A critical review of sampling standards for solid biofuels: Missing contributions from the Theory of Sampling (TOS)

Current standards for biofuel dealing with sample extraction, mass reduction and sample preparation are assessed with respect to the principles for representative sampling as set forward in the Theory of Sampling (TOS), which constitutes the only complete, scientific theory for sampling. Practical industrial sampling constitutes the only source for gaining data for reliable process monitoring and control - but involves a high error potential if not based on unambiguous, representative samples. For the comparatively new sector of biomass combustion or co-firing of biomass in converted coal power plants, reliable quality measures are crucial to assure stable fuel quality and for being able to optimize the combustion process. All so-called "incorrect sampling errors" (incorrect delineation, - extraction and - preparation) must be identified, reduced, if not altogether eliminated, lest representativeness is impossible. For reaching this target and to ensure representative sampling, a minimum working understanding of TOS is required. Sampling standards serve the purpose to delineate the foundation and assurance for reliable, representative sampling under all circumstances for the material class(es) involved, and must for this reason be in full compliance with TOS. This critical review shows that many recommended or allowed sampling procedures for solid biofuels do not comply herewith, and neither are all the necessary rules of TOS followed for the subsequent mass reduction procedures in the analytical laboratory. We point out all such error sources in the current standards and discuss what measures are necessary to rectify this incomplete state-of-affairs. The current review is but one activity within the context of formulating an even more general, "horizontal" sampling standard intended to cover all material classes.