For an ultrafiltration system, how to evaluate it is a question we should pay attention to. There are many technical indicators to measure and evaluate an ultrafiltration system from different angles. The selected part is defined as follows.
1 Bubble point test [BP] Bubble point is a common method used to test and monitor the performance of membranes and the integrity of membrane components. Bubble point means that the membrane is completely wet and immersed in the liquid, and a certain pressure is applied from one side of the membrane The lowest pressure at which a continuous gas bubble appears from the other side of the gas. The bubble point test is also often used to detect the maximum pore size of a membrane.
2 cross-flow filtration refers to the horizontal flow on the surface of the membrane. Water permeable passes through the membrane perpendicular to the direction of the inflow of water. The trapped material is concentrated in the remaining water. The component is discharged in the direction of inflow and returned to the water tank. Raw water is combined and returned to the ultrafiltration system. The greater the amount of circulating water, the higher the cross-flow cutting speed, the thinner the covering layer of the retained material on the membrane surface, and the lighter the fouling of the membrane.
3 Dead-end filtration Dead-end filtration means that the raw materials flow through the membrane in a manner perpendicular to the surface of the membrane, and all of the membrane passes through the membrane to produce water. Contaminants in the water are trapped by the membrane and deposited on the membrane surface.
4 Raw water feed The liquid entering the ultrafiltration system has not yet passed through the ultrafiltration membrane.
5 Ultrafiltration [UF] The process of separating and separating solid particles and substances with different particle sizes from liquids through an ultrafiltration membrane.
6 Permeability / flux Flux is generally used to indicate the rate of water and other liquids permeating through the membrane, usually expressed as the volume of water and other liquids per square meter of membrane filtration area per hour (such as 3 2m /m.h).
7 Fouling Solid matter that is retained by the membrane and deposited on the membrane surface. Contamination often results in a decrease in membrane permeability. Chemical cleaning is usually required to remove contaminants on the membrane surface and restore membrane permeability.
8 Hydrophobic (hydrophobic) Hydrophobic membrane material's water-repellent properties. Hydrophobic membrane materials have very low water absorption properties, so the water on the surface is often granular.
9 Hydrophilic Hydrophilic membrane materials have a strong attraction to water, and their surfaces are naturally wetting with chemical properties.
10 Trans-membrane Pressure [TMP] represents the actual driving pressure required for water to pass through the membrane, and is calculated as the difference between the average pressure on the raw water side and the average pressure on the water production side, that is, the transmembrane pressure difference = (P feed + P concentration) / 2-P production 11 Trans-membrane flow [TMF] A unit that proves the characteristics of membrane flow. It is defined as the initial volume of liquid permeating through the membrane in a certain period of time, which is related to the filtration area of the membrane and the transmembrane pressure difference. The general expression unit is: ml / min cm2 bar
12 Cut molecular weight Molecular Weight Cut Off The pore size of an ultrafiltration membrane is usually defined by the molecular weight of the material it retains. The molecular weight that can retain 90% of the material is the cut molecular weight of the membrane. Such determinations are generally performed using typical known molecular weight spherical molecules such as glucose, sucrose, bacitracin, myoglobin, pepsin, globulin, and the like as benchmarks.
13 Back flush The ultrafiltration permeate flows from the outside of the membrane filament (water-producing side) to the inside of the membrane filament (raw water side) under a certain pressure.
14 Recovery Rate Per unit ultrafiltration net water production (water required for backwashing) and total raw water percentage R% = net water production / total raw water ¡Á 100
15 Concentration Polarization Causes trapped suspended matter to accumulate on the membrane surface. Generally increasing the tangential velocity of the liquid on the surface of the membrane wire can effectively reduce the phenomenon of concentration polarization. How to determine the performance parameters of the ultrafiltration system required by your unit. When you want to choose a suitable ultrafiltration system, for those who do not understand the above Technical experts of other industries obviously need the support of equipment manufacturers with more experience. The company cooperates with the Chinese Academy of Sciences to jointly develop and manufacture ultrafiltration membranes, and its products have reached the international leading level. This is something that many traditional equipment manufacturers and engineering companies do not have.
