Biomass Torrefaction – A Promising P t t t M th d f Th Ch i l Pretreatment Method for Thermo-Chemical

Conversion Technologies

Sudhagar Mani, Jim , Jim KasterKaster, , & KC Das& KC DasFaculty of Engineering, University of Georgia, Athens, GAFaculty of Engineering, University of Georgia, Athens, GA

Email: Email: smani@engr.uga.edusmani@engr.uga.edu

IEA Bioenergy ConferenceBiofuels & Bioenergy: A Changing ClimateBiofuels & Bioenergy: A Changing Climate

Vancouver, BC CanadaAug 23-26, 2009

IntroductionIntroductionIntroductionIntroductionIssues with biomass feedstockIssues with biomass feedstock•• Wide range of moisture content (60Wide range of moisture content (60--15% 15% wbwb))

•• Low bulk density (4 Low bulk density (4 –– 8 lbs/ft8 lbs/ft33))

•• Low energy density (4,500Low energy density (4,500--7,500 Btu/lb)7,500 Btu/lb)

•• Uneven particle sizes (no flow)Uneven particle sizes (no flow)

Difficult to handle store and transportDifficult to handle store and transport•• Difficult to handle, store and transportDifficult to handle, store and transport

•• High transport and storage costHigh transport and storage cost

•• Self heating and emission of off gases during Self heating and emission of off gases during Self heating and emission of off gases during Self heating and emission of off gases during storagestorage

IntroductionIntroductionIssues with thermoIssues with thermo--chemical conversion chemical conversion technologiestechnologies•• Combustion:Combustion:

Difficult to coDifficult to co--fire with coalfire with coal

Low energy densityLow energy density

High energy demand for grinding biomassHigh energy demand for grinding biomass

•• GasificationGasification•• GasificationGasification

Tar formation

Low C/H ratio for liquid fuel production/ q p

•• PyrolysisPyrolysis: :

BioBio--oil instability & coke formationoil instability & coke formation

•• Densification: Densification:

Low energy density & self heatingLow energy density & self heating

Biomass Biomass PyrolysisPyrolysis to Liquid Fuelsto Liquid Fuels

PyrolysisUnit

Bio-oil

Critical ProblemsCritical Problems•• LongLong--term storage and stability of biomassterm storage and stability of biomass•• High energy input for grinding to defined particle sizeHigh energy input for grinding to defined particle size•• Formation of high molecular weight compoundsFormation of high molecular weight compounds•• BioBio--oil is unstableoil is unstable

Vi it i ith ti d t tVi it i ith ti d t tViscosity increases with time and temperatureViscosity increases with time and temperatureLow pH, corrosive Low pH, corrosive

•• Catalytic upgrading difficultCatalytic upgrading difficulty pg gy pg gHigh oxygen contentHigh oxygen contentCatalytic deactivation due to coke formationCatalytic deactivation due to coke formation

What is Torrefaction? What is Torrefaction? Solid-state thermal hydrolysis of biomass in an inert of biomass in an inert atmosphere (e.g.,Natmosphere (e.g.,N22))T t T t 180 t 300180 t 300ooCCTemperature range Temperature range –– 180 to 300180 to 300ooCCHemicelluloseHemicellulose is hydrolyzed is hydrolyzed via release of acetic acid via release of acetic acid and subsequent hydrolysis reactionand subsequent hydrolysis reactionand subsequent hydrolysis reactionand subsequent hydrolysis reactionMoisture reduction, oxygen content reducedMoisture reduction, oxygen content reducedSome extractives volatilized, but 70Some extractives volatilized, but 70--80% solids 80% solids recoveredrecoveredMost familiar example Most familiar example –– roasting coffeeroasting coffee

Green chip Torrefied chip

Torrefaction HistoryTorrefaction HistoryTorrefaction HistoryTorrefaction History1930’s 1930’s –– heat treatment of wood for high heat treatment of wood for high ggdurability, structural stability & fungal resistance (wood durability, structural stability & fungal resistance (wood roasting), provides aesthetic valueroasting), provides aesthetic value

