NO reduction capacity of four major solid fuels in reburning conditions – Experiments and modeling

Abstract

The combustion of solid fuels in the rotary kiln and in the calciner of a cement plant generates fuel and thermal NO. This NO can be reduced inside the reducing zone of the calciner. This occurs in two different ways: homogeneous reduction by hydrocarbons and heterogeneous reduction by char. The purpose of this paper is to identify the relative contribution of volatile matters or char on the NO reduction process, which largely depends on the nature of the solid fuel used for reburning. Experiments were undertaken in an Entrained Flow Reactor (EFR), at three temperatures: 800, 900 and 1000°C. Four major fuels used in the cement production process were studied: a lignite, a coal, an anthracite and a petcoke. Specific experiments were undertaken to determine (i) their devolatilisation kinetics and the gas species released. A wide range of species influencing the NO chemistry was carefully analyzed. Then, (ii) the char oxidation and (iii) the char NO reduction kinetics were characterized. Finally, (iv), the ''global'' NO reduction capability of each fuel was quantified through experiments during which all phenomena could occur together. This corresponds to the situation of an industrial reactor in reducing conditions. Anthracite and petcoke reduce only very small quantities of NO whereas lignite and coal reduce, respectively, 90% and 80% of the initially present 880 ppm of NO (at 1000°C after 2 s). The four types of experiments described above were then modeled using a single particle thermo-chemical model that includes heterogeneous reactions and detailed chemistry in the gas phase. This model reveals that both NO reduction on char and NO reduction by volatiles mechanisms contribute significantly to the global NO reduction. After short residence times (several tenth of a second), gas phase reactions reduce NO efficiently; after long residence times (several seconds) the char reduces larger quantities of NO.

Experimental validation of concentration profiles in an HCCI engine, modelled by a multi-component kinetic mechanism: Outline for auto-ignition and emission control

“…Much research has been performed, showing detailed kinetic mechanisms being compared to experimental results, concerning the profile of species as a function of time. Examples are the work of Baldwin et al [22], Morley [23], Slagle et al [24], Hughes et al [25], Baulch et al [26] and others [27][28][29][30][31]. Often, these mechanisms describe the oxidation or auto-ignition of one fuel and often the mechanisms are detailed.…”

Kinetic analysis of NO-Char reaction

“…The reaction of nitrogen monoxide with char is of special interest due to its importance in producing or reducing NO emission from combustion system such as fluidized bed or pulverized coal combustion boiler [1][2][3][4][5][6][7]. Most published studies focused on common temperatures in fluidized bed, which are between 873 and 1,273 K [8][9][10][11].…”

Numerical Simulation Research on the Process of Reburning South American Coal and Cornstalk

“…In the combustion process, mechanisms of the formation and reduction of NOx are extremely crucial and have been studied extensively [15][16][17][18][19]. Julien Cances [20] conducted experiments and modelling with four major solid fuels to identify the difference in the contributions of volatile matters and char to the NOx reduction, and found that for a short initial residence time, volatiles contribute more to the NOx reduction than char, and that after the short initial residence time, char contributes more. The influence of different factors (hydrocarbons, homogenous reactions, heterogeneous reactions, particle size, dried sludge, ash, etc.)…”