【作者】 李博；

【导师】 严建华； 王飞； 蒋旭光；

【作者基本信息】 浙江大学 ， 工程热物理， 2014， 博士

【摘要】 为实现污泥高效干化和污泥干化焚烧系统的优化运行,建立了污泥剪切试验方法和装置,搭建了桨叶式、圆盘式和倾斜桨叶式小型污泥干化试验系统,建立了污泥干化模型和污泥干化焚烧系统能量平衡模型,开展了深入的理论研究。通过对污泥固相组分及相关物理性质的详尽测定,深入分析了污泥中有机质、无机矿物质细颗粒和可结晶金属盐对污泥粘附性和粘结性的贡献。建立污泥剪切试验方法和装置,对污泥的粘附特性和粘结特性进行了研究,其中对污泥粘结特性的研究方法和结论在国内外尚属首次。研究表明,污泥在含水率区间为40%-65%时表现出显著的粘附性和粘结性,不同污泥略有差异。污泥干化全过程中,粘结剪切力均大于粘附剪切力,说明当施加在污泥上的机械外力足够大时,污泥会首先从换热面剥落,机械外力进一步加大时,污泥才可能进一步被破碎。提高换热面温度和加入添加剂均可在不同程度上影响污泥的粘附性和粘结性。使用自行研制的小型桨叶式污泥干化机对污泥干化特性进行了研究。研究发现,污泥在桨叶式干化机内干化过程的第一降速区和第二降速区之间存在一个显著的波动区。将干化特性与污泥粘附和粘结特性比对后发现,波动区对应的污泥含水率范围与污泥粘附性和粘结性最大时的含水率范围基本重合。这一发现,在国内外还未见报道。污泥的粘附性和粘结性是波动区产生的根本原因,桨叶对污泥的搅拌是波动区产生的直接原因,波动区是污泥干化过程粘滞区的直接体现,桨叶的搅拌有利于克服污泥干化粘滞区的不利影响。在粘滞区内污泥自身的粘结力远大于污泥与换热面的粘附力,桨叶易将污泥剥落,却不易将污泥破碎。因此,提高对粘结污泥团块的破碎效果,是提升污泥干化速率的关键。桨叶搅拌强度对干化速率的影响主要体现在第二降速区。提高热源温度不仅可以通过增加能量传递的方式提高污泥干化速率,还可降低污泥的粘附性和粘结性。生石灰可提高波动区和第二降速区内的干化速率。胰蛋白胨作为有机质会大幅提高污泥粘附和粘结剪切力,波动区更为显著。二氧化硅在污泥含水率较高时可降低其粘附和粘结剪切力,在污泥含水率较低时会提高其粘附和粘结剪切力。石英砂可有效降低污泥粘结剪切力,使污泥更易于被破碎。为比较圆盘式干化机与桨叶式于化机对污泥干化效率的差异,自行研制了小型圆盘式污泥干化机,进行了污泥干化试验,并将试验结果与小型桨叶式污泥干化机进行了对比。在以导热油为热源的情况下,圆盘式干化机较简单的导热油管路使导热油流速较高,更新较快,沿程温度也较高,可使污泥在干化过程中维持在较高的温度,有助于提升干化速率。污泥在圆盘式干化机内进入干化粘滞区时,污泥粘结并粘附在圆盘表面,圆盘转动难以对污泥进行充分的挤压、剪切和破碎,混合效果较差,难以对污泥干化速率起到改善效果。在实际应用的连续进料式圆盘干化机中,可能会出现污泥大量粘附,难以向出料端推进,处理能力下降等隐患。基于桨叶式干化机克服污泥干化粘滞区不利影响的作用,在国内首次提出了倾斜式桨叶的详细改进方案(已申请专利),自行研制了改进的小型倾斜桨叶式污泥干化机,进行了污泥干化试验,并将试验结果与小型普通桨叶式污泥干化机进行了对比。改进的倾斜桨叶式干化机在污泥含水率72%-83%之间可有效提高污泥的搅拌效果,并提高污泥干化效率；当污泥干化进入粘滞区时,倾斜桨叶先是随着转动而嵌入污泥层并形成沟壑,在紧随其后的某一含水率点上,倾斜桨叶可显著发挥对污泥的剥离和破碎效果,使污泥干化效率大幅跃升。根据污泥干化过程粘滞区特性的研究结果,在渗透模型基本原理的基础上,建立了更符合污泥在小型干化机内实际粘滞特性的数值模型。根据所掌握的污泥干化粘滞区含水率范围,在模型内对应的区域加入粘附热阻,可使模型符合污泥干化粘滞区的干化特性,计算结果与实际试验结果较为吻合。通过对模型中工况参数的调整,可对污泥在各种工况条件下的间接传热式干化特性进行计算。通过建立污泥干化焚烧系统的物料和能量平衡模型,对污泥干化焚烧工程实例进行了分析,确定了基于节能降耗的最佳入炉污泥含水率；针对污泥含水率、污泥热值、系统运行负荷等运行参数可能出现的变化,对整个系统的能量平衡状态进行了计算和分析,对实际工程的运行具有较好的应用意义。通过对污泥干化焚烧工程实例的能量损失分析,确定能量损失最大的工艺环节为污泥干化载气洗涤水换热器的散热损失等八项,可据此有针对性的提出能量回收或节能降耗措施。论文最后还对需要进一步开展或加强的工作进行了归纳和总结。更多还原

