Solid fuels. Coal.Sampling and testing

Natural carbonaceous products, such as coal and biomass, or processed products, such as coal and petroleum coke, are heterogeneous in their composition, requiring specific precautions to be taken during sampling, sample preparation and laboratory testing and analysis.

We need to distinguish between raw materials, either extracted from the mine or derived from plant production, which are characterized by their varied chemical composition, and processed products such as coal and petroleum cokes and wood pellets.

Biofuels (wood, industrial or agricultural waste, etc.) are not dealt with fundamentally in this article, but are covered for certain topics because of their similarity to solid fuels of fossil origin.

The precautions required to deal with them are common to all bulk materials, but they are particularly important in the case of coal and biomass prior to processing. For example, sensitivity to oxidation by atmospheric oxygen calls for appropriate measures to be taken during storage, sample transport and laboratory preservation.

The ability of hydrophilic porous materials to absorb or reject moisture depending on local atmospheric conditions means that strict rules must be observed when determining water content, which has both technical and commercial implications.

Finally, the mechanical fragility of coal, which results in more or less significant breakage of pieces and the formation of dust during handling operations, must also be taken into account, particularly when determining grain size and calorific value.

The quantity of material taken for analysis is directly related to the maximum size of the pieces (known as the maximum nominal size). With a few exceptions, relating to the direct determination of physical and mechanical properties on particles of various sizes, chemical analyses generally involve one to a few grams of product ground to the fineness of analysis.

As a result, sampling and sample preparation are of paramount importance, and this can be summed up in one figure: 90% of analytical errors are due to faulty sampling or preparation.

Sampling operations for solid fuels are the subject of studies that are as much the work of physicists and industrial chemists as of statisticians. In order to simplify these complex theses for the industrial sector concerned and field service providers, they have been described mainly in collections of internationally recognized standards. In this way, the minimum conditions for a representative selection of the coal or coke sample are specified to the laboratories, and have equal value in international trade. Petroleum coke, a material similar in appearance to...