竹炭用于水泥窑炉烟气脱硝的反应条件研究

竹炭是在无氧或缺氧条件下经过高温裂解生成的多孔固体颗粒状生物质炭材料,对氮氧化物具有吸附和还原作用.在分析竹炭化学组成与表面官能团基础上,研究竹炭质量比、反应温度和氧气浓度对竹炭脱硝率的影响,探讨竹炭用于水泥窑炉烟气脱硝的反应条件.结果 表明,竹炭富含C、N、O元素和少量金属化合物,可以有效还原水泥窑炉烟气中氮氧化物.900℃竹炭中的石墨碳C-C键和含氮官能团-NCO键的相对含量较高,对氮氧化物的还原具有较好的促进作用.反应温度和氧气浓度对竹炭脱硝率具有显著性影响,影响因素大小顺序为温度＞氧气＞质量比.反应温度900℃,氧气浓度1％和竹炭质量比为4％的反应条件下具有较高初始脱硝率.     

煤炭中温活化碳共价键解聚机理

为研究煤粉不同气氛和温度活化后的热半焦在微观结构上的变化规律，采用拉曼光谱对煤焦碳架结构进行表征，采用X射线光电子能谱(XPS)检测C和O的表面官能团，固态核磁共振碳谱(¹³C-NMR)表征碳共价键。将3种测量方法互相验证，提高结果可靠性，从微观层面表征半焦的化学结构，分析煤粉中温活化反应中温度和气氛对煤焦化学结构和表面官能团演变的影响，并探讨中温活化机理。结果表明，60～900℃下CO₂和水蒸气对半焦活性均有显著增强作用，这可能是气体分子与煤焦分子结合形成羰基或羧基，在羰基或羧基分子影响下相连的碳键削弱断裂，从而破坏芳香环，产生新的活性位点，增强煤炭反应活性。经800℃下CO₂活化或900℃下水蒸气活化后的半焦，活性位点数量均增加2倍以上，同时羰基和羧基占比之和由18%分别增至32%和34%,而CO₂中温活化引起接氧脂碳由0.02增至0.11,水蒸气活化后桥碳比为0.01,相比N₂热解半焦桥碳比大幅降低。煤粉中温活化反应主要通过形成羰基或羧基破坏芳香结构形成更多活性位点，但二...     

低阶碎煤有氧热解制备兰炭的工艺条件

以流化石英砂为介质,研究了热解温度、O2浓度、原煤停留时间及粒径等流化条件对由小粒径低阶碎煤所制半焦的理化性质的影响. 结果表明,1~13 mm小粒径低阶煤在热解温度大于850℃及O2浓度、热解时间分别不低于3%(j)和120 s的条件下,可制得固定碳含量高于82%(w)、挥发分含量低于7%(w)的兰炭. 热解温度由650℃升至950℃,碳晶格的微晶晶面间距(d002)由0.383 nm减小至0.372 nm,半焦晶格的有序化程度增加. 氧气浓度为7%(j)时,半焦的比表面积最大,为242.71 m2/g,同时氧化反应活性也最大. 延长有氧气氛下的热解时间,半焦孔隙结构因烧蚀而坍塌,半焦的比表面积和活性降低.     

热解气氛与温度对褐煤半焦“一步法”甲烷化活性的影响

为提高褐煤热解多联产技术中半焦的利用效率,本文提出将低温热解半焦用于"一步法"制甲烷技术,考察了热解条件对半焦性质和一步甲烷化活性的影响。利用管式炉制备了不同气氛和温度的褐煤热解半焦,采用傅里叶红外光谱、X射线衍射技术和固定床反应器,对半焦表面化学、微晶结构和甲烷化活性进行了表征。结果表明,与N2和H2氛围相比,褐煤在水蒸气氛围中进行热解,半焦表面含氧官能团受到保护而含量更高,同时石墨化程度因受阻而降低,甲烷化活性更高;在水蒸气氛围中,773~873K范围内,随着热解温度升高,褐煤裂解反应进行程度加深,半焦表面含氧官能团数量降低,石墨化程度增加,致使甲烷化活性降低。总之,在水蒸气氛围中,773K时热解形成了一步甲烷化反应活性最好的褐煤半焦,对于低阶褐煤热解过程与气化过程优化联产具有重要指导意义。     

