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WOOD PELLETS
QUALITY CONTROLQUALITY CONTROL
Roger MertensRoger Mertens
1010thth of June 2010of June 2010
WHO IS INSPECTORATE
A staff of over 5000 people.
Global inspection and testing in over 100 countries100 countries.
A global network of laboratory and sample preparation facilities.
A wide range of commoditiesA wide range of commodities.
ISO 17025 (Accreditation)
ISO 17025 (Accreditation)
ISO 17025 (Accreditation)
1 General requirements
SUBJECTS
1. General requirements.2. Requirements for trace elements.3. Pellets particle size requirements.4. Sampling.5. Theoretical approach - some terms from ISO 18283.6. Sample preparation.6. Sample preparation.7. Analysis.8. Repeatability – reproducibility.9. Size distribution.10. Fiber particle size.11. Mechanical durability.y12. Bulk density.13. Visual aspect - conclusions.
General RequirementsParameter ÖNorm M 7135 DIN 51731 ElectrabelParameter ÖNorm M 7135 DIN 51731 Electrabel
Diameter D 4 – 10 mm 4 – 10 mm < 10 mm
Length L 5 x D mm < 50 mm < 40 mm
Dust content < 10 %
Moisture < 10 % < 12 % < 10 %
Ash < 0.50 % < 1.50 % < 1.50 %
Sulphur (S) < 0.04 % < 0.08 % < 0.2 %
Nitrogen (N) < 0.3 % < 0.3 % < 0.5 %
Fluoride (F) < 70 ppm
Chloride (Cl) < 0.02 % < 0.03 % < 0.05 %
Nett calorific value > 18 MJkg 17.5 – 19.5 MJkg > 16 MJ/kg
Press aids < 2 % Not allowed Vegetable oils
AFT (DFT) red. atm. > 1200 °C
Phosphor (P) < 300 ppm
Bulk density > 600 g/l
Requirements for Trace Elements
Element DIN 51731 Electrabel
A i (A ) 0 8 k 2 /kArsenic (As) < 0.8 mgkg < 2 mg/kgCadmium (Cd) + Titanium (Ti) < 0.5 mgkg < 1 mg/kg
Chrome (Cr) < 8 mgkg < 15 mg/kg
Copper (Cu) < 5 mgkg < 20 mg/kg
Lead (Pb) < 10 mgkg < 20 mg/kgMercury (Hg) < 0 05 mgkg < 0 10 mg/kgMercury (Hg) < 0.05 mgkg < 0.10 mg/kgZinc (Zn) < 100 mgkg < 20 mg/kgEOX < 3 mgkgBenzo-a-pyrene < 0.5 mg/kgPenta-chlore-phenol < 3 mg/kg
Pellets Particle Size Requirements
Size Electrabel
< 4 mm 100 %
< 3 mm 99 % 3 mm 99 %
< 2 mm 95 %
< 1 5 mm 75 %< 1.5 mm 75 %
< 1 mm 50 %
Sampling
Size of increments (in liter):
According CEN/TS 14778-1 (NTA 8202)
Size of increments (in liter):V min = 0.5 for d ≤ 10 mm.V min = 0.05 x d for d ≥ 10 mm.
Sampling
From a falling stream
On stopped or moving conveyor
Sampling
Number of increments (n)
Sampling
Number of increments (n)
Stationary material Moving material
Group 1 n = 5 + 0.025 x M lot n = 3 + 0.025 x M lot
Group 2 n = 10 + 0.040 x M lot n = 5 + 0.040 x M lot
Group 3 n = 20 + 0.060 x M lot n = 10 + 0.060 x M lot
Sampling of Small Stock Piles (< 100 m3)
Increments in function of the volume (weight) per sectionIncrements in function of the volume (weight) per section.If the material in the pile is segregated, move the material into a new pile and take increments during the removal.
Sampling of Large Stock PilesVisual inspection if there are regions containing significantly different material.How was the pile formed?pWith a conical heap, coarser particles tend to collect at the outside and at the base and finner particles collect in the interior of the pileinterior of the pile.
Some Terms From ISO 18283
Primary increment variance VI
Some Terms From ISO 18283
Preparation and test variance VPT
Some Terms From ISO 18283
Overall precision PL
Sample Preparation
According CEN/TS 14780
Main purpose of the sample preparation:
Mass-reduction of the sample by division.
