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题名: 水泥窑共处置固废过程中二恶英和类二恶英的生成机制研究
作者: 赵宇阳1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 郑明辉 ; 刘国瑞
关键词: 水泥窑共处置固体废物,UP-POPs,生成机理,理论计算 ; Cement kiln co-processing solid waste, UP-POPs, Formationmechanism, Theoretical calculation
其他题名: Formation Mechanism of Dioxin and Dioxin-likeCompounds during Co-processing Solid Wastes in CementKilns
学位专业: 环境科学
中文摘要: 水泥窑共处置固废是非故意排放的持久性有机污染物( UP-POPs)的重要 来源之一。尽管水泥窑共处置固废过程中二恶英和类二恶英污染物(PCDD/Fs、 PCBs、PCNs 和 PBDD/Fs)的排放水平已经有了较多研究报道,关于不同工艺 阶段的颗粒物中的 UP-POPs的生成机理的研究还较少。在大规模开展水泥窑共 处置固体废物之前,很有必要对水泥窑共处置过程中这些化合物的生成机理进 行深入的研究。现场研究和理论计算相结合的研究手段可以为 UP-POPs的生成 和相互转化的反应路径的推断提供新的思路,进而为抑制二恶英和类二恶英的 生成提供关键数据,本研究所得到的结果有利于水泥窑共处置固体废物行业的 可持续发展。 本研究选取了水泥窑共处置城市生活垃圾、污水厂污泥以及水泥窑综合利 用氯碱行业电石渣生产熟料进行现场研究,分析了 UP-POPs的排放特征、同类 物和同系物分布特征,发现了水泥窑共处置固废行业有区别于冶金等行业的 UP-POPs排放特征。理论模型和量子化学计算结果能够支持所提出的 UP-POPs 生成机理。主要研究结果如下: (1)在水泥窑共处置城市生活垃圾和污泥的工厂开展了对不同工艺阶段颗 粒物样品的 PCDD/Fs的生成和分布特征的现场研究,发现在窑尾主要生成阶段 四到六氯代呋喃的比例较高,可以使用理论模型和理论计算结果给出合理的解 释。研究中识别出一级预热器出口,窑尾锅炉和增湿塔,和窑尾布袋收尘是水 泥窑共处置 MSW和污泥过程中 PCDD/F的主要生成工艺段,且发现∑Cl4–6CDFs 对 PCDD/F的 TEQ贡献较高。在水泥窑共处置 MSW生产水泥过程中,在这些 工艺段颗粒物中 PCDD/Fs的浓度分别为 46.2、55.3和 61.3 pg I-TEQ g−1。在水 泥窑共处置 MSW和污泥生产水泥的窑尾区域∑Cl4–6CDFs占到了同系物浓度总 和的 50–80%,占到了 I-TEQ浓度的 62–87%。这些比例显著高于原生铜和再生 铜冶炼行业。结合理论预测模型和热力学计算,揭示了可能是较低的 O2、铜元 素含量和碱性条件导致水泥窑共处置 MSW和污泥过程中 PCDF对 TEQ贡献较 高。 (2)研究了水泥窑使用氯碱行业电石渣为主要原料生产熟料过程中 PCDD/Fs、PCBs和 PCNs的排放水平和生成特征,整个水泥窑综合利用电石渣 过程中 UP-POPs 的质量平衡显示水泥生产对 UP-POPs 的毒性当量的削减较为 显著,烟气排放中 PCNs的毒性当量的贡献甚至高于 PCDD/Fs和 PCBs,PCNs 的控制是该固废综合利用过程中需要重视的一个问题。按每吨熟料计算的 PCDD/Fs、PCBs和 PCNs的排放因子分别估算为 23.0 ng WHO-TEQ t−1、3.8 ng WHO-TEQ t−1和 112.1 ng TEQ t−1。颗粒物和烟气样品中 MonoCBs是窑尾烟囱 烟气中主要的 PCBs同系物。∑Cl1–2CNs分别占到了颗粒物和烟气样品中 PCNs 总浓度的 48%和 98%。在水泥窑使用该类固废为原料的生产过程中,在多种 UP-POPs的减排中 PCNs的削减是一个关键点。 (3)研究了水泥窑共处置 MSW 的各个工艺阶段颗粒物中的 PBDD/Fs 的 水平和分布特征,研究发现含量较高的七溴代二苯并呋喃可能与固废中含有的 溴代阻燃剂类有关。水泥窑共处置 MSW 生产水泥过程中,窑尾区域的主要生 成工艺阶段颗粒物样品中 PBDD/Fs的浓度为 30.4–216 pg g–1。所有颗粒物样品 中溴代二恶英类以六溴和七溴代二苯并呋喃同类物的浓度最高。在采集的所有 颗粒物样品中 PBDF与 PBDD浓度的平均比值为 16。水泥窑共处置 MSW生产 水泥过程中各工艺段颗粒物中 1,2,3,4,6,7,8-HpBDF和 BDE-209浓度的相关系数 为 0.74,推测 PBDD/Fs可能来源于溴代阻燃剂的转化。水泥窑共处置 MSW过 程中含阻燃剂的固体废物的掺入可能会导致 PBDD/Fs的排放水平升高。 (4)通过量子化学理论计算,研究了 OH 自由基引发的 PCBs 转化为 2,3,7,8-PCDFs的可能反应路径,热力学和动力学结果都支持四到六氯代呋喃生 成为主的实验现象。本研究以氧气存在条件下,CB-77生成 2,3,7,8-TeCDF的反 应路径为例进行讨论,并与多氯联苯醚(PCDEs)参与的反应进行对比。从热 力学角度可以推测工业热过程中不论是以 PCBs 还是以 PCDEs 作为前驱体, PCDFs可能都是主要的 PCDD/Fs产物;从反应势垒角度发现高氯代 PCBs生成 PCDFs 的反应可能因为较高的空间位阻而难以发生。研究结果为热过程中 PCDD/Fs 的生成以四到六氯代二苯并呋喃(∑Cl4–6CDF)为主的现象进一步提 供了理论支持。