【Abstract】 This thesis presents a study on efficient sludge drying and optimal energy efficient of sludge drying-incineration system. To achieve these purposes, a sludge shear test method and apparatus was built; a bench scale sludge drying test system with paddle dryer, disc dryer and diagonal paddle dryer was developed; sludge drying model and energy balance model of sludge drying-incineration system was established.The contributions of organic matters, inorganic minerals with fine particle size and crystalline metal salts to the sludge adhesion and cohesion were discussed, based on the detailed measurement of sludge contents and related physical properties. The adhesion and cohesion characteristics of the sludge were studied by using the shear test apparatus. This test method for sludge cohesion characteristic is reported for the time. Results show that the sludge sample exhibit significant adhesiveness and cohesiveness in the moisture range of45%-65%, and the moisture range varies with different sludge samples. The cohesion forces of sludge are greater than the adhesion force during the whole process of sludge drying. This indicating that when the mechanical force applied to the sludge is large enough, the sludge will firstly stripped away from the heating surface; a further increasing of the mechanical force is needed to break the sludge bulk into pieces. The temperature of heating surface and additives can affect the sludge adhesion and adhesion characteristics.The drying characteristics of sludge samples were studied by using bench scale paddle dryer. A significant fluctuation period between the first and second falling rate period was observed. It is found that the moisture range of fluctuation period is overlap with that when adhesion and cohesion force shows peak, after the comparison of sludge drying characteristics and adhesion/cohesion characteristics. The adhesiveness and cohesiveness of sludge is the basic reason for fluctuation period, and the stirring of paddles is the direct cause of fluctuation period. The fluctuation period is a direct reflection of sludge drying sticky phase, and the stirring of paddles helps to overcoming the negative impact of sticky phase. It is easier for the stirring paddles to strip the sludge away from the heating surface than to break the sludge bulk into pieces, because the cohesiveness of sludge is larger than its adhesiveness. Therefore, it is more important to break the sludge into pieces for the purpose of improving sludge drying rate. The impact of stirring intensity is significant in the second falling rate period. Rise the temperature of the heating source can not only improve the sludge drying rate by increase heat transfer, but also reduce the negative impact of the sludge sticky phase. Lime as additive can increase sludge drying rate in fluctuation period and second falling rate period. Tryptone as a kind of organics can largely improve the adhesiveness and cohesiveness of sludge. Silica as additive can reduce the adhesiveness and cohesiveness of sludge in higher moisture content, but increase the adhesiveness and cohesiveness at lower moisture content. Quartz sand as additive can effectively reduce the cohesiveness of sludge, make the broken of sludge more easily.In order to compare the differences between the disc dryer and paddle dryer, a bench scale disc dryer was established. The drying characteristics of sludge samples in bench scale disc dryer were studied and compared with the results of paddle dryer. In the case of using heating oil as the heat source, the sludge drying rate is higher in the disc dryer. Due to simple setup of oil pipes in disc dryer, the flow of heating oil is more efficient, and makes it maintaining a higher temperature, thus benefits the drying of sludge. When it comes to sticky phase, the sludge adheres on the disc surface and stick together to form a plastic sludge layer. The rotation of disc could barely extruding, shear and break the sludge layer, and play no role in maintaining the drying rate. In the real application of continuous feeding disc dryer, the sludge would probably sticky seriously, difficult to move towards the discharge, drying ability of sludge dryer may decline.On account of the positive effects of paddle sludge dryer on overcoming the negative impact of sticky phase, a modified bench scale diagonal paddle dryer was developed. The drying characteristics of sludge samples in this modified dryer were studied and compared with the results of traditional paddle dryer. The sludge drying rate and stirring effect of diagonal paddle dryer is effectively improved in the moisture range between72%and83%. When the sludge drying comes to sticky phase, the diagonal paddles could embed in the sludge bulk and form ravines, at a followed moisture point, diagonal paddles can largely improve the striping and breaking of sludge bulk and improve the drying rate significantly.A drying model for bench scale sludge dryer, which is more consistent with actual drying process, was established based on the fundamental of penetration model. A thermal resistance of stickiness was introduced to the model at corresponding region, based on the responsible moisture range of sticky region. The simulation results can better match the actual drying process. The drying characteristics of sludge in varieties of operation conditions of indirect dryer can be simulated by adjustment of operation parameters in the model.The operation mode of a real sludge drying and incineration project was analyzed, based on the established energy balance model for sludge drying and incineration system. The optimal moisture content of sludge sent to the furnace is determined. The impacts of the variation of sludge nature and operating parameters could be predictable. Through the energy loss analysis of the sludge drying and incineration project, eight kinds of greatest energy loss is determined. Targeted methods for energy recovery and saving can be further studied.Further works are summarized and presented at the last of this thesis.更多还原