ISU Research Center Works to Reduce Utility Boiler Emissions

AMES, Iowa -- Iowa State University and a Pittsburgh-based company are working together to find a "green" answer to acid rain.

ISU's Center for Sustainable Environmental Technologies is collaborating with Energy Systems Associates to explore a new method for reducing nitrogen oxide emissions from coal-fired utility boilers by using agricultural crops and residues. The emission, commonly known as NO_x, is a precursor to acid rain and creates smog in large cities.

The project combines CSET's expertise in biomass energy with ESA's experience in advanced pollution-control technology. The researchers propose to inject a mixture of water and plant material such as cornstover (leftover corn stalks and leaves), switchgrass and alfalfa above the fireball in coal-fired boilers. The material, called biomass, decomposes almost instantly at high temperatures in the boiler to produce a gas. When this biomass-derived gas combines with burning coal gas, it promotes chemical reactions that break down 40 percent to 60 percent of the NO_x emissions into harmless nitrogen gas.

The project is led by Robert C. Brown, director of CSET, and Bernard Breen, president of ESA. Brown is an ISU professor of mechanical engineering and chemical engineering. Breen holds a Ph.D. in chemical engineering from ISU. They received $150,000 from the U.S. Department of Energy's National Energy Technology Lab and $70,000 in cost-sharing support from ESA and ISU to conduct this research. As part of the Biomass Cofiring Program, the grant reflects the Department of Energy's efforts to encourage use of biobased resources as a replacement for fossil fuels.

Biomass, which includes plant material and animal waste, offers many environmental benefits, including drastically reduced greenhouse gas emissions. However, biomass is typically more expensive than fossil fuels, especially when it has to be transported over long distances. While coal is less expensive, environmental considerations make biomass technologies increasingly attractive.

The team's project takes into account the economic concerns of biomass use -- only 5 percent to 20 percent of the total mass burned would be biomass material. "The relatively small amount of biomass required to achieve substantial NO_xreduction makes it possible to use this application in large coal-fired boilers," Brown said.

DOE's Oak Ridge National Laboratory is collaborating on the project because of its researchers' expertise in biomass resource economics. "Oak Ridge is going to help us determine the costs of supplying biomass material and the acreage necessary to grow it to fuel a large-scale boiler," Brown explained.

Currently, the researchers plan to identify the optimal location in a boiler for adding biomass. They are also examining how different types of biomass perform. "They all produce the chemical reactions that break down NO_x, but some plant materials may yield superior results because of differences in composition," Brown said. If lab-scale tests in a 35-kilowatt combustor offer positive results in reducing NO_x emissions, the team will seek out a large-scale utility boiler for further testing.

The DOE provided a total of $675,000 to universities conducting similar small-scale research and feasibility studies on biomass cofiring. Other schools receiving funding include the University of North Dakota, Pennsylvania State University, University of Pittsburgh and Texas A&M University.

The Center for Sustainable Environmental Technologies is a member of the Institute for Physical Research and Technology, a network of research and technology-transfer centers and industrial-outreach programs at ISU.

Last updated September 6, 2006 rbm