Question bank for theoretical exams of chemical plant operators

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Question Bank for the Theoretical Exam of Chemical Plant Operators I. Fill-in-the-blanks 1. The size of our company’s coke oven is (7.63) meters, making it the largest coke oven in Asia. 2. The main toxic and harmful gases in our company are (methanol), (CO), (benzene), (naphthalene), (H2S), (SO2), and (NH3). 3. The molecular formula of methanol is (CH3OH). 4. The full name of NHD is (polyethylene glycol dimethyl ether). 5. The factors that affect the rate of chemical reactions are (concentration), (temperature), and (catalyst). 6. The contents of winter prevention: (freezing prevention), (slip prevention), (fire prevention), (poisoning prevention). 7. The outlet valve should be in the (fully open) position before starting the positive displacement pump. 8. The purpose of using deoxygenated water in the system is to prevent pipe corrosion and scaling. 9. The main working components of a centrifugal pump are (impeller), (pump shaft), (suction chamber), (pump casing), (shaft seal box) and (seal ring). 10. There are generally four methods for noise control, namely (sound absorption), (sound insulation), (noise cancellation), and (personal protection). 11. The 3 conditions necessary for combustion: (fuel), (oxygen), and (ignition source). 12. Liquid level measurement methods include direct-reading, (hydrostatic), (buoyancy), and (electromagnetic) types. 13. The three ways of heat transfer are (heat conduction), (convection), and (radiation). 14. Ways to increase the heat transfer rate include (increasing the heat transfer area), (increasing the temperature difference for heat transfer), and (improving the heat transfer coefficient). 15. The main products manufactured by our company are (coke), (methanol), (sulfur), (tar), (liquid oxygen), and (liquid argon). 16. The molecular formula of sulfuric acid is (H2SO4). 17. Pressure measuring instruments include single-tube, (U-type pressure gauge), (pressure gauge), and (pressure transmitter). 18. The factors that affect chemical equilibrium are (concentration), (pressure), (temperature), and (catalyst). 19. The four key aspects of summer prevention include (rain protection), (flood control), (lightning protection), and (heat relief). 20. The outlet valve should be in the (fully closed) position before starting the centrifugal pump. 21. The purpose of using deoxygenated water in the system is to prevent pipe corrosion and scaling. 22. The main performance parameters of a centrifugal pump are (speed), (flow rate), (head), (power), and (efficiency). 23. The heat exchange methods in industry include (mixed), (regenerative), and (wall-type). 24. The common heat exchangers include (jacketed heat exchangers), coil-type heat exchangers, (shell-and-tube heat exchangers), (tube-type heat exchangers), (plate heat exchangers), spiral heat exchangers, plate-fin heat exchangers, finned heat exchangers, and air coolers. 25. The basic methods of extinguishing fires include (isolation method), (smothering method), (cooling method), and (chemical interruption method). 26. The connection methods for pipelines include (threaded connection), (welded connection), (flange connection), and socket connection. 27. The main components of a piston compressor include: the cylinder block, piston assembly, crankshaft, bearings, connecting rods, crossheads, packing, and gas valves. 28. Commonly used level gauges include glass tube level gauges, differential pressure type level gauges, float type level gauges, etc. 29. Replacement criteria for entering the equipment container: (CO ≤ 0.03 mg/l, NH3 ≤ 0.03 mg/l, H2S ≤ 0.01 mg/l, H2 ≤ 0.2% (V), O2: 18–21% (V)). 30. The basic methods of fire extinguishing include: (isolation method, smothering method, cooling method, chemical interruption method). 31. The basic modes of heat transfer are (conduction), (convection), and (radiation). 32. Pressure vessels are composed of main components such as a pressure-resistant shell (connectors, sealing elements, fittings, openings and their reinforcing structures, supports), etc. 33. The industrial analysis of coal includes four standard analyses: (moisture), (volatile matter), (fixed carbon), and (ash content). 34. The working processes of a reciprocating compressor include: suction process, compression process, discharge process, and expansion process. 35. The common safety accessories used in pressure vessels are: safety valves, rupture disks, pressure gauges, level gauges, and thermometers. 36. Reasons for insufficient flow rate in centrifugal pumps include: gas presence in the pump due to inadequate filling, blockages in the suction line or pipeline, air leaks in the suction line, clogged or damaged impellers, the pump being installed at too high an altitude, and incorrect rotation direction or speed. 