Cleaner-burning industrial furnaces and utility boilers that will help reduce acid rain, photochemical smog and hazardous tropospheric ozone are now coming on line, partly as a result of a new burner design for power-generation boilers based on MIT research.
The Radially Stratified Flame Core (RSFC) burner is now under exclusive license to ABB-Combustion Engineering Inc. (ABB-CE), which has deployed the technology at two client sites with more installationsexpected. The prototype burner design was the work of researchers at the Energy Laboratory's Combustion Research Facility under the direction of Janos Beer, professor emeritus of chemical and fuel engineering.
"In pilot-scale MIT studies with the RSFC burner, very large nitrogen oxide (NOx) reductions of up to 90 percent were achieved with natural gas as the fuel, and 70 to 80 percent when burning pulverized coal and heavy fuel oil, respectively," Professor Beer said. Nitrogen oxides are precursors of acid rain and smog.
"The prospects are good for significant reductions in emissions in the full-sized industrial application," he added. ABB-CE has the device in operation at an oil- and gas-fired plant in Connecticut and recently installed RSFC burners in an electric-utility boiler.
STAGED COMBUSTION
Researchers, said Professor Beer, have long known that one of the most effective ways of reducing NOx emissions is through the use of "staged combustion." This form of combustion in conventional burners is achieved in physically separated regions of a combustion chamber. This design provides a fuel-rich (oxygen deficient), high-temperature environment early in the flame to allow the chemical conversion of the NOx precursors to harmless molecular nitrogen. A subsequent lower-temperature, fuel-lean environment, in which the remainder of the air is mixed with the remaining fuel, then ensures complete combustion.
While staged combustion can be achieved by maintaining fuel-rich and fuel-lean environments in physically separated regions of a combustion chamber, RSFC burners use "internal staging," a process in which all the combustion air is supplied through a single burner for better aerodynamic control of the air/fuel mixing. "The design ensures sufficient time for the fuel-rich pyrolysis reactions to reduce NOx emissions," Professor Beer said. "It also allows full oxidation of combustibles by means of vigorous mixing of the residual fuel with the burner airflow."
Following mathematical modeling and experimental studies at MIT, ABB-CE Services Inc. scaled up and developed the design to a commercial product. They did so with the help of large-scale experiments and computational studies carried out at the ABB-CE Power Plant Laboratory and by members of the MIT team, respectively.
In addition to Professor Beer, MIT people involved in the work were Dr. Majed Toqan, a co-inventor of the burner who played a pivotal role in the research leading to its development (Dr. Toqan is now with ABB-CE); Dr. Laszlo Barta, who led the pulverized coal studies (Dr. Barta has returned to his native Hungary); Energy Lab research affiliate Dr. Paul F. Lewis, who holds an appointment with Textron Corp.; Don Bash, who was chief of the technical staff (he has since retired); graduate student Alan Shihadeh of mechanical engineering; Dr. Joel Haynes (PhD '96); Norman Sun (SM '94), and Larry Berg (SM '91).
PRACTICAL DESIGNS
"It's a special strength of MIT that we can work so well with companies to solve problems like these in a way that makes devices practical for industry," said Professor Beer of the collaborative and mutually instructive burner-development effort with ABB-CE engineers.
"Our original design had seven control points for air flow and velocity swirl distribution--far too many for a practical device. In the course of changes by ABB-CE to the design of the commercial burner, this was reduced to two control points based on ABB-CE's goal of retaining the burner's flexibility but making it simpler for greater reliability and availability in the field."
The MIT work was sponsored by ABB-CE, Babcock and Wilcox, Eniricerche (Italy), ENEL (an Italian utility company), Electric Power Research Institute, Empire State Electric Energy Research Corp., Florida Power & Light, Southern California Edison, and the US Department of Energy.
(This story is adapted from one that appeared in the February 1997 issue of The MIT Report.)
A version of this article appeared in MIT Tech Talk on May 14, 1997.
