【作者】 马旭丹；

【导师】 王乐勤；

【作者基本信息】 浙江大学 ， 化工过程机械， 2014， 博士

【摘要】 中浓技术是一种环保节能高效的造纸制浆技术,是目前国内外造纸制浆技术发展的趋势。在中浓带压漂白工艺中,高扬程的中浓纸浆泵是中浓技术的核心设备之一。通常,中浓设备的设计和研究离不开大量的试验和累积的经验。国外已有数十年的研究基础,形成了系列化的优秀产品。但是国内由于起步较晚,目前在中浓纸浆泵的设计制造上还存在大量的空白。在中浓带压漂白工艺中使用的大量高扬程中浓纸浆泵多为国外进口产品,价格昂贵。因此,高扬程中浓纸浆泵的设计和性能研究具有很大的工程意义。本文首先分析了中浓纸浆泵的输送介质——中浓纤维悬浮液的流变特性,对中浓纤维悬浮液在转子剪切室内剪切流动的流动机理进行了数值研究。其次,针对中浓悬浮液的特殊性质,对中浓纸浆泵的整体结构进行了分析,重点对水力部件的重要参数进行了分析和设计,并对中浓纸浆泵和清水泵的一些重要的不同之处进行了对比。最后,设计和搭建试验台,对中浓纸浆泵在不同运行条件下的运行特点和性能进行了试验研究和结果分析。本文的主要工作包括：1)基于纤维悬浮液非牛顿流变特性,对转子剪切室内中浓纤维悬浮液的流动机理进行数值模拟。为了重点研究浆料受到剪切力后的流动特点,将气体和纤维对浆料流动的影响考虑到纤维悬浮液的流变特性中,将纤维悬浮液视为一种具有屈服应力和剪切稀化特性的非牛顿流体。建立非牛顿流体的数值模拟方法并验证。用数值方法研究转子剪切室内的流动特点。分别分析了纤维悬浮液在受到不同剪切力的作用下不断屈服的过程,以及各种物性参数、剪切叶片参数、剪切室尺寸等不同条件下剪切室内的流动状态。本节工作为湍流发生器的工作机理研究和设计提供参考依据。2)设计中浓纸浆泵的结构和水力部件。由于输送浆料的特殊性,中浓纸浆泵的结构不同于普通的清水泵。质量分数超过7%浓度的纤维悬浮液丧失流动性,当浆料受到足够强烈的剪切作用后,浆料湍流化,具有流动性。针对中浓浆料剪切流动的特点,设计了与叶轮同轴安装的湍流发生器,在浆料进入叶轮前使其流动起来。由于纤维和纤维网络对气体的吸附作用,中浓浆料中还含有大量的气体,为了顺利输送浆料,必须将气体分离出去,因此在叶轮后侧设置气体分离系统。考虑到中浓浆料的特殊性,对叶轮、蜗壳等水力部件进行分析设计,讨论一些重要结构参数在设计中的注意事项。分析中浓纸浆泵与清水泵的一些不同之处。3)试验研究中浓纸浆泵的性能。设计和搭建中浓纸浆泵性能测试试验台,改变试验条件,研究中浓纸浆泵的运行特性。采用不同浓度的纸浆,对比输送中浓纸浆与输送清水时中浓纸浆泵的性能变化规律。研究转速对输送不同浓度浆料时泵性能的影响。为了防止中浓纸浆泵出口流道堵塞,设计三种具有相同轴面流线不同宽度的叶轮,分别更换三组宽度的叶轮测试,研究叶轮宽度对泵性能的影响。具有半开式叶轮的中浓纸浆泵在运行中,叶顶间隙是一个重要参数。调节不同的叶顶间隙,研究不同浓度下叶顶间隙以及间隙比对泵性能的影响。中浓浆料中包含大量的气体,一般而言气体含量随着纸浆浓度的增高而增高。气体在除气系统中所受压差对气体分离起重要作用。气体分离所受压差可通过真空泵调节,研究不同纸浆浓度下,真空度大小对中浓纸浆泵性能的影响。此外,还给出了中浓纸浆泵运行过程中浆料在不同流速下的流动状态,以及中浓纸浆泵在运行中的一些注意事项等。根据本文对纤维悬浮液的模型简化与数值模拟,中浓纸浆泵的设计工作,以及系列的试验研究结果,为国内中浓纸浆泵的设计和现场运行提供一些参考依据。更多还原

