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水热炭化污泥热解过程典型污染物生成和释放特性研究
Alternative TitleThe generation and emission of typical pollutants during pyrolysis of hydrothermally carbonized sewage sludge
刘婷婷
Subtype博士
Thesis Advisor刘振刚
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学博士
Degree Discipline环境工程
Keyword水热 炭化 污泥 热解,重金属, 氮转化, 多环芳烃 hydrochar, Pyrolysis, Heavy Metal, Nitrogen Transformation, Pahs
Abstract

      城市污泥是城市污水处理过程产生的副产物。 随着 我国 城镇化建设的快速推进 污水产 生 量逐年递增 我国 城市污泥产量不断增 加 。 城市污泥成分非常复杂,不仅含有多种 重金属 (镉 、铬、汞 、铅、砷 等 )、 难降 解 有机污染物( 多氯联苯、二噁 英、 多环芳烃 等 、内分泌干扰物、抗生素等 、多种寄生 虫卵、 致病菌和病毒,并且在城市污泥中还发现了 纳米材料、微塑料等 多种 新兴污染物 ,基本涵盖了污水中 污染物的所有种类 。 因此, 大量 城市 污泥 若 得不到 妥善处理,会 二次污染 环境 、 危害 人类健康 。 焚烧是污泥无害化 最彻底 、减容量最有效的污泥处理手段 。但由于污泥含水量高、脱水性能低, 因此, 焚烧前需要进行高能耗的 热处理此外, 污泥焚烧还面临着污泥热值有限、燃烧行为不稳定以及 氮氧化物、多环芳烃、重金属 等污染物 的二次 污染 等问题 。 热解是焚烧过程的初始阶段, 会影响焚烧过程中污染物排放,同时也是 重要且有效的污泥处理处置手段。 研究 污泥热解过程中污染物 的 排放规律,有助于 控制 污泥热解和焚烧过程 中 污染物的排放 。 水热炭化是处理高含水率生物质的有效技术手段,用于污泥热化学处理前的预处理,不仅可以提高污泥的脱水性能,并且可以提升污泥的燃料特性。 基于此 本论文提出了将水热炭化耦合焚烧 /热解技术用于污泥的处理处置, 发挥水热炭化处理和焚烧 /热解处理方式 各自 优势,实现污泥的快速无害化处置。 因此,本论文主要研究了水热炭化 处理 对 污泥性质和燃料性能的影响, 揭示了 污泥 水热炭化 处理后含氮污染物、重 金属 和 多环芳烃 在热解过程 生成 和 排放规律 评价了水热炭化作为污泥焚烧 /热解前预处理 手段 的合理性,为 减少 焚烧 /热解过程污染物排放提供理论支持。 具体研究内容和结果如下:
      (1) 首先 研究了 水热 炭 化 条件 对 污泥性质 的影响 ,结果表明 水热炭化预处理后污泥的脱水性能明显提高, 可 节省 超过 30%的 热 干燥能量消耗 。 对比了污泥和 水热炭化处理污泥(简称水热 炭化 污泥) 在空气和富氧条件下的燃烧行为, 并通过 Flynn-Wall-Ozawa模型和 Avrami’s理论 得到了 污泥和 水热炭化污泥 的 表观活化能 、 指前因子和反应级数等动力学参数。结果表明 水热炭化污泥 具有较高的点火温度、较高的燃烧指数和较窄的燃烧区间 燃烧性能更稳定 ;灰分分析表明, 水热炭化有效降低 了 污泥 燃烧过程中 积灰结渣 和结垢 等灰分问题 。
      (2) 研究了污泥和 水热炭化污泥 于 最优温度 200 °C下 产生 热解过程中含氮污染物的释放规律。 结果表明 水热 炭 化 能 有效去除 污泥中的 无机 -N和不稳定 -N,并通过脱氨、脱氢和聚合 反应 将氮转化为更稳定的 存在形态 在热解过程中将更多的氮保留在焦炭中,降低焦油中 Amine-N和杂环 -N的含量。 水热炭化污泥 热解过程 (NH3+HCN)-N产率 显著 低于污泥热解的 (NH3+HCN)-N产率, 尤其是 当温度 >650 °C时。 此外, 水热炭化污泥 热解 过程中 的总 (NH3+HCN)-N排放量仅为污泥热解的 35.6–48.2%。 因此 污泥 水热炭化 预处理可以实现含氮污染物减排的 目的 。
      (3) 研究了 污泥中典型 重金属 锰 、 铬 、 镍 、 铜 、 锌 、 铅 、 镉 和 汞 在 水热炭化和热解 过程中 的分布 和赋存形态 。 结果表明 水热炭化污泥 中重金属 的 酸溶 态 和可还原态 占比 降低 、 潜在 生态 风险 下降 。 污泥 热解焦炭中重金属 比 原 污泥中的 稳定态占比更高、潜在 生态 风险更低。 与 污泥 相比 水热炭化污泥 热解后得到的焦炭中重金属稳定性更高 、 潜在生态风险更 低。因此, 水热炭化 处理有效钝化了污泥中的重金属。
       (4) 研究了水热炭化预 处理过程 中以及 水热炭化污泥 热解过程中 16 种优先控制多环芳烃 生成和 释放规律 。 结果 表明 污泥 水热炭化过程 中 多环芳烃 在 水热炭化污泥 中 发生 富集; 污泥和 水热炭化污泥 热解 过程中 多环芳烃 总产率 分别 为73.84−1988.26 mg kg-1和 105.97−1927.13 mg kg-1。 水热炭化污泥 热解的 多环芳烃产率在 500、 650和 800 °C均 高于污泥热解 多环芳烃 的 产率, 且 水热炭化污泥 热解产生的 多环芳烃 中的中等分子和大分子占比更大, 而在低温 350°C和 高温950 °C时 低于污泥热解 多环芳烃 产率 。 污泥和 水热炭化污泥 热解 过程中 大部分 多环芳烃 进入了焦油中 而 焦 炭中 的 多环芳烃 浓度 较低 3.62−23.88 mg kg-1 。 由此可见,污泥和水热炭化污泥热解过程中焦油中多环芳烃应该引起重视 。

Other Abstract

       Sewage sludge, the byproduct from wastewater treatment, has been produced in a large scale and increased fast with China fast urbanization process and the increased discharge amount of wastewater. Sewage sludge contains various types of pollutants including heavy metals (Cd, Cr, Hg, Pb and As et al.), persistent organic pollutants (polychlorinated biphenyls, dioxins, polycyclic aromatic hydrocarbons, endocrine disruptors, antibiotics), various parasitic