内在矿物质对煤焦燃烧特性影响的实验研究

以宁夏地区两种烟煤和两种无烟煤为原料,用浮沉方法得到灰分在40%左右的煤粉,然后在马弗炉900 ℃制焦,再用HCl-HF酸制取脱灰焦.通过比较煤焦脱灰前后热重燃烧曲线的特征参数的变化和转化速率的快慢,分析了内在矿物质对煤焦燃烧特性的影响.结果表明,内在矿物对两种烟煤焦前期的着火有阻碍作用,对后期燃尽有一定促进作用;内在矿物质对两种无烟煤焦的着火有促进作用,对后期燃尽有阻碍作用.     

等温热重分析法对煤焦反应动力学特性研究

针对工业气化炉二级旋风分离器的气化后半焦,同时选取京能烟煤在1173K,1273K和1373K三个温度下快速热解焦炭作为比较,在TGA/SDTA851e型热重分析仪上,对四种经历不同热过程的焦炭进行等温热重实验,实验温度范围为773K～1023K,研究煤焦燃烧反应动力学特性及其影响因素.煤焦制取方式和热解温度的不同决定了煤焦反应性的不同,在这四种煤焦中,气化半焦JC的反应性最小,而京能烟煤三种热解煤焦的反应性随着热解温度的升高而减小.随着燃烧温度和氧含量的升高,煤焦的反应速率在增大.同时,用半转化率法确定了煤焦燃烧的转捩温度和各个反应区域的活化能,在化学反应动力区,JC,JN-1,JN-2和JN-3活化能分别为115kJ/mol,57kJ/mol,70kJ/mol和97kJ/mol,与等转化率法所求得的平均活化能相近.随着煤焦转化率的增大,反应越来越困难,活化能也在增大,而且煤焦燃烧反应离开化学反应动力区的转捩温度也在升高.     

基于非等温热重法的煤焦燃烧特性及反应动力学

利用非等温热重法研究了由津凯褐煤、万泰烟煤、冀中能源无烟煤和骊达宁无烟煤4种煤在不同变质情况下制备所得煤焦的燃烧特性,利用随机孔模型(RPM)、收缩核未反应芯模型和体积模型模拟了煤焦燃烧反应过程. 结果表明,煤焦燃烧性能与煤粉变质程度、灰分含量和升温速率有关;降低煤粉灰分含量、提高升温速率能够明显加快煤焦燃烧速率,缩短燃烧时间. 动力学计算表明,RPM模型表征煤焦燃烧效果最优,由其所计算的4种煤焦的表观活化能分别为55.74,88.26,84.27和101.30 kJ/mol.     

不同煤质煤焦燃烧模型的研究

在高温悬浮反应试验台架上,对烟煤、无烟煤、高挥发分褐煤等煤焦的燃烧模型进行了研究。通过传递函数修正后的燃尽率与时间的关系曲线与收缩核模型、收缩圆柱体模型、化学反应级数等模型进行拟合,通过相关系数来选取最合适的燃烧模型。运用这种方法求取了D烟煤、X低挥发分煤、K褐煤的煤焦燃烧模型和S无烟煤、L无烟煤等煤焦的燃烧模型。列举了D烟煤与S无烟煤煤焦燃烧模型的实验曲线与模拟曲线,并用求出的模型对同种煤焦的其它工况进行求解,所得的结果与实验的测定值比较吻合,说明了求取模型方法的可靠性。模型的正确选择为分解炉中煤粉燃烧与碳酸钙分解的耦合研究奠定了基础。     

高温悬浮态的煤焦燃烧反应动力学研究

在高温气固悬浮态试验台上,对无烟煤、烟煤的煤焦燃烧模型进行了研究。在恒温条件下,分别获得A煤(无烟煤)煤焦与B煤(烟煤)煤焦的燃烧曲线,通过传递函数进行修正后的燃尽率与时间的关系曲线与已知的机理函数进行拟合,采用相关性系数选取最佳反应模型。对A煤煤焦与B煤煤焦的模型的动力学参数进行求解并拟合理论燃烧曲线,结果与实验的测定值吻合良好,表明动力学分析结果的可靠性。     

