Incident in the DCU at VEBA OEL Refinery Horst Leads to 1 Death after 10 Days in Hospital
The incident happened on the 21st. of August at 12:45, 15 minutes after unheading a quenched coke drum. Two shift mechanics had opened up the coke drum routinely. They had replaced the top flange for the drilling flange, that is adjusting the drilling equipment. The injured had had to fix the last screws on the adjusting flange, while the coke drum burped over. The injured was hit by a hot water fountain. About 60% of the skin had been scalded (grade 2 and 3).
First aid had been given by the second mechanic, who had informed the fire brigade and refinery ambulance at the same moment the incident occurred. The ambulance arrived at 13:05. First indications showed, that there was no acute risk of mortal danger. The injured was immediately brought to the Hospital Bergmanns Heil nearby (10 km). During the time, kept on intensive care, the situation didn’t get worse. No indications were given for unstable conditions of the injured. On the 31st. of August the man died, caused by an embolism and collapsing blood circulation.
It has been the first time after starting up the coker unit in 1972, that a critical situation occurred at the top of the coke drum. The unheading procedure has been changed a few times optimizing the working conditions for the mechanical folks. At least a procedure has been taken in place, that assures, that there are no hot vapors leaving the coke drum while open up the top flange: A seal of 3 to 4 meters of quench water is covering the coke bed, preventing the people around. Analysis of the drum gases show that the concentration of hydrocarbons, in especially benzene, toluene and benzo(a)pyrene and H2S are kept below critical values by that procedure.
The drum procedure carried out on the drum that failed, followed the defined way:
The coke drums are quenched bottom to top; the quenching is automatically done, pressure and temperature controlled, in order to limit flaring
In the first step of quenching, the drums are filled with water up to the second radar level control; success criteria are as follows (values of the drum that failed in brackets):
1. Top drum temperature below 130°C (110°C)
2. Amount of water minimum 120 t (172 t)
In the second step of quenching, water is circulated through the coke drum until the top drum temperature falls below 90°C; during that step the system is connected to the atmosphere; the water enters the bottom of the drum and leaving over top to the open pit.
During that particular drum cycle, there had been a delay referring to a mechanical failure of the conveyor belts for the green coke. Therefore, the quenching by circulating the water through the drum, had been continued. Finally, when the acceptance for unheading had been given, top drum temperature was at around 82°C instead of the necessary 90°C.
Before unheading, the coke drum is drained by open up the bottom valve for a minimum of 90 seconds. This step is necessary in order to be sure, that there is no water flooding out of the drum when the top flange is removed.
The unheading is manually done by two mechanics. The flange is removed and changed out for the drilling flange, adjusting the drilling equipment later on.
If the drilling flange is fixed, at least, the height of the coke bed will be measured with a plumbline, and the work at the top head of the drum will be completed.
The drum is ready to be drained by control room staff.
After putting the drilling flange in place, one of the mechanics had been called to interphone by the control room. The second person, which had to fix the flange with screws was injured by a hot water fountain (1,5 – 2 meters height) that came out of the drum. This happened about 15 minutes after unheading and about 5 hours after reaching the criteria to open the drum (top drum temperature below 90°C).
Hypothesis of Explanation
It is assumed that a hot coke reservoir within the coke bed, not quenched down before, got in contact with quench water. The water might have migrated through to that hot spot with an immense delay in time.
Immediately, the mechanical staff is protected by a fire and hot water resistant clothing: ISO-TEMP. The clothes are necessary for all the mechanical jobs related to the opening of the coke drum, top and bottom as well. In the long term, it will be checked out, whether a hydraulic system could be used instead of manual working.
The radar level control should be replaced by an infrared level detector, any way. Besides continuously measuring of the coke bed height from the top of drum, the final checking of the height by the use of a plumbline will be obsolete as well.
Draining the drum completely before unheading is not acceptable. As mentioned before, the hot coke drum gases, while not sealed with quench water, are far off the allowed concentrations of critical components. Benzene, Toluene and Benzo(a)pyrenes are suspected to cause cancer diseases.