Biomass Torrefaction – A Promising
P t t
Pretreatment
tM
Method
th d ffor Th
Thermo-Chemical
Ch i l
Conversion Technologies
Sudhagar Mani,, Jim Kaster,
Kaster, & KC Das
Faculty of Engineering, University of Georgia, Athens, GA
Email: smani@engr.uga.edu
IEA Bioenergy Conference
Biofuels & Bioenergy: A Changing Climate
Vancouver, BC Canada
Aug 23-26, 2009
Introduction
„
Issues with biomass feedstock
• Wide range of moisture content (60
(60--15% wb)
wb)
• Low bulk density (4 – 8 lbs/ft3)
• Low energy density (4,500
(4,500--7,500 Btu/lb)
• Uneven particle sizes (no flow)
• Difficult to handle,
handle store and transport
• High transport and storage cost
• Self heating and emission of off gases during
storage
Introduction
„
Issues with thermothermo-chemical conversion
technologies
• Combustion:
„
Difficult to coco-fire with coal
„
Low energy density
„
High energy demand for grinding biomass
• Gasification
„
Tar formation
„
Low C/H
/ ratio for liquid
q
fuel p
production
• Pyrolysis
Pyrolysis::
„
Bio--oil instability & coke formation
Bio
• Densification:
„
Low energy density & self heating
Biomass Pyrolysis to Liquid Fuels
Pyrolysis
Unit
„
Bio-oil
Critical Problems
• Long
Long--term storage and stability of biomass
• High energy input for grinding to defined particle size
• Formation of high molecular weight compounds
• Bio
Bio--oil is unstable
„
„
Vi
Viscosity
it iincreases with
ith ti
time and
d temperature
t
t
Low pH, corrosive
• Catalytic
y
upgrading
pg
g difficult
„
„
High oxygen content
Catalytic deactivation due to coke formation
What is Torrefaction?
„
„
„
„
„
„
Solid-state thermal hydrolysis of biomass in an inert
atmosphere (e.g.,N2)
T
Temperature
t
range – 180 to
t 300oC
Hemicellulose is hydrolyzed via release of acetic acid
and subsequent hydrolysis reaction
Moisture reduction, oxygen content reduced
Some extractives volatilized, but 7070-80% solids
recovered
Most familiar example – roasting coffee
Green chip
Torrefied chip
Torrefaction History
„
„
„
„
„
1930’s – heat treatment of wood for high
g
durability, structural stability & fungal resistance (wood
roasting), provides aesthetic value
1939 – US Patent (Bergstrom
(Be gst om et al) on thermal
the mal heating of
wood >220oC
1976 – Pyrochar
y
process
p
for solid biomass into fuels
1980’s – heat treatment of wood logs (180
(180-220oC), retifaction/torrefaction process
(Yvan,
(Yvan 1985
1985, Bourgeois et al,
al 1988),
1988) Torrefaction process
development & reactor design (four patents)
2000 - Significant research & development on biomass
torrefaction process
Mass & Energy
gy Balance
Condensable:
Non-condensable:
H2, CO, CO2, CH4,
Toluene, benzene
Volatile off
gases
0.3 m
Biomass
1m
1E
Water
Organic acids, alcohols
Furans, ketones
Terpenes, phenols
l d
Waxes, tannins, lipids
~0.2 E
Torrefaction
Process
~0.1 E
External heat supply
T
Temp:
180
180-280
280oC
Heating rate: <50oC/min
Residence time: > mins
0.7 m
0.9 E
Torrefied
biomass
Research Objectives
„
Bi
Biomass
T
Torrefaction
f ti
kinetics
ki ti
• Does it improve biomass storability and
transportability?
t
t bilit ?
• Does it improve biomass grindability and reduce
energy input?
i
t?
