【作者】 马学文；

【导师】 翁焕新；

【作者基本信息】 浙江大学 ， 环境科学， 2008， 博士

【摘要】 随着我国城市化进程的加快,越来越多的污水产生并得到处理,同时大量的污泥也同时产生。污泥具有高含水率高体积的特点,而且含有大量的有毒物质。如果不能妥善地处理处置城市污泥,将会造成二次污染,并且影响污水厂的正常运行。如何经济而有效地处理处置污泥是目前国内外共同研究的重点。目前常见的污泥处理方法有:卫生填埋、土地利用、热干燥和焚烧,热干燥已经成为污泥处理的重要步骤。本文通过对污泥干燥特性的研究,结合利用烟气余热处理污泥发明专利技术的工程实践,提出了污泥干燥工艺的改进方法,并建立了一套新的污泥干燥工艺。4种不同质量等级的污泥颗粒在100～200℃的条件下进行了恒温干燥实验。结果表明,污泥干燥过程包括预热阶段、恒速干燥阶段、第一降速干燥阶段、第二降速干燥阶段4个阶段。在100～120℃时,污泥为弱强度干燥,临界含水率受温度和颗粒大小影响不明显;在140～200℃时为高强度干燥,临界含水率随温度升高或颗粒变大而增大。污泥干燥速率不仅取决于温度,还取决于污泥颗粒表面单位面积上实际用于蒸发水分的热量:减小污泥颗粒不仅可以增大比表面积,而且可以提高单位面积的干燥速率:而污泥的干燥时间与温度呈二次方关系,与污泥的表面积呈线性关系。污泥颗粒在200～500℃条件下干燥时,经历了预热阶段、类恒速干燥阶段和降速干燥阶段,类恒速干燥阶段的干燥速率并不是恒定的,而是呈波动型的,其中类恒速干燥阶段占据了总干燥时间和总失重率的70%左右。干燥过程中会产生裂纹,且前期由小变大而后期由大变小,主要是由于内外层失水不均匀所致。干污泥的粒径主要为砂级、粉砂级和粘土级,实际工程中干污泥产生的灰尘可以通过水膜除尘去除,结合污泥的热重分析确定了污泥的干燥温度可以在100～300℃,该温度范围内干燥冷凝水中最主要的有机物是链状烷烃、芳香烃和含氮杂环化合物,苯、邻二甲苯和苯酚是主要污染物。通过对江阴污泥处理工程的实际经验总结,并结合实验结论,我们认为可以通过低温干燥、自然干燥、太阳能干燥和余热回收利用等途径,利用热管和热泵等先进技术,对现有的污泥干燥工艺进行改进,改进后的工艺可以将煤的热利用率从44.62%提高到64.60%,并且将每吨湿污泥的能耗成本从104.07元/吨降到42.61元/吨,并且可以大大地减少二氧化碳和二氧化硫的排放量。更多还原

【Abstract】 With the development of urbanization in China,more and more municipal wastewater as well as sewage sludge is produced.Sewage sludge formed during wastewater treatment has high water content and large volume as well as various toxic substances. Any improper disposal of the sewage sludge will result in secondary environmental pollution and influence the operation of sewage treatment plant.How to dispose of it economically and efficiently has become a newly worldwide problem,and is being sought after both in China and abroad.There are four general sludge disposal methods:land application,landfill,drying and incineration.Drying has become an important step in sludge disposal.Drying characteristics of sludge granules were studied,and a project drying sludge by waste heat from flue gas was summarized.Based on these,improvement schemes of sludge drying technique were proposed,and a new sludge drying technique was established.Four different weight grades of sludge granules were dried at constant temperature of 100～200℃.Results showed that sludge drying process included four periods:preheating period,constant rate drying period,the first falling rate drying period and the second falling rate drying period.Sludge drying process was a weak intensity drying process at 100～120℃,critical moisture content was constant.It was a high intensity drying process at 140～200℃,and critical moisture content increased with the drying temperature or granule size increasing.The drying rate was affected with not only drying temperature but also the quantity of water evaporating heat in a unit surface area.Reduction of granule size can increase specific surface area and drying rate in a unit surface area.There were a quadratic nonlinear relationship between drying time and temperature,and a linear relationship between drying time and sludge surface area.Sludge drying process at 200～500℃included three periods:preheating period, constant-like rate drying period,falling rate drying period.Drying rate during constant-like rate drying period was not constant,but fluctuant.It took 70%of total drying time and total loss.Cracks were produced,which became larger in earlier stage then became smaller in later stage,it was because of water loss imbalance in sludge surface and inner.The particle size of dried sludge were mainly sand,silty sand and clay.Dust produced during sludge drying could be collected by water film dust collector.On the basis of thermogravimetric analysis,it was suitable to dry sludge at 100～300℃.Main organic matters in condensate at this temperature were chain alkane,aromatic hydrocarbon and nitrogenous heterocyclic compounds,and main pollutants were benzene,o-xylene and phenol.There were no PAHs in consendate. On the summarize of Jiangyin Sludge Drying Project and experiment conclusion, several techniques as low temperature drying,nature drying,solar drying and waste heat recovery,also some advanced equipments as heat pipe and heat pump,could be used in sludge drying technique.Heat utilization efficiency of improved technique could be enhanced from 44.62%to 64.60%,and emission of CO₂ and SO₂ was reduced significantly.更多还原