半焦催化裂解煤焦油试验研究

为了提高褐煤热解制得半焦对焦油的催化裂解效果,采用煤热解制备的半焦催化裂解煤热解过程中产生的煤焦油。采用两段式固定床反应器,在反应器上段放置煤样热解,下段放置半焦催化剂催化裂解上段产生的焦油。研究了制焦温度、半焦用量、经O_2活化后半焦对焦油催化裂解效果的影响。结果表明,增加褐煤的制焦温度,焦油产率明显下降,褐煤900℃制备的活化半焦1 g时的焦油产率仅6.3%,提高半焦制焦温度有利于焦油中的大分子芳香类物质催化裂解成少环物质和小分子气体组分;增加半焦用量对焦油脱除效果作用不明显,焦油产率缓慢减少。与未活化半焦相比,O_2活化后的半焦对焦油的脱除效果更好。半焦的比表面积及孔隙分析(BET)表明,活化后半焦的比表面积更大,且孔隙更丰富;能谱分析(EDS)发现,活化后半焦表面金属元素总量高于未活化半焦。     

天然矿物共混活性焦联合低温脱硫脱硝

以P1/Ti2-15@AC天然矿物共混改性活性焦,模拟研究移动床反应器系统中活性焦联合脱硫脱硝反应过程。研究结果表明,采用新型天然矿物共混改性活性焦,结合加热再生设计,可以很好地将烟气脱硫和脱硝过程结合,从而实现高效率、低成本的一体化联合脱硫脱硝。研究表明,循环脱硫再生后P1/Ti2-15@AC-Rn的脱硝活性得到显著提升,P1/Ti2-15@AC-R1和P1/Ti2-15@AC-R2的脱硝NO转化率接近100.0%,第三次再生后降低至85.0%左右并保持基本稳定。这主要是因为脱硫再生后活性焦表面酸性C—O、C—S等酸性官能团增加,增强了脱硝时活性焦表面NH₃的吸附过程,从而提升脱硝反应效率。     

淖毛湖煤慢速热解过程官能团相互作用

采用滴管炉,在短停留时间下,制备具有一定低温反应活性而消除主要低温交联位点的淖毛湖煤（NMHcoal）快速热解半焦（NRPchar）,再将NMHcoal和NRPchar混合进行慢速热解,研究官能团间的相互作用。热重分析结果表明,NMHcoal/NRPchar混合比为5∶5,温度为500℃热解时具有较强的负协同作用。固定床热解结果表明,NMHcoal热解生成的挥发物部分扩散至NRPchar中,?CH₃与芳碳自由基以及?O有更多的结合概率与时间,使焦油中含甲基的萘、酚类增多,半焦中烷基化邻氧芳碳结构与醚类结构增加。析出的酚类增多,使半焦中连氧芳碳结构减少。NRPchar中生成较多的多环芳烃前体,它们与酚类物质发生反应生成多环芳烃和CO,使共热解焦油中5、6环化合物含量增加,而另一部分滞留在半焦中使其比表面积降低。     

煤热解半焦结构及其对制备型煤成型特性的影响

以不同热解条件下制取的陕西烟煤(YL)半焦为原料,使用预糊化淀粉为黏结剂冷压成型制取成型燃料,分析不同热解条件下获得的煤焦成型后的物理特性,研究热解条件对半焦挥发分和表面含氧官能团的影响规律,揭示热解半焦特性对其成型的影响机理。结果表明:热解停留时间和热解终温对半焦成型特性具有显著影响。热解停留时间增加和热解终温升高会降低半焦挥发分含量和表面含氧官能团,影响黏结剂颗粒和半焦颗粒之间的黏结作用,从而会降低半焦成型后的冷压强度和跌落强度。结果表明:挥发分质量分数在16%以上的半焦成型后冷压强度大于450 N,适宜成型;热解终温小于600℃且热解停留时间小于5 min的半焦表面含氧官能团含量较高,成型后冷压强度大于450 N,可用于成型。半焦的成型特性受其挥发分含量和表面含氧官能团的综合影响。     

