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Among the various unit operations in ammonia synthesis production, the process that is probably the simplest is the desulfurization system. However, in actual production, desulfurization is precisely the process where the most problems occur. As an experienced chemical engineering expert said when evaluating desulfurization catalysts, every proper desulfurization catalyst can effectively solve the desulfurization problem; however, there are not many manufacturers that actually use such catalysts well. This is determined by the complexity and variability of the desulfurization system. For over two decades, the author has been engaged in the production and technical management of desulfurization systems. In recent years, due to work-related responsibilities, I have had more exposure to the desulfurization units in ammonia synthesis plants. Below are some of the common problems that occur in these desulfurization units; I welcome feedback from colleagues if there are any inaccuracies. I. Guiding sulfur control in the entire ammonia synthesis process using systems engineering principles: In ammonia synthesis, due to differences in the process flows – such as those with and without methanol incorporation, as well as variations in the shift reaction type ranging from full low-temperature shift to medium-low-temperature shift – the requirements regarding H2S also vary. Therefore, it is necessary to take into account the specific manufacturing process of the enterprise as a whole in order to establish reasonable H2S targets. The author believes that, regardless of the process used, the general principle and guiding concept should be to minimize the control parameters for semi-water gas desulfurization and shift gas desulfurization, as long as it is possible to ensure the requirements of the shift catalyst. The minimum H2S concentration required for low-temperature catalysts is a fixed value at a certain reaction temperature and a certain gas-to-vapor ratio; its level mainly depends on the other two factors. After the reduction in variability, sulfur has only adverse effects and no benefits on ammonia synthesis production. Therefore, by setting a lower limit for the H2S level after the desulfurization of semi-water gas while meeting the requirements for low-variation catalysts, it is possible to more effectively reduce the pressure associated with desulfurization in subsequent processes, thereby making production easier to control. However, in reality, many plants fail to do this. In particular, in some plants, when there is a slight issue with the low-temperature catalyst, instead of conducting a thorough analysis of the causes of the problem and focusing on reducing steam consumption or adjusting temperatures, they blindly increase the inlet H2S levels. The author encountered such a company in Anhui; since it employed a fully low-temperature conversion process, the company believed that the higher the imported H2S concentration, the better. Guided by this principle, the semi-water gas desulfurization unit in this plant was shut down for a long time; the gas exiting the shift reactor was routed in two ways: one stream went directly to pressure swing adsorption for carbon removal, while the other stream passed through a shift gas desulfurization tower to have its carbon removed. The two streams of gas pass through activated carbon desulfurization tanks respectively before converging back to the third inlet of the compressor. In the semi-water gas produced by this plant, the H2S concentration is generally between 500–700 mg/m3. Moreover, the desulfurization capacity of the shift reactor is limited, resulting in an H2S concentration that remains at around 200–300 mg/m3 even after desulfurization. This leads to a series of problems: the high H2S concentration in the gas obtained through pressure swing adsorption causes severe carbon corrosion ； The activated carbon desulfurization agent needs to be replaced frequently ； Due to sulfur poisoning, the methanol catalyst needs to be replaced every three months ； Synthetic catalysts also have a short lifespan due to sulfur poisoning. Later, on the author’s suggestion, it was decided to keep the desulfurization system operating continuously; after desulfurization, the H2S level was kept between 50–70 mg/m3. This approach not only met the sulfur requirements of the low-temperature catalyst but also minimized the load associated with desulfurizing the shift gas. Of course, to completely resolve the sulfur issue, the plant must fundamentally increase its capacity for desulfurizing the shift gas, ensuring that the H2S level after desulfurization remains below 10 mg/m3. Therefore, it is practically meaningful to consider the semi-desulfurization, modified desulfurization, precision desulfurization, and advanced desulfurization processes in ammonia synthesis production as a systematic project, so as to reasonably allocate and control the tasks and objectives at each stage. II. A complete desulfurization process is necessary. The production process for desulfurizing ammonia synthesis is relatively simple and constitutes a classic approach. Over the course of several decades of development, there has only been an increase in the specifications of the equipment, as well as some efforts made to improve dust