Grantee Research Project Results
1999 Progress Report: A Nitric Oxide/Ammonia Sensor for Fossil Fuel Combustion Control Applications
EPA Grant Number: R826164Title: A Nitric Oxide/Ammonia Sensor for Fossil Fuel Combustion Control Applications
Investigators: Vetelino, John F.
Institution: University of Maine
EPA Project Officer: Hahn, Intaek
Project Period: January 21, 1998 through January 20, 2000
Project Period Covered by this Report: January 21, 1998 through January 20, 1999
Project Amount: $197,761
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
This research project seeks to develop an in situ sensor array to continuously monitor the NOx and NH3 levels at the output of the SCR system near the stack to provide real-time control of the NH3 injection and hence, minimize the NOx emissions released into the environment. The increased awareness of the potential hazards of various gases emitted into the environment has created a critical need for sensitive and selective sensors to monitor these gases. Among the most dangerous gases are the oxides of nitrogen (NOx) that are emitted from the combustion of fossil fuels in coal-fired power plants, motor vehicles, and other fossil fuel burning systems. NOx emissions adversely effect human health, agricultural vegetation, and the environment. In many fossil fuel systems, such as coal-fired power plants, a selective catalytic reduction (SCR) technique is employed where ammonia (NH3) is injected into the flue gas stream to react with NO to form environmentally safe gases such as nitrogen and water vapor. Unfortunately, this process is usually incomplete, resulting in either NOx emissions or excess NH3 (NH3 slip) at the exhaust stack.
Semiconducting metal oxide (SMO) film technology has been exploited for a wide variety of sensing applications to create "chemiresistive" gas sensors. Chemiresistive gas sensors exhibit several advantages over other types of sensors. Chemiresistive gas sensors are small, robust, fast, sensitive, potentially selective, low power, reusable, and capable of in situ real-time monitoring even in harsh environments. This sensor technology can be utilized for a wide range of environmental, industrial, medical, and defense monitoring applications.
Progress Summary:
In this research project, SMO film technology is used to develop an SMO sensor array capable of selectively and sensitively detecting NOx and NH3. In particular, tungsten trioxide (WO3) films were utilized to engineer a two-sensor array to selectively detect NH3 and NOx gas concentrations typically found in coal-fired power plants. To design the chemiresistive sensor array, the effects of substrate material, film thickness, doping, deposition temperature, and operating temperature on the film's electrical response to NH3 and NOx were closely examined. As a result of this examination, two film recipes capable of selectively detecting NH3 and NOx were identified. The resulting two-sensor array was further characterized using graphical analysis techniques to evaluate response and recovery times, rates of response, sensitivities, dynamic ranges, stability, and selectivity to NH3 and NOx. The film growth reproducibility within a batch, as well as among batches also was examined. Finally, principal component analysis (PCA) techniques were employed for sensor array data interpretation and visualization. Specifically, the sensor array's response repeatability, selectivity, and film growth reproducibility were evaluated and presented using PCA.
The present work demonstrates that the electrical response characteristics of the WO3 films were highly dependent on the combinations of substrate material, film thickness, doping, deposition temperature, and operating temperature. The two-sensor array demonstrated sensitive, reversible, and repeatable responses to NH3 and NOx. Both sensors exhibited short-term and long-term baseline stability. The sensor array also responded selectively to NH3 and NOx over the concentration ranges typically found in coal-fired power plants. Preliminary results suggested that more work is required to improve reproducibility within a batch, as well as among batches. Furthermore, a third film recipe displayed all of the desired sensing characteristics to become an H2S sensor that eventually could be integrated into the current NH3 and NOx two-sensor array.
Future Activities:
Work will continue to focus on improving reproducibility within a batch and among batches. In addition, integration of an H2S sensor into the NH3 and NOx two-sensor array will be pursued.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
atmosphere, nitrogen oxides, innovative technology, engineering., RFA, Scientific Discipline, Waste, Environmental Chemistry, Incineration/Combustion, Environmental Engineering, combustion contaminants, flue gas emissions, Nitrogen dioxide, coal, selective catalytic reduction, chemical contaminants, ammonia sensor, Hydrogen sulfide, sulfur oxides, air pollutionProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.