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0 Introduction As is known, the volume percentage of CO2 in shift gas is generally between 25-30%, while in semi-water gas it is between 6-8%. The CO2 content in shift gas is much higher than that in semi-water gas. CO2 is an acidic gas; when sodium carbonate solution absorbs CO2, sodium bicarbonate is formed. The higher the CO2 content, the greater the amount of sodium bicarbonate produced. In the case of desulfurization using shifted gas, due to the high concentration of sodium bicarbonate in the desulfurization solution, on one hand, this not only lowers the pH value of the solution but also reduces the mass transfer coefficient of H2S within the tower, resulting in a decrease in desulfurization efficiency. Additionally, it increases the consumption of soda ash and catalysts, thereby keeping the desulfurization costs high. On the other hand, a high content of sodium bicarbonate in the solution increases its viscosity. As the temperature drops, sodium bicarbonate crystallizes and adheres to the filler along with sulfur paste; when this accumulation reaches a certain level, it blocks the tower, forcing a shutdown for cleaning, which results in significant economic losses for the enterprise. In recent years, with the adoption of new gasification technologies and adjustments to enterprises’ production capacity structures, the levels of carbon dioxide and hydrogen sulfide in pressurized feed gas have been increasing. The volume percentage of carbon dioxide in the feed gas is as high as around 45%, while the hydrogen sulfide content is over 3 g/Nm3. The impact of high-concentration carbon dioxide feed gas on wet flue gas desulfurization systems is becoming increasingly prominent. Below, the author will briefly illustrate, based on a typical case, the impact of high concentrations of carbon dioxide in the pressurized feed gas on the desulfurization system and the corresponding treatment measures. 1 The problem arose in June 2015, when our company designed a wet desulfurization unit for pressurized feed gas at a chemical manufacturing enterprise in Zhejiang. The main process parameters are as follows: the flow rate of the shifted gas is 22,000 NM3/h, the pressure of the shifted gas is 1.10 MPa; the H2S content in the shifted gas can reach up to 3.5 g/m3, while the volume percentage of CO2 is 44%. It is required that the H2S level after desulfurization be ≤ 20 mg/m3. For the aforementioned operating conditions, our company has adopted a two-stage desulfurization process in the design of the variable-pressure desulfurization tower, which combines a spray air tower with a series-connected composite mass-transfer desulfurization tower, in order to meet the requirements regarding hydrogen sulfide levels after desulfurization. Main configuration of the desulfurization absorption equipment: one Φ2800 spray air tower in series with one Φ2800 new type composite mass transfer desulfurization tower. The spray empty tower structure features four layers of DSP-type high-efficiency atomization nozzles inside the tower, with a designed desulfurization liquid circulation rate of 250 NM3/h ； The structure of the composite mass transfer desulfurization tower is as follows: three sections of Dg50 polypropylene bulk packing, each 5 meters high, are installed in the upper part of the tower, with three layers of liquid redistributors placed between each section. Three layers of QYD high-efficiency mass transfer internals are installed in the middle and lower sections of the tower, with a designed desulfurization liquid circulation rate of 300 m3/h. Among them, the desulfurization efficiency of the spray empty tower is over 60%, and it can effectively reduce the likelihood of tower blockage, ensuring the long-term stable operation of the system. Brief description of the process flow: In the gas phase, the shift gas passes through the water separator at the system inlet to remove any liquid water contained in the gas, after which it enters the lower part of the spray desulfurization tower. Inside the tower, the gas flows from bottom to top and comes into countercurrent contact with the atomized desulfurization liquid sprayed from the upper spraying section. Over 60% of the H2S in the gas is removed, and it is led from the top of the tower to the lower part of the composite mass transfer desulfurization tower. After the gas passes through the three layers in the tower from bottom to top, it has its hydrogen sulfide absorbed by composite mass transfer devices based on QYD internals. It moves upward to the third packing section to continue the absorption reaction of hydrogen sulfide, and is finally drawn out from the top of the desulfurization tower. After two stages of desulfurization, the vast majority of H2S in the gas, along with 20%-50% of the organic sulfur, is absorbed by the desulfurization liquid; the purified gas then proceeds to subsequent processing steps. Liquid phase: The rich liquid drawn from the bottoms of the two desulfurization towers enters the flash tank after being depressurized. The desulfurized rich liquid releases most of the CO2 dissolved during the