insect eggs, pathogenic bacteria and viruses, as well as some emerging contaminants such as nano materials and microplastics. Basically, sewage sludge covers all kinds of pollutants in waste water. If the sewage sludge is treated and discharged improperly and arbitrarily, it will pollute the environment and endanger human health. Incineration of sewage sludge can kill the pathogens thoroughly and reduce the sludge volume significantly, is a most effective sludge disposal method. However, due to the high-water content and poor dewatering performance of sludge, thermal drying treatment with high energy consumption is required before sludge incineration. In addition, sludge incineration is also faced with problems such as limited calorific value of sludge itself, unstable combustion behavior, and secondary emissions of nitrogen oxides, polycyclic aromatic hydrocarbons (PAHs), heavy metals and other pollutants. Pyrolysis is the initial stage of the incineration process, and it is a crucial stage that affects the emission of pollutants in the incineration process as well. At the same time, pyrolysis is also an important and effective technology of sludge treatment and disposal. Mastering the emission behaviors of pollutants in the process of sewage sludge pyrolysis is helpful to control the discharge of pollutants in the process of sewage sludge pyrolysis and incineration. Hydrothermal carbonization (HTC) is a promising technology in disposing biomass with high water content and can be used as the pretreatment of sewage sludge before thermochemical treatment. Based on this, a new technology of HTC coupled with incineration/pyrolysis is developed in this paper to achieve the disposal of sewage sludge. Consequently, this thesis investigated the influence of HTC conditions on sewage sludge properties and incineration performance, and revealed the generation and emission rules of nitrogenous pollutants, heavy metals and PAHs in the pyrolysis process hydrothermally carbonized sewage sludge (hydrochar). In addition, the feasibility of this new technology on sewage sludge disposal was evaluated. The specific research contents and results are as follows:
       (1) First, the effect of HTC temperature on characteristics of sewage sludge was investigated. The result indicated that the dewaterability of sewage sludge was substantially improved by HTC and more than 30% of drying energy consumption was saved prior to incineration. The incineration performance of sewage sludge and hydrochar derived from sewage sludge HTC treatment were compared under air as well as oxy-fuel by thermal-gravimetric analyzer. The kinetic parameters including energy activation, pre-exponential factor and reaction order were evaluated by Flynn-Wall-Ozawa model and Avrami's theory. The results showed that the hydrochars showed higher ignition temperature, higher ignition index and narrower combustion stage than sewage sludge, which implied incineration behaviors of SS was improved by HTC treatment. In addition, the ash analysis indicated that ash problems of the slagging and fouling were mitigated by HTC treatment.
