Consultation on post-furnace hydrogen mixing in high-pressure hydrogenation processes

Now hydrogen mixing is done in front of the furnace; mixing hydrogen behind the furnace is quite rare. The problem is that the old processing methods are still being used for farming.

The last edit to this post was made by ardance1977 on 2019-1-6 at 09:54. First of all, one thing is certain: there is no issue with using post-furnace hydrogen mixing in high-pressure hydrogenation! I have been working in high-pressure hydrogenation for over a decade, having worked on 4 different units, all of which involved hydrogen mixing after the furnace; I have never encountered the problem you mentioned. The heating furnace in the post-furnace hydrogen mixing process is a pure hydrogen furnace; it has a high operating temperature, the furnace tubes do not suffer from coking issues, and it is easy to operate. As for what you mentioned – that after the emergency pressure relief is activated at 21 bar/min, the crude oil will flow back into the heating furnace tubes – this cannot happen as long as the design of the pressure relief mechanism is proper. In typical hydrogenation units, emergency pressure relief occurs at the inlet of the circulating hydrogen buffer tank, which is also the outlet of the cold high-pressure gas phase. During this pressure relief process, the medium inside the reactor flows rapidly from front to back, with the pressure decreasing gradually in the same direction. The outlet pipeline of the heating furnace is connected to the inlet pipeline of the reactor; even in the absence of a check valve, it is impossible for the material inside the reactor or the oil in the feed oil pipeline to flow back into the piping of the heating furnace during pressure relief. There are only two possible explanations for the situation you described: first, during pressure relief, all the valves from the compressor inlet to the reactor inlet (including check valves) fail to function, thus creating a path ； Secondly, there is a problem with the design of the location for emergency pressure relief, which results in the pressure in the outlet pipeline of the heating furnace being lower than the pressure inside the reactor during pressure relief. Finally, one more thing to mention is that the unit often starts to release pressure at a rate of 21 bar/min, which is abnormal in itself and causes significant damage to the entire reactor bed and the equipment.

Thank you very much for your reply. Sharing: 1. The hydrogen mixing after the reactor was designed and manufactured in the 1980s, with no changes to that design or manufacturing process; there is a one-way valve at the outlet of the reaction reactor. The issue of oil backflow was addressed before 2012, and new imported valves were installed in 2017. Despite emergency pressure relief due to a compressor failure, oil backflow still occurred in the reaction reactor. Theoretically, there should be no problems with the pressure relief location or the process design! The compressor inlet and outlet are closed; the pressure in the reactor is higher than that at the cold high-pressure relief valve! Oil should not flow back. I also doubt the first possibility, but there are no domestic cases to draw from. 2. Be able to introduce domestic companies that use post-furnace hydrogen mixing devices. 3. There are data available on the stroke and time of closure of the compressor’s inlet and outlet valves

I thought about it, but it’s not necessarily correct. The oil leakage is likely caused by these two factors occurring simultaneously; first and foremost, it’s definitely the check valve at the hydrogen mixing point that has failed. Secondly, in normal furnaces, feeding is usually under automatic control; therefore, when pressure is released, the increased flow rate can cause the control valve to close. If the control valve closes quickly, it may result in the pressure in the furnace tubes being lower than that at the reactor inlet. Additionally, a failed check valve could lead to oil leakage – though this is just a guess. .

Thank you for your analysis: First of all, in Condition 1, the circulation flow rate of the reactor was always routed through a bypass (hydrogen-to-oil ratio of 843*feed oil); as a result, the control valve for the circulating hydrogen in the reactor was closed, which led to low pressure in the reactor. This aspect was not taken into consideration. 2. The check valve at the reactor outlet was replaced with a new one in 2017; therefore, by consulting information on similar devices as well as the structural parameters of the check valve, it can be assumed that the crude oil passes through the check valve and enters the reactor tubes. 3. Process description: “Compressor (emergency shutdown for pressure relief of the unit) → outlet valve → high-pressure exchanger → control valve for hydrogen in the reactor’s circulation hydrogen stream → reactor → check valve → raw oil mixed with hydrogen after the reactor””

Is it possible that there has been a high-rate leakage of the raw material? One condition in this case is that the anti-surge valve is open

In China, hydrocracking mostly involves hydrogen mixing after the furnace, right?