absorption process in the flash tank; it then enters the regenerator ejector under residual pressure (0.4–0.5 MPa). As the rich liquid passes rapidly through the ejector nozzle, a negative pressure is created in its suction chamber, which automatically draws in air. The rich liquid and air then flow together through the throat and diffuser, are discharged through the tail pipe, and flow upward from the bottom of the regeneration tank. At this time, the suspended sulfur particles in the rich liquid are floated by air to form sulfur bubbles that drift at the top of the regeneration tank. After separation from the sulfur foam, the clear liquid flows into the lean liquid tank via a level regulator. It is sent to the two desulfurization towers separately by the lean liquid pump. The sulfur foam separated from the upper part of the regeneration tank flows into the foam tank and is pumped to the filter via a foam pump. The filtrate is returned directly to the system for use, while the sulfur sludge obtained through filtration is sent to a sulfur melting vessel where it is processed into sulfur for sale. The desulfurization solution required for driving the equipment and the supplementary soft water are prepared in the alkali mixing tank. The 888 catalyst is continuously dripped into the system through the lean solvent pipe at the inlet of the lean solvent tank, as per supplementary requirements. The desulfurization unit was put into operation in mid-November of the same year; our company dispatched engineers to the site to provide guidance during the startup. When the gas flow rate reached the production load of 18,000 NM3/h, it was found that the pressure drop in the composite mass transfer desulfurization tower was too high, at 80–110 KP, and liquid carryover in the gas exiting the tower was severe. Measures such as reducing the circulation volume, adjusting the composition of the desulfurization solution, and decreasing production volume did not yield significant results, and ultimately the plant had to be shut down urgently. 2 Problem Analysis: After the problem occurred, the project owner’s management attached great importance to it and promptly organized relevant personnel to hold a special meeting to analyze and discuss the issue of liquid presence in the desulfurization tower. After discussion and analysis by the participants, the main reasons for the liquid leakage problem are as follows. 1) This shift gas not only has a high hydrogen sulfide content but also a relatively high carbon dioxide content, which is uncommon in the fertilizer production industry; the focus of the problem lies in the high concentration of carbon dioxide in the shift gas. 2) Carbon dioxide itself is a foaming agent. Especially under pressurized conditions, the high concentrations of carbon dioxide and hydrogen sulfide in the converted gas cause an increase in the viscosity of the desulfurization fluid during its absorption process, leading to more intense foaming within the desulfurization tower. 3) Excessive foaming of the solution inside the tower hinders the downward flow of liquid in the liquid redistributors between the packing sections, resulting in liquid accumulation. 4) The liquid retention inside the tower leads to an increase in the pressure difference across the tower; coupled with the high viscosity of the desulfurization fluid, this results in an increase in bubbles. When the pressure difference across the tower exceeds 80 KPa, the desulfurization liquid is carried out along with the gas exiting the tower into the gas-liquid separator. 3 Once the root cause of the liquid accumulation issue in the desulfurization tower was identified, a solution plan was promptly developed together with the client, as follows: (1) Remove the liquid redistributors located between the three packing sections inside the tower and discontinue using them. To address the liquid retention issue caused by severe foaming of the solution inside the tower and poor flow of the liquid beneath the filler. (2) Due to the high concentration of carbon dioxide and the presence of hydrogen sulfide in the transformed gas under pressurized conditions, which result in increased solution viscosity and high foaming tendency, a certain amount of vegetable oil can be added to eliminate foam. The optimal amount of vegetable oil to add needs to be determined through experimentation during the production process. Oils have an antifoaming effect, but if added in excessive amounts, it will make it difficult for sulfur foam to form in the regeneration tank, thereby affecting the regeneration process. 4 After processing according to the formulated plan, production verification showed that good results were achieved. The reformer gas flow rate is around 22,000 Nm3/h, the pressure of the reformer gas is 1.10 MPa, and the H2S concentration in the reformer gas is 3.5 g/m3, with a maximum of 4.5 g/m3. After desulfurization, H2S remains consistently between 5 and 8.5 mg/Nm3. The circulation rate of the desulfurization liquid is 280–300 m³/h. Moreover, the φ2800 spray air tower has not yet been put into operation due to issues with the desulfurization pump. The amount of vegetable oil to be added has been determined through production experience; 5–10 ml per day is sufficient to keep the tower pressure difference within normal ranges. 