REACTOR CHARACTERISTICS RELATED TO MODERATE OR INTENSE LOW-OXYGEN DILUTION FOR CLEAN/CLEANING COMBUSTION PLANTS

Combustion processes evolving in mild conditions are correcterized by working temperature lower than the flame temperature of the traditional combustion systems, allowing for a drastic reduction of pollutant formation. Such operating conditions' need of specific plant configurations related to the recovery of flue gases generally used for diluting and preheating the reacting stream. The internal or external exhaust recirculation and the high mixing level with fresh feed needed in order to gain the "mild combustion" mode, present several technological problems. These problems are considered in this paper in relation to the feasibility of a reliable plant. It is demonstrated that the power consumption for the treatment of high temperature flue gases is in an acceptable range for working conditions characteristic of mild combustion. Complete and reduced models of methane oxidation have been considered in order to study the feasibility of batch and Well-Stirred Reactor (WSR) configurations. It is shown that a WSR is not only desirable for mild combustion but, also, that this reactor configuration is technologically interesting for a combustion process only if a high initial temperature (greater than 1000 K) and a very diluted condition (oxygen molar fraction of 0.05) are considered. Only in this case, residence times of practical interest are related to the suitable conversion level of reactants. The end of this paper discusses a fluid-dynamic configuration for a WSR operating in mild combustion mode.