【作者】 李燕；

【导师】 岑可法； 张玉卓； 王智化； 黄镇宇；

【作者基本信息】 浙江大学 ， 热能工程， 2015， 博士

【摘要】 近年来,我国经济快速发展对能源的需求急速增加,煤炭生产与利用的快速增长为社会经济持续发展做出了巨大贡献,同时也导致了严重的环境问题,并引发了一系列的社会经济问题。开发煤炭资源高效清洁的转化技术对我国社会经济的进一步发展具有极其重要的意义。随着高品质煤炭资源的不断消耗,储量巨大的低品质煤炭资源的开发和利用逐渐被重视起来。煤基分级转化多联产技术是将煤作为原料利用的代表,集合了电力、化工和建材等多个系统,将煤炭资源利用的多个工艺作为整体考虑,将整体效率最优化,从而实现煤炭资源的高效清洁利用。但是,多联产系统目前还缺乏全面和深层次的研究,尚未形成完整的理论体系,相关理论研究滞后于工程应用发展。煤炭分级利用多联产系统的一次产品包括裂解产生的半焦、低热值煤气及合成气等,提高系统的总体效益,深入了解煤炭的裂解机理、拓展裂解产品的综合利用以及探索合适的裂解原料煤等成为煤基分级转化技术的关键问题。文本选取神华准混2#煤、新疆准东煤、内蒙宝日希勒煤和云南昭通煤等不同煤阶的煤种作为研究对象,采用固定床裂解炉对不同煤阶的煤种进行裂解机理研究,分析了不同颗粒尺寸、不同裂解温度对挥发分析出速度、析出总量以及轻质组分和大分子焦油组分的变化的影响规律。结果表明,挥发分的析出速率和析出总量随裂解温度的升高大幅增加,当裂解温度从500℃升高至1000℃时,神华煤裂解气析出总量从93ml/g增加至395ml/g；在固定床实验装置中,颗粒尺寸对挥发分的析出总量和挥发分的析出速率影响效果不明显。800℃以上的高温裂解,煤阶相对较高的煤种由于芳香结构的缩聚和脱氢反应,裂解气中CH4和H2的产量急剧增加。裂解气轻质组分热值随温度的升高不断增大,当裂解温度从500℃升高至1000℃时,神华煤裂解气轻质组分热值从15.33MJ/Nm3升高至16.33MJ/Nm3,昭通褐煤热值从7.16MJ/Nm3升高至16.71MJ/Nm3。当裂解气氛中存在CO2和水蒸气时,CO2与水蒸气在高温高压的条件下可与碳发生部分气化反应,进一步增加裂解气的产量。本文通过热分析的方法,分析了常压条件下不同反应温度和不同反应气氛对煤焦的部分气化反应的影响,从碳转化率、反应速率和反应活化能评价煤焦的部分气化反应的难易程度。研究结果表明气化温度越高,碳转化率越高,反应越容易进行,在常压条件下,CO2-60%/H2O-40%的反应气氛中,宝日希勒褐煤煤焦1000℃温度下的碳转化率可达到80.63%。半焦是煤基多联产系统的主要产品之一,可以直接作为燃料用于燃烧、或者经过活化制备成活性炭、吸附剂等用途,也可以将其制备成水焦浆用于煤气化和煤化工等行业。本文以褐煤在不同温度下氮气气氛中裂解得到的半焦为原料,制备高品质水焦浆,水焦浆成浆浓度由原煤的40%提高至60%以上,且具有良好的流变特性和稳定性。根据傅里叶红外光谱对样品的官能团结构测量结果显示,随着裂解温度的提高,样品中亲水性含氧官能团急剧减少,是导致褐煤成浆特性得到显著改善的原因。褐煤因为其活性很好,是一种很好的裂解气化原料,但是褐煤水分含量很高,在运输和使用过程中都会增加成本,因此本文采用非蒸发水热提质法对低品质煤进行提质处理,研究提质煤的裂解及燃烧特性,从初始失重温度、最大失重速率、失重结束温度以及着火点温度、燃尽点温度等特征参数评价提质过程对低品质煤裂解燃烧宏观特性的影响。同时,本文还对提质后煤样的煤质特性、微观孔隙结构以及碱金属含量的变化进行分析,从机理上探讨水热改性法对低品质煤宏观特性影响的原因。研究结果表明,经过改性提质后的低品质煤的裂解及燃烧特性曲线均向高温区推迟,提高了低品质煤的稳定性；同时,最大失重速率均有所提高,昭通煤的裂解和燃烧最大失重率分别提高32.46%和66.67%,有利于低品质煤的裂解和燃烧。水热改性后低品质煤的裂解及燃烧活化能均提高,昭通煤和准东煤的裂解反应活化能分别提高16.43KJ/mol和5.03KJ/mol,裂解及燃烧特性向高阶煤靠近。针对我国煤炭储量巨大、煤质多变、结构复杂的特点,而煤质特性是影响煤炭的裂解特性的最主要的因素之一,选择合适的煤种作为裂解原料往往需要对研究煤种进行大量的基础实验。本文采用煤裂解CPD预测模型,对煤粉裂解过程中挥发分释放特性以及煤粉裂解产物的分布情况进行模拟,并与实验结果对比。结果显示,CPD模型对于煤裂解的轻质组分释放特性的预测和裂解产物的分布的计算具有一定的准确性,对C02和CO等一次气体产量预测值与实验值偏差均在2%以内,而对于CH4和H2等会在煤焦油的二次裂解以及裂解气体与焦炭的二次作用产生的气体预测的准确性偏低。更多还原

