OCR Text |
Show I N T R O D U C T I ON General acceptance of the need to minimize oxides of nitrogen has become a fact only during the last few years. Very many existing fired heaters, boilers and furnaces are not discharging satisfactory emissions to meet present and projected stringent regulations• The probable use of newly available synfuels, containing large amounts of combined nitrogen, as well as the increasing need to conserve energy could aggravate the problem for the future. Past work has demonstrated that control of NOx during the combustion process is both technically feasible and economically attractive compared with other methods. Burner designs must be improved to use all current proven techniques for reducing NOx formation in the flame itself, without sacrificing overall combustion performance or process efficiency. This paper briefly describes one such burner apparatus which has been applied in a large number of fired heater applications, and more recently in one type of boiler. It is a staged air design, with a refractory lined, substoichiometric pre-combustor and a second stage, low excess combustion air system. It uses both internal and external flue gas recirculation, and a high exit velocity flame to promote jet entrainment, lower flame temperature, and improve heat transfer characteristics. A simple method of approximating expected NOx levels is described. A few field measurements of NOx, particulates and noise are included, and some conclusions are drawn. 13/2 |