Advanced SNCR NOx Reduction Experience on Multiple Large Utility Boilers

摘要

Fuel Tech has recently completed full-scale demonstrations of Advanced Selective Non- Catalytic Reduction systems on a number of large utility boilers (>600MW) firing a variety of fuel types. The systems use the latest flexible injection technology and are controlled with a balanced algorithm utilizing unit load, a full grid of continuous furnace temperatures and the plant continuous emissions monitoring system (CEMS). Fuel Tech has more installed SNCR applications than any other technology supplier, with more than 590 units firing all types of fossil, biomass, and industrial fuels. These systems are currently installed and operating on units ranging in size from small industrial furnaces to some of the largest utility boilers in the world. Over the last 15 years, Fuel Tech has completed nearly 50 installations on units larger than 400MW, where the majority of these units are larger than 600MW. Large units pose a particularly difficult challenge to SNCR emission control systems, as these modern units generally have higher furnace exit gas temperatures, incorporate low- NOx burners (LNB), over- fired air (OFA) and have very low baseline NOx emissions. Each of these factors potentially limits the effectiveness of SNCR. Fuel Tech uses the most advanced computational fluid dynamics (CFD) and chemical kinetics modeling to design sophisticated injection strategies that anticipate varying load and fuel conditions in the furnace. The analysis is translated into engineering systems that incorporate numerous injector types to deliver the reagent as effectively as possible. The target injection zone varies based on temperature, NOx baseline, CO concentration and furnace residence time. CFD modeling is required to accurately predict these shifts in the target region. Furnace temperature has traditionally been an important control signal for the Fuel Tech SNCR system, and recent installations have included full contour mapping of the furnace temperatures using either laser-based or acoustic pyrometers to control the system operation, while limiting ammonia slip. Recent systems have achieved more than 35% NOx reduction from low baseline furnaces that already utilize primary control measures such as LNB and OFA. This has been accomplished while controlling ammonia slip below environmental requirements and limiting the impact on balance of plant. Furthermore, this is achieved without the use of excess dilution water, which would reduce boiler efficiency. Specific recent examples will be discussed including the use of on-line temperature mapping, multiple nozzle lances and CFD modeling to provide effective control on large utility furnaces.