Development of a fiber optic continuous emissions monitor using a photometric cell and fiber optics

The feasibility of utilizing fiber optics for transmission of signals from the light source to the sampling cell and back to the detectors in a continuous emissions monitoring system was studied. The overall objective of this research was to develop a system which would allow a sampling cell to be mounted on an emissions stack and connected to the analyzer. The system consists of a flue gas extraction and conditioning system, and a sampling cell which are mounted remotely from a photometric analyzer via fiber optic cables. The analyzer with dual channel/wavelength capability can be used to monitor flue gas concentrations of SO₂ and NO₂. Absorption spectroscopy is used for the detection and analysis of the pollutants. Light from the xenon lamp in the analyzer enters a fiber optic cable which connects to the sampling cell. Light returning from the cell to the analyzer via a fiber optic cable is divided at the analyzer into four paths by a four- way fiber optic splitter. Two branches go to the measuring and reference detectors of each of the pollutants. Laboratory analyses of the system have been conducted. The response to each pollutant is linear with a response time of 150 seconds. Studies were conducted to determine if it is feasible to convert NO to NO₂ by oxidizing the extracted sample with ozone prior to its being introduced into the sampling cell so that total NO_x can be monitored as NO₂.