Detailed explanation of 16 desulfurization process technologies and their practical applications

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Coke oven gas is a flammable gas, and the gases it contains such as H2S, HCN, and CO are highly toxic, posing serious threats to human health and the environment. At the same time, **appropriate policies have also been introduced to encourage enterprises to make full use of coke oven gas, which helps to reduce pollution and save resources. Among them, the sulfur compounds in coke oven gas that are highly toxic include organic sulfur and inorganic sulfur. Currently, the sulfur treatment processes for coke oven gas mainly consist of dry desulfurization and wet desulfurization. The greatest advantage of wet flue gas desulfurization is its high desulfurization efficiency and relatively low cost. Next, Xiao Qi will introduce to you the wet flue gas desulfurization process, which is most widely used in factories. Wet flue gas desulfurization: Based on the desulfurization mechanism, wet flue gas desulfurization processes can be classified into chemical absorption, physical absorption, physicochemical absorption, and wet oxidation methods. The greatest advantage of this method is its ability to remove the vast majority of sulfides from exhaust gases, making it cost-effective and practical. The disadvantage is that the desulfurization efficiency of some methods is unstable, and the precision of desulfurization is not high. 1 Chemical absorption method: The chemical absorption method, also known as the chemical solvent method, uses an alkaline solution as an absorbent that reacts with acidic gases in the gas to achieve desulfurization. The main chemical absorption methods are the alcohol amine method and the thermal potassium alkali method. (1) Alcohol amine method: The alcohol amine method includes methods using monoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA), diisopropylamine (DIPA), methyldiethanolamine (MDEA), etc. The alcohol amine method is a commonly used technique for natural gas desulfurization; it can also remove some CO2 as needed, in addition to carrying out desulfurization. The alcohol amine method is widely used in factories in Shandong, Sichuan, and other regions. In 2007, the Yongping Refinery switched to the alcohol amine method for desulfurization, resulting in improved desulfurization efficiency and product quality. (2) Thermal potassium alkali method – Process diagram of the catalytic thermal potassium alkali method. The thermal potassium alkali method uses an aqueous solution of potassium carbonate at a high concentration as an absorbent, which can directly absorb hydrogen sulfide and hydrogen cyanide from gas. This method has a slow rate of acid gas absorption and low efficiency, and has gradually been replaced by the catalytic thermal potassium-alkali method. The catalytic thermal potassium-alkali method involves adding a certain amount of catalyst to the potassium carbonate solution to accelerate the reaction rate. Process flow of the vacuum potassium carbonate method: The vacuum potassium carbonate method involves the direct absorption of acidic gases by a potassium carbonate solution. The desulfurization unit is located after crude benzene recovery, at the end of the coke oven gas process flow. This process was initially introduced from Germany; the acidic gases resulting from desulfurization and decyanation using this method can be used either in the Claus process to produce elemental sulfur or in the contact process to produce sulfuric acid. Subsequently, based on the adoption of advanced domestic and international technologies as well as production practices related to vacuum potassium carbonate, Chongne Jiaonai Company collaborated with universities to develop new processes owned by its own company. These processes have been put into use at factories such as Baosteel Chemical’s Meishan branch, Shaanxi Coking, and Handan New Area Coking Plant. This process features high efficiency in desulfurization and decyanidation, as well as a fast reaction rate. 2 Physical absorption method: The physical absorption method involves using organic solvents to physically absorb sulfur dioxide under certain pressures, and then releasing the gas under reduced pressure to regenerate the solvent. The physical absorption methods mainly include the low-temperature methanol process (Rectisol), the polyethylene glycol dimethyl ether process (NHD), and the propylene carbonate process (Fluar), among others. This method has low energy consumption and high purification efficiency, making it suitable for small and medium-sized enterprises. (1) Rectisol process http://mmbiz.qpic.cn/mmbiz/OrdlBGICgPN7tRkTYtKJUd0BGXickMnu9bfQ8qr0Loch40JSbAGrG94yKZ5PRVUlopO1M8YicaBaRiclsmtViaPLNA/0?wx_fmt=gif The Rectisol process is a purification technique that was developed in the early 1950s by the German companies Linde and Lurgi. This process uses methanol as an absorbent to remove acidic gases under pressure at temperatures below 0°C. This process is the most mature, stable, advanced, and reliable in terms of comprehensive technology; however, it requires a large investment and is suitable for large enterprises. Henan Kaixiang Chemical uses this process for desulfurization and decarbonization. (2) Polyethylene glycol dimethyl ether method (NHD) In the 1960s, the American company Allied developed a gas purification process named the polyethylene glycol dimethyl ether method. In the 1980s, the research