【作者】 马德刚；

【导师】 季民； 张书廷；

【作者基本信息】 天津大学 ， 环境工程， 2007， 博士

【摘要】 污泥的减量化、稳定化、无害化和资源化是城市污泥处理与处置的基本原则和目标,而脱水和干燥是其基本的单元操作。在干燥过程中,污泥的粘附问题对干燥设备的运行效率和稳定性具有很大影响,特别对于间接式干燥过程,一直是工艺设计与操作中必须面对的问题。文章以污泥的粘壁问题为研究对象,分析了污泥性状与操作条件对其粘壁特性的影响,提出了加热面阴极化干燥方法并实验考察了其操作条件的影响,进一步利用分形与时间序列相关理论分析了其蒸发速度的变化规律,并通过数理模拟的方法分析了微观传质特性。污泥的性状和操作条件对其粘壁特性具有直接的影响,其中污泥含水率和有机粘性物含量及加热面温度尤其重要。在含水率高于60%时,随着含水率的降低,粘壁量增加,在含水率60%附近达到最大值,随后随着含水率的降低,粘壁量下降。另外,污泥中的有机粘性物含量与粘壁量也有直接的关系,有机粘性物质较多的未消化污泥的粘壁量大于其有机粘性物含量较少的消化污泥。在较常用的以热水或低压蒸汽加热的较低温度范围内,,随着温度增加污泥粘壁量降低,如120℃的加热面温度产生的粘壁量小于100℃时。实验考察了加热面阴极化干燥过程中操作条件的影响,当污泥饼厚度为10mm时,从粘壁量、干燥时间和电能消耗等方面综合而言,最佳的电压梯度为4-5V/cm,其电场电能的消耗为3.87 kWh/t。通过现象观察和分析可以认为加热面阴极化对粘壁的克服作用是由以下三种因素综合作用的结果,即电渗透作用改变了加热面处污泥的水份分布,加热面产生了负电位变化,电化学反应产生的气膜阻止了污泥的粘附。通过对污泥干燥时蒸发速度曲线的直接观察和功率谱分析可以证明其传质过程具有分形特性,利用变换法和Hausdorff维数计算法得到了其反应内部传质动力特性的分形维数,为理论分析提供了依据。通过R/S分析发现,蒸发速度时间序列属正相关序列,Hurst指数介于0.7~1.0之间。通过对污泥干燥过程的数理模拟分析进一步证实加热面阴极化干燥方法可以有效促进污泥内部水份的运动能力,对传质具有促进作用。更多还原

【Abstract】 Volume reduction, stabilization, harmlessness and resourcefulness are the fundamental and object of urban sludge treatment and disposal. Dewatering and drying are the basic processes of them. But when the drying process is designed and operated, the problem about sludge adhesion has to be considered, because it can bring some bad effects to drying efficiency and stability, especially for indirect drying. This paper based on the problems of sludge adhesion to the dryer wall, analyzed the effects of sludge properties and working conditions on adhesion, gave and studied experimentally an application of a polarized electric field to reduce adhesion of a biological sludge to the dryer wall by contact drying of a sludge cake deposited on a heated metal plate serving as the cathode. Some theories about fractal and time series were used to analyze the variety of evaporation speed in sludge drying. A symbolic simulation was taken to analyze the microcosmic matter transfer.The sludge properties and working conditions directly affected the sludge-to-wall adhesion, especially including water contents, sticky organic matter and plate temperature. When the sludge contained water above 60% wb, the adhering intensity increased with the decreasing of water contents, and got to the maximum at around 60% wb. After that, it began to decrease following the moisture. The adhering intensities of indigested sludge with more sticky organic matter were more than the one of digested sludge. In the range of low temperatures which were applied on usual hot water or vapour drying, the sludge adhering intensities decreased with increase of plate temperature, for example, the plate temperature of 120℃made the adhering intensities more than the one of 100℃.The experiments were made to research the working conditions of sludge drying by applying a polarized electric field. The results showed, when sludge samples were 10mm thick, the voltage gradient of 4 to 5 V/cm was found to be optimal for adhering intensity, drying time and electric energy. Here, the electric energy consumption amounted to 3.87 kWh/t. By observing and analyzing, the reasons of reducing adhering intensity with a polarized electric field were thought to be following three results: the electro-osmosis changed the water distributing of sludge around the plate, the zeta potential of heat plate became negative, the gas generated owing to electrochemistry on the cathode wall stopped the sludge adhering to wall.The visual judgement and power spectral of drying speed were used to prove the fractal occurred during matter transfering. The methods of variety and hausdorff were used to calculate the dimensions that estimated or supported the kinetics of heat and matter transfer. The R/S analysis showed, the drying speed series belong to positive correlative series and its Hurst index existed between 0.7 and 1.0. The paper also gave a symbolic simulation that results showed applying polarized electric field could boost the water transfer of drying sludge.更多还原