removal and temperature control; no decisions were made regarding which core components to retain or discard. However, some factories do not pay enough attention to this issue and are too arbitrary. The author has seen in both Shanxi and Shandong some factories that, for various reasons, have removed the dust removal and cooling tower in front of the desulfurization tower, allowing the gas coming out of the Roots blower to enter the desulfurization tower directly. For example, in mid-July, a company in Shandong called to report abnormalities in the desulfurization of semi-water gas, with no sulfur foam appearing for several consecutive days. When the author arrived at the site, it was found that in this plant, the gas exiting the Roots blower went straight into the desulfurization tower without being dust removed or cooled first. At that time, actual measurements were taken, and the semi-water gas at the inlet of the desulfurization tower was above 70°C. Furthermore, the heat exchange area of the solution cooler in this plant is relatively small, and the temperature of the desulfurization liquid at the inlet of the desulfurization tower is high. At such high temperatures, the viscosity and surface tension of the desulfurization liquid decrease significantly, making it difficult for bubbles to form in the regeneration tank. Even if it forms, the adhesiveness of the bubble membrane is very poor; sulfur particles find it difficult to adhere to its surface, and the bubbles break easily once they reach the interface. On the other hand, an increase in temperature inevitably affects the polymerization and flotation of elemental sulfur. Moreover, high temperatures facilitate the formation of by-products salts and are unfavorable for the flotation of sulfur. So, it’s quite natural that there is no sulfur foam for a long time. There is also a factory in Hunan where the amount of residue in the sulfur melting vessels is high, at four to five times the normal level. Not only is the steam consumption too high, but it also affects the quality of the desulfurization solution. Upon investigation, the reason is also an issue with the process. The residual liquid after sulfur melting in the plant’s sulfur melting tank is not sent back to the regeneration tank after treatment, but rather is poured into the foam tank. In this way, not only does a portion of the residual liquid remain in circulation within the sulfur melting system, thereby increasing the load on the sulfur melting tank and leading to unnecessary high consumption of steam, but also, when the level of the sulfur foam mixture in the sulfur foam tank reaches a certain height, this mixture overflows automatically into the regeneration tank. This untreated mixture has a severe negative impact on the quality of the desulfurization solution. Later, changes were made to the process, and the operating conditions quickly returned to normal. Therefore, in the absence of solid theoretical basis and confidence, major changes to the process flow are generally not recommended; it is necessary to maintain a relatively complete desulfurization process flow. III. Emphasize investment in technological upgrades and utilize advanced and appropriate technologies. In actual production, it is common to find that some plants have no issues with the control of their desulfurization solution or with other operational aspects, yet their desulfurization performance still does not meet the required standards. This indicates serious defects in the equipment. For example, some factories expand their production scale, but fail to upgrade their desulfurization equipment in a timely manner, causing the desulfurization system to operate under overload ； Some equipment is outdated and in poor condition, failing to reach its rated capacity. Such phenomena are particularly common in small ammonia synthesis plants with a capacity of 40,000 to 50,000 tons. This problem must be solved through technological upgrades. When carrying out technical upgrades, it is necessary to give full consideration to the use of relatively advanced and suitable technologies. For the renovation of transformation gas desulfurization systems, using the QYD type gas-liquid mass transfer tower internals produced by Toyo Seiki Company, commonly known as filler-free desulfurization tower internals, is an excellent choice. The application of this device not only **improves gas purification efficiency and increases production capacity, but also fundamentally solves the problem of tower blockage in desulfurization towers. This internal component features a simple structure, easy installation, high operational flexibility, reduced tower resistance, low investment costs, and quick results. It is particularly suitable for the renovation of old desulfurization towers; after renovation, the production capacity of each such tower increases significantly (by 30-50%), and the purification efficiency is also effectively improved. If used in the design of new towers, investment costs can be reduced by 1/3 to 1/2. Recently, I have been working at our company specifically on the installation of internal components for fill-free degassing towers as well as on their commissioning. Through my experience in installing and commissioning such systems at various manufacturers, I have gained firsthand knowledge in this area. The