英文摘要: Cement kilns co-processing solid waste are a major source of unintentionally produced persistent organic pollutants (UP-POPs). Many studies have been performed on the stack gas emissions of dioxins and dioxin-like compounds from cement kilns co-processing solid waste. These studies have focused on the emission levels of polychlorinated dibenzo-p-dioxins/furans, polychlorinated biphenyls, polychlorinated naphthalenes, and polybrominated dibenzo-p-dioxins/furans (PCDD/Fs, PCBs, PCNs and PBDD/Fs). However, the formation mechanisms of these POPs in different process stages in the cement kiln during co-processing solid wastes have not been thoroughly investigated. These types of studies need to be performed on a pilot scale before scaling up to studies in cement kilns. Field studies and theoretical studies could provide insight into the formation and transformation of UP-POPs. This research could provide key data for further research on the inhibition of the formation of dioxins and dioxin-like compounds. In addition, the results could be used for sustainable development of cement kiln co-processing of solid wastes. Cement kilns co-processing municipal solid waste and sewage sludge, and a cement kiln using carbide slag from the chlor-alkali industry were investigated in this study. The emission characteristics, and congener and homolog profiles of UP-POPs were analyzed for these cement kilns. The profiles of the cement kilns co-processing solid wastes were different from those of metallurgical industries. Theoretical models and quantum chemistry calculations were performed to support the proposed formation mechanism. The results main aspects of this study are detailed below. (1) A field study was used to evaluate the emission characteristics and congener profiles of PCDD/Fs in particulate matter samples from different process stages of cement kilns co-processing municipal solid wastes and sewage sludge. The first stage preheater outlet, kiln back-end boiler and humidifier tower, and bag filter at the kiln back end were the main stages of PCDD/F formation. The ∑Cl4–6CDFs contributed to a high proportion of the PCDD/F toxic equivalents (TEQ). During co-processing of municipal solid waste in the cement kiln, the PCDD/F concentrations at the first stage preheater outlet, kiln back-end boiler and humidifier tower, and bag filter at the kiln back end were 46.2, 55.3, and 61.3 pg I-TEQ g–1, respectively. The ∑Cl4–6CDFs contributed to a high proportion of the homologs at the kiln back-end areas, with proportions of 50% to 80% for the mass concentrations and 62% to 87% for the TEQs. These proportions are much higher than those generated from primary and secondary metallurgical processes. A field study combined with theoretical results from a predictive model and thermodynamic calculations revealed the low oxygen concentrations, copper element, and the alkaline condition in the kilns contributed to PCDF being the dominant TEQ contributor in the cement kilns. (2) The levels and profiles of PCDD/Fs, PCBs, and PCNs in cement kilns using carbide slag from the chlor-alkali industry as a major raw material component for clinker production were clarified in this study. The emission factors for PCDD/Fs, PCBs, and PCNs