37. The safe voltages for preventing electric shock to humans are generally specified as (36 volts), (24 volts), and (12 volts). 38. The selection of a pressure gauge is primarily based on its range; when the pressure being measured is relatively stable, the pointer should be located at the (1/3–2/3) of the gauge’s scale. 39. There are four safety colors in total: (red), (yellow), (blue), and (green). The meaning of yellow is (warning) and (caution). The three-stage filtration for lubrication of the 40 equipment consists of (oil tank), (oil pot), and (refueling point). 41 The types of lubricants include (liquid lubricants), (semi-solid lubricants), (solid lubricants), etc. 42 Common fire extinguishing equipment includes (portable chemical foam fire extinguishers), (portable carbon dioxide fire extinguishers), (1211 fire extinguishers), and portable dry powder fire extinguishers. 43 The standards for wastewater discharge in our factory are (ammonia nitrogen ≤ 60 mg/L), (oil ≤ 10 mg/L), and (COD ≤ 150 mg/L), among others. 44 The common colors for gas cartridges are white for ammonia, yellow for hydrogen sulfide, and gray for carbon monoxide. II. Term Explanations: 1. Solubility: The amount of a substance that can dissolve in a certain volume of solvent at a specific temperature and pressure when equilibrium is reached is called solubility. The solubility of a substance is the amount of solute present in a saturated solution at a certain temperature and pressure. 2. Catalyst: A substance that alters the reaction rate while its own composition and chemical properties remain unchanged before and after the reaction; it is also known as a catalyzer. 3. Production operation accident: In production, losses of raw materials, semi-finished products, or finished products occur due to violations of the process procedures, operational protocols, or mistakes in handling; this includes reductions in output or shutdowns, and such incidents are considered production operation accidents. 4. Classification of pressure vessels: Vessels with a working pressure of ≥0.1 MPa and ≤1.6 MPa are considered low-pressure vessels; those with a working pressure of ≥1.6 MPa and ≤10 MPa are medium-pressure vessels; those with a working pressure of ≥10 MPa and ≤100 MPa are high-pressure equipment; and those with a pressure of ≥100 MPa are ultra-high-pressure vessels. 5. Composition of the Distributed Control System (DCS): It consists of four main parts: (1) Process input/output interface unit. (2) Process control unit. (3) CRT operation station. (4) High-speed data path. 6 Fluids: Liquid and gaseous substances that have no fixed shape and can flow freely; such substances are generally referred to as fluids. 7 strict requirements for operators: strictly carry out shift handovers, strictly conduct routine inspections, strictly control process parameters, strictly follow operating procedures, strictly abide by labor discipline, and strictly comply with relevant safety regulations. 8. Applications of DCS distributed control systems: Multiple microprocessors are used for process control, while operations, display, and alarms are carried out in a highly centralized manner through communication buses, CRT monitors, keyboards, and printers. 9. Quality accidents refer to situations where products or semi-finished goods do not meet **or the quality standards set by the enterprise, where the quality of construction projects does not satisfy the design requirements, or where raw materials deteriorate due to improper storage or packaging. 10. Temperature: Temperature is a physical quantity that indicates the degree of hotness or coldness of an object. 11. Pipeline resistance: Fluids must overcome certain pipeline resistance during transportation; there are two common types of such resistance: pipeline resistance includes straight-line pipe resistance and local resistance. 12. Straight-line pipe resistance: The resistance that arises due to friction when fluid flows through a straight pipe of a certain diameter, also known as frictional resistance. 13. Local resistance: The resistance caused by the flow of fluid passing through local obstacles such as fittings, valves, and sudden reductions or increases in the cross-sectional area of the pipes. 14. Fluid transport machinery: To transfer fluid from a lower to a higher or farther location, or to increase its pressure, energy must be supplied. Machinery used to increase the energy of fluids is called fluid handling machinery: 15. Distillation: In general, distillation involves using the difference in boiling points of two substances to repeatedly partially condense the mixed vapor and partially evaporate the mixed liquid, thereby achieving separation. 