HPF desulfurization method

Your introduction is a bit too simple. :handshake

Could the poster provide more detailed information, such as the tower diameter and the hydrogen sulfide content entering the tower, so that we can use it as a reference!

It’s too simple; at the very least, something should be said about how wastewater is treated

As is well known, the purification process for coke oven gas is commonly referred to as the recovery process, which involves recovering chemical substances such as tar, hydrogen sulfide, hydrogen cyanide, ammonia, benzene, and naphthalene during the gas treatment process. As people’s awareness of environmental protection grows, the purpose of gas treatment is to remove pollutants from the gas, which is why it is referred to as a gas purification process. Gas purification technology involves numerous chemical reactions (acid-base reactions, catalysis, cracking, oxidation, etc.) and physical processes (mass transfer, heat transfer, absorption, desorption, etc.). Therefore, the gas purification process is a relatively complex one. Over the years, gas purification technology has been continuously developing and improving. It can be said that there are still many problems unresolved in current gas purification technology. Some people say that gas purification technology is the core technology in coking technology, and I agree. With the introduction and development of desulfurization and decyanidation technologies for coke oven gas, new changes have taken place in the gas purification process, making it more complex. It can be said that different desulfurization processes result in different purification processes. Different purification processes determine different levels of purification, environmental protection, and technological advancement. Therefore, the selection of gas desulfurization and decyanidation processes is crucial for the integration of the coke oven gas purification process, and it holds special significance for the development of coking technology. 2 Analysis of the traditional purification process Over decades of practical production experience, a traditional process for gas purification has been developed. This process boasts advantages such as simplicity, ease of operation, stable performance, and low construction costs, and it has played an important role in coking production over the years. With the continuous advancement of coking technology, the following disadvantages of traditional processes have been identified. (1) The specified initial cooling assembly temperature is unreasonable; it is generally set at 36°C. Due to the high operating temperature in the primary cooling stage, tar and naphthalene in the gas cannot be recovered during this process; as a result, these substances move further down the production chain, causing severe contamination in subsequent stages, such as contamination of the acid tar systems and those used for removing and dissolving naphthalene. Therefore, the collection temperature must be reduced to as low a level as possible in order to significantly lower the dew point of naphthalene, allowing most or all of it to be recovered in the primary cooler and thus making the integration of the purification process more efficient. (2) The ammonia recovery process in traditional purification processes has had a tortuous development history. The concentrated ammonia water process failed repeatedly due to issues such as equipment corrosion, and ultimately ended in failure. For decades, bubble-type saturators have been used to recover ammonia. These devices offer advantages such as stable operation and high ammonia recovery rates, but they also have drawbacks including poor corrosion resistance, high resistance, and small ammonium sulfate particles, which have long posed challenges to the integration of gas purification processes. (3) In the traditional process, final cooling is carried out using direct cooling towers; a large amount of cooling water is forced to cool on cooling racks, resulting in significant amounts of pollutants being released into the atmosphere, making this area the most serious source of pollution in coking plants. (4) Most coking plants using traditional processes do not have desulfurization units, and hydrogen sulfide in the gas cannot be removed, which constitutes one of the biggest challenges in the gas purification process. Analysis of 3 Coke Oven Gas Desulfurization and Decyanidation Technologies 3.1 Review of Key Stages in the Development of Gas Desulfurization and Decyanidation Technologies (1) Post-process desulfurization stage. The so-called post-process refers to the situation where the desulfurization unit is located at the end of the process, that is, after the benzene removal tower. The typical desulfurization technologies at that time were the modified ADA method and the arsenic-alkali method, and due to the demand for city gas, independent coking plants commonly used these methods for desulfurization. (2) Phase of introducing Japanese desulfurization technology. During the construction of Baosteel, advanced TH method for desulfurization and decyanidation was introduced from Japan for the first time, serving as a model for the advancement of coal gas desulfurization technology in China. However, due to high investment costs and technical complexity, this desulfurization technology was not widely adopted across the country. (3) The promotion stage of the AS method for desulfurization and decyanidation. During this period, our country imported 12 AS-process desulfurization units from West Germany, with one unit installed at each large coking plant (except Ansteel and Baosteel). Years of practical production experience have shown that the AS desulfurization technology is not suitable for widespread adoption due to high investment costs and other factors. (4) Popularization stage of HPF ammonia desulfurization. According to incomplete statistics, hundreds of HPF systems (including PDS, ZL, etc.) have been installed in coking plants across China to date, and this trend is likely to continue. Despite some existing problems, this technology represents an achievement of China’s independent innovation, and it should be strongly supported, improved, and promoted. 