were estimated to be 23.0 ng WHO-TEQ t–1, 3.8 ng WHO-TEQ t–1, and 112.1 ng TEQ t–1 for the clinker, respectively. Monochlorinated biphenyls were the dominant homolog in stack gas samples collected at the kiln back end. The ∑Cl1– 2CNs accounted for 48% and 98% of total PCN concentrations in the particulate and stack gas samples, respectively. Emissions of PCNs in stack gases were much higher than those of PCDD/Fs and PCBs, which shows PCNs are important when considering the reduction of unintentionally production of POPs from cement kilns using this waste as a raw material. The calculated mass balance indicated that PCDD/F, PCB, and PCN TEQs were reduced in this cement kiln system. (3) The emission levels and characteristics of PBDD/Fs in particulate samples from different process stages of cement kilns co-processing municipal solid waste and sewage sludge were investigated. During co-processing of municipal solid waste in the cement kiln, the PBDD/F concentrations in the main formation stages ranged from 30.4 to 216.0 pg g–1. The proportions of hexa- to hepta- brominated dibenzofurans dominated for the 2,3,7,8-PBDD/Fs in all the particulate samples. In all of the collected particulate samples, the average ratio of PBDF to PBDD was 16. During co-processing of municipal solid waste in the cement kiln, the correlation coefficient of the concentrations of 1,2,3,4,6,7,8-HpBDF and decabromodiphenyl ether in all the stages was 0.74. These results inferred that the formation of PBDD/Fs was related to transformation of brominated flame retardants. Therefore, co-processing of waste containing brominated flame retardants in a cement kiln might increase the emission of PBDD/Fs. (4) The OH radical initiated formation pathways of 2,3,7,8-PCDFs from PCBs were studied using quantum chemistry calculations, and the theoretical results were consistent with the experiment results. In the presence of oxygen, the formation of 2,3,7,8-TeCDF from CB-77 were was selected as an example, and compared with the reactions of polychlorinated diphenyl ethers (PCDEs). The results inferred that PCDFs were the dominant product of the reactions from PCB and PCDE precursors. PCDFs were thermodynamically more favored than PCDDs. Reaction barrier data indicated that reactions involved in the formation of higher chlorinated dibenzofurans would be difficult because of high steric hindrance. These results theoretically support the experiment results of a high contribution of ∑Cl4–6CDFs to the total PCDD/Fs in industrial thermal processes.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38754
Appears in Collections:环境化学与生态毒理学国家重点实验室_学位论文

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作者单位: 1.中国科学院生态环境研究中心

Recommended Citation:
赵宇阳. 水泥窑共处置固废过程中二恶英和类二恶英的生成机制研究[D]. 北京. 中国科学院大学. 2017.
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