Scaling of Pulverized-Fuel Jet Flames That Apply Large Amounts of Excess Air—Implications for NOx Formation

Rikard Edland,Fredrik Normann,Klas Andersson,Christian Fredriksson,Thomas Allgurén

doi:10.3390/en12142680

Abstract

Measures to reduce nitrogen oxides (NOx) formation in industrial combustion processes often require up-scaling through pilot-scale facilities prior to being implemented in commercial scale, and scaling is therefore an important aspect of achieving lower NOx emissions. The current paper is a combined experimental and modelling study that aims to expand the understanding of constant velocity scaling for industrial jet flames applying high amounts of excess air. These types of flames are found in e.g., rotary kilns for production of iron ore pellets. The results show that, even if the combustion settings, velocity, and temperature profiles are correctly scaled, the concentration of oxygen experienced by the fuel during char combustion will scale differently. As the NO formation from the char combustion is important in these flames, the differences induced by the scaling has important impacts on the efficiencies of the applied primary measures. Increasing the rate of char combustion (to increase the Damköhler number), by using, for example, smaller-sized particles, in the pilot-scale is recommended to improve scaling.

Highlights

Nitrogen oxide (NOx ) is a pollutant involved in the formation of several hazardous phenomena, most notably acid rain and photochemical smog
Regarding nitrogen oxides (NOx) emissions from stationary sources, the focus of legislative measures has been on power generation, which has driven the development of technological measures that are suited to these types of facilities, whereas industrial combustion processes have received less attention
The current paper examines constant velocity scaling of pulverized fuel (PF)-jet flames that apply a high degree of excess air and its implications on NOx formation

Summary

Introduction

Nitrogen oxide (NOx ) is a pollutant involved in the formation of several hazardous phenomena, most notably acid rain and photochemical smog. Regarding NOx emissions from stationary sources, the focus of legislative measures has been on power generation, which has driven the development of technological measures that are suited to these types of facilities, whereas industrial combustion processes have received less attention. This situation is changing, as emissions from industrial combustion plants typically lie significantly above heat and power plants applying state-of-the-art technologies. Some of the industrial combustion processes differ significantly from conventional combustion systems and state-of-the-art technologies are not always applicable. Since measures that affect the combustion process are usually tested in pilot-scale facilities prior to being applied in full-scale, it is critical that the effects of scaling are well understood

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Conclusion