1939 1939 US Patent (Be gst om et al) on the mal heating of US Patent (Be gst om et al) on the mal heating of 1939 1939 –– US Patent (Bergstrom et al) on thermal heating of US Patent (Bergstrom et al) on thermal heating of wood >220wood >220ooCC

1976 1976 –– Pyrochar process for solid biomass into Pyrochar process for solid biomass into fuelsfuelsy py p

1980’s 1980’s –– heat treatment of wood logs (180heat treatment of wood logs (180--220220ooC), retifaction/torrefaction process C), retifaction/torrefaction process (Yvan 1985 Bourgeois et al 1988) Torrefaction process (Yvan 1985 Bourgeois et al 1988) Torrefaction process (Yvan, 1985, Bourgeois et al, 1988), Torrefaction process (Yvan, 1985, Bourgeois et al, 1988), Torrefaction process development & reactor design (four patents)development & reactor design (four patents)

2000 2000 -- Significant research & development on biomass Significant research & development on biomass torrefaction processtorrefaction process

Mass & Energy BalancegyCondensable:WaterNon-condensable:

Volatile off gases

WaterOrganic acids, alcoholsFurans, ketonesTerpenes, phenols

l d

H2, CO, CO2, CH4,Toluene, benzene

gases

0.3 m ~0.2 E

Waxes, tannins, lipids

Torrefaction Process

Biomass Torrefied biomass

1 m 0.7 m

1 E 0.9 E

External heat supplyT 180 280 C

~0.1 E

Temp: 180-280oCHeating rate: <50oC/minResidence time: > mins

Research Objectives Research Objectives Bi T f ti ki ti Bi T f ti ki ti Biomass Torrefaction kinetics Biomass Torrefaction kinetics •• Does it improve biomass storability and Does it improve biomass storability and

t t bilit ?t t bilit ?transportability?transportability?

•• Does it improve biomass Does it improve biomass grindabilitygrindability and reduce and reduce i t? i t?energy input?energy input?

•• Effect of torrefaction on, Effect of torrefaction on,

bi il t bilitbio-oil stability

Eliminate or reduce coke forming precursors and improve catalytic upgrading of bio-oil to fuelsimprove catalytic upgrading of bio-oil to fuels

Syngas quality and tar concentration during gasificationg

Pellet quality

Combustion behavior

Mass loss with time for a range of torrefaction conditions – TG-MStorrefaction conditions TG MS

90

100

70

80

90

nin

g

200

50

60

70

s re

main

215

230

245

20

30

40

% m

ass

245

260

275

0

10

20% pyr. @ 700

00 2000 4000 6000 8000

time / s

Proposed Torrefaction Kinetics Proposed Torrefaction Kinetics M d lM d lModelModel

Hemicellulose (A)Depolymerised Intermediate (B) Solid products (C)Intermediate (B)

k1

kv2

k2

Volatile productskv1

Model equations:Model equations:For components a, b and c:For components a, b and c:

a’(t) = a’(t) = --(k1+kv1)*a(t), (k1+kv1)*a(t), a(0) = 1 a(0) = 1 ((normalized vs. starting mass)normalized vs. starting mass)b’(t) = k1*a(t)b’(t) = k1*a(t)--(k2+kv2)*b(t)(k2+kv2)*b(t) b(0) = 0b(0) = 0c’(t) = k2*b(t)c’(t) = k2*b(t) c(0) = 0c(0) = 0

Torrefaction Experiment

Condensed liquids

Torrefaction Reactor

300

Experiment 1.3.2 - Torrefaction - Pine Chips30 minutes - 280oC - 30% Moisture

Non-condensable gasesForest Residue chips

100

150

200

250

mpe

ratu

re (o

C)

0

50

0 15 30 45 60 75 90 105 120

Tem

Time (minutes)

Torrefied biomass

TorrefiedTorrefied Auger Reactor Auger Reactor -- UGAUGA•Continuous Reactor

•Capacity – 5 to 10 kg/hCapacity 5 to 10 kg/h

•Capability to collect

condensable

• Non-condensables gases can

be recalculated in the auger

Rotary drum reactor Rotary drum reactor –– UGAUGA(indirect heating)(indirect heating)

Capacity = 400 lbs/run

Results Results –– TorrefiedTorrefied biomass yieldbiomass yield

100%

Pine Chips30 Minute run

80%

d (%

)

60%

biom

ass

yiel

d

40%

Torr

efie

d b

10%M.C.

