NOx Reduction with Oxygen-Fuel Combustion

The minerals, metals, and waste incineration industries rely heavily on combustion for materials processing. These industries are being forced to upgrade their current combustion technology since increasingly stringent regulations are being written to limit NOx production. There are different strategies for reducing NOx. The more expensive strategy post-treats the flue gas to remove NOx after its formation. The less expensive method is to minimize NOx formation in the flame using combustion modification techniques. However, this often also reduces combustion efficiency. Oxygenfuel combustion is a modification technique that not only lowers NOx but also increases efficiency. Air Products conducted an extensive set of experiments in a large scale instrumented furnace to compare the NOx emissions from both air-fuel and oxygen-fuel burners under controlled conditions. The oxygen-fuel burners produced an order of magnitude less NOx than the air-fuel burners. For both the air-fuel and oxygen-fuel burners, NOx was a strong function of the oxygen level in the oxidizer and of the stoichiometry. The paper discusses the lab results and shows how NOx is affected by the various parameters. Implementation of oxygen-fuel combustion technology has produced dramatic NOx reductions while actually increasing efficiency compared to previously employed air-fuel systems. Examples of NOx in specific applications are presented.