Datang Duolun Coal Chemical’s coal gasification unit, capable of processing the largest amount of lignite per batch, sets a new record for continuous operation

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Datang Dolun Coal Chemical Plant sets new record for continuous operation of gasification unit with highest capacity for processing lignite Author/Source: Datang Dolun Coal Chemical Plant Date: May 26, 2020 Clicks: 5 On May 5, Unit 2’s gasification plant achieved 200 days of continuous operation at Class A level; during this period the average oxygen load was 100%, with a maximum oxygen load of 110%. This achievement set a new record for continuous operation of a gasification unit at Class A level within the company, placing it among the leaders in terms of operational performance among similar gasification units in China. It also established a world record for the longest continuous operation time of a gasification furnace using lignite as raw material. As of the time of writing on May 20, the gasification unit had been operating at high load for 215 consecutive days, with all process parameters under control, and it is on its way to setting a new operational record. The gasification unit is the core facility for the company’s coal-to-olefins production; it utilizes the advanced Shell gasification process and boasts significant advantages in terms of efficiency, safety, and environmental sustainability. Raw coal is fed into the gasifier where it burns to produce syngas composed mainly of CO and H2. The gasification unit consists of 15 drying production lines, 9 coal grinding systems, 3 Shell pressurized fluidized bed coal gasifiers, as well as subsequent devices for treating ash, slag, and wastewater. Its designed capacity is 3×2870 tons per day of dry coal powder processing, with an effective syngas production rate of 3×157000 Nm3/h; simultaneously, it generates 3×170 tons per hour of medium-pressure saturated steam at 5.51 MPa and 271°C. In actual operation, a single set can process 4,300 tons of raw coal per day (with a lignite proportion of 85%-90%), the operating load of each furnace remains between 105%-110%, and the maximum effective gas production reaches 175,000 Nm3/h. Using lignite as raw material, the company took on the challenge and set a precedent – its gasification unit is the world’s first Shell gasifier to utilize low-quality lignite. Due to the lack of precedents, everything had to be figured out from scratch during the initial operation phase. Furthermore, because lignite has high activity, high sulfur content, high ash content, high internal moisture, strong caking tendency, and high ash viscosity, there are various bottlenecks that need to be overcome in terms of coal drying, the stability of coal powder transportation, and reaction control. Improving the operational efficiency of the equipment has become a prominent and urgent issue, which at one point served as a major bottleneck restricting the production operations of the entire company. Faced with difficulties, all the employees of the company stepped up to meet the challenges, took on heavy responsibilities, and tackled these obstacles with tenacious perseverance and a spirit of striving for excellence. After overcoming countless difficulties and obstacles, enduring countless storms and harsh weather conditions, and surviving numerous long nights, they finally succeeded, through hard work and diligent effort, in surmounting one challenge after another. The production operation load, process parameters, specific consumption, and stability of the gasification unit have seen a qualitative improvement. It became the first company in China to successfully apply Shell’s gasification technology to lignite, setting a precedent for the large-scale use of low-quality lignite in chemical production worldwide. Emphasis should be placed on practical safety management to lay a solid foundation for stable operations. In the development of enterprises, safety comes first. During the daily operation of the gasification unit, the company always gives top priority to safety; it conducts joint inspections for potential hazards on a weekly basis, maintains a ledger of on-site leaks in the gasification unit, encourages inspection personnel to improve the quality of their inspections, records any detected leaks, addresses them promptly, and ensures proper closure of the inspection process. At the same time, operation teams are regularly organized to study safety accident cases, learn from them and apply the lessons to similar situations; the principles of “three emphases and one implementation” are fully applied, and strict controls at various levels create a robust framework to ensure safe operations. Seeking shortcuts through technological upgrades and optimizations, taking multiple measures to eliminate potential risks. Since 2017, the company has made great efforts to carry out technological upgrades and improvements to its facilities, promoted the localization of imported technologies, and focused on tapping internal potential and driving technological innovation in order to improve efficiency. First, substantial technical upgrades were carried out on the gasification