institute of China’s Nanhua Company conducted tests on the polyethylene glycol dimethyl ether method, and successfully identified optimal solvent components for removing hydrogen sulfide and carbon dioxide; this method was named the NHD method. This method features high purification efficiency, good selectivity, no corrosion, low requirements for equipment, and a short process. Yankuang Guotai Chemical Co., Ltd. uses the NHD method for desulfurization. (3) Propylene carbonate method (Fluar): The decarburization and desulfurization technology using propylene carbonate (abbreviated as PC) takes advantage of the special affinity of this polar organic solvent for various acidic gases such as CO2 and H2S, in order to selectively remove the acidic components from these gases. It is a desulfurization process suitable for small-scale enterprises. The PC decarburization and desulfurization technology was developed by the Research Institute of Nanhua Group. In May 1977, this project was included in the Ministry of Chemical Industry’s science and technology development plan. This method has the advantages of low energy consumption, simple process flow, and reliable operation. 3. Physicochemical absorption methods (1) Sulfinol method: Developed by Shell in 1964, the Sulfinol solvent represented a significant advancement over the alcohol amine method; it is commonly referred to as the sulfinol method in China. The absorbent used in the sulfone amine method consists of cyclosulfone (40%-45%) with physical absorption properties, diisopropanolamine (40%-45%) with chemical absorption properties, and a small amount of water (15%). The disadvantage of the Sulfinol solvent is severe co-absorption when processing heavy hydrocarbons; additionally, it degrades under certain conditions. To further improve the performance of the solvent, Shell developed a method using a bridgehead amine to prevent its degradation and co-sorption, achieving excellent results. The purification plant of the Sichuan-Chongqing gas field uses the sulfide removal process based on thiolamine. 4 Wet oxidation desulfurization process: The wet oxidation desulfurization process is a general term for a series of desulfurization methods. It is characterized by the use of alkaline solutions to react with acidic sulfides in gases, thereby forming sulfides that are not easy to vaporize, followed by the recovery and reuse of these products. Based on the differences in active substances and alkali solutions, this process is mainly divided into 11 types: (1) Modified ADA method. The ADA method, also known as the sodium anthraquinone disulfonate method, is widely used in countries such as the UK, France, and Canada; it is also one of the desulfurization processes commonly employed in China. The one-component catalytic system consisting of sodium anthraquinone disulfonate and an aqueous solution of soda ash is known as the ADA method ； The mother liquor, consisting of sodium anthraquinone disulfonate, aluminum pentoxide, and potassium tartrate as a binary catalytic system, forms the modified ADA method. The biggest drawbacks of this method are severe equipment corrosion and high energy consumption. It is gradually being replaced by other methods in the domestic market. (2) TH method: The TH method, also known as the Takahakesu method, is a technology developed by Nippon Steel in Japan. In this process, ammonia from coal gas and ammonia distilled from ammonia water are used as the alkaline solution; sodium 1,4-naphthoquinone-2-sulfonate serves as a catalyst for decyanidation, followed by desulfurization. The advantages are that no external alkali source is required, the operation is simple, and it occupies little space. However, it has high operating costs, low desulfurization efficiency, and the catalysts need to be imported; therefore, this process is rarely used in China. Baosteel once used this process for desulfurization and decyanidation. (3) FRC method: The FRC method, also known as the picric acid method, is a process developed by Osaka Gas Company in Japan. This process uses ammonia in coal gas as the base source and picric acid as a catalyst. The advantages of this process are high desulfurization efficiency, low cost, and the ability to avoid secondary pollution. The disadvantage is that it has a long production process and requires a large amount of space, making it suitable for large-scale projects. This process is used in the third phase of Baosteel’s coking project. (4) PDS method: The PDS method is a desulfurization process developed by Northeast Normal University, which was applied at the Shanghai Pudong Gas Plant in 1994. PDS is a sodium dicobalt phthalocyanine sulfonate catalyst, with a co-catalyst and an alkaline substance being added simultaneously during the reaction process. The desulfurization unit employing the modified ADA method requires only the addition of some PDS solution dosing equipment to be converted into a PDS method. The main advantages of this process are its high efficiency in desulfurization of inorganic sulfur and easy separation of the products; however, the desulfurization effect is unstable, and it has low efficiency in removing organic sulfur. The Coking and Gas Plant of Tangsteel uses a PDS desulfurization system to remove sulfur from waste gases. In 2004, Kunming Coke and Gas Plant replaced the ADA method for desulfurization with the PDS process. (5) HPF method: The HPF method is a highly efficient desulfurization process jointly developed by the Anshan