OCR Text |
Show of the adsorber is unchangeable, the increase of the recycled NOx reduction efficiency in the combustor will improve the overall system NOx removal efficiency. The reduction of recycled N Ox in the combustor is similar to the "reburning" process [6], which is a combustion modification ' approach. However, they are different in three ways. First, in the NOx "recycle" concept, NOx is recycled into a main combustion zone and the recycle location is adjustable, which can be at the primary air duct, the secondary air duct, or other favorable locations. In the "reburning" process, NOx is rebumed in a secondary combustion zone which is located at the upper portion of the main combustion zone. Secondly, the NOx concentration in the NOx "recycle" stream is very high, in the range of 0.3 % to 2.0%, while NOx concentration in the reburning zone of the "reburning" process is normally 0.06% to 0.1 %. Thirdly, in the "reburning" process, NOx generated from the main combustion zone normally consists of about 95% NO and 5% N02• However, in the NOx "recycle" stream, the N02 could be as high as 65 % of total N Ox depending on the nature of the sorbent and regeneration conditions. Because of these differences, an investigation of NOx reduction by the NOx recycle approach is needed. There are two postulated general mechanisms for NO reduction in the N Ox "recycle" approach: thermodynamic-kinetic conditions and reducing. atmospheres . . In general, NO from combustion consists of thermal NO, fuel NO, and prompt NO. The thermal NO is formed by the following reactions [7]: 0+ N2~ NO+N N+02~ NO+O If these equations are combined, the formation of NO can be described by: Nl + 02 <=:> 2NO 5 (2) (3) (4) |