Seeking advice on tannin desulfurization

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The methanol desulfurization system uses an atmospheric-pressure fixed-bed gasifier, and the caustic gum method is employed for desulfurization. The desulfurization is working properly at present, but there is no foam layer in the regeneration tank and the suspended sulfur level is high. I would appreciate it if experts could provide a diagnosis. 1. The plant’s production capacity is 100,000 tons per year of methanol; the solution circulation rate is achieved through 1 desulfurization pump and 1 regeneration pump, with a pump flow rate of 792 M3/H, and the pumps operate at one-third of their full capacity. The desulfurization tower has a diameter of 4800; it features three layers of packing. The regeneration tanks have dimensions of φ8000/φ8800/φ9400×8000, while the circulation tank has dimensions of Φ5000×9000. The lean liquid tank has dimensions of Φ5000×6750. 2. Solution composition: pH value, total alkalinity, tannin, Na2CO3, NaHCO3, NaVO3, Na2S2O3, suspended sulfur, sulfates – in units of g/L: 8.45, 28.89, 2.36, 7.52, 33.88, 0.95, 1.67, 1.23, 26.32. 3. On-site details: The inlet pipe of the injector has a diameter of DN100; the throat section has a diameter of 30, and the expansion section has a diameter of 150. There are 8 sets of injectors in total, with a regeneration pressure of 0.49 MPa. The foam layer in the regeneration tank consists of only a single layer of weak foam; no sulfur foam is formed, so the pressure of the injector needs to be adjusted. Increasing the number of injectors does not result in a foam layer. During the adjustment process, a foam layer formed when the number of injectors was increased. After 2 hours, mechanical oil was added twice; 4 hours after those additions, the foam layer disappeared and more sulfur was produced, but subsequently the suspended sulfur level rose. Main problems: high suspended sulfur and no foam layer in the regeneration tank. What could be the causes?