Jun 7, 2012 - Not (grilling) charcoal. Not bio-char (soil additive). Not bio-carbon (high-end technical carbon product). Note: Especially confusing in ...
Chemical Physical Properties of Bio-coal Defining the thermal regime known as torrefaction David Agar1 Margareta Wihersaari2 1 Department
of Chemistry 2 Department of Biological and Environmental Science University of Jyväskylä
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
Bio-coal Bio-char Bio-carbon
Biohiili
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 Energy 0.1 Mass 0.3 Torrefaction gases
Raw Biomass
Energy 1.0 Mass 1.0
Torrefaction T = 220-300 C (inert atmosphere) Heating value increase = 0.9/0.7 = 1.29 29% increase
Torrefied Biomass
Energy 0.9 Mass 0.7
The Composition of Woody Biomass Component
Chemical Formula
Hardwood mass (%)
Softwood mass (%)
Cellulose
(C6H10O5)n
43
43
Hemicellulose
(C5H8O4)n
34
28
[(C9H10O3)(CH3O)0.9-1.7]n
23
29
Lignin
Rate of thermal degradation of the three components of woody biomass cellulose
Torrefaction Regime 220-300 C
Yang H et al., Characteristics of hemicellulose, cellulose and lignin pyrolysis, Fuel 2007
Volatile matter and fixed carbon content of fuels 35
100
Volatile matter (%)
90
70 25
60 50 40
20
30 20
15
10 0
10 wood
sod peat
torrefied wood
Pine wood (T = 285 C, t = ?) Bourgeois & Doat (1984)
coal
wood charcoal
Typical Polish coal used in Finland
higher heating value (MJ/kg)
composition (%)
Fixed carbon (%)
30
80
Ash content (%) Higher heating value (MJ/kg)
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 1000
= 10 MJ
Mass balance – 1 kg of wood
900
Pelletointiraja (ligniini ei riittää) Limit of pelletisation
800
(lignin decomposition)
700 600
g
500
tuhka N O
9 MJ
400
H
300
C
6 MJ
200 100 0
Wood hake chips
torrefioitu puu Torrefied wood
Woodpuuhiili charcoal
Extent of pyrolysis
H20
Bio-coal production is an optimisation problem Minimise Reaction time Reactor size Process complexity Investment expenses
Maximise Raw material particle size Ability to pelletise/briquette Heat transfer Use of torrefaction gas Grindability of product
Bio-coal versus conventional wood pellets
Wood pellets
∆E = 10%
Bio-coal
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 peerreviewed literature for modelling of economics and GHGemission balance.
