水泥窑烟气脱硝烧成系统的改造

介绍了水泥窑烟气脱硝窑头和窑尾烧成系统改造的技术原理和改造方案,探讨采用窑头低氮煤粉燃烧技术可实现降低回转窑内热力型NOx产生量,采用窑尾分解炉还原燃烧控制技术可实现将回转窑内产生的热力型NOx还原,大大降低了整个系统NOx产生量。实践表明,窑头低氮煤粉燃烧技术和分解炉高强还原燃烧控制技术可实现脱硝效率60%以上,大大减少NOx排放总量,降低了氨水用量和脱硝成本。     

水泥窑烟气脱硝烧成系统的改造

介绍了水泥窑烟气脱硝窑头和窑尾烧成系统改造的技术原理和改造方案,探讨采用窑头低氮煤粉燃烧技术可实现降低回转窑内热力型NOx产生量,采用窑尾分解炉还原燃烧控制技术可实现将回转窑内产生的热力型NOx还原,大大降低了整个系统NOx产生量。实践表明,窑头低氮煤粉燃烧技术和分解炉高强还原燃烧控制技术可实现脱硝效率60%以上,大大减少NOx排放总量,降低了氨水用量和脱硝成本。     

我国水泥行业NOx排放与污染控制现状分析

1 水泥行业NOx产生机理 根据目前的认识水平,在水泥熟料煅烧过程中,存在三种NO形成方式,即热NO形成、瞬时NO形成和燃料NO形成,其中瞬时NO形成方式必须有碳氢原子团存在,形成量很少,在工业窑炉中一般不予考虑.由燃料氮形成的NO量主要与挥发性的氮含量和反应条件如温度、过剩空气系数等因素有关.水泥窑产生的NO主要来源于助燃空气中的氮以及燃料、原料中的氮经氧化而成,常称为热力型氮氧化物,它的生成与温度、氧气过剩量和反应时间等因素有关,通常情况下,燃烧温度越高,生成的NO愈多;氧分子浓度愈高,NO生成速度愈快,NO愈多;高温区停留时间愈长,NO生成量愈多.在水泥回转窑系统中主要生成NO,NO2的量很少.     

低氮分级燃烧技术在CDC预分解系统的应用

对分解炉进行燃料分级燃烧改造,将燃料分级加入,在分解炉锥部形成还原区,还原窑内产生的热力型NOx,并抑制燃料型NOx的产生,同时配合操作优化调整,控制窑内燃烧气氛,减少窑头煤粉燃烧空气过剩系数,降低窑尾烟气氧含量,从而降低并稳定NOx的排放量.     

低氮燃烧器在5000t/d生产线上的应用

河南省禹州市锦信水泥有限公司有一条5 000t/d生产线,2013年7月开始使用低氮燃烧器,通过与厂家的共同探讨研究,改善燃煤方案、加强工艺管理措施和改进工艺煅烧等方法,顺利实现了低氮燃烧器的使用,达到了理想降氮效果。1煤粉燃烧过程产生NOx的机理分析NOx主要是通过热力型NOx,燃料型NOx和瞬时型NOx三种途径生成的．并且都在煤燃烧过程中出现。瞬时刹NOx是由燃料挥发物中的碳氢化合物高温分解生成的CH自由基和空气中氮反应生成的HCN和N,再进一步与氧作用以极快的反应速率生成NO,它的生成与温度关系不大。瞬时型NOx仅占NOx总排放量的5％左右。     

烧成论坛 栏目寄语

正本期文章重点涉及到水泥行业中两个较为关键的问题:一是脱硝技术,二是篦冷机改造。水泥回转窑中NO_x以热力型NO_x和燃料型NO_x为主。回转窑内不仅仅产生热力型NO_x,燃料型NO_x也可能很高。理论计算表明,煤中的氮元素全部被氧化,烟室NO_x超过2 000 ppm,实测中个别烟室NO_x高达3 000 ppm,与窑内温度、过剩空气系数、煤粉与热空气混合程度等紧密相关。喷煤管一次风压     

