department of Energy. Another three-year, $450,000 grant from the Iowa Energy Center funds the simulation and virtual-reality model of bio-oil gasification.
The Iowa State engineers visualize raw crop biomass transported to small, local fast pyrolysis plants that convert the raw biomass into liquid bio-oil. The bio-oil would then be transported to bigger regional facilities for gasification and processing into transportation and boiler fuels.
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