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Chemical methods for solid biofuels
Martin Englisch
ofi – Österreichisches Forschungsinstitut für Chemie und Technik
Fritz Bakker
ECN- Energy Research Centre of the Netherlands
Solid fuels
solid biofuel
combustiblefraction
non combustiblefraction
water volatiles charash
Composition of wood
Chemical composition:
51% carbon
42% oxygen
6% hydrogen
< 1% nitrogen
< 0,1% sulphur, halogenes
Components:
50% cellulose
25% hemicellulose
25% lignin
< 5% resins etc.
< 1% ash formingminerals
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 adhesives
Sulphur− Mainly from organic sulphur 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 biofuels higher concentrations are often found – very critical chemical parameter!
NOx-formation
Aerosol formation
Chemical test methods
EN 15104 Solid biofuels — Determination of total content of carbon, hydrogen and nitrogen — Instrumental methods
EN 15289 Solid biofuels — Determination of total content of sulphur and chlorine
EN 15105 Solid biofuels — Methods for determination of the water soluble content of chloride, sodium and potassium
EN 15290 Solid biofuels — Determination ofmajor elements
EN 15296 Solid biofuels — Determination ofminor elements
EN 15297 Solid biofuels — Calculation of analyses to different bases
EN 15104 Determination of total content of carbon, hydrogen and nitrogen — Instrumental methods
Principlesample 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 gas-analysis procedures are removed
Carbon dioxide, water vapour and nitrogen are determined quantitatively by appropriate instrumental gas- analysis procedures
EN 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!
EN 15104 carbon, hydrogen and nitrogen — Instrumental methods
ProcedurePreparation of test sample and test portionCalibration of systemAnalysis of sampleExpression and calculation of resultsPerformance of methods:
Maximum acceptable differences between results
(on dry basis)
repeatability reproducibility
Carbon content 0,5 % absolute 1,5 % absolute
Hydrogen content 0,25 % absolute 0,5 % absolute
Nitrogen content 10 % relative if N > 0,5 %
0,05 % absolute if N < 0,5 %
20 % relative if N > 0,5 %
0,1 % absolute if N < 0,5 %
Results from BioNormII nitrogen
Precision of method
Nitrogen Contentmean
[wt %, d.b.]
R abs [%]
R rel[%]
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 (olive) 1,314 0,333 25,3 0,090 6,8
Reproducibility Repeatability
EN 15289 Determination of total content of sulphur and chlorine
PrincipleCombustion 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 EN15290 (method B).
EN 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 andchloride 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
EN15289 sulphur and chlorine
Combustion in a closed bombMost frequently used method, combination with NCV1 g sample is pressed to a pellet, put into a quartz glass or metal crucible and combusted in 30 bar oxygenEventual use of combustion aid− Liquid combustion aid e.g. dodecane− Solid combustion aid: combustion bag or capsule with known weight
Combustion in a closed bombAfter 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)
EN 15289 sulphur and chlorine
EN 15289 sulphur and chlorine
Detection methodsIon 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 11885photometric (colorimetric) X DIN 51727
Turbidimetric 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)
EN 15289 sulphur and chlorine
Precision of method
Maximum acceptable differences between resultsContent of sulphur and chlorinedry basis
Same laboratory(Repeatability)
Different laboratories(Reproducibility)
Chlorine ≤ 500 mg/kg> 500 mg/kg
50 mg/kg10 % of the mean result
100 mg/kg20 % of the mean result
Sulphur ≤ 500 mg/kg> 500 mg/kg
50 mg/kg10 % of the mean result
100 mg/kg20 % of the mean result
Results from BioNormII for chlorine
Precision of method
Chlorine contentmean
[wt %, d.b.]
R abs [%]
R rel[%]
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 (olive) 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
Reproducibility Repeatability
EN15105 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).
EN 15105 water soluble content of chloride, sodium and potassium
Precision of method
Maximum acceptable differences between resultsContent of water solubleelement,
as analysed same laboratory(repeatability)
different laboratories(reproducibility)
Chloride ≤ 500 mg/kg
> 500 mg/kg
50 mg/kg
10 % of the mean result
100 mg/kg
20 % of the mean result
Sodium / potassium ≤ 100 mg/kg
> 100 mg/kg
10 mg/kg
10 % of the mean result
20 mg/kg
20 % of the mean result
EN15290 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).
