【作者】 成珊；

【导师】 乔瑜； 徐明厚；

【作者基本信息】 华中科技大学 ， 热能工程， 2018， 博士

【摘要】 污泥是污水处理过程中沉淀或其他分离方式而产生的半固体或固体物质,具有高含水率、高有机质、易压缩、难脱水的特点。降低其水分含量一直是污泥处理过程的重要目标,干化过程依然是处置前必不可少的环节。然而污泥中含有的大量易降解物质,在干化过程中将释放大量含硫、氮的恶臭气体,带来严重二次污染。因此,本论文针对现有的调理-脱水-干化方式和新兴水热干化方式,进行了直接热干化条件下调理剂对含硫、氮物质转化路径的影响研究,以及水热干化方式下含硫、氮物质转化路径的研究。其中涉及的关键科学问题包括:调理剂对含硫气体释放的控制机理;调理剂对含氮气体释放的控制机理;水热干化过程中水对于硫、氮转化路径的影响机理;水热处理终温对含硫、氮物质分布规律的影响。为了解决上述科学问题,本论文开展了全面而深入的研究。在水平固定床直接热干化系统进行了碱性调理剂对硫转化的影响研究。通过含硫物质化学形态分析,结合含硫模型化合物验证等手段,确定了污泥低温热解过程中添加氢氧化钙等碱能极大地减少含硫气体的释放,并且添加的碱碱性越强,效果越好。这是由于碱能促进脂肪族和芳香族硫化物氧化为更为稳定的亚砜和砜类,从而抑制脂肪族和芳香族硫化物分解产生H2S等含硫气体。并且添加的碱同时还能将硫以无机硫化物和无机硫酸盐形式固定在焦中,进一步减少含硫气体释放。碱对有机硫转化过程影响的关键因素在于其碱性强度,碱性越强则参与反应的OH自由基越多,对脂肪族和芳香族硫化物的氧化及固定效果越好。在满足脱水等工艺环节需求的基础上,优选碱性调理剂,可以增强对后续热干化过程中含硫恶臭气体的控制效果。在此基础上,选择呈现碱性的醋酸盐,避免单纯的碱性环境促进含氮气体如NH3的释放。通过对氮元素进行全过程平衡分析,明确了添加醋酸钙可以抑制蛋白质氮的分解,并促进更稳定的含氮化合物形成,从而保留更多的氮在焦中;但添加醋酸钠,促进蛋白质氮和无机氮等含氮物质分解。醋酸钙和醋酸钠对污泥直接干化过程中氮转化过程的影响,主要来自于阳离子的催化作用。Ca和Na可以催化氨基酸直接分解和后续的酰胺脱氢过程,促进腈类氮的生成。同时,金属阳离子在高温下,促进吡咯氮的开环作用。污泥直接干化过程中产生的含氮焦油主要有胺类氮、杂环氮,以及少量腈类氮。添加醋酸钙后,由于抑制了蛋白质的分解作用,焦油中的含氮成分减少。醋酸钙和醋酸钠均能大幅减少含氮气体的释放,这与醋酸盐热解过程中释放的丙酮有关。丙酮能补集NH3生成酮亚胺,并发生缩聚作用形成胺类,进而将NH3固定在焦油中。在满足生化池调节碳/氮比等工艺环节需求的基础上,优选醋酸盐,可以促进后续热干化过程中含氮恶臭气体的控制效果。采用间歇式反应釜进行水热干化过程硫元素迁移转化路径研究。发现水热处理过程中,主要由脂肪族硫化物和芳香族硫化物分解产生含硫气体。其成分以H2S和CH3SH为主,其他还有少量SO2,并且含硫气体产量随温度上升而增加。有机硫成分在水热过程中会与水发生反应,水产生的大量OH*作为亲电试剂攻击有机硫中的硫原子,将氧原子转移至硫原子上,通过对脂肪族化物和芳香族硫化物的氧化,形成对应的亚砜、砜类,甚至无机硫酸盐。反应强度随水热处理温度升高而增强。脂肪族硫或芳香族硫化物氧化而来的亚砜和砜类,热稳定性相对氧化前更低,通过C-S键断裂,形成气体中SO2或SO3,以及水溶液中SO32-、SO42-。水热处理过程中,由于大量水参与有机硫分解反应,并且能溶解部分含硫产物,如硫酸盐和SO2等,因而大部分硫元素转移至水溶液中,减少了固体产物中含硫量以及含硫气体释放量。在不考虑固体产物中残留总有机物含量的情况下,水热处理温度提升有利于产生含硫量更低的固体产物。对于氮元素而言,随着水热处理温度升高,更多的氮由固态向焦油态和水溶态转变。在210℃及更高水热处理温度下,转移至焦油和水溶液中的氮多于固体中残留的氮。因此提高水热处理温度更有利于制备清洁能源、控制氮在焦中残留。水热处理过程中,主要的反应路径为:蛋白质分解和水解,依次产生胺类、水溶性有机氮、NH3和NH4+,其次为无机氮与水反应生成NH4+和NO3-等含氮离子。反应速率随温度上升而增加。焦中残留的含氮物质包括未分解的蛋白质氮,吡咯、吡啶等杂环氮,季氮和少量腈类氮。焦油中的含氮物质为胺类氮和杂环氮两类,未有腈类氮出现。水溶液中以水溶性有机氮为主,其次有大量NH4+。释放的含氮气体主要为HCN。在综合考虑固体产物中残留总有机物含量与残余含硫、氮量的情况下,水热处理温度可选择在180℃至210℃之间。综上所述,对于直接热干化过程,选择呈现碱性的醋酸盐,既可利用碱性环境控制含硫气体释放,又可利用醋酸盐自身分解产物捕捉含氮气体,实现同时控制两类污染物的释放;对于水热干化过程,提出了硫、氮转化路径及其受水热处理终温的影响规律,为控制含硫、氮气体两类污染物提供了理论依据。更多还原

【Abstract】 Sewage sludge is a semi-solid or solid substance produced by sedimentation or other separation methods in the process of wastewater treatment.It has high moisture and high organic compounds content,with easy compressive and difficult dewater characteristics.Reducing water content has always been an important goal in the sludge treatment process,and the drying process is still an indispensable link before its disposal.However,the large amount of unstable organic substances in sludge would lead to serious release of sulfur-containing or nitrogen-containing odorous gases during the drying process,causing severe secondary pollution.Therefore,this paper aims to investigate i)the effect of conditioner addition on sulfur/nitrogen transformation during conventional conditioning-dewatering-thermal drying process,ii)the transformation path and influencing factors during hydrothermal drying process.The key scientific and theoretical issues involving: the control mechanism of alkali addition on the sulfur-containing gases release;the possibility of simultaneous control of sulfur and nitrogen gases;whether the existence of water affects the sulfur and nitrogen