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Question Bank for Chemical Water Engineering I. Fill-in-the-blanks 1. The impurities in natural water can generally be classified into three categories based on their particle size: suspended solids, colloidal substances, and dissolved substances. 2. Natural water can be classified into four categories based on its salt content: low-salt-content water, medium-salt-content water, high-salt-content water, and very high-salt-content water. 3. In the coagulation process in water, the commonly used coagulants are iron salts and aluminum salts. 4. Total hardness refers to the sum of calcium and magnesium ions per unit volume. 5. Dissolved solids are the amount of solids remaining after filtering a water sample and then evaporating the filtrate. It includes the total amount of various dissolved substances in water, excluding dissolved gases. 6. The total salt content of water refers to the sum of the concentrations of cations and anions in water, with the unit being mg/L. 7. Hardness can be classified into carbonate hardness and non-carbonate hardness based on anions. Carbonate hardness is also known as temporary hardness, while non-carbonate hardness is known as permanent hardness. 8. The total alkalinity of water refers to the total amount of OH-, CO32-, HCO3-, and other weak acid salts per unit volume of water. 9. The commonly used indicators for titrating alkalinity are methyl orange and phenolphthalein; alkalinity is classified into phenolphthalein alkalinity and methyl orange alkalinity based on the results of titration using these different indicators. 10. The pH value is the negative logarithm of the hydrogen ion concentration in water, and it is an indicator of the acidity or alkalinity of water. 11. Conductivity refers to the ability of ions in water to conduct electricity, and its unit is ms/cm. 12. Boiler make-up water refers to the water that, after being purified through various methods, is used to compensate for water loss. 13. The filtration process has two functions: one is mechanical screening, and the other is adsorption and coagulation. 14. The entire process of coagulation and flocculation is called coagulation. 15. The factors affecting coagulation efficiency include pH value, coagulant dosage, raw water alkalinity, raw water turbidity and dissolved solid content, contact medium, and water temperature. 16. The extent of a redox reaction can be expressed by the value of its equilibrium constant. 17. In electrolysis, the electrode where an oxidation reaction occurs is called the anode, while the electrode where a reduction reaction occurs is called the cathode. 18. A standard solution is a reagent solution whose exact concentration is known. 19. The color change range of the phenolphthalein indicator is pH=8.2~10.0 ； The color change range of methyl orange is pH=3.1~4.4. 20. Under standard conditions, the volume of 1 mole of any gas is approximately 22.4 L; this volume is known as the molar volume of the gas. 21. The pretreatment of water generally includes three steps: coagulation, clarification, and filtration. 22. The alkalinity of water refers to the amount of substances in water that can accept hydrogen ions. 23. The sodium sulfate solution is neutral ； Sodium carbonate solution is alkaline ； Ammonium chloride solution is acidic. 24. Sulfur trioxide reacts with water to form sulfuric acid, releasing heat in the process. 25. Measuring water hardness mainly involves determining the levels of calcium and magnesium ions in the water. 26. Hydrocarbons are compounds composed of two elements: carbon and hydrogen. 27. Common instruments used in titrimetric analysis include burettes, pipettes, volumetric flasks, and conical flasks. 28. The atomic nucleus is composed of two types of particles: protons and neutrons. 29. Any compound that can conduct electricity in an aqueous solution or in a molten state is an electrolyte. 30. The characteristic of a chemical change is the formation of new substances. The properties that a substance exhibits during chemical changes are called chemical properties. 31. Alkaline burettes are suitable for containing alkaline solutions, but not for containing oxidizing solutions. 32. In dilute solutions, the degree of ionization of weak electrolytes is related to their concentration, but it is also affected by temperature. 33. The main types of chemical reactions are neutralization reactions, precipitation reactions, redox reactions, and complexation reactions. 34. During the titration process, the point at which the indicator undergoes its color change is called the end point of titration. 35. In the water supply system, the parts most prone to corrosion are the water supply pipes and the economizer. 36. Titration error refers to the difference between the titration endpoint and the theoretical endpoint. 37. Water deoxidation is usually achieved through thermal deoxidation and chemical deoxidation. 