晋城无烟煤与杨树木屑共气化特性

为分析生物质对晋城无烟煤气化过程的影响,以晋城无烟煤和杨树木屑为试验对象,研究无烟煤、脱灰无烟煤与木屑在气化介质CO2下的共气化特性,通过热重分析法考察了木屑掺混比、升温速率、煤样脱灰处理等因素对气化过程的影响。结果表明,掺混生物质木屑能降低无烟煤、脱灰无烟煤共气化温度,且增加生物质掺混比例能显著降低起始反应温度;脱灰无烟煤共气化反应起始温度更低。10、20℃/min升温速率下共气化试验结果表明,升温速率对共气化过程有一定影响;低升温速率下开始气化反应温度低,高升温速率下最大质量变化速率值大;煤样脱灰处理后,失去矿物质使煤孔结构发达,生物质与气化剂反应活位点增加,能提高气化反应性。     

平顶山高灰熔融性温度煤的气化反应性研究

介绍了平顶山地区有代表性的7种煤样在800℃～1 200℃下,其脱灰煤焦-CO2气化反应活性的实验,主要考察了煤种、灰含量及粒径对煤焦反应性的影响,实验结果表明:煤种对煤焦-CO2气化反应有明显影响;煤中灰分对煤焦气化反应的影响主要表现在两个方面,一是灰成分对煤焦气化反应的催化作用,二是灰熔融性影响煤焦气化排渣行为。脱灰既可以除去煤焦中具有催化作用的矿物质,又可以增大煤焦的内表面积。     

不同煤焦微观表征及其对燃烧反应性的影响

从时间尺度和放热量来看,焦炭的反应在煤的整个燃烧过程中占有主导地位,而煤焦的微观结构与燃烧反应性有很大的关系,因此有必要进一步研究其影响因素和关系.本次研究选取了22种样品(涵盖了无烟煤、烟煤、贫煤、褐煤、煤泥和气化细渣)进行实验,用XRD对煤焦的微观晶体结构进行测量,用TGA对煤焦的燃烧反应性进行测量,从统计上研究不...     

烟煤与无烟煤混合煤粉燃烧过程的动力学研究

利用热重分析(TGA)方法系统研究了配加烟煤对无烟煤燃烧特性的影响。结果表明:煤粉燃烧主要由3个阶段组成,烟煤配加量和升温速率对燃烧过程有重要影响,随着烟煤配加量的增加,燃烧DTG曲线向低温区移动;实验所用煤种中的主要矿物元素是Si,Ca,Al,Fe,S,P,其中Mg,Zn,K,Na,Cl等含量较低,这些元素主要以氧化物、硅酸盐、碳酸盐、硫酸盐、氯化物和磷酸盐等形态存在,在低温燃烧过程中,矿物质挥发损失量对煤粉燃烧率的影响较小。采用非等温模型Flynn-Wall-Ozawa(FWO)对主要燃烧过程进行动力学分析,当烟煤配加量从0增加到100%时,煤粉燃烧活化能从133.94 kJ/mol降低到78.03 kJ/mol,且烟煤的配加量低于60%时,能够显著降低煤粉燃烧的活化能。     

半焦-烟煤混燃特性及动力学分析

掺烧烟煤是解决低挥发分热解半焦着火难、燃尽差的一种有效方法。采用热重实验研究了半焦、无烟煤与烟煤混燃特性的差别,分析了混燃过程中的交互作用和反应动力学。结果表明:陕煤半焦的燃烧过程分为可燃质的燃烧和CaCO_3的分解两个阶段。半焦-烟煤混烧的主失重峰靠近燃料比接近的单燃料的DTG峰。半焦-烟煤混合燃料较无烟煤-烟煤混合燃料的综合燃烧特性更优。掺混烟煤比例越高,混燃的表观活化能越低,可燃性和综合燃烧特性越好。烟煤与半焦或无烟煤混燃过程中存在一定的交互作用,且无烟煤-烟煤的交互作用较半焦-烟煤更显著。可燃性指数和综合燃烧指数与燃料比呈负线性相关性,表观活化能E与燃料比呈正线性相关性。     

半焦-烟煤混燃特性及动力学分析

掺烧烟煤是解决低挥发分热解半焦着火难、燃尽差的一种有效方法。采用热重实验研究了半焦、无烟煤与烟煤混燃特性的差别,分析了混燃过程中的交互作用和反应动力学。结果表明：陕煤半焦的燃烧过程分为可燃质的燃烧和CaCO₃的分解两个阶段。半焦-烟煤混烧的主失重峰靠近燃料比接近的单燃料的DTG峰。半焦-烟煤混合燃料较无烟煤-烟煤混合燃料的综合燃烧特性更优。掺混烟煤比例越高,混燃的表观活化能越低,可燃性和综合燃烧特性越好。烟煤与半焦或无烟煤混燃过程中存在一定的交互作用,且无烟煤-烟煤的交互作用较半焦-烟煤更显著。可燃性指数和综合燃烧指数与燃料比呈负线性相关性,表观活化能E与燃料比呈正线性相关性。     

