Evaluation of Gas Reburning and Low-NOx Burners on a Wall-Fired Boiler

Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed therein do not necessarily state or reflect those of the United States Government or any agency thereof. (EER). In October 1990, EER entered into a cooperative agreement with DOE to conduct this study, 158-MWe (net) wall-fired Cherokee Station Unit 3 located in Denver, Colorado. Unit 3 is a 172-MWe wall-fired boiler that uses Colorado bituminous, low-sulfur coal. Over 4,000 hours of operation were achieved. Low-NO x burners achieved a NO x reduction of 65% at an average gas heat input of 18% compared to the performance goal of 70%. The performance goal of 70% reduction was met on many runs, but at higher gas heat inputs. DOE provided 50% of the total project funding of $17.8 million. Gas reburning (GR) involves firing natural gas (up to 25% of total heat input) above the primary combustion zone in utility boilers and industrial furnaces. This upper-level firing creates a slightly fuel-rich zone. NO x produced in the primary zone of the boiler is "reburned" in this zone and converted to molecular nitrogen and other reduced nitrogenous species. Overfire air is injected downstream of the reburn zone to burn out the remaining combustibles and convert the reduced nitrogenous species to molecular nitrogen. Low-NO x burners (LNBs) positioned in the coal combustion zone retard the production of NO x by staging the burning process so that the coal-air mixture can be carefully controlled at each stage. The combination of these two technologies is referred to as GR-LNB. The combined effect of adding a reburning stage to wall-fired boilers equipped with LNBs was intended to lower NO x emissions by up to 70%. In this project, GR was operated with and without the use of flue gas recirculation. 2 The …