The problem of desulfurization of coke oven gas

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Coke oven gas from coking plants contains hydrogen sulfide at levels of ≥4 g/m³; this substance corrodes equipment and pollutes the environment during production, and it also has a significant impact on subsequent processing steps. Therefore, hydrogen sulfide purification is a key process in enabling the recovery of valuable products from coking enterprises. Previously, coke oven gas was primarily treated using PDS catalysts together with ammonia or sodium carbonate as the alkaline source to remove hydrogen sulfide; this desulfurization process generated large amounts of by-products in the form of salts, requiring large quantities of desulfurization liquid to be discharged on a daily basis to maintain normal operations, which posed significant environmental challenges. As **environmental regulations become increasingly strict, desulfurization liquid is forced to be used in salt extraction or acid production facilities. However, whether it is salt extraction equipment or acid production equipment, these systems involve high capital costs, severe equipment corrosion, high operating expenses, high energy consumption, poor product quality, and difficulties in selling the products, all of which place significant environmental and economic pressures on enterprises. Under these circumstances, starting in 2018, domestic coking plants began to attempt to remove hydrogen sulfide using iron complexes in coke oven gas, in the hope of addressing the problem of large amounts of desulfurization liquid being discharged by employing iron complex desulfurization catalysts. According to incomplete statistics, over 100 coking plants across the country are currently using or have used chelated iron desulfurization catalysts from various manufacturers. During use, issues such as a decrease in desulfurization efficiency due to the instability of these catalysts, resulting in excessive hydrogen sulfide levels after desulfurization; the accumulation of various salts that block pipes, fillers, nozzles, heat exchangers, and sulfur melting reactors; sulfur clogging the fillers; the formation of weak sulfur foam; and equipment corrosion have arisen. Through follow-up statistical analysis, it was found that the main reasons for the aforementioned problems in the removal of hydrogen sulfide from coke oven gas using iron-based complexation catalysts are as follows: 1. Existing coke oven gas desulfurization units are all designed based on HPF desulfurization using PDS catalysts; they have poor compatibility with iron-based complexation catalysts, and many of the older units suffer from inherent limitations due to being underpowered for the tasks at hand. 2. The stability of complexed iron catalysts is the foundation for the long-term stable operation of the system. There are no unified standards or industry norms for such catalysts, and the formulations used by different manufacturers vary greatly in quality; as a result, many problems arose during the use of these catalysts in the purification of hydrogen sulfide from coker gas, causing significant impacts and losses to coking manufacturers and leading to negative consequences. 3. If the various material balances in the desulfurization system are not effectively controlled, it will lead to a loss of balance in the desulfurization process, which in turn affects the stability and activity of the catalysts. This results in a decrease in desulfurization efficiency as well as problems such as clogging of the packing. 4. The recycling and production of chemical products feature strong continuity, as well as numerous processes that are interrelated and influence one another. The same is true for hydrogen sulfide removal; sometimes problems arise in the desulfurization system, but these are not necessarily due to issues with the system itself, rather they result from failures in the preceding processes. Therefore, it is necessary to systematically consider various factors affecting the desulfurization process in order to ensure long-term stable operation. 5. The operational requirements for using complexed iron catalysts to remove hydrogen sulfide are quite precise; compared with PDS, there are significant differences in terms of operational concepts, adjustment strategies, process control, and process management. This imposes higher demands on the technical service personnel from catalyst manufacturers, on site managers, and on workshop operators. There are many manufacturers of chelated iron on the market; they only offer products made from chelated iron, but in reality these products do not actually contain true chelated iron. Their desulfurization efficiency is poor, and they can cause tower blockages and corrosion. Some manufacturers even add PDS catalysts to the chelated iron, which leads to various problems, and the desulfurization solution also turns green ； And there is no supporting technology. Currently, there are very few companies in China that offer chelated iron catalysts and desulfurization technologies. When making a choice, it is essential to be cautious and select a technical service provider with strong capabilities, experienced on-site technicians, and the ability to provide comprehensive services ranging from scheme design and equipment modification, to the research and development and upgrading of catalyst formulations, system commissioning, employee training, resolution of on-site issues, as well as follow-up maintenance during operation.