Handling of hydrogenation accidents

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Accident handling in hydrogenation units 1. Principles of accident handling: When an accident occurs, operators are required to correctly determine the cause of the accident based on the symptoms observed, and take prompt action to prevent the accident from worsening. At the same time, reports and requests should be made to the workshop and plant dispatch. The handling of accidents should adhere to the following principles: a. Prevent leakage, spillage, or mixing of oils and solutions; avoid overpressure in tanks, as well as excessive temperature or pressure. Control the rate of temperature and pressure reduction carefully; b. Ensure accurate assessment of accidents, take swift and decisive actions, provide timely reports and updates, and maintain regular communication among team members; c. Pay attention to protecting the catalyst, and try to prevent situations such as coking, overheating, crushing, and poisoning of the catalyst; d. Do not discharge oil and gases indiscriminately to avoid serious incidents such as fires and explosions. 2 Power outage 2.1 Transient power outage 2.1.1 Phenomena: a. Some or all pumps and machines stop operating; the flow rate indicators return to zero; b. Circulating compressors and boosters stop operating; the flow rates of circulating hydrogen and make-up hydrogen return to zero; c. Lights flicker. 2.1.2 Procedures: a. Cool down or shut off the heater; b. Emergency start of the circulator and booster compressor; c. Emergency start of the reaction feed pump and other pumps; d. Promptly adjust the liquid levels in the high-pressure separator, towers, and other vessels to prevent overfilling or depletion; e. Restore operations to normal. 2.2 Prolonged Power Outages 2.2.1 Phenomenon: Indoor lighting goes out, and pumps stop operating. 2.2.2 Handling: a. Shut down the heater; increase the opening of the flue dampers and air valves, allowing smoke to flow directly from furnace-104 into the flue; b. Vent the high-pressure gas at a rate of 1.5 MPa/h; c. Try to maintain the liquid levels in furnaces-104 and heat exchangers-105. When the tanks are full, close the feed water shut-off valve and drain the excess water from the bottom. When there is a water shortage, the steam returned by the system is discharged at the bottom to cool down and protect the boiler; d. Monitor the liquid levels in the high-pressure section and the tower, and close the large valve at the bottom if necessary to prevent high pressure from affecting the low-pressure area; e. Install a temporary potentiometer to measure the temperature of the reactor bed – continue to discharge steam if the temperature exceeds 430°C, and stop discharging it if it is below 420°C, striving to maintain the system pressure. Finally, if the pressure falls below 0.3 MPa, nitrogen should be supplied from the compressor outlet to maintain a pressure of at least 0.5 MPa; f. Try to keep the liquid levels in all tanks and containers at normal levels; g. Stop feeding in crude oil. 3 Shutting down water supply 3.1 Shutting down fresh water supply a. Symptoms: The pressure gauge on the main pipe for fresh water shows a decrease in pressure, and the valves at various service stations cannot release fresh water. b. Treatment: Except for the water used for line shutdown washing, the water used in production in this facility is all recycled water; stopping the supply of fresh water has no significant impact on production. Upon noticing that the fresh water supply has stopped, one should determine the cause of the interruption. After the water resumes flowing, be sure to close the relevant valves to prevent leaks. 3.2 Stop the circulating water 3.2.1 Phenomenon: The circulating water in this unit is divided into two circuits, with the hydrogenation section using the circuit for circulating water on the left side. When the circulating water stops flowing, the flow rate and pressure of the circulating water decrease, the cooling efficiency of each cooler declines, the pressure in the tower rises, and gas is emitted from the reflux tank. The compressor and pump units will experience an increase in oil temperature and ambient temperature due to a water supply interruption, which leads to the shutdown of these units. 3.2.2 Procedures: a. Completely shut down the heating furnace, put the product on circulation, and halt operations following the normal procedures; b. Cease receiving raw materials; c. Contact relevant parties to determine the cause of the water outage and the expected time for water restoration. In case of a prolonged outage, each unit shall take further actions in accordance with the shutdown procedures. After the water arrives, start operations according to the startup procedure. 4 Stop steam supply 4.1 Stop the 3.5 MPa steam 4.1.1 Phenomenon: After stopping the 3.5 MPa steam, it causes the circulation compressor to stop operating, the circulation hydrogen flow rate drops to zero, and this leads to overheating of the reactor. 