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REMOVAL O F SODIUM FROM LIGNITE C Y ION EXCHANGING WITH CALCIUM CHLORIDE SOLUTIONS L . E. Paulson and J. R. Futch Grand Forks Energy Technology Center, DOE Box 8213 University Station Grand Forks, ND 58202 Lignite resources in North Dakota are estimate? at 350 billion tons, comprising 20 percent of the nation's total coal resources on a tonnage basis. Using present technology, 16 billion tons of this lignite is mineable (1). Analyses of over 400 samples of coal taken throughout the region show that the average sodium oxide content is 5.5 percent o f the ash (2). The major use of lignite is as fuel for electric power generation. These large power plants (u p to 450 MW) cannot operate efficiently burning high sodium lignite because of fouling of heat transfer surfaces. Field tests and boiler experience have shown that when sodium oxide content in the ash becomes greater.than 5 percent, excessive boiler fouling can be expected (3). Sodium does not occur as in the discrete mineral particles in lignite b ut i s evenly dispersed throughout the coal matrix (4,5). Sodium, along with calcium, magnesium, iron and aluminum cation, is attached t o exchange sites on the lignite structure and can b e replaced b y ion exchange with other elements (6). Combustion tests using lignite in which sodium has been replaced by calcium in ion exchange have shown less fouling than untreated lignite. This paper presents selected results based on laboratory batch tests in which calcium from calcium chloride solution is used to replace sodium i n a high sodium lignite. Test parameters include coal moisture content, particle size, solution concentration, temperature, solid-to-liquid ratio and contact time. EXPERIMENTAL PROCEDURE Lignite selected for the tests was from the Beulah mine (North Dakota) and contained 8 . 7 percent sodium oxide in the ash. Ash analysis, as determined by x-ray fluorescence, is shown in Table 1. Ash content of the coal was 10.8 percent on Table 1 . - Ash Analysis o f Test Coal by X-ray Fluorescents: (Beulah mine, North Dakota) Element S i 0 *l2'3 Fe203 Ti02 '2'5 Percent 19.7 12.0 1 . 6 0.5 0 . 3 22 4
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