38. Metal corrosion can be divided into two main categories based on its scope: general corrosion and local corrosion. 39. If the water used in boiler systems of thermal power plants is not purified or is improperly treated, it can cause scaling in thermal equipment, corrosion of such equipment and systems, as well as salt accumulation in the flow paths of superheaters and turbines. 40. In natural water, the main compounds fall into four categories: carbonates, silicates, iron compounds, and nitrogen compounds. 41. According to water treatment technology, natural water can be divided into two main categories: alkaline water and non-alkaline water. 42. Water softening is the process of removing calcium and magnesium ions from water ； Chemical desalination of water involves removing all dissolved salts from the water. 43. The operation process of a cation exchanger operating in the forward flow mode can generally be divided into five steps: exchange, backwashing, regeneration, displacement, and forward washing. These five steps constitute one operating cycle. 44. The purpose of backwashing an ion exchanger is to wash away the regenerant solution and regeneration products that are filled in the pores of the exchange resin particles. 45. The purpose of backwashing an ion exchanger is to loosen the exchange resin layer ； Remove the suspended solids from the upper layer of the exchange medium ； Remove broken resin and bubbles in the resin layer. 46. During the operation of a strongly acidic H-type exchanger, it is essential to monitor changes in water quality parameters such as sodium ion concentration and acidity (or pH value). 47. During the operation of the mixed-bed ion exchanger, key water quality parameters such as conductivity, silicon content, and sodium ion concentration are monitored. 48. The main measures to prevent metal corrosion in the water supply system are water deoxidation and adjusting the pH value of the water supply. 49. The wastewater discharge volume refers to the amount of water discharged by the boiler per hour. The emission rate refers to the percentage of waste emissions relative to the boiler’s rated evaporation capacity. 50. The main difference between metal corrosion and metal erosion lies in their causes and the condition of the metal surface. 51. Colloidal destabilization is the process by which a colloid loses its stability due to a decrease in potential or other reasons. 52. The flocculation process is the process in which small flocculants collide with each other under hydrodynamic forces to form larger flocculants. 53. Ion exchange resins consist of three basic components: monomers, crosslinking agents, and exchange groups. 54. In the chemical desalination of water, the most commonly used ion exchange resins are strong acid cation exchange resins, weak acid cation exchange resins, strong base anion exchange resins, and weak base anion exchange resins – a total of four types. 55. After long-term use, ion exchange resins darken in color and their working exchange capacity decreases, due to contamination by iron, aluminum and their oxides, as well as organic substances. It can generally be treated with HCl solution and NaOH solution. 56. The wet true density of ion exchange resin refers to the ratio of the mass of the wet resin to its true volume, and is expressed in g/mL. 57. The wet specific gravity of ion exchange resin refers to the ratio of the mass of the wet resin to its packed volume. 58. The chemical properties of ion exchange resins mainly include antioxidant capacity, acidity and alkalinity, selectivity, exchange rate, and exchange capacity. 59. The process properties of ion exchange resins mainly include working exchange capacity, backwash expansion ratio, water consumption for cleaning, water flow resistance in the resin layer, and stratification performance. 60. During the operation of a floating-bed ion exchanger, the exchange resin remains in a suspended state, but it stays orderly; the exchange reaction still takes place with the resin layer remaining compacted. 61. The principles for selecting mixed-bed ion exchange resins generally include ensuring a certain density difference between anionic and cationic resins, possessing high mechanical strength, and using large-pore resins. 62. The corrosion resistance of metal materials itself is mainly related to the metal’s chemical composition, microstructure, internal stresses, and surface condition. 63. Among the thermal equipment and systems in thermal power plants, the ones most prone to corrosion are water treatment equipment and systems, as well as feedwater equipment and systems. Condensate equipment and systems are the most susceptible to carbon dioxide corrosion. 64. Fixed-ion exchangers are classified according to the flow direction of water and regeneration fluid into co-current regeneration type, counter-current regeneration type (including counter-current regeneration ion exchangers and floating-bed ion exchangers), and split-flow regeneration type. 65. Fixed ion exchangers are classified according to their function into cation exchangers, anion exchangers, and mixed ion exchangers. 