16. Insulation: To reduce heat loss from equipment, pipes, and their accessories to the surrounding environment, insulation layers are applied to their surfaces. 17. Functions of lubricating oil: 1) Control friction and reduce wear. 2) Cool down to reduce the frictional internal energy of various moving components. 3) Sealed isolation. 4) Damped vibration. III. Multiple-choice Questions 1. The moving parts of compressors often require lubrication, and the purpose of this is (1.2) (1) Lubrication (2) Cooling (3) Saving energy (4) Heat conduction 2. The performance indicators of metal materials include: (1) (1) Elasticity (2) Density (3) Material type (4) Toughness 3. The fire extinguishing facilities in chemical plants include (1.2.4) (1) Water (2) Steam (3) Wrenches (4) Fire hydrants 4. Under the following (1) conditions, pressure-based operations without displacement are not allowed. (1) Unstable production, sealed containers; (2) Sealed containers, severe corrosion of equipment and pipelines; (3) Unstable production, severe corrosion of equipment and pipelines. 5. The lower explosion limit of carbon monoxide: (3) (1) 25% (V); (2) 21.3% (V); (3) 12.5% (V); (4) 13.5% (V). 6. Which of the following is not a property of ammonia? (3) (1) Colorless; (2) Has an irritating odor; (3) Not easily soluble in water; (4) Used as a refrigerant. 7. Which of the following belongs to safe voltage? (4) (1) 220 volts; (2) 380 volts; (3) 45 volts; (4) 24 volts. 8. The contents of the operator’s “three understandings” are (1, 2, 4). (1) Understand the production principles. (2) Understand the process flow. (3) Understand maintenance. (4) Understand the equipment structure. 9. The flash point of flammable liquids is (1). (1) ≤45℃ (2) >40℃ (3) ≤50℃ 10. The correct colors for common gas filter canisters are: (1) Ammonia – white, hydrogen sulfide – yellow, carbon monoxide – gray (2) Ammonia – yellow, hydrogen sulfide – white, carbon monoxide – gray (3) Ammonia – gray, hydrogen sulfide – white, carbon monoxide – black 11. Reasons for excessive current in centrifugal pumps include: (3) (1) Air leakage in the suction pipeline (2) Head exceeding the specified value (3) Friction between the impeller and the pump casing (4) Erosion caused by flow 12. Factors affecting conversion reactions include: (1) (1) Temperature (2) Concentration (3) Liquid level (4) Gas-to-liquid ratio 13. The difference between soft water and hard water lies in the concentration of calcium and magnesium ions in the water; water with a higher concentration is considered hard water, while that with a lower concentration is soft water. (1) (1) 0.5mmol/L (2) 0.5mol/L (3) 0.05mmol/L (4) 5mmol/L 14. Performance indicators of metal materials include: (1) (1) Elasticity (2) Density (3) Material type (4) Toughness 15. Insulation is necessary when the surface temperature of pipes and their accessories reaches (2): (1) 333K (60℃) (2) 323K (50℃) (3) 373K (100℃) 16. At what pressure should one leave a toxic area using an oxygen respirator? (1) (1) 3.0MPa (2) 3.5MPA (3) 4.0MPa (4) 4.5MPa 17. The lower explosion limit of carbon monoxide is (3): (1) 25.2 (2) 21.3 (3) 12.5 (4) 13.5 18. The standard oxygen content required before entering equipment or containers is: (1) (1) 18–21% (V) (2) 20–22% (V) (3) 18–20% (V) 19. The lower explosion limit of ammonia is (4): (1) 25.2% (V) (2) 25.7% (V) (3) 12.7% (V) (4) 15.7% (V) 20. Reasons for high bearing temperatures in centrifugal pumps include: (2) (1) Low pump speed (2) Lack of oil in the bearings or severe wear (3) Excessive tightness of the packing gland 21. The molecular formula of ammonia is (a): (1) NH3 (2) NH2 (3) N2H (4) N2H2 22. Which of the following is not a property of ammonia? (c) (1) Colorless (2) Has a pungent odor (3) Poorly soluble in water (4) Used as a refrigerant 23. Which of the following represents safe voltage? (4) (1) 220 volts (2) 380 volts (3) 45 volts (4) 24 volts 24. The lower explosion limit of carbon monoxide is (3): (1) 25.2% (V) (2) 21.3% (V) (3) 12.5% (V) (4) 13.5% (V) 25. Factors affecting conversion reactions include: (1) (1) Temperature (2) Concentration (3) Liquid level (4) Gas-to-liquid ratio 26. Performance indicators of metal materials include: (1) (1) Elasticity (2) Density (3) Material type (4) Toughness 27. Which of the following does not belong to the conditions required for welding? (4) (1) Proper cleaning and gas displacement (2) Isolation from the production system (3) Successful welding gas analysis (3) Lack of an approved welding permit 28. Our company’s standards for wastewater pH value are: (1) (1) 6–9 (2) 5–8 (3) 7–9 (3) 9–10 29. The acceptable oxygen content in deoxygenated water is: (2) (1) ≤0.020mg/l (2) ≤0.010mg/l (3) ≤0.0015mg/l 30. The “three understandings” in the “three understandings and four skills” concept refer to: (2) (1) Understanding the process flow diagram (2) Understanding the principles of production (3) Understanding equipment maintenance 31. The main properties of coke oven gas include (1, 2, 3): (1) Colorless, odorous, and toxic. (2) It contains large amounts of hydrogen and methane, has a high calorific value, burns rapidly, and produces a short flame during combustion. (3) Low ignition point, with a wide explosion limit range of 6–32%. 