Close to 90 percent of first-generation U.S. ethanol plants are dependent on natural gas to power operations, but the new generation of ethanol plants coming on line may deviate from that trend. Not only is Abengoa Biomass Energy LLC forging the path to commercial-scale cellulosic ethanol, it is taking a new road when it comes to fuel.
Besides cellulosic ethanol, the Hugoton, Kan., facility, located in the southwest corner of the state, also produces power, a segment of the facility that was brought on line in December. Abengoa began conceptualizing a plan for a joint power and cellulosic ethanol plant about 10 years ago. While navigating through pilot- and demonstration-scale developments, the master blueprint, which was modified over time, began to take its final shape.
The initial plan was to produce a significantly greater quantity of electricity—with the majority sold to the grid—but the U.S. DOE, which provided Abengoa a $132 million loan guarantee in August 2011, wanted a greater volume of liquid fuel production, says Christopher Standlee, executive vice president of operations. “We worked closely with the DOE, which has supported the project from day one, and they wanted the focus to be a little more on ethanol,” Standlee says. “But, they understood the desire to have a power side to provide our energy needs—both electric and steam.”
So rather than generate 120 MW of power and 17 MMgy, the facility modified plans to produce up to 22 MW and 25 MMgy ethanol. Construction began in spring 2012, and a milestone was reached in late December, when power operations commenced at the plant, and a small portion was sold to the grid. “This was a test—we needed to start it up and make sure it works before the rest of the plant comes on line, which we’re getting ready for,” Standlee says.
The power source will be primarily corn stover—the same feedstock used for liquid fuel production—wheat straw, prairie grasses, and, potentially, some dedicated energy crops such as switchgrass, as there is a switchgrass farm in the area, Standlee says.
Once fuel is brought on site, it will be treated and stored similarly, but some will be processed for ethanol and some for power. First, baled biomass is unloaded onto conveyors supplying grinding lines, or at a biomass storage field, both of which are constantly active. A grinding process begins with delivering bales to a single-process, in-feed conveyor line consisting of a pan-style chain conveyor capable of moving two side-by-side bales. The two grinding lines are equipped with an automatic bale destringer, rotochopper grinder with discharge conveyor and conveyor magnets, and dust hood on the in-feed. Next, displacement blowers pneumatically transfer the ground biomass to either the enzymatic hydrolysis plant weigh belt or biomass-fired boiler metering bins.
In addition, the remaining lignin from the ethanol production process—what’s left over after sugars are extracted from the feedstock—will be recycled back to the boiler as fuel. Fuel requirements for both the power and fuel component of the facility will top out at about 320,000 dry tons per year, with nearly 300 tons per day being combusted for power, plus the ethanol-making residues.
The power component setup consists of a Factory Sales & Engineering-supplied water tube stoker boiler, with a GE steam turbine that drives one GE-supplied generator. In its final move toward power production, wet stillage cake, or lignen, is fed by conveyors into vibrating grates and into the boiler, and lignen syrup is sprayed into the grate overfire air stream.
So why power up with biomass, rather than natural gas? “It’s just something we wanted to do,” Standlee says. “It’s always been our intention to produce renewable power, but it also spreads risk—it’s another product to sell, and you’re able to get long-term contracts in the power market. Primarily, we wanted to make sure we’re independent and not subject to natural gas markets. We have feedstock coming in, and lignin is a byproduct that is a good source for power, so it just seemed to make sense for us.”
Author: Anna Simet
Managing Editor, Biomass Magazine