furnace, addressing the bottleneck issue of \"frequent erosion and leakage in the cyclone separator\" that hindered the long-term operation of the equipment ； Secondly, it has enabled the localization of coal line speedometers; by ensuring the stability of the coal flow, it has significantly shortened the equipment procurement time and reduced procurement costs. Moreover, these domestically produced speedometers can also be used for density measurement, offering multiple benefits in one solution ； Third, the sequential control system has been optimized, eliminating the need for manual intervention in the feeding of powder into the gasification furnace and in ash removal, thereby minimizing the risk of human error. Refine daily management to ensure the long-term operation of the equipment; for proper equipment operation, the coal supply chain is of utmost importance. However, lignite has a high internal water content, which severely limits the stability of transportation. To this end, the company’s technical staff started with the coal drying and grinding units, carrying out a series of operational optimizations and improvements to reduce the moisture content to the level required for pneumatic conveying. Before starting up the equipment, they conducted tests on coal circulation under different operating conditions and adjusted the formulas related to the coal flow rate, thereby ensuring the accuracy of the instruments as well as stability in the coal supply line and uniformity in the combustion area. This prevented issues such as uneven burning in the furnace and frequent shutdowns of the coal burners, which could cause significant fluctuations in operating conditions. These measures also resolved the problem of leaks in the burner covers. At the same time, based on daily operation condition analysis, parameter comparison, analysis of the quality of raw coal, daily specific oxygen consumption, and specific coal consumption, specific guidance is provided for control parameters such as the temperature of the gasifier. This helps to prevent ash accumulation at the inlet of the syngas cooler SGC due to overheating, as well as blockages at the slag outlet caused by low temperatures, thereby optimizing temperature control and improving the economic efficiency of the plant’s operation. In daily operations, the company adheres to the production organization principles of \"not ignoring any fluctuations, considering reduced output as a serious error, and treating complete shutdowns as even more serious issues.\" It has established records such as the \"Coal Burner Failure Log\" and the \"Gasification Unit Alarm Log\" to analyze the causes of abnormal situations, develop preventive measures, and guide teams in carrying out precise operations in order to ensure the stable operation of the coal handling system. Actively carry out labor competitions in the “Hengda Class” to motivate each operator to perform their tasks carefully, with the aim of ensuring the stable operation of the equipment and increasing production while reducing costs. Emphasis is placed on \"two focuses and one special care\" to continuously improve equipment maintenance: one focus is on the availability of spare equipment, with a strict implementation of equipment inspection systems; any issues identified are addressed without delay, and personnel are sent to handle them right away to ensure that the equipment remains in good condition ； Second, focus on regular inspections of equipment; for critical equipment, especially those in the coal grinding system, regular inspections and maintenance must be carried out to ensure the proper operation of these key devices. At the same time, special records are maintained for critical equipment, and \"special care\" management is implemented to continuously improve the health status of these devices, thereby ensuring their reliable operation over long periods of time. By blending multiple coal types, high output and low consumption are ensured. To achieve the goal of reducing costs and increasing efficiency, the company actively explores various coal blending methods; through optimal mixing of different coal types, it manages to keep the gasification furnace operating at high load levels for extended periods while minimizing coal consumption. At its peak, as many as 9 different coal types were fed into the gasification furnace simultaneously, with a single furnace capable of using a mixture of four different coal types. The dryer is a key device for gasification feeding and coal blending. To ensure its high operational rate, the company established a task force to continuously carry out technical improvements to the coal feeding system, focusing on equipment maintenance, regular inspections, and emergency repairs. By synchronizing maintenance, upgrades, and measures to address powder leakage, the company successfully achieved the goal of stable, long-term operation with a high proportion of lignite. Since October 19, 2019, the coal blending formula for each gasification furnace has been adjusted 12 times; the proportion of lignite reached as high as around 90%, which significantly reduced the production costs of the company’s products.