选择性非催化还原(SNCR)技术及其应用前景

介绍了SNCR工艺原理及反应机理,详细讨论了反应温度、NH3/NOx摩尔比、不同还原剂、不同添加剂以及烟气中氧对SNCR反应过程和脱硝效率的影响。展望SNCR技术的发展方向,介绍了SNCR与其他脱硝技术的联合应用。     

高固气比悬浮预热分解系统脱硝优势理论分析

随着水泥行业氮氧化物的污染越来越严重,研究并发展实用于水泥行业的脱硝技术也越来越迫切.本文首先介绍了水泥工业中NOx排放类型及其主要的脱硝技术,这些技术目前已经投入使用,但都存在一些问题,仍需进一步研究与实践;最后介绍了高固气比悬浮预热分解系统脱销理论并通过对其技术鉴定,NOx排放可降低50％以上.     

SNCR脱硝装置对CFB锅炉运行的影响研究

介绍了CFB锅炉性能试验情况,并结合性能试验分析了SNCR脱硝装置对CFB锅炉运行的影响。结果表明：CFB锅炉SNCR脱硝工艺的脱硝效率可以达到60%以上;氨逃逸浓度高会加速空气预热器积灰阻塞;烟气中的逃逸氨与SO3相互作用,极易在空气预热器低温段形成积垢,引起空气预热器阻力增加,但能降低二者在空气预热器出口的排放浓度。     

SNCR+SCR烟气联合脱硝工艺在电站锅炉中的应用

简述了选择性非催化还原（SNCR）+选择性催化还原（SCR）烟气联合脱硝技术原理,针对某电厂5号机组（装机容量130 MW）氮氧化物（NOx）排放超标问题,通过CFD数值模拟,制定了SNCR+SCR烟气联合脱硝工艺。首先采用低氮燃烧技术,将锅炉NOx排放控制在350 mg/m3以下,并且保证SNCR区域较低CO浓度;其次采用SNCR技术,将SCR脱硝装置前NOx质量浓度控制在200 mg/m3以下;最后采用SCR技术,将锅炉出口烟气NOx质量浓度控制在90 mg/m3以下,实现了重点地区NOx达标排放。     

Action of oxygen and sodium carbonate in the urea-SNCR process

Experimental researches are focused on the effects of O₂ concentration and sodium carbonate on Selective Non-Catalytic Reduction (SNCR) performance in a tube reactor, and plug flow reactor model and perfectly stirred reactor model in CHEMKIN are adopted to simulate the reactions processes. It is found that there is a conversion temperature point (CTP), on the two sides of which oxygen performs different effect. Below CTP, which is 1273 K in our experiments, higher NO reduction efficiency can be gained with higher oxygen concentration because more O₂ results in more radicals to drive the reduction chain reactions by speeding up the reactions O₂ + H = O + OH and H₂O + O = 2OH. At 1473 K without oxygen, 60% of NO reduction efficiency can be achieved and a 15 ppm Na₂CO₃ addition improves it to 90%. In this case the reaction H₂O + H = OH + H₂ becomes fast enough to provide the radical OH without the aid of O₂ to produce NH₂ which reduces NO. And H₂ is the byproduct of this reaction. Na₂CO₃ addition shifts the optimal temperature of SNCR 50 K towards lower temperature and more NO is removed in the temperature window. The reactions NaO + H₂O = NaOH + OH and NaOH + O₂ = NaO₂ + OH and NaOH + M = Na + M + OH offer new pathways to produce OH radical, which results in more OH and more NH₂ to reduce NO. The promotion effect of Na₂CO₃ is significant when temperature is lower or O₂ concentration is lower, which means the radicals are insufficient.     

循环流化床锅炉烟气脱硝系统优化模拟

随着电站锅炉氮氧化物（NO_x）排放标准的日趋严格,具有低NO_x排放特征的循环流化床（CFB）锅炉也需增设烟气脱硝设备。通过在CFB锅炉旋风分离器喷入氨水或尿素等还原剂,实现高温下的选择性非催化还原（SNCR）反应,可有效降低锅炉NO_x排放。以某185 t/h CFB锅炉为例,利用ANSYS Fluent^􀅹软件,对分离器及附属尾部烟道流场进行性能优化模拟,并设计了相应的SNCR烟气脱硝系统。计算结果表明：当喷入点个数较多且位于进口段内侧时,还原剂在分离器内分布较为均匀;提高平均雾化粒径和喷雾锥角有助于扩大还原剂在分离器内的分散范围,而喷射速度对分散范围的影响则有限。     

对用烃类和氨为还原剂的脱硝技术的计算分析

采用Chemkin 4．0软件包中基状流反应器和Miller等人的化学动力学模型,对再燃、先进再燃、选择性非催化还原（SNCR）以及加入烃类的SNCR反应的原理进行了模拟计算和比较分析,研究了不同反应温度、再燃燃料比和停留时间对脱硝效率的影响。计算结果表明,先进再燃引入氨基还原剂,可以拓宽脱硝的有效温度区间,加快反应速率,提高脱硝效率约20％,优于常规再燃技术;SNCR反应中加入很少量烃类（烃／NO〈1）可以增加其有效的脱硝温度范围,加快脱硝反应速率,使完成脱硝反应所需时间缩短一半,在较低的反应温度下达到较高的脱硝效率;而先进再燃达到相当的脱硝率则需要消耗超过15％的再燃燃料。