Analysis of the Application Process of one-in-use and one-standby Softened Water equipment

　　Pretreatment system

　　Industrial water supply treatment involves multiple processes. Generally, electrodialysis, reverse osmosis, ion exchange and other treatment processes are the main ones. To ensure the safe and economical operation of these main processes, the raw water needs to be treated to the influent water quality indicators allowed by these water treatment devices. In engineering, we often refer to the water purification, pre-softening or water quality adjustment before entering the main process as water quality pretreatment, or simply pretreatment. The main targets of pretreatment are mechanical impurities, colloids, silica, microorganisms, organic matter and residual chlorine, etc., which have adverse effects on the subsequent treatment facilities. The quality of pretreatment directly affects the technical and economic effects and long-term operation of major treatment processes such as electrodialysis, reverse osmosis, and ion exchange. It is a very important part of industrial water supply treatment. In this plan, the term "influent" used in the following text refers to the influent that meets the water quality requirements of the subsequent water treatment device. At the same time, the changes in water quality and its components caused by pretreatment and the resulting impacts are also taken into account.

　　This scheme designs a pretreatment system composed of dosing devices, water supply pumps, activated carbon filters and other equipment. According to the relevant requirements of water supply and drainage design, the total water inflow required for this system is50.0m3/h. To address the contamination of suspended solids and colloids that make reverse osmosis membranes particularly sensitive and ensure the turbidity of the reverse osmosis feed water≤1.0NTU,Adopt oneΦ2600mmThe mechanical filter, with the flow rate controlled at8-10m/hLeft and right, the normal output of this equipment48.0m3/hIt can effectively remove most suspended solids, colloids and granular mechanical impurities in water, ensuringROThe pollution index of the system's influent(SDI)≤4. Under normal circumstances, when the pressure difference between the inlet and outlet reaches a certain value orSDIGreater than4when,It indicates that the filter material is contaminated. The operation of the equipment must be stopped and backwashing carried out. This equipment is designed to use air-water scrubbing for backwashing, with external compressed air as the air source. Backwashing can effectively remove sediment, suspended solids and other substances from the filter layer and prevent the filter material from caking, thus fully restoring its dirt-holding capacity. Adopt oneΦ2600mmThe flow rate of the activated carbon filter is controlled at8-10m/hLeft and right, the normal output of this equipment48.0m3/hIt can effectively adsorb organic matter and residues in tap waterCl2Reduce harmful substancesCODContent to prevent residual chlorine from oxidizing the composite film.

　　The function of the scale inhibitor dosing unit is to add a dedicated scale inhibitor of a certain rate before the pre-treated raw water enters reverse osmosis, in order to prevent scaling on the concentrated water side of reverse osmosis. The working process of reverse osmosis is that the raw water flows from one end to the other on one side of the membrane. Water molecules pass through the membrane surface and reach the other side from the raw water side, while inorganic salt ions are retained on the original side. As the flow of the raw water gradually increases, water molecules are constantly removed from the raw water, and the salt content remaining in the raw water gradually increases. That is, the raw water is gradually concentrated and eventually becomes concentrated water, which is discharged from the device. The concentration of various ions in concentrated water will increase several times after it is concentrated. In natural water sourcesCa2+,Mg2+,Ba2+,Sr2+,HCO3-,SO42-,SiO2The concentration products of ions that tend to form scale are generally less than their equilibrium constants, so no scale will occur. However, after concentration, the concentration products of various ions may far exceed the equilibrium constants, thus causing severe scaling. The criteria for judging water scaling are:

　　a)For carbonate scale, the Langley index is used(LSI)As the benchmark: whenLSIOWhen scaling;

　　b)For sulfate scale, it is determined by the saturation index. The ratio of the concentration product of cations and anions in water to the saturation equilibrium constant is the saturation index.

　　When the saturation index is less than1When not, scale will form; conversely, scale will form.

　　The dosage of the scale inhibitor used in this system design is approximately3-4mg/L. It can increase the saturation of insoluble salts in water and effectively prevent scaling on the concentrated water side of reverse osmosis. This part is composed of a dedicated dosing tank, imported electromagnetic diaphragm metering pumps and connecting pipelines. Among them, the dosing tank is importedPERaw materials, rotational molding in one step. It is smooth both inside and out, does not leak, does not grow moss or scale, and is easy to clean inside the bucket. It has good hygiene and corrosion resistance.

　　Reverse osmosis desalination system

　　The filtration accuracy is5μmThe main purpose of setting up the security filter here is to retain particles, colloids and suspended solids in the water before the membrane, so as to prevent large particles from entering the reverse osmosis membrane and affecting the membrane's performance. The housing of the security filter is made of stainless steel, and the internal installation is of high precision5μmThe filter element. Under normal working conditions, the filter element can be maintained3～6The service life is about one month(It varies depending on the quality of the raw water)When it exceeds the set pressure difference(Usually0.2MPa)It should be replaced when necessary. This system selectsΦ400mmOne security filter.

　　Reverse osmosis60A new membrane separation technology developed in modern times is a process that relies on reverse osmosis membranes to separate solvents from solutes in solutions under pressure. To understand the principle of desalination by reverse osmosis, one must first understand the concept of "osmosis". Penetration is one A physical phenomenon is that when two types of water containing different concentrations of salts are separated by a semi-permeable membrane, it will be found that the water on the side with less salt will pass through the membrane and seep into the water with higher salt content, while the salt does not permeate. In this way, the salt concentrations on both sides are gradually mixed to be equal. However, it takes a long time to complete this process, which is also called natural infiltration. However, if a pressure is applied to the water side with a high salt content, the result can also stop the above-mentioned osmosis. The pressure at this time is called osmotic pressure. If the pressure is increased further, water can seep in the opposite direction while the salt remains. Thus, the principle of reverse osmosis desalination is that in water with salt(Like raw water)By applying a pressure greater than the natural osmotic pressure, the osmosis proceeds in the opposite direction, pushing the water molecules in the raw water to the other side of the membrane and turning it into clean water, thereby achieving the purpose of removing salt from the water. This is the principle of reverse osmosis desalination.

　　Reverse osmosis membrane modules are currently the main desalination devices in the field of water treatment. The pore size of reverse osmosis membranes is very small, generally within0.2-1.0nm;The diameters of various ions in water are about a few nanometers, while those of viruses are tens of thousands or even tens of thousands of nanometers. Therefore, reverse osmosis membranes can effectively remove inorganic salts, viruses, pigments, pyrogens, ions, fertilizers, detergents, colloidal substances and other pollutants in water. Therefore, reverse osmosis systems utilize the characteristics of reverse osmosis membranes to remove the vast majority of soluble salts, colloids, organic matter and microorganisms from water.

　　The main reverse osmosis equipment in the reverse osmosis device is imported in its original form from Dow Chemical Company of the United StatesBW30-400-FRThis series of low-pressure anti-pollution aromatic polyamide composite membranes have been chemically and physically modified by Dow Chemical Company using patented technology to enhance their performance under high microbial fouling conditions. Not only in terms of water production, but also in terms of washability, they have achieved high efficiency. This component is composed of three layers of films. The surface layer is made of aromatic polyamide material, with a thickness of200It is supported by a layer of microporous polysulfone, which can withstand high pressure and has good resistance to mechanical tension and chemical erosion. This component has a large membrane area and a large water production capacityNaCl,CaCl2,MgCl2Has99.5%A stable desalination rate.