BS EN 15290:2011 pdf download – Solid biofuels — Determination of major elements — Al, Ca, Fe, Mg, P, K, Si, Na and Ti
NOTE2 lf the maximum pressure limit of the vessel is exceeded during the digestion and by that an opening of therelief valve has occurred, the digestion should be discarded due to possible loss of Si(in form of gaseous SiFa).
NOTE3 Some available digestion bomb systems use fluoropolymer vessels, which cannot withstand temperaturesabove 170 “℃. In such cases this lower temperature can be used,provided that the sample is held longer at thistemperature and that comparable results can be obtained, e.g.by the use of equivalent biomass reference materials,
c)After cooling to room temperature, HF is neutralised by adding 10 ml H,BO3(4 %).
NOTE4 lf 2,0 ml HF(40 %) was used for the digestion 20 ml HBOs(4 % ) should be used for the neutralisation.
d)Reheat the sample according to the following heating programmes for neutralisation:
1)Resistance heating1 ): step 1: Heat rapidly to 180 c
Step 2: Hold for 15 min at 180 c
2)Microwave heating2′.: Step 1: Heat rapidly to 150°C
Step 2: Hold for 15 min at 150 °℃
e) After cooling, transfer the digest to a volumetric flask. Rinse the digestion vessel carefully and transfer the
rinse solution to the volumetric flask. Add deionised water to the digest to an appropriate volume,depending on the detection method to be used.
9.1.2Part B: Determination on a prepared 550 C ash
a)Heat the sample according to the procedure described in EN 14775 to obtain ash.Take care that the
ashing procedure is performed exactly according to this procedure as deviations in ashing temperature,time and air refreshing rate will influence the results. In deviation of EN 14775 only crucibles made ofplatinum or graphite can be used for the preparation of the ash, but larger types of crucibles may be used.The use of the stated additives in EN 14775 to ensure complete combustion is not allowed in thepreparation. Also a continuous ashing by refilling of the sample on the previous ash in the crucible is notallowed.
NOTE1 To prepare a sufficient amount of ash for the digestion larger amounts of sample,compared to theprocedure given in EN 14775, will often be necessary.
The ash percentage on dry basis obtained for the prepared ash thus shall be calculated and compared toobtained results for the ash content on dry basis determined exactly according to EN 14775.
NOTE2 lf the ash content for the prepared ash is known also the results for major elements determined for theprepared ash may be calculated to fuel basis.
b) Homogenise the prepared ash in an agate mortar and reignite the homogenised ash at 550 °C for 30 min.
The weighing of the test portion of the ash for the digestion has to be carried out immediately after thepreparation.
For the digestion of the ash similar working steps, as for the digestion of the fuel, are evident:
c) Mix 50 mg of ground and homogenised ash, weighed to the nearest 0,1 mg, with 2,0 ml H 2 O 2 (30 %), 3,0 ml HNO 3 (65 %) and 2,0 ml HF (40 %) in a closed decomposition vessel. A reaction time of minimum 5 min shall be kept before closing the vessel.
d) Digest the sample following one of the heating programmes described in 9.1.1 for digestion.
NOTE 3 If the maximum pressure limit of the vessel is exceeded during the digestion and by that an opening of the relief valve has occurred, the digestion should be discarded due to possible loss of Si (in form of gaseous SiF 4 ).
e) After cooling to room temperature, the HF is neutralized by adding 20 ml H 3 BO 3 (4 %) and 10 ml deionised water.
NOTE 4 The water is necessary to keep K in solution for bio-ashes with high KCl content.
f) Reheat the sample according to the heating programmes for neutralisation described in 9.1.1.
g) After cooling, transfer the digest to a volumetric flask. Rinse the digestion vessel carefully and transfer the rinse solution to the volumetric flask. Add deionised water to the digest to an appropriate volume, depending on the detection method to be used.