The ammonium bisulfate (ABS) widely exists at air preheater. The ABS may deposit and foul at the heating surface of air preheater because of the chemical reaction between SO~3~ at flue gas side and ammonia slip from SCR excess injection. The heat transfer equation between flue gas side and air side is constructed and simplified using physical and mathematical models accordingly. The finite difference method is applied to solve numerically by means of iterative computation. In order to calculate the temperature field inside the rotary air preheater, the flue gas inlet and outlet temperature at air preheater is initiated as boundary condition from the Distributed Control System (DCS) data in utility boilers. The temperature field at air preheater could be simulated at any time. The numerical simulating results agree well with the practical temperature distribution in the rotary air preheater. The calculated temperature distribution of flue gas, combustion air and rotating matrix under different work conditions, collectively reflected the temperature field at rotating direction along air preheater height and width. Through numerical simulation, the ABS formation, deposition and fouling could be predicted by the three dimensional temperature filed matrix inside air preheater more detailed than the conventional cold-end average temperature. With the numerical calculation, the temperature filed distribution of the rotary air preheater under different working conditions is achieved. According to the results from temperature field, analysis on the metal wall temperature distribution at rotary air preheater is acquired. The temperature characteristic curve according to the calculation results of heat transfer elements, combined with the ABS solidification characteristic is applied to forecast the deposition and fouling area under various conditions at cold-end and even hot-end at air preheater, the deposition and fouling of ABS area with load following to extend the high temperature heating surface. Based on the NH~3~ and SO~3~ concentration data from the real time data in the actual operation and the discrete calculation of the temperature field, the Radian number (Ra) is used to evaluate the possibility of ABS fouling and the developing trend of heating surface at the air preheater. The evaluation method could be applied to forecast the exact wall temperature and blow off the fouling at suitable time. A 1000MW ultra supercritical boiler is selected as example. The ABS deposit area is simulated under different working conditions 100%BMCR, 75% BMCR and 50% BMCR. The possible ABS deposition and fouling is analyzed for operators to evaluate the risk of cold-end and hot-end heating surface plate at air preheater. As the working load decreases lower than 50%BMCR, the deposition and fouling position could extend to the hot-end area of heating surface at air preheater. The fouling may block the empty area between cold-end and hot-end areas. The fouling is difficult to be cleaned after the fouling is formed at this situation.


Study on Formation, Deposition and Fouling Prediction of Ammonium Bisulfate (ABS) at Air Preheater in Utility Boiler

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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