Chemical methods for solid biofuels
Martin Englisch
ofi – Österreichisches Forschungsinstitut für Chemie und
Technik
Solid fuels
solid biofuel
non combustible
fraction
water
ash
combustible
fraction
volatiles
coke
Composition of wood
Chemical composition:
Components:
51% carbon
50% cellulose
42% oxygen
25% hemicellulose
6% hydrogen
25% lignin
< 1% nitrogen
< 5% resins etc.
< 0,1% sulphur,
halogenes
< 1% ash forming
minerals
Harmful substances, pollutants
N, S, halogenides are environmental harmful substances
Nitrogen
− Fuel nitrogen is mainly responsible for NOx-emissions
− Origin in wood: natural content up to 0,3%, higher concentrations are due to glues
or other adheasives
Sulfur
− Mainly from organic sulfur compounds SO2 is formed during combustion which
forms sulphurous acid causing acidic rain
− Origin in wood: usually very low concentrations, significant amounts may occur if
e.g. lignosulphonate is used as binding agent in pellets
Chlorine
− Forms hydrochloric acid in combustion which is mainly responsible for corrosion
− Origin in wood: usually very low concentrations, contamination from plant sprays,
fertilizers, thawing salts. In other solid biofules higher concentrations are often
found – very critical chemical parameter!
NOx-formation
Aerosol formation
Chemical test methods
CEN/TS 15104 Solid biofuels — Determination
of total content of carbon, hydrogen and
nitrogen — Instrumental methods
CEN/TS 15289 Solid biofuels — Determination
of total content of sulphur and chlorine
CEN/TS 15105 Solid biofuels — Methods for
determination of the water soluble content of
chloride, sodium and potassium
CEN/TS 15290 Solid biofuels — Determination
of major elements
CEN/TS 15296 Solid biofuels — Determination
of minor elements
CEN/TS 15297 Solid biofuels — Calculation of
analyses to different bases
CEN/TS 15104 Determination of total content of carbon,
hydrogen and nitrogen — Instrumental methods
Principle
sample is burnt completely in oxygen
gaseous products: carbon dioxide, water vapour, elemental
nitrogen and/or oxides of nitrogen, oxides and oxyacids of sulphur
and hydrogen halides
Treatment of gases: hydrogen associated with sulphur or halides is
liberated as water vapour
Oxides of nitrogen are reduced to elemental nitrogen
products of combustion which interfere with the subsequent gasanalysis procedures are removed
Carbon dioxide, water vapour and nitrogen are determined
quantitatively by appropriate instrumental gas- analysis procedures
CEN/TS 15104 carbon, hydrogen and
nitrogen — Instrumental methods
Instruments and reagents
Automatic systems are used e.g. Leco, Elemental
− Requirements on performance of systems is given in the standard
Calibration standards are used for calibration
Accuracy of method is tested by certified reference materials
For Nitrogen, the Kjeldahl method may be used!
CEN/TS 15104 carbon, hydrogen and
nitrogen — Instrumental methods
Procedure
Preparation of test sample and test portion
Calibration of system
Analysis of sample
Expression and calculation of results
Performance of methods:
Maximum acceptable differences between results
(on dry basis)
repeatability
reproducibility
0,5 % absolute
1,5 % absolute
Hydrogen content
0,25 % absolute
0,5 % absolute
Nitrogen content
10 % relative if N > 0,5 %
20 % relative if N > 0,5 %
0,05 % absolute if N < 0,5 %
0,1 % absolute if N < 0,5 %
Carbon content
Results from BIONORM nitrogen
Precision of method
Nitrogen
Content
mean
[wt %, d.b.]