transformation path during hydrothermal drying process;how the hydrothermal treatment temperature affect the distribution of sulfur and nitrogen products.In order to solve the above scientific issues,this paper has carried out a comprehensive and in-depth study.The effect of alkali addition on sulfur transformation was studied on a horizontal fixed-bed direct-heating drying system.The sulfur-containing species speciation analysis and the sulfur-containing model compounds experimental verification were adopted.Confirmed that: the addition of alkali,such as Ca（OH）2,greatly reduces the emission of the sulfur-containing gases,with more significant effect for the stronger alkalis;the presence of alkali promotes the oxidation of aliphatic and aromatic sulfurs into more stable sulfoxides and sulphonic acid,suppressing the generation of H2 S from aliphatic and aromatic sulfur decomposition at low temperatures;also,the alkalis fix the sulfur in the form of inorganic sulfide and sulphate in char,further reducing the release of sulfur into gas phase.The key factor that influencing the organic sulfur transformation is the base strength of alkali.Stronger alkali can provide more OH radicals,thus leads to better oxidation and fixing effect on aliphatic and aromatic sulfur.On the basis of meeting the technology requirements of the treatment process such as dewater,choosing alkali conditioner can suppress the sulfur-containing odorous gases release in the subsequent thermal drying process.On the bases of conclusion of alkali on sulfur evolution,the alkaline acetates were selected for further study to avoid the promoting effect of alkali on NH₃ releasing.Through the nitrogen balance analysis during the whole process,several important conclusions can be obtained: the addition of Ca acetate increases the nitrogen retention in char,mainly due to the inhibition of protein decomposition as well as the formation of stable N species,while Na acetate enhances the decomposition of nitrogen species in sludge such as proteinand inorganic-N;the effects of Ca and Na acetates on nitrogen transformation during sludge pyrolysis is due to their different catalytic effects on the decomposition of N species in sludge;Ca and Na acetates can catalyze direct cracking of amino acids and subsequent dehydration of amides intermediates to increase nitriles formation;the ring-opening reaction of pyrrole is also promoted by metal cations at high temperatures;the N species in tar are mainly in the form of amine-and heterocyclic-N,with less nitrile-N;the N species in tar is greatly suppressed by Ca acetate,due to its inhibition effect on the decomposition of protein;both Ca and Na acetates significantly reduce the emission of nitrogen-containing gases,as acetates can release acetone during thermal drying process which easily reacts with NH₃ to produce binary clusters or amines in tar.On the basis of meeting the technology requirements of the treatment process such as regulating carbon/nitrogen ratio of biochemical pool,choosing alkaline acetates can suppress the nitrogen-containing odorous gases release in the subsequent thermal drying process.The migration and transformation path of sulfur compounds during hydrothermal treatment