3.2 Explanation of several desulfurization and decyanidation technologies. Looking at the desulfurization and decyanidation technologies available both domestically and internationally, the typical technologies currently used in China include the TH method (commonly known as wet oxidation), the FRC method (commonly known as catalytic oxidation), the HPF method (commonly known as catalytic ammonia oxidation), the AS method (commonly known as combined ammonia-sulfur washing), the SARFEBAN method (also known as the MEA method), the VACA method (also known as vacuum alkali method), and the improved ADA method. (1) TH method. This method uses ammonia in the gas as the base source and sodium 1,4-naphthoquinone disulfonate as a catalyst for an oxidation-based desulfurization and decyanation process. In the absorption tower, an ammonia-containing circulating desulfurization solution is used to absorb H2S and HCN from the gas, while in the regeneration tower, air is used for regeneration. The waste liquid is treated in a wet oxidation tower under high temperature and pressure, where (NH4)2S2O3 and NH4CNS in the waste liquid are converted into ammonium sulfate and sulfuric acid. The prominent advantage of this method is its efficient treatment of waste liquids, converting (NH4)2S2O3 and NH4CNS in these liquids into sulfur and sulfuric acid, thereby increasing the production of ammonium sulfate and reducing sulfuric acid consumption. Wastewater treatment must be carried out in oxidizers that can withstand high temperatures, high pressures, and strong corrosion (273°C, **MPa, made of zirconium material). Such equipment is expensive to produce and difficult to manufacture; it must be imported, which constitutes the biggest obstacle to the widespread use of the TH process for desulfurization and decyanidation. (2) FRC method. This method is also an oxidation-based desulfurization and decyanidation process that uses ammonia in gas as the base source and picric acid as a catalyst. In the absorption tower, ammonia-containing desulfurization liquid is used to absorb H2S and HCN from the gas; this liquid is regenerated in a regeneration tower using air, and part of the desulfurization liquid is sent to a centrifuge for the separation of sulfur. The filtrate and sulfur are sent to the acid production plant. In the FRC process, the efficient regeneration process using premixed nozzles results in a high desulfurization efficiency, with the H2S and HCN contents in the clean gas being below 100 mg/m3 respectively. However, since ammonia cannot be recovered in the regeneration process, there is significant loss of ammonia during the dry-contact acid production using waste liquid, which reduces the ammonia supply in the gas and affects the absorption efficiency for desulfurization. As a result, the process becomes longer, the investment required is higher, and it is not economically viable. (3) AS process for desulfurization and decyanidation. Similarly, using NH3 in gas as the base source, the rich liquid from the ammonia washing tower is employed to absorb H2S and HCN. To ensure the efficiency of NH3 absorption, the ammonia content in the rich ammonia circulation liquid cannot be too high; as a result, the desulfurization efficiency is low, and generally the levels of H2S and HCN after the tower can only be reduced to 500 mg/m3. This represents the fundamental technical issue of the combined ammonia-sulfur washing process. The desulfurized rich liquid is desorbed in an ammonia and acid removal tower; the ammonia and acidic gases released must be treated to remove ammonia and produce acid, which requires a large amount of corrosion-resistant materials and catalysts. The process is lengthy and not easy to implement effectively. (4) HPF method. This method is a desulfurization process developed through independent innovation in China. It also uses ammonia in coal gas as the alkaline source, but instead of washing and absorption processes for recovering the ammonia from the gas after desulfurization, a saturator method is employed. As a result, the ammonia content in the desulfurization solution can be increased to 3–4 g/L, thereby achieving high desulfurization efficiency. The levels of H2S and HCN in the gas after desulfurization can reach 10–20 mg/m3, which is considered the greatest technical advantage of this method. HPF is a composite catalyst that acts as a catalyst for both desulfurization and regeneration, simplifying the desulfurization and decyanidation processes. Desulfurization waste liquid can be reused in coal. Research has shown that (NH4)2S2O3 and NH4CNS in the waste liquid are mostly decomposed into gases and released before 360°C during the coking process, without altering the cohesiveness of the coal. Upon pyrolysis, NH4CNS turns into thiourea, whose molecule does not contain a CN group; as a result, HCN is not produced, but rather H2S and NH3 are formed. . . . . . In the HPF desulfurization process, the sulfur content in the sulfur paste or molten sulfur obtained through oxidation