Water/Steam Injection for NOx Reduction in Process Burners

Liquid water or steam injection is a technique that has been used for years to reduce NOx primarily by reducing the flame temperature which reduces thermal NOx. There is also evidence to suggest it reduces NOx by modifying the flame chemistry. While it is well proven for reducing NOx, there are some potential disadvantages including reduced thermal efficiency, flame instability, and increased emissions of other pollutants such as CO and unburned hydrocarbons. Water/steam injection has been used in a wide range of applications, particularly in boilers and gas turbines. Much less information is available on using this technique in process heaters which have some key differences compared to most combustors which include a highly varying fuel composition and natural draft to provide the combustion air. This paper will consider how water or steam may be injected into process burners including some predictive methods for determining NOx.