Grantee Research Project Results

Final Report: Active-Core Optical Fiber Ammonia Sensor

EPA Contract Number: 68D03012
Title: Active-Core Optical Fiber Ammonia Sensor
Investigators: Turchi, Craig S.
Small Business: ADA Technologies Inc.
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $69,964
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)

Description:

The goal of this research project was to develop and demonstrate a completely new approach for detecting trace concentrations of ammonia (resolution of > 1 ppm) in combustion flue gas streams. The central technology of the new monitor is an active-core optical fiber sensor. The technique promised to be more sensitive and more compact than active-coating optical-fiber (effervescent wave) sensors that are being investigated for various environmental applications. The active-core sensor was impregnated with a heat-tolerant, inorganic agent that combines with ammonia to create a metal/ammonia complex that can be readily detected by absorption using light transmitted through the optical fiber. The small sensor would be mounted in-duct, without the need for sample extraction or conditioning. Because absorption occurs via an ammonia complex within the solid fiber, fly ash particles and other gaseous species should not have interfered with the detection method. The basic technology was tested successfully under limited laboratory conditions at the Diagnostic Instrumentation and Analysis Laboratory (DIAL) at Mississippi State University prior to this Phase I research project. The focus of this project was to extend the sensitivity of the method and demonstrate a suitable level of deduction (> 1 ppm) in the presence of flue-gas constituents.

To test the prototype sensors, ADA Technologies, Inc. (ADA), designed and assembled a test fixture to provide a simulated flue gas environment. Included in the simulated flue gas stream were representative concentrations of sulfur dioxide (SO2), nitrogen oxide (NOx), and water vapor. The simulated flue gas was supplied to the sensors over a temperature range typical of flue gas subjected to selective catalytic reduction systems for the destruction of NOx in flue gas, from about 250°F to 750°F. An extensive series of tests were completed to evaluate the performance of the sensors under simulated flue gas conditions.

Summary/Accomplishments (Outputs/Outcomes):

ADA completed the test program with the assistance of team member and sensor supplier, DIAL. New, longer fiber optic sensors were created at DIAL and subsequently tested at ADA under simulated flue gas environments (temperatures between 250°F and 750°F, humidity from 0 to 5 percent, NOx from 20 to 200 ppm, SO2 from 200 to 2,000 ppm, and oxygen [O] from 0 to 5 percent). It was determined that the sensor is highly sensitive to temperature fluctuations and equally as sensitive to changes in NOx and SO2 concentrations as to NH3 concentration changes when used in a gas stream with 5 percent or less O. Therefore, as configured, this novel active-core optical fiber is not suitable for use at coal-fired utilities. In addition to the lack of selectivity of the sensor for the given application, the mechanical configuration of the sensor was found to be unacceptable for robust use, and it is believed that much of the drift of the sensor over time may have been because of crazing in the fiber as a result of thermal expansion. The results to date do not warrant continued research, and ADA did not submit a Phase II proposal.

Conclusions:

Although more weaknesses were identified than could be addressed in this limited Phase I research project, several potential improvements to the technology were identified for future research. In particular, it should be possible to create a solid sol-gel disk (instead of a fiber) and pass a light beam through it without having to mechanically couple the fiber ends in the high- temperature environment. In addition, other chemistry formulations would lead to better selectivity. Finally, although making use of a reference fiber to compensate for interactions between the gas stream and the sol-gel fiber was attempted with little success, it should be possible to create a suitable reference sensor and perform differential spectroscopy for this application. This activity would require a more controlled manufacturing process than was employed during this research project.

Supplemental Keywords:

ammonia, combustion flue gas, active-core optical fiber sensor, active-coating optical fiber, fly ash, sulfur dioxide, SO2, nitrogen oxide, NOx, sol-gel disk, differential spectroscopy, monitoring, measurement, air monitoring, small business, SBIR., RFA, Air, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, INDUSTRY, Industrial Processes, Engineering, Air Quality, Environmental Chemistry, Engineering, Chemistry, & Physics, Analytical Chemistry, Monitoring/Modeling, Atmospheric Sciences, Environmental Engineering, Environmental Monitoring, trace element speciation, air sampling, field portable monitoring, combustion gas streams, trace gases, field portable systems, flue gas monitor, emission control, emissions monitoring, combustion, combustion gases, ambient emissions, field monitoring, diode laser, wavelength division multiplexing