Experiencing Petrochemical Plant Accidents 1, 2, 3, 4, 5, Part 6
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This post was last edited by Ma Boyou on 2016-6-28 at 15:15. I have been working in the petrochemical industry for 24 years, having worked on various plants related to catalysis, atmospheric processing, asphalt production, hydrogen production, diesel hydrogenation, gasoline hydrogenation, catalytic reforming, benzene extraction, gas separation, MTBE production, biodiesel production, and LNG production; I can consider myself an experienced professional in this field. I have also become a regular member of the Haichuan Forum. There, I not only acquired a great deal of knowledge and shared many resources, but I also made many friends among my peers, which was extremely beneficial for me. I have now left the petrochemical industry, and in my free time I reflect on the production accidents I have experienced over the years. I will post them on the forum one by one whenever it’s convenient, for my colleagues to use as reference. I. Accident of deformation of the oil transfer line and fracture of the support in the heating furnace of the asphalt plant 1. Course of the accident: Our company’s 1.5 million tons per year asphalt plant was scheduled for shutdown for maintenance. On October 24, the plant was drained of oil for cleaning, and the cleaning work was nearing completion on the 26th. The shift supervisor ordered that the amount of steam used for cleaning the pipelines be reduced. Around 11:30, a low-frequency sound similar to thunder was heard in the area of the atmospheric pressure furnace and atmospheric pressure tower. The workshop immediately sent personnel to investigate the issue. About 10 minutes later, the noise intensified, with obvious water hammer sounds being heard. Along with these sounds, there was significant shaking in the oil transfer line connected to the atmospheric pressure furnace; the frame of the oil transfer line also shook, and steam leakage occurred at the flanges connecting the oil transfer line to the atmospheric pressure tower, as well as at the expansion joints of the oil transfer line. Upon receiving the report, I rushed to the scene; after a brief inquiry, I determined that it was a water hammer issue in the furnace tubes. I immediately instructed the operator to shut off all the purge steam in the atmospheric pressure tower, to activate the overhead air cooling system, and to increase the purge steam flow in the atmospheric pressure furnace in order to break through the water seal. After air cooling was activated, the water hammer noise and vibrations decreased significantly. A few minutes later, the temperature at the furnace outlet indicated that steam had flowed through, and the water hammer and vibrations disappeared immediately. Air cooling was then turned off, and the purging steam was stopped. 2. Damage situation: The welds at the two elbows of the expansion bend in the φ900mm oil transfer line have cracked ； The gasket of the oil transfer line and the atmospheric tower is damaged ； Deformation in 4 locations of the oil transfer line hanger ； 6 spring brackets damaged ； 6 sliding pipe supports were damaged. The atmospheric pressure tower and furnace tubes were found to have no significant damage after inspection; the direct economic loss was approximately 500,000 yuan. 3. Accident cause analysis: After the amount of purge steam was reduced, only one stream of φ25mm purge steam remained for the atmospheric pressure furnace tubes. The flue dampers in this furnace already had leakage issues; the heat generated by the purge steam was insufficient to offset the cooling effect on the furnace tubes, causing the heater to function as a condenser. As the steam condensed, a liquid seal was formed, allowing steam from the atmospheric pressure tower to flow back into the heater, creating a \"water hammer\" effect that resulted in severe vibrations. 4. Lessons from the accident: Monitor the process continuously during device purging to ensure that the steam supply for purging remains unobstructed; special attention should be paid to areas where condensation is likely to occur, such as heat exchangers and heating furnaces ； During the shutdown of the facility, the lax mindset of management and employees, along with their carelessness in operating the equipment, were the root causes of this accident.
Looking forward to more series shares! ! !
It would be better if there were a schematic diagram
This post was last edited by Ma Boyou on 2016-5-30 09:30. II. Incident of a φ400mm pipeline falling from the flare line in the gasoline hydrogenation unit 1. Course of the incident: Around 9:00 on November 16 of that year, the company’s control room received a call from the storage and transportation workshop reporting that a pipeline with a diameter of φ400mm, approximately 100 meters long, had fallen off its support frame in the pipe gallery located to the north of the refined oil tank area; it was hanging in a U-shaped position, with no leakage of fluid occurring. An operator was immediately sent to the site for investigation; it was confirmed that the pipeline in question was the flare line of the temporary shutdown gasoline hydrogenation unit. The point where the pipeline broke away was located about 500 meters from the gasoline hydrogenation unit and about 700 meters from the flare. 2. Accident losses: 9 pipe supports were damaged, and one pipe rack at the far end bend of the pipe gallery was deformed and displaced. The costs for pipeline realignment and the repair of pipe supports and pipe racks are approximately 30,000 yuan. 3. Accident cause analysis: Our company’s OCT-MD gasoline hydrogenation unit is part of an expansion project. The capacity of the existing flare pipeline was insufficient, so it was necessary to install a separate flare pipeline for this unit; accordingly, the existing flare pipe rack was extended by 1 meter to accommodate the φ400 flare pipeline for this unit. After the construction of the gasoline hydrogenation facility was completed, and since the National V standard had not yet been implemented, the unit was temporarily shut down after trial operation. On November 15, Erlianhe received instructions from the control room to put the anti-freezing and anti-condensation facilities of that device into operation. At 17:00 in the afternoon, during the external operation for the middle shift, while heating the water jacket of reflux line D201 at the top of the distillation tower of the installed unit, the purging steam for D201 was mistakenly used as the steam for heating the water jacket. This steam entered D201, and since the bypass line of D201’s safety valve was not closed in time after the shutdown and purging process, a large amount of steam flowed into the flare line. The flare line expanded due to the heat, and the straight section at the point of separation was relatively long; moreover, the pipe supports from the original flare line were present at both ends, preventing the expansion force from being released in those directions. As a result, the flare line was displaced outward from its middle section and came loose. 4. Lessons from the accident: The operator was not familiar with the process flow, lacked experience, and failed to conduct checks and confirmations after completing the operation ； During pipeline construction, the heat tracing was installed together with the purging steam within the insulation material, and the markings were not in place, which led to operators opening the wrong valves ； After the unit was shut down, the staff became lax in their attitude; they failed to follow the required procedures for shutting it down and restarting it, and the teams also did not carry out proper inspections of the shut-down unit.
