A New Ultra Low NOx Combustion Technique for Preheated Combustion Air Applications

The feasibility of generating ultra low NOx emissions with high air preheat and fuel (natural gas) rich combustion has been demonstrated. With combustion air preheat temperatures of 732 C (1350 F) NOx emissions of less than 20 ppm have been measured. Data analysis and theoretical considerations indicate that these ultra low levels can be further reduced by designing an optimized combustion system. The new combustion technique can be used for many industrial processes. The technique is especially well suited for heating to very high process temperatures such as heating for forging, forming, and rolling and for processes with even higher process temperatures such as melting of ferrous scrap or other metals. Major economic benefits are obtained when the rich products of combustion (reducing atmosphere) generated in the first step are used to prevent oxidation in the form of scaling or slagging of ferrous metals. The economic benefits of avoiding metal losses and increasing metal yields can far exceed the entire energy cost for melting or reheating of ferrous alloys. This economic benefit can potentially pay for a new furnace or melter in a relatively short time. The technique proves to be applicable also to more moderate process temperatures such as heating of crude oils and other chemicals. It can also be employed for indirect heating applications. The technique is based on a novel burner which can produce very rich combustion products, especially with highly preheated combustion air. At high temperatures any NOx that may have formed is reduced by the residual hydrogen contained in the combustion gases. This residual hydrogen and carbon monoxide is reacted to completion before leaving the furnace. This completion reaction is initiated at lower temperatures where formation of NOx is retarded. In this paper the theoretical background of the technique is discussed, the experimental facility used for demonstrating the concept is described, and major experimental results are given. Application of the new ultra low combustion technique to industrial processes is reviewed and its advantages are discussed. Patent applications have been filed in an effort to protect the technology.