30% C

0%

20%30%M.C.

50%M.C.

0%220 250 280

Temperature

Torrefaction of Pine ChipsTorrefaction of Pine Chipspp

Torrefaction Process

Torrefaction ResultsTorrefaction ResultsGC/MS of Non-condensables (gas phase)•• Acetaldehyde, Acetaldehyde, αα--pinenepinene, , ββ--

pinenepinene, camphene, , camphene, phellandrenephellandrene observed at low observed at low temperatures (220C)temperatures (220C)

•• Acetaldehyde evolution increased with timeAcetaldehyde evolution increased with time•• Acetaldehyde evolution increased with timeAcetaldehyde evolution increased with time•• PinenesPinenes decreased with holding timedecreased with holding time•• As temperature increased, acetic acid, As temperature increased, acetic acid, methylestermethylesterp , ,p , , yy

and furans appeared (220 to 250C and above)and furans appeared (220 to 250C and above)Furan, 2Furan, 2--methylfuran, 250Cmethylfuran, 250C2 32 3 dihydrofuran and 2 5dihydrofuran and 2 5 dimethylfuran 280Cdimethylfuran 280C2,32,3--dihydrofuran and 2,5dihydrofuran and 2,5--dimethylfuran, 280Cdimethylfuran, 280C

Results Results –– NonNon--condensable at 280condensable at 280ooCC

9

Non-Condensables vs. Time; Torrefaction at 280oC

Methane

6

7

8

%)

Carbon dioxide

Methyl acetylene

Propylene

4

5

6

mou

nt (m

ole

%

n-Butane

Ethylene

Ethane

2

3

Am

0

1

0 10 20 30 40 50 60

Time (min)

Results Results –– Condensable at 280Condensable at 280ooCC

35000000

Condensables vs. Time; Torrefaction - 280oC

α-pinene

25000000

30000000

ance

α pinene

camphene

β-pinene

β phellandrene

20000000

25000000

elat

ive

Abu

nda β-phellandrene

10000000

15000000Re

0

50000000

0 10 20 30 40 50 600 10 20 30 40 50 60

Time (min)

Results Results –– Compositional changesCompositional changesF t id C ll l H i ll l Li i H ti lForest residue chips

Cellulose(% wt)

Hemi-cellulose(% wt)

Lignin (% wt)

Heating value(Btu/lb)

Non-torrefied(10% m c )

43.1 18.4 20.9 7,774(10% m.c.)

Torrefied at 220oC 40.7 12.0 25.1 8,474

Torrefied at 250oC 37.3 5.0 31.8 9,376,

Torrefied at 280oC 20.6 2.9 47.3 10,167

F t id C H O N S A h (% t)Forest residue chips

C H O N S Ash (% wt)

Non-torrefied(10% m c )

45.3 5.9 48.5 0.3 0.1 0.6(10% m.c.)

Torrefied at 220oC 49.4 5.5 44.1 0.3 0.0 1.1

Torrefied at 250oC 50.5 5.4 41.8 0.4 0.0 1.2

Torrefied at 280oC 56.4 5.4 36.1 0.9 0.1 1.4

Results Results –– Compositional changesCompositional changesF t id M i t V l til C Fi d C A h (%)Forest residue chips

Moisture (%)

Volatile C(% wt)

Fixed C(% wt)

Ash (%)

Non-torrefied(10% m c )

10 75.3 16.3 0.4(10% m.c.)

