Regarding the foaming problem in a packed tower after adding acid

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The new equipment in the chlorine plant includes a primary packed tower, a secondary packed tower, and a bubble column. After the concentrated sulfuric acid was added for the first time, the liquid level reached the overflow level of each tower. However, when the pump was started, it seemed to contain air inside, resulting in surging behavior. The outlet valve was set to a very low position, around 10%, yet surging still occurred occasionally, and the outlet pressure gauge fluctuated. By opening the manhole at the top of the tower to inspect the distributor, it was found that the amount of acid fed in and the pressure were not ideal, but the nozzles of the distribution tube were not blocked and the distribution was even. The distributor is the type with holes in the spray pipe, not a distribution trough. Moreover, the acid shown in the overflow sight glass contains a large amount of foam; it’s not clear how this happens, as the acid concentration, as measured by testing, is around 98. (Actually, after the acid treatment was completed, the pump operated well for three days without any abnormalities, but this issue arose in the following days.) 1. The original design included a Y-type filter at the pump inlet, but it was removed as it was not suitable. The possibility of air leakage in the pump inlet pipeline has been ruled out, and the liquid level in the tower, at around 1.5M, has been confirmed to be the actual level. 2. The inlet pipe of the stuffing pump has a diameter of DN250, while the outlet pipe has a diameter of DN200. Pump model: IHF-125-80-160. Flow rate: 176.63 m3/h; head: 30.3 M; rotation speed: 2900 r/min. Problems: Uneven feeding by the stuffing pump, accompanied by surging phenomena; fluctuations in the outlet pressure gauge; the acid flowing to the first stage of overflow contains foam. These issues do not occur with the bubble column circulation pump, which operates normally. I wonder, fellow teachers, have you never encountered a situation like this either? How should it be handled to ensure normal feeding by the pump? As for how foam is formed? What are the ingredients? I hope the teachers can help answer this; I would be very grateful for your advice. I will certainly reward you generously once it is resolved.