【作者】 张辉；

【导师】 吴祖成； 胡勤海；

【作者基本信息】 浙江大学 ， 环境工程， 2013， 博士

【摘要】 城市污泥是污水处理工艺过程中产生的固体废弃物。随着我国城市化进程的加快,污水处理设施的建设完善,污泥产生量也越来越大。污泥具有含水率高、力学性质差、含有大量的有毒有害物质,且占地面积大等特点,如果得不到妥善地处理处置,将会带来严重的环境问题。随着人们观念的转变和技术进步,各类所谓的“污染物”开始被视作“放错位置的资源”而加以回收利用。有研究表明,污泥中含有大量的有机组分,占污泥干重的50%左右,其热值与褐煤相当,可以进行能源化利用。到目前为止,污泥作为能源而加以利用的方法主要包括厌氧消化、微生物燃料电池、气化和热解、燃烧和混烧等。其中,燃烧和混烧可直接实现能量转化,且设备技术相对成熟,被认为是当前最经济可行的污泥能源转化方式。本文采用污泥-煤混合成型→干化→热利用→灰渣利用的过程,在不增加能耗基础上,实现污泥中能量的回收利用之目的,并对产生的灰渣进行完全利用。80%左右的含水率是污泥燃烧利用的主要障碍,通过将煤和污泥复合成型制备成复合燃料,可以实现燃烧过程的能量供给平衡,同时可加速复合燃料中污泥含水的干化速率。本文研究了污泥含水率、污泥添加比例和冷压成型压力等因素对复合燃料成型的影响,以及不同温度条件下复合燃料的干化特点,结果表明利于复合燃料成型的工艺条件为：污泥初始含水率60-70%,成型时固含70-80%。10-30MPa范围内的成型压力对落下强度影响较小。制备得到的成型燃料的落下强度可达到采用商用黏结剂制备得到的型煤水平。混合成型后的污泥复合燃料,和污泥相比明显有利于水分的扩散和挥发,可在室温及不高于100℃条件下快速干化,同时实现了污泥脱水及能源化利用的目的。对污泥、煤以及二者的复合燃料在空气及氮气条件下进行热分析,研究了总失重量、失重速率、热效应、燃烧及热解参数特点及焦炭生成等内容。结果表明,与煤相比,污泥具有较高的灰分和挥发分,但所含的有机组分的燃烧和热解温度均低于煤。污泥的加入可以降低复合燃料的着火点,提高燃料的活化能。复合燃料的燃烧和热解过程中,污泥和煤表现各自的热特征,无明显的交互作用。污泥中的焦炭含量低于煤,且不稳定,在1000℃热过程中几乎完全分解。研究了污泥、煤以及复合燃料燃烧的污染物排放特征,分析了不同复合比例燃料及温度条件下SO2、NOX等污染物的排放特征,以及灰渣的重金属浸出特征。结果表明燃烧过程中,复合燃料中污泥具有一定的固硫和固氮作用,污泥中的s、N含量较高,燃烧过程中SO2、NOX排放的绝对量有所上升但固硫率、固氮率随复合燃料中污泥含量的升高而提高。灰渣的重金属浸出均可达到国家的相关标准规定。不同条件下对燃烧后的污泥灰及复合燃料燃烧后的灰渣进行团粒或压力成型,形成烧结坯料,采用两步烧结法制备得到不同性能的陶粒产品。表征并分析了产物的吸水率、密度及物相。对于污泥／污泥灰,采用两步烧结,在低温烧结后,在温度1050℃,时间5-20min条件下,可以烧结得到吸水率45.32-4.11%,密度1.67-0.84g/cm3的陶粒产品。对于复合燃料,在低温烧结后,在温度1150℃,时间5-30min条件下,可以烧结得到吸水率56.35-1.12%,密度1.609-0.758g/cm3的陶粒产品。和纯污泥/污泥灰的烧结条件相比,复合燃料灰需要更高的烧结温度和更长的烧结时间。物相分析表明,随着温度的升高,污泥灰逐渐发生变化,石英相峰值明显降低,转化出现莫来石、斜方钠沸石等物相,并有非晶态无定形物相出现。复合燃料灰渣的烧结过程中,莫来石等物相的存在可能是引起烧结温度提高的原因。通过本研究的工艺过程,充分利用现有燃烧设备,解决了污泥含水率高不利于热利用弊端,在不增加能耗的基础上实现了对污泥中能量的回收,具有良好的实用性和推广性。同时,充分利用污泥灰及复合燃料灰渣的材料特征,对最终的灰渣进行了陶瓷化利用,实现了污泥“零排放”及完全的资源化利用。更多还原