regeneration is low, making it difficult to apply this method industrially. Investigations have shown that by adjusting the operating procedures (initial cooling) and changing the production methods (pressure filtration, centrifugation), the sulfur content in the desulfurized product can be increased to 80%–90%, thereby enabling the practical use of such products. Reputable authorities are conducting research on using this sulfur product to produce sulfuric acid, thereby providing an acid source for ammonium sulfate production; this approach is fully in line with the principles of a circular economy and aims to improve HPF technology. (5) Desulfurization and decyanidation processes using the SARFEBAN method, VACA method, and modified ADA method. All three methods are post-process desulfurization processes, meaning that the desulfurization units are placed at the end of the gas purification process. They cannot use ammonia present in the gas as a base; instead, alkalis and desulfurizing agents must be purchased externally. Moreover, the desulfurization process cannot be integrated into the gas purification process. For this reason, these desulfurization methods are not advisable. It should be noted that the wastewater treatment and sulfur purification technologies for these desulfurization processes are not simple; rather, they are even more complex. By analyzing the desulfurization and decyanidation processes using the TH, FRC, AS, and HPF methods, it is easy to see that these four processes share the same principle, all relying on ammonia in the gas as the base. The desulfurization unit is located before ammonia removal. However, through a comparison of desulfurization efficiency, energy consumption, capital investment, and production costs, it is considered that the technical advantages of the HPF method for desulfurization and decyanidation are evident, making it a worthy recommendation. 4 Integration of the gas purification process (1) Considering the modifications to the traditional purification process and the selection of desulfurization and decyanidation processes, Gas Purification Process I is recommended as follows: primary cooler → electrostatic tar catcher → blower → intermediate cooler → desulfurization → benzene washing tower → indirect final cooling tower → spray saturator → gas heater. Process description: ① A horizontal tube cooler is used as the primary cooler, equipped with a light tar spraying system for naphthalene removal; it is cooled by low-temperature water to maintain an aggregate temperature of 22–23°C. This processing technique is closely related to the smooth progress of subsequent steps. ② To keep the desulfurization temperature below 32°C, a gas intermediate cooler must be installed in front of the desulfurization tower to ensure low-temperature absorption during desulfurization. ③ To increase the ammonia content in the desulfurization solution, ammonia gas from the ammonia distillation tower is added to the solution in order to improve the desulfurization efficiency. These are the technical advantages of the desulfurization and decyanation process for ammonia recovery using the semi-direct method. ④ Ammonia is recovered from the desulfurized gas in a spray saturator, ensuring a reduction in ammonia and nitrogen levels in the wastewater. ⑤ The final cooler uses an indirect cooler to prevent contamination by direct cooling water. ⑥ The unreasonable temperature gradient in Purification Process I is shown in Figure 1. After initial cooling, after the blower, after the intermediate cooler, after the desulfurization tower, after the gas heater, and after the saturator. Figure 1 shows the unreasonable temperature gradients in Gas Purification Process I. (2) To ensure a reasonable temperature gradient in the gas processing flow, Process II is recommended: initial cooler → electrostatic tar catcher → desulfurization tower → blower → gas heater → saturator → final cooler → debenzene tower. Explanation of Process II: Since the desulfurization unit is located before the blower, the intermediate cooler in Process I is omitted, resulting in a more reasonable temperature gradient and thus a **reduction in energy consumption across the entire process. The more reasonable temperature gradient for Purification Process II is shown in Figure 2: after initial cooling, desulfurization, aeration, gas heater treatment, and then the saturator. Figure 2 illustrates the more reasonable temperature gradient for Gas Purification Process II. 5 Conclusions: (1) The key to integrating the gas purification process lies in the selection of desulfurization and decyanidation processes; different purification processes determine different levels of gas purification and environmental protection, which in turn affect the technical and economic efficiency of coking plants. (2) Various desulfurization and decyanidation processes were analyzed, and it is recommended that the HPF desulfurization and decyanidation process is a reasonable choice considering China’s national conditions; the problems existing in this process should be actively addressed and improved. (3) Ansteel Chemical Plant follows its own path firmly; both of its large-scale gas purification units, with a gas treatment capacity of 100,000–110,000 m3/h, employ the HPF desulfurization and decyanidation process (also known as the ZL process). It is foreseeable that China’s independently developed gas purification processes and desulfurization and decyanation technologies will be established in the near future, and will continue to be improved.

I learned it! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !