泥浆真空抽滤泥水分离中堵塞机理及规律性研究

河湖底泥的疏浚工程因为使用绞吸式的疏浚方式,底泥与水混合后变成大量高含水率的泥浆。为了减少泥浆的体积,对泥水进行分离就显得非常重要。在将泥浆中水分抽滤分离的过程中,经常会发生堵塞,产生了抽滤效果低,抽滤不能持续的问题。针对这一问题,研究了不同泥浆粒径分布、泥浆的初始含水率、土工布的孔径、真空负压以及添加絮凝剂对泥水分离效果的影响,探讨了堵塞的机理。发现了由土工布过滤形成的泥皮的渗透系数将成为制约脱水效果的主要因素,当形成堵塞性泥皮时,其他因素如土工布的孔径、泥浆初始含水率等对脱水的影响可以忽略。添加絮凝剂会使颗粒聚团从而提高泥皮渗透系数是泥水分离变好的原因,并且絮凝泥浆中较小的团粒粒径决定了泥皮的渗透系数,因此可以通过检测絮凝后泥浆中较小团粒的粒径如D_(10),D_(15),D_(20)的方式比选絮凝剂、决定最优添加量、预测脱水效果。添加絮凝剂对泥浆中结合水含量的改变影响较小,因此认为絮凝使水分结合方式的改变并不影响泥水分离的效果。

Clogging mechanism and effect of cake permeability in soil-water separation using vacuum filtration

The cutter suction dredger is often used in dredging of rivers and lakes. The core of this method of dredging is to extract the mixture of sediment and water after the agitating process. It usually results in large residue of high water content slurry, which must be reduced through soil-water separation process. However, the clogging problem often occurs in the process of the soil-water separation, resulting in lower efficiency of dewatering. To solve this problem, the vacuum filtration tests are carried out to explore the related factors within the separation process. These factors include particle-size distribution of the slurry, initial water content of the slurry, pore size of the geotextiles and vacuum pressure, which might explain the cause mechanism of the clogging. The results indicate that the permeability of the cake accumulated on the surface of geotextiles is the major factor influencing the soil-water separation. When the permeability of cake is low, it comes to clog, and other factors are ignored. The permeability of the cake increases due to the particle aggregation caused by the addition of the flocculants, which improve the effects of separation. What is more, the smaller flocs dominate the permeability of the cake. Therefore the parameters of the smaller flocs such as D₁₀, D₁₅ and D₂₀ will help select better flocculants and dosages, or predict the separation process of slurry. The addition of the flocculants barely alters the bound water content. Thus, when assessing the effects of soil-water separation, the bound water should not be considered.