【Abstract】 The demand for energy of the rapid domestic economy development increased sharply in recent years. Coal production and utilization made a great contribution to the sustainable development of social economy, lead to some serious environmental problems and also a series of socio-economic issues. Therefor, it is important to explore some kinds of high efficient and clean coal conversion technology. Meanwhile, the exploitation and utilization of low quality coals with a large amount of reserves are taken into account gradually due to the continuously comsuption of high quality coal.Coal fractional conversion polygeneration technology is one of the represent of coal resource utilization. In this technology, electric power, chemical industry and construction materials are gathered together as an integrated system and to realize the optimization of overall efficiency. However, an integrated theoretical system isn’t formed and the corresponding theoretical research is lagged behind the development of the engineering application due to the laking of comprehensive and profound research of the polygeneration system. In addition to electricity, the char, low caloric value coal gas and synthesis gas are also the primary production of polygeneration system. Therefore, the system integrated benefit improvement, the deep-understanding of the coal pyrolysis mechanism, the expansion of pyrolysis products comprehensive utilization and the rational distribution and optimization of the system become key issues of the polygenration tehchnology.In this article, diffirent rank of coals such as Shenhua coal (SH), Zhundong coal (ZD), Baorixile coal (BRXL) and Zhaotong coal (ZT) were conducted as the research objects. The influences of particle size and pyrolysis temperature on the characterization of devolatilization and the varying pattern of tar components were studied through fixed pyrolyzer. Results show that, the devolatilization rate and volume increased greatly along with the rising pyrolysis temperature, the volume of decomposed volatile increased from 93ml/g to 395ml/g when the pyrolysis temperature increased from 500℃ to 1000℃. While the effect of particle size on the volume and rate of devolatilization is not as obvious as that of pyrolysis temperature. When the pyrolysis temperature is higher than 800℃, the concentration of CH4 and H2 in coal gas increased rapidely for the polycondensition and dehydrogenation reaction of aromatic structure in high rank coals. Furthermore, the calorific value of coal gas increased incessantly with the pyrolysis temperature also. For example, calorific value of coal gas of SH and ZT increased from 15.33MJ/Nm3 to 16.33MJ/Nm3, and 7.16MJ/Nm3 to 16.71MJ/Nm3 respectively.In this study, the existence of CO2 and vapour which act as heat carrier may promote the gasification reaction between semicoke and CO2 and vapour at high temperature circumstance. The influence of temperature and atmosphere on semicoke gasification properties were tested by thermal analysis. The carbon conversion efficiency, reaction rate and activation energy were applied to evaluate the difficulty of semicoke gasification properties. Study results confirms that the higher the gasification temeperature, the higher the carbon conversion of semicoke, and also the easier the gasification reaction well be. The conversion of BRXL semicoke reach 80.63%at 1000℃ and atmospheric pressure.Semicoke which is one of the main produts of the polygeneration system, can be used for combustion derectly or as activated carbon and absorbent. And also can be used in coal gasification and chemical industry as coke-water-slurry. Semicokes obtained in different pyrolysis temperature were made into slurry. The solid concentration of semicoke water slurry elevated to more than 60% from 40% of raw coal water slurry and possessed a favourable rheological behavior and stability because of the reduction of hydrophilic oxygen-containing functional group.Lignite is very active and is a suitable pyrolysis material. But the transformation and utilization is very high due to the high moisture concentration. Hence, a kind of nonevaporation upgrading method, hydrothermal dewatering, was applied to upgrade lignite in this study. The pyrolysis and combustion properties of upgraded coals were evaluated by characteristic parameters, such as initial mass loss temperature, terminate mass loss temperature and maximum mass loss rate, et al. Meanwhile, the coal properties, micro pore structure and the content of alkali element were also detected to investigate the deep reason of hydrothermal dewatering influence on lignite macroscopic properties. The results reveal that, the pyrolysis and combustion characteristic curves of upgraded coals are postponed towards to high temeperature and stability of lignites are improved. The maxmum mass loss rates are also promoted which is benefit for the pyrolysis and combustion of lignite. For example the maxmum mass loss rates of ZT pyrolysis and combustion improved 32.46% and 66.67% respectively. Whatmore, the reaction activation energy of upgraded coal are improved indicating that lignite pyrolysis and combustion properties get closer to high rank coals. The pyrolysis activation energy of ZT and ZD increased 16.43KJ/mol and 5.03KJ/mol respectively.A lot of infratest are required to choose a suitable pyrolysis coal with the characteristics of large reservation, versatile quality and complex structures. To cut down large amount of experiments, an advanced coal pyrolysis model, CPD model, was employed to predict the devolatilization characteristics and coal pyrolysis products distribution. Compared with the experimental results, simulative results of coal pyrolysis products distribution and devolatilization characteristics by the CPD model present to be accurate to some extent. The deviations of CO2 and CO simulative results, which produced only in the first pyrolysis round, are within 2%. While the deviations veracity of CH4 and H2 are a little lower due to the secondary craking of tar and the interaction between semicoke and gas.更多还原