66. Metal corrosion is divided into two main categories based on the mechanism of the corrosion process: electrochemical corrosion and chemical corrosion. 67. A system composed of an H-type cation exchanger and an OH-type anion exchanger is called a mixed-bed. 68. Factors affecting ultrafiltration include operating pressure, flow rate, temperature, operating time, feed concentration, feed pretreatment, membrane lifespan, and membrane cleaning. 69. Ultrafiltration is suitable for macromolecules and colloids with a molecular weight greater than 500 and a diameter of 0.005–10 mm, while reverse osmosis is generally used to separate substances such as sugars and salts with a molecular weight below 500 and a diameter of 0.0004–0.06 mm, which have a high osmotic pressure. 70. Ion exchange softening is a water treatment method that utilizes the ion exchange process to remove or reduce hardness from water. 71. Ion exchange desalination refers to the process of using H-type cation resins to exchange various cations in water for H+, and using OH-type anion resins to exchange various anions in water for OH–. 72. There are three methods for removing dissolved salts from water: ion exchange, membrane separation, and distillation. 73. The deposits in boilers mainly include scale, salt scale, sludge, and corrosion products. 74. Indicators for characterizing dissolved salts in water include salinity, dissolved solids, and conductivity. 75. The indicators for characterizing scaling substances in water are carbonate hardness and non-carbonate hardness. 76. The indicator for alkaline substances in water is alkalinity. 77. Indicators for characterizing organic matter in water are chemical oxygen demand (COD) and biological oxygen demand (BOD). 78. The hazards caused by poor quality of steam and water in thermal power plants include scaling of thermal equipment, corrosion of thermal equipment, and salt accumulation in superheaters and turbines. 79. The purpose of pre-treating boiler make-up water is to remove suspended solids, colloidal substances, and some organic materials from the water. 80. In thermal power plants, limestone is used primarily to reduce the alkalinity in water, that is, to decrease the level of bicarbonates. 81. Common boiler scales include carbonate scale, sulfate scale, phosphate scale, silicate scale, mixed scale, iron oxide scale, ferric phosphate scale, and copper scale. 82. Common types of corrosion in boilers include oxygen corrosion, acid-base corrosion, corrosion fatigue, stress corrosion, oxidation \"peeling\" at high temperatures, pitting, and corrosion under deposits. 83. The most commonly used aluminum salt coagulants are aluminum sulfate and polyaluminum. 84. The most widely used iron salt coagulants are ferrous sulfate and polyferric sulfate. 85. The chemical stability of a membrane refers primarily to its antioxidant and hydrolysis resistance. 86. Compared with acetate fiber membranes, composite membranes have advantages such as better chemical stability, better biological stability, better transport performance, a desalination rate that does not change over time, lower power consumption, a longer lifespan, and a water production rate that remains constant over time. 87. The key performance indicators for membrane separation include desalination rate, recovery rate, water flux, and water flux decay coefficient. 88. The water flux and desalination rate of membranes are affected by factors such as pressure, temperature, recovery rate, feedwater salinity, and feedwater pH value. 89. Water flux refers to the amount of water produced per unit area of membrane per unit time. 90. The structural types of reverse osmosis membranes include plate-type, tubular-type, hollow fiber-type, and spiral-wound type. II. True or False Questions 1. Natural water always contains impurities. ( √ )2. The water used in the boilers of thermal power plants must be properly purified. ( √ )3. In the water and steam cycle systems of thermal power plants, it is inevitable that some amount of water and steam is lost. ( √ )4. A colloid is a collection of many molecules or ions, and the surface of colloidal particles is charged. ( √ )5. The total amount of impurities contained in water is referred to as the salt content of water. ( × )6. The total amount of scaling substances in water, that is, the total concentration of metal salts with high valence in water, is referred to as the hardness of water. ( × )7. The temporary hardness of water is also known as the non-carbonate hardness of water. ( × ) 8. In the production process of thermal power plants, water serves as a medium for transferring energy and cooling. ( √ )9. The calcium and magnesium ions in natural water mainly originate from the dissolution of calcium and magnesium carbonates