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Wet Torrefaction of Lignocellulosic Biomass

Wei Yan, Tapas Acharjee, M. Toufiq Reza, Charles Coronella*, Victor Vasquez

Chemical & Materials Engineering Dept.University of Nevada, Reno

TCS 2010 SymposiumSeptember 22, 2010

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University of Nevada, Reno

Wet torrefaction of lignocellulosic biomass

Gasification of biomass

Low mass density

– Complex, expensive logistics

Seasonal availability

Widely distributed

Low fuel density

Unique challenges:

– Generation of tars during gasification

Related to high Oxygen content

– Poor storage stability

– Expensive to mill

– Diverse handling characteristics

3



Goals

Develop a process

– To homogenize diverse biomass feedstocks

– To increase the energy density of biomass

– To produce solid with increased Carbon content

Characterize solid fuel

Mass & Energy Balances

Reaction kinetics

4



Wet torrefaction:Hydrothermal carbonization

Hot compressed water (200 – 280 °C)

Short contact time (< 10 min)

Increased fuel values

200 – 260 ˚CBiomass

Water

Gases

Aqueous sugars

Solid fuel

Organic acids

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Torrefaction:Two approaches

Dry torrefaction– 250 – 300 ˚C (inert environment)

– 30 min- 90 min. residence time

– Modest fuel densification

– Very friable product

Wet torrefaction (carbonization, pretreatment)– 200 – 260 ˚C

– 5-10 minute residence time

– Modest fuel densification

– Significant oxygen elimination

– Pressure is up to 50 atm (water vapor pressure)

– Very friable product

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Experimental method

High-pressure 100-mL Parr reactor

200 °C ≤ T ≤ 260 °C

Pressure is monitored, not controlled

Batch experiments

5 minutes residence time

5:1 water:biomass (w:w)

Various feedstocks

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Results

Product is soft, friable solid

Odor of “charcoal”

Loblolly pine Treated at 260 °C

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Yields

Mass yield = mass dry product fraction of bone dry biomass feedstock

Energy Densification = Ratio of HHV of product to HHV or raw biomass

Energy yield = Fuel value of solid product as a fraction of fuel value of raw biomass

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Mass yield

0

10

20

30

40

50

60

70

80

90

100

Rice hull Corn

stover

Switch

grass

Poplar Loblolly

pine

Ma

ss

Yie

ld (

%)

200 °C

230 °C

260 °C

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Energy yield

0

10

20

30

40

50

60

70

80

90

100

Rice hull Corn

stover

Switch

grass

Poplar Loblolly

pine

En

erg

y Y

ield

(%

)

200 °C

230 °C

260 °C

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Fuel densification

0.9

1.0

1.1

1.2

1.3

1.4

Rice hull Corn

stover

Switch

grass

Poplar Loblolly

pine

HH

V d

ensi

fica

tio

n

200 °C

230 °C

260 °C

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Ultimate analysisLoblolly pine

van Krevelen diagram

“Coalification” of woody biomass?

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Proximate analysisLoblolly pine

50%

60%

70%

80%

90%

100%

Raw 200 °C 230 °C 260 °C

Fixed carbon (%)

Volatiles (%)

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Fiber analysis

0%

25%

50%

75%

100%

Raw 200 °C 230 °C 260 °C

Aqueous solubles

Lignin

Cellulose

Hemicellulose

Loblolly pine

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Hydrophobic solid fuel?

Use the equilibrium moisture as a proxy for hydrophobicity

Measured at 30 °C in enclosed chamber with humidity controlled by saturated aqueous salt solution

Solid takes up moisture for 7 – 14 days, depending on final EMC

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Equilibrium moisture content

0

5

10

15

20

Raw 200 °C 230 °C 260 °C

RH = 11.3%

RH = 83.6%

EMC measurements at T = 30 °C

Pretreatment reducesequilibrium moisturecontent.

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EMC

0%

5%

10%

15%

20%

25%

30%

0% 20% 40% 60% 80% 100%

H R (%)

EM

C (

%)

Raw biomass

Wet, 200 °C

Wet, 230 °C

Wet, 260 °C

Dry, 300 °C

Model Raw

Model 200

Model 230

Model 260

Dry, 300

Raw biomass

Wet, 200 ˚C

Wet, 230 ˚C

Wet, 260 ˚C

Dry 300 ˚C

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Reactor Additives

Acetic acid

– Acid catalyzes degradation of cellulose

– Acetic acid is produced in hydrothermal carbonization: yield 3-5%

LiCl

– Salt solutions reduce vapor pressure of hot water

– Use as a tool to reduce reactor pressure

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Effect of Acetic Acid, LiCl on Fuel Densification

5000

5250

5500

5750

6000

6250

6500

0.0 0.2 0.4 0.6 0.8 1.0

Acetic Acid Added per g Loblolly Pine (g/ g Pine)

HH

V (c

al/g

)

0 g LiCl/ g pine Added

1 g LiCl/g pine Added

2 g LiCl/ g pine Added

Loblolly pine

Hydrothermal treatment at 230 °C

HHV of raw loblolly is 4510 cal/g

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Future work

Further characterization

– Pelletization

– Gasification (GTI)

Measurements of reaction kinetics

Optimize reactor conditions for different feedstocks

Demonstration of continuous hydrothermal carbonization (DRI, GTI)

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Acknowledgements

Analytical assistance of Kent Hoekman and colleagues at the Desert Research Institute in Reno, NV

Gasification studies and meaningful discussion with Larry Felix at the Gas Technology Institute in Birmingham, AL

Financial Support from the US DOE– DE-FG36-01GO11082

– EE-0000272

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Thank you for your attention

Questions?

Chuck [email protected]

“Thermal pretreatment of lignocellulosic biomass” W. Yan, T. Acharjee, C. Coronella, V. Vasquez Environmental Progress and Sustainable Energy 28(3) 435-440 (Oct., 2009)

“Mass and Energy Balances of Wet Torrefaction of Lignocellulosic Biomass” W. Yan, J. Hastings, T. Acharjee, C. Coronella, and V. Vasquez Energy and Fuels In press, 2010

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