Active-Core Optical Fiber Ammonia Sensor

Oxides of nitrogen, or NOx, are common air pollutants in congested urban areas. NOx contributes to a variety of environmental problems, including ground-level ozone (smog), acid rain, and visibility impairment. NOx emissions are generated by motor vehicles, industrial facilities, and electric power plants. The Clean Air Act Amendments of 1990 required that stationary sources, such as power plants, implement controls to reduce NOx emissions. Coal-fired power plants have adopted two basic methods to reduce NOx: installation of low-NOx burners and use of post-combustion reduction technologies. Both typically are required to achieve the necessary reduction efficiency. In the latter process, ammonia is used to convert NOx into harmless nitrogen and water. However, ammonia itself is a pollutant, so care must be taken not to release excess ammonia¿an event referred to as ¿ammonia slip.¿ To operate at peak efficiency and minimize ammonia slip, plant operators must be able to track the concentration of ammonia in the flue gas. Despite years of effort, no ammonia monitor has been proven capable of operating reliably in this hot and corrosive flue gas environment. The objective of this multiphase research project is to develop and demonstrate a completely new approach to ammonia detection. The central technology of the new monitor is an active-core optical fiber sensor. The sensor is impregnated with a heat-tolerant, inorganic agent that combines with ammonia to create a complex that can be readily detected by light absorption through the optical fiber. The compact sensor mounts in-duct, without the need for sample extraction or conditioning. The basic technology has been successfully tested under laboratory conditions. The focus of this research project is to extend the sensitivity of the method and demonstrate a suitable level of detection in the presence of flue gas constituents. ADA Technologies, Inc. (ADA), has built a project team consisting of the sol-gel fiber experts at Diagnostic Instrumentation and Analysis Laboratory (DIAL) and Monitor Labs, a supplier of continuous emission monitors (CEMs) to the utility sector. During Phase I, this team will demonstrate the feasibility and performance of the basic sensor and test it under realistic flue gas conditions. In Phase II, ADA and Monitor Labs will integrate the sensor into a complete CEM package and demonstrate the performance at a utility site. Successful deployment of the CEM will provide a robust, sensitive monitor to plants that rely on ammonia injection to meet current strict NOx emission standards.