Job application due to abnormal pressure fluctuations in the heavy aromatic hydrocarbons reflux tank

Thread Content

My unit is a disproportionation unit; the top product of the heavy aromatic hydrocarbons column is C9+, which serves as the reaction feedstock. The vapor at the top of the tower splits into three streams; one of these streams goes directly to the top of the reflux tank, where a pressure difference control valve is used to regulate the opening degree based on the set pressure difference. One path supplies heat to the benzene tower, while the other path controls the steam generation in the steam drum; the materials from the benzene tower and the steam drum return to the bottom of the reflux tank. It was recently observed that the pressure in the reflux tank dropped from 0.1 MPa to 0.06 MPa within a few minutes. The pressure difference control valve ranges from 0.12 to 0.16, with the valve opening degree between 40% and 70%; the temperature of the return tank varies from 175°C to 189°C, and as a result the opening degree of the pressure control valve fluctuates (even increasing?) ), the steam volume in the drum also fluctuates, and the temperature of the outlet oil circuit decreases slightly. The opening degree of the key pressure difference valve was set at 40% to 70%, yet the pressure in the return tank failed to increase; sometimes it could be maintained at 0.06 MPa, with the pressure difference control valve open at 70% and the temperature in the return tank at 189°C for several days. In such cases, the opening degree of the pressure control valve would increase, or sometimes it would remain unchanged. Then, after remaining at that level for a while, the pressure in the tank rises suddenly and returns to normal, with all other parameters also returning to normal; this represents intermittent fluctuations. It is certain at present that the pressure in the heavy aromatic hydrocarbons tower remains relatively stable, the liquid level in the reflux tank fluctuates little, there are no fluctuations in the benzene tower, and there is no temperature in the vent line of the reflux tank or in the downstream side of the safety valve. Upon on-site verification of the valve positions and their fluctuations, it was found that all the differential pressure control valves function properly. The pressure sampling points on the high and low sides of the differential pressure control valve are separate from those for the pressure in the return tank. At the same time, it is suspected that the pressure in the return tank has indeed dropped. I would be extremely grateful if experts and seasoned professionals could help analyze the possible causes. Question: What could cause a sudden drop (or rise) in the pressure of the reflux tank? Could gas blockage in the drum be the reason? Or is there a leak in the reflux tank at 0.1 MPa? There is no leakage at 0.06 MPa, and a liquid seal is formed in the pipeline. Is it possible for there to be an obstruction downstream of the steam drum?