负载复合金属催化剂的活性半焦脱除烟气中NO的非等温动力学研究

对负载复合金属催化剂的活性半焦脱除烟气中NO进行了非等温动力学研究,并对其反应机制进行了探讨.使用热重分析仪进行程序升温脱硝实验,采用Flynn-Wall-Ozawa(FWO),Kissinger-Akahira-Sunose(KAS)和Coats-Redfen(CR)非等温动力学方法,计算纯活性半焦和负载金属催化剂的活性半焦脱硝的表观活化能.使用X射线衍射仪(XRD)对催化剂脱硝前后的金属活性相进行了分析.结果表明:在活性半焦上负载铜铁复合金属催化剂后,降低了脱硝反应的表观活化能、反应所需温度和反应能耗;当活性半焦的碳转化率≤0.3时,脱硝过程主要由化学反应控制,当碳转化率0.3时,脱硝过程转向扩散控制为主;通过XRD结果分析可知,金属催化剂的低价态活性相具有较高的催化活性,随着脱硝反应的进行,金属活性相被氧化成为活性较低的高价态;复合金属氧化物铁酸铜能在反应过程中分解成为活性更高的金属活性相,提高了脱硝性能.     

沉降炉中生物质热解产物的脱硝特性

利用连续沉降炉模拟白酒糟循环流化床解耦燃烧再燃区的反应气氛,研究各因素对半焦、焦油和热解气脱硝效率(比脱硝效率)的影响. 结果表明,反应温度由800℃升至1050℃,热解产物比脱硝效率均增大;半焦和焦油达到最佳比脱硝效率所需的停留时间为3.4 s;随反应气中NO浓度由400′10-6(j)增加到1000′10-6(j),热解产物比脱硝效率均呈降低趋势,但NO绝对还原量却呈增加趋势;随反应气中O2浓度增加,半焦比脱硝效率增大,热解气比脱硝效率降低,焦油比脱硝效率呈先增加后减少的趋势,在O2浓度为1.6%(j)时达最大,为60.1%. 在本研究的反应条件下,焦油比脱硝效率最好,热解气次之,半焦效果较差.     

煤焦直接还原脱除烟道气氮氧化物

选用3种不同煤焦,采用程序升温和恒温实验方法,在固定床上考察了不同实验条件下的NO转化率和C对NO选择性,分析了煤焦脱硝的机理和影响因素。实验结果表明：NO和O₂在煤焦表面发生化学吸附所形成的络合物在脱硝过程中起着关键作用,影响C-NO反应和C-O₂反应的竞争与协作关系。在所考察的煤焦中锡林浩特褐煤焦脱硝效果最好,当温度为723 K时烟道气中NO还原率可达99%;在温度623～923 K、O₂浓度0～5%范围内,提高温度和O₂浓度均有利于提高NO转化率,而降低O₂浓度有利于提高C对NO选择性;烟道气中NO浓度越高,其转化率越低,但C对NO选择性越高。     

Characteristics of oxygen chemisorption on porous coal char

Oxygen chemisorption on a porous coal char was investigated by a typical consecutive pyrolysis and chemisorption experiments in a thermogravimetic analyzer. Small amounts of carbon-oxygen surface complexes are gasified to CO and CO₂ during the oxygen chemisorption at 423 K. The kinetic equation of oxygen chemisorption on porous char including gasification of surface oxides well represents the chemisorption/gasification behavior of oxygen on the coal char. The activation energy and the frequency factor for oxygen chemisorption on coal-char are found to be 57 kJ/mol and 9.16×10⁶/hr, respectively.     

