洁净煤技术

2019, (04) 111-118

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煤粉燃烧过程强化脱硝技术研究
Research on enhanced denitrification technology in pulverized coal combustion process

周棋;王勇;刘松霖;刘一;陈灿;范卫东;
ZHOU Qi,WANG Yong,LIU Songlin,LIU Yi,CHEN Can,FAN Weidong

摘要(Abstract):

为进一步提高炉内燃烧过程的脱硝效率,尤其是解决燃用挥发分低的贫煤和无烟煤时炉内NO_x排放浓度高的问题,基于高温燃尽区喷氨还原NO机理,提出了多级燃尽风布置区的高温强化还原区喷氨脱硝技术——多级强化还原煤粉燃烧技术(MERC)。借助50 kW下行燃烧炉,开展了氨氮比(RNSR)、还原剂与烟气混合程度、还原剂载气等关键技术参数对脱硝效率的影响,同时开展了MERC和SNCR对比试验研究,并进行了MERC技术的工程应用试验。结果表明:采用双支喷枪对喷能提高还原剂与炉内烟气的混合程度,双支喷枪对喷使脱硝效率从单支喷枪的45%提高到70%;空气作为载气,氨氮比超过1. 2时,NO浓度在500~700 mg/Nm~3,随着氨氮比增加,NO_x浓度先升后降;烟气作为载气时NO_x浓度大幅降低,仅为100 mg/Nm~3左右,因此还原剂的载气中含氧量越低,越有利于增强高温中喷氨还原NO的效果,还原剂载气需尽可能降低氧含量或采用无氧媒介。通过对比SNCR和MERC试验结果发现,氨氮比小于2时,常规SNCR的NH3耗量高于MERC;氨氮比超过2. 5后,NH3同NO的反应趋于饱和,过量的NH3同SO_2发生反应生成(NH4)2SO3和NH4HSO3,这是工程上出现SNCR过量喷尿素后造成空气预热器堵塞的原因。对某电厂125 MW燃煤锅炉进行低氮改造,由于该电厂1、2号锅炉燃用无烟煤+贫煤+烟煤的混煤,2015年低氮燃烧系统改造后一直存在锅炉出口NO_x浓度不稳定的情况,尾部脱硝装置入口最低在500 mg/m~3以下,最高为1 200 mg/m~3。为确保改造达到超低NO_x排放目标值,在原有燃烧优化试验+SNCR改造+SCR优化提效的设计方案的基础上增加了燃尽风前的尿素喷枪。结果表明:炉内脱硝效率高于65%,结合锅炉尾部SCR装置能实现烟囱位置NO_x浓度不高于30 mg/m~3的超低排放,达到了预期效果。
In order to further promote the denitrification efficiency in the combustion process,especially to solve the problem of high NOx emission in the furnace when burning low volatile meagre coal or anthracite,a technology with ammonia injection denitrification in the high temperature intensified reduction zone-multi-staged enhanced reduction pulverized coal combustion technology (referred to as MERC) was proposed based on the reducing NO mechanism by ammonia.By means of a 50 kW down-fired furnace facility,the effects of key technical parameters,i.e.,ammonia-nitrogen ratio (RNSR),mixing degree of reductant and flue gas,and carrier gas type of reductant on denitrification efficiency were studied.The comparative experiments of MERC and SNCR were carried out,and the engineering application test of MERC was performed.The results show that the mixing degree of reducing agent and flue gas in the furnace can be improved by using double-spray guns,and thus,the denitrification efficiency can be increased from 45% to 70%.The NO concentration is between 500-700 mg/Nm3 when air acts as a carrier gas and the ammonia-nitrogen ratio exceeds 1.2.The NOx concentration rises firstly and then falls as the ammonia-nitrogen ratio increases.When the flue gas is used as the carrier gas,the NOx concentration is greatly reduced to be only ca.100 mg/Nm3.The results show that the lower oxygen content in the carrier gas of the reducing agent,the more beneficial it is to enhance the effect of ammonia reduction in high temperature.The reducing agent carrier gas needs to reduce oxygen content as much as possible or use oxygen-free medium.By comparing the results of SNCR and MERC experiments,it is found that the NH3 consumption of conventional SNCR is higher than that of MERC when the ammonia-nitrogen ratio is less than 2,then the reaction of NH3 with NO tends to be saturated after the ammonia-nitrogen ratio exceeds 2.5,and the excess NH3 reacts with SO2 to form (NH4)2SO3 and NH4HSO3,which is the reason of clogging of the air preheater caused by excessive SNCR injection in the project.Laboratory research results are further practiced in engineering.Low nitrogen technological reform was applied to 125 MW coal-fired boiler in a power plant.Since the No.1 and No.2 boilers in this power plant were fed anthracite+lean and coal+bituminous coal mixture,the concentration of NOx at the outlet of the boiler was unstable since the retrofit of the low nitrogen combustion system in 2015.The inlet of the tail denitrification unit is below 500 mg/m3 and the maximum is 1 200 mg/m3.In order to ensure that the retrofit achieves the target value of ultra-low NOx emission,the urea spray gun before exhaust air was added on the basis of the original design scheme of combustion optimization test+SNCR retrofit+SCR optimization.The results show that the denitrification efficiency in the furnace is higher than 65%.Combining with SCR device at the tail of the boiler,the ultra-low emission of NOx concentration at the chimney position is achieved,which is not higher than 30 mg/m3.Eventually,the MERC application was realized,and the field test of retrofit project proved the MERC application achieved the desired effect.

关键词(KeyWords): 下行炉;强化还原;还原剂;燃尽风;脱硝效率
down-fired furnace facility;enhanced reduction;reductant;burnout air;denitration efficiency

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作者(Author): 周棋;王勇;刘松霖;刘一;陈灿;范卫东;
ZHOU Qi,WANG Yong,LIU Songlin,LIU Yi,CHEN Can,FAN Weidong

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