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题名: 城市垃圾有机组分水热提质及燃烧过程PAHs分布特性的研究
作者: 彭娜娜1
学位类别: 博士
答辩日期: 2017-06
授予单位: 中国科学院大学
授予地点: 北京
导师: 刘振刚
关键词: 城市垃圾,水热炭化,多环芳烃,重金属,混煤燃烧 ; Municipal solid waste, Hydrothermal carbonization, PAHs, Heavy metals, Combustion with coal
其他题名: A study on PAH distributions during hydrothermal upgrading and resultant combustion of organic components of municipal solid waste
学位专业: 环境工程
中文摘要: 随着我国城镇化进程的加快和人民生活水平的提高,城市垃圾不仅产量迅速增加,而且有机组分所占比重不断增加,热值显著提高。垃圾焚烧发电技术以其减容减量化程度高、无害化彻底、资源化效率高等优点受到国内外广泛关注,代表了城市垃圾处理处置的重要发展方向。然而,城市垃圾自身的固有属性,如水分含量较高、热值较低等问题严重阻碍了垃圾焚烧发电技术的应用与推广。此外,垃圾燃烧过程中易产生SO2和NOX等污染物,特别是PAHs等有机污染物的释放严重威胁着人类健康。因此,提高城市垃圾燃料特性,从源头上减少垃圾燃烧过程中污染物的生成是实现垃圾清洁焚烧发电大规模应用的关键环节。基于国内外研究进展,本文以城市垃圾为研究对象,首次开展了水热炭化对城市垃圾重金属和PAHs分布特性的影响及燃烧过程中PAHs释放规律的研究。主要研究发现包括: 1、开展了水热炭化提质城市垃圾的研究。探讨了水热垃圾和液相产物中重金属和PAHs含量,并系统研究了水热炭化提质城市垃圾过程重金属在不同产物中分配规律。结果表明,在所研究的水热温度窗口内(160-260 oC),水热炭化提高了城市垃圾碳含量,降低了氧含量并增加其热值。对于重金属,城市垃圾中Cr含量较高为93.29 μg/g。水热垃圾中Cr含量仍较高,在34.53-63.30 μg/g范围内。计算发现水热垃圾中重金属留存率均低于100%,其中Hg留存率最低(6.16-24.54%),其次是Cr和Cd(最低留存率分别为13.96%和14.46%)。液相产物中所研究重金属均有检出,说明水热炭化可去除城市垃圾中部分重金属。重金属平衡结果表明,在160-260 oC内,液相中Hg占城市垃圾中Hg总质量的79.71-103.78%,Zn占53.32-68.94%。对于PAHs,城市垃圾中4环PAHs占自由PAHs总量的63.17%,液相产物中4环PAHs占自由PAHs总量的77.85-91.85%,而水热垃圾以3环PAHs为主,占自由PAHs总量的53.14-72.79%。 2、采用热重技术(TGA)考察了水热垃圾燃烧行为,并对其动力学进行了分析。研究表明,温度在200 oC以下,水热垃圾燃烧过程TG-DTG曲线包含三个主要失重阶段;当温度不低于200 oC,水热垃圾燃烧过程整体呈现两个失重阶段。从整体来看,随水热温度提高,水热垃圾着火点温度由267.2 oC升高至389.4 oC,燃烧区间减小并向高温区偏移。这说明水热炭化优化了城市垃圾燃烧行为。通过与煤混烧进一步缩短水热垃圾燃烧区间,提高了其热转化效率。当线性升温速率从5 oC/min提高到60 oC/min, H-200的TG-DTG曲线向高温区延迟。采用非预置模型法Vyazovkin法计算了H-200表观活化能。随转化率升高,H-200表观活化能由α=20 wt.%的68.53 kJ/mol增加到α=80 wt.%的117.78 kJ/mol,其均值为80.55 kJ/mol。 3、研究了城市垃圾及水热垃圾单独燃烧过程中PAHs释放规律。研究表明,在所研究燃烧温度窗口内(500-900 °C),样品燃烧过程烟气中PAHs含量最高,占PAHs总量的60.91-96.12%;其次为飞灰,占PAHs总量的3.83-39.08%,最后是底渣,占PAHs总量的0.01-9.50%。与城市垃圾相比(PAHs释放量为1111-10047 μg/g),水热垃圾燃烧过程中PAHs释放量较少(1131-7649 μg/g),说明水热炭化可有效减少城市垃圾燃烧过程中PAHs释放量。PAHs毒性TEQ值计算表明水热炭化有效降低了城市垃圾燃烧过程中PAHs毒性。当燃烧温度为900 °C时,城市垃圾毒性由1199 μg TEQ/g下降至252 μg TEQ /g。 4、开展了城市垃圾/煤以及水热垃圾/煤混合燃烧过程中PAHs释放规律的研究。在500-900 °C,城市垃圾/煤以及水热垃圾/煤燃烧过程中PAHs释放量分别在120-2402 μg/g 和110-392 μg/g范围内,其毒性分别为1.24-75.19 μg TEQ/g和2.31-50.31 μg TEQ/g,明显低于城市垃圾、水热垃圾以及褐煤燃烧过程中PAHs释放量及毒性。研究表明,混煤燃烧过程中城市垃圾和水热垃圾与褐煤之间存在明显的协同作用,该协同作用有效抑制了PAHs生成并显著降低其毒性。综上所述,水热炭化处理耦合混煤燃烧控制技术能有效抑制城市垃圾燃烧过程中PAHs的产生并降低其毒性,为垃圾资源化利用提供理论支持。
英文摘要: The amount of municipal solid waste (MSW) was constantly increased by the rapid increase of urbanization and people’s living standard. In addition, the percentages of organic components of MSW gradually increased to improve the high heating value (HHV). MSW incineration has received considerable attention as a promising method for significant volume reduction, high degree detoxicity and effective energy recovery. However, inherent properties of MSW are the main drawbacks for widespread use of the incineration, such as low energy content and high moisture. The pollutants, such as SO2, NOx and potential toxic heavy metals, especially for polycyclic aromatic hydrocarbons (PAHs) are produced from solid fuel combustion, which are harmful to the environment and human health. Therefore, it is important to find a new way to improve the fuel properties and reduce the pollutants. Based on the domestic and abroad research progresses, MSW was chosen in the present study. The objective of this study was to determine the content and distribution of heavy metals and PAHs during hydrothermal carbonization (HTC) of MSW and the emissions of PAHs from combuation of MSW or hydrochars obtained from HTC of MSW (H-MSW) and co-combustion with coal. The significant results were shown below: 1. HTC was employed to convert MSW into homogenized, energy-dense, and carbon-rich hydrochars with low energy consumption. Meanwhile,the effect of hydrothermal temperature on fate of heavy metals and PAH concentrations in hydrothermally treated municipal solid waste (H-MSW) and process waters (PWs) were evaluated. The results showed that HTC served as a novel thermal pretreatment process