Particle size-reduction of the sampleParticle size reduction of the sample.
Keeping all the sub-samples representative for the original sample.
Sample Division
Manual cooning and quartering
Sample Division
Riffle dividers
Sample Division
Rotary dividers
Sample Division
Rotary dividers
Particle size-reduction
Cutter mill
Analysis
Total moisture (Mar):Norm CEN/TS 14774-1 : reference method.
Drying at 105 °C in air atmosphere till constant weight and including a procedure for buoyancy effects.
Norm CEN/TS 14772-2 : simplified method.Drying at 105 °C in air atmosphere till constant weightDrying at 105 C in air atmosphere till constant weight.
Sample weight in both cases minimum 300 g and preferably more than p g g p y500 g.
Thickness maximum 30 mm.
Loading of the dishes or trays about 1 g/cm2.Loading of the dishes or trays about 1 g/cm .
Analysis
An unusual expression:Total moisture on wet basis (Mar) and on dry ( ar) ybasis (Ud)The reference method CEN/TS 14774-1 expresses the relationship between moisture on dry and on as received basis:
U = (M x 100) / (100 M )Ud = (Mar x 100) / (100 – Mar)
M (U 100) / (100 U )Mar = (Ud x 100) / (100 + Ud)
Analysis
Moisture in the analysis sample (Mad):
Norm CEN/TS 14774-3Drying at 105 °C in air or nitrogen atmosphere till
t t i htconstant weight.
Particle size maximum 1 mm.
Loading of the dishes or trays about 0 2 g/cm2Loading of the dishes or trays about 0.2 g/cm .
Sample weight minimum 1 g.
Analysis
Ash content (Adb):
Norm CEN/TS 14775Heating at 550 °C or 815 °C (ISO 1171) till constant weightHeating at 550 C or 815 C (ISO 1171) till constant weight.
Particle size maximum 1 mm.
Loading of the dishes or trays about 0.1 g/cm2.
Sample weight minimum 1 g.
Analysis
Ash content (Adb):
Possible differences between 550 and 815 °C:
Loss of volatile inorganic compounds.
Further oxidation of inorganic compounds.
D iti f b t f i CODecomposition of carbonates, forming CO2.
Analysis
Volatile matter (Vd):
Norm CEN/TS 15148Heating at 900 °C for 7 minutesHeating at 900 C for 7 minutes.
Particle size maximum 1 mm.
Sample weight between 0.9 – 1.1 g.
Oven temperature to be regained
within 4 minutes after insertion
of a cold stand and its crucibles.
Analysis
Total sulphur (S) and chlorine (Cl):
Norm CEN/TS 15289 (two steps or automatic equipment)
Two steps:
1. Digestion of the pellets and transfer of acidic gaseous components into solution.
2. Determination of sulphate and chloride in the receiving solutionsolution.
Analysis
Total sulphur (S) and chlorine (Cl):
Automatic equipment:
Analysis
Total carbon (C) – hydrogen (H) and nitrogen (N):
N CEN/TS 15104 ( t ti i t)Norm CEN/TS 15104 (automatic equipment)Burning the sample in pure oxygen.
Measuring the resulting gasses of CO H O and NMeasuring the resulting gasses of CO2, H2O and N2
Analysis
Calorific value:Norm CEN/TS 14918 (automatic equipment)Gross calorific value (GCV) dry at constant volume (qV,gr,d).
Burning a pellet of the sample in a bomb calorimeter (add aspike) and measuring the temperature rizespike) and measuring the temperature rize.
Analysis
Calorific value:
Net calorific value (NCV) at constant volume (qV net m).( ) (qV,net,m)
In cal/g or kcal/kg:q V,net,m = [ q V,gr,d – (49,2 x Hd) ] x [(100 – MT) / 100 ] - 5,51 x MT
In J/g or kJ/kg:q V,net,m = [ q V,gr,d – (206 x Hd) ] x [(100 – MT) / 100 ] - 23,0 x MTV,net,m V,gr,d d T T
Analysis
Calorific value:Net calorific value (NCV) at constant pressure (qp,net,m).