Synthetic coal chars for the elucidation of NO heterogeneous reduction mechanisms

In the present work, the mechanisms involved in NO–char heterogeneous reduction have been studied using a synthetic coal char (SC char) as carbon source. Another synthetic char (SN char) without nitrogen in its composition has also been employed in these studies. Isothermal reduction tests at different temperatures have been carried out. Two temperature regimes were considered: low temperature (T < 250 °C) where NO chemisorption takes place and high temperature (T > 250 °C) where NO–C reaction occurs. Step response experiments combining consecutive reaction stages with NO and ¹⁵NO were performed in order to determine the role of nitrogen surface complexes, C(N), in the reduction process. The results revealed N₂ and CO₂ to be the main reduction products under the experimental conditions employed in this work. NO chemisorption at lower temperatures results in N₂ emission and surface complexes (mainly oxygenated) formation, while char gasification by NO involves a direct NO attack on the char surface to form surface complexes. As a consequence of desorption of these complexes new sites of reaction are created.     

煤燃烧过程中NOx的生成和还原

燃煤过程中ＮＯｘ 的排放是一个复杂的过程, 既包括ＮＯｘ 的生成过程又包括生成的ＮＯｘ 进行均相和多相还原反应． 简述了煤燃烧过程中ＮＯｘ 生成和还原的机理． 认为燃料氮是ＮＯｘ的主要来源,ＮＯｘ 的排放与煤阶、煤中氮含量以及温度等因素有关;ＮＯｘ 与半焦的多相反应是ＮＯｘ还原的主要原因, 其中包括ＮＯｘ 在半焦表面的化学吸附、表面络合物的生成以及产物的生成和脱附等过程     

Effect of oxygen chemisorption on char gasification reactivity profiles obtained by thermogravimetric analysis

The gasification reactivity of an Illinois No. 6 bituminous coal char was determined in oxygen and carbon dioxide using thermogravimetric analysis (TGA). Extensive tests were carried out to ensure the absence of diffusional limitations. Measurements of chemically controlled rates were verified by analysing the activation energies for reactions of the char at various conversion levels. The effect of stable carbon-oxygen complex formation on TGA reactivity profiles was investigated. For disordered carbons (e.g. coal chars) gasified in oxygen, the results showed that the observed differences between reactivity profiles obtained by TGA and those obtained by product gas analysis (e.g. non-dispersive infrared spectroscopy, i.r.) can be attributed to significant amounts of stable complex being formed during the initial stages of reaction. The fact that TGA reactivity profiles become equivalent to i.r. reactivity profiles, when corrected to account for stable complex formation, suggests that the former may not be accurate representations of the variations in intrinsic reaction rates and should be used with caution when attempting to validate proposed models of char gasification kinetics. The extent to which stable complex forms during char gasification was used to explain the observed differences in the reactivity profiles obtained for reactions of char in oxygen and carbon dioxide.     

Kinetic relationship between NO/N2O reduction and O2 consumption during flue-gas recycling coal combustion in a bubbling fluidized-bed

