洁净煤技术

2019, (05) 86-92

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660 MW超超临界循环流化床锅炉超低NOx排放研究
]Study on ultra-low NOx emission technology of 660 MW ultra-supercritical circulating fluidized bed boiler

李影平;辛胜伟;王凤君;
LI Yingping,XIN Shengwei,WANG Fengjun

摘要(Abstract):

循环流化床(CFB)发电技术具有良好的炉内脱硫抑氮等优势,得到了广泛推广。随着环保形势的日趋严峻,CFB锅炉仅依靠炉内低氮燃烧无法满足NOx超低排放要求,因此必须深入研究CFB锅炉炉内低氮燃烧理论,并在660 MW高效超超临界CFB锅炉实现突破。基于流态重构节能型CFB锅炉的设计理念,通过试验和数值模拟研究了炉内NOx生成还原机理与炉内实现NOx全部脱除的技术方案。结果表明,影响660 MW超临界CFB锅炉NOx排放的因素包括:燃用煤质、燃烧温度及均匀性、过量空气系数(运行氧含量)、分级燃烧等。660 MW超超临界CFB锅炉采用单炉膛、单布风板、M型布置、4个旋风分离器、4个外置式换热器的炉型结构,锅炉热一次风从水冷风室后侧6点给入,保证了锅炉一次风静压分布均匀,进而保证了物料流化均匀性;采用“前墙给煤、后墙给煤泥”的给煤方式,前墙布置12个落煤口,后墙布置8支煤泥枪,同时后墙布置8点排渣,保证给煤均匀性;采用4旋风分离器布置结构保证了物料均匀性,不同旋风分离器之间流率偏差的最大值为7.9%;采用4个外置式换热器均匀布置保证床温的均匀性。同时炉内温度场及过量空气系数对NOx排放起关键作用,锅炉设计床温确定为860℃,既保证了锅炉效率,又减少了NOx排放,同时保证低负荷工况下满足选择性非催化还原(SNCR)脱硝系统反应温度窗口;锅炉过量空气系数选取1.15,进一步增强了还原性氛围。分级燃烧时一、二次风比例为4∶6,并适当调整锅炉二次风口位置及倾角,形成较大的还原性氛围。通过上述措施可实现炉内高效抑氮,最终使锅炉NOx原始排放浓度低于50 mg/m3,炉外选取以尿素为还原剂的SNCR技术为辅助脱硝手段,在低投资、低成本、全负荷条件下实现最终烟气中NOx超低排放。
Circulating fluidized bed(CFB)power generation technology is one of the clean coal power generation technologies developed in recent decades. Because of its good advantages of desulphurization and nitrogen suppression in furnace,it has been widely popularized. With the increasingly serious environmental situation,the CFB boiler can not meet the NOx ultra-low emission requirement by means of the low-nitrogen combustion in the furnace,so it is necessary to study the low-nitrogen combustion theory of the CFB boiler,and the breakthrough should be realized in 660 MW high efficiency ultra-supercritical CFB boiler. In this paper,based on the design concept of flow pattern reconstruction energy-saving CFB boiler,the generation and reduction mechanism of NOx in furnace and the technical scheme of NOx removal in furnace were studied by experiment and numerical simulation. The results show that the factors affecting NOx emission of 660 MW supercritical CFB boiler include burning coal quality,combustion temperature and uniformity,excess air coefficient(operating oxygen),graded combustion and so on. The 660 MW ultra-supercritical CFB boiler adopts the furnace structure of single furnace,single air distribution plate,M-type arrangement structure,four cyclones and four external heat exchangers. The hot primary air of the boiler is fed from the back side of the water-cooled air chamber at 6 points,which ensures the uniform distribution of the static pressure of the primary air of the boiler,and thus ensures the uniformity of the fluidization of the material. The coal feeding mode of "coal feeding on the front wall and sludge for the back wall" is adopted. The front wall is equipped with 12 coal falling ports,the rear wall is equipped with 8 sludge guns and 8 slag discharge ports to ensure the uniformity of coal feeding. The arrangement structure of the 4-cyclone separator ensures the uniformity of the material,the maximum deviation of flow rate between different cyclones is 7.9%,and the uniform arrangement of the four external heat exchangers ensures the uniformity of the bed temperature. The temperature field and excess air coefficient play a key role in NOx emission. The boiler design bed temperature is 860 ℃,which not only ensures the boiler efficiency,but also reduces the NOx emission,at the same time,it ensures the reaction temperature of selective non-catalytic reduction(SNCR)denitrification system under low load conditions. The excess air coefficient of boiler is 1.15,which further enhances the reductive atmosphere. The ratio of primary to secondary air is 4∶6 in staged combustion,and the position and inclination angle of boiler secondary tuyere are adjusted properly to form a large reductive atmosphere to ensure the furnace combustion atmosphere. The comprehensive effect of the above measures can realize high efficiency nitrogen suppression in the furnace,and finally make the original emission concentration of boiler NOx less than 50 mg/m3,as The SNCR technology with urea as reductant outside the furnace is selected as the assistant denitrification method realize the final NOx ultra-low emission in the flue gas under the condition of low investment,low cost and full load.

关键词(KeyWords): 超超临界;循环流化床;锅炉;NOx;超低排放
ultra-supercritical unit;circulating fluidized bed(CFB);boiler;NOx;ultra-low emission

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作者(Author): 李影平;辛胜伟;王凤君;
LI Yingping,XIN Shengwei,WANG Fengjun

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