What is an appropriate amount of hydrogen to add during reformation pre-hydrogenation?

It depends on the sulfur and arsenic content in the pre-treated refined oil, right?

It depends on the properties of the pre-hydrogenation feedstock and the processing volume, as well as the hydrogen consumption in the hydrogenation reaction; there is no absolute value.

We are using UOP technology for continuous reforming. From last night until this morning, I observed that the hydrogen supply to our system was around 800 NM3/h, while the processing capacity was between 130 and 160 T/h. The normal hydrogen consumption is around 600 NM3/h; the flow rate of the hydrogen produced as a result of reforming varies significantly after recontact； Last night, the hydrogen supply was increased to over 1100 NM3/h; after re-contact, the fluctuations in hydrogen flow were very small, with the flow rate curve being almost linear. The temperature drop in the four reactors increased from 207 degrees to 220 degrees compared to usual ； In terms of operational performance, when the hydrogen supply to our unit is above 1100 NM3/h, the effects of pre-hydrogenation for desulfurization and denitration are more stable, which is beneficial for the reforming reaction. Therefore, I personally believe that the pre-hydrogenation hydrogen supply should be set at a somewhat higher level, and it shouldn’t be too tight. I hope friends will share more for communication.

Does your pre-hydrogenation produce waste hydrogen? The hydrogen supplied during pre-hydrogenation is determined by controlling the pressure of the high-pressure stream from pre-hydrogenation; reformation does not control the purity of the recycle hydrogen used in pre-hydrogenation by discharging waste hydrogen, as is the case in hydrofinishing units. If the amount of supplementary hydrogen is increased arbitrarily, it will result in more supplementary hydrogen than is consumed during the reaction process, causing the pressure in the pre-hydrogenation system to rise. So unless you have waste hydrogen, it’s impossible to increase the amount of supplementary hydrogen at will. Regarding the impact of the pre-hydrogenation system on reforming, it is mainly the effect of the refined oil components. A difference of 1000 units has little impact when dealing with values over 40,000 units. Therefore, it is recommended that you figure out why the hydrogen addition amount increases, what are the differences in test results before and after oil purification, whether the raw material has been changed (this depends on whether it’s a vacuum distillation or atmospheric distillation raw material), and whether the valve positions in the control system have increased. The key is to understand these concepts correctly; otherwise, you will end up taking detours.

By increasing the amount of supplementary hydrogen, there is a pressure control valve at high pressure; then how can the pressure in the pre-hydrogenation system rise? With the reforming feed unchanged and the reaction conditions intact, why has the valve position of the control valve in the contact system increased? Just steady.

Where conditions permit, increasing the supplementary hydrogen is beneficial for the reforming pre-hydrogenation reaction! We don’t have a flow display for the hydrogen being added, but the hydrogen emissions at the outlet are around 4000–5000 NM3/h.

Is your voltage control released directly? The few 2.4MPA systems I’ve come across all have direct control over the amount of hydrogen added, with only one option for emergency venting; if waste hydrogen has to be discharged, the energy consumption will definitely be higher. What is your pressure level? In other words, the impurity content in your pre-hydrogenation feedstock is relatively high, which requires more stringent reaction conditions; our facility can meet the purification requirements simply by increasing the reaction temperature!

The pressure at the outlet of our pre-hydrogenation compressor is 2.6 MPa; the inlet pressure of the hydrogenation reactor is 2.28 MPa, while the pressure in the high-pressure section is 1.9 MPa. The gas is released continuously, not as an emergency vent – it is sent to the double desulfurization unit to be used as fuel gas. There is a safety valve in the high-pressure section, but its function is different. What is the hydrogen sulfide content in the recycle hydrogen used in your plant’s pre-hydrogenation process?

The amount of hydrogen supplied to the reforming pre-hydrogenation system should be controlled in a cascade manner based on the pressure in the high-pressure tank; the exact amount depends on the set pressure value for that tank, with the output value corresponding to that pressure serving as the set value for the hydrogen supply. If the original poster is involved in chemical processing, the process parameters for internal operations are available.

For the NHT units I have worked on (UOP technology, formerly SHELL systems), the units operate properly without emitting any exhaust gases; H2S is either washed away or carried along with the reaction products to downstream towers for separation. The reaction pressure and the purity of the recycled hydrogen manage to remain balanced at around 67%. Therefore, the hydrogen addition amount in steady state is not an active process control parameter, but is regulated serially by the pressure in the compressor inlet tank.