Experimental Analysis on Influencing Factors of NO_(x)emission in Gas-Fired Heating and Hot Water Combi-Boilers

To study the influencing factors of NO_(x)emission in gas-fired heating and hot water combi-boilers,a boiler with the maximum heat input of 26.0 k W was selected,and influencing factors including flue restrictor diameter,fan power,nozzle aperture,nozzle ejection distance and air relative humidity on NO_(x)formation were determined.The NO_(x)test rig has been built and the concentration of NO_(x)at the rated heat input and the NO_(x)weight value(NO_(x))_(pond)with different heat input in the dry flue gas have been tested respectively according to the test methods in Chinese national standard GB 25034-2010.The results show that with the increase of the diameter of flue restrictor at exhaust outlet,the NO_(x)concentration at the rated heat input and the NO_(x)weight value(NO_(x))_(pond)with different heat input in the dry flue gas decreased by 26.9%and 5.9%;with the increase of the diameter of flue restrictor at air intake inlet,the NO_(x)and(NO_(x))_(pond)decreased by 36.5%and 16.0%;with the increase of fan power,the NO_(x)and(NO_(x))_(pond)can be decreased by 48.4%and 16.1%;with the increase of ejection distance of nozzle,the NO_(x)and(NO_(x))_(pond)decreased by 7.7%and 6.8%;with the increase of aperture of nozzle,the NO_(x)and(NO_(x))_(pond)increased by 5.2%and 2.3%;with the increase of air relative humidity,the NO_(x)decreased by 16.4%and the(NO_(x))_(pond)basically remains unchanged.The analysis of the influence factors of NO_(x)emission can be provided as reference for the optimization design of combi-boilers with low NO_(x)emission.