Abstract: The problem of ammonia escape has been existing prevalently in the selective catalytic reduction(SCR) system of coal-fired power plants. In order to better control the concentration of escaping ammonia, the study on field testing of ammonia concentration in flue gas is carried out by adopting the indophenol blue spectrophotometry. Taking the example of a 200-MW power plant in Inner Mongolia as the study case, the operation procedures and process of the indophenol blue spectrophotometry in the field testing are described in details. Then the comparison between the testing results and the online monitoring data is conducted with the impacts of the fly ash on the test results analyzed as well. The study results show that the concentrations of escaping ammonia can be obtained at different sampling points in the field test, which is helpful for ammonia spraying control. The presence of ash may enhance the absorbance of the samples substantially, which will cause higher testing result value. Therefore, for the sake of data accuracy, strict precautions should be taken to prevent ashes from polluting the samples in the sampling process.

Key words: coal-fired power plant, flue gas denitrification, escaping ammonia, detection, indophenol blue spectrophotometry, ash