Experimental study on NO emission and burnout characteristics during semi-coke preheating combustion
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摘要: 为探究更高预热温度下（>1000 ℃）半焦预热燃烧工艺的降氮潜力，在两段电炉串联组成的沉降炉系统上考察了预热温度（600-1400 ℃）、燃烧温度（1200-1400 ℃）和过量空气系数（α=0.6-1.4）对半焦燃烧NO释放和燃尽的影响。结果表明，进一步提高预热温度（>1000 ℃）能够同时降低NO排放和提高燃尽率，并且富燃料工况下，预热温度升高带来的NO降低幅度比贫燃料工况下降低幅度大，预热温度从800 ℃升高至1400 ℃时，NO降幅最大可达74%（α=0.6），明显高于贫燃料条件下NO降幅20.6%（α=1.4）。但是，富燃料工况下，预热温度升高带来的飞灰含碳量降幅比贫燃料工况下降低幅度小，贫燃料条件下飞灰含碳量最大降幅为26.8%（α=1.4），高于富燃料条件下降幅15.95%（α=0.6）。对于燃烧温度对半焦燃烧NO释放的影响，发现存在一临界过量空气系数α=1，当过量空气系数高于该临界值时，随燃烧温度提高，NO排放量增加，当过量空气系数低于该临界值时，随燃烧温度的提高，NO排放量减小。Abstract: To explore the De-NOx potential of the semi-coke preheating combustion technique at higher preheating temperatures(>1000 ℃), the effects of preheating temperature(600-1400 ℃), combustion temperature(1200-1400 ℃) and excess air coefficient(α=0.6-1.4) on the NO emission and burnout of semi-coke combustion were studied on a two-stage drop-tube furnace. The results show that higher preheating temperature can reduce both NO emissions and carbon content in fly ash. Besides, under the fuel-rich conditions, the reduction of NO caused by increasing preheating temperature is larger than that under the fuel-lean conditions. When the preheating temperature increases from 800 to 1400 ℃, there is a maximum NO reduction of 74%(α=0.6), which is much higher than that of 20.6%(α=1.4) under fuel-lean conditions. On the contrast, under fuel-rich conditions, the decrease of carbon content in fly ash caused by increasing preheating temperature is smaller than that under fuel-lean conditions. Under fuel-lean conditions, the maximum decrease of fly ash carbon content is 26.8% (α=1.4), which is higher than that of 15.95% (α=0.6) under fuel-rich conditions. About the effect of combustion temperature on the NO emission, it is found that there is a critical excess air coefficient. When the excess air coefficient is higher than the critical value, the NO emissions increase as the combustion temperature increases. However, when the excess air coefficient is lower than the critical value, the trend is opposite.
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Key words:
- preheating /
- NO /
- semi-coke /
- burnout /
- excess air factor
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图 3 某工况下NO、CO、O2、SO2值随时间的变化
Figure 3 Changes of NO, CO, O2 and SO2 values with time under certain conditions
preheating temperature: 1000 ℃; combustion temperature: 1200 ℃
图 4 预热温度和过量空气系数对NO排放的影响
Figure 4 Influence of preheating temperature and excess air coefficient on NO emission
combustion temperature: 1200 ℃
图 5 600与800 ℃下, 高温石炭焦反应活性差异
Figure 5 Difference in reactivity of high temperature carboniferous coke at 600 and 800 ℃
(experimental process: firstly, the coke was heated to the set temperature in the N2 atmosphere and maintained at that temperature for 30 min, and then the nitrogen atmosphere was changed to the air atmosphere for 30 min)
图 6 预热温度和过量空气系数对飞灰含碳量的影响
Figure 6 Influence of preheating temperature and excess air coefficient on carbon content of fly ash
combustion temperature: 1200 ℃
图 7 燃烧温度和过量空气系数对NO排放的影响
Figure 7 Effects of combustion temperature and excess air coefficient on NO emission
图 8 燃烧温度和过量空气系数对飞灰含碳量的影响
Figure 8 Effects of combustion temperature and excess air coefficient on carbon content of fly ash
表 1 石炭煤、石炭焦的工业分析和元素分析
Table 1 Proximate and ultimate analyses of carboniferous coal and semi-coke
Proximate analysis w/% Ultimate analysis wad/% Mad Aad Vdaf FCad C H O N S Carboniferous coal 1.49 29.60 33.90 45.60 54.90 3.26 9.20 1.12 0.46 Semi-coke 0.71 39.49 7.29 55.44 51.85 1.73 5.47 1.11 0.35 
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