General Electric - Energy and Environmental Research Corporation (GE-EER) is carrying out a two Phase research program to develop novel Advanced Reburning (AR) concepts for high efficiency and low cost NOx control from coal-fired utility boilers. AR technologies are based on combination of basic reburning and N-agent/promoter injections. Phase I of the project was successfully completed and EER was selected to continue to develop AR technology during Phase II. Phase I demonstrated that AR technologies are able to provide effective NOx control for coal-fired combustors. Three technologies were originally envisioned for development: AR-Lean, AR-Rich, and Multiple Injection AR (MIAR). Along with these, three additional technologies were identified during the project: reburning plus promoted SNCR; AR-Lean plus promoted SNCR; and AR-Rich plus promoted SNCR. The promoters are sodium salts, in particular sodium carbonate. These AR technologies have different optimum reburn heat input levels and furnace temperature requirements. For full scale application, an optimum technology can be selected on a boiler-specific basis depending on furnace temperature profile and regions of injector access.

The Phase I experimental program included combustion tests in 20 and 200 kW facilities. Pilot scale studies in the 200 kW combustor demonstrated the ability of the AR technologies to achieve NOx reductions of 95+% during gas firing and 90+% during coal firing. Byproduct emissions were found to be lower than those generated by commercial reburning and SNCR technologies.

A detailed reaction mechanism was developed to model the AR chemical processes. The mechanism (355 reactions of 65 species) includes the following submechanisms: GRI-Mech-2.11, SNCR chemistry, sodium chemistry with Na₂ CO₃ decomposition reactions, SO₂ /SO₃ reactions, and interaction of HCl with flue gas components. Modeling provided insight into the controlling factors of the process and qualitatively described the observed reaction trends. Modeling predicted and explained the effect of sodium promotion under both fuel-rich and fuel-lean conditions. The sensitivity analysis revealed the most significant elementary reactions affecting formation and destruction of NO and other N-containing compounds in the reburning and burnout zones.

The AR design methodology was updated by using experiments and analytical models to include the second-generation improvements. This methodology was then used for application of the novel AR concepts to a 100 MW tangentially fired utility boiler, and to predict the impacts of the AR systems on boiler performance and NOx emissions. A parallel AR-Lean demonstration (outside the scope of this project) provided an opportunity to test several novel AR components in the field.

Economic analysis demonstrates a considerable economic advantage of AR technologies in comparison with existing commercial NOx control techniques, such as basic reburning, SNCR, and SCR. Particularly for deep NOx control, AR results in 2-3 times lower costs (in $/ton of NOx removed) than SCR for the same level of NOx control. The market for AR technologies is estimated to be above $1.5 billion.

During Phase II, GE-EER will continue the analytical and experimental work including: (1) development of alternative AR promoters, (2) optimization of prospective AR variants via combustion tests and combined chemistry/mixing modeling, (3) scale up tests at 10 x 106 Btu/hr and tests of selected elements in a boiler, and (4) validation of the design methodology and application to a full scale boiler with updated economics and market assessments.