Individual burner air/fuel ratio control optical adaptive feedback control system
Author(s)Beér, James Miklós; Jacques, M. T.; Teare, J. Derek
Conventional combustion control systems for multiburner installations which rely on monitoring the average C02 and/or 02 content of the gases have a number of inherent limitations on their ability to maintain efficient plant operation. Air infiltration'into the flue or sampling lines has the same effect as an instrumental error in causing the control system to adjust the stoichiometry to an incorrect level. Even' when the overall stoichiometry of the furnace is correctly and accurately controlled it is still extremely difficult to ensure that no individual burners are operating inefficiently due to local maldistributions of air or fuel, or to poor nozzle spray characteristics. The potential for fuel savings and for'improved limitation of pollutant emissions has provided strong incentive for the development of individual burner fuel/air ratio control systems which would eliminate the shortcomings associated with the global control method. The present report first reviews past attempts to identify some unique property of an individual flame which can be reliably interpreted as an indicator of the flame behavior over a wide range of operating conditions.. Information potentially usable in this manner could be contained in the acoustic characteristics of the flame, in the local distribution of key chemical species, or in the electromagnetic radiation or absorption behavior of regions of the flame. For many reasons the previous studies have tended to concentrate on the optical portion of the electromagnetic spectrum, with particular emphasis on emission from flames over much of the ultraviolet (u.v.), visible and infrared (i.r.) wavelength regions. A brief review is given of the pioneering work of Penzias and his associates, and of the later work carried out at Sheffield University by Smith which led to the development of the LandTM control system. All of these studies dealt with the infrared emission from flames, wilth particular emphasis on the CO2 barnd at 4.3 pm, and on the H0/CO2 binds near 2.8 m. The report then addresses the experimental work carried out at M.I.T under the sponsorship of five utility companies supporting the M.I.T. Energy Laboratory Electric Power Program. This focused initially on attempts to use a Land control system in the Combustion Research Facility (CRF), with limited success in terms of achieving stability and adequacy of control when operating conditions were varied over a moderate range. The experiments in the CRF also yielded very useful data on the intensities and sources of u.v. emission from No. 6 fuel oil flames over a wide range of fuel equivalence ratio. One other set of experiments carried out in the CRF made use of equipment and personnel supplied by the Foxboro Company, and results of this work are discussed. Also included in the report is a summary of measurements carried out on a small methane-fueled burner which add appreciably to the available information on the dependence of the infrared emission on viewing location relative to the flame front and on fuel equivalence ratio. The overall results obtained under this program do not leave the prospect of individual fuel/air ratio controllers within immediate grasp, but they substantially advance the state of knowledge required for attainment of such control. They give a strong indication that satisfactory control could be obtained over a wide range of furnace operating conditions if both i.r. and u.v. signals were monitored and used in the control system.
On cover : Combustion Research Facility.
MIT Energy Laboratory
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