If you grew up before World War II, you probably remember “town gas.” Until the 1940s, town gas — also known as coal gas or manufactured gas — was made by small, local gas works and piped to businesses and homes for lighting and cooking. The fuel was manufactured by converting coal or wood into synthesis gas, a process called gasification. After the war, town gas was replaced by cheaper natural gas.
Now, high natural gas and oil prices are sparking renewed interest in small-scale gasification. This time around, though, the feedstock isn’t coal but renewable biomass — plant and animal materials such as crop residue, manure and wood waste. Processing companies that generate their own low-value biomass coproducts are especially interested in this emerging technology, says Michael Sparby, AURI project director.
For example, an ethanol plant in Little Falls, Minn., is building an on-site gasifier that will convert wood waste and distiller’s grains to gas for generating electricity and heat. The University of Minnesota, Morris is building a corn stover gasification unit, which will produce synthesis gas to run the college’s steam plant.
Other state groups are looking seriously at gasification. A Williams, Minn., grass seed cooperative recently tested seed-chaff gasification. Instead of going to a landfill, the chaff could be used to generate electricity for the seed cleaning plant. Minnesota’s sugar beet industry has started talking about gasifying beet pulp, Sparby says. The soybean crushing sector, which already co-fires hulls, is also asking about gasification. A local Indian tribe is considering wood gasification, and a small Minnesota town is studying a plan to gasify corn stover to make methane for an industrial park.
What’s behind this swelling interest in biomass gasification?
“Burgeoning world demand for natural gas, accompanied by sharply-rising prices,” says engineer Cecil Massie, a renewable energy systems expert at Sebesta Blomberg, a Roseville, Minn. engineering firm that specializes in energy utilities. “That’s creating opportunities for these other fuels.”
The average annual price of natural gas delivered to commercial customers rose 42 percent between 2000 and 2004, according to the Energy Information Administration (EIA). In 2005, prices soared, hitting an average of $14.61 per thousand cubic feet in October — up 60 percent from the previous October. For 2006, the EIA is forecasting that commercial natural gas prices in the Midwest will range from $11.56 to $13.31 per thousand cubic feet.
Cheaper to make syngas
At those prices, manufacturing synthesis gas from renewable biomass is cheaper than burning natural gas, Massie says. Last year, for example, AURI and Sebesta Blomberg helped the city of Morris project the costs of a municipal gas utility that would produce methane from corn-stover gasification. The proposal called for the city to invest $9 million to produce 500 million cubic feet of pipeline-quality gas for use by the local ethanol plant and other light industry. The study estimated that the city could manufacture methane for $10.44 per million British thermal units. That’s nearly 30 percent less than the average 2006 contracted price, according to Massie.
The economics of renewable syngas production look “attractive when competing with natural gas,” says Darren Schmidt, research manager for the University of North Dakota’s Energy & Environmental Research Center (EERC), a national leader in biomass energy systems. That’s especially true for facilities that already have gas boilers and infrastructure, which could be retrofitted for syngas, he says. In addition, Massie says, syngas supply and price would be more predictable and stable than natural gas.
Small systems most promising
Schmidt and Massie say biomass gasification is best suited for relatively small power systems — between about 5 kilowatts and 5 megawatts. That’s because biomass is a widely-dispersed, bulky, low-energy fuel, which is very expensive to collect and transport. “It’s not economical to haul biomass more than about 20 miles,” Massie says. Small gasification systems could be customized to use whatever biomass was available in the immediate area. And the power could be consumed on site.
“Where you really gain an advantage is when you have a manufacturer that produces its own biomass waste stream,” Schmidt says — especially if it costs money to dispose of the waste. For example, EERC is working with a Nevada roof truss manufacturer, which is building a 300-kilowatt gasification system. The plant will gasify its leftover wood scraps, generating its own renewable power to run the manufacturing operation.
In Minnesota, biomass gasification has great potential “for every one of our ag processing plants,” Massie says. “All of them produce coproducts that earn very little money.” He says materials such as barley, oat and soybean hulls, beet pulp, distiller’s grains, vegetable processing residues and mill waste often sell for “far less money than the value of the energy they could produce for the plant.”
Minnesota is set to become a leading producer of dedicated energy crops, too, says AURI’s Al Doering. Hybrid poplars (the state already has 25,000 acres), willows and switchgrass could all support a biomass gasification industry, says Doering, who is doing a market analysis of Minnesota gasification opportunities.
Eventually, renewable syngas will be converted not only to power but to chemicals, just as natural gas is today. “That’s where you’re going to get the greatest added value,” Schmidt says. In the next few years, biomass gasification technology will come into its own, Schmidt says, and “within 10 years, you’ll see lots of demonstration plants in place.”