NOx Reduction by NOx Recycle Approach

NOx recycle is a new approach for NOx reduction. It uses regenerable sorbent to adsorb NOx in the flue gas from a combustor followed by desorption, producing a highly concentrated NOx-laden stream containing both NO and N02. This stream is then sent back to the same combustor or to a separate combustor, where the NOx is reduced in the flame. Experimental studies have been performed to prove the concept of the NOx recycle approach. Results show that about 40% to 90% of NOx reduction efficiency can be achieved depending on experimental conditions. The NOx destruction efficiency in the combustor is affected by the recycle location, the amount of exit air and the composition of recycle gases. The most favorable recycle location is at the primary air duct. When NOx is recycled into the secondary air duct, the lower the exit 02, the better for the NOx destruction in the flame. Higher NOx reduction efficiency is obtained for the N02 recycle in comparison with the NO recycle. The concept of the NOx recycle approach has been employed in the NOXSO process, which is a dry, post-combustion flue gas treatment technology for coal-fIred boilers. The NOx recycle approach is expected to be a new alternative for NOx removal from flue gas, especially for integrated systems which use regenerable sorbent to simultaneously remove NOx, S02, and other pollutants emitted from combustion.