Key operating points of the wet flue gas desulfurization system

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The adequacy of desulfurization is primarily reflected in the level of desulfurization efficiency, which in turn depends on the process conditions used for desulfurization. Therefore, the selection of desulfurization operating conditions is primarily aimed at controlling the optimal process conditions during production. (1) Regularly adjust the total alkalinity in the solution, and check that various components such as 888 are within the specified range. (2) Adjust the solution circulation rate appropriately according to changes in load. (3) Enhance oxidative regeneration by ensuring the residence time of the rich liquid in the spray regeneration tank to achieve the purpose of regeneration. 1. Solution components: The solution components are a prerequisite for determining the efficiency of desulfurization. Timely and appropriate replenishment of the raw materials consumed in the desulfurization process, based on the process parameters and analysis data, is a fundamental requirement to ensure the proper operation of the desulfurization process. 2. Regenerated air volume: Under normal conditions, the liquid-to-gas ratio is 1:2–1:4. If the amount of gas is too high, sodium thiosulfate will be oxidized to sodium sulfate ； The volume flow rate is too low, regeneration is incomplete, and too little elemental sulfur is precipitated. The amount of regenerative air can be adjusted by changing the number of injectors. 3. Solution circulation rate: Under normal conditions, the flow rates of the desulfurization pump and the regeneration pump should be balanced. When the gas load on the system increases or the hydrogen sulfide concentration rises, and provided that all components of the solution are within appropriate ranges, the solution circulation rate should be increased appropriately to maintain the gas-liquid ratio and the spraying density inside the desulfurization tower, thereby meeting the production requirements. At the same time, the sulfur precipitation time of the solution in the desulfurization tower and the oxidation time in the regeneration tank should be taken into account (in other words, the circulation rate must ensure a relative balance between the absorbent solution and the regenerated solution). 4. pH value of the solution: Since H2S is an acidic gas, the desulfurization solution must maintain a certain pH value. It is generally kept between 8.5 and 9.5; a too low pH value hinders the absorption of H2S as well as the oxidation of the desulfurization solution, resulting in poor solution regeneration. However, if the pH value is too high, side reactions will accelerate, the formation of by-products will increase, which affects the speed of sulfur precipitation, results in poor sulfur recovery, and increases alkali consumption. The pH level depends mainly on the total alkalinity and the content of sodium carbonate; the pH can be adjusted by modifying these values. 5. Potential value: Whether it is the tannin method or the 888 method for desulfurization, both sulfur precipitation and regeneration involve redox processes. The desulfurization solution is a mixed solution composed of various substances with redox properties, and it has a certain electrode potential; this potential value can effectively reflect the conditions of the desulfurization process. A low potential value indicates poor oxidative regeneration of the solution as well as unsuitable components in it; the levels of HS- and V+4 in the solution are high ； A high potential value indicates thorough oxidative regeneration of the solution, with relatively high dissolved oxygen levels of V+5 in it. However, the potential of the depleted solution after regeneration should not be too high; an excessively high potential, along with an increase in the V+5/V+4 ratio, inevitably leads to an increase in side reactions, particularly an increase in SO42-. Therefore, by measuring the potential value of the solution, it is possible to accurately, simply, and quickly determine the quality of the system’s absorption and regeneration. The typical potential value is maintained between -180V and -220V. 6. Absorption temperature: When it is between 15–30°C, temperature has little impact on absorption and regeneration ； When the temperature is above 30°C, the rate of H2S absorption increases, which in turn accelerates the precipitation of sulfur; however, at excessively high temperatures, the side reaction leading to the formation of NaS2O3 intensifies ； At too low temperatures, the sulfur capacity is too small, resulting in incomplete reactions, low desulfurization efficiency, and an impact on water balance. Under normal conditions, the temperature should be controlled at 38-42°C. When the temperature is high, contact the control room staff to reduce the gas temperature ； When the temperature is low, the solution can be heated using the heat transfer oil in the chemical dosing tank, or the gas temperature can be adjusted. 7. Side reactions: During the desulfurization process, it is inevitable that some side products are generated. If the concentration of these side products reaches a certain level, it can affect normal production. Therefore, it is necessary to strictly adhere to the process parameters, improve the management of the solution, and maintain stable operation of the process. Analysis should be conducted on the waste liquid before it can be recycled; only if it does not exceed the specified limits can it be reused, ensuring that the concentration of side products in the system’s solution remains stable and within acceptable limits. 8. Level of suspended sulfur content: During the regeneration of the desulfurization solution, the level of suspended sulfur content determines the amount of sulfur that is floated during regeneration as well as the size of the elemental sulfur particles formed, thereby affecting the production process as a whole. Suspended sulfur reflects the production status and changes in solution regeneration and sulfur recovery. Excess sulfur suspended in the solution, if not separated and recovered in a timely manner, will lead to a decrease in desulfurization efficiency, blockages in the desulfurization system, and the accumulation of sulfur on the inner walls of the pipes. If scaling on the pump body and impeller is severe, it will increase power consumption and reduce the flow rate. A low level of suspended sulfur indicates good solution activity, which leads to an effective desulfurization effect; it is also possible that sulfur precipitates rapidly, resulting in fine sulfur particles that cannot be filtered out. At high potentials, sulfate ions are likely to form, accelerating the rate of corrosion. 9. Liquid level and solution volume (1) Closely monitor changes in various areas, especially the liquid level in the lean liquid tank ； It is essential to maintain a normal liquid level and make adjustments in a timely manner. (2) Pay attention to the overall changes in the system solution, and correctly determine whether the amount of treatment solution is increasing or decreasing.