Ion exchanger

Ion Exchanger Ion Exchanger Ion exchangers are categorized into: sodium ion exchangers, cation-anion beds, mixed beds, and other types. Sodium ion exchangers are used to remove calcium and magnesium ions from water to produce softened water. Acrylic ion exchange devices are corrosion-resistant, colorless, and transparent, making them suitable for small-scale pure water preparation in the food, pharmaceutical, sugar, and electronics industries. 1. Terminology Explanation Ion Exchanger A softener refers to a sodium ion exchanger. Ion exchangers are classified into: sodium ion exchangers, cation-anion beds, mixed beds, and other types. The outer shell of an ion exchange column (exchanger) is typically made of materials such as rigid polyvinyl chloride (PVC), rigid PVC composite fiberglass (PVC-FRP), acrylic (PMMA), acrylic composite transparent fiberglass (PMMA-FRP), rubber-lined steel (JR), or rubber-lined stainless steel. Applications Ion exchangers are primarily used for the preparation of pure and high-purity water. They are widely applied in various industrial fields such as pharmaceuticals, chemicals, electronics, coating, beverages, and medium-to-high-pressure boiler feedwater. They are used in pre-treatment processes for boilers, thermal power plants, chemical, light industry, textile, pharmaceutical, biological, electronics, atomic energy, and pure water treatment. They are also employed in scenarios requiring hard water softening and deionized water preparation in industrial production. Additionally, they are used for decolorization and purification of food and pharmaceuticals, recovery of precious metals and chemical raw materials, and treatment of electroplating wastewater. 2. Classification Dynamic softeners refer to sodium ion exchangers, mainly used in pre-treatment processes for boilers, thermal power plants, chemical, light industry, textile, pharmaceutical, biological, electronics, atomic energy, and pure water treatment. Mixed Bed A mixed bed is filled with cation and anion exchange resins in a specific mixed ratio within the same ion exchanger. Since H⁺ and OH⁻ ions generated after mixed ion exchange immediately form water molecules with low ionization, the exchange reaction proceeds thoroughly. Mixed beds are generally placed after the primary dual-bed system for further purification of water quality. They can also be used independently when water quality requirements are not high. Cation-Anion Bed Cation-anion exchange beds, also known as dual beds, consist of cation and anion exchangers connected in series to achieve water desalination. Mixed Bed A mixed bed is filled with cation and anion exchange resins in a specific mixed ratio within the same ion exchanger. Since H⁺ and OH⁻ ions generated after mixed ion exchange immediately form water molecules with low ionization, the exchange reaction proceeds thoroughly. Mixed beds are generally placed after the primary dual-bed system for further purification of water quality. They can also be used independently when water quality requirements are not high. Sodium Ion Exchanger A sodium ion exchanger, or softener, is used to remove calcium and magnesium ions from water to produce softened water. Calcium and magnesium ions, which contribute to water hardness, exchange with the ion exchange resin in the softener. Sodium ions replace calcium and magnesium ions in the water, preventing the formation of carbonate and sulfate scales, thereby producing softened water. Acrylic Acrylic ion exchange devices are corrosion-resistant, colorless, and transparent, making them suitable for small-scale pure water preparation in the food, pharmaceutical, sugar, and electronics industries. Rubber-lined carbon steel ion exchange devices offer advantages such as high water production capacity, strength, and low cost, making them suitable for large-scale boiler water softening and pure water preparation. Purified water is ordinary water treated by electrodialysis, which significantly reduces the original mineral content while disinfecting and sterilizing, resulting in "purified water." http://img.album.toocle.com/140-140-1/2015/08/31/toocle/album/9e/55e3c5e2b559e.jpg Physical Image 3. Typical Process Flow Typical Electrodialysis Process Flow: 1. Brackish Water Desalination and Groundwater Defluoridation Raw water → 101 filter → Precision filter → Electrodialysis device → Hollow fiber ultrafilter → UV sterilizer → Finished water 2. Production of Drinking Purified Water and Space Water Raw water → Mechanical filter → Activated carbon filter → Precision filter → Electrodialysis device → Cation exchanger → Anion exchanger → Mixed ion exchanger → Hollow fiber ultrafilter → UV sterilizer → Ozone sterilizer → Finished water 3. Pharmaceutical Industry: Preparation of Injections and Large Infusion Water Raw water → Activated carbon filter → Precision filter → Electrodialysis device → Cation exchanger → Anion exchanger → Mixed ion exchanger → Multi-effect distilled water machine → Finished water 4. Water for Fertilizer and Machinery Industries Raw water → Mechanical filter → Precision filter → Electrodialysis device → Cation exchanger → Degassing tower → Anion exchanger → Finished water For disinfection of purified water, "ozone" is recommended, as it leaves no residues after disinfection. 