The blank space in the middle was originally a simple diagram; it turned out this way after being uploaded, and it cannot be edited. Please ask the moderator to handle this.
This post was last edited by Ma Boyou on 2016-5-26 at 20:56. For the subsequent layers, may I ask the moderator if it’s possible to continue the content at this layer?
It can be continued; I also can’t see the image – I don’t know what’s going on. :$
I don’t know how to continue it on the first floor? Could you let me know?
This post was last edited by Ma Boyou on 2016-5-30 09:34. I. Fatal accidents caused by explosions in asphalt heating furnaces: 1. Accident details: In June of year N, our company’s newly built 1.5-million-ton heavy traffic asphalt production facility was put into operation for the first time. The atmospheric pressure furnace F101 was ignited to raise its temperature; three burners were used, with dry gas mixed with combustion gases. When the temperature at the furnace outlet reached 250°, efforts were made to maintain this temperature. The maintenance crew was tasked with carrying out further thermal tightening. Around 17:20 in the afternoon, two maintenance workers carried out thermal tightening on the flange at the outlet of F101 (the outlet was located outside the elbow box in the convection chamber, at a height of about 15 meters above the ground). Suddenly, F101 exploded, and the shock wave caused the outer panels of the elbow box to be destroyed, throwing the two workers who were performing the thermal tightening into the heating furnace. Despite attempts to save them, they died tragically. The unit is shut down urgently. 2. Accident losses: This accident resulted in the death of two logistics workers ； Disposal of F101 air preheater ； Damage to flue dampers and explosion-proof doors ； The insulation lining cast material in the furnace chamber has collapsed, and the insulation foam has fallen off ； Some of the furnace tube suspensions in the radiation chamber have broken ； The chimney is slightly tilted ； The box plates of the convective chamber elbow box came loose and were damaged, resulting in direct economic losses of around 4 million. 3. Accident cause analysis: The steam pipeline network of this facility serves the end-users of our company. When the steam consumption at the facility is low, the temperature often falls below 170°. At the beginning of operation, when the temperature of the heater is low, the superheated steam system in the convection chamber fails to achieve the purpose of superheating; in fact, it even contributes to lowering the steam temperature. The F101 burner uses \"superheated\" steam for vaporization. At the beginning of ignition, when the temperature is low, the gas is burned out, allowing steady operation. Once the temperature at the furnace outlet needs to rise to 200°, it becomes necessary to use oil along with gas for combustion. However, due to the low temperature of the vaporization steam, the fuel has a high viscosity, resulting in very poor atomization; as a result, the fuel burns intermittently, the furnace interior remains dim, and smoke is emitted from the chimney. During the mixed oil and gas combustion in the morning shift of that day, F101 shut down and restarted multiple times. Around 15:00, instructions were received from the workshop to maintain a temperature of 250°. After the furnace operator adjusted the amounts of oil and gas used, the temperature inside the F101 furnace stabilized, and the operator then switched the temperature control valve for F101 to automatic mode (since the heat load was low at the start of the morning shift and the fuel used was dry gas, this temperature control valve was set to control the flow rate of dry gas). After taking over the shift, the constant temperature was maintained. The DCS showed that the furnace temperature dropped rapidly at 16:30; this was likely due to the burners going out. It was not until around 16:50 that the crew members realized that the furnace had stopped burning. The shift leader immediately ordered the furnace operator to attempt to restart the furnace. However, worried about the excessive drop in furnace temperature, the operator failed to follow the procedural requirements for purging the furnace and shortened the purging time instead. Before any steam could emerge from the chimney, he opened the dry gas control valve to attempt ignition. Since the furnace temperature control valve regulated the flow of dry gas, and this valve was in automatic mode, it remained fully open after the furnace stopped burning. As a result, a large amount of dry gas entered the furnace. Combined with the inadequate purging by the shift operator, this led to an accumulation of large amounts of dry gas in the upper part of the furnace. Upon ignition, an explosion occurred instantly, causing the accident. 4. Lessons from the accident: The boiler operator failed to strictly follow the operating procedures by arbitrarily reducing the purging time, which was the main cause of this accident ； At the beginning of operation, various parameters were adjusted frequently; the fact that the F101 temperature control valve was used to regulate the dry gas and set to automatic mode under unstable operating conditions was a secondary cause of this accident, and there were serious risks in the workshop’s technical management ； The poor maintenance of the company’s utility systems is also a secondary cause of the accident.