École Nationale Supérieure de
Techniques Avancées

Résumé

Emissions of sulphur oxides (SOx) produced after a combustion process are a key source of atmospheric pollution (especially of the acid rain), mechanical damages (above all low-temperature corrosion and plume opacity) on plant equipments, and are responsible for some adverse effects on human health. On the one hand, the increasing price of refined low-sulphured petroleum and the difficulty to obtain it, as well as the interest in creating more efficient facilities have encouraged industries to use high sulphur heavy fuel oils. On the other hand, the severe regulations and the growing concern on environmental problems and sustainable development have aroused the improvement of new techniques such as oxycombustion permitting, among other advantages, either a reduction or an easier treatment of the pollutants. The most abundant SOx in combustion flue gases are SO2 and SO3.The amount of SOx is constant in oxycombustion and air combustion whereas the concentration is higher in oxycombustion due to a lower flue gas volume. SO2 depends basically on the sulphur contained in the fuel and the amount produced is easily and accurately predictable with stoichiometric calculations. On the contrary, SO3, albeit representing a small fraction of all the SO2, provokes much more harmful effects than SO2 and its formation depends not only on the sulphur contained in the fuel but also on the flame temperature, the excess of oxygen injected into the reactor, the combustion conditions, catalysts and flue gas characteristics, but above all on the first two parameters. By using a furnace and an innovating boiler in which fumes can be recycled and by controlling the amount of excess oxygen in the reactor, it is possible to control the flame temperature and the excess of oxygen in the hearth of the reactor and thus, study their impact on the formation of SOx. The lack of accurate industrial devices for measuring SO3 concentrations in the fumes and the complex and not yet completely known mechanisms of formation of SOx make the study and modelling of SOx formation and acid dew-point temperatures more arduous and a largely open field of research. The present work makes some contributions to these points. This project investigates and widens the present knowledge on the factors that affect the formation of SOx in non-catalytic reactors. It provides some results and alternative ways to estimate SOx concentrations and dew-point temperatures in oxycombustion processes which can be useful for industrial processes using high-sulphur fuel oils. It shows as well a method for calculating an ideal temperature to be maintained in the facilities both to avoid the risk of corrosion and to get the maximum efficiency in the reactor.