• Effect of torrefaction on,
„
„
„
bi
bio-oil
il stability
t bilit
Eliminate or reduce coke forming precursors and
improve catalytic upgrading of bio-oil to fuels
Syngas quality and tar concentration during
g
gasification
„
Pellet quality
„
Combustion behavior
Mass loss with time for a range of
torrefaction conditions – TG
TG-MS
MS
100
% mass
s remain
ning
90
80
70
200
60
215
230
50
245
40
260
30
275
20
pyr. @ 700
10
0
0
2000
4000
time / s
6000
8000
Proposed Torrefaction Kinetics
M d l
Model
Hemicellulose (A)
k1
Depolymerised
Intermediate (B)
k2
Solid products (C)
kv2
kv1
„
Volatile products
Model equations:
For components a, b and c:
a’(t) = -(k1+kv1)*a(t), a(0) = 1 (normalized vs. starting mass)
b’(t) = k1*a(t)k1*a(t)-(k2+kv2)*b(t) b(0) = 0
c’(t) = k2*b(t)
c(0) = 0
Torrefaction Experiment
Condensed liquids
Torrefaction Reactor
Forest Residue chips
Non-condensable gases
Experiment 1.3.2 - Torrefaction - Pine Chips
30 minutes - 280oC - 30% Moisture
300
250
Tem
mperature (oC)
200
150
100
50
0
0
15
30
45
60
75
Time (minutes)
90
105
120
Torrefied biomass
Torrefied Auger Reactor - UGA
•Continuous Reactor
•Capacity
Capacity – 5 to 10 kg/h
•Capability to collect
condensable
• Non-condensables gases can
be recalculated in the auger
Rotary drum reactor – UGA
(indirect heating)
Capacity = 400 lbs/run
Results – Torrefied biomass yield
Pine Chips30 Minute run
Torrefied b
biomass yield
d (%)
100%
80%
60%
40%
10%M.C.
20%
30% C
30%M.C.
50%M.C.
0%
220
250
Temperature
280
Torrefaction of Pine Chips
p
Torrefaction Process
Torrefaction Results
„
GC/MS of Non-condensables (gas phase)
• Acetaldehyde, α-pinene
pinene,, βpinene,, camphene, phellandrene observed at low
pinene
temperatures (220C)
• Acetaldehyde evolution increased with time
• Pinenes decreased with holding time
• As temperature
p
increased,, acetic acid,, methylester
y
and furans appeared (220 to 250C and above)
„
„
Furan, 2
2--methylfuran, 250C
2
2,3
2,33-dihydrofuran and 2,52 5-dimethylfuran,
2,5
dimethylfuran 280C
Results – Non
Non--condensable at 280oC
Non-Condensables vs. Time; Torrefaction at 280oC
9
Methane
8
Carbon dioxide
Methyl acetylene
Am
mount (mole %
%)
7
Propylene
6
n-Butane
5
Ethylene
Ethane
4
3
2
1
0
0
10
20
30
Time (min)
40
50
60
Results – Condensable at 280oC
Condensables vs. Time; Torrefaction - 280oC
35000000
α-pinene
α
pinene
camphene
Re
elative Abunda
ance
30000000
β-pinene
25000000
β phellandrene
β-phellandrene
20000000
15000000
10000000
50000000
0
0
10
20
30
Time (min)
40
50
60
Results – Compositional changes
Forestt residue
F
id
chips
Cellulose
C
ll l
(% wt)
Hemi-cellulose
H
i
ll l
(% wt)
Lignin
Li
i
(% wt)
Heating
H
ti
value
l
(Btu/lb)
Non-torrefied
(10% m.c.)
mc)
43.1
18.4
20.9
7,774
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
Forestt residue
F
id
chips
C
H
O
N
S
A h (% wt)
Ash
t)
Non-torrefied
(10% m.c.)
mc)
45.3
5.9
48.5
0.3
0.1
0.6
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 – Compositional changes
Forestt residue
F
id
chips
Moisture
M
i t
(%)
Volatile
V
l til C
(% wt)
Fixed
Fi
dC
(% wt)
A h (%)
Ash
Non-torrefied
(10% m.c.)