Coking and Refractories Design and Research Institute and Wuxi Coking Plant. The HPF method is an improved process of the PDS method; HPF is a composite catalyst composed of hydroquinone, a PDS catalyst, and ferrous sulfate. The advantages of this process are high catalyst activity, simple operation, and few required devices; however, the quality of the sulfur produced is low, and the waste liquid poses a significant threat to the surrounding environment. Companies such as Shanxi Meijin Group use the HPF method for desulfurization. (6) The 888 desulfurization catalyst is a non-toxic and highly efficient catalyst developed by Changchun Dongshi Company; it belongs to the category of mono-catalytic desulfurization catalysts. Due to its unique chemical structure, it possesses an extremely strong ability to absorb and carry oxygen, as well as high catalytic activity. The main component of the 888 desulfurization catalyst is an ammonium cobalt phthalocyanine sulfonate metal-organic compound, with sodium carbonate as the base source. This process features good catalytic activity, low consumption, and stable desulfurization efficiency. It is suitable for desulfurization of various types of gases and liquids, and has now entered the international market. Companies such as Shandong Minsheng Coal Chemical Co., Ltd. and Hebei Qianan Fertilizer Co., Ltd. all use the 888 method for desulfurization. In 2009, Shanxi Haizi Coking Co., Ltd. replaced the ADA method with the 888 method for desulfurization. (7) MSQ method: The MSQ method was developed by Zhengzhou University. It uses sodium carbonate (or ammonia water) as the alkaline absorption medium, while a composite catalyst is formed by combining hydroquinone, salicylic acid, and manganese sulfate. This method offers high operational flexibility and low operating costs, as well as low tower resistance, but its desulfurization efficiency is relatively low. The SMQ-type desulfurization catalyst has been applied in provinces and cities such as Shandong and Jiangsu. (8) OPT method: The OPT method was developed by Anshan Thermal Energy Research Institute and the Coking Plant of Su Steel. This process is a coal gas desulfurization method that uses ammonia as the alkali source, an OP-type composite catalyst as the desulfurization catalyst, and produces products such as ammonium thiocyanate from the desulfurization waste liquid. The OPT method reduces the corrosion of gases on equipment, lowers energy consumption, enables full utilization of ammonia in gas, saves capital, features a short process flow, good desulfurization efficiency, and high operational flexibility. (9) DDS method: The DDS method is a patented technology invented by Dr. Wei Xionghui from Peking University. It creatively combines biotechnology with wet flue gas desulfurization technology, addressing the problems of easy degradation and high consumption of complexed iron in the desulfurization solutions using the \"complexed iron method\". “It is an abbreviation for the \"iron-alkali solution catalytic method for gas decarburization, desulfurization, and decyanidation\", which is a new type of desulfurization technology. The DDS solution is composed of a DDS catalyst (accompanied by aerobic bacteria), DDS catalyst additives, Type B DDS catalyst additives, active ferrous carbonate, sodium carbonate (or potassium carbonate), and water. This process has the advantages of high desulfurization efficiency, low energy consumption, and high overall benefits. DDS desulfurization technology is gradually being recognized by a wide range of enterprises for its unique technical features and outstanding desulfurization capabilities, and it holds promising market prospects. The Fertilizer Factory in Kenli County, Shandong Province, switched to the DDS desulfurization technology in 2000; enterprises such as the Dong’e Fertilizer Factory of Luxi Chemical Group, Jiangsu Linggu Chemical Co., Ltd., Yangmei Pingyuan Chemical Co., Ltd., and Fujian Shunchang Fubao Industrial Co., Ltd. all employ the DDS desulfurization process. (10) TV method: The TV method is also known as the tannin method. Tannin is a complex mixture composed of many structurally similar phenolic derivatives, mainly containing tannins and water-insoluble substances. The molecular formula of tannin is C14H10O9; it is the product of the condensation of two gallic acids. The hydroxyl groups present in tannin molecules have a certain complexing effect on metal ions; during the desulfurization process, they act both as catalysts and complexing agents, effectively preventing the loss of vanadium from the system. The disadvantages of this process include the tendency for pipes to get clogged with sulfur, and the need for pretreatment of tannin. Shanxi Jinxiang Coal Chemical Co., Ltd., Hunan Xiangdan Industrial Co., Ltd., etc. adopt the baking method for desulfurization. (11) AS Process: The AS process for desulfurization and decyanation is an advanced desulfurization technology introduced from Germany in the 1980s. It is widely used by major coking plants in China, promoting the advancement of gas desulfurization technology in the country. Problems that commonly occur in the AS method include easy clogging of heat exchangers and corrosion in the ammonia water system, among other drawbacks. Today, the most commonly used methods are the AS method and the glue-baking method, in combination with technologies such as the Claus plant. Shougang, Shijiazhuang Coking Group, etc. use the AS desulfurization process.