Praxair is developing an oxygen-enhanced combustion and oxygen-enhanced secondary control technologies for controlling NOx, as well as a novel oxygen separation process. Oxygen enhanced combustion can be used to control both thermal and fuel NOx. The concept of adding oxygen to the combustion process appears counter intuitive due to the higher flame temperatures typically associated with oxy-fuel firing. For example, when small amounts of combustion air are replaced with oxygen, a significant increase in flame temperature can be realized. The key to this project is the use of controlled conditions to take advantage of the combustion benefits of oxy-fuel firing and reduce NOx emissions below the 0.15 lbs/MM Btu goal.

Effect of Oxygen-Enhancement on NOx Emissions

Oxygen-fired combustion has been utilized in industrial furnaces to improve energy efficiency and reduce emissions. NOx emissions reductions of as much as 80-90% have been demonstrated at commercial glass melting furnaces that have been converted to oxy-fuel firing. One of the required keys to successfully implementing oxygen-fired or enhanced combustion is an economical source of oxygen, which also can benefit numerous other technologies. Praxair is developing a novel oxygen separation technology at its Tonawanda, New York facility, using an Oxygen Transport Membrane (OTM). Ceramic membranes are attractive since they can have virtually infinite selectivity for oxygen, thereby allowing only the oxygen to pass through. There are two basic types of ceramic membranes, pressure and electrically driven. This project will use pressure as the driving force for separation.

Ultimately, the technology is looking to reduce the cost of NOx emissions reductions. Preliminary calculations show a potential for savings of 25-75% versus SCR. Teaming with Praxair are the University of Utah, the University of Arizona, Reaction Engineering, and Alstom Power. Modeling and laboratory testing will be conducted at REI, the University of Utah, and the University of Arizona, while full-scale testing of an oxygen-enhanced LNB will be carried out at Alstom's Power Plant Laboratories in Windsor, Connecticut.