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The main sources of chloride ions in the desulfurization system consist of two parts: process water and flue gas. The first source is the process water used in the desulfurization system, which is usually ordinary industrial water containing a certain amount of chloride ions. If the chlorine ion content in this water is already high, it further increases the chloride ion level in the desulfurization system ； The second source is flue gas; the HCl gas present in the flue gas, along with the chlorides in the dust, cause a significant amount of chlorides to enter the slurry when the flue gas undergoes desulfurization. Upon dissolution, these chlorides yield chloride ions. Even the sources of these two types of Cl ions are not sufficient to reach the 20,000 ppm limit; sometimes the chlorine concentration can reach as high as 40,000 ppm or even higher. This is mainly due to the recycling of wastewater, which keeps chloride ions in the solution, allowing them to accumulate over time and result in such high concentrations. I. Hazards of high chloride ion levels 1. An excessive amount of chloride ions in the slurry of the absorption tower can cause severe corrosion in the pipes, towers, and equipment that come into contact with this slurry within the desulfurization system. This leads to serious corrosion of devices such as the slurry circulation pumps and agitators, thereby reducing their service life. 2. In the slurry of the wet flue gas desulfurization system, chlorides mostly exist in the form of calcium chloride. An increase in calcium ion concentration, under the effect of the common-ion effect, inhibits the dissolution of limestone. This, in turn, affects both the physical and chemical absorption of SO2, hindering the smooth progress of the desulfurization reaction and resulting in a decrease in desulfurization efficiency. Furthermore, in order to compensate for the decline in desulfurization efficiency, it is necessary to increase the supply of limestone slurry, which leads to an increase in the residual limestone content in the absorber slurry, an increase in impurities, a sharp decline in the dewatering performance of gypsum, and poor quality of the gypsum after dewatering. At the same time, as the chlorine content in the slurry in the absorption tower increases, the properties of the slurry may change; a large number of bubbles will form in the slurry within the tower, leading to overflow in the absorption tower and the creation of an artificial liquid level. This interferes with the operators’ ability to make judgments and make adjustments, can cause cavitation or tripping of the slurry circulation pump, and may even result in the slurry entering the main flue. Furthermore, due to the strong coordination ability of chloride ions, at high concentrations they rapidly coordinate with metal ions such as Al, Fe, and Zn present in the dust to form complexes, which encapsulate the Ca or CaCO3 particles and significantly reduce their chemical activity. This leads to a decrease in the efficiency of using the slurry, ultimately resulting in an excess of CaCO3 in the absorber slurry; yet the pH value does not increase, thereby reducing the desulfurization efficiency. If the liquid-to-gas ratio needs to be increased to ensure desulfurization efficiency and meet emission standards, it will result in higher electricity consumption for the slurry circulation system. It affects the quality of gypsum. An increase in the chloride concentration in the slurry of the absorption tower inhibits the dissolution of sulfur dioxide to produce bisulfite, leading to an increase in the calcium carbonate content and chloride content in the gypsum. This reduces the dehydrating capacity of the gypsum and deteriorates its quality. To obtain gypsum of higher quality, it is necessary to significantly increase the amount of water used for flushing, which creates a vicious cycle in the entire system; as a result, the chloride ion content in the desulfurization wastewater increases greatly, making wastewater treatment more difficult. II. Measures Among the various factors affecting chloride ions entering and leaving the absorption tower, increasing the wastewater discharge volume and thereby raising the amount of chloride ions carried away by the absorption tower is the main method for reducing the chloride ion concentration in it. Reduce the amount of water used for gypsum flushing, strictly control the chloride content in the gypsum to keep it within a reasonable range, and increase the amount of chlorine removed during the dehydration process ； Regularly monitor the chloride content in the absorbent tower slurry, and strictly keep the chloride level in this slurry below 10,000 mg/L; the chloride content in the gypsum slurry should also be kept below 10,000 mg/L. If an increase in chloride levels is detected, it is necessary to increase the amount of wastewater discharged and to dehydrate the gypsum slurry, thereby replacing it with fresh gypsum slurry ； Operate the desulfurization wastewater treatment system to ensure that the desulfurization wastewater is discharged in sufficient quantities and in compliance with standards. At the same time, enhanced maintenance of the filtrate pump and filtrate pipelines should be carried out to prevent failures, which is also an important means of reducing the harm caused by chloride ions. A failure in the filtrate pump, along with pipe ruptures, can result in an inability to discharge wastewater for extended periods, causing the chloride ion concentration in the slurry in the absorption tower to soar.