Thread Content
—The Struggle to Improve the Shell Gasifier at Datang Dolun Coal Chemical Company / Author/Source: Sinochem News Network, Date: 2020-06-11, Clicks: 8. As of June 8, Unit A of the coal gasification plant in Datang Inner Mongolia Dolun Coal Chemical Company’s project with an annual production capacity of 460,000 tons of coal-derived olefins had been operating continuously at a high load for 233 days. This marks another update to the world’s record for the longest continuous operation of a gasifier using lignite as feedstock, following the first time on May 5th that this furnace achieved 200 days of continuous operation. How did Datong Coal Chemical achieve such a long period of continuous operation? Pioneering efforts and multiple approaches were taken to overcome the challenges. Datang Datong Coal Chemical’s plant, with an annual production capacity of 460,000 tons of coal-based polypropylene, is one of the first modern coal chemical projects in China to carry out demonstrations of coal-based olefin production; the gasifier is the key equipment in this plant. The company’s gasification unit is the world’s first Shell gasifier to use low-quality lignite as feedstock, and it is also the largest single gasifier in the world to date. It consumes more coal than similar units introduced in China in the early years, by more than twice as much. When it comes to Shell gasifiers, the industry speaks highly of them, but they also inspire fear. This gasification furnace features advanced technology and boasts advantages such as high efficiency, safety, and environmental friendliness. The Tonglun coal chemical gasification plant consists of 15 drying production lines, 9 coal grinding units, 3 Shell pressurized fluidized bed gasifiers, as well as subsequent systems for treating ash, slag, and wastewater. The gasifiers are designed to process 3×2870 tons of dry coal powder per day, generating 3×157,000 standard cubic meters of synthetic gas per hour. In actual operation, a single gasification unit can process 4,300 tons of raw coal per day (with lignite accounting for 85%~90% of this amount), while the operating load of each furnace remains between 105%~110%. The effective gas production rate can reach up to 175,000 standard cubic meters per hour. The Shell gasifier used in the Tonglun coal chemical plant is designed to process low-quality lignite, and doing so presents challenges that are beyond imagination. Lignite possesses the characteristics of \"five highs and one strength\" – high activity, high sulfur content, high ash content, high internal moisture, high ash viscosity, and strong slagging tendency – and is considered the \"rough grain\" in coal chemical industry. There are bottleneck issues that need to be addressed in terms of coal drying, the stability of coal powder transportation, and reaction control. Faced with challenges, businesses rise to the occasion and undertake one challenge after another. After years of intense efforts, Dolun Coal Chemical finally tamed this unruly gasification furnace. As the operating cycle of the gasifier continued to lengthen, there was a significant improvement in the production load, process parameters, specific consumption, and stability of the coal gasification facility. As a result, Tolon Coal Chemical 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 applications. Overcoming challenges and achieving record-level operations: Before 2016, the best operating record for Shell’s gasifier in the Dolun coal chemical complex was less than 58 days; this was already the best result that could be achieved after years of efforts, but it was not sufficient to meet the project’s requirements for high-volume production. Since 2017, Dolun Coal Chemical has thoroughly analyzed the problems existing in its gasification furnaces, accelerated the process of localizing imported technologies, and focused on tapping internal potential and pursuing technological innovation. They carried out extensive technical upgrades to the gasification furnace, resolving the bottleneck issue of \"frequent abrasion and leakage in the cyclone separator\" that hindered its operation; they achieved localization of the coal linear velocity meters; and by optimizing the sequential control system, manual intervention was eliminated in the process of feeding powder into the gasification furnace as well as in ash removal, thereby minimizing the risk of human error. Lignite has a high internal water content, which severely limits the stability of transportation. The technical staff started with the coal drying and grinding units, carrying out a series of operational optimizations and efforts to reduce the moisture content to the level required for pneumatic conveying. Before starting up the plant, they conducted coal circulation tests under various operating conditions and adjusted the formulas related to the coal flow rate, thereby ensuring stability in the coal supply system and uniformity in the combustion area. On a daily basis, they provided specific guidance regarding control parameters such as the temperature of the gasifier, based on analyses of operating conditions, comparisons of parameters, and analyses of the quality of the raw coal. This approach helped to prevent blockages at the slag outlet and improved temperature control, thus enhancing economic efficiency. Coal blending: Achieving high yields with low consumption. The Tolon coal-based olefin plant uses lignite as raw material to produce high-purity polypropylene, thereby turning \"black coal into white polymer\". However, due to a shortage of lignite in the area where the enterprise is located, it is necessary to purchase various types of coal with different calorific values from other regions and mix them with lignite for combustion. As a result, it increases the operational difficulty of the gasification furnace. To address these challenges, Tonglun Coal Chemical Industry implements a strategy of \"two focuses and one special protection\": focusing on the availability rate of equipment by strictly enforcing equipment inspection protocols to ensure that any issues are resolved promptly; and focusing on regular maintenance of equipment, with particular attention paid to critical systems such as the coal grinding system, to ensure that these key pieces of equipment operate properly. Special records are maintained for critical equipment, and special care measures are implemented to continuously improve their operational condition, thereby ensuring their reliable operation over extended periods of time. To achieve the goals of cost reduction and efficiency improvement, Tolon Coal Chemicals actively explores various coal blending methods. By optimizing the combination of different types of coal, it manages to minimize coal consumption while ensuring the gasifier can operate at high loads over extended periods of time. At its peak, the company used as many as 9 different coal types simultaneously in the furnace, allowing for a quad-component coal mixture per furnace. Since October 19, 2019, the coal blending formula for each gasification furnace at the Tonglun Coal Chemical Plant has been adjusted 12 times; the proportion of lignite reached as high as around 90%, **which helped reduce the production costs of the products.