ISO 21404 specifies a method for the determination of the characteristic temperatures for the ash melting behaviour of solid biofuels.
Ash from biofuel is prepared under controlled conditions of time and equipment specifications to a controlled temperature of (550 ± 10) °C. This ash is homogenized, and a test piece is made from the prepared ash.
ISO 21404 on ash melting behaviour is beneficial for:
Ash melting is a complex process where also sintering, shrinkage and expansion or swelling can occur. The terms ash fusibility and ash softening are synonyms to ash melting.
The test method described in ISO 21404 provides information about fusion and melting behaviour of the composite inorganic constituents of the solid biofuel ash at high temperatures. The test method is empirical. The ash used for the test is a homogeneous material, prepared from the fuel by ashing at 550 °C (alternatively, ashing temperatures of 710 °C or 815 °C may be used). The determination is performed at a controlled rate of heating in a controlled atmosphere. In contrast, under full-scale conditions, the complex processes of combustion and fusion involve heterogeneous mixtures of particles, variable heating rates and gas compositions. The determined characteristic temperatures in the test can be used for comparison of the tendency of the ashes from different types and qualities of solid biofuels to form fused deposits or to cause bed agglomeration on heating.
Overall, ISO 21404 is helpful as it describes about the shape factor of the test piece which is determined when a computer is used for image analysis of the test piece during heating. To determine the shape factor, the circumference of a perfect semicircle with the same area as the test piece’s shadow is calculated.
EN ISO 21404:2020
ISO 21404