【Abstract】 Sewage sludge is the solid residue produced in the process of wastewater treatment. The production of sewage sludge has been gradually increased along with the rapid development of urbanization and perfect construction of wastewater treatment facilities. Sewage sludge has the characteristics of high moisture content, poor mechanical properties, containing a lot of poisonous and harmful substances as well as covering a big area. If not properly disposed, it would bring serious problems to environment.With the change of people’s conscious and the progress of technologies, kinds of so-called "pollutant" have been considered as "resources located in wrong places", and being recycled. Researches have indicated that sludge contains a lot of organic matters accounting for about50%of the dry weight, and it could be adopted as energy due to that its calorific value is the same as that of lignite. Up to now, the major methods of energy-oriented utilization of sludge have included anaerobic digestion, microbial fuel cell, gasification and pyrolysis, combustion and co-combustion. Wherein, the combustion and co-combustion with the advantage of the realization of direct energy conversion and relatively mature equipments and technology, is considered as the most economically viable way for utilization of sludge as energy nowadays.With the purpose of energy-oriented utilization of sewage sludge without increase of energy consumption, the paper adopted the process of sludge-coal mixed and molding, drying, heat utilization, and ash utilization, and consequently realized the recycle of sewage sludge and fuel ash.The main obstacle of sewage sludge combustion is the80%moisture content. By means of compound preparation into composite molding fuel, the mixture of coal and sludge can achieve the balance of energy supply in the combustion process, and can simultaneously accelerate the drying of sludge in the mixture. Experiments were conducted in this paper including the effects of initial water content, amount of addition of sewage sludge and moulding pressure on characteristics of combined fuel, as well as the drying characteristics of the combined fuel at different temperatures. Results showed that the optimized conditions for moulding combined fuel were60-70%of initial moisture content of sludge and70-80%of solid content in the mixture of sludge and coal. The drop shatter had been less affected by moulding pressure at range of10-30MPa. Combined fuel prepared from sludge had good strength of drop shatter, which was satisfied with the commercial leve of briquette. Compared with the sewage sludge alone, the moulded sludge-coal could be dried more easily and quickly at room temperature or lower than100℃. Thus, the purposes of rapid dehydration of sewage sludge as well as its utilization as a potential energy were achieved.Thermal characteristics of sludge, coal and mixture fuel were analyzed under air and N2condition, respectively. The parameters of total loss of weight, weight loss rate, heating effect, combustion and pyrolysis parameters, coke formation were studied. Results showed that compared with coal, sewage sludge had higher content of ash and volatile, however, combustion and pyrolysis temperature were lower than those of the coal. The addition of sludge improved the ignition temperature and activation energy of the combined fuel. Sludge or coal was expressed its own thermal characteristics during combustion and pyrolysis process of the combined fuel, and no obvious interaction was observed. The content of coke in the sludge was lower than that in the coal, and was completely decomposed at1000℃.The emission of pollutants during the combustion process of sewage sludge, coal and the combined fuel was studied, including the characteristics of SO2and NOx emissions under different ratio of sludge/coal and temperatures and also the leaching characteristics of heavy metals in the ash. Results showed that addition of sludge could maintain sulfur and nitrogen retention during combustion process of the combined fuel. The absolute quantities of SO2and NOx emission were increased because of the higher content of S and N in the sludge, but the capture efficiency of sulfur and nitrogen was enhanced with the increasing addition of sludge in the combined fuel. Leaching of heavy metal from the ash satisfied the national related standards.The combustion ash of sludge and combined fuel were prepared for ceramsite products under different conditions with two step sintering process, respectively, and different performances of haydite were obtained. Water absorption and bulk density were characterized, and the mineral phases of raw materials and the formed haydite were determined by X-ray Diffraction (XRD). Results showed that for the sludge ash, the products of haydite with the range of45.32-4.11%of water absorbent and1.67-0.84g/cm3of bulk density, respectively, were obtained by the control of material formula and process conditions such as temperature and sintering time. As for the ash of combined fuel, products with56.35-1.12%of water absorbent range and1.609-0.758g/cm3of bulk density, were obtained at1150℃and sintering time range of5-30min. Higher sintering temperature and longer sintering time were needed during the process of sintering the ash of the combined fuel as compared with the ash of sludge. XRD analysis showed that material phase changed with the increase of temperature, the peak of quartz phase obviously decreased, and the phases such as mullite, rhombic sodium zeolite and amorphous appeared. Sintering temperature of combined fuel ash increased might be related to the presence of mullite content.By means of the processes discussed in the paper, the purpose of energy-oriented utilizationof sludge could be realized, which can make full use of the existing combustion equipments, and avoid the defects of high moisture content of the sludge. The methods in this paper perform good practicability and popularization.Meanwhile, the final ash of sludge and combined fuel can be adopted for preparation of ceramic materials, and consequently achieve the sludge "zero emissions" and complete utilization as resources.更多还原