BIO-COAL AND TORREFACTION TECHNOLOGY

David Agar

Department of Chemistry University of Jyväskylä

YMPS392 Energy Systems: Carbon, Energy & Emission Balances 21 September 2012

LECTURE OUTLINE Introduction

EU Energy policy Why is bio-coal interesting? What is bio-coal?

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

Bio-coal production – current status Active players and technologies in Europe Pilot-scale and commercial plants Production process overview Challenges in production ECN report 2005

Assessing the present state of technology Key properties of bio-coal for co-firing Scientific research on torrefaction Popular claims versus experimental facts

Conclusions

EUROPEAN UNION ENERGY POLICY The EU Climate and Energy Package has two

main objectives:

1. to reduce greenhouse gas emissions by member states

2. to provide more secure inland sources of energy

Increase renewable energy production to 20% by the year 2020.

For many member states the fastest/easiest way to achieve this aim is to increase biomass use through co-combustion in coal power plants – WHY?

COAL-FIRED POWER PLANTS (BLACK DOTS)

Helsingin Sanomat 28.10.2010

PULVERISED COAL POWER PLANT

GOOD IDEA BUT THERE ARE SOME PROBLEMS… Most coal-fired plants use pulverised-fuel boilers Coal-fired plants are not designed for biomass Biomass fuels are not like fossil coal Most coal-fired plants are large and located far

from biomass resources Note: Grate and fluidised-bed boilers are designed

for biomass but they are not common outside Nordic countries (nor are CHP plants in general)

FUEL HANDLING PROPERTIES SIZE REDUCTION ENERGY REQUIREMENTS

Biomass*: 236 kWh/t Coal: 7 – 36 kWh/t

Scanning electron microscope images of (a) coal and (b) sawdust (Zulfiqar, 2006)

Flow Properties: spherical particles versus needle-like particles

(Phanphanich 2011) *forest residues

CONCLUSION If we want to burn significantly more biomass

fuels (in coal plants) we need to I. make biomass more like fossil coal

OR II. invest in new power plants or upgrades

WHAT IS BIO-COAL? Solid fuel made from biomass (renewable) Fossil coal substitute

High heating value (MJ/kg) 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

BIO-COAL IS NOT Charcoal (grilling) Bio-char (soil additive) Bio-carbon (high-end technical carbon product) Warning: 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

WHAT IS TORREFACTION? Torréfaction means roasting (pyrolysis) Thermal process used to roast biomass Similar to coffee roasting

TORREFACTION – THE PRINCIPLE

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

THERMAL DEGRADATION OF BIOMASS: TORREFACTION FOR 50 MIN. AT 270 DEG C IN NITROGEN GAS (TGA)

65

70

75

80

85

90

95

100

105

110

15 25 35 45 55 65 75

time (min.)

norm

alise

d m

ass

(%

)

100

120

140

160

180

200

220

240

260

280

tem

pera

ture

(C)

hemp hurdpine/sprucetemperature

78%

68%

270 C

(Agar & Wihersaari, unpublished)

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

TORREFIED WOOD: ELEMENTAL COMPOSITIONAL CHANGES

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

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

Torrefaction vs. charcoal production 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

TORREFACTION TECHNOLOGY DEVELOPERS IN EUROPE

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

Direct or Indirect heating

NATIONAL RENEWABLE ENERGY CENTRE (CENER), SPAIN (ROTARY DRUM REACTOR, INDIRECT HEATING).

• Uses standard industrial component except specially modified torrefaction reactor (manufactured by LIST) •Heat transfer via thermal oil in walls of drum

CENER PILOT PLANT IN AOIZ, SPAIN

Production: 500 kg/hour (bio-coal pellets) Start-up date: May 2011 Feedstock: Straw, beech and pine wood chips End use: Research services and on-site gasification

THERMYA (NOW ARIVA), FRANCE (DIRECT HEATING)

Source: Thermya SA

TORREFIED BIOMASS

THERMYA COMMERCIAL PLANT IN URIETA, SPAIN (TORSPYD PROCESS)

Production: 20 000 t/year (torrefied wood chips, no densification) Start-up date: January 2012 (?) Feedstock: recycled wood and forest wood biomass End use: co-firing at coal plant near San Sebastian (<20 km)

TOPELL, THE NETHERLANDS (TORBED REACTOR, DIRECT HEATING)

• High velocity gas stream forced through stationary blades • High impact velocity with particles results in high heat and mass transfer rate • Proven technology in other sectors (i.e. foods)

TORBED® is a registered Trademark of Mortimer Technology Holdings Ltd

TOPELL COMMERICAL PLANT IN DUIVEN, NETHERLANDS

Production: 60 000 t/year (bio-coal pellets) Start-up date: Autumn 2011 (?) Feedstock: woody biomass chips End use: co-firing at Amercentrale Power Plant (Geertruidenburg, ~110km)

Torbed reactor (1 of 3)

BIO-COAL VERSUS CONVENTIONAL WOOD PELLETS

∆E = 10%

Bio-coal

Wood pellets

Agar D., Wihersaari M., Torrefaction technology for solid fuel production - a move towards greater sustainability, Global Change Biology Bioenergy (2011).

ENERGY CENTRE OF NETHERLANDS (ECN) REPORT 2005

Bergman, P.C.A., Combined torrefaction and pelletisation – the TOP process, Energy Energy Centre of the Netherlands (ECN), ECN-C—05-073, Petten, NL, (2005). www.ecn.nl

CHALLENGES IN BIO-COAL PRODUCTION COMPLEX OPTIMISATION PROBLEM

Minimise Maximise

Feedstock transport 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: ARE THE EXPECTIONS REALISTIC?

KEY PROPERTIES OF BIO-COAL FOR CO-FIRING APPLICATIONS Regardless of which reactor technology used to

produce it, there are key properties of bio-coal that will have a significant impact on its feasibility. Three of these are:

Mass/energy balance of torrefaction Grindability of the bio-coal Equilibrium moisture content (EMC)

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 7-36 kWh/t Same as fossil coal

52-150 kWh/t Improved

Equilibrium Moisture Content (EMC)

Hydrophobic or 3-6% max. 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 Bio-coal is NOT charcoal 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.