随机孔模型研究煤焦O2/CO2燃烧动力学特征

在热重分析仪上对焦作无烟煤焦和云浮烟煤焦O₂/CO₂条件下燃烧特性进行研究。确定在不同温度下不同煤焦O₂/CO₂燃烧的特征。利用随机孔模型(RPM)表征两种煤焦反应速率与碳转化率的关系,同时与未反应缩核模型(Model Ⅰ)和混合模型(Model Ⅱ)的拟合结果进行比较。研究表明,在不同反应条件下,随机孔模型具有最佳的拟合效果,相关系数都在0.986以上。比较RPM、ModelⅠ和Model Ⅱ计算结果发现,焦作无烟煤焦的O₂/CO₂等温燃烧的活化能比云浮烟煤焦的高,且同一煤种燃烧反应温度越高反应速率常数越大。由于随机孔模型的结构参数ψ可以很好地表现孔结构变化对煤焦燃烧反应的影响,因此随机孔模型能更加准确地描述煤焦O₂/CO₂燃烧特征。     

煤与浒苔混合燃烧过程分析及动力学研究

为了满足电力需求,缓解煤炭短缺矛盾,采用ZTC-B型综合(同步)热分析仪对大同无烟煤与大同烟煤分别与浒苔混合燃烧过程进行了热重分析,并对其进行了动力学分析。结果表明:煤与浒苔单独燃烧及混合燃烧过程均可以划分为三个阶段,掺烧时随着浒苔质量分数的增加,主要燃烧阶段活化能升高,综合燃烧特性指数变小;大同无烟煤掺烧25%的浒苔时,二者存在明显的协同效应,相对值可达35%,大同烟煤掺烧25%的浒苔时,二者在480℃左右存在一定的抑制作用,相对值可达-11%;动力学分析表明:采用2个连续一级反应模型,可以很好地描述其掺烧过程,活化能和指前因子存在动力学补偿效应。     

煤拔头半焦燃烧特性

利用喷动载流床模拟煤拔头工艺,在550, 650, 750和850℃温度下对大同烟煤进行热解得到拔头半焦,采用非等温热分析方法对原煤及拔头半焦的燃烧特性进行了研究. 由热分析实验数据归纳提出了表征煤和半焦着火、燃烧及燃烬性能的无量纲综合燃烧指数Z. Z值越大,煤样综合燃烧性能越佳. 结果显示,大同烟煤在2℃/min升温速率下Z值为0.41;4个热解温度(由低到高)下所得拔头半焦的Z值分别为0.39, 0.35, 0.31, 0.21,且拔头半焦的燃烧性能均低于原煤,但高于阳泉无烟煤,且随热解温度升高Z值降低,燃烧反应性降低. Z值与着火温度及表观燃烧活化能表现出的反应性一致.     

The characterization of surface properties and steam reactivities of two Spanish coals of high ash content

Studies were made on two Spanish coals of high as content (a semi-anthracite and a high volatile bituminous coal) and on the coals after heat treatment and on acid demineralisation in HCl and HF. X-ray diffraction revealed that the mineral matter content of the coals included quartz, siderite and aluminosilicate minerals; siderite and the aluminosilicates were decomposed by heat treatment. Mineral matter content was substantially reduced by acid treatment, but the metallic element content, as revealed by EDAX, remained similar to that of the raw coals. N₂ and CO₂ adsorption isotherms and mercury porosimetry show that the coals contain mainly micropores and macropores, the semi-anthracite having the greater microporosity. For bituminous coal, macro- and micro-porosity increase substantially upon heat treatment; for anthracite there is a smaller increase in macroporosity and a decrease in microporosity. Microporosity in both coals is unaffected by acid demineralisation, but macroporosity is increased. The steam reactivity of the bituminous coal char is greater than that of the anthracite coal char, and demineralisation of the coals increases steam reactivity. N₂ surface areas and steam reactivities for both coal chars follow trends with parent coal rank previously established for US coals.     

