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Show COMPUTATIONAL FLUID DYNAMICS BASED ANALYSIS OF BUBBLING FLUIDISED BED COMBUSTION Sirpa Korhonen, Tommy Jacobson and Kari Jaaskelainen Imatran Voima Oy, FDSf-01019 IVO, Finland ABSTRACT Computational fluid dynamics (CFD) has proven to be an efficient tool in the analysis of combustion of gas, oil and pulverised fuels. Imatran Voima Oy has applied the CFD based combustion modelling package called ARDEMUS mainly to the design of the low-NOx technology for pulverised coal combustion since 1990. Recently, ARDEMUS has also been applied to studying freeboards of bubbling fluidised bed (BFB) boilers. In this case the freeboard is modelled with the 3D computational fluid dynamics where the bed is treated as a boundary condition for the freeboard computation. The applicability of ARDEMUS is demonstrated by two cases: The modernisation of Vanaja 60 MWcoal grate-fired furnace to BFB-furnace burning peat and the trouble shooting case ofKuusamo 30 MWpea, BFB. 1. INTRODUCTION Fluidised bed combustion has become one of the most important techniques in burning low-grade fuels like wastes and biofuels. Imatran Voima Oy (IVO) has long-term experience in the design, construction and operation of power plants utilising this type of combustion arrangement. This full-scale experience, together with active testing of fuels and research of the fundamental phenomena of combustion offers good understanding of and capability to design fluidised bed combustion processes. Recently, the computational fluid dynamics (CFD) based modelling tool A R D E M U S has been applied to studying freeboards of the bubbling fluidised bed (BFB) boilers. The benefits of the CFD-based modelling lie in its ability to identify and model key mechanisms, trends, and cause and consequence relationships. In some cases, this type of modelling can eliminate the need for experimental work, or make up for a lack of empirical data. In troubleshooting cases, C F D modelling is one of the most descriptive and useful tools available for identifying the cause of the problems and to provide solutions to them. Modelling can also reveal detailed information about processes, as well as the behaviour of quantities that are difficult or even impossible to measure. As the first example, we present the case of Vanaja power plant is presented, where the 60 MAY^i grate-fired furnace was converted to a BFB-type firing peat. In this retrofit project, the change of primary fuel and combustion technology was analysed with A R D E M U S . In another example, the reasons and solutions were investigated in case of the cold running bubbling fluidised bed at the Kuusamo power plant 2. MODELLING METHOD Since 1991, IVO has applied a computational fluid dynamics based combustion modelling package called A R D E M U S to studying flow fields, combustion, heat transfer, pollutant reduction and slagging in pulverised and liquid fuel-fired furnaces. The development of A R D E M U S was in 1990 in co-operation with Technical Research Centre of Finland. The structure of A R D E M U S is presented in Figure 1. It is based on the use of commercial computational fluid dynamics programs like Phoenics or Fluent in which models for the most essential phenomena prevailing in furnaces are implemented [Kjaldman 1993]. |