Flue-gas recycling combustion of a sub-bituminous coal and its rapid pyrolysis char at 1120 K has been simulated experimentally in a bubbling fluidized-bed. O₂, CO₂ and H₂O, and NO or N₂O were pre-mixed and fed into the bed together with coal/char particles with the O₂ concentration in the exit gas maintained at 3.5 vol%. Increasing the inlet O₂ concentration, thus increasing the O₂ consumption rate and decreasing the flue-gas recycling ratio, caused the once-through conversion of fuel-bound nitrogen into N₂O to decrease while the conversion to NO to remain unchanged. The in-bed reductions of NO and N₂O were both first order with respect to the respective nitrogen oxide, with the rate constants to increase linearly with the rate of O₂ consumption in the bed and thus also with that of char/volatiles consumption. This finding, which indicated linear increase in the concentrations of reactive species involved in NO/N₂O reduction with the rate of O₂ consumption, enabled consideration that the homogeneous and heterogeneous reduction rates of NO and N₂O were proportional to the consumption rates of O₂ by the volatiles and char, respectively. The rate analysis of the kinetic data revealed the relative importance of burning volatiles and char as the agents for the reduction of NO and N₂O. While the reduction in the gas phase was fully responsible for the NO-to-N₂O conversion, the reactions over the char surface governed the NO-to-N₂ reduction. The volatiles and char had comparable contributions to the reduction of N₂O to N₂. The NO-to-N₂ and N₂O-to-N₂ reductions over the char surface were, respectively, accelerated and decelerated by increasing the H₂O concentration.     

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.     

煤焦燃烧中氢氧化物生成因素的研究

在一固定床反应器上研究了3种煤焦在不同氧浓度、不同温度下燃烧时NO及N_2O生成特性,还研究了燃烧后气体停留时间对NO和N_2O生成的影响,以及NO的加入对N_2O对生成的影响.研究表明,煤焦燃烧中NO主要由氧气吸附于(-CN)基上形成(-CNO)基后而生成,而N_2O的生成机理则有3个,本文比较了这3个反应机理的相对重要性.     

Identification of the mechanism of coal char particle combustion by porous structure characterization

Two limiting models—the shell progressive mechanism and the homogeneous mechanism—can describe combustion of a single coal particle. Some information about the real mechanism can be obtained from investigation of the porous structure development during combustion. Using the principles of gas adsorption and mercury penetration, the porous structure of a partially combusted particle was estimated. Experiments were carried out in an equipment by applying the thermogravimetric method and using a single devolatilized coal particle. The inlet concentration of oxygen was 5 and 15 mol%. The initial temperature of combustion was in a range from 450 to 800 °C. The mechanism of coal char particle combustion depends on the initial temperature and the inlet concentration of oxygen. At low temperature and low inlet concentration of oxygen, the rate of principal chemical reactions is comparable with the rate of diffusional transport of oxygen inside the particle. Combustion is governed by the diffusion mechanism. This is evident from the values of the specific surface area of pores and proportional representation of individual pore types. At higher temperatures and low inlet concentrations of oxygen, combustion proceeds by the shell progressive mechanism. The specific surface area is lower in comparison with the previous case. There is a sharp interface between the particle core and the ash shell. The core exhibits a higher value of specific surface area than in the case of a non-combusted coal char particle. This fact can be explained by the consecutive reaction of carbon dioxide with carbon in the core of the particle. The rate of this reaction is sufficiently high at temperatures above 800 °C.     

Chemical reduction of sulphur dioxide to free sulphur with lignite and coal. 2. Kinetics and proposed mechanism

The reactivity of lignite and different ranks of coal with sulphur dioxide has been investigated in a corrosive-gas, thermogravimetric reactor system. With all coals, the reaction occurred in two distinct stages. A rapid initial stage was controlled primarily by the devolatilization rate of the coal. The second stage limited the overall rate and was controlled by surface properties of the coal char. The portion of lignite associated with the second stage of reaction exhibited a much higher rate of SO₂ reduction than the corresponding material from all other coals. Correlation of the data showed an inverse relation between the reactivity of coal chars and the relative rank of the parent coal. Activation energies associated with the reduction of SO₂ by the coal chars increased slightly from 134 kJ mol^?1 for lignite char to 150 kJ mol^?1 for HVB bituminous coal char. The higher reactivity of lignite or lower-rank coals was due in part to entropy factors or available catalytic sites on the surface of coal. Formation of a thermally stable CS complex on the surface of coal appeared to poison the surface and thus limit further reaction. Alkali and alkaline earth metals in lignite served as active sites for catalysing the reaction of SO₂ with the CS complex and thus enhanced the rate of SO₂ reduction with lignite.