was studied in a batch reactor.The following conclusions can be generated: the sulfur-containing gases were mainly produced by decomposition of aliphatic and aromatic sulfur,mainly composed by H2 S,CH₃SH and a small amount of SO₂;the production of sulfur-containing gas increases with temperature increase;the organic sulfur compounds would react with water during hydrothermal treatment;the large amount of OH* radicals generated by water would act as electrophilic reagent to attack the sulfur atom in organic sulfur compound,add oxygen on to sulfur atom,oxidize aliphatic and aromatic sulfur compounds to the corresponding sulfoxides and sulphonic acid,even inorganic sulfate;the reaction rate increases with the increase of temperature;the formed sulfoxides and sulphonic acid has lower thermal stability than before oxidation,through C-S bond breaking,SO₂ or SO₃ in gas,and SO₃2-and SO42-in aqueous solution were generated.During the whole process,a large amount of water participate in organic sulfur decomposition and dissolve parts of products,such as sulphate and SO₂,leading to major sulfur species migrate to the aqueous solution,reduce the sulfur content in the solid product and sulfur-containing gases release.Without considering residue content of total organic matters,the increase of hydrothermal treatment temperature is beneficial to produce solid products with lower sulfur content.For nitrogen,with hydrothermal treatment temperature increase,more nitrogen compounds convert to tar-N and solution-N.The nitrogen content in tar and solution are higher than char-N when temperature rise to 210 °C.Thus higher temperature is more conducive to the preparation of clean energy and the control of nitrogen residue in char.The main pathways can be described as: protein decomposition and hydrolysis,produce amine,water-soluble organic nitrogen,NH₃ and NH4+ in turn;followed by the reaction of inorganic nitrogen and water,generate NH4+ and NO₃-and other nitrogen-containing ions.The reaction rate increases with temperature rise.Nitrogen residues in char include undecomposed protein-N,heterocyclic-N such as pyrrole and pyridine,quaternary-N and a slight amount of nitrile-N.The nitrogen-containing species in tar are amine-N and heterocyclic-N without nitrile-N.In the aqueous solution,water-soluble organic nitrogen is the main part,followed by a large number of NH4+ ions.HCN is the dominant nitrogen-containing gas that released.In the comprehensive consideration of residue content of total organic matters,and residue sulfur,nitrogen content in the solid product,the hydrothermal treatment temperature is better to choose between 180 °C to 210 °C.To sum up,for direct thermal drying process,choose alkaline acetate,can create an alkaline environment to control sulfur-containing gases release,and can take advantage of its decomposition by-product to capture nitrogen-containing gas,realized the aim of simultaneous control of sulfur-and nitrogen-containing gases;for hydrothermal drying process,the transformation pathways of sulfur and nitrogen as well as the influence characteristics of the final treatment temperature are proposed,which provides a theoretical basis for the control of these two of pollutants.更多还原