by CO2 in water. ( √ )10. When the pH of water is less than 4, the carbonic compounds present in the water are only free CO2, with no other carbonates present. ( √ )11. The lower the degree of cross-linking of the ion exchange resin, the higher its water content and the greater its swelling capacity. ( √ )12. After being treated with a Na-type ion exchanger, the calcium and magnesium salts in water are essentially removed, so the salt content in the water decreases. ( × )13. The working exchange capacity of an ion exchanger refers to its exchange capacity during operation. ( × )14. To ensure that the downward washing in a floating bed starts without any layer disturbance, the following three conditions must be met: high flow rate, uniform water distribution, and a certain height of the exchanger layer. ( √ )15. The main purpose of adding ammonia to the feedwater is to raise its pH value and prevent acidic corrosion caused by free carbon dioxide. ( √ )16. The presence of impurities in steam is known as steam contamination. ( × )17. The main function of lime treatment is to remove non-carbonate substances from water. ( × )18. A higher water content in the resin indicates a greater porosity, as well as a higher degree of cross-linking. ( × )19. The contamination of saturated steam is mainly caused by two factors: water carried in the steam and impurities dissolved in the steam. ( √ )20. Periodic blowdown can be used as a measure to rapidly reduce the salt content in the boiler water. ( √ )21. The distinction between alkaline water and non-alkaline water is primarily determined by the level of alkalinity in the water. ( × )22. During the regeneration of an ion exchanger, the higher the concentration of the regeneration solution, the better the regeneration effect. ( × )23. At a constant level of ion exchanger regeneration, the higher the resin layer inside the exchanger, the greater the working exchange capacity of the resin. ( √ )24. Regeneration is done to restore the exchange capacity of the resin. (× )25. Chemical oxygen demand can represent the total amount of organic matter in water. ( × )26. The process of removing all dissolved salts from water is called chemical desalination of water. ( × )27.201×7 denotes a strongly acidic styrene-based cation exchange resin. ( × )28. The basic principle of thermal deaeration is to heat water to its boiling point, thereby causing all dissolved gases in the water to be released. ( × )29. The ability of steam to dissolve certain substances is related to its vapor pressure; the higher the pressure, the greater the dissolving capacity. ( √ )30. Strongly acidic H-type cation exchange resins expand in volume after failing. ( × )31. Colloidal particles consist of three parts: the colloidal nucleus, the adsorption layer, and the diffusion layer. ( √ )32. The main parameters of filtration operation are filtration velocity, filtration cycle, and the dirt-holding capacity of the filter bed. ( √ )33. The wet true density is used to calculate the mass of wet resin required when loading resin into an ion exchanger. ( × )34. Methyl orange alkalinity is also known as total alkalinity. ( √ )35. The main wastewater types from power plants include ash removal wastewater, wastewater generated by treatment equipment, wastewater from chemical cleaning, and oily wastewater. ( √ )36. Ammonia treatment of feedwater is primarily intended to prevent acidic corrosion of the feedwater system caused by free CO2 in the feedwater. ( √ )37. When using iron salts as coagulants, water temperature has a significant effect on the coagulation efficiency ； When using aluminum salts as coagulants, water temperature has little effect on the coagulation efficiency. ( × )38. During resin regeneration, in order to ensure thorough contact between the regenerating agent and the resin and achieve complete regeneration, it is better for the flow rate of the regenerating solution to be as slow as possible. ( × )39. Ion exchange resins can be regenerated and reused after becoming ineffective, because the resin exhibits reversibility in ion exchange reactions. ( √ )40. Floating beds have a wide range of water quality compatibility and are particularly suitable for systems with frequent start-ups and shutdowns, as well as intermittent water supply. ( × )41. Countercurrent regeneration is superior to co-current regeneration because it is less prone to layer disruption. ( × )42. The purpose of mixing the anion and cation resins in a mixed-bed reactor is to recombine the separated resins evenly. ( × )43. As long as a sufficient amount of regenerant is used, the higher the concentration of the regenerant solution, the higher the degree of resin regeneration. ( × )44. When the cation exchange resin fails, sodium ions are the first to leak out, which is determined by the selectivity of the ion exchange resin. ( √ )45. The function of minor backwashing in counter-current regeneration equipment is to loosen the