【Abstract】 Medium consistency technology (MC technology) is an environment friendly, energy saving and high efficiency pulping technology. It is the tendency of the development of the pulping process in the world. In the MC pressured bleaching unit operation, MC pump with high head and efficiency is one of the most important devices. Usually, the development of devices in MC technology is dependent on repeated experiment and accumulated experience. There are several decades of research experiences abroad and series of products with effective performance have been developed. But in China, because the development of MC technology is late, an enormous gap exists in MC pump design and manufacturing. Nowadays, most of the MC pumps used in MC bleaching unit process are imported which are very expensive. So, the design and experimental study on the MC pump is of great importance in engineering application.In this these, the rheology of the medium concentration pulp suspension, which is the transported medium of the MC pump, is firstly analyzed. The flow mechanism of the suspension in a rotating tester is numerically studied. Then, considering the specificity of MC pulp suspension, the structure of the MC pump is designed. Some of the important geometry parameters of the hydraulic components are carefully analyzed and determined. Differences between MC pump and water pump are compared. A test rig is designed and built. Series of experiments are conducted to get the pump performance curve in different operating conditions. The following main contents are included in this thesis.1) Internal flow field in a rotating shear tester is numerically simulated based on the non-Newtonian characteristic of fiber suspension. In order to study the pulp flowing characteristic in the shear forces, the influence of the air and fiber networks are taken into account to the rheology of the fiber suspension. The suspension is considered as a non-Newtonian fluid with yield stress and shear thinning characteristic. The numerical method to simulate the non-Newtonian fluid is developed and validated. Simulate the flow field in a rotating shear tester. The yield process in gradually increased shear force is shown. The influence of the material physical parameters, the blade height and the size of the rotating tester are analyzed. These studies can provide some reference to the mechanism study and design of the turbulence generator.2) Design the structure and hydraulic components of the MC pump. Because of the specificity of the transported medium, the structure of the MC pump is different from that of water pump. Once the pulp mass concentration exceeds7%, it stopped flowing and acts like a solid. When sufficient shear stress is exerted, the suspension started to flow again. According to the shear-flowing characteristic of MC suspension, a turbulence generator is designed and installed coaxially with impeller to make the suspension flow before it gets into the impeller. The fiber and networks has an adsorption effect to the air. Plenty of air exists in the suspension which makes it impossible to be transported by a centrifugal pump. So a gas separation system is designed in the back case of the impeller. Considering the specificity of the MC pulp suspension, some important parameters of the hydraulic component, such as impeller, volute and so on, are analyzed. Some differences between MC pump and water pump are also analyzed.3) Experimentally study the MC pump performance. A test rig is designed and built to study the MC pump performance in different operating conditions. Suspensions in several different concentrations are adopted. Compare the pump performance when transporting water and suspension. Study the influence of the speed to the MC pump performance when transporting different concentration pulp suspensions. In order to avoid the blockage of the flow channel, three impellers with the same axial structure and different blade outlet width are designed. Study the pump performance change with the change of blade width. In the operation of a semi-open impeller, the tip clearance is a very important parameter. Regulate the tip clearance and study the pump performance changes with different tip clearance and different tip clearance ratio when transporting different pulp concentrations. Abundant air is included in the pulp suspension. Usually, the air content increases with the increase of the fiber mass concentration. The pressure difference in the degas system is important to the separation of the air. The pressure difference is regulated by the vacuum pump. Study the influence of the vacuum degree to the pump performance in different pulp concentrations. In addition, the flow conditions in different flow rate and other specificity during the operation of the MC pump are shown.The simplicity and simulation of the fiber suspension, design and series of experiment of MC pump in this thesis can provide some reference to the design and operation of the MC pump.更多还原