洁净煤技术

2019, v.25;No.124(06) 118-125

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新型低氮旋流燃烧器NO_x排放特性
NO_x emissions characteristics of a novel low-NO_x swirl burner

龚彦豪;许鑫玮;王登辉;王学斌;谭厚章;牛艳青;惠世恩;李在让;刘愿武;
GONG Yanhao;XU Xinwei;WANG Denghui;WANG Xuebin;TAN Houzhang;NIU Yanqing;HUI Shien;LI Zairang;LIU Yuanwu;State Key Laboratory of Multiphase Flow in Power Engineering,School of Energy and Power Engineering,Xi′an Jiaotong University;Taishan Group Co.,Ltd.;Xi′an Jiaoda Siyuan Technology Co.,Ltd.;

摘要(Abstract):

为应对燃煤工业锅炉日益严苛的排放标准,提出了一种新型低NO_x旋流燃烧器,将煤粉预燃与燃烧器空气分级、炉膛空气分级进行耦合,通过改变燃烧系统的配风布置对煤粉预燃燃烧状态进行调整,研究了一次风率、内外二次风率、外二次风入射方式、循环风率和燃尽风率对NO_x排放特性的影响。结果表明:在试验工况下当一次风率从15.4%提高到28.7%,预燃室内氧气浓度增大,一次风携带的氧气可直接将煤粉热解释放挥发分中含氮化合物HCN、NH_3等中的N氧化为NO,NO_x生成量由284.4 mg/m~3逐渐增至326.7 mg/m~3。当内外二次风率比由0.46增大到1.4,NO_x排放浓度先下降后上升;由于内二次风量影响预燃室内过量空气系数和湍动强度,外二次风量影响炉膛内部主燃区煤粉发生燃烧反应的湍动混合强度,在二次空气配比变化的综合作用下,内外二次风率比为1.0时,NO_x排放值最低为211.2 mg/m~3。随着外二次风内部入射风量与端面入射风量比值由0增大到4.56,NO_x生成浓度先下降后上升;由预燃室端面入射的外二次空气射流边界较长,主燃区相对较大,燃烧整体较为均衡,而从预燃室内部入射的外二次风促进了预燃室出口气粉混合物在炉膛内与助燃空气的混合;当外二次风内部、端面射流风率比为0.25时,煤粉在预燃室出口区域的湍动强度提高,在局部还原性气氛下,NO_x生成浓度有最低值230.9 mg/m~3。当循环风率从0增大到30.6%时,内外二次风中氧气浓度降低,预燃室和炉膛主燃区还原性气氛增强,挥发分中含氮化合物HCN、NH_3等中的N迁移形成N_2的概率增加,NO_x排放量由250.7 mg/m~3逐渐降低到221.1 mg/m~3。随着燃尽风率由0提高到29%,NO_x排放值先减小后增大;燃尽风率提高时二次风率随之降低,内外二次风湍动扩散能力减弱,主燃区还原性气氛增强;燃尽风率进一步提高使得主燃区氧量不足,燃尽区氧化性氛围较强,大量焦炭和含氮化合物在燃尽区发生氧化反应,导致NO_x生成量增加;当燃尽风率为19.6%时,NO_x生成值最低为253.5 mg/m~3。整体上,当一次风率为17%~19%,内外二次风率比为0.8~1.0,外二次风由预燃室端面入射,循环风率为15%~20%,燃尽风率为19%~22%时,NO_x排放值为212~231 mg/m~3,相比试验工况下最大NO_x排放量下降29%~35%。
Aiming at increasingly stringent emission standards of coal-fired industrial boilers,a novel low-NO_x swirl burner was proposedin this paper. The pulverized coal preheating was coupled with the air staging of burner and furnace,and the pulverized coal preheating combustion state was adjusted by changing the air distribution of the combustion system. The effects of primary air rate,inner and outersecondary air rate,outer secondary air injection method,recirculating flue gas rate and over fire air(OFA) rate on NO_x emissions werestudied. The results show that with the increase of primary air rate from 15.4% to 28.7% in the experimental conditions,the oxygen con-centration in the preheating chamber increases,and N which is present in nitrogen-containing compounds HCN,NH_3,etc. in the vola-tile matter from the pyrolysis of pulverized coal is directly oxidized to NO by the oxygen carried by primary air,resulting in increasing NO_x formation from 284.4 mg/m~3 to 326.7 mg/m~3. When the ratio of internal and external secondary air increases from 0.46 to 1.4,the NO_x emission concentration decreases first and then increases. The inner secondary air volume affects the excess air ratio and turbulence inten-sity in the preheating chamber,and the outer secondary air volume affects the turbulence intensity of pulverized coal combustion reaction inthe primary combustion zone inside the furnace. Due to the combined effects of changes in secondary air distribution,the lowest NO_x emission value is 211.2 mg/m~3 when the ratio of inner and outer secondary air is 1.0. As the ratio