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Show IFRF Doc. No. K 70/a/12 August 1989 SUMMARY - 1 - Mathematical Modelling of Pulverised Coal Flames Predictions of two pulverised coal flames issued from a swirl burner are compared with measurements. Both flames are from a high volatile Canadian coal; one is a low NOx flame while the other is a high NOx flame. The paper focuses on flame properties inside and just downstream of the burner quarl. In the computations, the numerical errors have been minimised by application of a second-order numerical scheme and very fine grids. As a turbulence closure, an algebraic stress model appropriate for swirling flows predictions is used. Good quantitative predictions of the flow pattern, temperature, oxygen and carbon dioxide concentrations are achieved. However, the carbon monoxide concentrations are only in qualitative agreement with those measured. Substantial differences in the near-burner-zone properties of the two flames are highlighted in the predictions. 1. INTRODUCTION The impact of fossil fuel combustion on the environment is substantial. In many countries, stringent regulations concerning pollutant emissions from coal fired power plants have already been introduced. In order to conform to the NOx emission limits, the power generating industry has to apply low NOx combustion technologies and/or flue gas cleaning methods. Considerable reductions in NOx emissions are achievable through the careful design of the pulverised coal burner. This requires good understanding of pollutants formation and destruction mechanisms. Experiments leading to development of low NOx burners are usually carried out at small or semi-industrial scale. If these are successful, the burner still has to be scaled to full industrial size. Although scaling requires a number of similarity parameters to be kept constant it is not possible to meet this requirement in practise. A reasonable good mathematical model accounting for all the important processes occurring in the combustion zone should be a powerful scaling tool. Such a model should be based on a 2 or 3-dimensional procedure for turbulent (swirling) flow computations accompanied by models of combustion and heat transfer. It is particularly important to predict accurately the flame characteristics in the zone in which the major NOx formation and destruction reactions occur. For a swirled pulverised coal flame, this zone can be defined as the region inside and one quarl diameter downstream of the burner quarl, see Figure 1. A number of computer codes for predicting properties of pulverised coal flames have been developed [1-4]. Predictive capabilities of these codes were assessed using in-flame measurements typically taken two quarl diameters, or more, downstream of the burner quarl. To the best of authors knowledge, this paper contains first |