Design And Experimental Study On Medium Consistency Pump

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.