CFD ANALYSIS OF THE COMBUSTION CHAMBER OF A WASTE-TO-ENERGY PLANT

The operation of waste to energy plants based on incineration inevitably implies the production of greenhouse gases and the emission of harmful species to the human health. Post-combustion technologies are often used to reduce pollutants. Alternatively, it is possible to act directly on the combustion process to reduce emissions at the source, while also maximizing energy conversion efficiency. This is the reason why the European Directive on the construction and operation of incineration plants fixes strict rules concerning both the temperature and the residence time of the combustion products within the combustion chamber [1, 2]. The peculiar characteristics of the treated waste or Refuse Derived Fuel (RDF) may also cause problems to the burner long term operation. One of these is related to deposits formation, due to the presence of ash, which may have a slow melting temperature consequent the relatively high alkali content. Ash particles in the in-chamber flow may be sticky even at relatively low temperatures and deposit over the walls. Ash deposition modifies the heat transfer coefficient, reduces the systems efficiency and requires frequent stops for overhauling [3]. Therefore, the characterization of the phenomena occurring in a combustor through experimental and numerical techniques is strongly demanded for both identifying the kind of RDF most suitable for certain system and assisting its optimal maintenance. Present work introduces a CFD (computational fluid dynamics) model for the numerical simulation of a real scale waste to energy plant operating in Italy, which allows investigating the turbulent reacting flow within the combustion chamber and, in particular, studying the temperature and residence time of the combustion products, or the effects deriving from any change in the heat transfer coefficient of the refractory covered surfaces.