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Abstract: A model for the release of sodium during the combustion of single Loy Yang brown coal char particles is presented. The model is combined with further analysis of recently published measurements of the release of sodium from single brown coal particles burning in a flat flame to estimate the rate constant for sodium release as a function of burnout time for these experiments. A char combustion and heat transfer model is also used to predict the char burnout behaviour and surface temperature of the particle as a function of time during combustion for each of the experiments. By combining the predicted time–temperature history of the particles with the estimated rate constant for sodium release, an Arrhenius expression for the release of sodium during char combustion is determined as: A full mechanism for sodium release during the various stages of coal combustion is also proposed. Utilising the proposed mechanism, the rate-determining step for sodium release during char combustion is proposed to be the formation of a reduced form of sodium in the char which subsequently leads to the rapid loss of sodium from the particle. [Copyright &y& Elsevier]

Abstract: The concentration of atomic sodium in the plume of single brown-coal particles burning in a flat flame environment is measured using quantitative planar laser-induced fluorescence (LIF). A run-of-mine Loy Yang brown coal (LY-ROM) and two Loy Yang brown coals (MTE1 and MTE2) that were processed using Mechanical/Thermal Expression, which removed a fraction of the inherent moisture and concomitant dissolved salts, were investigated. By applying a chemical equilibrium model, at an appropriate location in the flame, the total sodium release is estimated from the measured atomic sodium concentration profile. For LY-ROM, MTE1 and MTE2 the total proportion of sodium release following devolatilisation, as a percentage of the initial sodium in the coals, was 80.9±19.5%, 87.9±19.0% and 93.0±28.0% respectively. Using this data, it is inferred that approximately 67% of water-bound sodium and approximately 100% of the organically-bound sodium is released following devolatilisation. Furthermore, in the present experiments up to 60% of the total sodium is released during the period in which the ash remains within the flat flame, following char combustion. A mechanism is proposed to explain this observation in which Na2O in the ash reacts with ambient water vapour at high temperature. [Copyright &y& Elsevier]

Abstract: Simultaneous measurement of the concentration of released atomic sodium, swelling, surface and internal temperature of a burning black liquor droplet under a fuel lean and rich condition has been demonstrated. Two-dimensional two-colour optical pyrometry was employed to determine the distribution of surface temperature and swelling of a burning black liquor droplet while planar laser-induced fluorescence (PLIF) was used to assess the temporal release of atomic sodium. The key findings of these studies are: (i) the concentration of atomic sodium released during the drying and devolatilisation stages was found to be correlated with the external surface area; and (ii) the insignificant presence of atomic sodium during the char consumption stage shows that sodium release is suppressed by the lower temperature and by the high CO2 content in and around the particle. [Copyright &y& Elsevier]

Abstract: The quantitative measurement of atomic sodium (Na) release, at high concentration, from a burning black liquor droplet has been demonstrated using a planar laser-induced fluorescence (PLIF) technique, corrected for fluorescence trapping. The local temperature of the particle was measured to be approximately 1700°C, at a height of 10mm above a flat flame burner. The PLIF technique was used to assess the temporal release of atomic Na from the combustion of black liquor and compare it with the Na concentration in the remaining smelt. A first-order model was made to provide insight using a simple Plug Flow Reactor model based on the independently measured concentration of residual Na in the smelt as a function of time. This model also required the dilution ratio of the combustion products in the flat flame entrained into the plume gas from the black liquor particle to be estimated. The key findings of these studies are: (i) the peak concentration of atomic Na from the combustion of the black liquor droplets is around 1.4ppm; (ii) very little atomic Na is present during the drying, devolatilisation or char combustion stages; and (iii) the presence of atomic Na during smelt phase dominates over that from the other combustion stages. [Copyright &y& Elsevier]

Abstract: The influence of boron on the temporal release of atomic sodium during a burning black liquor droplet has been assessed using planar laser-induced fluorescence (PLIF) technique. Single 10mg droplets were burned in a flat flame at temperatures ranging from 1600 to 1725°C with an equivalence ratios of 0.8, 0.9 and 1.25 and excess oxygen concentrations of 3.7, 1.8 and 0 (vol%), respectively. Under these conditions, the magnitude and temporal release of atomic sodium for the liquors with and without boron were not significantly influenced by the boron. However, the addition of boron to the liquor clearly reduced the total atomic sodium released, especially during the char consumption stage. [Copyright &y& Elsevier]