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TECHNOLOGIES DE RECOMBUSTION AVANCEE DES OXYDES D'AZOTE : ETUDES EXPERIMENTALE ET CINETIQUE SUR PILOTE SEMI-INDUSTRIEL

Duy Quang Dao 1
1 PC2 - Physicochimie de la Combustion
PC2A - Physicochimie des Processus de Combustion et de l’Atmosphère - UMR 8522
Abstract : Nitric oxides (NOx) play an important role in main of actual environmental problems such as tropospheric ozone formation and acid rain. Among the NOx reduction industrial processes, the Reburning and Selective Non Catalytic Reduction (SNCR) processes, that use respectively hydrocarbons and nitrogen - containing compounds (ammonia, urea or cyanuric acid) as reducing agent, have been showed to be very effective with simple installation and low investments costs. The objectives of this study is to evaluate the influence of main working parameters on the NO reduction efficiency of Reburning and SNCR processes by using respectively methane (CH4) and ammonia (NH3) as reducing agent. The parametric studies of NO reduction were performed in a lab-scale plug flow reactor. The gaseous effluents were analyzed by Fourier Transform Infrared spectroscopy (FTIR). The effect of the main operating parameters such as the flue gas temperature, the residence time, the NO initial concentration and the reducing agent amount were systematically evaluated for the Reburning and SNCR NO reduction modes. As a result, the methane gas Reburning shows to be a very effective NO reduction technique in our experimental conditions with a very high NO reduction efficiency up to 90%. The reduction performance of the Reburning approach increases as a function of the main working parameters such as: the flue gas temperature, equivalence ratio of reburn zone, average residence time and initial NO concentration. According to the experimental conditions, a competition between two chemical processes can occur: NO reduction Reburning and NO formation via prompt-NO mechanism. The experimental results are compared with the modeling ones obtained with the SENKIN-CHEMKIN II calculation code by using four detailed kinetic mechanisms: GDF-Kin®3.0_NCN (El Bakali et col., 2006), Glarborg (Glarborg et col., 1998), GRI3.0 (Smith et col., 1999) et Konnov (Konnov et col., 2005). By using ammonia NH3 as reducing agent, a maximal NO reduction efficiency up to 80% is obtained in the optimal conditions of SNCR process. The study of the effects of the main working parameters has shown that a kinetic competition between the NO formation by NH3 oxidation and the NO reduction via SNCR process may occur. Several chemical compounds such as CH4, C2H2, C2H4, C2H6, CH3OH, C2H5OH, CO and H2 have been evaluated as additives to SNCR process. As a result, these additives lead to a downwards shift of about 100 K of the optimum temperature window for the reduction process. Moreover, the addition of these compounds improves very sensitively the NO reduction performance for the lower temperatures conditions. The detailed kinetic of Coda Zabetta and Hupa (2008) has been evaluated and optimized to reproduce the experimental results in our working conditions. A good agreement between the experimental results and the modeling ones is obtained. A kinetic analysis explains the effects of additives on the NO reduction process by using ammonia.
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Submitted on : Friday, December 9, 2011 - 2:24:31 PM
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Duy Quang Dao. TECHNOLOGIES DE RECOMBUSTION AVANCEE DES OXYDES D'AZOTE : ETUDES EXPERIMENTALE ET CINETIQUE SUR PILOTE SEMI-INDUSTRIEL. Chimie analytique. Université des Sciences et Technologie de Lille - Lille I, 2010. Français. ⟨tel-00650087⟩

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