Hazards of frothing in the absorption tower slurry and preventive measures

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1. Main hazards of slurry foaming in the absorber: False liquid level readings, leading to improper operations and overflow. The foam layer significantly interferes with the operation of level gauges, causing the actual liquid level to be much lower than the indicated value. To maintain the \"liquid level,\" operators may reduce the discharge of slurry or add excessive water. Once the foam breaks or collapses, the actual liquid level rises sharply, leading to massive overflow through overflow pipes, manholes, etc., which contaminates the area and corrodes the equipment foundations. Slurry overflow, contamination of flues, and corrosion-induced leakage of foam and slurry can enter the flue gas system (especially when there is no GGH or a low-leakage air system for the GGH), where they accumulate on the flues, damper doors, and even fan blades, causing severe corrosion, disruption of dynamic balance, difficulties in cleaning, and even damage to the fans. Desulfurization efficiency decreases; an excessively thick foam layer hinders gas-liquid contact, increasing mass transfer resistance. As a result, the SO₂ absorption efficiency drops, and the outlet SO₂ concentration may exceed the standard limits. At the same time, the foam blocks the spray coverage area, resulting in uneven gas-liquid distribution. When the demister becomes clogged and the pressure difference increases, foam can carry a large amount of gypsum crystals and slurry into the demister; it is difficult for the washing water to remove these substances completely. Over time, this leads to scaling and blockage in the demister, an increase in its pressure difference, and in severe cases, there is a risk of collapse. It also causes corrosion in the equipment downstream. The oxidation effect deteriorates, and the quality of gypsum declines. The foam layer reduces the effective distribution of oxidizing air, hindering the oxidation of calcium sulfite to calcium sulfate, which results in an increased amount of unoxidized CaSO3. This makes it difficult to dehydrate the gypsum, results in a high water content, reduces the purity of the gypsum, and lowers the utility value of the by-products. Cavitation and vibration of the circulation pump and agitator, as well as foam ingestion, can lead to cavitation in the circulation pump, insufficient output, and severe vibration; in serious cases, this may damage the impeller and mechanical seal. If the mixer draws in a large amount of foam, it will also cause vibration and bearing damage. Wastewater and the slurry that forms abnormal bubbles in the cyclone system contain a large amount of fine bubbles and suspended particles, which may clog the overflow pipe of the gypsum cyclone and reduce the efficiency of solid-liquid separation ； The solid content and COD in wastewater increase, thereby intensifying the burden on wastewater treatment. Safety hazards such as excessive leakage, sludge accumulation in flues, and dust sticking to fan blades can cause equipment damage or even unplanned shutdowns, posing a threat to stable production and personnel safety. II. Prevention and control measures for foaming in the absorber slurry: Strictly control the quality of water used for process makeup; avoid using industrial wastewater that contains oil, high COD levels, high hardness, or surfactants as makeup water. High-quality process water, such as deionized water, clean industrial water, or treated recycled wastewater, should be used, with regular monitoring of parameters such as organic matter and oils. To ensure the quality of limestone, it is necessary to use limestone with a high CaCO3 content, low MgO levels, low acid-insoluble substances, and low organic impurities. Check whether the limestone contains flotation reagents, oil, etc., and conduct tests if necessary. Controlling the flue gas conditions at the inlet improves the efficiency of the dust collector and reduces the dust concentration at the inlet of the absorption tower, particularly preventing unburned carbon, oil mist, heavy metals, and organic substances from entering along with the flue gas. If the upstream process discharges oily or organic components, pre-treatment is required to prevent direct impact. Optimize slurry operation parameters and control density through regular replacement: Maintain the slurry density within a reasonable range (typically 1080–1150 kg/m³), as too high a density can exacerbate foaming; gypsum should be removed promptly. Wastewater discharge: Wastewater is discharged continuously and in appropriate amounts, to remove substances that promote foaming such as concentrated Cl⁻, F⁻, organic matter, and fine particles. pH management: Maintain the pH between 5.2 and 5.8 to avoid sharp fluctuations; excessively high values can lead to an increase in fine crystals and more foam formation. Oxidizing air adjustment: Adjust the amount of oxidizing air appropriately based on the load and SO₂ concentration, to prevent excessive oxidation of air from causing an increase in the thickness of the foam layer. Use antifoam agents appropriately: when foaming tends to occur, an appropriate amount of specialized desulfurization antifoam agents (such as polyether and silicone-based ones) can be added. Care should be taken to determine the optimal dosing point and dosage through experiments, in order to avoid excessive defoamers from affecting mass transfer and dehydration, or even becoming a source of COD load. Strengthen the maintenance of level measurement instruments by using level gauges that are not affected by foam (such as radar level gauges) or by implementing multi-point redundant measurements. Regularly flush the pressure tapping pipes and calibrate the instruments, and set up alarms for changes in liquid level rate to detect false liquid levels in a timely manner. Washer flushing and internal inspection of the absorption tower: Ensure the pressure and flushing cycle of the demister washing water to prevent impurities carried by foam from adhering there for long periods. Regularly check the condition of the oxidation air ducts and agitators to prevent uneven gas distribution from causing intense bubbling in certain areas. To prevent the slurry from circulating at a low load for an extended period, even during periods of low-load operation or shutdown of the unit, it is necessary to maintain a certain level of circulation and oxidation, as well as intermittently discharge the slurry, so as to prevent its aging and the accumulation of organic matter. Monitor the trends in slurry composition by regularly analyzing parameters such as Cl⁻, F⁻, COD, and oils in the slurry; when the level of impurities rises abnormally, increase the wastewater discharge volume or investigate external sources of pollution. Precise operation and management protocols are used to control the start-up and shutdown processes, thereby preventing large fluctuations in liquid level. When putting the gypsum cyclone into use, pay attention to the stability of the overflow to prevent foam blockage. It was found that at the early stage of foam formation, measures such as promptly using defoamers, lowering the liquid level, and increasing slurry discharge should be taken to prevent the situation from worsening. Through the above comprehensive measures, foaming in the absorber slurry can be effectively suppressed, its hazards reduced, and the safe and efficient operation of the desulfurization system ensured.