Design and Test of a Selective Noncatalytic Reduction (SNCR) System for Full-Scale Refinery CO Boilers To Achieve High NOx Removal

Selective noncatalytic reduction technology (SNCR) is an effective and economical method of reducing NO emissions from a wide range of industrial combustion systems. It is widely known that the SNCR process is primarily effective in a narrow temperature window, around 900-1000 degrees C, and that high CO concentrations can both shift the temperature window and limit its effectiveness. While the application of SNCR on a utility boiler is challenging because or a number of factors that can have negative impacts on SNCR NOx reduction performance, the implementation of SNCR technology on an industrial or refinery boiler has unique challenges intrinsic to these boiler designs and fuels fired. This paper describes the design and test of SNCR technology on two refinery CO boilers. The work presented consisted of (1) baseline testing, (2) process analysis, (3) computational fluid dynamics (CFD) simulations, and (4) optimization testing. A three-dimensional full-scale CFD model was constructed for the boiler and was calibrated using baseline test data to simulate the flow characteristics, temperature profile, and oxygen/combustibles distribution of the boiler. The CFD model was also used to design and optimize a reagent injection system that resulted in fast and effective distribution of the reagent in the flue gas of the boiler. The CFD model, which incorporates a reduced SNCR chemistry model, was further applied to predict NOx reduction efficiency and ammonia slip. After installation and commissioning of the SNCR system, a series of parametric optimization tests were performed on both units. The final performance tests showed that the application of SNCR technology could reduce NOx emissions by at least 50%, with less than 5 ppm of ammonia slip, at a nitrogen stichiometric ratio (NSR) of 1.5. The test results are shown in the paper for a comparison to the model predictions made during the design phase.