of the air volume injected from the inside ofthe preheating chamber to injected from the end face of the preheating chamber of the outer secondary air increases from 0 to 4.56,the NO_x formation concentration reduces first and then increases. The outer secondary air injected from the end face of the preheating chamber has alonger injection boundary,which makes the primary combustion zone relatively larger and the overall combustion is relatively uniform.Whereas,the outer secondary air injected from the inside of the preheating chamber promotes the mixing of preheating products at the outletof the precombustion chamber with combustion air in the furnace. When the inside/end face injection air ratio of the outer secondary air is 0.25,the turbulence intensity of pulverized coal in the outlet area of the preheating chamber is improved,and the NO_x formation has a minimum value of 230.9 mg/m~3 in a partially reducing atmosphere. As the recirculating flue gas rate increases from 0 to 30.6%,the oxy-gen concentration in the inner and outer secondary air decreases,which makes the reducing atmosphere in the preheating chamber and theprimary combustion zone enhanced. The probability that N which is present in nitrogen-containing compounds HCN,NH3,etc. in the volatile matter reacts to form N_2 increases,and NO_x emission gradually decreases from 250.7 mg/m~3 to 221.1 mg/m~3. As the OFA rate increa-ses from 0 to 29%,the NO_x emission value decreases first and then increases. With the increase of the OFA rate,the secondary air rate de-creases,and the turbulence diffusion capacity of the inner and outer secondary air is weakened,meanwhile,the reducing atmosphere in theprimary combustion zone is enhanced. The further increase of the OFA rate makes the oxygen content in the primary combustion zone insuf-ficient,and the oxidizing atmosphere in the burnout zone is strong. At this time,a large amount of coke and nitrogen-containing compoundsundergo oxidation reactions in the burnout zone,resulting in the increase in the NO_x formation. When the OFA rate is 19.6%,the lowest NO_x emission value is 253.5 mg/m~3. Overall,When the primary air rate is 17%-19%,the inner and outer secondary air ratio is 0.8-1.0,the outer secondary air is injected from the end face of the preheating chamber,the recirculating flue gas rate is 15%-20%,and the OFArate is 19%-22%,the NO_x emission value is 212-231 mg/m~3,which is 29%-35% lower than the maximum NO_x emissions in the experi-mental conditions.

关键词(KeyWords): 工业锅炉;燃烧器;煤粉预燃;空气分级;NOx排放
industrial boiler;burner;pulverized coal preheating;air staging;NOx emissions

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基金项目(Foundation): 国家重点研发计划资助项目(2017YFB0603900)

作者(Author): 龚彦豪;许鑫玮;王登辉;王学斌;谭厚章;牛艳青;惠世恩;李在让;刘愿武;
GONG Yanhao;XU Xinwei;WANG Denghui;WANG Xuebin;TAN Houzhang;NIU Yanqing;HUI Shien;LI Zairang;LIU Yuanwu;State Key Laboratory of Multiphase Flow in Power Engineering,School of Energy and Power Engineering,Xi′an Jiaotong University;Taishan Group Co.,Ltd.;Xi′an Jiaoda Siyuan Technology Co.,Ltd.;

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