Analysis of Influencing Factors on NO_x emission in Gas-Fired Heating and Hot Water Combi-Boilers Based on Orthogonal Method

In order to determine the sensitivity of influencing factors on NOx emission in gas-fired heating and hot water combi-boilers,the orthogonal method was adopted in this paper.Five predominant factors affecting the formation of NOx and four levels were selected to be analyzed,including the diameter of flue restrictor,power of fan,ejection distance of nozzle,aperture of nozzle and relative humidity of air.The test plan was designed by employing L16(45)orthogonal array,and 16 groups of experiments were conducted.The test results were analyzed with range analysis and variance analysis.The results indicated that the power of fan has the greatest influence on the formation of NOx of the gas-fired combi-boilers,followed by the diameter of flue restrictor and the relative humidity of air,while the ejection distance of nozzle and aperture of nozzle have little effect on the formation of NOx.In addition,with the selected optimal combination of five factors,a minimum NOx volume fraction is obtained,which confirms the superiority of the orthogonal test.The research finding has a certain guiding significance for the reduction of NOx formation of gas-fired heating and hot water combi-boiler.

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.