entire resin layer and remove contaminants, impurities, and broken resin particles from it. ( √ )46. When countercurrent regeneration is used, if it’s not possible to ensure that the resin layers remain undisturbed during the regeneration process, then the advantages of countercurrent regeneration are lost. ( √ )47. The purpose of installing a carbon remover in a double-bed desalination system is to remove free CO2 from the water, thereby reducing the load on the OH exchanger. ( √ )48. Under a certain pressure, the solubility of both oxygen and carbon dioxide in water decreases as the water temperature rises. ( √ )49. Chemical deoxygenation is the main method for removing oxygen from feedwater, while thermal deoxygenation is an auxiliary method for this purpose. ( × ) III. Multiple-choice questions 1. After coagulation treatment of natural water, the hardness in the water ③ . ① Slightly decreased ② Slightly increased ③ Basically unchanged. 2. After treatment with a Na-type ion exchanger, the salt content in natural water ② . ① Slightly decreased ② Slightly increased ③ Basically unchanged. 3. For H-type cation exchangers, hydrochloric acid is generally used for regeneration, and the properties of hydrochloric acid are ③. ① It is acidic, has no oxidizing properties, and has no reducing properties. ② It is acidic, has oxidizing properties, and has reducing properties. ③ It is acidic, has no oxidizing properties, but has reducing properties. 4. The higher the degree of cross-linking in ion exchange resins, the faster the rate of ion exchange reaction ①. ① The slower ② The faster ③ No effect 5. After regeneration of strong base OH-type anion exchange resin, ①. ① Volume increases ② Volume decreases ③ Volume remains unchanged 6. The basic principle of thermal deaeration is ③. ① Heat the water to its boiling point. ② Heat the water to its boiling point at the corresponding pressure. ③ Heat the water to above 100°C. 7. When regenerating an ion exchanger, the regeneration solution’s ③. ① The higher the concentration, the greater the degree of regeneration. ② The lower the concentration, the greater the degree of regeneration. ③ Within a certain range of concentrations, the degree of regeneration is maximized. 8. Water from which calcium and magnesium salts have been removed is called ②. ① Pure water ② Softened water ③ Demineralized water. 9. After prolonged use, the volume of strong-acid H-type cation exchange resin ②. ① Volume increases ② Volume decreases ③ Volume remains unchanged. 10. When ion exchange resins are contaminated by iron, aluminum, and their oxides, ① . ① Color darkens ② Color lightens ③ Color remains unchanged. 11. Natural water that has not undergone any treatment is called ①. ① Raw water ② Make-up water ③ Tap water. 12. When natural water is classified by its hardness, those with a hardness of 1–3 mmol/L belong to ①. ① Soft water ② Moderately hard water ③ Hard water. 13. After the raw water is treated by an Na-type ion exchanger, the alkalinity of the water becomes ③. ① Increase ② Decrease ③ Unchanged. 14. In a chemical desalination system, the arrangement of the exchangers should theoretically be ①. ① The cation exchanger is before the anion exchanger. ② The anion exchanger is before the cation exchanger. ③ In general, it doesn’t matter which one is ahead. 15. The equilibrium constant of the ion exchange reaction increases as the amount of resin that has been exchanged increases. ③ ① Decrease ② Increase ③ Unchanged. 16. During the operation of a floating-bed ion exchanger, in order to prevent the layer from becoming disordered, the exchanger resin layer must be in a compacted state; at this time, the water flow rate must not be lower than ②. ① 5m/h ② 7m/h ③ 10m/h. 17. The pH value of boiler water should not be lower than ②. ① 7 ② 9 ③ 1118. When it is ion exchanger ②, regeneration should be carried out. ① The resin is completely ineffective. ② The quality of the water discharged is not up to standard. ③ Operating resistance increases. 19. When it is difficult to separate the still-functional cationic resin from the ineffective anionic resin in a mixed-bed reactor, method ① should be employed. ① After introducing sodium hydroxide, perform backwashing for layer separation. ② Increase the amount of water used for backwashing. ③ Introduce compressed air. 20. If the resin is contaminated by organic substances, method ③ can be used for treatment. ① Compressed air scrubbing ② Cleaning with saturated salt water ③ Cleaning with hot alkaline salt water. 21. If ion exchange resin loses water and dries out, it should be ③ before use. ① Soak in water ② Soak in 8% saltwater ③ Soak in saturated saltwater. 22. In the desalination system, use the effluent level ① as the control endpoint for operating the cation exchanger. ① Na+ ② HSiO3- ③ HCO3-23. In a desalination system, the effluent stream ② is used as the operating control endpoint for the anion exchanger: ① Na+ ② HSiO3- ③ HCO3-. IV. Essay questions 1. What are solution, solvent, and solute? Answer: A stable and homogeneous system composed of two or more substances is called a solution. A substance that can dissolve other substances is called a solvent. A substance dissolved in a solvent is called a solute. 