Free-Swelling Index

The material thought to be responsible for conferring the plastic properties on coal can be removed by solvent extraction to leave a nonplastic residue (Pierron and Rees, 1960). Plastic properties can be restored to the coal be recombining the solvents extracts with the insoluble residue. The fluid behavior or plasticity of coal in the temperature range 300 to 550°C (572 to 1022°F) is widely used to estimate coking characteristics and may be important for predicting coal properties with respect to coal conversion processes. 

The agglomerating index is a grading index based on the nature of the residue from a 1-g sample of coal when heated at 950 20°C (1740 35°F) in volatile matter determination (ASTM D-3175). 

The agglomerating for agglutinating) tendency of coal may also be determined by the Roga test (ISO 335), and the Roga index (calculated from the abrasion properties when a mixture of a specific coal and anthracite is heated) is used as an indicator of the agglomerating tendencies of coals (Table 7.4). 

The free-swelling index (FSI) is a measure of the increase in volume of coal when heated under specified conditions (ASTM D-720 ISO 335). 

Coal Type Swelling Index Dilation (%) Roga Index 

The FSl of coal is a measure of the increase in volume of a coal when it is heated (without restriction) under prescribed conditions (ASTM, 2011g ISO, 2011a). The ISO test (ISO, 2011a), Roga test, measures mechanical strength rather than size profiles of coke buttons another ISO test (ISO, 2011b) gives a CSN of coal. 

The nature of the volume increase is associated with the plastic properties of coal (Loison et al., 1963) and, as might be anticipated, coals which do not exhibit plastic properties when heated do not, therefore, exhibit free swelling. Although this relationship between free swelling and plastic properties may be quite complex, it is presumed that when the coal is in a plastic (or semiflnid) condition the gas bubbles formed as a part of the thermal decomposition process within the flnid material cause the swelling phenomenon which, in turn, is influenced by the thickness of the bubble walls, the fluidity of the coal, and the interfacial tension between the fluid material and the solid particles that are presumed to be present under the test conditions. 

The test for the FSI of coal (ASTM, 2011g) reqnires that several 1 g samples of coal be heated to 820°C (1508°F) within a specified time to prodnce bnttons of coke. The shape, or profile, of the buttons (Table 9.15) determines the FSI of the coal (BSI, 2011). Anthracites do not usnaUy fnse or exhibit a FSI whereas the FSI of bituminous coals will increase as the rank increases from the high-volatile C bituminous coal to the low-volatile bituminous coal. 

Agglomerating and Caking Properties of Coals as Indicated by the Residue from the Volatile Matter Determination 

Non-agglomerating (button shows no swelling or cell structure and will not support a 500 g weight without 

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Eor the free swelling index which is also known as the cmcible swelling number (ASTM D720), a coal sample is rapidly heated to 820°C in a covered cmcible. Then the profile of the resulting char is compared to a series of standard numbered profiles (18). Eor the Roga index weighed amounts of coal and standard anthracite are mixed and carbonized, and the product coke is tested in a Roga dmm for its resistance to abrasion (89). 

Physical Properties The free-swelling index (FSl) measures the tendency of a coal to swell when burned or gasified in fixed or fluidized beds. Coals with a high FSl (greater than 4) can usually be expected to cause difficulties in such beds. Detads of the test are given by the ASTM D 720 (American Society for Testing and Materials, op. cit.) and U.S. Bureau of Mines Report of Investigations 3989. 

DILATATION AND FREE SWELLING INDEX RESULTS FOR ORIGINAL AND HYDROGENATED PHALEN SEAM COAL... 

Softening temperature Maximum contraction Maximum dilatation Free Swelling Index... 

The free swelling index (FSI) was determined on each of the size fractions for the top samples the values ranged from 5% to 9, whereas the bottom size fractions ranged from 6% to 9 (see Table I). In each case the lowest values occur in the intermediate size fractions—namely, those ranging from 2X1% inch to % X Vfe inch. These show a rough relationship with the increase in fusinite and semifusinite and the decrease in vitrinite in these... 

In ordar to determine the effect of coal rank (at established by reflectance measurement of vitrinite in coal) on the reactions of coal as related to carbonization, gasification, combustion, and other processes, a wide range of bituminous coals were studied. The results show that reflectance measurements can be used effectively (1) to determine accurately yields of coal carbonization products such as coke, tar, gas, light oil, and liquor from pilot and commercial coke oven (2) to obtain the heating value and specific gravity properties of gases from these processes (3) to determine the free swelling index and B.t.u. content of coals ... 

In this paper, we demonstrate how mean maximum reflectance of vitrinite in oil (hereafter referred to as R ) can be used in place of conventional chemical-rank parameters (volatile matter and fixed carbon) to estimate the relative yields of carbonization products, specific properties of gas produced by carbonization, and chemical properties of coal such as calorific value and free swelling index (FS1). Further, we illustrate that measured R can be used to detect coal oxidation, to categorize coals for certain combustion uses, and to help classify coals by rank. 

Figure 3. Relationship between reflectance and free swelling index...

Other important chemical and physical tests performed to characterize coal include (I) Heating value (Btu content) (2) sulfur forms (31 ash fusibility temperatures (4) ash analysis (5) trace elements (6) free swelling index and (7) hardgrove grindability. 

Free-Swelling Index (Crucible Swelling Number) Roga Index Dilatometer Gray- King... 

ASTM D-720. Standard Test Method for Free-Swelling Index of Coal. 

Free swelling index Measure of the increase in volume when a coal is heated without restriction... 

The free-swelling index of bituminous coals generally increases with an increase in rank (Table 7.5). Values for individual coals within a rank may vary considerably. The values for the lower-rank coals are normally less than those for bituminous coals, whereas anthracite does not fuse and shows no swelling value. 

Some problems associated with the method are the proper heating rate, oxidation or weathering of the coal sample, and an excess of fine coal in the analysis sample. Failure to achieve the proper temperature in the furnace or, more important, the proper heating rate for the sample in the crucible leads to unreliable results. Uneven heat distribution along the walls of the crucible may also cause erratic results. Oxidation or weathering of the coal sample leads to a low free-swelling index. To minimize oxidation and the effects on the free-swelling index, samples should be tested as soon as possible after they are collected and prepared. If oxidation of the coal is suspected, the test should be repeated on a known fresh sample of the same coal. 

The size consist of the analysis sample may influence the free-swelling index values of some coals. There is evidence that for many coals, an excess of fine coal (100 to 200 mesh) may cause FSI values to be as much as two index numbers high. The amount of fine coal in the analysis sample should be kept at a minimum for this test (and others). Reducing the coal from a large particle size to a small particle size in one step tends to produce a high concentration of fine coal. The reduction of coal samples should be done in an appropriate number of steps to avoid this. 

In another test method (ASTM D-5515), a dilatometer is used to measure the swelling of bituminous coal. The test method is limited in applicability to coal that has a free swelling index < 1 (ASTM D-720). The principle of this test method is that the final volume of char obtained at the conclusion of a standard dilatation test is dependent on the mass of coal in the coal pencil and on the radius of the retort tube. This test method incorporates a procedure that determines the mass of air-dried coal in the coal pencil, provides a means to measure the average retort tube radii and employs a means to report coal expansion on an air-dried coal weight basis. The value of the dilatation properties of coals may be used to predict or explain the behavior of a coal or blends during carbonization or in other processes, such as gasification and combustion. 

Free-swelling index measure of the agglomerating tendency of coal heated to 800°C (1470°F) in a crucible. Coals with a high index are referred to as coking coals, those with a low index are referred to as free-burning coal. 

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