4. Working Principle The working principle is ion exchange. During operation: Cation resin (H-R) + (M⁺) → (M-R) + (H⁺) Anion resin (OH-R) + (X⁻) → (X-R) + (OH⁻) Where M⁺ represents metal ions and X⁻ represents anions. The regeneration process is the reverse. Failure Control of Ion Exchangers The simplest process for ion exchange desalination water treatment is a primary dual-bed desalination system composed of a cation bed and an anion bed. Some primary dual-bed desalination systems adopt a unit system, where each set includes one cation bed, (decarbonator), and one anion bed. During ion exchange desalination operation, whether the cation bed or anion bed fails first, both are regenerated simultaneously. Other primary dual-bed desalination systems adopt a header system, where cation beds or anion beds operate in parallel. The exchanger that fails is regenerated individually. 1. Detection and Control Principle The adsorption order of strong acid cation resin for various cations in water is: Fe³⁺ > Al³⁺ > Ca²⁺ > Mg²⁺ > Na⁺ > H⁺. From this, it can be seen that Na⁺ has the weakest adsorption capacity. Therefore, during ion exchange, the adsorption layers of various ions in the resin bed gradually move downward, and H⁺ is eventually replaced by other cations. When the protective layer is penetrated, the first to leak is the lowest layer of Na⁺. Thus, the failure of a cation exchanger is monitored based on sodium leakage. The reaction equation is (A represents metal cations, R represents resin groups): Aⁿ⁺ + nRH → RnA + nH⁺ HCO₃⁻ + H⁺ → H₂O + CO₂↑ The adsorption order of strong base anion resin for various anions in water is: SO₄²⁻ > NO₃⁻ > Cl⁻ > OH⁻ > HCO₃⁻ > HSiO₃⁻. From this, it can be seen that HSiO₃⁻ has the weakest adsorption capacity. Therefore, during ion exchange, the adsorption layers of various ions in the resin bed gradually move downward, and OH⁻ is replaced by other anions. When the protective layer is penetrated, the first to leak is the lowest layer of HSiO₃⁻. Thus, the failure of an anion exchanger is monitored based on silica leakage. The reaction equation is (B represents acid radical anions, R represents resin groups): Bᵐ⁻ + mROH → RmB + mOH⁻ 2. Control Points and Methods Since the header system includes the unit system and offers advantages such as full utilization of resin, improved water production capacity of exchangers, and reduced acid and alkali consumption, our study focuses on ion exchange desalination water treatment systems based on this structure. Taking the pure water station of the protein separation workshop at Chengdu Biological Products Research Institute as an example, the system is a header water treatment system with the structure: sand filtration - activated carbon filtration - coarse filtration - cation bed - first anion bed - second anion bed - mixed bed - precision filtration - pure water tank. The system's water production capacity is 5 t/h. In the study of failure control, we propose the concept of unit failure control, which fully utilizes the advantages of the header water treatment system for failure control. (1) The removal rate of various organic solutes by RO is higher than that by NF membranes. (2) The removal rates of different organic solutes vary, with some even differing significantly (for example, the absorbance removal rates of acetic acid by RO and NF membranes are 95.34% and 81.45%, respectively, while those of aniline are 61.50% and 46.82%, respectively). 3. Effluent Water Quality After primary dual-bed desalination, the conductivity (25°C) of the raw water is below 10 μS/cm, and the silicon content is below 100 μg/L. 5. Common Faults and Solutions Ion exchangers can be damaged and deteriorate under the action of environmental media, which is commonly referred to as corrosion. The forms of ion exchanger corrosion can be divided into two categories: overall (uniform) corrosion and localized corrosion. The former occurs uniformly over the entire surface of the equipment, while the latter occurs only locally, such as pitting, crevice corrosion, intergranular corrosion, stress corrosion cracking, corrosion fatigue, hydrogen corrosion cracking, erosion corrosion, delamination corrosion, etc. This is particularly prominent in the petroleum, chemical, and marine atmospheric environments. To address the issue of ion exchanger corrosion, frequent replacement of equipment components is a common method adopted by enterprises. However, due to the influence of materials and processing techniques, the value of these components is generally high.