EN 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.
EN 15290 major elements - Precision
5,18110,31651 5981,47315Oliveresidues
6,6411,76545,56915Wood chips
Fe
4,36077,31 03514 21606513Oliveresidues
1,6246,61001 5021,85411Wood chips
Ca
4,71107,21702 36405511Oliveresidues
4.121884755712Wood chips
%mg/kg%mg/kgmg/kg%Al
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15290 major elements – Precision
1,94686,41 56524 5245,55211Oliveresidues
1,81211,1776913,16313Wood chips
K
3,9588,51271 48806513Oliveresidues
3,426,75743,65311Wood chips
P
4,71497,72423 14306513Oliveresidues
1,737,21419406012Wood chips
%mg/kg%mg/kgmg/kg%Mg
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15290 major elements – Precision
4,467,9111381,85411Oliveresidues
5,90,327,40,405,54,4439Wood chips
Ti
5,49234017104910Oliveresidues
142486130449Wood chips
Na
7,776912,21 22610 0434,04910Oliveresidues
11,236331063202,5398Wood chips
%mg/kg%mg/kgmg/kg%Si
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15296 Solid biofuels — Determination ofminor elements
Minor elements: Arsenic, Cadmium, Cobalt, Chromium, Copper, Mercury, Manganese, Molybdenum, Nickel, Lead, Antimony, Vanadium and Zinc principle
Method similar to major element
EN 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.
EN 15296 minor elements - Precision
5,40,056120,1281,041,85411Oliveresidues
2,90,0109,70,0330,344,4439Wood chips
Co
200,0050230,00570,0250408Oliveresidues
2,90,0096,40,0210,323,16313Wood chips
Cd
6,00,0369,50,0570,607,3388Oliveresidues
340,012640,0230,03610276Wood chips
%mg/kg%mg/kgmg/kg%As
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15296 minor elements - Precision
220,0026400,00480,0122,24410Oliveresidues
130,0010230,00160,00723,6276Wood chips
Hg
3,40,858,602,22507515Oliveresidues
7,000,091120,161,296,65712Wood chips
Cu
7,61,08243,414,347215Oliveresidues
210,077310,120,374,4439Wood chips
%mg/kg%mg/kgmg/kg%Cr
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15296 minor elements - Precision
5,40,686,50,8212,51,85411Oliveresidues
70,042170,1030,6004710Wood chips
Ni
8,20,018250,0560,227,5378Oliveresidues
410,012520,0150,0280235Wood chips
Mo
3,61,462,52,5440,22,77315Oliveresidues
1,43,781817,72611,46914Wood chips
%mg/kg%mg/kgmg/kg%Mn
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15296 minor elements - Precision
4,50,83111,9718,235,37115Olive residues
4,80,67141,9413,845,47015Wood chips
Zn
4,90,21110,454,267,35111Olive residues
120,009230,0180,0764,5429Wood chips
V
110,010150,0140,0944245Olive residues
100,001310,00420,0130255Wood chips
Sb
9,30,357150,5753,836,75613Olive residues
9,60,072160,1170,7510,9419Wood chips
%mg/kg%mg/kgmg/kg%Pb
CVrsrCVRSRxoln
n= number of lab. i=individual values, o=% % of replicate determ. x= overall meanSR=reproducibility std dev. CVR= coefficient of variation of reprod. sr= repeatability std.devCVr= coefficient of the variation of the repeatability
EN 15296 minor elements
Precision of methodComing soon!
Validation in progress
EN 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 (EN 14775)
− C total carbon content (EN 15104)
− Cl total chlorine content (EN 15289)
− qp,net net calorific value at constant pressure (J/g) (EN 14918)
− H total hydrogen content (EN 15104)
− M moisture content (EN 14774)
− N total nitrogen content (EN 15104)
− O total oxygen content (percentage by mass)
− S total sulphur content (EN 15289)
EN 15297 Calculation of analyses to different bases
Hydrogen
Oxygen
Net calorific valuedifficult – still errors in standard!
EN 15297 Calculation of analyses to different bases
Thank you for the kind attention!
ofi – Österreichisches Forschungsinstitut für Chemie und TechnikFranz-Grill Str. 5, Arsenal Objekt 213A-1030 WienTel.: +43-1-7981601-490Fax: +43-1-7981601-480
www.pelletstesting.com