      (2) The nitrogen transformation during pyrolysis of SS and hydrochar (the hydrochar obtained from HTC of sewage sludge at 200 °C) among pyrolysis char, tar and precursor of NOx (NH3 and HCN) were studied. The results showed that HTC can effectively remove inorganic-N and unstable-N in sludge and convert nitrogen into more stable form by deamination, dehydrogenation and polymerization. More nitrogen retained in the char for the hydrochar pyrolysis and the amount of amine-N and heterocyclic-N in tar were lowered. The yield of (NH3+HCN)-N emission from hydrochar pyrolysis was significantly lower than that from SS pyrolysis, especially at temperatures higher than 650 °C. In addition, the total (NH3+HCN)-N emission calculated from the hydrochar pyrolysis was only 35.6–48.2% of that from sewage sludge pyrolysis. The results suggested that HTC pretreatment of sewage sludge has the additional environmental benefit of mitigating nitrogenous pollutant emission.
      (3) The heavy metals distribution and existing forms of Mn, Cr, Ni, Cu, Zn, Pb, Cd and Hg during HTC and pyrolysis of sewage sludge were investigated. The results showed that HTC reduced acid-soluble and reducible fraction of heavy metals and lowered the potential risk of heavy metals in sewage sludge. The heavy metals in pyrolyzed char were more stable and exhibited lower risk to environment than sewage sludge itself. Compared to the chars from sludge pyrolysis, heavy metals in the chars derived from hydrochar pyrolysis was more stable and showed less risk. The present study demonstrated that HTC is a promising pretreatment prior to pyrolysis from the perspective of immobilization of heavy metals in sewage sludge.
      (4) The generation and emission of 16 priority PAHs during HTC of sewage sludge and the pyrolysis of the derived hydrochar were studied. The results showed that the PAHs were concentrated in the resultant hydrochar during HTC. The PAHs yields from sewage sludge and hydrochar pyrolysis were 73.84−1988.26 mg kg-1 and 105.97−1927.13 mg kg-1, respectively. The PAHs yields from hydrochar pyrolysis at 500, 650 and 800 °C were higher and the proportions of highly toxic middle molecular weight and high molecular weight PAHs in hydrochar tar were much higher. The PAHs yields from hydrochar pyrolysis were lower at 350 and 950 °C than the PAHs yields from SS pyrolysis. Most PAHs were distributed into pyrolytic tar while the PAHs in pyrolytic char was less (3.62−23.88 mg kg-1). Therefore, more attention should be paid to PAHs in tar during sewage sludge and hydrochar pyrolysis.

Pages144
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42253
Collection固体废弃物处理与资源化实验室
Recommended Citation
GB/T 7714
刘婷婷. 水热炭化污泥热解过程典型污染物生成和释放特性研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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