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
2
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
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
6
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
Results
Product is soft, friable solid
Odor of “charcoal”
Loblolly pine Treated at 260 °C
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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
9
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
11
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
Ultimate analysisLoblolly pine
van Krevelen diagram
“Coalification” of woody biomass?
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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
Proximate analysisLoblolly pine
50%
60%
70%
80%
90%
100%
Raw 200 °C 230 °C 260 °C
Fixed carbon (%)
Volatiles (%)
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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
Fiber analysis
0%
25%
50%
75%
100%
Raw 200 °C 230 °C 260 °C
Aqueous solubles
Lignin
Cellulose
Hemicellulose
Loblolly pine
15
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
16
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
18
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
19
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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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University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
Future work
Further characterization
– Pelletization
– Gasification (GTI)
Measurements of reaction kinetics
Optimize reactor conditions for different feedstocks
Demonstration of continuous hydrothermal carbonization (DRI, GTI)
21
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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
22
University of Nevada, Reno
Wet torrefaction of lignocellulosic biomass
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