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Author/Source: Zhao Zhihou, Peng Qimeng, Li Caiyan (Engineering Research Center for Water-Coal Slurry Gasification and Coal Chemicals, Tengzhou 277527) Date: 2009-2-6 Fluidized-bed gasification is the most advanced gasification technology available internationally today. Compared with water-coal slurry gasification technology, pulverized coal fluidized bed pressurized gasification technology offers advantages such as wide adaptability to different coal types, low raw material consumption, high carbon conversion rate, high efficiency in producing cold gas, large coal processing capacity, cleanliness, and high efficiency. It represents the mainstream trend in gasification technology and possesses greater market competitiveness. **“Under the 15th National Key R&D Project — Research and Development of New Technologies for Producing Syngas via Pressurized Coal Gasification — a pilot-scale pressurized coal gasification facility with independent intellectual property rights was successfully built and put into operation. This technology fills a gap in China, indicating that the country has mastered key technologies such as pressurized dense-phase transportation of pulverized coal, as well as the design, construction, and operation of pilot-scale facilities, achieving process technology parameters at an internationally leading level. Subsequently, it took the lead in carrying out a pilot test of powder coal gasification using CO2 as the transport medium on an international scale, obtaining important process operation data. 1 Pilot-scale process for pressurized gasification of pulverized coal. The pressurized gasification process of pulverized coal can be divided into four units: pulverized coal preparation, dense-phase transportation of pulverized coal, gasification, and preliminary gas purification; the pilot-scale process is shown in Figure 1. http://nmtech.yf116.cn/upload1/071126846186162.jpg After impurities are removed from the raw coal, it is fed into a coal grinder for crushing; at the same time, it is dried using heated low-pressure nitrogen. The resulting qualified coal powder is stored in a silo, and most of the low-pressure nitrogen used for heating can be reused. The coal powder in the silo is carried by nitrogen, passing through both the low-pressure silo and the high-pressure silo before being conveyed by a coal powder pressurization tank to 4 oppositely arranged gasification nozzles and entering the gasification furnace. The gasification agents, oxygen and steam, also enter the gasification furnace through these nozzles, where they undergo a gasification reaction with the coal powder under high temperature and pressure. The high-temperature syngas is quenched and washed before being fed into the gas holder, while the molten ash is cooled and solidified in the quenching chamber of the gasifier; it is then collected in lock hoppers and discharged periodically. The wastewater exiting the washing tower undergoes two stages of flashing; water vapor and some of the acidic gases dissolved in the wastewater (such as CO2 and H2S) are rapidly flashed out. The flashed gas is condensed and separated before being processed, while the flashed wastewater is cooled in a heat exchanger before being sent to the wastewater treatment system. The coal powder preparation unit in the pilot plant serves primarily to produce coal powder with specific particle size and moisture content requirements for use in the gasification reaction and dense-phase transportation of coal powder. This ensures adequate reaction within the fluidized bed gasifier, where the residence time is short, and prevents blockages as the coal powder passes through key components such as transport pipelines and gasification nozzles. The moisture content of pulverized coal is generally kept below 2%, and the particle size of pulverized coal is 100% < 0.01 mm. For safety reasons, the oxygen volume fraction in the powder production system is kept at <5%. Pulverized coal dense-phase transportation is a key technology for pressurized gasification of pulverized coal. Four pulverized coal pipelines are led out in parallel from the bottom of a pressurized pulverized coal tank, supplying pulverized coal to the four-nozzle gasifier. By combining the action of a pulverized coal regulator with the conveying pressure difference, a uniform, stable, and controllable dense-phase transportation of pulverized coal at high pressure is achieved. The core technologies for pressurized coal powder transportation have now been largely mastered, enabling the system to meet the requirements for scale expansion. The use of pipes, valves, and instruments in this project was a first attempt; various challenges were encountered regarding their materials, structure, and performance, which helped to gain experience for future efforts to achieve localization. The powder coal gasifier is a four-nozzle opposed-type gasifier with independent intellectual property rights, developed and built during the Ninth Five-Year Plan period. The 4 nozzles are arranged horizontally opposite to each other, with an angle of 90° between any two nozzles. After entering the gasifier, the materials form a turbulent flow; this type of turbulent flow fluidized bed has significant advantages in enhancing heat and mass transfer. Compared with water-coal slurry gasification, this device allows for the selective shutdown of any pair of burners to meet various operational requirements, and after simple processing, it enables continuous feeding at the system’s operating pressure, offering great flexibility and convenience. 2 Pilot operation of pressurized coal gasification 2.1 Process operating conditions Operation pressure of the gasifier: 2.0–2.5 MPa. Operating temperature of the gasifier: 1,300–1,400°C. Briquette coal flow rate: 1,200–1,800 kg/h. Oxygen: 650–1,100 m3/h (at standard conditions), 20–110°C, –4.0 MPa. Steam: 180～550 kg/h, ~390 ℃, ~3.2 MPa. 2.2 Process Technical Specifications The technical specifications under different operating conditions are shown in Table 1, while a comparison of the evaluation criteria for various operating conditions is provided in Table 2. http://nmtech.yf116.cn/upload1/071126847213085.jpg As can be seen from Table 3, under the aforementioned process conditions, when CO2 is used as the transport medium, part of this CO2 can also act as a gasifying agent, reacting with coal tar to produce CO. This reduces the nitrogen content in the syngas significantly, which is important for enabling the pressurized gasification of pulverized coal to be utilized more effectively in the production of methanol, acetic acid, dimethyl ether, and other substances. At the same time, Table 4 also shows that the dry coal pressurized gasification technology features a high effective gas content and a high carbon conversion rate, with its various indicators being roughly on the same level as those of the Shell and GSP gasification technologies ； Compared with water-coal slurry gasification, it saves 2%–4% in coal consumption and 16%–21% in oxygen consumption, with the effective gas components being 6%–10% higher (by volume fraction). http://nmtech.yf116.cn/upload1/071126847554729.jpg http://nmtech.yf116.cn/upload1/071126848451893.jpg 2.3 Characteristics of pilot-scale technology: (1) It overcomes the limitation imposed by coal type on slurry preparation; it can be used with a wide range of coal types, including lignite, bituminous coal, and anthracite. (2) The gasifier has a wide load adjustment range, allowing for easy control. (3) The process technical indicators have reached the international advanced level. (4) The engineering technology is easy to scale up, safe to operate, and suitable for large-scale gasification plants. (5) This technology is an environment-friendly clean production technique; the wastewater contains no components such as light oil or tar, and the graywater can be recycled. 3 Application Prospects: The successful application of this technology will provide advanced gasification techniques for altering the raw material pathways used in the production of chemical products such as ammonia, methanol, and carbonyl compounds, as well as for IGCC power generation. It is compatible with China’s energy structure and aligns with the strategy of **sustainable development**. Pressurized coal gasification technology is one of the **clean coal technologies that are being vigorously developed; it meets the increasingly stringent environmental protection requirements and helps to improve the overall level of environmental protection in our country.