Effect of CaO on NOx Reduction by Selective Non-Catalytic Reduction under Variable Gas Compositions in a Simulated Cement Precalciner Atmosphere.

Ye Sun,Weiyi Fan,Xiaowei Hong,Tianle Zhu

doi:10.3390/ijerph14121474

Abstract

High-concentration CaO particles and gas compositions have a significant influence on NOx reduction by selective non-catalytic reduction (SNCR) in cement precalciners. The effect of gas composition on NOx reduction by SNCR with NH3 was studied in a cement precalciner atmosphere with and without CaO at 700–1100 °C. It was found that CaO significantly lowers NOx reduction efficiency between 750 °C and 1000 °C, which is attributed to the catalytic oxidation of NH3 to NO. Although increasing NH3 concentration was advantageous to NOx reduction, the existence of CaO led to the opposite result at 750–900 °C. Adding H2O can suppress the negative effect of CaO on NOx reduction. Decreasing O2 content from 10% to 1% shifts the temperature range in which CaO has a significant effect from 750–1000 °C to 800–1050 °C. CO has a variety of influences on the CaO effect under different experimental conditions. The influences of NH3, H2O, O2, and CO on the effect of CaO can be attributed to the impacts of the gas compositions on gas-phase NH3 conversion, gas-solid catalytic NH3 oxidation, or both processes. A proposed pathway for the effect of gas compositions on NOx reduction in CaO-containing SNCR process was developed that well predicted the CaO-containing SNCR process.

Highlights

Air pollution is one of the most serious environmental problems worldwide
Since selective non-catalytic reduction (SNCR) is typically conducted in the cement precalciner, where the temperature ranges from 850 ◦ C to 1200 ◦ C and conforms to the temperature window of SNCR, some countries have introduced full-scale SNCR into the cement industry
When CaO is added, NOx reduction efficiency follows a bimodal distribution against temperature

Summary

Introduction

Air pollution is one of the most serious environmental problems worldwide. Nitrogen oxides (NOx , including NO and NO2 ) emitted from cement rotary kilns are major contributors to acid rain, photochemical smog and haze [1]. In China, 1.7 Mt NOx was emitted by the cement industry in 2015, accounting for 9.1% of total NOx emissions from anthropogenic sources [2]. The cement industry has become the third-largest NOx emission source in China, after the thermal power industry and vehicles. As the largest cement-producing country in the world, “Emission Standard of Air. Pollutants for Cement Industry” (GB4915-2013), which is regarded as the strictest in history, has been issued by the Chinese government to reduce NOx , SO2 , NH3 and Hg0 emissions. Current NOx emission control technologies in the cement industry include low-temperature sintering, staged combustion, low NOx burners, over-fire air, SNCR and selective catalytic reduction (SCR) [3]. SNCR is the predominant deNOx technology in cement rotary kilns due to its suitable, efficient, and cost-effective performance. As opposed to SNCR for electric power generation, NOx reduction efficiencies have

Methods

Discussion

Conclusion