In cal/gq p,net,m = {q V,gr,d - 50,6 x w(H)d - 0,19 x [w(O)d + w(N)d ] } x [(100 - MT) / 100 ] - 5,83 x MT
In J/gq p,net,m = {q V,gr,d - 212 x w(H)d - 0,8 x [w(O)d + w(N)d ] } x [(100 - MT) / 100 ] – 24,43 x MT
Analysis
Major, minor and trace elements:
Depending on the element to be measured:Digestion of the sample in a closed vessel.
Fl i f th h i Pt di hFluxing of the ashes in Pt dishes.
Measurement:Measurement:
Flame atomic absorption (FAA).
Graphite furnace atomic absorption (GFAA).
Inductive coupled plasma (ICP)
Repeatability - Reproducibility
Parameter Repeatability Reproducibility
Total moisture Not applicable Not applicableTotal moisture Not applicable Not applicable
Ash content < 10 % 0.2 % absolute 0.3 % absolute
Volatile matter 3 % of the mean result 4 % of the mean result
Sulphur or chlorine ≤ 500 mg/kg 50 mg/kg 100 mg/kg
Sulphur or chlorine > 500 mg/kg 10 % of the mean result 20 % of the mean result
Carbon 0.5 % absolute 1.5 % absolute
Hydrogen 0.25 % absolute 0.5 % absolute
Nitrogen ≤ 0.5 % 0.05 % absolute 0.1 % absolute
Nitrogen > 0 5 % 10 % of the mean result 20 % of the mean resultNitrogen > 0.5 % 10 % of the mean result 20 % of the mean result
GCV - NCV 120 J/g 300 J/g
Size Distribution
Norm CEN/TS 15149-1Oscillating screen method using sieve apertures > 3.15 mm.
A minimum sample size of 8 liter.
Round holes.
Moisture content < 20 %.
Manual or mechanical sieving allowed.
Horizontally oscillating (one or two dimensial).
Size DistributionN CEN/TS 15149 2Norm CEN/TS 15149-2Vibrating screen method using sieve apertures < 3.15 mm.
A minimum sample size of 50 g.
Combination of round and square holes.
Moisture content < 20 %.
M l i i t ll dManual sieving not allowed.
Recommended for sawdust:
3.15 mm round, 2.8 – 2.0 – 1.4 – 1.0
0.5 and 0.25 mm square wire cloth.
Size DistributionN CEN/TS 15149 3Norm CEN/TS 15149-3Rotary screen method
Fiber Particle Size (Meal Spectrum)
Grinding finer produces better quality pellets.Grinding finer produces better quality pellets.
The following spectrum should be approached:The following spectrum should be approached:
> 3 mm Up to 1 %> 3 mm Up to 1 %2 – 3 mm Up to 5 %1 – 2 mm Around 20 %%0,5 – 1 mm Around 30 %0,25 – 0,5 mm Around 24 %< 0,25 mm Not less than 20 %
Fiber Particle Size (Meal Spectrum)Fib ti l iFiber particle size
Mechanical Durability DUN EN 15210 1Norm EN 15210-1 Collision against each other and the walls of a specified rotating test chamber.
Test portion 500 ± 10 g > 3,15 mm round holes .
500 rotations at 50 ± 2 rpm.
DU = (mA / mE) x 100
Electrabel requirement: > 94 % and < 98 %.Electrabel requirement: 94 % and 98 %.
Bulk DensityN EN 15103Norm EN 15103
Cylindric bucket of 5 l or 50 l.
A ratio height to diameter between 1,25 and 1,50.
Free falling from a height of 15 cm for the settling of the pellets.
Bulk densities:
# Pellets about 650 kg / m3# Pellets about 650 kg / m3.
# Fraction < 3,15 mm about 400 kg / m3.
# Fraction < 1,00 mm about 320 kg / m3.g
Visual Aspect - Conclusions
The visual aspect of the wood pellets is the first quality control.
The colour is an indication if more than one type of wood has been
used.
Due to the big difference in bulk density is it hard to estimate the
undersize visuallyundersize visually.
Wet spots are easy to detect, due to colour difference or
desintigration of the pellets.g p
Wood pellets have to be concidered as dangerous, due to possible
CO gas formation in closed spaces.
Visual Aspect - Conclusions
Check for free water in barges, because this can accelerate the danger of self combustion.
Tempeature monitoring is strongly advised:Tempeature monitoring is strongly advised:
20 – 40 °C Enzymatic heat.
40 – 75 °C Microbiological heat.
> 75 °C Chemical heat.
SELF COMBUSTION AT…..?