2. What is a double bed? What is primary double-bed desalination? Answer: A system composed of H-type anion exchange resins and OH-type cation exchange resins is called a mixed-bed. When raw water passes through a strong acid H-ion exchanger and a strong base OH-ion exchanger only once in sequence for desalination, this is referred to as primary double-bed desalination. 3. What is water hardness? Into how many categories can hardness be divided? What is its common unit? Answer: The total concentration of calcium and magnesium ions in water is called hardness. The total amount of calcium and magnesium ions bound to bicarbonates and carbonates per unit volume of water is referred to as carbonate hardness. The total amount of calcium and magnesium ions bound to chlorides, sulfates, and nitrates per unit volume of water is referred to as non-carbonate hardness. The common unit for hardness is mmol/L or mmol/L. 4. Are the salt content of water and the dissolved solids in water the same? What is the relationship between them? Answer: The salt content of water refers to the sum of the concentrations of various cations and anions in the water. Suspended solids are the residues left after water is filtered, evaporated, and then dried at a temperature of 105–110°C. Salt content is closely related to dissolved solids. The water has a high salt content, as well as a high level of dissolved solids. But when expressing the salt content in terms of dissolved solids, a correction must be applied; the correction value is usually: salt content ≈ dissolved solids + 5. What is an ion exchanger? Answer: An ion exchanger is a reactive polymeric electrolyte. It contains active groups within it, and these active groups can release exchangeable ions, which are capable of exchanging places with ions of the same charge in the solution. Therefore, any substance that contains exchangeable ions and has the ability to undergo ion exchange is called an ion exchanger. 6. Why is treatment necessary before using new resin? Answer: Ion exchange resins for industrial products often contain some excess solvents, low-molecular-weight polymers resulting from incomplete reactions, and certain heavy metal ions. If these substances are not removed, they will contaminate the quality of the effluent water during the use of the ion exchange resin. Therefore, new ion exchange resins must be treated before use. Doing so not only improves its stability but also activates the resin, thereby increasing its working exchange capacity. 7. What is the purpose of backwashing a exchanger? What precautions should be taken during backwashing? Answer: The purpose of backwashing a exchanger is: a. To stir up the compacted resin layer; b. To remove suspended impurities attached to the surface of the resin through the action of water flow and the friction caused by the resin particles. c. Remove broken resin and bubbles accumulated in the resin layer. When performing the backwashing operation, the following points should be noted: a. Whether the drainage is normal; b. Whether the resin rises slowly and gradually, without any clumps of resin floating to the surface. c. If the resin rises in lumps, the water inlet valve should be closed immediately and the drain valve opened; once the resin is stirred and loosened, backwashing can be resumed. d. The backwashing time is determined by the cleanliness of the water; it should not be too long, as this can lead to severe degradation, resulting in poor regeneration efficiency and increased water consumption. 8. What are the main factors affecting the regeneration efficiency of ion exchangers? Answer: There are many factors that affect the regeneration efficiency. The main factors include: the type of resin, the regeneration method, the amount of regenerant used, the concentration of the regeneration solution, the flow rate of the regeneration solution, the temperature of the regeneration solution, the type and purity of the regenerant, as well as the quality of the water used to prepare the regeneration solution. 9. What are the main factors that affect the exchange efficiency of ion exchangers? Answer: The main factors affecting the efficiency of ion exchange are: the operating mode of the ion exchanger, the salt content in the incoming water, the flow rate of water, the height of the resin layer, the pH value of the water, the water temperature, the degree of regeneration, the contamination and aging of the resin, as well as the size and uniformity of the ion exchange resin particles. 