And the winner is . . . the microbes. After more than a year of study, the St. Paul Port Authority has recommended that the Midway area’s Rock-Tenn plant pursue anaerobic digestion (AD) as a fuel source for its paper recycling operation.
AD is a process whereby microorganisms break down organic material, turning it into biogas, which consists of methane and carbon dioxide. The resulting product can be used to generate heat and electricity. AD occurs naturally, and the process can be harnessed with special equipment designed to capture the gas that would otherwise escape into the atmosphere.
An AD plant, according to the Port Authority’s recommendation, would be located somewhere in outstate Minnesota, near a source of organic waste — most likely an ethanol plant. The biogas generated there would not be used directly by Rock-Tenn, which would continue to burn natural gas at its St. Paul facility. Instead, the production of biogas would enable the company to qualify for a reduced price on natural gas, making that relatively clean fuel more economically viable.
Nina Axelson, who coordinates public outreach for Rock-Tenn’s fuel study, compared the use of biogas generated for Rock-Tenn’s energy needs to that of electricity generated by wind power.
“If you ‘buy’ electricity that’s been generated by wind, there isn’t a power line that goes from the wind turbine to your house,” she said. “Instead, that power goes into the grid, where it replaces electricity you use that would otherwise have been generated using fossil fuels.”
Some of the biogas produced at an AD plant would be used to fuel the organic processing operation at that site — for example, an ethanol plant, which turns corn into a product that can be mixed with gasoline and burned in cars and trucks.
Waste from the plant would undergo AD to produce biogas. The excess gas, which is about 60 percent methane and 40 percent CO2, would be “cleaned” so that it’s the same quality as natural gas. It would then be put into the network of gas pipelines. Thus, the amount of natural gas used would be decreased by the use of biogas.
The facility would not change at Rock-Tenn, which has been burning natural gas and fuel oil in its on-site boilers since losing its source of steam heat from Excel Energy’s coal-powered High Bridge plant a year ago. What would change is the financial picture, according to the Port Authority’s Pete Klein.
Generating biogas to offset the use of fossil fuels (natural gas and fuel oil) would qualify an AD facility for “carbon credits.” These credits would be used to reduce the cost of energy to Rock-Tenn, enabling the company to use natural gas as its primary source of energy, with fuel oil as a backup.
Rock-Tenn has been looking at alternative fuels for the last year. That effort was under-written by the Minnesota legislature, which appropriated $4 million to study the matter and appointed the St. Paul Port Authority to direct the study.
One component of the legislation was the creation of a community advisory panel to assure broad input in decision making. The panel — RCAP — has been meeting for a year.
RCAP and the Port Authority assessed the viability of a wide variety of renewable fuel sources, including solar, wind and biomass. The latter category includes agricultural residue (e.g., oat hulls, corn stover and cobs, straw), energy crops (e.g., willow, perennial grasses), urban and manufacturing wood waste, and processed garbage, or refuse-derived fuel (RDF). RDF created the most controversy, and it does not appear in the Port Authority’s final recommendation.
That recommendation is actually three-fold. In addition to AD, the Port lists two other viable options: a co-generation facility at Rock-Tenn that would use natural gas to fuel the company’s burners and would also generate electricity, and gasification of renewable biomass.
Even after substantial energy conservation efforts, Rock-Tenn’s fuel needs are considerable, and the AD facility being planned would be the largest in the United States. According to Klein, the plant would cost $40 to $70 million to build. That kind of capital outlay would require federal assistance, he said, and the Port plans to submit an application for financing to the U.S. Department of Energy by the end of September.
AD works with a variety of organic materials. The leading candidate for a Minnesota processing facility, according to Klein, is residue from the manufacture of ethanol, though a manure treatment plant is also being considered. He added that AD, in addition to cutting methane emissions at an ethanol plant, would reduce water consumption by up to 50 percent.
Regardless of the fuel Rock-Tenn uses, the company’s boilers produce a significant amount of waste heat — enough, said Klein, to accommodate as many as 300 buildings along the Central Corridor. One hoped-for outcome of the study is capturing and redirecting much of this waste heat.
Bob Carpenter, Rock-Tenn’s assistant general manager, said that when the company was purchasing steam heat from Excel, it paid a flat rate. By using its own onsite boilers, which burn natural gas and fuel oil, Rock-Tenn is subject to market fluctuations in the price of those fuels. That reality has prompted the company to increase its energy efficiency. Carpenter said Rock-Tenn will spend $800,000 this year and $2 million next year to improve the plant’s efficiency, efforts that so far have resulted in a 23 percent decrease in peak energy demand.
Klein stressed that much work remains to be done to bring a new AD plant online. Talks have begun regarding potential sites, but there are still many details to work out. The biggest challenge, he said, will be arranging financing.
At its final meeting on August 18, RCAP discussed the Port Authority’s proposal and offered full support for the AD option. RCAP’s recommendations are included in section 9 of the Port’s report, which is available for review at the St. Anthony Park and Merriam Park libraries, as well as at www.rtadvisory.org, where other relevant documents can be found.
Before the Port Authority submits its final report, it will host two public meetings, on September 6 and 15, at the Wilder Center, 451 Lexington Pkwy. (on the SW corner of Lexington and University). Public comments, limited to three minutes, will be invited.
Written comments are also welcome and can be sent to email@example.com or Energy Recommendations, St. Paul Port Authority, Suite 1900, 345 St. Peter St., St. Paul, MN 55102.