ISO 21404-2020 pdf download.Solid biofuels – Determination of ash melting behaviour.
Check the pyrometer at least once a year and when required e.g. after changing heating elements under routine test conditions by observations of the melting point of gold (5.2) and, if possible in the maximum temperature of the furnace (6..4) the melting point of palladium (5.4). Place the reference wire at different locations in the oven. Test the reducing atmosphere by observing the melting point of nickel (5).
If the observed melting points for gold or palladium differ by more than 10 °C from the melting points of the materials given in 5.2 and 5A readjust or recalibrate.
An alternative to the observations of the melting points of gold and palladium is to check the pyrometer using a thermocouple certified by a recognized reference laboratory or with a calibration which is traceable back to a standard reference laboratory.
If the observed melting point for nickel differs by more than 10 °C from the melting point given in Li it can be due to oxidation of nickel caused by an insufficiently reducing atmosphere. Examine the apparatus for leakages, control the flow rate and the quality of the gases and recheck the melting point of nickel.
NOTE The correct melting point of nickel is not a guarantee that the composition of the reducing atmosphere is correct, as deviations could be considerable before the fusibility is affected.
9 Procedure
9.1 Preparation of ash
Load a sufficient amount of the analysis sample of the solid biofuel in the ashing dish or dishes (6.1) to obtain a minimum of 1 g ash and spread in an even layer over the bottom surface. The use of additives to ensure complete combustion is not allowed. Continuous ashing by refilling of the sample on the previous ash in the crucible is also not allowed.
Place the dish(es in the cold furnace 6,Z) and heat in air atmosphere in accordance with the following temperature program.
— Raise the furnace temperature evenly to a temperature between 230 °C and 250 °C with a heating rate of (3 to 5) °C/min. Maintain temperature at this level for at least 180 mm to allow the volatiles to leave the sample. The sample shall not ignite during this step of preparation of the ash. Do not open the furnace to check! An evidence olignition is a sudden rise of oven temperature. If the sample ignites repeat the ashing procedure with a lower heating rate and/or a lower hold temperature.
— Continue to raise the furnace temperature evenly to (550 ± 10) °C (or to an alternative higher final ashing temperature ±10 °C) with a heating rate of —10 °C/min. Maintain temperature at this level for at least 120 mm.
— Stop heating and let cool down the furnace with sample to below 200 °C.
Remove the dish with its content from the furnace. Allow the dish and its content to cool on a heat resistant plate to ambient temperature. Either proceed with preparation of test pieces or store the sample in sample containers or bags (6.3).ISO 21404 pdf download.