NOx/CO Thermal Abatement Emission Management Through Dynamic Active Burner Control
Adam Stover
(centrotherm Clean Solutions)
Gas abatement via combustion processes are a common semiconductor industry practice to minimize emissions of hazardous process precursors and byproducts, however the combustion process generates CO and NOx as byproducts. NOx is a group of nitrogen oxide pollutants that are environmentally controlled as they are hazardous to both the environment and humans. NO2 reacts with OH. radicals in the atmosphere to form HNO3, leading to the generation of acid rain. NOx can irritate the lungs, exacerbating the effects of bronchitis, emphysema and heart disease. Unfortunately NOx is byproduct of gas combustion abatement processes and unless selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) is employed then the only way to manage NOx generation is to ensure the gas abatement combustion chamber is at the optimal temperature and O2 concentration. However, CO and NOx vary inversely. Oxygen rich environments reduce CO emissions at the expense of NOx formation, with the converse relationship holding true. Therefore, a ‘Goldilocks’ zone must be found that minimizes the formation of both pollutants. Certain process gases, such as SiH4 and H2, have high heats of combustion and promote the formation of thermal NOx. This phenomenon requires a combustion abatement system to be able to dynamically tune the thermal environment to stay in said zone. To that end, centrotherm Clean Solutions have developed a gas abatement combustion burner that moves beyond the concept of ‘high fire’ and ‘low fire’ and can tune the combustion environment in real time. Extensive laboratory and field data regarding the effect of O2 excess and burner power density on NOx/CO generation will be discussed.