32. What do the codes AG, BD, PC, and IA on the flowchart represent respectively? (3) (1) Ammonia, emissions, computer, current alarm; (2) Gaseous ammonia, emissions, computer, analysis; (3) Gaseous ammonia, emissions, process coolant, instrument air. Section 4: Essay questions: 1. What are the factors that can cause a fire in oxygen delivery pipelines? Answer: (1) When the valve suddenly opens between the high-pressure and low-pressure sections, the low-pressure oxygen is compressed rapidly, causing a sharp rise in local temperature, which serves as a source of ignition. (2) Due to the acceleration of the moving particulate matter and its collisions with valve plates, elbows, or other objects protruding into the airflow, as well as friction between the particles and the surfaces and their mutual collisions. (3) When opening or closing the valve, there is impact between the valve disc and the valve seat, as well as friction between the various valve components. (4) Grease, debris, dust, rust, or other impurities are present inside the pipeline, or sparks are generated due to electrostatic reactions caused by poor grounding. 2. What are the requirements for routine inspections? Answer: (1) It is necessary to determine the location, time, route, and content. (2) General areas should be inspected once per hour, while critical areas and those with defects require more frequent inspections. (3) Any issues discovered should be reported promptly and recorded in detail. (4) After completing the inspection of the entire station, mark “√” in the station’s procedural record book to indicate that the routine inspection procedures for this station have been carried out for the current hour. 3. How to use pressure vessels correctly? Answer: (1) When using pressure vessels, it is necessary to check the opening and closing status of all valves, the reading on the pressure gauge, as well as the sensitivity of the safety valve and alarm devices. (2) When opening or closing the inlet and outlet valves, ensure everything is correct before taking action. (3) When adding materials to the container, the quantity of materials added, the sequence of different types of materials, the interval between additions, and the process conditions must all comply with the specified requirements, in order to prevent violent reactions resulting from the sudden mixing of materials with incompatible properties. (4) The opening and closing of the valve should be done slowly, to allow the container time for preheating and to adjust to pressure changes, thereby preventing sudden cooling of the container that could cause significant thermal stress. (5) It is strictly prohibited to operate pressure vessels under conditions of overpressure, overheating, or overload. 4. How are pressure vessels classified? Answer: A vessel is considered a low-pressure vessel when its operating pressure is ≥0.1 MPa and ≤1.6 MPa; it is a medium-pressure vessel when the operating pressure is ≥1.6 MPa and ≤10 MPa; it is a high-pressure equipment when the operating pressure is ≥10 MPa and ≤100 MPa; and it is an ultra-high-pressure vessel when the operating pressure is ≥100 MPa. 5. Briefly describe the function and types of safety valves. Answer: The function of a safety valve is to open when the pressure of the medium inside a pressure vessel exceeds the allowable level; it emits an alarm sound and then opens fully to release a certain amount of medium, thereby preventing the pressure inside the vessel from rising any further ； When the pressure drops to the specified value, the valve closes promptly, thereby ensuring the safe operation of the equipment. Based on their overall structure and the type of loading mechanism, they can be divided into three types: lever-type, spring-type, and pulse-type. 6. Why are most of the parts in oxygen compressors that come into contact with oxygen made of copper or stainless steel? Answer: Pure oxygen has a strong oxidizing effect, especially under conditions of high temperature during compression. Parts that come into contact with oxygen are more prone to oxidation and rusting. Rusting not only causes unacceptable damage to these parts but also leads to the peeling off of rust layers, which can generate sparks when impacted by the oxygen stream, thereby causing fires and explosions. Therefore, in oxygen compressors, all parts that come into contact with oxygen should be made of steel or stainless steel with high oxidation resistance and low tendency to produce sparks. 