Defining the thermal regime known as torrefaction

Chemical Physical Properties of Bio-coal

David Agar1 Margareta Wihersaari2

1 Department of Chemistry

2 Department of Biological and Environmental Science

University of Jyväskylä

Nordic Environmental Chemistry Conference, Kakskerta, Turku, 4-7 June, 2012

Presentation Outline Introduction What is Bio-coal? Why Bio-coal?

Torrefaction Process overview The torrefaction regime Solid fuel properties of torrefied wood Torrefaction versus carbonisation

Bio-coal production Active players in Europe Three key properties of bio-coal from experiment data Conclusions

What is Bio-coal? Solid fuel made from biomass (renewable) Fossil coal substitute High heating value (MJ/kg, compared to untreated biomass) High bulk energy density (MJ/m3) Handling properties like fossil coal (easy to grind)

Fuel for coal-fired power plants (large-scale production)

Bio-coal as briquette Bio-coal as pellets

What Bio-coal is NOT Not (grilling) charcoal Not bio-char (soil additive) Not bio-carbon (high-end technical carbon product) Note: Especially confusing in Finnish

Biohiili Bio-coal Bio-char Bio-carbon

The Finnish language may have many different words for snow but this is not the case for high-carbon products

Why Bio-coal? EU Climate & Energy Package Reduce GHG emissions by 2020 Secure inland energy sources (inland biomass)

Untreated biomass not feasible (i.e. wood pellets) Enabling technology: co-combustion using bio-coal would be

a fast method of cutting CO2 emissions significantly because…

Coal-fire power plants (black dots)

Helsingin Sanomat 28.10.2010

Torrefaction (roasting or incomplete pyrolysis) at the heart of bio-coal production

Torrefaction T = 220-300 C

(inert atmosphere)

Raw Biomass

Torrefied Biomass

Torrefaction gases

Energy 1.0 Mass 1.0

Energy 0.9 Mass 0.7

Energy 0.1 Mass 0.3

Heating value increase = 0.9/0.7 = 1.29 29% increase

The Composition of Woody Biomass Component Chemical Formula Hardwood

mass (%) Softwood mass (%)

Cellulose (C6H10O5)n 43 43

Hemicellulose (C5H8O4)n 34 28

Lignin [(C9H10O3)(CH3O)0.9-1.7]n 23 29

Rate of thermal degradation of the three components of woody biomass

Yang H et al., Characteristics of hemicellulose, cellulose and lignin pyrolysis, Fuel 2007

cellulose

Torrefaction Regime 220-300 C

Volatile matter and fixed carbon content of fuels

10

15

20

25

30

35

0

10

20

30

40

50

60

70

80

90

100

wood sod peat torrefied wood coal wood charcoal

Volatile matter (%)

Fixed carbon (%)

Ash content (%)

Higher heating value (MJ/kg)

com

posi

tion

(%)

higher heating value (MJ/kg)

Pine wood (T = 285 C, t = ?) Bourgeois & Doat (1984)

Typical Polish coal used in Finland

Elemental compositional changes

Composition of beech wood and torrefeed beech wood (T= 220-280C) in van Kravelen diagram

Prins et al. More efficient biomass gasification via torrefaction (2006)

Torrefaction versus carbonisation Heating value, as received = 10 MJ

9 MJ

6 MJ

Extent of pyrolysis

Pelletointiraja (ligniini ei riittää)

g

0

100

200

300

400

500

600

700

800

900

1000

hake torrefioitu puu puuhiili

tuhka

N

O

H

C

H20

Limit of pelletisation (lignin decomposition)

Mass balance – 1 kg of wood

Wood charcoal Torrefied wood Wood chips

Bio-coal production is an optimisation problem

Minimise Maximise

Reaction time Reactor size Process complexity Investment expenses

Raw material particle size Ability to pelletise/briquette Heat transfer Use of torrefaction gas Grindability of product

Bio-coal versus conventional wood pellets

∆E = 10%

Bio-coal

Wood pellets

Torrefaction technology developers in Europe

Kiel J, Torrefaction for upgrading biomass into commodity fuel, 2011.

Are the expectations of bio-coal realistic = based on scientific findings?

Key Property Popular Claim Experimental Data*

Mass/Energy Balance 70/90% 29% heating value increase

61-82/73-92% 7-21% (woody) 7-15% (agro)

Grindability Same as fossil coal 7-36 kWh/t

Improved, grinding energy reduced 68-89% (reactivity?) 52-150 kWh/t

Equilibrium Moisture Content (ECM)

Hydrophobic or 3-6% max. 2.2% (RH 11.3%) 8.7% (RH 83.6%) Measured at 30 degrees C

*Experimental data from peer-reviewed scientific journal publications. Agar D, Wihersaari M. Bio-coal, torrefied lignocellulosic resources – key properties for its use in co-firing with fossil coal – their status, Biomass & Bioenergy (2012).

Conclusions Bio-coal is a fossil coal substitute for coal-fired power plants Potential to cut CO2 emissions significantly from energy sector Torrefaction is a distinct thermal regime in which mostly

hemicellulose undergoes degradation (220-300 C) Bio-coal production is an optimisation problem and is not trivial Three key properties of bio-coal are available from recent peer-

reviewed literature for modelling of economics and GHG-emission balance.

Thank You For your attention

David Agar1 Margareta Wihersaari2

1 Department of Chemistry

2 Department of Biological and Environmental Science

University of Jyväskylä

Nordic Environmental Chemistry Conference, Kakskerta, Turku, 4-7 June, 2012