10. What are the main reasons for the decrease in the working exchange capacity of an ion exchanger during operation? Answer: The reasons for the decreased operating capacity of ion exchangers during operation are as follows: a. When new resin is first put into use, its working exchange capacity is high; as operation time increases, this capacity gradually decreases, and after some time it tends to stabilize. b. The surface of the exchanger particles is contaminated by suspended solids, and even bonding may occur. c. The raw water contains ions such as Fe2-, Fe3+, and Mn2+, which poison the exchanger and cause it to darken in color. d. The dose of the regenerant is low, resulting in insufficient regeneration of the components. e. The operating flow rate is too high. f. The salt content and hardness in the raw water are too high during the dry season. g. The resin layer is too low or the resin is gradually decreasing. h. The regenerant is of poor quality and contains too many impurities. i. Blockage or damage to the water distribution device, drainage device, and regeneration fluid distribution device causes uneven flow. j. During the backwashing of the ion exchanger, if the backwashing intensity is insufficient, a large amount of suspended solids accumulate in the resin layer and stick to the resin, forming sludge balls or cakes that cause water to flow in an abnormal direction. 11. What are the reasons for the decreased exchange capacity of floating-bed ion exchangers? How to handle it? Answer: The reasons for the decreased exchange capacity of floating beds include a. During regeneration, the resin at the top of the exchanger is exposed to air, which affects the effectiveness of regeneration. b. When the water outlet device and the regenerant inlet device are shared, the nylon mesh covering the surface becomes partially blocked by broken resin, resulting in uneven distribution of the regenerant. 12. What are the properties of hydrazine? Answer: Hydrazine, also known as hydrazoic acid, has the chemical formula N2H4. Hydrazine is a colorless liquid at room temperature, and it reacts with water to form stable hydrated hydrazine (N2H4·H2O). Hydrazine is volatile, toxic, flammable, and soluble in water and ethanol. Hydrazine is a reducing agent with weak basic properties, and it decomposes when heated. 13. What is the purpose of adding N2H4 to the feed water? What conditions should be maintained? Answer: The functions of adding N2H4 to the feed water are a. to assist in deoxidation, and b. to act as a reducing agent for iron oxide and copper oxide, thereby preventing the formation of iron and copper scale inside the boiler. The reaction rate between hydrazine and dissolved oxygen in water is closely related to temperature, pH value, and the excess amount of hydrazine. To ensure that the reaction between hydrazine and dissolved oxygen in water proceeds rapidly and completely, the following conditions must be maintained: a. The water must be at a sufficient temperature, generally above 150°C. b. The water must be maintained at a certain pH level. The pH is between 9 and 11. c. An appropriate excess of hydrazine in the water must be ensured. 14. What are the consequences of adding too much phosphate when adjusting the water quality in furnace water? Answer: The amount of unwanted substances in the boiler water should not be too high. Excessive amounts not only lead to an increase in the dosage of chemicals used for treatment, thereby raising consumption of such chemicals, but also cause the following adverse effects: a. An increase in the salt content of the boiler water, which affects the quality of the steam. b. There is a possibility of the formation of Mg3(PO4)2, and the precipitate of Mg3(PO4)2 tends to adhere to the inside of the pot, making it difficult to remove. c. If the iron content in the boiler water is high, there is a possibility of the formation of iron phosphate scale. d. Temporary disappearance of Na3PO4 can occur easily. 15. What are the main aspects of chemical water treatment? Answer: a. Purify water quality. Prepare the amount of make-up water required for boilers and other processes. Including pretreatment methods such as coagulation, clarification, and filtration to remove suspended solids and colloids from natural water ； Softening treatment to remove calcium and magnesium ions from natural water, or desalination treatment to remove all ionizable salts from water, etc. b. Deoxygenation of boiler feed water, pH value adjustment, etc. c. Perform in-boiler chemical treatment and blowdown treatment, etc., on the boiler. d. Supervisory testing of the water and steam masses in the aforementioned process, etc. 16. What is the difference between chemical desalination of water and ion exchange softening of water? Answer: Depending on the process used, there are mainly the following differences: a. The ions to be removed from water vary; softening involves removing only the hardness ions in water (such as Ca2+, Mg2+ 등) and alkalinity (such as file:///C:/Users/lenovo/AppData/Local/Temp/ksohtml11696/wps1.jpg etc.). Chemical desalination involves removing all