Primary properties moisture content

The particle size and moisture content were the two primary properties requiring a lot of pre-treatment of the samples to fit into the desired limits mentioned above. The particle size distribution was determined by normal sieving procedure. 

The primary factors that affect the flowability of the final blend (or almost any powder), such as moisture content, particle shape/size/distribution, temperature/humidity and others, are discussed in more detail later in this chapter. Note that the measurement of flow properties and the design parameters they provide can also be applied to troubleshooting and developing corrective actions for flow problems in the preblending steps. 

Grindability (in its many different definitions) is a composite material property, and depends on many primary material properties (e.g. particle hardness, bulk and shear moduli of elasticity) as well as its flow properties and other conditions like moisture content, humidity of the atmosphere or material composition (rank or ash content of coal, for example). It also depends on the type of mill used for its evaluation. There have been some attempts made by several authors to find correlations relating different measures of grindability the reader is referred to the literature for details of these54. 

The water in coal is bound in different forms to its constituents. It can be divided into three types (1) Free moisture, also referred to as external moisture, superficial moisture, or the primary moisture fraction, which is present in large cracks and capillaries. Water bound in this way retains its normal physical properties. (2) Inherent moisture, also referred to as internal moisture or the secondary moisture fraction, whose vapor pressure is lower, since it is absorbed within the pore structure of the coal. (3) Water of constitution, which is mainly combined with mineral matter normally present in coal. This water is generally driven off only at temperatures higher than those normally used for the determination of moisture content. Standard methods do not make use of these terms and define (1) the total moisture content of a coal and (2) the moisture content of the coal analysis sample. Total moisture determination must be made over the sample as received in the laboratory, in an air-proof recipient. The determination consists in drying in an oven at 105 °C till constant weight. Its value is of huge interest both in international and domestic coal trade (ISO 589, ASTM D3173). 

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