7. What are the methods of routine inspection? Answer: The inspection methods should involve using sight, hearing, smell, and touch to assess the situation and identify any problems. Specifically: Observation means using instruments or other effective monitoring methods to check whether the process parameters are within the normal range, and to determine if there are any abnormalities in the surrounding environment. Listen: Listen for any abnormalities in the operating equipment, pipelines, and the surrounding area. Check: Whether there are any leaks, seepages, drips, or omissions in the equipment’s valves and pipelines. Feel: Feel the vibration and temperature of the equipment pipelines. Smell: Check if there are any unusual odors at the production site. 8. Briefly describe the “workers’ responsibilities for safe production”. Answer: (1) Be familiar with and master the relevant instructions, regulations on safe production issued by superiors, as well as the technical knowledge related to safe production. (2) Abide by labor discipline, avoid leaving one’s post, sleeping at work, or engaging in activities unrelated to one’s duties; strictly follow safety production regulations, and have the right to refuse orders that involve illegal operations. (3) Operate with care, adhere strictly to procedural standards, keep proper records, and ensure that safety production conditions are communicated during shift handovers. (4) Strengthen routine inspections to promptly eliminate safety hazards; those that cannot be resolved on one’s own should be reported to the team leader immediately. (5) It is required to wear the appropriate attire and carry a valid permit when going to work, as well as to take good care of and use fire-fighting equipment and protective gear correctly. (6) Actively put forward reasonable suggestions regarding safe production, ensure safe operations, strengthen equipment maintenance, keep the work site clean, and promote civilized production practices. (7) In the event of an accident, it is necessary to report it promptly and truthfully to the workshop and dispatch department, and to preserve the scene or keep detailed records. 9. What is work inside equipment? Answer: Operations carried out inside various towers, reactors, tanks, furnaces, piping systems and containers in chemical production areas, as well as in basements, cellars, pits or other enclosed spaces. 10. What are plant-controlled process parameters? Answer: Important process parameters that have a significant impact on product quality, production volume, and consumption, or that have a major effect on equipment safety and environmental protection, or that are interrelated among different factories, are designated as factory-controlled process parameters. 11. What are the basic measures for controlling and eliminating fire sources to prevent fires and explosions? Answer: 1) Control and elimination of open flames 2) Elimination of shocks and friction 3) Avoiding high temperatures 4) Elimination of electrical sparks 5) Elimination of fire sources. 12. How to use an oxygen respirator? Answer: 1) Place a qualified respirator on the right shoulder and around the waist on the left side, securing it with a belt. 2) Open the oxygen valve, check the pressure, and use manual replenishment to discharge the gas already present in the airbag. 3) Place the mask on your head, with the four fingers inside and the thumb outside; pull the mask up from the lower jaw. Take a few deep breaths to check that the internal components of the respirator are in good condition. Once it is confirmed that all parts are functioning properly, you can proceed to work in the toxic area. 13. How to safely discharge the drain? Answer: (1) Stand upwind, (2) avoid the drain outlet. (3) The valve cannot be opened fully. (4) The hand must not be removed from the valve. (5) Leave only after closing the valve. 14. What are the common prime movers for centrifugal compressors? Answer: The common prime movers for centrifugal compressors are electric motors, steam turbines, and gas turbines – a total of 3 types. 15. What are panel-mounted instruments? Panel-mounted instruments are commonly used in systems where local panel operation, display, and automation control circuits are relatively simple. Common examples include temperature monitoring devices, electric regulating indicators and electric three-pin indicators, pneumatic three-pin indicating regulators, flash alarms, and paperless recorders. 