(82a) Anti-Agglomeration Strategy Study of High Sodium Coal Gasification in a Commercial Circulating Fluidized Bed Gasifier

High-sodium coal is mainly located in Australia, Germany, the United States, China, Indonesia and other places. The utilization of high-sodium coal has attracted worldwide interest in recent years. Gasification seems to be an ideal route for high-sodium coal utilization because of high reaction activity, high efficiency and low pollution emissions. Among various gasification technologies, circulating fluidized bed (CFB) gasification is one of the most popular gasification technologies. Some advantages of CFB gasification are that it can use low-cost pulverized coal, has satisfied adaptability of a wide range of solid fuels, can use poor quality coals and emits lower amounts of pollutants. However, the high-sodium content in coal ash may cause serious ash-related problems, such as agglomeration, fouling and contamination. Therefore, it is important to understand the agglomeration mechanism and provide anti-agglomeration strategy for the successful utilization of high-sodium coal.

Institute of Engineering Thermophysics (IET) has built up 28 sets of CFB gasifiers. During the commercial operation process, high-sodium Indonesia coal was used as feedstock in Guangxi Province. In order to reduce the operating risk, SiO₂-Al₂O₃-Na₂O ternary phase diagram calculation and lab scale blended coal gasification experiments were carried out. The calculation result of SiO₂-Al₂O₃-Na₂O ternary phase diagram indicates that Indonesia coal ash is located in the liquidus region and has serious agglomeration tendency. Via phase diagram optimization analysis, proper blending coal was selected for utilization of high-sodium Indonesia coal, and the thermodynamic prediction was in accordance with the fundamental experimental results. 75% of Indonesia blended coal gasification was conducted in one set of commercial CFB gasifier. The system temperature and pressure are stable, and no slagging phenomena occur. The cold gas efficiency is 71.96%, the carbon conversion is 86.90% and the gas heat value is 5.59 MJ/Nm³. In addition, more than 320 days of long-term and stable operation was achieved. The results indicate that blended coal gasification is an efficient method to alleviate the agglomeration tendency of high sodium coal. The essence of the strategy is to change the ash properties via chemical reactions, and phase diagram can provide some clue for the identification of blending coal and suitable conditions.