Torrefied at 220oC 3.2 76.8 19.1 1.1

Torrefied at 250oC 2.3 74.9 20.6 1.2

Torrefied at 280oC 2.1 70.8 25.6 1.4

Change in bulk density during Change in bulk density during T f tiT f tiTorrefactionTorrefaction

200

179.51

175/m

3

160.43

152.13sity

, kg

/

150

ulk

den

s

125

220 250 280

B

Torrefaction temperature oC

Forest biomass chips – 18% change

Improved Improved PelletingPelleting ProcessProcess

Raw material Drying process DryingRaw material Torrefaction

Torrefaction Pelletization ProductsGrinding P ll ti tiHigh quality

Torrefaction Pelletization ProductsGrinding Pelletization Pellets

Effect of Torrefaction on Pellet Density

1200

1000

1100

m3

220

900

1000

ty,

kg

/m

Control

800

et

Den

sit Control

220

250

600

700

Pell

e 250

280 280

0 2000 4000 6000 8000

Applied Forces, N

TorrefactionTorrefaction-- Pellet Production CostPellet Production Cost

50

/t Packing cost $40

30

40

cost

, $

/

Land use & building

Personnel cost$27 $24 $30

20

30

uct

ion

c

Miscellaneous equipmentScreening

100.00

6.45et

Pro

du

Pellet cooler

Pellet mill

0 0.00 0

Pelle

Hammer mill

Torrefaction

2424Drying operation

Torrefaction PyrolysisTorrefaction - Pyrolysis

TG/MS Analysis of Torrefied BiomassBiomass

TGA/MS (TGA/MS (MettlerMettler Toledo)Toledo)P f d d P f d d l til ti diti diti NN AAPerformed under Performed under pyrolyticpyrolytic conditions conditions –– NN22 or or ArArcarrier gascarrier gas10mg sample, 50 ml/min, 3010mg sample, 50 ml/min, 30--900900°°C at 10C at 10°°C/minC/minMonitored Off Gas in Selective Ion Mode (SIM)Monitored Off Gas in Selective Ion Mode (SIM)

• Non-condensables, CO-28, CO2-44, H2-2, H2O-18 2 2 2• Potential tar compounds,

Benzene – 78 Guaiacol – 124 Naphthalene – 128 Phenol – 94

• Potential hemicellulose breakdown productsAcetaldehyde 29 Acetaldehyde – 29 Acetic acid – 60 Acetol – 45

Effect of Torrefaction on Pyrolysis Kinetics (TGA Analysis)

Pine Pellet Pyrolysis

1012

0 8

1Pine Pellet Pyrolysis

1012

0 8

1Torrified Pine Pellets at 250C

1012

0 8

1Torrified Pine Pellets at 250C

1012

0 8

1

2

468

Mas

s, m

g

0 2

0.4

0.6

0.8

X, m

ass

2

468

Mas

s, m

g

0 2

0.4

0.6

0.8

X, m

ass

2468

Mas

s (m

g)

0.2

0.4

0.6

0.8

X, m

ass

2468

Mas

s (m

g)

0.2

0.4

0.6

0.8

X, m

ass

02

0 500 1000Temperature, C

0

0.2

02

0 500 1000Temperature, C

0

0.202

0 500 1000

Temperature, C

002

0 500 1000

Temperature, C

0

Torrified Pine Pellets at 300C

10

12

0 8

1

Torrified Pine Pellets at 300C

10

12

0 8

1X, fractional biomass conversionX, fractional biomass conversion

Higher temperature torrefaction Higher temperature torrefaction

2

46

810

Mas

s (m

g)

0 2

0.4

0.6

0.8

X, m

ass

2

46

810

Mas

s (m

g)

0 2

0.4

0.6

0.8

X, m

ass

g e e pe a u e o e ac og e e pe a u e o e ac o(> 300(> 300°°C) appears to reduce C) appears to reduce biomass thermal decomposition biomass thermal decomposition and alter and alter pyrolysispyrolysis kineticskinetics

More research needed to More research needed to 02

0 500 1000Tem perature, C

0

0.2

02

0 500 1000Tem perature, C

0

0.2More research needed to More research needed to confirm effectconfirm effect

Torrefaction-Pyrolysis-Solids PropertiesOxygen content reducedOxygen content reducedFixed carbon increased