16. Briefly describe the working principle of a centrifugal pump? Answer: Before starting a centrifugal pump, it is necessary to fill the pump and the suction pipeline with liquid. During operation, the motor drives the impeller to rotate at high speed through the pump shaft. The shaft of the impeller forces the liquid to move, thereby generating centrifugal force. Under this force, the liquid is thrown toward the edges of the impeller and accumulates in the flow channels within the pump casing. The liquid gains energy in the impeller, with both its pressure energy and kinetic energy increasing. It is this energy that enables the liquid to be transported along the flow channels and via the discharge pipes to a higher storage tank or directly to the location where it is needed. As the impeller throws the liquid outward, a vacuum is created at its center; as a result, the liquid continues to flow in from the center of the impeller under the influence of external pressure, and then is discharged from the outer edges of the impeller, thus achieving the purpose of transporting the liquid. 17. What are the control components of a circuit? Answer: (1) Miniature circuit breaker. (2) Iron-clad switch. (3) AC contactor. (4) Button, 18. Briefly describe the mechanism and hazards of cavitation. Answer: As liquid flows through the pump impeller, there are certain local low-pressure areas near the inlet of the blades. When the pressure of the liquid in these low-pressure areas drops to the saturated vapor pressure corresponding to its temperature, the liquid begins to vaporize and form bubbles. These bubbles travel with the liquid flow through the flow channels; when they reach areas with higher pressure, they instantly condense, resulting in local cavitation. At the moment of vaporization, the liquid surrounding the bubble rushes into the cavity rapidly, accompanied by localized high temperatures and high pressures due to water hammer, resulting in cavitation. Harm of cavitation: When cavitation occurs, the flow-through components of the pump suffer mechanical damage and chemical corrosion. The pump also experiences vibration and noise. When cavitation becomes severe, the presence of numerous bubbles blocks the flow cross-section, reducing the energy obtained by the fluid from the impeller. This leads to a decrease in head, lower efficiency, and even a complete interruption of flow. 19. What are the measures to prevent pump cavitation? Answer: (1) Depending on the specific conditions of the installation, it is advisable to install the pump as low as possible; this is an effective measure. However, it is necessary to avoid making the structure too tall, as that would be uneconomical. ⑵Reducing the pump’s speed can decrease the cavitation head required by the pump and improve its suction performance. This measure can only be adopted when the pump’s head and flow rate still meet the process requirements at the reduced speed. ⑶Using a double-suction pump can reduce the net positive suction head required by the pump. ⑷Increase the diameter of the suction pipe and reduce the number of valves and elbows in order to minimize the pressure loss in the suction pipeline system; ⑸ Install a pre-inducer wheel on centrifugal pumps and a pre-centrifugal impeller on vortex pumps to improve suction performance. ⑹The impeller is made of a material with good cavitation resistance to minimize the impact of cavitation on it. 20. Briefly describe the basic structure of a piston compressor. Answer: A piston compressor consists of a main unit and auxiliary devices. The main unit is generally divided into the following parts: (1) The casing, which serves as the structural foundation of the compressor and is composed of the body, the middle section, and the crankcase. ⑵The transmission mechanism consists of transmission devices such as clutches, pulleys, or couplings, as well as moving components like crankshafts, connecting rods, and crossheads. Through them, the rotational motion of the drive mechanism is converted into the reciprocating linear motion of the piston. ⑶The compression mechanism consists of a cylinder, piston assembly, intake and exhaust valves, etc.; as the piston moves back and forth, it cyclically completes the working process. ⑷The lubrication system consists of a gear pump, an oil injection pump, an oil filter, and an oil cooler. The gear oil pump is driven by the crankshaft to supply oil at low pressure to the moving parts for lubrication. ⑸The cooling system of the air-cooled type mainly consists of a cooling fan and an intercooler, among other components. It consists of water-cooled cylinder jackets at various stages, intercoolers, pipes, valves, etc. ⑹The