The Applying Characteristic Research Of Low NOx Pulverized-coal Burner

Pulverized-coal combustion, BFG and pulverized-coal co-firing and its numerical simulation methods of the conventional pulverized-coal burner and low NOx pulverized-coal burner have been studied deeply and widely in 350MW tangentially fired pulverized-coal utility boiler.The experimental results of the conventional pulverized-coal burner show that with the increase of O₂ volume fraction from 3% to 5%, NOx emission increases by over 26.7% (350MW), and that when 15% BFG (calorific value) was co-fired, NOx emission decreases by 27.6%, and that with the increase of the operating load from 210MW to 350MW, NOx emission increases by over 45.4%. After the bottom one conventional pulverized-coal burner of 5 layers total was refitted into a low NOx pulverized-coal burner, the low NOx pulverized-coal burner of 5 layers total can reduce 5.5% of NOx emission when operating at 350MW, coal combustion, 3% O₂ volume fraction. The difference of (NOx,HIJK—NOx,GHIJ) is three times of the refitted to the primary in operating of 4 layers burners. The measuring of temperature and gas content in the front-waterwall shows that: during the same operating condition the O₂ volume fraction near waterwall of burner G (low NOx burner) section is the highest among GH,H,HI sections of the burners, and its distribution decreases with the journey of the flame. The NOx concentration near waterwall of burner G (low NOx burner) is the lowest among GH, H, HI sections of the burners, its NOx concentration near the waterwall is increased with along the furnace height. The distribution of NOx concentration near the front-waterwall has a maximum value in center and lower value with farther away of the center. With increased of load and O₂ volume fraction, the NOx concentration in the front-waterwall keeps increasing. Datong coal burning has a higher NOx emission in the front-waterwall than Datong coal and Shenhun coal co-firing.Numerical simulation shows that with the increase of the O₂ volume fraction from 3% to 5%, NOx emission increased from 406ppm to 522ppm (6%O2), the difference between experiments and numerical simulation is about +3.3%^-2.7%. Inthe primary air section and secondary air section of combustion zone, the difference between the highest temperature and average temperature of the sections is respectively 473°C and 524°C, the difference between the highest O2 volume fraction and average O2 volume fraction of the cross section is respectively 0.122 and 0.126, and the difference between highest fuel mass fraction and average fuel mass fraction is respectively 0.1581 and 0.0178. In the burnout cross section, the difference between the highest temperature and average temperature is 134°C, the difference between the highest O2 volume fraction and average O2 volume fraction is 0.0457, the difference of fuel is 0.0048. NOx is produced mostly in the combustion zone, the highest value of NOx appears near the top of the burners along the furnace height. Its NOx distribution has two peaks in cross section of the burner's zone, and the maximum NOx concentration is in annular area. The temperature distribution of conventional burner and low NOx burner is almost the same. The low NOx pulverized-coal burner has obviously reduced NOx emission for 22% (numerical simulation) to 28% (experiments). The low NOx burner has a lower NOx producing ratio than the conventional burner. The co-firing of pulverized-coal and BFG shows that NOx emission decreased from 25% to 34.1% when 19%BFG and 24%BFG wre used, and that NOx is also produced mostly in the burner's zone, and that the difference between experiments and numerical simulation is about +13.5% +16.8%.Calculation of the non-premixed PDF combustion method and species transport method shows that these two methods can get the same distribution in the temperature, species and NOx concentration. The non-premixed PDF combustion method can get closer results with experimental data, but its volatile and carbon only have a burnout ratio of 92.8% and 84.9% respectively, while the species transport method burns its fuel completely and get a higher temperature and a bigger NOx concentration in the furnace.