I would like to ask: the pressure difference on the shell side of the crude benzene hydrogenation pre-evaporator is high, and the washing effect is not significant

1. Too much water injected! The pressure difference will also increase significantly, or it’s simply because not enough water is being injected! Either wait, or 2. The pre-inlet temperature is low; heat exchange is not effective, the tubes of the heat exchanger are caked with deposits, and excessive water is injected into the shell side, all of which affect heat exchange. What is the temperature coming out from your system?

The main reactor outlet temperature is around 340. Previously, we used continuous water injection, and there was no such problem; increasing the amount of water injected or stopping the injection did not yield good results. Could it be that the pre-reactor inlet temperature is too low, resulting in a small temperature difference and incomplete hydrogenation of the unsaturated olefins? Is the presence of unsaturated olefins in the main counter-current shell side a concern?

Please have an expert analyze the impact of continuous blockage in the tube side of the evaporator (due to self-polymerization of unsaturated hydrocarbons) on the pressure difference on the shell side, using the Uhde, K.K. method. It would be best to explain it in detail. Thank you

Around 340°C for the main outlet temperature is quite high. Our situation is the opposite of yours; in our case, the temperature of the hydrogenation oil rises. But it’s likely due to a blockage in the pre-evaporator. Solution: Clean the pre-evaporator, as well as the reboilers in the multi-stage evaporator, and increase the heat load of the tubular furnace at the same time.

The heat exchanger needs to be cleaned and repaired, or there may be a problem with the design of the heat exchanger itself.

The scenario you described is highly unlikely. If there are still unsaturated olefins at the main reactor outlet, then your thiophene has not reacted completely. In such a case, it is possible to test the total sulfur and thiophene content in the hydrogenation oil within the stabilizer tower. Additionally, it is possible to check for the presence of thiophene and the bromine value at the main reactor outlet, in order to determine whether the reaction has been completed

If the increase in the shell-side pressure difference is caused by salt deposition, I wonder if you monitor the total chlorine content in the crude benzene feedstock? The crystallization point of ammonium chloride is higher than that of ammonium hydrosulfide, and it is related to its concentration in the recycle gas! To what extent should I check for pipe blockage? Personally, I don’t think there’s any direct connection! Has the water injection point changed? Have you checked the on-site pressure difference? You can go to the site to see exactly where the pressure difference occurs, and then adjust the water injection location accordingly

Based on what the original poster has said, I personally think it might be a problem with the raw materials; it’s very likely that the levels of sulfur, nitrogen, and chlorine in them are abnormal. This causes the reaction products after hydrogenation to form salts rapidly at the appropriate low temperature during the cooling process, resulting in high pressure differences and a significant reduction in heat exchange efficiency, which in turn leads to a lower temperature at the inlet of the pre-reactor； Solution: First, monitor the source where the raw materials are cut off, and then identify the location to increase the water supply volume (it is possible to use both pumps at their maximum capacity) ； Additionally, the blockage in the tube side should have little impact on the pressure difference across the shell side; the issue of insufficient pre-reaction before the main reaction, along with the possibility of hydrogen addition, is also not too serious ； The above are purely personal opinions; I hope they can be helpful to you!