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Show USE OF SPECTRAL FLAME ANALYZER FOR COMBUSTION CONTROL IN INDUSTRIAL BOILERS Sushil K. Batra, William E. Cole, Christopher I. Metcalfe Thermo Electgron Corporation Waltham, Massachusetts, USA ABSTRACT Large industrial boilers incorporate a multiplicity of burners. Combustion controls regulate the quantity of fuel and airflow to these burners in an amount appropriate to the load demands. The combustion controls have two purposes: (1) maintain constant steam conditions under varying loads by adjusting fuel flow, and (2) maintain an appropriate air-to-fuel flow for complete combustion of the fuel. The optimum excess air level for the best boiler efficiency occurs when the sum of the loss due to incomplete combustion and the loss due to heat in the flue gas is minimum. Presently, the combustion control system monitors the emissions (02, C02' CO) in the flue gas and, based on these measurements, varies the fuel and/ or air supplied to a set of the burners. Although the overall stOichiometry of the combustion process may be optimized by the present control system, for the majority of the industrial boilers, the individual burners may have very different operating characteristics due to varying burner parameters. These may result in local reducing conditions if the air supply is insufficient, and result in incomplete combustion, slagging, and an increase in unburned combustibles . A high level of "excess air" would result in significant energy loss, increased SOx and NOx formation, and increased power consumption by forced and induced draft fans. An instrument based on spectral emissions has been under development for several years at Thermo Electron for assessment of the combustion conditions in individual burners in a multiburner boiler. A prototype instrument has been designed, built, and tested in a Combustion Research Facility. Further tests are planned in an industrial boiler to evaluate the benefits of this emerging technology. Besides providing optimum individual burner performance, the instrument can be used as a diagnostic tool to detect improper functioning of individual burners, and for burner tuneup. 221 This paper describes the principle of operation of the Spectral Flame Analyzer (SFA) test results in the MIT Combustion Research Facility, the developmental program for industrial application, and potential benefits of this technology. INTRODUCTION LARGE INDUSTRIAL AND UTILITY coal-fired boilers incorporate a multiplicity of burners arranged in rows or banks. The fuel is fed to the individual burners in response to the load demands on the boiler. Simultaneously, a combustion control system feeds air to the boiler in an amount appropriate to the quantity of the fuel. Currently, the combustion control system monitors the emissions in the flue gas and, based on these measurements, the fuel and/or air supplied to a set of burners is varied. The objective of the combustion control system is to provide an optimum ratio of air to fuel in order to completely burn the fuel, maximize thermal efficiency, while at the same time minimize the emitted air pollutants. Whereas, the overall stoichiometry of the combustion process may be optimized by the present combustion control system, the individual burners may have different operating characteristics due to differences in wearing rates of the burner hardware, fuel flow, and airflow. Also, the geometry of the boiler may require different air fuel conditions in different regions of the boiler. These may result in local reducing conditions if the air supply is insufficient, and result in incomplete combustion, slagging, and an increase in unburned combustibles. A high level of "excess air" would result in significant energy loss, increased SOx and NOx pollutant formation, and increased power consumption by forced and induced draft fans. The closer the boiler can be made to operate at its theoretical air- |