Drawing on the \"Case Study per Week\" (accident handling training) approach, an analysis was conducted on the failure of control valves in a hydrogenation unit that led to excessive temperature rise
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Case Study of the Week (Accident Handling Training): Failure of a control valve in a hydrogenation unit leading to excessive temperature rise. 1. Accident sequence: In a hydrogenation cracking unit at a certain plant, the control valve T-1156, which regulates the circulating hydrogen fed into the heating furnace, suddenly stopped functioning and began to close. The auxiliary line control valve was also in the manual closed position; as a result, the circulating hydrogen supply to furnace BA-102 was interrupted, causing the furnace tubes to overheat for 10 minutes. Once valve T-1156 was reopened, circulating hydrogen flowed back into the heating furnace, pushing the heat from the furnace tubes into the cracking reactor. This led to an excessive temperature rise in the first and second beds of the cracking reactor, reaching 930°C, prompting the emergency activation of a 21-bar vent system to relieve pressure. Post-inspection revealed that some of the furnace tubes were bent, and the catalysts in beds 1 and 2 of the cracking reactor were deactivated. 2. The lessons learned are: (1) Instruments and control valves must be carefully and thoroughly verified. (2) Be careful when performing dry burning treatment on the furnace tubes; do not rush to put them into use until the temperature of the furnace tubes has dropped to normal levels. (3) It is necessary to strengthen the training of operational skills and enhance accident drills. 3. In actual production, the DCS operator must constantly monitor the on/off status and valve positions of various key control valves, so as to detect and address any issues promptly.
There are too many monitoring points and not enough personnel; too many alarms are set up, which leads to complacency over time~~~~ The automatic operation of control valves poses a risk, and this issue must be thoroughly investigated~~~~ To prevent accidents from occurring
(The control valve for the circulating hydrogen entering the heating furnace) Valve T-1156 suddenly lost control and started to close, while the secondary line control valve was in the manually closed position. I’m not quite sure about the function of the secondary line valve. Here, hydrogen is mixed after the furnace; there are two flow control valves for the circulating hydrogen entering the heating furnace. Since there is no issue with uneven flow, these valves remain in their fully open position at all times, to prevent surging in the circulation pump and dry burning of the furnace tubes as a result of sudden closures.
This situation can occur in the circuit, and it may be caused by inaccurate flow rates and pressures. Those monitoring the instruments should pay close attention to the auxiliary parameters, as even the best instruments can fail at times
10 minutes – it’s crucial to keep an eye on the clock. Auxiliary parameters such as the compressor current, furnace temperature, outlet temperature of the furnace, and system pressure can all change significantly. Safety is of utmost importance, so one must stay vigilant at all times
Isn’t it usually done by mixing hydrogen right at the furnace? Even if the hydrogen supply is turned off, isn’t there still feedstock being supplied?
After the hydrogen and the mixed feed oil are combined, they enter the high-pressure heat exchanger; the control valve is a bypass valve for the high-pressure heat exchanger, which corresponds to the cold circuit of the mixed feed