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Show This is because the modelling is limited and each technique is relevant only to the effects being modelled. Whilst it is anticipated that computer modelling using computational fluid dynamics (CFD) will eventually enable industrial combustion and heat transfer problems to be modelled using only this technique, this is not yet the case and its application is generally restricted to the less complex problems at the present time. Whilst the purpose of this paper is to describe the application of modelling techniques to the energy and emission reductions on real plants, rather than the modelling techniques themselves, a brief explanation of the techniques is not out of place in order to provide the background for an understanding of their application. 2.1 Combustion and Heat Transfer Modelling Combustion modelling is a complex problem, often involving aerodynamic modelling, modelling of mixing systems and heat transfer modelling. In certain complex processes two phase flow modelling is also required. A basic explanation of the combustion process is necessary in order to understand the principles of modelling. Combustion takes place in four stages: MIXING - IGNITION - CHEMICAL REACTION - DISPERSAL OF PRODUCTS In industrial combustion systems employing turbulent diffusion flames, ignition and chemical reactions are very fast whilst mixing is relatively slow. Therefore, the flame characteristics are largely mixing controlled, hence the saying of combustion engineers "If its mixed, its burnt". The success of modelling depends entirely on similarity between the processes investigated processes occurring in the full size installation. ensuring in the that model there and is the Both physical and mathematical modelling may be used to model combustion systems. The choice depends on the complexity of the system being studied, the information available and the accuracy and reliability of the answers required. Three types of physical modelling and three types of mathematical modelling are used by FCT to investigate combustion systems:- 1. Water modelling 2. Air modelling 3. Acid/Alkali modelling 4. Well stirred furnace mathematical model. S. Zone furnace mathematical model. 6. Computational fluid dynamic models. Water and air modelling are used to investigate the aerodynamics of air ducting, windboxes and burners. Acid/Alkali modelling is used to investigate the fuel/air mixing within the combustion chamber. The well stirred furnace model or the zone furnace model are then used to calculate the heat transfer from the flames to the product and furnace walls, depending on the characteristics of the furnace being modelled. |