Low NOx with Oxygen Enhanced Combustion in High N2 Environments

It has been well-established that oxygen can be used to enhance the combustion processes. Typical benefits include increased productivity and thermal efficiency and lower flue gas volumes and pollutant emissions. In particular, it has been shown in the glass industry that replacing preheated air with ambient temperature oxygen can reduce NOx emissions by an order of magnitude. However, one of the challenges of using oxygen in combustion processes is minimizing NOx emissions when a substantial amount of N2 is present in the combustor. This N2 can come from air infiltration, from the incoming batch materials, or from the fuel and/or the oxidizer. Recent developments in oxygen production have shown that vacuum swing adsorption (VSA) can produce oxygen much less expensively than traditional cryogenic distillation but at the cost of the 02 purity which is typically around 90-93% with much of the impurity being N2. It has been shown in the secondary aluminum smelting industry that using an oxidizer consisting of a combination of air and 02 often has better economics compared to using high purity 02. In the case of using either VSA oxygen or a combination of air and 02, NOx emissions are often much higher than using either air or high purity 02. This paper first shows the theory of why it is often preferable economically to operate with oxygen-enriched combustion processes in high N2 environment. The paper then shows lab data, computational fluid dynamics modeling, and field measurements for several methods of reducing NOx emissions under the conditions of oxygen-enriched combustion in high N2 environments.