Citation: Hernik, B. Numerical Research of Flue Gas Denitrification Using the SNCR Method in an OP 650 Boiler. Energies 2022, 15, 3427. https://doi.org/10.3390/en15093427 Academic Editor: João Fernando Pereira Gomes Received: 13 April 2022 Accepted: 5 May 2022 Published: 7 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Numerical Research of Flue Gas Denitrification Using the SNCR Method in an OP 650 Boiler Bartlomiej Hernik Department of Power Engineering and Turbomachinery, Silesian University of Technology, Konarskiego 18, 44-100 Gliwice, Poland; bartlomiej.hernik@polsl.pl; Tel.: +48-32-237-1196 Abstract: The presence of Poland in the European Union obliges the domestic economy and the professional energy sector to improve the condition of the natural environment by reducing the emissions of harmful substances into the environment. One of the substances that have a negative impact on the environment is nitrogen oxides. The results of numerical calculations of flue gas denitrification using the SNCR method in an OP 650 boiler are presented in the paper. The method of verifying the combustion of the numerical model, in terms of measurement and calculations with a zero-dimensional model, is presented. Then, the results of numerical tests of flue gas denitrification using the SNCR method with the use of urea solution injection in a specific temperature window for various nozzle positions are presented. In this paper, three variants of the reagent’s injection into the furnace chamber were carried out, depending on the height of the position of the nozzle. It is shown in this paper that thanks to combined NOx reduction systems, it is possible to adjust the emission of nitrogen oxides to a level below 200 mg/m 3 n with an oxygen content of 6% in the dry flue gas, with relatively low investment costs. Keywords: SNCR; denitrification; boilers; numerical simulations 1. Introduction The presence of Poland in the European Union obliges the domestic economy and the professional energy sector to improve the condition of the natural environment by reducing the emissions of harmful substances into the environment. There are increasing restrictions on the presence of compounds considered harmful in exhaust gases, forcing manufacturing and industrial plants to invest in equipment and installations to reduce emissions. One of the substances that have a negative impact on the environment is nitrogen oxides. The NOx emission standards and legal requirements for the emission of nitrogen oxides resulting from the combustion of fuels in energy are presented in the Industrial Emissions Directive (IED) [1]. The benchmark for the values of the emission standards is the Best Available Technique (BAT) reference document [2]. For the combustion of coal fuel in units with a rated thermal input greater than 300 MW, this limit is 200 mg/m 3 n , with a 6% oxygen content in the flue gas. Nitrogen oxides are formed during the combustion of fuel in boilers. NO X is one of the major pollutants of the environment. In order to reduce the emissions of nitrogen oxides, primary and secondary methods are used. Secondary methods for reducing nitrogen oxides include selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) [3]. Primary methods for reducing nitrogen oxides include air staging and fuel staging. Compared to secondary methods, they are cheaper to build and operate. Air staging is used in low-emissions combustion. As a rule, it is related to the division of the furnace chamber according to its height into zones that differ in air concentration—the sub-stoichiometric combustion zone (first zone) and the above-stoichiometric combustion zone (second zone). In the second zone, fuel particles are burnt with air from Overfire Air (OFA) nozzles [4]. Research on air staging in fossil fuel- and biomass-fired boilers has Energies 2022, 15, 3427. https://doi.org/10.3390/en15093427 https://www.mdpi.com/journal/energies