Material

Characteristic PP BM PP T250 PP T300 PP T350 PP P500

C 52.6 53.9 73.2 78.0 82.5 H 5.7 5.3 4.7 3.7 2.6 N 0.2 0.1 0.2 0.2 0.2 S 0.0 0.1 0.1 0.1 0.0O 38.9 37.6 19.6 15.0 4.4

Moisture 7 2 0 0 1 0 2 0 3 2Moisture 7.2 0.0 1.0 2.0 3.2Volatiles 79.8 71.2 42.4 32.2 28.1

Ash 0.5 3.0 2.2 2.9 2.8 Fixed Carbon 19.7 25.8 55.4 64.9 69.1

HHV (MJ/kg) 20.6 20.9 28.8 29.7 31.0

PP, pine pellets; BM, biomass; T, torrefaction, P, pyrolysis

ParameterBio-Oil Characteristics

Pa PUb TPc TPUd

Ultimate analysis (wt % dry)

C 69 6 73 1 71 3 73 9C 69.6 73.1 71.3 73.9H 7.65 8.1 7.97 7.93N 0.74 0.4 0.19 0.17S 0.05 0.0 0.01 0.02Oe 22.0 18.4 20.5 18.0

HHV 29.1 30.9 28.6 30.7(MJ/kg, wet basis)

H2O 2.4 4.0 9.3 6.7(wt %)(wt. %)

pH 3.1 3.2 3.7 3.5aP: Pyrolysis (catalytic upgrading feedstock, no torrefaction)bPU: Pyrolysis + catalytic Upgrading (no torrefaction)bPU: Pyrolysis + catalytic Upgrading (no torrefaction)cTP: Torrefaction + Pyrolysis (catalytic upgrading feedstock)dTPU: Torrefaction + Pyrolysis + catalytic Upgrading

Torrefaction CombustionTorrefaction - Combustion

Comparison of combustion of torrefied biomass, untreated biomass and coalbiomass, untreated biomass and coal

1

1.2

0.8

1

ctio

n

t225

t235

0.6

nin

g f

rac t235

t250

t260

t275

0.4

rem

ain t275

t285

t300

0

0.2 raw pine

coal

0

0 1000 2000 3000 4000

Time

ConclusionsConclusionsCondensable compounds are mainly released from extractives in the biomass as α, β-pinene, camphene t Th d b di t d t l etc. These compounds can be redirected to supply

heat energy during torrefaction

D i t f ti h i ll l i l t d During torrefaction, hemi-cellulose is almost removed and results in higher energy density product with a heating value of 10 000 Btu/lb Torrefaction heating value of 10,000 Btu/lb. Torrefaction temperature plays a major role in defining the energy density of biomass and can be optimized for any y p yspecific applications.

Torrefaction followed by pelleting costs about $30/t of y p g $pellets. Torrefaction process alone costs about $6.5/t.

ConclusionsConclusionsBiomass torrefaction process can produce high energy Biomass torrefaction process can produce high energy density and consistent feedstock for thermal conversion density and consistent feedstock for thermal conversion density and consistent feedstock for thermal conversion density and consistent feedstock for thermal conversion technologies (gasification, cotechnologies (gasification, co--firing & firing & pyrolysispyrolysis))

PelletingPelleting of Torrefaction of biomass may be difficult due of Torrefaction of biomass may be difficult due PelletingPelleting of Torrefaction of biomass may be difficult due of Torrefaction of biomass may be difficult due to hydrophobic nature of the material and require to hydrophobic nature of the material and require additional binders to increase the bulk densityadditional binders to increase the bulk densityadditional binders to increase the bulk densityadditional binders to increase the bulk density

Future research at UGA is focused on optimizing the best reactor configuration for a torrefaction process g pand promote its application to co-firing, gasification and pyrolysis processes

AcknowledgementAcknowledgement

Financial support from Financial support from • University of Georgia Research

FoundationFoundation• State of Georgia – Traditional Industries

ProgramProgram• Georgia Power – Southern Company

Thank youThank you Densification

Direct combustion

Gasification

BiocoalCo-firing with coal

Biomass Torrefaction Technology