control system includes regulating devices such as unloading valves, load regulators, etc., as well as safety valves, instruments, and lubricating oil, cooling water, and parameters related to exhaust pressure and temperature. The auxiliary devices mainly include: air filters, turning gear, drive mechanisms, rear cooler buffers, oil-water separators, air storage tanks, cooling water pumps, cooling towers, various pipelines, valves and electrical equipment as well as protection devices, and safety shielding nets. 21. What are the types of metal corrosion? Answer: The corrosion of metals can be divided into chemical corrosion and electrochemical corrosion, depending on the nature of their corrosion processes. ⑴Chemical corrosion is the damage caused by a chemical reaction that occurs when a metal comes into contact with an external medium. Since no electric current is involved in this corrosion process, it is called chemical corrosion. ⑵Electrochemical corrosion is a form of degradation that occurs when a metal comes into contact with other substances, resulting in electrochemical reactions; an electric current is generated during this corrosion process, which is why it is called electrochemical corrosion. 22. What is the function of the control valve bypass line? Can the auxiliary line be eliminated by using a handwheel mechanism? Answer: In continuous production processes, to prevent production interruptions or accidents caused by failures in the control valves, these valves are usually equipped with bypass lines. These allow for manual adjustment using the bypass valves when necessary, as a temporary substitute for automatic control. Alternatively, the shut-off valves before and after the control valve can be closed, allowing the valve to be removed for replacement or maintenance. Whether a handwheel mechanism can be used to eliminate the auxiliary line depends on the importance of the control system in production. For important and critical control systems, the auxiliary line cannot be removed; for ordinary control systems, a handwheel mechanism can be used as a substitute for the auxiliary line. 23. What are the conditions that must be met for an automatic adjustment system to achieve a disturbance-free switchover? In an automatic control system, the switch from “manual” to “automatic” must bring the deviation to zero in order to achieve a disturbance-free transition. “To achieve a seamless switch from “Automatic” to “Manual”, the “Manual” output value must be set to the same value as the “Automatic” output value. 24. What are the main factors that affect absorption operations? ⑴Effect of gas flow velocity: Gas absorption is a mass transfer process of diffusion between the gas and liquid phases. The gas flow velocity directly affects this mass transfer process. ⑵Effect of spray density: Excessively high spray density reduces the efficiency of absorbing solutes, while too low a density fails to ensure the purity of the gas after absorption. ⑶Effect of temperature: Lowering the temperature can increase the degree of gas absorption. ⑷Effect of pressure: Since gas absorption is a unidirectional mass transfer process from the gas phase to the liquid phase, increasing the system pressure is beneficial for absorption. ⑸Effect of absorbent concentration: The lower the concentration of the absorbent substance in the absorbent, the more gas can be absorbed at the same gas concentration. 25. What is throttling? When a gas or liquid flows through a constriction or a valve in a pipe, the flow is hindered; vortices, collisions, friction and other resistances occur at the valve. For the fluid to pass through this valve, it must overcome these resistances, which results in the pressure downstream of the valve being much lower than the pressure before the valve. This process of a significant drop in pressure due to encountering local resistance is commonly referred to as the throttling process. In fact, when fluid flows through pipes or passes by various devices, there is also flow resistance, and the pressure decreases as well. Therefore, when referring generally to the throttling process, it should also include the pressure reduction that occurs during flow in pipes and equipment. However, the pressure drop in pipes and equipment is relatively small and occurs gradually, whereas the pressure drop during throttling by a throttle valve is large and sudden. 