5 Experience and measures: Through this typical example of desulfurization production, it is evident that for wet desulfurization units processing feed gases with relatively high concentrations of carbon dioxide and hydrogen sulfide, the higher the concentration of carbon dioxide, the greater its impact on the desulfurization system. In particular, the tendency of carbon dioxide to form bubbles due to its chemical reaction with alkaline solutions must be given serious attention during the design and production of desulfurization systems. On the one hand, effective measures are taken to suppress the formation of sodium bicarbonate resulting from the absorption of carbon dioxide in the feed gas by the alkaline solution. On the other hand, the effect of solution foaming on the regeneration efficiency of desulfurized rich liquor should be considered. For the design of wet desulfurization processes for feed gases with high concentrations of carbon dioxide and hydrogen sulfide, we have adopted the following measures: 1) Desulfurization absorption unit: The selection of the diameter and height of the desulfurization tower involves key parameters such as the empty-tower gas velocity, spray point density, and liquid-to-gas ratio. Based on the composition of the raw gas provided by the customer, process parameters, and other relevant information, along with engineering design experience data, we select the appropriate specifications for the desulfurization tower taking local conditions into account. For the design of the desulfurization tower structure, a packing-free mass transfer technology is employed – the new QYDIM high-efficiency mass transfer internals – to replace the packing inside the tower. This mass transfer internals are generally designed with three to four layers inside the tower. It makes full use of the reaction principle of absorption by H2S and alkaline solutions; depending on the levels of CO2 and H2S in the feed gas, it employs special gas-liquid contact devices and bubble redistribution mechanisms to ensure dynamic contact and turbulent mass transfer between the gas and liquid. It not only **increases the gas-liquid contact area, but also allows the gas to mix thoroughly with the alkaline solution in a very short time, thereby improving the desulfurization efficiency. Due to the reduced gas-liquid contact time, the impact of CO2 in the feed gas on the absorption by the alkaline solution was significantly diminished; the formation rate of NaHCO3 in the solution decreased to varying degrees, thereby enhancing the cyclic absorption capacity of the alkaline solution. Desulfurization towers that utilize filler-free mass transfer technology can adapt well to conditions with high sulfur and carbon dioxide content in the feed gas, as well as to pressurized operating conditions. Compared with traditional packed towers, the new QYDIM filler-free mass transfer internals desulfurization tower offers advantages such as stable pressure drop, no tower clogging, high sulfur capacity, and low overall consumption. 2) Desulfurization rich liquid regeneration unit: The regeneration of the desulfurization rich liquid is carried out using the mature spray oxidation regeneration technology in the industry. The oxidation regeneration tank not only performs the task of oxidizing and regenerating the desulfurization rich liquid and catalysts, but also serves to strip out some of the CO2 from the solution through gas lift and to float and separate sulfur bubbles. The ejector in the regeneration tank uses the PSC type air-self-priming ejector designed and manufactured by our company. The jet oxidation regeneration technology offers advantages such as high oxidation regeneration efficiency, good sulfur foam flotation, and low suspended sulfur in the solution, making it particularly suitable for use in conjunction with the 888 catalyst. 3) Sulfur recovery unit: Intermittent sulfur melting technology is employed. To reduce the interference of sulfur melting residue on the solution regeneration process, the sulfur foam floated in the regeneration tank is allowed to settle in a high-level tank before being fed into a specialized filter for sulfur foam; the filtrate is then returned directly to the system for use, while the filtered sulfur paste is sent directly to the sulfur melting vessel where it is processed into sulfur for sale. 6 Conclusion Wet flue gas desulfurization is itself a systematic project, and the absorption, regeneration, and sulfur recovery processes are three essential components of such a system. Any problem in any part will affect the stable operation of the entire system. 30% is skill, 70% is management. For the production management of wet flue gas desulfurization systems, effective process operation procedures are necessary to standardize the operations ； Strong process and equipment management measures are also needed to enhance oversight. Only in this way can the long-term stable operation of the desulfurization system be ensured.