Handling of the shutdown incident of the recycle hydrogen compressor in the residue hydrodesulfurization unit.

Emergency pressure relief is required; otherwise the reactor temperature will soar

I would also like those who have actually worked on residue hydrogenation units to share their experiences, talking about the accidents they have encountered; those who haven’t encountered any accidents can discuss the contingency plans outlined in the operating procedures. Do not rely on the experience from other hydrogenation units; in some units, the shutdown of the circulator triggers an interlocked pressure relief mechanism, while in others it does not.

Do you mean to say that the catalyst is taken out of the reactor?

It’s not related to a certain issue that arises after pressure release. It’s mainly about discussing the entire process: whether pressure is released or not, and what the bed temperature is in the case of no pressure release Should the feed pump be stopped? If it is stopped, how to replace the fluid? If it keeps running, how to switch the raw material? Are there any advantages and disadvantages to different treatment methods? In short, you can talk about whatever comes to mind; as long as it’s related to this topic, feel free to express your thoughts freely.

The shutdown of the cyclic hydrogen compressor in the residue hydrodesulfurization process does not lead to any serious overheating incidents. We have encountered such shutdowns several times before; usually, after the compressor stops, emergency pressure relief is initiated. The pressure was reduced to 80 kilograms while the system pressure remained at 150 kilograms. The reaction feed pump is not equipped with an interlock mechanism, so when the pressure drops, the amount of material fed into the reaction increases sharply, causing the level in the high-pressure tank to rise and the heater to shut down. At such times, it is essential to monitor the flow rate at the outlet of the reaction feed pump to ensure that it does not exceed certain limits. It is necessary to restart the heater as soon as possible, and once the cyclic hydrogen compressor starts operating again, everything will be fine. If the recycle hydrogen compressor cannot be started, then the process should be switched from distillation to recycling mode; if there are two series, one of them should be shut down, and the distillation unit should operate with 50% of its normal feed rate. Once the reaction temperature drops, paraffin oil should be introduced, and diesel should be used to replace the reactants in the system. The recycle hydrogen compressor can be repaired during this time, and diesel can also be introduced at low temperatures while the recycle machine is shut down. The new hydrogen compressor should remain operational, and waste hydrogen should be discharged at full capacity, thereby allowing the reaction system to be brought back online more quickly.

A shutdown due to hydrogen flow issues generally involves interlocks for the feed pump, furnace burners, new hydrogen compressor, and 7 bar pressure. However, if hydrorefining is used, the temperature rise is not as high; it may not be necessary to stop the pump or carry out emergency pressure relief – it is sufficient to open the waste hydrogen valve slightly.

When the hydrogen circulation pump stops, the furnace must be shut down and the feed pump stopped as well; pressure relief is required based on the temperature rise in the reactor. Generally, pressure relief is necessary, and we have never experienced excessive temperature rises – pressure relief is carried out immediately once the pump stops, as a temperature increase is inevitable.

Hydrorefining generally does not require pressure relief

The last edit to this post was made by Fat Cat Dong on 2019-8-2 at 10:49. Whether to activate the emergency pressure relief system needs to be determined based on the specific circumstances at the time; if the hydrogen circulation pump stops operating due to issues such as incorrect instrument readings, the system should be restarted as soon as possible； Or if there is no significant change in temperature across the reactor beds after the interlocking of the main burner in the heating furnace, emergency pressure relief is generally not required. Since the feedstock for residue hydrogenation is heavy, the reaction proceeds slowly, and excessive temperature rise generally does not occur; it is sufficient to open the waste gas flare to allow the recycle hydrogen to flow. Emergency pressure relief in residue hydrogenation units generally only includes manual pressure relief determination, without automatic pressure relief. If emergency pressure relief is required, it will not be carried out to the absolute minimum level as in a cracking unit; instead, the bed temperature is monitored, and pressure relief is stopped once there is a downward trend in temperature. There are usually several pressure thresholds at 12 Mpa, 10 Mpa, and 8 Mpa, so that the next course of action can be determined while maintaining a certain system pressure.