Thermodynamics and Kinetics of HT-Processes

The present chapter aims to point out the limits of the traditional thermodynamics in treating complex reaction systems, as those related to waste incineration or ferrous slag production. Yet, preserving the elementary formalism of the equilibrium thermodynamics and leaving the field description aside, it is possible to provide representations to model transformations even occurring at non-ideal conditions (i.e. conditions at which real processes take place). In such a view, attention is paid to two crucial aspects of deviation from ideality: (i) exchange of matter with a reservoir, leading to the notion of “open systems”, whose composition is not invariant any more. Although these systems exhibit peculiarities, they can still be modelled by extensions of elementary thermodynamics formalism; (ii) off-equilibrium systems, whose reactions have undergone interruption before achievement of natural equilibration. These systems, which are governed by the laws of kinetics, often occur in industrial processes, where an abrupt halt of heating is used to curb production costs, at the expenses of the achievement of equilibrium of the final products. In the context of waste, we mention here two classical examples of products whose formation lies in the realm of high-temperature non-ideal thermodynamics: fly and bottom ash from municipal solid waste incineration and ferrous slag.