【Principles of Chemical Process Safety Design】Valves
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I. Control valves: In the manufacturing process, it is often necessary to adjust certain process parameters: flow rate F, temperature T, and pressure P. This is achieved through control valves, which include flow control valves (FV), temperature control valves (TV), and pressure control valves (PV). When designing control valves, it is important to determine the emergency valve position, that is, the failure mode. The general principle for designing the accident valve position is to, in the event of an accident, reduce the impact on downstream units by reducing heat input, increasing heat removal, releasing heat, or isolating upstream process equipment, depending on the specific conditions of the process flow. II. Emergency Shut-off Valve The function of an Emergency Shut-off Valve (ESV for short) is to isolate hazardous materials from potential leakage points, thereby reducing the leakage of such materials in emergency situations and minimizing the severity and likelihood of serious accidents. From the function of the emergency shut-off valve, it is necessary to determine two aspects: one is to identify the areas most prone to leakage, with a focus on pumps and compressors (leakages caused by seal failure, bearing failures, etc.), heating furnaces (burnout of furnace tubes), and pipelines (due to corrosive substances) ； Another aspect is to consider the fire hazard of the substances in the process flow, including the inherent hazardous properties of the substances themselves and the amount stored (both of these factors need to be taken into account simultaneously). The location and type of ESV are determined based on the equipment layout and dimensions. The ESV should be as close as possible to the quantity of hazardous liquid and as far away as possible from potential leakage and fire points.
II. Safety Valves The primary principle behind the design of safety valves is to protect process equipment and personnel. If the equipment experiences overpressure during operation, the safety valve will open automatically to release the excess pressure, thereby protecting the equipment and the operators. Once the pressure drops to a safe level, the valve will close automatically. If the safety valve does not function properly, it may cause the equipment to break, and could even lead to serious safety accidents. III. Isolation valves: The design principle of isolation valves is to be able to completely shut off the flow of fluid when necessary, thereby allowing certain sections of a process flow to be isolated during equipment maintenance or in emergency situations. When designing, the size and type of the valve must be considered to ensure it can effectively shut off the flow of fluid. IV. Check Valves The design principle of check valves is to prevent fluid from flowing in the reverse direction, thereby protecting equipment and pipelines. These types of valves generally do not require manual operation; they open automatically when the fluid flows in the forward direction and close automatically when it flows in the reverse direction. During design, the operating pressure and sealing performance of the valve, as well as its suitability for the type of fluid to be processed, must be confirmed. The design of these four types of valves should all adhere to some universal principles, such as considering the corrosion and pressure resistance of materials, the ease of operation and maintenance of the valves, as well as any relevant environmental factors. At the same time, in practical operation, regular inspection and maintenance are also crucial. .
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