for homogenizing MSW and increasing higher calorific value and carbon content to improve the HHVs. Among detected heavy metals, Cr was the most abundant metal in MSW (93.29 μg/g) and the hydrochars (34.53-63.30 μg/g). To investigate the transformation of heavy metals during HTC, the retention rate of heavy metal in the hydrochar was calculated. The retention rates of Hg in the hydrochars were the lowest, at the value of 6.16-24.54%, followed by Cr and Cd. The lowest retention rates of Cr and Cd were observed at 260 oC (13.96% for Cr and 16.46% for Cd, respectively). All detected heavy metals exsited in PWs, indicating that a certain fraction of heavy metals in MSW entered into PWs during HTC. According to the distribution of heavy metals in the hydrochars and PWs, the percentages of Hg and Zn in PWs were 79.71-103.78% and 53.32-68.94%, respectively. With regard to PAHs, significant percentage of four-ring PAHs was observed in MSW, at a value of 63.17%. The three-ring PAHs were dominant in the hydrochars in the range of 53.14-72.79%, while for PWs, the percertages of the four-ring PAHs were 53.14-72.79% of total free PAHs. 2. Thermogravimetric analysis and kinetic analysis were employed to investigate combustion characteristics of the hydrochars derived from MSW. The results showed that three stages of mass loss were observed during the combustion of MSW and hydrochar produced below 200 oC, while two stages of mass loss were observed for that of hydrochar higher than 200 oC. With increased hydrothermal temperature, the ignition temperature of the hydrochars increased from 267.2 oC to 389.4 oC, the whole weight loss of combustion of the hydrochar shifted to higher temperature zones, and combustion range decreased, indicating that HTC improved the combustion behavior of MSW. The blending of H-MSW and coal improved the combustion efficiency of H-MSW. As for the hydrochar produced from 200 oC, in the 20-80 wt.% conversion range, the apparent activation energy of the hydrochar was increased from 68.53 kJ/mol to 117.78 kJ/mol. The average apparent activation energy was 80.55 kJ/mol. 3. Emission characteristics of PAHs from coal, MSW and H-MSW combustion alone were investigated at different temperatures (500-900 °C). The results showed that for all samples, flue gas had the highest yields of PAHs, which were in the range of 60.91-96.12% of total PAHs, followed by fly ash (3.83-39.08%) and bottom ash (0.01-9.50%). MSW combustion generated high levels of total PAHs with the range of 111-10047 μg/g and had high toxicity equivalent value (TEQ). H-MSW combustion generated less PAHs, at the value of 1131-7649 μg/g, and had lower TEQ values than that of MSW. For example, the TEQ values of MSW and H-MSW combustion were 1199 μg TEQ/ g and 252 μg TEQ /g at 900 oC, respectively. The result showed that HTC reduced total PAH emissions and decreased the toxicity from MSW combustion. 4. Emission characteristics of PAHs from the blending of MSW/coal and H-MSW/coal co-combustion were determined. The results showed that the emissions of PAHs and TEQ values from MSW/coal were 120-2402 μg/g and 1.24-75.19 μg TEQ/g, respectively. Low concentrations of PAHs from H-MSW/coal co-combustion in the range of 110-392 μg/g were observed and TEQ values were 2.31-50.31 μg TEQ/g. Compared to MSW, H-MSW and coal combustion alone, the blending with coal had minimum yields of PAHs and TEQ. In addition, positive interactions were observed between the blending with coal during co-combustion to reduce PAHs and decrease the toxicity. The present study illustrated that significant reduction of PAH emissions and toxicity from MSW combustion could be achieved by pretreatment of HTC and the blending of coal.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38683
Appears in Collections:固体废弃物处理与资源化实验室_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:
彭娜娜. 城市垃圾有机组分水热提质及燃烧过程PAHs分布特性的研究[D]. 北京. 中国科学院大学. 2017.
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