Low rank coals such as lignite naturally have high moisture content. For efficient gasification, the lignite must be dried to a lower moisture content before being used. There are several advantages to drying the lignite before gasification. Lignite handling and high-pressure lignite feed equipment performs more reliably with drier lignite. Drier lignite results in a higher syngas heating value. The evaporated water from the lignite can be condensed and re-used for plant processes, which improves plant economics. The fluid bed dryer (FBD) system at the Kemper Integrated Gasification Combined Cycle (IGCC) power plant uses low grade waste heat to efficiently dry the lignite, resulting in reduced operating cost for the FBD and the gasifier. The lignite preparation section of the plant consists of six parallel dryer trains to dry and pulverize lignite for feeding to two gasifiers. The Kemper lignite drying system is the largest of its kind in terms of total water evaporated. This paper presents a detailed overview of the FBD system at Kemper and discusses various factors that influence the system performance, including lignite quality, lignite feed rate, gas flow rates, retention time, bed level, and bed temperature. Closed-loop, waste heat, fluidized bed dryer systems provide the most thermally efficient means of drying the lignite. The lignite processing system at the Kemper County IGCC power plant features an FBD system to dry high moisture lignite (>48%), resulting in a large amount of water evaporated (360-420 KPPH). For environmental and efficiency purposes, the lignite preparation design includes a way to re-use the evaporated water in plant processes. The evaporated water from the lignite is condensed and used in the water gas shift, syngas cooling, ammonia removal, and sour water systems. The closed loop system for the water and gas systems in the lignite preparation area minimizes makeup requirements and keeps costs low for the area operation. The lignite preparation process improvements made during startup and commissioning created a more reliable dryer operation in the lignite preparation system. The lignite preparation improvements overcame lignite quality issues that affected equipment operation. The two most significant improvements involved dryer operation and recovered water filters. The dryer feed system and fluidization changes allowed for more reliable lignite feed rates to the dryer. The flocculation, sedimentation, and filtration improvements resulted in higher reliability water feed rates to the downstream process from lignite preparation.
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