On‐line, real‐time alkali monitor for process stream analysis

• Published in: Review of scientific instruments 1987-09, Vol.58 (9), p.1647-1654
• Main Authors: Hensel, J. P., Goff, D. R., Logan, R. G., Pineault, R., Romanosky, R. R., Wachter, J. K.
• Format: Article
• Language: English
• Subjects: Applied sciences; coal; combustion; Exact sciences and technology; fiber optics; fuels; monitoring; online systems; Other techniques and industries; realtime systems; signal detection
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1139362

In order to acquire real‐time transient alkali data on coal‐derived gaseous fuel and combustion streams often at low ppb levels, an extractive, total (vapor and particle‐bound) sodium and potassium monitor has been designed, constructed, and tested. This fiber‐optic alkali monitor (FOAM) utilizes state‐of‐the‐art fiber‐optic light transfer, a novel light‐filtering background correction method, and high sensitivity photodiode signal detection. The sample enters the monitor’s high‐temperature flame, which supplies energy to both decompose and excite the sample. The flame then emits light at the characteristic wavelengths of sodium and potassium. The resulting emissions are transferred by the fiber‐optic bundle to the detection system, where the signal is filtered, background corrected, and transferred to the data system. The FOAM has advantages over previous instrumentation in being rugged, portable, and compact. Laboratory testing of the FOAM has been completed. The FOAM was determined to be highly sensitive (mid‐ppt detection limits) with a wide linear dynamic range (four orders of magnitude). The results of field monitoring of alkali levels in the exhaust stream of a pressurized combustor using the FOAM indicated that the monitor was capable of real‐time, fast tracking of transient alkali behavior in a high‐temperature/high‐pressure process stream.