Reproducibility
R abs
R rel
Repeatability
r abs
r rel
[%]
[%]
[%]
[%]
wood without bark
0,060
0,060
99,2
0,027
45,1
woodchips
0,106
0,087
82,0
0,079
74,7
hardwood with glue
0,342
0,144
42,2
0,036
10,5
rapestraw
0,406
0,159
39,2
0,090
22,1
bark
0,669
0,221
33,1
0,076
11,4
straw
0,713
0,191
26,7
0,078
10,9
cynara
1,006
0,241
24,0
0,107
10,6
orujillo
1,314
0,333
25,3
0,090
6,8
CEN/TS 15289 Determination of total content of
sulphur and chlorine
Principle
Combustion and transfer of acidic gaseous components into solution
• Combustion in an oxygen bomb and absorption of the acidic gas
components in an absorption solution (method A);
• Decomposition in closed vessels as described in CEN/TS 15290 (method B).
CEN/TS 15289 Determination of total content of
sulphur and chlorine
Determination of sulphate and chloride in receiving solution
• Ion chromatography applying the principles of EN ISO 10304-1;
• ICP, applying EN ISO 11885
• Other suitable analytical methods.
• A large number of methods for the quantification of sulphate and
chloride exists but detection limits and precision vary significantly.
Automatic equipment may be used when the method is validated with
biomass reference samples of an adequate biomass type
X-ray fluorescence may be used to determine sulphur and chlorine
directly in the solid biofuel samples
CEN/TS 15289 sulphur and chlorine
Combustion in a closed bomb
Most frequently used method, combination with NCV
1 g sample is pressed to a pellet, put into a quartz glass or metal crucible
and combusted in 30 bar oxygen
Eventual use of combustion aid
− Liquid combustion aid e.g. dodecane
− Solid combustion aid: combustion bag or capsule with known weight
CEN/TS 15289 sulphur and chlorine
Combustion in a closed bomb
After combustion absorption solution is filled in a flask (50 or 100 ml)
Attention:
− Check complete combustion
− Thoroughly rinse the bomb
− Eventual chemical treatment
of the solution
− Check losses during venting
(gas washing bottle)
CEN/TS 15289 sulphur and chlorine
Detection methods
Ion chromatography
− is the recommended method for the detection of sulphate and
chloride (EN ISO 10304-1)
− use a syringe equipped with a 0,45 µm pore size filter
Other analytical methods:
Method
Cl
S
References (examples)
ICP
X
X
EN ISO 11885
photometric (colorimetric)
X
Turbidimetric
DIN 51727
X
ASTM D516 - 02
photometric titration
X
ISO 587
Coulometric
X
DIN 38405 - 1 (method D1-3)
potentiometric titration
X
DIN 38405 - 1 (method D1-2)
CEN/TS 15289 sulphur and chlorine
Precision of method
Content of sulphur and
chlorine
dry basis
Maximum acceptable differences between results
Same laboratory
(Repeatability)
Different laboratories
(Reproducibility)
Chlorine ≤ 500 mg/kg
> 500 mg/kg
50 mg/kg
10 % of the mean result
100 mg/kg
20 % of the mean result
Sulphur ≤ 500 mg/kg
> 500 mg/kg
50 mg/kg
10 % of the mean result
100 mg/kg
20 % of the mean result
Results from BIONORM for chlorine
Precision of method
Chlorine
content
mean
[wt %, d.b.]
Reproducibility
R abs
R rel
[%]
[%]
Repeatability
r abs
r rel
[%]
[%]
wood without bark
0,003
0,006
174
0,003
93
woodchips
0,005
0,010
185
0,006
103
bark
0,010
0,010
99
0,005
53
hardwood with glue
0,015
0,012
83
0,007
51
straw
0,11
0,030
26
0,016
14
orujillo
0,20
0,043
21
0,013
7
rapestraw
0,28
0,065
23
0,027
10
cynara
1,59
0,44
27
0,18
11
CEN/TS 15105 Solid biofuels — Methods for determination of
the water soluble content of chloride, sodium and potassium
Principle
The fuel sample is heated with water in a closed container at
120 °C for 1 hour.
The concentrations of chloride, sodium and potassium in the
obtained water extract are determined by:
− Chloride: Ion-Chromatography (IC) or potentiometric titration with silver nitrate
(any contents of water soluble bromide and iodide will be included in the
determination)
− Sodium and potassium: Flame Emission Spectroscopy (FES) or Flame Atomic
Absorption Spectroscopy (FAAS) or Inductively Coupled Plasma Optical Emissions
Spectroscopy (ICP-OES).
