Mild Combustion

Mild combustion processes evolve in a temperature and concentration range outside the sphere of interest of standard combustion processes, with the aim of lowering the maximum temperature of the whole process below the value at which substantial pollutant formation occurs. It represents a trade-off between optimizing fuel conversion in terms of energy saving and pollutant abatement, and maintaining the configurations of traditional processes. Stability, near-homogeneous temperature and concentration profiles, reduction and abatement of pollutants as well as very specific oxidative structures, different from the traditional thin flame, makes mild combustion a unique process, in terms of environmental sustainability. Starting from the rigorous definition of mild combustion, in this chapter an overview of the main features of this process is given, underlining the gaps in basic knowledge that have to be filled so as to optimize the process for specific applications. It is followed by the classification of possible mild combustion in different configurations on the basis of the acquired categories both in fundamental and traditional combustion processes. Despite the various lacunae in our basic understanding of mild combustion, empirical knowledge of the process suffices to make several industrial facilities work in these operative conditions. The main characteristics of such applications are then described with particular regard to energy conversion, material treatment and pollution abatement plants.