salt-forming ions from water. b. The ion exchange resins used in the treatment processes are different. Softening treatment uses only cation exchange resins, while chemical desalination employs both strongly acidic cation exchange resins and strongly basic anion exchange resins. c. Different regenerants are used. Water ion-exchange softening resins can be regenerated using salts such as NaCl after aging. In chemical desalination processes, once the exchange ions become ineffective, strong acids such as HCl and H2SO4 as well as strong bases like NaOH must be used for regeneration; salts cannot be used as regenerants. d. The exchange processes are different. Ion exchange softening can be carried out using a single bed or multiple beds. Chemical desalination, on the other hand, must employ a multi-bed treatment process. 17. How to determine if the cation bed has failed? Answer: H-type cation exchange resins have different exchange capacities for common cations in water. In terms of exchange capacity, the order is Ca2+ > Mg2+ > Na2+ > H+. This property of H-type cation resins can be used to determine when the cation exchange bed fails. As the raw water passes through the cation exchange resin, Ca2+ in the water is adsorbed first, followed by Mg2+, with Na+ being adsorbed last. In other words, as long as the poorly adsorbable Na+ can be adsorbed (i.e., the Na+ content in the effluent from the cation exchange resin is below a specified value), the cation exchange resin has not failed. The failure of cation exchange resins is first manifested by its inability to adsorb Na+. Therefore, as long as the Na+ concentration in the effluent from the cation exchange resin exceeds the specified value, it can be considered that the cation exchange resin has failed. 18. What are the characteristics of mixed-bed operation? Answer: Compared with mixed-bed reactors, stacked-bed reactors have the following advantages: a. High-quality effluent water. In a mixed bed composed of strongly acidic and strongly basic resins, the residual salt content in the effluent is below 1.0 mg/L, the conductivity is below 0.2 µS/cm, the residual SiO2 content is below 20 mg/L, and the pH value is close to neutral. b. The quality of the effluent water remains stable. When the mixed-bed starts producing water after being regenerated and cleaned, the conductivity of the output water drops very rapidly, as the residual regenerants and regenerated substances in the resin can be immediately exchanged by the mixed resin. When operating conditions change, a mixed bed generally has little effect on the quality of the effluent water. c. Intermittent operation has little impact on the quality of the effluent water. d. The endpoint is distinct. Before failure at the end of the mixed-bed operation, the conductivity of the effluent water increases rapidly, which is beneficial for monitoring. e. There are fewer mixed-bed units, and they are centrally arranged. f. Its disadvantages are low resin exchange efficiency, high resin loss, complex regeneration processes, and high consumption of regenerants. 19. What are the characteristics of floating beds? Answer: In addition to the characteristics of the convective regeneration process, floating bed systems also have their own unique features: a. Since most floating beds use a fully filled design (that is, the exchange medium fills the entire bed), and the water and sulfur flow from bottom to top in such systems, this reduces water flow resistance. Therefore, the floating bed can increase the equipment’s output, resulting in a higher cyclic water production volume, better effluent quality, and a low regeneration ratio. b. Due to the relatively thick resin layer, under conditions that meet the operational cycle requirements, an appropriate operating flow rate can be selected based on the salt content of the water fed into the system. c. Floating beds can achieve “compacted regeneration,” eliminating the problem of “disordered layers.” d. The floating bed has few regeneration steps, and its operation is simple and reliable. e. Save water used for backwashing. f. The resin cannot be backwashed within the bed, therefore high requirements are placed on the turbidity of the water fed into the bed. g. Special backwashing tanks and a backwashing system need to be added. h. The fine resin particles within the bed accumulate at the top of the resin layer, making it easy for them to be carried away by the water flow through the water outlet device. 20. What are the effects of an excessively high reverse osmosis recovery rate? Answer: The higher the system recovery rate, the less water is consumed. However, an excessively high recovery rate can lead to the following problems: a. A decrease in the desalination efficiency of the product water ； b. Precipitation of slightly soluble salts may occur ； c. The osmotic pressure of the concentrated water is too high, resulting in a decrease in the water production rate of the element.