|
Studies have shown that nitrogen oxides released to the atmosphere as a result of combustion processes can be linked to the formation of acid rain and ground level ozone (smog). Several different processes to reduce the amount of NOx (deNOx process) have been developed and applied. A common factor in all is the need to control the ammonia slip below the low PPM levels. The flue gas stream contains ammonia, nitrogen oxides and in some cases sulfur dioxide. These components all absorb UV radiation, and therefore can be monitored by a UV diode array process spectrometer. In some applications, however, the sulfur dioxide concentration in the gas can be too high to allow for the accurate and direct measurements of the ammonia slip. To overcome this difficulty a fast separation cell is utilized to remove the SO2 from the stream prior to measurement. The analyzer measures the spectrum of the almost separated components; the spectra are then analyzed by a multicomponent method to give the concentration of the individual components. Withdrawing a representative sample across the stack is a crucial factor in this application; spatial averaging across the stack is obtained by drawing a sample through 12 holes with non-equal diameters. The spectroscopic methods, separation of stream components, and the in-situ sampling will be discussed.
|