CEN/TS 15105 water soluble content of chloride,
sodium and potassium
Precision of method
Content of water soluble
element,
same laboratory
(repeatability)
different laboratories
(reproducibility)
50 mg/kg
100 mg/kg
> 500 mg/kg
10 % of the mean result
20 % of the mean result
≤ 100 mg/kg
10 mg/kg
20 mg/kg
> 100 mg/kg
10 % of the mean result
20 % of the mean result
as analysed
Chloride
Sodium /
potassium
Maximum acceptable differences between results
≤ 500 mg/kg
CEN/TS 15290 Solid biofuels — Determination of
major elements
Major ash forming elements:
Al, Ca, Fe, Mg, P, K, Si, Na, Ti
Principle
The sample is digested in a closed vessel
by reagents, temperature and pressure.
The digestion is either carried out directly
on the fuel (part A)
− 500 mg sample, 3,0 ml H2O2 (30 %), 8,0 ml
HNO3 (65 %) and 1,0 ml HF (40 %) in the
vessel.
− The heating of the vessel should not be to
fast. A heating procedure is given in the
standard
− After cooling HF is neutralised by H3BO3 (4
%). Reheat the sample.
− After cooling, transfer the digest to
volumetric flask.
or on a 550 °C prepared ash (part B).
CEN/TS 15290 major elements
Detection methods
For the detection of the concentrations of Al, Ca, Fe, Mg, P, K,
Si, Na, Ti in the digests the following methods can be used:
− ICP/OES according to EN ISO 11885.
− ICP/MS according to EN ISO 17294-2.
− AAS according to EN ISO 7980, ISO 9964-1 and ISO 9964-2.
− FES according to ISO 9964-3.
CEN/TS 15290 major elements
Precision of method
Coming soon!
Validation in progress
CEN/TS 15296 Solid biofuels — Determination of
minor elements
Minor elements:
Arsenic, Cadmium, Cobalt, Chromium, Copper,
Mercury, Manganese, Molybdenum, Nickel, Lead,
Antimony, Vanadium and Zinc principle
Method similar to major element
CEN/TS 15296 minor elements
Detection methods
As, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn can be
detected by ICP-MS, ICP-OES or GF-AAS provided that the
detection limits of the used method are sufficient for the fuel
specifications
As and Se can be determined by HG-AAS (EN ISO 11969).
Hg can be determined using CVAAS (EN 12338)
ICP/OES (EN ISO 11885)
ICP/MS (EN ISO 17294-2)
Other instrumental methods may be used after validation with
biomass reference material of a suitable type.
CEN/TS 15296 minor elements
Precision of method
Coming soon!
Validation in progress
CEN/TS 15297 Solid biofuels — Calculation of
analyses to different bases
Symbols
The symbols employed in the subsequent clauses are as follows, with
the suffixes "ad" (air dried), "ar" (as received), "d" (dry), "daf" (dry,
ash free) where appropriate:
− A
ash (CEN/TS 14775)
− C
total carbon content (CEN/TS 15104)
− Cl
total chlorine content (CEN/TS 15289)
− qp,net net calorific value at constant pressure (J/g) (CEN/TS 14918)
− H
total hydrogen content (CEN/TS 15104)
− M
moisture content (CEN/TS 14774)
− N
total nitrogen content (CEN/TS 15104)
− O
total oxygen content (percentage by mass)
− S
total sulphur content (CEN/TS 15289)
CEN/TS 15297 Calculation of analyses to
different bases
Hydrogen
Oxygen
Net calorific value
difficult – still errors in standard!
CEN/TS 15297 Calculation of analyses
to different bases
www.pelletstesting.com
Thank you for the kind
attention!
ofi – Österreichisches Forschungsinstitut für Chemie und Technik
Franz-Grill Str. 5, Arsenal Objekt 213
A-1030 Wien
Tel.: +43-1-7981601-490
Fax: +43-1-7981601-480