A reactivity study of chars obtained at different temperatures in relation to their petrographic characteristics

This study reports on the reactivity of chars obtained at 1000°C and 1300°C (within the range of temperatures reached by coal particles in the near-burner zone of pulverised fuel boilers) from three different coals. The coals were selected according to petrographic criteria: two of them are high volatile bituminous coals differing in maceral composition and the third one is a vitrinite-rich low volatile bituminous coal.The morphology and optical texture of the chars were studied by optical microscopy. The kinetic parameters for the combustion of the high temperature chars under Regime I (combustion controlled by chemical kinetics) have been obtained and related to the optical texture and reflectance of the chars. The intrinsic reactivity of the high temperature chars was found to be lower than that of the low temperature chars, whereas the enhanced porosity observed in the high temperature chars had a positive effect on their combustion reactivity under Regime II (combustion controlled by oxygen pore diffusion). The intrinsic reactivities of the chars decreased following the sequence: vitrinite-rich low rank char>inertinite-rich char>vitrinite-rich high rank char. As the combustion temperature increases, the reactivity of the inertinite-rich char approaches that of the low rank vitrinite-rich char, which justifies the good performance observed for high volatile bituminous inertinite-rich coals in power plants.     

Enhancement of combustion efficiency with mixing ratio during fluidized bed combustion of anthracite and bituminous blended coal

In order to investigate the effect of mixing ratio of bituminous coal to blended coal on the enhancement of combustion efficiency, combustion experiments of blended coal with anthracite and bituminous are done in a laboratory scale fluidized bed combustor (10.8 cm ID and 170 cm height). The gross heating values of anthracite and bituminous coal used in this study are 2,810 cal/g and 6,572 cal/g, respectively. Experimental parameters are fuel feed rate, superficial gas velocity and mixing ratio of bituminous coal to blended coal. The combustion efficiency increases with the mixing ratio of bituminous coal due to the lower unburned carbon losses and higher burning velocity of bituminous coal. The rate of combustion in the combustor was increased with mixing ratio resulted from a higher burning velocity of bituminous coal. The measured combustion efficiency experimentally is about 3.5-12.4% higher than that of the calculated value based on the individual combustion of anthracite and bituminous coal under the same operating conditions. The optimum mixing ratio (MR) of bituminous coal determined is around 0.75 in this study. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

基于热重-质谱联用的煤粉富氧燃烧动力学及污染物生成特性

富氧燃烧是最具工业化前景的燃烧中碳捕集技术之一,为更深入掌握煤粉富氧燃烧的着火模式和污染物生成特性,本文构建了热重-质谱联用实验系统,以烟煤和无烟煤标准煤样为对象,针对3个不同的氧气体积分数：21%、30%和50%,研究了O₂/Ar和O₂/CO₂气氛下煤粉的富氧燃烧特性。结果表明,O₂/CO₂气氛下煤粉着火温度和燃尽温度均降低,燃烧速率提高,燃烧时间缩短;两种煤粉在O₂/Ar气氛下的燃烧都属于非均相着火,而富氧燃烧都属于均相着火模式;氧气体积分数在30%以上时,无烟煤O₂/CO₂燃烧的表观活化能明显低于O₂/Ar气氛,在相同工况下烟煤的表观活化能均低于无烟煤;O₂/CO₂气氛促进了CO和挥发分NO的逸出,生成温度均低于O₂/Ar气氛,CO会对NO起到还原作用。     

Reactivity of bituminous coal chars during the initial stage of pulverized-coal combustion

The reactivities of pyrolysed and partially burned char particles prepared in an entrained-flow reactor have been investigated. The results indicate that chars collected at the end of the active devolatilization stage are more reactive than those collected before or after this stage. Deactivation of the pyrolysed chars was accompanied by the development of micropores. The chars produced from a liptinite-rich fraction of an HVA bituminous coal showed higher reactivities than those generated from an inertinite-rich fraction. It is suggested that residual volatiles play a more important role in determining char reactivity than the microporosity and the optical anisotropy of the chars. A new expression for TGA reactivity is suggested for use in deriving char combustion kinetics. Relatively constant activation energies of ≈ 125 kJ mol⁻¹ were obtained for chars prepared from a wide range of coal precursors. Calculated char combustion rates at high temperatures extrapolated from such reactivity parameters were in agreement with experimentally determined rates.