新型干法水泥窑氮氧化物脱除技术

1 水泥窑烟气特性 新型干法水泥生产工艺中．回转窑是NO的主要来源。煅烧水泥熟料时生成NO的途径主要有四种。即第一种热力NO．它是燃料在水泥窑头1400℃以上燃烧时会产生大量NO;第二种瞬发NO,它是有碳氢根存在时,于火焰前端瞬发形成的NO．一般这种瞬发NO生成量的比例很小：第三种燃料NO。它是由燃料中所含的化学接合氮所产生的。例如煤中约含有0．5％～2％的氮（按质量计）。因为燃料中氮原子的接合能较小,所以在水泥窑系统相对较低温的分解炉内产生的燃料NO较多：     

回转窑燃烧器降低氮氧化物机理分析

回转窑内的氮氧化物(NO_X)生成量占水泥厂NO_X总生成量的比例相对较小,且仅产生因窑内高温而形成的热力型NO_X,并可通过正确选用燃烧器得到有效控制。本文通过阐述回转窑内热力型NO_X的形成过程,以中材装备集团有限公司的大推力燃烧器为例进行了机理分析。     

SO2对氮氧化物生成的影响

研究了燃料燃烧过程中 N- S间的相互作用 .分别从实验和数值计算的角度总结 SO2对 NOx 及含氮中间产物生成和释放的影响 ,并试图通过反应机理来解释 .SO2 在贫燃料状态下能降低热力型 NO的释放 ,抑制富燃料状态下快速型 NO的生成 ,对贫燃料及富燃料状态下燃料型NO释放的影响不能得到统一定论 ,但 N- S间确实发生了复杂的相互作用 .数值计算的结果与实验相差较大 ,但具有一定参考价值 ,且能得到实验难以测量的中间产物的浓度变化趋势     

焦化炉中分级燃烧对降低氮氧化物排放的影响

延迟焦化炉是延迟焦化技术中的重要设备,燃烧过程中会产生氮氧化物对空气和人体产生很大的危害,研究表明,NO主要为温度型NO,快速型NO,燃料型NO,其中温度型NO占很大一部分。燃料分级是通过将燃料分级燃烧,使部分燃料在较大过剩的空气系数下燃烧,部分燃料在过小的空气系数下燃烧,使得燃料在非当量化学计量比下燃烧,从而降低燃烧温度,抑制氮氧化物的产生。     

NO reduction capacity of four major solid fuels in reburning conditions - Experiments and modeling

The combustion of solid fuels in the rotary kiln and in the calciner of a cement plant generates fuel and thermal NO. This NO can be reduced inside the reducing zone of the calciner. This occurs in two different ways: homogeneous reduction by hydrocarbons and heterogeneous reduction by char. The purpose of this paper is to identify the relative contribution of volatile matters or char on the NO reduction process, which largely depends on the nature of the solid fuel used for reburning.Experiments were undertaken in an Entrained Flow Reactor (EFR), at three temperatures: 800, 900 and 1000 °C. Four major fuels used in the cement production process were studied: a lignite, a coal, an anthracite and a petcoke. Specific experiments were undertaken to determine (i) their devolatilisation kinetics and the gas species released. A wide range of species influencing the NO chemistry was carefully analyzed. Then, (ii) the char oxidation and (iii) the char NO reduction kinetics were characterized. Finally, (iv), the “global” NO reduction capability of each fuel was quantified through experiments during which all phenomena could occur together. This corresponds to the situation of an industrial reactor in reducing conditions. Anthracite and petcoke reduce only very small quantities of NO whereas lignite and coal reduce, respectively, 90% and 80% of the initially present 880 ppm of NO (at 1000 °C after 2 s).The four types of experiments described above were then modeled using a single particle thermo-chemical model that includes heterogeneous reactions and detailed chemistry in the gas phase. This model reveals that both NO reduction on char and NO reduction by volatiles mechanisms contribute significantly to the global NO reduction. After short residence times (several tenth of a second), gas phase reactions reduce NO efficiently; after long residence times (several seconds) the char reduces larger quantities of NO.     

