Hazardous factors and preventive measures during normal production

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1. Adhere to the principle of \"cooling first before reducing the flow rate.\" When making normal operational adjustments to the hydrogenation unit, it is necessary to follow the principles of \"cooling first before reducing the flow rate\" and \"increasing the flow rate first before raising the temperature,\" in order to prevent \"temperature spike\" accidents. 2. Control of reaction temperature: The reaction temperature in a hydrogenation unit is the most important control parameter; it is necessary to strictly regulate the hydrogenation reaction temperature as well as the temperature rise in each bed layer in accordance with the process technical specifications. 3. Liquid level control in the high-pressure separator: The liquid level in the high-pressure separator is a very important process control parameter in hydrogenation units; if the level is too high, it can cause the recycled hydrogen to contain liquid, thereby damaging the recycled hydrogen compressor ； If the liquid level is too low, it can easily lead to an accident where high pressure penetrates into the low-pressure area, resulting in damage to low-pressure equipment, leakage of oil and flammable gases, and even more serious consequences. Therefore, the liquid level in the high-pressure separator should be strictly controlled, and the accuracy of the level gauge should be regularly checked. 4. Pressure control of the reaction system: The pressure in the reaction system of a hydrogenation unit is an important process control parameter. The reaction pressure affects the hydrogen partial pressure, thereby having a direct impact on the hydrogenation reaction. There are many factors that influence the pressure in the reaction system of such units; therefore, an economical, reasonable, and convenient control scheme should be chosen to regulate this pressure. 5. Control of recycled hydrogen purity The purity of recycled hydrogen affects the hydrogen partial pressure, which in turn has a direct impact on the hydrogenation reaction. It is an important process control parameter in hydrogenation units. There are many factors that influence the purity of recycled hydrogen, including the properties of the catalyst, the properties of the feed oil, reaction temperature and pressure, the purity of fresh hydrogen, and the amount of off-gas hydrogen emitted. Among these, the operable condition is the amount of off-gas hydrogen emitted. Increased tail hydrogen emissions, higher purity of recycled hydrogen ； Reducing tail hydrogen emissions leads to a decrease in the purity of recycle hydrogen. A high purity of recycle hydrogen results in a higher hydrogen partial pressure, which is beneficial for the hydrogenation reaction. However, achieving such high purity comes at the cost of substantial venting of off-gas and increased material consumption ； If the purity of the recycled hydrogen is low, the hydrogen partial pressure will be low, which hinders the progress of the hydrogenation reaction. Moreover, when the purity of recycled hydrogen is low, its average molecular weight increases; with the speed of the recycled hydrogen compressor remaining unchanged, the system pressure difference rises, and the power consumption of the recycled hydrogen compressor also increases. Therefore, the purity of circulating hydrogen must be controlled appropriately. 6. Control of heating furnaces: Heating furnaces are important equipment in hydrogenation units; their use should be given due attention. The flow rates in various circuits of the heating furnace should be kept uniform and not lower than the specified values, to prevent coking of the furnace tubes ； Maintain uniform combustion in all nozzles of the heating furnace, and strive to keep the temperature even throughout the furnace chamber ； Ensure that the temperature at various points in the heating furnace does not exceed the specified limits ； Maintain good combustion in the heating furnace. 7. Check with the lights turned off. The hydrogenation unit system is under high pressure, and since the medium is hydrogen, leaks can occur easily. Leaks of high-pressure hydrogen can lead to fires; hydrogen flames are usually pale blue in color, making them difficult to detect during the day. However, with the lights turned off at night, such hydrogen leaks can be easily identified. Therefore, conducting such regular night-time inspections with the lights turned off is of great significance for identifying leaks, nipping accidents in the bud, and ensuring the safe and stable operation of the equipment. 8. Prevention of freezing in the unit: The feedstock used in hydrogenation units is generally heavy and has a high freezing point, typically between 20–30°C, which makes freezing likely to occur. In the event of freezing, it not only affects the stable operation of the unit but also easily leads to safety accidents. Therefore, sufficient attention should be paid to the anti-freezing measures for hydrogenation units. 9. Surge prevention in circulating hydrogen compression: The circulating hydrogen compressors in hydrogenation units are mostly centrifugal compressors, and these compressors are prone to surge problems. Therefore, it is necessary to ensure that the compressors operate under normal conditions during operation in order to prevent surge. 10. Control of raw material quality: The properties of the raw materials used in hydrogenation units have a significant impact on their operation, and strict control is necessary. Generally, the dry point of the raw materials is controlled within a specified range, with Fe content not exceeding 1×10^-6. If the iron content is high, the pressure difference across the reactor increases too rapidly, preventing the unit from operating over a long period. N is not greater than 1×10-6; since N is below the specified value, there is no free water in the raw material. 11. Prevention of hydrogen sulfide poisoning: The feed materials for hydrogenation units contain sulfur, which is converted into hydrogen sulfide during hydrogenation. This hydrogen sulfide accumulates at the top of the debutane tower and in the desulfurization section, resulting in high concentrations of hydrogen sulfide. Hydrogen sulfide is highly toxic, with a permissible maximum concentration of 10 mg/m3. Therefore, the hydrogenation plant must pay close attention to preventing hydrogen sulfide poisoning, especially when performing tasks such as liquid cutting and sampling in areas with high sulfur levels; it is required to use gas masks and have someone on standby for supervision. 12. Keep the cold hydrogen line unobstructed at all times. The quench hydrogen in the hydrogenation unit is an important means for controlling the temperature of the hydrogenation reactor bed, and it plays a crucial role in suppressing increases in reaction temperature. High-viscosity oil sometimes flows back into the cold hydrogen line and condenses there, blocking it; such a situation can be very dangerous. Therefore, it is essential to keep the cold hydrogen line unobstructed at all times during operation. 13. Pay close attention to the operating conditions of the hot oil pumps and light hydrocarbon pumps. Some of the hot oil pumps in the hydrogenation unit operate at temperatures that are high enough to exceed the auto-ignition point of the oil; in the event of a leak, fires can easily occur. Therefore, during operation, it is necessary to pay attention to the operating condition of the hot oil pump, as well as to check for any leaks in the pump body and seals; if leaks are detected, they must be addressed immediately. The hydrogenation unit contains large amounts of light hydrocarbons, and a leak could lead to a serious accident. Therefore, sufficient attention must also be paid to the operating condition of light hydrocarbon pumps.