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• A TGT that uses a steam heater to raise the temperature is experiencing a drop in quencher pH after shutdown maintenance and startup. In this TGT, passivation was done at shutdown for shutdown maintenance, and pre-sulfurization was done at startup and startup. The TGT reactor has thermometers at the top, middle, and bottom, and since startup, the temperatures at the middle and bottom have been the same, indicating that the catalyst in the lower layer is losing activity. The operation to raise the pH of the quencher with caustic soda had to be repeated two to three times a day, and by raising the H2S/SO2 of the SRU upstream to 5, the SO2 leak from the reactor was reduced, and the quencher pH drop is now only once a week. No unusual operations have been performed. The catalyst has been in use for 10 years, which is not a short period of time, but we do not believe it is a period of use during which a rapid decline in activity occurs. If anyone has experienced similar problems or has knowledge of the possible causes of the problems, it would be helpful.

  Jun-2024

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Answers

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• Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

  The low pH informed in the quench water indicates higher concentration of SO2 in the hot gas from the hydrogenation reactor that feeds the quench tower due to the sulphuric acid formation in the water phase. This fact can be understand as a symptom of poor performance of the hydrogenation section that is reinforced by the absence of temperature variation between the middle and bottom catalytic beds of the hydrogenation reactor informed in the question.

  Once was mentioned a recent maintenance shutdown, I understand that the catalyst preservation and activation procedure during the shutdown and start up steps should be verified aiming to identify eventual failures. It seems that the catalyst was damaged or poisoned during the shutdown or start up procedure, leading to activity loss which could explain this behaviour.

   

  Jun-2024