1. Technical advantages of ultrafiltration system Compared to other membrane separation technologies such as reverse osmosis membrane and gas separation membrane, the separation process of ultrafiltration has the following significant features:
1. Separation at normal temperature and low pressure, so low energy consumption, so that equipment operating costs are low.
2. The equipment is small in size and simple in structure, so the investment cost is low.
3. The ultrafiltration separation process is just a simple pressurized liquid transfer, the process is simple, and it is easy to operate and manage.
4. The ultrafiltration membrane is a homogeneous continuum made of polymer materials, which is filtered by pure physical methods, and the substance does not undergo qualitative changes during the separation process. And no impurities will fall off during use, ensuring the purity of the ultrafiltration.
The ultrafiltration system also has significant advantages in the process of use, summarized as follows:
(1) Multiple sets of alternating operation, continuous recoil (2), large flow cross-flow, pollution equalization (3), recoil dosing, suppression of pollution (4), chemical washing, timely recovery (5), recoil Flush water reuse, water saving (6), easy automatic control, intuitive and efficient. The above characteristics determine that the application of ultrafiltration membranes is very wide. There are large-scale applications from the purification of ordinary domestic drinking water to high-tech fields, so ultrafiltration Membrane separation technology is a membrane separation technology with broad development prospects.
Ultrafiltration system process flow In the membrane separation technology, the membrane with a micropore diameter of 20 ¡Á 10-10m ～ 1000 ¡Á 10-10m is called an ultrafiltration membrane, which is between 0.002-0.1um, and the general colloid volume Both are ≥0.1um, latex ≥0.5um, bacteria volume such as coliform and staphylococcus ≥0.2um, suspended solids, microparticles and other volumes ≥5um, so the ultrafiltration membrane can filter out bacteria, colloids, suspended solids, proteins, etc. in the solution Macromolecular substances.
Ultrafiltration system selection guide 1. The basic form and application range of ultrafiltration are divided into four types from the structure: plate and frame, tube, roll and hollow fiber; the dense layer (separation layer) of the membrane is in the hollow The inner or outer surface of the fiber is divided into three types: internal pressure, external pressure and internal and external pressure. According to the operation mode, it is divided into three types: dead end, cross flow and partial cross flow. From the operation mode, it is divided into: Pressure, constant current and variable pressure flow.
Forms of application: plate and frame waste water reuse, food, chemical and pharmaceutical concentration or purification, tubular food, chemical and pharmaceutical concentration or purification, roll electrophoretic paint reuse, hollow fiber wastewater reuse, surface water treatment, etc. , Reverse osmosis pretreatment, etc. 2. Internal pressure and external pressure hollow fiber ultrafiltration membranes a. Internal pressure type: That is, the raw liquid first enters the inside of the hollow fiber, driven by the pressure difference, and penetrates the hollow fiber from the inside to the outside in the radial direction to become The permeate liquid, the concentrated liquid stayed inside the hollow filament and flowed out from the other end.
The function of epoxy resin end seal is to seal the gap between the membrane filaments at the ends of the hollow fiber membrane filaments, so as to separate the original liquid from the permeate and prevent the original liquid from penetrating directly into the permeate without filtering through the membrane filament .
b. External pressure type hollow fiber ultrafiltration membrane is the raw liquid that penetrates the hollow fiber from the outside to the inside through the pressure difference in the radial direction to become the permeate, and the trapped substances are collected outside the hollow fiber.
c. Hollow fiber ultrafiltration membrane filtration methods are mainly divided into two types: full filtration and crossflow filtration.
The full filtration method means that all the water molecules in the original solution have penetrated the ultrafiltration membrane, and no concentrated solution has flowed out.
In the cross-flow filtration method, a part of the concentrated liquid is discharged from the other end of the ultrafiltration membrane during the filtration process.