分解炉空气分级燃烧及NOx排放特性研究

随着我国经济的飞速发展,作为重要基础材料的水泥产品需求量极大且趋于稳定。水泥生产过程中的NOx排放与燃煤火电厂和汽车尾气产生的NOx排放已成为空气污染的主要来源,而分解炉是降低水泥生产工艺中NOx排放的有效设备。笔者在引入高温烟气的模拟分解炉内进行空气分级燃烧试验,研究配风位置、配风比例以及石灰石/煤比例对分解炉内燃烧和NOx排放特性的影响规律。试验稳定过程中,高温烟气发生装置的给煤量和配风量保持不变。此时,高温烟气发生装置的时间平均温度为911℃,其产生的高温烟气温度稳定在750℃左右,高温烟气中NOx主要以NO和N2O的形式存在,其浓度分别为261.49×10^-6和12.96×10^-6。该股高温烟气将模拟实际回转窑产生的烟气进入分解炉内。在分解炉的上部区域(距离顶部0~2 000 mm区域)的温度为800~1 000℃,与实际分解炉运行温度一致,排放烟气中NOx主要以NO和N2O形式存在。随着中间配风位置的下移,煤粉燃烧放热区域下移,而顶部区域的石灰石吸热量变化较小,则原有热量平衡被打破且原有吸热量高于现有放热量,导致顶部区域内燃烧温度降低。此时,还原气氛中煤粉燃烧和石灰石分解反应时间均变长,导致NOx的还原反应更加充分。但石灰石分解产生的氧化钙(CaO)作为中间产物会促进NO的生成反应,其反应时间增加也促进了NO的生成;另一方面,石灰石作为催化剂参与焦炭和挥发分还原NO的反应过程,分解炉顶部区域的温度下降使得该还原反应变弱。综上,NO的最终排放浓度是以上反应的综合结果。随着配风位置的下移,该变化对NO的生成作用更加明显,故NO的排放浓度逐渐升高。当一级风量与二级风量的配风比例降低时,分解炉上部区域的煤粉燃烧份额减少和石灰石分解量降低,而分解炉下部区域的煤粉燃烧份额增加和未分解的石灰石份额增加,但石灰石的吸热增加量高于燃烧增加份额的放热量,因此分解炉内整体温度均降低。分解炉内NO浓度是由石灰石催化的氧化过程和还原过程综合决定的。一级风量变小时,尾部CO浓度随之增加,烟气中NO浓度呈现降低的趋势。当石灰石/煤比例增加时,分解炉内沿程温度逐渐下降。随着石灰石给粉量增加,分解炉内石灰石受热分解产生的CaO浓度增加,CaO催化NO还原反应更剧烈,从而NO浓度逐渐降低。而石灰石给粉量增加和分解炉温度降低的过程导致尾部的CO浓度升高。     

利用“外燃式高温煅烧碳酸盐矿物质旋窑”实现窑尾废气CO2减排及脱硫的技术

随着以CO2为首的温室气体排放量急剧增加，全球气候变暖等环境问题日益严峻。在此背景下，分析了目前水泥窑减排CO2的技术措施及应用情况，介绍了外燃式高温煅烧碳酸盐矿物质旋窑技术，分析了该技术及相关装备的研究开发过程。重点介绍了利用“外燃式高温煅烧碳酸盐矿物质旋窑”实现窑尾废气CO2减排及脱硫的技术方案及原理，该技术虽还没有在水泥行业得以实际生产应用，但可在水泥窑减排CO2方面提供有益的参考。     

碳中和目标下的水泥工业低碳技术研究

介绍了世界水泥工业低碳技术。水泥行业的碳减排对我国实现碳中和目标的影响重大,迫切需要水泥行业通过技术创新驱动实现绿色低碳发展。针对水泥工业的碳排放主要来源,碳减排技术路径主要包括能源效率提升、原/燃料替代、低碳水泥、碳捕集利用和封存。比较分析了国内外典型的水泥窑替代燃料技术。从水泥窑尾烟气中捕集CO2,除了富氧燃烧和化学吸收法外,还包括直接分离的捕碳技术。介绍了水泥窑捕集到的高浓度CO2进行资源化利用的技术途径。     

模拟分解炉中煤焦燃烧生成NO的特性

对国内水泥行业中几种煤焦在模拟的分解炉中NO生成特性进行了研究,考察了煤种、温度、生料对焦炭氮的释放特性的影响,探讨了焦炭氮在工业分解炉中的释放机理.研究结果表明,不同煤种的NO生成特性有较大的不同;温度对NO的生成特性也有明显的影响,基本随温度的升高而加大,但有时也有下降现象;生料的加入大大加速了NO的生成速率和转化率,表明生料对NO生成有显著的催化作用.工业分解炉中产生的NO主要来源于燃料NO,焦炭氮转化为NO的概率主要有两个互相竞争的反应决定：包括N的氧化反应和NO的还原反应.     

