Reaction Characteristics of NOx and N2O in Selective Non-Catalytic Reduction Using Various Reducing Agents and Additives

Artificial nitrogen oxide (NOx) emissions due to the combustion of fossil fuels constitute more than 75% of the total NOx emissions. Given the continuous reinforcement of NOx emission standards worldwide, the development of environmentally and economically friendly NOx reduction techniques has attracted much attention. This study investigates the selective non-catalytic reduction (SNCR) of NOx by methane, ammonia, and urea in the presence of sodium carbonate and methanol and the concomitant generation of N2O. In addition, the SNCR mechanism is explored using a chemical modeling software (CHEMKIN III). Under optimal conditions, NOx reduction efficiencies of 80–85%, 66–68%, and 32–34% are achieved for ammonia, urea, and methane, respectively. The N2O levels generated using methane (18–21 ppm) were significantly lower than those generated using urea and ammonia. Addition of sodium carbonate and methanol increased the NOx reduction efficiency by methane to ≥40% and 60%, respectively. For the former, the N2O level and reaction temperature further decreased to 2–3 ppm and 850–900 °C, respectively. The experimental results were well consistent with simulations, and the minor discrepancies were attributed to microscopic variables. Thus, our work provides essential guidelines for selecting the best available NOx control technology.

OVERVIEW OF POST-COMBUSTION NOX EMISSION CONTROL MECHANISM IN INDIAN COAL FIRED POWER PLANTS

The importance of Coal in generation of electricity is well established. But, during the combustion of coal for generation of electricity, oxides of nitrogen (NOx) are also released. These oxides of nitrogen are pollutants which have an adverse effect on both the human life as well as the environment. Due to the increased pollution level from Coal Fired Power Plants, Ministry of Environment & Forests (MOE&F) on Dec 2015, announced stringent standards for coal based thermal power plants under the Environment Protection Act of 1986. Though various NOx control systems have been installed and functioning properly worldwide, but their provenness in the Indian scenario is yet to be established. As the coal in which the Indian power plants operates have a very different characteristics than the coal used abroad for power plants. This paper aims to address and explore the various methods and challenges in reducing the NOx emissions from Coal Fired Power Plants while firing Indigenous coal.

Nonlinear responses of particulate nitrate to NO_x emission controls in the megalopolises of China

Nitrate is an increasingly important component of fine particulate matter (PM2.5) in Chinese cities. The production of nitrate is not only related to the abundance of its precursor, but also supported by atmospheric photochemical oxidants. The control of nitrogen oxides (NOx) emissions may thereby lead to nonlinear changes of nitrate concentrations, raising a new challenge to the current emission control actions in China. This paper uses comprehensive measurements and a regional meteorology-chemistry model with optimized mechanisms to establish the nonlinear responses between particulate nitrate and NOx emission controls in the megalopolises of China. Nitrate is an essential component of PM2.5 in eastern China, accounting for 9.4–15.5 % and 11.5–32.1 % of the PM2.5 mass for the warm and cold seasons. The hypothetical NOx emission reduction scenarios (−10 %~−80 %) during summer-autumn result in almost linearly lower PM2.5 by −2.65 % in Beijing-Tianjin-Hebei (BTH) and −2.79 % in Yangtze River Delta (YRD) per 10 % cut of NOx emissions, whereas they increase the oxidant levels and lead to a rather complicated response of PM components in winter. Wintertime nitrate is found to increase by 4.28 % in BTH and 4.60 % in YRD, with higher dinitrogen pentoxide (N2O5) intermediate products produced from increased ozone introduced by lower NOx emissions. An inflexion point appears at 40–50 % NOx emission reduction, and a further cut in NOx emission is predicted to cause −8.74 % reduction of nitrate for BTH and −10.59 % for YRD per 10 % cut of NOx emissions. In addition, the 2012–2016 NOx control strategy actually leads to no change or even increase of nitrate in some areas (8.82 % in BTH and 14.41 % in YRD) during winter. This paper helps understand the nonlinear aerosol and photochemistry feedbacks, and defines the effectiveness of proposed mitigations for the increasingly serious nitrate pollution in China.

Preparation and Performance of Cerium-Based Catalysts for Selective Catalytic Reduction of Nitrogen Oxides: A Critical Review

Selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) is still the most commonly used control technology for nitrogen oxides emission. Specifically, the application of rare earth materials has become more and more extensive. CeO2 was widely developed in NH3-SCR reaction due to its good redox performance, proper surface acidity and abundant resource reserves. Therefore, a large number of papers in the literature have described the research of cerium-based catalysts. This review critically summarized the development of the different components of cerium-based catalysts, and characterized the preparation methods, the catalytic performance and reaction mechanisms of the cerium-based catalysts for NH3-SCR. The purpose of this review is to highlight: (1) the modification effect of the various metal elements for cerium-based catalysts; (2) various synthesis methods of the cerium-based catalysts; and (3) the physicochemical properties of the various catalysts and clarify their relations to catalytic performances, particularly in the presence of SO2 and H2O. Finally, we hope that this work can give timely technical guidance and valuable insights for the applications of NH3-SCR in the field of NOx control.

Study on Coupling Effect of Additives on NOx Control in Coal Pyrolysis-Combustion

A large amount of nitrogen oxides produced by loose coal combustion has an important impact on the ecological environment. To solve this problem, it is proposed to prepare clean coke instead of loose coal combustion to reduce the emission of nitrogen oxides from civil coal combustion. Clean coke is prepared by pyrolysis raw coal adding additives, and the gas generated by pyrolysis is collected uniformly, thus avoiding the emission problem in the process of loose burning. In addition, the clean fuel catalyzes the reduction of nitrogen oxides to produce N2 in the combustion process, thus reducing the emission of combustion nitrogen oxides. In this paper, the additives were investigated, and finally it was found that loading 1 wt.% Fe and Ni had a better effect of decrease nitrogen content in coke through pyrolysis of coal and denitrification during the combustion of coke, and had a coupling effect on nitrogen oxide control in the pyrolysis-combustion process.