Combustion and emissions

Abstract

The paper examines the relation to emissions of substances of environmental interest, deriving from combustion. Such substances, generally referred to as emissions (acid gases, nitrogen oxides, particulate, micropollutant of different origin, etc.), show specific effects upon the ecosystem and need therefore to be kept under control. As a consequence, standards, rules, and regulations have been introduced to limit, in certain ways, the admissible concentrations. This fact from one side has brought to development of control systems based upon gas cleaning after combustion, and from the other has introduced the need to modify the combustion process in order to minimize the production of pollutants. This latter aspect of the problem is specifically considered in this paper. After a general discussion about criteria employed to contain emissions, the influence upon the process of a specific parameter, namely turbulence, is analyzed. Emphasis is given to the fundamental role of this parameter in order to optimize the process; evidence is also given to how the introduction of more severe rules brings as a consequence the need to modify turbulence parameters in order to meet the required standard emissions. A model is introduced to allow to relate the turbulence parameters to the required emissions concentrations. Such a relation allows the designer of the combustion system to meet the required standards. Particular evidence is given to the fact that, when very low emission levels are imposed, high turbulence levels are required in order to optimize the process.