Precautions for operating pressure vessels

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Safe operation: During long-term use, pressure vessels are subject to various complex factors such as pressure, temperature, and medium corrosion, which can lead to abnormalities or defects in certain parts of the vessel. The operation of pressure vessels involves safe control of process parameters during operation, with the aim of minimizing or preventing such abnormalities or defects. Process parameters include temperature, pressure, flow rate, liquid level, and material ratios. Temperature control: Temperature is one of the key control parameters for pressure vessels and their systems. Excessively high temperatures can lead to intense reactions that result in a sudden increase in pressure, causing material to be ejected or the pressure vessel to explode, or it can lead to the decomposition and ignition of the reactants. At the same time, excessively high temperatures can weaken the mechanical properties of pressure vessel materials (such as high-temperature strength), reduce their load-bearing capacity, and cause the pressure vessels to deform. Too low a temperature can cause the reaction rate to slow down or come to a halt. When the temperature returns to normal levels, excessive unreacted material may lead to intense reactions that result in explosions. Low temperatures can also cause certain materials to freeze, leading to blockages or ruptures in the pipelines, which in turn can cause flammable substances to leak and result in fires and explosions. To strictly control the temperature, measures should be taken in the following aspects: ① Prevent a sudden interruption of heat exchange during the reaction. ②The correct selection of a heat transfer medium is crucial; common heat carriers include steam, water, mineral oil, biphenyl, molten salts, soft molten metals, and flue gas. Choosing the right heating medium is of great importance for the safety of the heating process; substances that are incompatible with the properties of the reaction materials should be avoided as heating media as much as possible. ③Strengthen insulation measures. Proper insulation is beneficial for controlling process parameters, reducing fluctuations, and stabilizing production. It also prevents high-temperature equipment and pipelines from posing a fire or explosion risk to surrounding flammable and explosive materials. When providing insulation, it is advisable to use leak-proof and impermeable metal sheets as the outer cover, thereby preventing external flammable substances from leaking into or accumulating within the insulation layer and creating potential hazards. Feed control ① Feed amount control. For devices involved in exothermic reactions, the amount and rate of material feed must not exceed the heat transfer capacity of the equipment; otherwise, the temperature of the material will rise sharply, leading to decomposition and boiling over, which can result in accidents. If the feeding temperature is too low, it often leads to an excessive accumulation of material; once the temperature becomes appropriate, the reaction accelerates. Moreover, since heat cannot be removed in time, both the temperature and pressure exceed normal levels, thereby causing accidents. ②Feeding sequence control. Especially in the petrochemical industry, the feeding sequence is determined based on the properties of the materials and the reaction mechanisms; reversing this sequence can very likely lead to an explosion. Fluctuation range control ① Control of the fluctuation range of pressure and temperature. Pressure vessels may suffer fatigue failure under repeatedly varying loads. Fatigue failure begins in the high-stress areas of pressure vessels. Local peak stresses exist at the nozzles, welds, openings, corners, and support points of pressure vessels. Intermittent startup operations in the manufacturing process can cause significant fluctuations in pressure and temperature. Especially for lined pressure vessels, extra care must be taken during operation. ②Temperature and filling volume control. For pressure vessels filled with liquefied gas, the filling quantity must be strictly regulated to ensure that there is a gas phase space inside the vessel at the design temperature. This is because the liquefied gas within the vessel exists in a two-phase state of gas and liquid, reaching dynamic equilibrium at a certain temperature; in other words, the temperature of the medium determines its pressure. Only by strictly controlling the amount of gas filled can safe operation at the highest temperatures be ensured.