26. What are the factors that affect the rate of chemical reactions? Answer: (1) Effect of concentration on reaction rate: The higher the concentration of the reacting substances, the faster the reaction rate; conversely, it is slower. ⑵The effect of temperature on reaction rate: Raising the temperature is a common method to accelerate reaction rates; when the concentration of reactants remains constant, changing the temperature results in a change in the reaction rate. It can be seen that the reaction rate constant K increases as the temperature rises. ⑶The effect of catalysts on reaction rate: Catalysts, also known as accelerants, are substances that can alter the rate of chemical reactions, while their composition, mass, and chemical properties remain unchanged before and after the reaction. A catalyst that can accelerate the reaction rate is called a positive catalyst ； A catalyst that can slow down the reaction rate is called a negative catalyst. Different chemical reactions require different catalysts, which is the selectivity of catalysts. Each catalyst must operate within an appropriate temperature range to achieve its maximum catalytic efficiency; this temperature range is known as the catalyst’s active temperature range. V. Calculation problems: 1. At 70°C, the solubility of KNO3 is 135 g. Determine (1) how many grams of KNO3 are dissolved in 100 g of a saturated solution at 70°C? (2) How many grams of water are required to dissolve 100 g of KNO3 at 70°C? Solution: (1) At 70°C, the solubility of KNO3 is 135 g, and the mass of a saturated solution is 100 + 135 = 235 g. Let X be the mass of KNO3 dissolved in 100 g of saturated solution; then 235 : 135 = 100 : X. Therefore, X = 100 × 135 / 235 = 57.45 g. (2) At 70°C, 100 g of water is required to dissolve 135 g of KNO3; it can be assumed that 100 g of water is also needed to dissolve 100 g of KNO3. Let Y be the amount of water required to dissolve 100 g of KNO3. Then: 235 : 100 = 100 : Y, so Y = 100 × 235 / 100 = 235; therefore, 74.07 g of water is needed. Answer: (1) 74.07 g of KNO3 needs to be dissolved. (2) 74.07 grams of water are required. 2. At 850°C, the conversion reaction of CO is carried out in a 1 m3 closed reactor: CO + H2O(g) = CO2 + H2. If 150 mol of CO and 500 mol of water vapor are introduced for this reaction at said temperature, the equilibrium constant Kc is 1. What is the conversion rate of CO? Solution: Let the amount of CO converted at equilibrium be X mol. Then:
CO + H2O ⇌ CO2 + H2
Initial amounts: 150, 500; Equilibrium amounts: 150 – X, 500 – X.
Kc = X² / [(150 – X)(500 – X)] = 1
Solving for X gives X = 115.38.
The conversion rate of CO is: αCO = (115.38 / 150) × 100% = 76.92%.
Answer: The conversion rate of CO is 76.92%. 3. 34.3 g of a saturated NH4Cl solution at 20°C was evaporated to dryness, yielding 9.3 g of NH4Cl. What is the solubility of NH4Cl at this temperature? Solution: Solubility refers to the number of grams of solute that can be dissolved in 100 grams of solvent at a certain temperature to reach saturation. According to the given information, in a 34.3 g solution of NH4Cl, the amount of water is: 34.3 – 9.3 = 25 (g). That is, at 20°C, 25 g of water can dissolve up to 9.3 g of NH4Cl. If X grams of NH4Cl can be dissolved in 100 g of water at 20°C, then: 25 : 9.3 = 100 : X. Therefore, X = 100 × 9.3 / 25 = 37.2 g. In other words, the solubility of NH4Cl at 20°C is 37.2 g. Answer: The solubility is 37.2 grams. 4. At 476°C and 101.33 KPa, the equilibrium constant Kc for the CO conversion reaction is 2.6. If a 90% equilibrium conversion rate of CO is required for production, determine the feed ratio of CO to H2O(g). Solution: Since the reactor is constant, the ratio of the initial concentrations of CO and H2O(g) is equal to the ratio of their initial moles. Let the initial concentration be 1 mol/L and that of X be X mol/L; with a CO conversion rate of 90%, we have: CO + H2O = CO2 + H2. Initial concentrations (mol/L): 1, X, 0, 0. Equilibrium concentrations (mol/L): 1–0.9, X–0.9, 0.9, 0.9. Then Kc = 0.92 = 1 / [(1–0.9)(X–0.9)], which gives X = 4.016. The ratio of the reactant gases is therefore 1:4.016, or approximately 1:4. Answer: The ratio of the reactant gases is 1:4. 5. How to prepare a 20% solution using 65% and 5% solutions? Solution: Let 1 part of the 65% solution be taken, and X parts of the 5% solution be taken. The concentration of the resulting mixture is 20%. Since the mass of solute remains constant before and after mixing, we have: 1×65% + X×5% = (1+X)×20%. Solving for X gives X=3. Therefore, when 1 part of the 65% solution and 3 parts of the 5% solution are mixed together, a 20% solution is obtained. 6. Calculate how many m3 of nitrogen and hydrogen gas (under standard conditions) are required to produce 1 ton of ammonia, given that the volume ratio of nitrogen to hydrogen is 1:3. Solution: Let X be the volume in m3 of nitrogen and hydrogen gas required. According to the reaction 3H2 + N2 → 2NH3, (3+1)×22.4 m3 = 2kmol X; therefore, X = 4×22.4×1000/17 = 2640 m3. Answer: 2640 m3 of nitrogen and hydrogen gas is required.