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Chapter 3 | Sampling and Sample Preparation
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Preliminary to any laboratory testing of coal, it is imperative that a representative sample be obtained; otherwise, the most carefully conducted analysis is meaningless. Reliable sampling of a complex mixture such as coal is difficult, and handling and preparation of the sample for analysis presents further problems. Variations in coal handling facilities make it practically impossible to publish a set of rules that would apply to every sampling situation. The proper collection of the sample involves an understanding and consideration of the minimum number and weight of increments, the particle size distribution of the coal, the physical character and variability of the constituents of coal, and the desired precision.Guidelines for the collection of gross samples of coal are given in ASTM Standard Practice for Collection of a Gross Sample of Coal (D2234/D2234M) and in ASTM Standard Practice for Mechanical Sampling of Coal (D7430). The newer standard ASTM D7430 is a combination of several previous sampling standards. Another ASTM Standard Practice for collecting gross samples is Manual Sampling of Stationary Coal from Railroad Cars, Barges, Trucks, or Stockpiles (D6883). ASTM D6609 is a guide for part-stream sampling of coal. Also found in Volume 05.06 of the Annual Book of ASTM Standards is a standard practice for the collection and preparation of coke samples (D346).Some specific terms used in coal and coke sampling are “gross sample,” “lot,” “representative sample,” “laboratory sample,” and “analysis sample.” A gross sample is defined as a sample representing a quantity, or lot, of coal and is composed of several increments on which neither reduction nor division has been performed. A lot is a discrete quantity of coal for which the overall quality to a particular precision needs to be determined. For quantities of coal up to approximately 1000 Mg (1000 tons), it is recommended that one gross sample represent the lot. The number of increments to be taken for the gross sample depends on the type of coal being sampled as shown in Table 3.1. The size of each increment depends on the top size of the coal being sampled.