Mitigating Thermal NOx by Changing the Secondary Air Injection Channel: A Case Study in the Cement Industry

Domenico Lahaye,Franjo Juretić,Marco Talice,Mohamed el Abbassi,Kees Vuik

doi:10.3390/fluids5040220

Domenico Lahaye, Franjo Juretić + Show 3 more

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https://doi.org/10.3390/fluids5040220

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Abstract

This work studies how non-premixed turbulent combustion in a rotary kiln depends on the geometry of the secondary air inlet channel. We target a kiln in which temperatures can reach values above 1800 degrees Kelvin. Monitoring and possible mitigation of the thermal nitric-oxide (NOx) formation is of utmost importance. The performed reactive flow simulations result in detailed maps of the spatial distribution of the flow, thermodynamics and chemical conditions of the kiln. These maps provide valuable information to the operator of the kiln. The simulations show the difference between the existing and the newly proposed geometry of the secondary air inlet. In the existing configuration, the secondary air inlet is rectangular and located above the base of the burner pipe. The secondary air flows into the furnace from the top of the flame. The heat release by combustion is unevenly distributed throughout the flame. In the new geometry, the secondary air inlet is an annular ring placed around the burner pipe. The secondary air flows circumferentially around the burner pipe. The new secondary air inlet geometry is shown to result in a more homogeneous spatial distribution of the heat release throughout the flame. The peak temperatures of the flame and the production of thermal NOx are significantly reduced. Further research is required to resolve limitations of various choices in our modeling approach.

Highlights

Rotary kilns are long cylindrical furnaces [1]
In the following three paragraphs, we review literature on non-reactive flow, turbulent combustion and thermal NOx formation in rotary kilns, respectively
The results of the non-reactive flow computations using the rhoSimpleFoam solver show reasonable agreement with results obtained using the IB-Raptor solver and results on scale models published in the literature

Summary

Introduction

Rotary kilns are long cylindrical furnaces [1]. They are widely employed by the material processing industry to manufacture, e.g., cement or zinc-oxide, to treat waste or to recycle materials such as bitumen.We target a direct-fired counter-current flow rotary kiln in which the temperature reaches levels above 1800 degrees Kelvin. Rotary kilns are long cylindrical furnaces [1]. They are widely employed by the material processing industry to manufacture, e.g., cement or zinc-oxide, to treat waste or to recycle materials such as bitumen. We target a direct-fired counter-current flow rotary kiln in which the temperature reaches levels above 1800 degrees Kelvin. A burner producing a flame is installed at the low end the kiln. The material leaves the furnace at the low end to be further processed. High temperatures are required to heat the material to reach the sintering reactions. This makes the process prone to the formation of thermal nitric-oxides (NOx)

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