Swelling true coal

Figure 6. Dependence of true coal volume fraction at equilibrium swelling in pyridine at 57 2°C on the (O) carbon and (%) oxygen contents (%, daf) of various American coal samples.

At first consideration, there may appear to be little, if any, relationship between the physical and chemical behavior of coal, but in fact the converse is very true. For example, the pore size of coal (which is truly a physical property) is a major factor in determining the chemical reactivity of coal (Walker, 1981). And chemical effects that result in the swelling and caking of coal(s) have a substantial effect on the means by which coal should be handled either prior to or during conversion operations. This is the reason for the study and measurement of these very important properties of coal. 

The true value of O2 s (equation 10) is the one to be used for the determination of Ac since it refers to the swelling of the coal matrix, excluding the pore structure. Use of the value of O2 (from equation 5) in equation (1) would lead to unaccept afcf I values of Mc. This is an error frequently made in previous studies. 

TABLE II. True Swelling Behavior of Crosslinked Structure in Coal Samples ... 

Other effects which can influence the FSI of coal include the weathering (oxidation) of the coal. Hence, it is advisable to test coal as soon as possible after collection and preparation. There is also evidence that the size of the sample can influence the outcome of the free swelling test an excess of fine (-100-mesh) coal in a sample has reputedly been responsible for excessive swelling to the extent that the FSI numbers can be up to two uumbers higher than is the true case. 

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