The primary goal of this project was to evaluate a technology called advanced layered technology application (ALTA) as a means to achieve NOx emissions below 0.15 lb/MMBtu in a cyclone boiler. Reaction Engineering International (REI) conducted field testing and combustion modeling to refine the process design, define the optimum technology parameters, and assess system performance.

The ALTA NOx control technology combines deep staging from overfire air, rich reagent injection (RRI), and selective non-catalytic reduction (SNCR). Field testing was conducted during May-June 2005 at AmerenUE's Sioux Station Unit 1, a 500 MW cyclone boiler unit that typically burns an 80/20 blend of Powder River Basin subbituminous coal and Illinois No. 6 bituminous coal. Parametric testing was also conducted with 60/40 and 0/100 blends. The testing also evaluated process impacts on balance-of-plant issues such as the amount of unburned carbon in the ash, slag tapping, waterwall corrosion, ammonia slip, and heat distribution.

Prior to field testing, computational fluid dynamics (CFD) modeling was conducted to optimize the number and location of the urea reagent injection locations for both the RRI and SNCR systems. Previous ALTA testing in 2001 and 2002 had used 20 RRI injectors and four SNCR injectors. As a result of the CFD modeling, eight additional RRI injectors and 14 additional SNCR injectors were installed for the 2005 field testing. The majority of field testing was conducted using the 80/20 coal blend at 480 MW under two levels of overfire air (OFA) staging, resulting in baseline NOx emission rates of 0.25 lb/MMBtu with normal air staging and 0.20 lb/MMBtu with deep staging.

Parametric testing was conducted separately for RRI and SNCR, as well as in combination. RRI reduced NOx emissions to 0.16 to 0.17 lb/MMBtu with less than 1 ppm ammonia slip when firing the typical 80/20 coal blend. Parametric testing with SNCR alone demonstrated that NOx emissions of 0.16 to 0.19 lb/MMBtu were achievable with both the 80/20 and 0/100 coal blends and less than 5 ppm ammonia slip under most test conditions.

The accompanying figure shows the NOx emission rate for the baseline condition using only OFA and the various parametric test combinations using OFA with RRI only, SNCR only, and the complete ALTA configuration with RRI and SNCR conducted with the 80/20 coal blend. The NOx emission rate achieved with ALTA varied from 0.117 to 0.15 lb/MMBtu depending on urea flow rate and averaged approximately 0.12 lb/MMBtu with ammonia slip typically less than 5 ppm. For the 60/40 and 0/100 coal blends and the ALTA configuration, the NOx emission rates were 0.15 and 0.165 lb/MMBtu, respectively.