Exergy analysis of thermal processes in the building materials industry

A method is proposed to calculate the chemical exergy with allowance for the chemical composition and the ambient temperature. The exergy analysis of cement clinker burning is performed. It is found that the maximal energy saving for a rotary cement kiln can be achieved by decreasing the sludge humidity and optimizing the fuel combustion and the clinker cooler operation. The analysis of thermal processes in terms of exergy characteristics is demonstrated to be more efficient than that in terms of thermal parameters, since the optimization and intensification of industrial kilns requires not only heat loss reduction but also more efficient use of heat.     

超临界CO2中合成聚碳酸酯

在超临界CO₂介质中由双酚A（BPA）和碳酸二苯酯（DPC）合成了双酚A型聚碳酸酯（PC）。反应生成的苯酚能够溶解扩散到超临界流体中。用红外光谱（FT-IR）、核磁共振谱（¹H-NMR）表征了产物的结构。凝胶渗透色谱（GPC）测试表明，合成过程中存在线形缩聚和成环两种不同的反应机理，产物的重均分子量高达117740，分子量分布指数P_d=1.33;差示扫描量热法（DSC）测试表明，超临界CO₂能增塑PC致使其玻璃化转变温度（T_g）降低。考察了反应时间、搅拌转速、反应温度等因素对PC分子量的影响。在反应压力为10 MPa下较佳反应时间为50 h，较佳搅拌转速为800 r·min^-1，较佳反应温度为120℃。     

Rotary cement kiln coating estimator: Integrated modelling of kiln with shell temperature measurement

Coating thickness protection in the burning zone of a rotary cement kiln during operation is important from the viewpoint of the kiln productivity. In this paper, an integrated model is presented to estimate the coating thickness in the burning zone of a rotary cement kiln by using measured process variables and scanned shell temperature. The model can simulate the variations of the system, thus the impact of different process variables and environmental conditions on the coating thickness can be analysed. The presented steady‐state model derived from heat and mass balance equations uses a plug flame model for simulation of gas and/or fuel oil burning. Moreover, the heat transfer value from shell to the outside is improved by a quasi‐dynamic method. Therefore, at first, the model predicts the inside temperature profile along the kiln, then by considering two resistant nodes between temperatures of the inside and outside, the latter measured by shell scanner, it estimates the formed coating thickness in the burning zone. The estimation of the model was studied for three measured data sets taken from a modern commercial cement kiln. The results confirm that the average absolute error for estimating the coating thickness for the cases 1, 2, and 3 are 3.26, 2.82, and 2.21 cm, respectively.     

Improving Pulverized Coal and Biomass Co‐Combustion in a Cement Rotary Kiln by Computational Fluid Dynamics

The cement industry is one of the largest pollutant emitters. One way to cope with high pollutant emissions is to co‐combust biomass with pulverized coal. A mathematical model was developed, which is detailed enough to consider the complex physical and chemical behavior of the co‐combustion process but simple enough to perform simulations with a real geometry of cement rotary kiln within reasonable time. Numerical simulation with a 20‐% share of pulverized biomass of total fuel heating value was performed. An industrial rotary kiln geometry was simulated; temperature and velocity fields along with mass fractions of released volatiles and combustion products were analyzed. The model allows better insights in the co‐firing process with the main goal to reduce CO₂ emissions by optimizing the combustion process inside the rotary kiln.     

Numerical Simulation of Pollutant Formation in Precalciner

For cement plants, great attention is being paid to the emission of the pollutant gases, especially NO, CO and CO₂. Precalciner is an important equipment in a cement plant in that it can reduce not only the heat loading of rotary kiln but also the NO emission because of its relative low operating temperature. In this paper, the mechanisms for the formation of NO and CO are analyzed and a numerical simulation technique is applied to model the coal combustion, raw material decomposition and concentration distribution of the pollutant gases in a full scale DD‐PRC (dual combustion and denitrator process precalciner). The predicted results agree well with the measured data.