New Practical Filtration Technology

Author: Ding Qisheng / Editor-in-Chief: Zhang Weizhen
Publisher:
Publish Date: 2000-01-01
Features: This book introduces new achievements in filtration theory, such as modern filtration theory, squeezing theory, non-Newtonian fluid filtration theory, and multiphase filtration theory. It also elaborates on new filtration technologies, including dynamic filtration, microporous filtration, rapid filtration, high-gradient magnetic and electric separation technologies, etc. Based on years of experience in the design, research, and application of filtration technology, the authors highlight common and new filtration equipment, auxiliary equipment for filtration machines, installation, system debugging, fault troubleshooting, filtration experimental technology devices, scale-up of filtration machines, design calculations for filtration machines, selection of filtration machines, and the application of filtration technology in fields such as mineral processing, metallurgy, coal, petroleum, chemical industry, pharmaceuticals, light industry, food, and environmental protection. This book serves as a reference for engineering and teaching personnel engaged in research, design, manufacturing, and use in the field of filtration technology.
Excerpt:
1 Introduction
1.1 Solid-Liquid Separation, Filtration, and Dewatering [1]
1.1.1 Solid-Liquid Separation
In recent years, people have further recognized the importance of solid-liquid separation, understanding its close relationship with the effective utilization of resources and energy, as well as environmental issues. Consequently, extensive research has been conducted in theory and technology, yielding encouraging results. Solid-liquid separation refers to the mechanical method of separating discrete insoluble solid particles from a liquid, including filtration, gravitational sedimentation, flotation, and separation using centrifugal force in centrifuges and hydrocyclones. These methods are distinctly different from unit operations such as distillation, crystallization, adsorption, and diffusion. The materials in those unit operations are solutions, not solid-liquid mixtures. The applications of solid-liquid separation technology are extremely broad, ranging from environmental control to the production of chemical and food products, from water purification to protecting sensitive hydraulic circuits in aircraft. Separation technology can be applied to liquids with solid particle concentrations ranging from over 50% to less than a few parts per million. With the rapid and diversified development of industry, a large number of solid-liquid separation problems need to be addressed, which has promoted the development of solid-liquid separation machinery and its auxiliary equipment. This mutually beneficial interaction has benefited both the theory and practice of solid-liquid separation.
1.1.2 Filtration
Filtration is a component of solid-liquid separation, utilizing a filtration medium or porous membrane to retain insoluble particles in a liquid. Sometimes, the use of ion exchange beds to soften water, or of bentonite beds to remove acid and color from mineral oils, is also included under filtration. Microbial methods have been widely used for filtration in water treatment (both upper and lower water) and industrial wastewater treatment, despite the issue of soluble impurities, and are still classified as biological filtration. Reverse osmosis was originally a process of solution diffusion, but due to its close relationship with ultrafiltration and microporous filtration in membrane separation technology, it is introduced here as a special case. The earliest filtration technology was used for clarifying wine. To this day, filtration technology is still widely used in the beverage industry, aiming to remove tiny yet difficult-to-eliminate solid particles while avoiding the filtration of aromatic proteins. Water purification not only requires the removal of various solid substances, including bacteria, from a large amount of water but also must be cost-effective. It relies on gravitational sand filtration to meet this need, but it has increasingly been replaced by pressure sand filtration and, in some cases, by precoat filtration. The purification of swimming pool water is a modern branch of water purification, with reversible filtration machines as its typical filtration devices. The construction of wastewater treatment plants has greatly promoted the development of filter presses and vacuum drum filters, elevating the importance of belt filter presses. The sugar industry, in addition to using filtration machines, has focused more on filter centrifuges, which has significantly stimulated the development of this type of centrifuge. The large volume of wastewater from the paper industry requires treatment using devices such as vacuum disc filters, which has also contributed to the advancement of filtration machines. The development of modern chemical industry and related fields, such as petroleum, gas, mineral processing, and plastics, has driven the development of new filtration machines and auxiliary equipment.
1.1.3 Dewatering
Dewatering refers to the mechanical operation of removing liquid from wet particle beds or wet cakes. It can be divided into gravitational dewatering, centrifugal dewatering, aeration dewatering, and special dewatering methods. These dewatering methods are all related to the capillaries in the wet particle bed. The purpose of centrifugal dewatering is to separate the liquid rising in the capillaries, which cannot be removed under gravity. Aeration dewatering is not drying but rather the removal of the liquid rising in the capillaries using compressed air at room temperature. Special dewatering methods include using hygroscopic fibers to form felt layers that absorb moisture, dewatering through compressing the wet particle bed to deform it and expel the internal liquid, and enhancing dewatering effects by applying additional vibration.
1.1.4 Combined Filtration and Dewatering
The filter cake obtained from filtration usually needs to be thermally dried before storage or use. Therefore, the moisture content of the filter cake should be as low as possible before entering the drying chamber to reduce energy consumption. Many filtration machines with dewatering functions have been developed for this purpose, such as drum vacuum filters equipped with roller-belt dewatering devices, ( filter presses) with squeezing diaphragms, ( filter machines) with squeezing diaphragms, and belt filter presses.
1.2 Classification of Filtration [2]
Filtration is a unit operation that separates solids and liquids using a filtration medium, which can be divided into clarification filtration (clarification filtration) and cake filtration (cake filtration), as shown in Figure 1-1.