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强粘结煤低温预氧化降粘及热解研究
富迎辉
学位类型硕士
导师林伟刚 ; 李松庚
2016-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词预氧化 降粘 热解 固体核磁共振
摘要

煤炭资源占我国能源消费结构的主导地位,为实现煤炭的清洁高效转化,中国平煤集团已在平顶山地区建成一套60万吨级煤热解分级利用中试装置,以实现热、油、气的多联产。但平顶山地区出产的粘结性煤在热解过程中形成的半焦会粘结成块,最终堵塞反应器,本课题受平煤集团委托,研究强粘结煤的低温预氧化降粘技术,以保证现有中试装置连续、稳定运行。目前,低温预氧化降粘的研究主要以工艺为主,机理方面的认知尚有不足,此外,就强粘结煤氧化降粘后热解产物的组分变化及产率影响关注较少。本文研究氧化条件对强粘结煤粘结性的影响规律,同时考察降粘对煤热解产物品质及产率的影响,并对降粘机理进行了探讨。本文通过固定床低温预氧化实验考察了载气中氧气浓度与氧化终温对中鸿二矿煤粘结性的影响规律。研究发现,提高载气中氧气浓度有利于煤粘结性的降低,但氧气浓度高于10%时,进一步提高其浓度对降低煤粘结性的影响不大。在150℃的氧化终温下,中鸿二矿煤的粘结指数随氧化时间的延长缓慢下降,此温度下很难对中鸿二矿煤快速、有效降粘;在200~300℃的氧化终温下,中鸿二矿煤的粘结指数随氧化时间的延长迅速下降,降粘效果显著。其中,250℃与300℃下处理的样品粘结指数随时间的下降趋势相同且数值相近。本文通过13C固体核磁共振表征中鸿二矿煤低温预氧化前后的样品并探究降粘机理。研究发现,低温预氧化后,粘结性的降低是煤多种化学结构变化共同作用的结果。醚键影响胶质体的流动性:低温预氧化使煤中醚键增多,加强了煤大分子结构中的支链、桥键间交联程度,使煤中芳香结构在热解时失去流动性,形成的胶质体不能充分扩散使煤颗粒粘结。脂肪碳链、羰基影响胶质体的量:低温预氧化使煤中脂肪碳链变短、羰基含量升高,使煤受热时形成的胶质体液相的量减少,不利于粘结。本文通过固定床热解实验考察降粘对中鸿二矿煤煤热解产物品质及产率的影响。研究发现,低温预氧化后,煤的热解半焦、焦油、热解气(除CO2与CO)都会出现一定程度的损失,损失量随氧化时间的延长与氧化终温的提高而增大。若要使其达到粘结指数15~20的水平,热解焦油产率损失严重,高达60~70%左右;热解半焦产率损失3~4%左右;热解气中CH4、H2和C2~C5的烃类减产严重,CO2、CO大幅增产。这说明将强粘结性的中鸿二矿煤单独通过低温预氧化的方式降粘至弱粘结煤水平,需牺牲大量热解焦油以及CH4、H2和C2~C5的烃类。本文通过在中鸿二矿煤中掺混弱粘结性的中鸿香山矿煤后对混合煤种进行低温预氧化处理发现:在氧化终温200~300℃,含氧10%的气氛中氧化1h后,混合煤种的粘结指数与中鸿香山矿煤的掺混比例有着很好的线性相关性。而且相对于单独使用低温预氧化的方法对对强粘结煤处理较长时间,将弱粘结煤掺混后再氧化处理较短时间能够取得相近的降粘效果,同时大幅减少热解产物损失。

其他摘要

Most of electricity in China is produced from coal. In order to realize clean and effective conversion of coal, Pingmei Group built a coal pyrolysis and cascade utilization pilot plant at Pingdingshan District, whose throughput could reach 600 thousand ton per year. However, plenty of local coal have strong caking property, which will result in difficulties in operation. The objective of this work aims at decaking of strong caking coal by pre-oxidation at low temperature and ensuring the stable operating of the pilot plant. At the moment, the process of decaking by pre-oxidation at low temperature draws great attention but knowledge of its mechanism is limited. Besides, effect of decaking via pre-oxidation at low temperature on pyrolysis behaviors of coal drew little attention. This research focused on the effect of oxidation conditions on coal’s caking property and pyrolysis products’ composition and yield. Mechanism of decaking by pre-oxidation at low temperature was also discussed. Pre-oxidation decaking experiments at low temperature with a fixed bed were carried out to find the effect of oxygen concentration and oxidation final temperature on coal’s caking property. It was found the increase of oxygen concentration was benefit for decaking. However, its effect on decaking became weak when the concentration was over 10%. At the final oxidation temperature of 150℃, the caking property of coal decreased slowly with the oxidation time, indicating that it was difficult for decaking at this temperature. At the oxidation temperature of 200~300℃, the coal’s caking property decreased rapidly with the oxidation time. The caking index decreased with time in a similar tendency at 250℃ and 300℃. 13C solid state NMR was carried out to characterize coal samples and explore decaking mechanism. It was found that various changes in coal’s molecule structure resulted in the decrease of caking index. The content of ether was increased by pre-oxidation at low temperature, which enhanced the cross-link of the branched chain and bridged bond in coal’s macromolecular structure. Thus the aromatic rings lost fluidity during pyrolysis, and diffusion of plastic mass was not enough to hold all the coal particles together. The shortening of aliphatic carbon chains and the increase of carbonyl content resulted in the decreasing of liquefied plastic mass, which was also benefit for decaking. Pyrolysis experiments within a fixed bed were carried out to investigate the effect of decaking on pyrolysis products’ composition and yields. It was found that the pyrolytic gas except for CO2/CO, char and tar would decrease to some extent after pre-oxidation at low temperature. The loss would increase with the oxidation time and final temperature. Around 60~70% of tar and 3~4% of char were lost when the caking index of strong caking coal sample decreased to 15~20. Besides that, H2 and hydrocarbon (CH4, C2~C5) suffered serious losses, while CO2 and CO increased. It was indicated that decaking strong caking coal to weak caking coal would reduce plenty of char, tar, CH4, H2, and hydrocarbon of C2~C5. To reduce the loss of volatile matter during decaking, a small percentage of weak caking coal was added into strong caking coal. The mixed coal was decaked by pre-oxidation at low temperature. It was found that the final caking index showed a good linear dependence on the blend mass ratio of weak caking coal after an hour’s oxidation in atmosphere containing 10% O2 at 200, 250, 300℃. Compared with counterpart results given by pure strong caking coal, mixed coal lost less pyrolysis products while its caking index was kept at similar level. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/22927
专题研究所(批量导入)
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富迎辉. 强粘结煤低温预氧化降粘及热解研究[D]. 北京. 中国科学院研究生院,2016.
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