Chemical methods for solid biofuels

Martin Englisch

ofi – Österreichisches Forschungsinstitut für Chemie und Technik

Solid fuels

solid biofuel

combustible non combustible combustible fraction

non combustible fraction

water volatiles cokeash

Composition of wood

Chemical composition:

51% carbon

42% oxygen

6% hydrogen

Components:

50% cellulose

25% hemicellulose

25% lignin6% hydrogen

< 1% nitrogen

< 0,1% sulphur, halogenes

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 adheasives

� Sulfur

− Mainly from organic sulfur compounds SO2 is formed during combustion which − 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 � 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

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� 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

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 BIONORM nitrogen

Precision of method

Nitrogen Content

mean

[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

Reproducibility Repeatability

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− Solid combustion aid: combustion bag or capsule with known weight

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

CEN/TS 15289 sulphur and chlorine

− 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 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)

CEN/TS 15289 sulphur and chlorine

Precision of method

Maximum acceptable differences between resultsContent of sulphur and

chlorine

dry basisSame 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 contentmean

[wt %, d.b.]

R abs [%]

R rel [%]

r abs [%]

r rel [%]

wood without bark 0,003 0,006 174 0,003 93

Reproducibility Repeatability

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 (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

Maximum acceptable differences between resultsContent of water soluble

element,

as analysedsame 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

CEN/TS 15290 Solid biofuels — Determination ofmajor 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) 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.− 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 ofminor elements

Minor elements:

Arsenic, Cadmium, Cobalt, Chromium, Copper, Mercury, Manganese, Molybdenum, Nickel, Lead, Antimony, Vanadium and Zinc principle

� Method similar to major element� 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).� 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

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