Hidden safety issues are emerging in coal chemical engineering design

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In recent years, coal chemical projects in our country have been developing towards larger and super-large scales, with new technologies, processes, and materials beginning to be utilized. However, project design and material selection are mostly based on traditional coal chemical standards, and many companies proceed with design, construction, and exploration simultaneously. This makes the safety hazards resulting from inappropriate design and material selection in coal chemical projects relatively hidden; once the equipment is put into use, companies are unable to prevent accidents from occurring during production. In response to this situation, at the seminar on sulfur-resistant shift technology for coal gasification processes held in Qingdao in mid-March, experts agreed that the coal chemical industry should enhance the exchange of operational experience and establish unified design standards to lay a foundation for the healthy development of the industry. 　　Wang Yongsheng, deputy general manager of Zhongxin Chemical Co., Ltd. under Henan Yongmei Group, said that in coal chemical production, due to chloride ion corrosion, it is very common for high-pressure process gases to leak and cause fires at the pipes, flanges, and welds of conversion units. “Corrosion and leakage of local piping in conversion equipment is a common issue in the industry. ”He said. 　　Wang Yongsheng explained that as their scale continued to expand, coal chemical enterprises adopted some advanced technologies and processes from both domestic and international sources. However, the selection of materials for these projects did not keep up with these advancements; old standards were still used, and the equipment in question was mostly manufactured from austenitic stainless steel of types 304 and 316. Gasification technologies such as those used by Shell have only been put into use in recent years. The associated conversion units have experienced multiple instances of leaks and fires caused by high-pressure process gas at locations such as pipes, flanges, and welds; and whenever a leak occurred, operators did not dare to conduct inspections. Practice has shown that traditional materials are not resistant to chloride ion corrosion. 　　Industry experts analyze that corrosion is a common phenomenon during the use of pressure vessels; chloride ions can easily cause stress corrosion cracking in stainless steel. Given the large amount of stainless steel (austenitic stainless steel) used in coal chemical plants, finding effective ways to prevent chloride-induced corrosion in such facilities is an urgent issue that needs to be addressed. 　　Furthermore, in China, methanol synthesis towers used by coal chemical enterprises have experienced catalyst failure and failures to meet design specifications, which has drawn considerable attention from owners regarding every aspect of these tower systems, from the choice of materials to the design of the towers themselves. Tang Hongqing, deputy chief engineer at Sinopec Ningbo Engineering Co., Ltd., explained that in recent years, as methanol production facilities have become larger in scale, the methanol synthesis towers have also evolved to be larger. Their capacity has increased from initially 30,000 tons and 50,000 tons to 80,000 tons and 100,000 tons, and now it ranges from 200,000 tons and 300,000 tons per unit to even larger capacities. However, in China, there are still no standards established regarding the proper selection of materials for internal components of synthesis towers, material control, processing and manufacturing, and welding; as a result, problems can easily arise in terms of the welding of these materials and the distribution of flow channels. 　　It is understood that in coal chemical production, there are still no industry standards regarding the grades and chemical compositions of special materials such as zirconium and zirconium alloys used in the production of acetic acid, nitric acid, etc., nor are there any standards for pipes and pressure vessels. Similarly, there are no unified guidelines for selecting materials for large-scale low-temperature spherical tanks in coal-to-olefins plants. 　　Wang Yongsheng suggests that coal chemical industries, particularly those involving new types of coal-based processes such as coal-to-natural gas and coal-to-ethylene glycol, as well as the engineering design firms working in this field, should promptly summarize the experiences and problems encountered during operation by the clients, make necessary adjustments to the designs, and establish unified design standards. This will contribute to the healthy development of the coal chemical industry. 　　Regarding the hidden safety issues associated with material selection in coal chemical plant design, industry experts argue that the reasons for equipment failure are complex. In addition to design firms and project owners promptly drawing on experience to make rational choices regarding materials based on internal factors, it is also essential for owners to strictly control the specifications of the raw materials used. For example, when conducting hydrostatic tests on pipes and equipment, it is necessary to strictly control the chloride ion content. At the same time, when purchasing coal, factors such as chloride ions, ash fusion point, and carbon content must also be taken into account. The coal purchased should suit the requirements of the plant, as this is essential to ensure its safe and stable operation.