main advantages of this technology are as follows: first, the desulfurization efficiency; in the renovation of old towers, the desulfurization efficiency of towers without packing internals is higher than that before the renovation. Second is the solution circulation volume, which has seen a significant reduction across various manufacturers, resulting in notable energy savings. Third is the renovation cost, which is one-third lower than that of a filler tower with equivalent capacity. Fourth, it is convenient for maintenance, saving a great deal of manpower, material resources, and valuable maintenance time. This has received particularly warm praise from managers of various application companies, workshop supervisors, and even ordinary workshop operators and maintenance workers. It can be said that obvious economic benefits have been achieved among all manufacturers that have applied the modified degassing tower technology. Moreover, it should be noted that the benefits are even more significant if this technology is used in the design of new devices. Because, if it is used in the design of a new entire unit, the nature of this internal component allows the height of the reactive distillation column to be reduced by one-third compared to that of a packed column. Additionally, the solution circulation rate in a reactive distillation column without packing can be significantly lower than in a packed column; as a result, the volume of the regeneration tank in the newly designed unit can be reduced accordingly, and the head requirement of the pumps does not need to be very high. Taken all together, the use of internal components for reactive distillation without packing in the design of new units offers even greater advantages. Regrettably, to date, although this internal component has been widely and successfully used in the renovation of old towers with excellent results, it has not yet been adopted by manufacturers designing new installations. Here, we also welcome all knowledgeable individuals to contact our company in a timely manner should they have such needs, so that this new technology can be applied more widely at an early stage and bring greater benefits to enterprises. IV. Emphasize daily management: With the same production scale, the same equipment, and the same catalysts, there are countless examples of dramatic differences in desulfurization efficiency. The reason is the difference in daily management. In this regard, many manufacturers have excellent experience that can serve as a reference for everyone. One can imagine that if all our factories paid as much attention to analytical work as Shandong Qilu First Chemical does, and consistently carried out comprehensive analyses of desulfurization fluids, using the analysis results to guide production ； To pay as much attention to the operation of the regeneration tank as the Anyang Fertilizer Factory in Henan does, to treat the regeneration tank as a separate position, and to monitor closely the conditions related to foam flotation, air volume, and overflow ； Be able to pay as much attention to material consumption as the Anhui Guoyang Fertilizer Factory does, and link material consumption to the economic benefits of the operators ； Be bold enough to be the first to adopt new technologies and processes such as filler-free shift towers and sulfur foam filters, just like the fertilizer factories in Ningyang and Pingdu in Shandong Province ； To place as much emphasis on sulfur melting as Huanong Fertilizer Factory in Hunan does, and to offer operators a certain percentage of reward based on the amount of sulfur melted ； If a comprehensive desulfurization data archive can be established, like that of the Feixi Fertilizer Factory in Anhui, so that there are records and guidelines to refer to in case of any problems, then the overall level of desulfurization will surely reach a new level. In short, in the ammonia synthesis production process, excessive H2S levels are not detected as sensitively and promptly as other parameters; for example, if the height of the gas holder falls below the specified level, the plant must be shut down immediately, otherwise the gas holder may become deformed ； If the levels of CO and CO2 are high, it is necessary to reduce the load promptly; otherwise, issues such as excessive synthesis gas formation may occur. When the H2S level is high, production is generally not affected immediately, especially in the case of slight excess levels over time; therefore, it is rare for any factory to shut down or reduce production right away due to elevated H2S levels. In fact, frequent H2S levels exceeding the limits is more like chronic poisoning, causing greater harm to production. Fortunately, within the industry today, especially thanks to the establishment and operation of the desulfurization technology collaboration network, as well as the annual desulfurization technology exchange meetings, more and more enterprises are recognizing the importance and complexity of desulfurization work. The author believes that, through the joint efforts of colleagues in the industry, the desulfurization of synthetic ammonia will become increasingly standardized and improved. The progress and development of desulfurization technologies will also ensure more stable and long-term operation in ammonia synthesis production.