BS EN 14780:2011 pdf download – Solid biofuels — Sample preparation
6.2 Apparatus for particle size-reduction CAUTION — When analysing metals, take care that there is no contamination from the sample preparation or reduction equipment.
6.2.1 Coarse cutting mill or wood crusher Coarse cutting mills are used for cutting materials into lengths of about 1 0 mm to 30 mm (depending on the biofuel and the analyses to be performed). Drying of the material during coarse cutting should be avoided, by limiting heat production and air flow through the material. The equipment shall be designed so that it does not lose dust or contaminate the material with pieces of metal, and shall be easy to clean. NOTE To prevent losses of moisture during particle size reduction a grinder with as low a grinding speed as possible is preferred.
6.2.2 Cutting mill Cutting mills are used for reducing the nominal top size of materials used as biofuels from about 1 0 mm to 30 mm down to about 1 mm or less (depending on the biofuel and the analyses to be performed).
The mill shall be provided with screens of various aperture sizes covering this range, including an appropriate sieve to control the nominal top size of the material produced. Other apparatus may be used provided that they are designed so that they do not get blocked with the material that is being processed. Avoid the use of cutting mills whose cutting faces contain significant quantities of an element that is to be determined in the analysis. NOTE Cross beater mills can be used without any excessive dusting, when fitted with dust filters (like a filter sock) between the mill and the receiving container. They are suitable for final grinding of hard, wood type materials after the pre- grinding with cutting type mills.
6.2.3 Axe An axe is used for cutting wood logs or coarse material down to maximum 30 mm thickness or suitable size to be processed in a cutting mill provided with a 30 mm sieve.
6.2.4 Hand saw A hand saw is used to saw off wood logs or coarse material down to maximum 30 mm thickness or suitable size to be processed in a cutting mill provided with a 30 mm sieve. NOTE A chain saw may contaminate the sample by chain oil and should therefore not be used. A saw machine should not be used for size reduction to avoid the risk of losing moisture in the sample as a result of heat caused by friction.
6.3 Sieves A wire-mesh sieve with an aperture size of 1 ,00 mm is required to check the nominal top size of general analysis samples. A wire-mesh sieve with an aperture size of 0,25 mm will be required if sub-samples with this nominal top size are required.
6.4 Balance A balance is required that is capable of determining the mass of samples to an accuracy of 0,1 % of the sample mass, and the mass of sub-samples to an accuracy of 0,1 % of the sub-sample mass.
7 Sample reduction – general principles For every sample division stage to be carried out it is important that a sufficient mass of material is retained, otherwise the sub-samples produced or the test portions to be taken may not be representative of the original sample. Table 1 gives a guideline for minimum masses to be retained after each sample division stage, depending on the nominal top size of the material. In addition to the minimum masses stated in Table 1 , it shall be ensured that the mass after a sample division stage is sufficiently large for the actual test or tests to be performed. Supplementary requirements concerning the masses of the test portions are given in European Standards for test methods of solid biofuels.
8 Methods for sample division 8.1 General Combined samples may be divided into two or more laboratory samples and laboratory samples are in general further divided in sub-samples (test-portions). This clause describes the methods and procedures for sample division. For every division step the mass of retained material given in Table 1 shall be taken into account.