AN INTEGRATED MODEL TO STUDY THE EFFECTS OF OPERATIONAL PARAMETERS ON THE PERFORMANCE AND POLLUTANT EMISSIONS IN A UTILITY BOILE

Abstract

A gas fired tangentially boiler was modeled under full load conditions. Furnace was simulated by CFD andthen was joint with two mathematical models to calculate heat transfer in the convective section, and metal temperatureof waterwall tubes. Effects of changing the combustion excess air (0 to 20%) and burners tilt angle (-30° to +30°) werestudied. Results showed that the boiler efficiency is optimum if excess air= 10% and the burners have a negative angle.However, these optimum settings cannot produce a superheated and reheated steam of 538 °C which is desirable.Indeed, a zero or positive tilt angle with 10% excess air, or a negative burner angle with 15% excess air lead to highestefficiency by considering the potential of generating superheated steam of 538 °C. In addition, CO emission in lowexcess air values growths by increasing the burner tilt angle. NOx emission in low and high excess air ratios is lowerat positive burner angles while a moderate excess air (10%) needs a zero tilt angle to minimize NOx emission.Furthermore, a critical fouling thickness was computed, considering boiler's circulation ratio, in which the metaltemperature of the waterwall exceeds the short overheating threshold. With a certain thickness of scale layers insidethe tubes, a burner tilting equal to 0° or 30° postpones tube rupture. These results could be utilized by operatingengineers to keep their utility boilers in the most efficient state and avoiding overheating and tube rupture.