4.1.2 Procedures: a. Stop the feed to the reaction; b. Turn off the furnace, open the flue damper and air dampers; c. Vent the gas from the high-pressure separator to the flare line, reducing the pressure at a rate of 1.5 MPa/h; d. Ensure that the liquid levels in the high-pressure separator, tower, and other vessels remain normal; e. Install a temporary potentiometer to measure the temperature of bed反-101; continue venting if the temperature exceeds 430°C, and stop venting when it drops below 420°C, while striving to maintain system pressure. Finally, if the pressure drops below 0.3 MPa, nitrogen is fed into the system from the compressor outlet to maintain a pressure of at least 0.5 MPa; f. Stop receiving raw materials. 4.2 Shutting down 1.0MPa steam: The amount of 1.0MPa steam generated by our facility is greater than the amount consumed. When the 1.0MPa steam supply in the entire plant’s thermal network is shut down, the boundary pressure control device can be used to maintain the 1.0MPa steam pressure and ensure continuous production. 4.3 Stop the 0.35 MPa steam; in our unit, -107 and 302 use 0.35 MPa steam as a heat source. Model -105 and 307 produce steam at 0.35 MPa, and some of the high-pressure condensate, after passing through model -325 for expansion, also enters the 0.35 MPa steam system; generally, the output is greater than the consumption. When the steam at 0.35 MPa is cut off in the plant’s thermal network, the boundary pressure control device can be used to regulate the steam pressure at 0.35 MPa inside it. When no steam at 0.35 MPa is generated inside the device, steam at 1.0 MPa can be supplied after temperature and pressure reduction to achieve 0.35 MPa, ensuring normal operation. 5 Stop of instrument air 5.1 Phenomena: a. The air supply valve is fully closed and the air shut-off valve is fully open, resulting in changes in the values indicated by the process parameters; b. The pneumatic gauge gives no reading; c. An alarm is triggered due to low pressure of the instrument air; d. The control panel of the circulation compressor and the motor of the booster pump stop operating as a result of the cessation of positive pressure ventilation, causing the compressor to stop. The flow rates of recycled hydrogen and supplementary hydrogen indicate zero. 5.2 Handling: Refer to Section 3.5 for handling 3.5 MPa steam in case of an emergency shutdown. 6 Gas supply interruption
6.1 Symptoms:
a. The gas pressure control becomes ineffective, resulting in a rapid drop in gas pressure;
b. The flames in the heating furnace quickly diminish and eventually go out;
c. The temperature during the hydrogenation reaction drops rapidly; the outlet temperature of the reboiler and the temperature at the bottom of the tower also decrease.
6.2 Handling measures:
a. If the flames have not yet gone out, immediately close the main gas valve on the hydrogen production side. Redirect high- and low-pressure separator outputs to the high-pressure gas line within the unit to maintain operations. Immediately contact dispatch personnel to assess the situation.
b. If the heating furnace has already gone out, or if normal operations cannot be maintained even after implementing the above measures, and if the gas supply issue cannot be resolved promptly, then stop feeding hydrogen into the system and divert the product back to storage tanks. Resume operations once the fuel supply is restored.
c. If both hydrogen production and hydrogenation processes are in operation simultaneously, immediately extinguish all flames in the hydrogenation heating furnaces to ensure uninterrupted hydrogen production. Stop feeding hydrogen into the system and divert the product back to storage tanks.

7 Equipment accidents
7.1 Procedures for handling leaks and fires involving high-temperature equipment:
a. Immediately use steam to extinguish the fire (water or foam must not be used) to prevent the fire from spreading.
b. If the fire proves too intense to control, immediately call 119 to report it.
c. Immediately inform the shift supervisor and plant dispatch personnel to obtain instructions on how to proceed.
7.2 Procedures for handling ruptures in hydrogenation furnace tubes:
a. Extinguish the furnace flames, introduce fire-extinguishing steam into the furnace chamber, and open the flue dampers to cool down the system.
b. Divert flue gases via the improved flue route from Furnace-104; shut down Furnace-104.
c. Halt feedstock input; stop the circulation pump and booster compressor.
d. Open the emergency vent valve on the high-pressure separator to reduce system pressure at a rate of 1.5 MPa/h; discharge the gas through the flare line.
e. Inform the shift supervisor and plant dispatch personnel; in severe cases, report to emergency services.
f. Divert the product stream away from the non-conforming product line back to the raw material storage area.
g. Purge the entire system with nitrogen until it is completely cleaned; ensure that the system pressure remains above 0.5 MPa. Determine the repair measures based on the extent of damage.