mc)
10
75.3
16.3
0.4
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
T
Torrefaction
f ti
Bulk dens
sity, kg/
/m3
200
179.51
175
160.43
152.13
150
125
220
250
280
Torrefaction temperature oC
Forest biomass chips – 18% change
Improved Pelleting Process
Raw material
Drying process
Grinding
Torrefaction
Torrefaction
Drying
Pelletization
Pelletization
P
ll ti ti
High quality
Products
Pellets
Effect of Torrefaction on Pellet Density
1200
Pelle
et Densitty, kg/m
m3
1100
220
1000
900
Control
800
220
250
700
280
280
600
0
2000
4000
Applied Forces, N
6000
8000
Pelle
et Produ
uction c
cost, $/
/t
Torrefaction-- Pellet Production Cost
Torrefaction
50
Packing cost
$40
Land use & building
40
$27
$24
$30
30
Miscellaneous
equipment
Screening
20
0.00
Pellet cooler
10
0
Personnel cost
0.00
0
6.45
Pellet mill
Hammer mill
Torrefaction
Drying operation
24
Torrefaction - Pyrolysis
TG/MS Analysis of Torrefied
Biomass
„
„
„
„
TGA/MS ((Mettler
Mettler Toledo)
Performed
P f
d under
d pyrolytic
l ti conditions
diti
– N2 or Ar
A
carrier gas
10mg sample, 50 ml/min, 3030-900
900°°C at 10°
10°C/min
Monitored Off Gas in Selective Ion Mode (SIM)
• Non-condensables, CO-28, CO2-44, H2-2, H2O-18
• Potential tar compounds,
„ Benzene – 78
„ Guaiacol – 124
„ Naphthalene – 128
„ Phenol – 94
• Potential hemicellulose breakdown products
„ Acetaldehyde – 29
„ Acetic acid – 60
„ Acetol – 45
Effect of Torrefaction on Pyrolysis Kinetics
(TGA Analysis)
12
1
10
08
0.8
10
08
0.8
0.6
6
0.4
4
02
0.2
2
0
0
„
„
0.6
6
0.4
4
0.2
2
0
0
1000
0
X, fractional biomass conversion
Higher
g e temperature
e pe a u e torrefaction
o e ac o
(> 300°
300°C) appears to reduce
biomass thermal decomposition
and alter pyrolysis kinetics
More research needed to
confirm effect
500
0
1000
Temperature, C
Torrifie d Pine Pe lle ts at 300C
Mass (mg)
„
500
Tem perature, C
8
12
1
10
08
0.8
8
0.6
6
0.4
4
02
0.2
2
0
0
500
Te m pe rature , C
0
1000
X, mass
8
Mass (mg)
1
X, mass
Mass, mg
12
X, mass
Torrified Pine Pellets at 250C
Pine Pellet Pyrolysis
Torrefaction-Pyrolysis-Solids Properties
„
„
Oxygen content reduced
Fixed carbon increased
Material
Characteristic
PP BM
PP T250
PP T300
PP T350
PP P500
C
H
N
S
O
52.6
5.7
0.2
0.0
38.9
53.9
5.3
0.1
0.1
37.6
73.2
4.7
0.2
0.1
19.6
78.0
3.7
0.2
0.1
15.0
82.5
2.6
0.2
0.0
4.4
Moisture
Volatiles
Ash
Fixed Carbon
77.2
2
79.8
0.5
19.7
00.0
0
71.2
3.0
25.8
11.00
42.4
2.2
55.4
22.00
32.2
2.9
64.9
33.22
28.1
2.8
69.1
HHV (MJ/kg)
20.6
20.9
28.8
29.7
31.0
PP, pine pellets; BM, biomass; T, torrefaction, P, pyrolysis
Parameter
Ultimate analysis
(wt % dry)
C
H
N
S
Oe
HHV
(MJ/kg, wet basis)
H2 O
(wt %)
(wt.
pH
aP:
Pa
Bio-Oil Characteristics
PUb
TPc
TPUd
69.66
69
7.65
0.74
0.05
22.0
29.1
73.11
73
8.1
0.4
0.0
18.4
30.9
71.33
71
7.97
0.19
0.01
20.5
28.6
73.99
73
7.93
0.17
0.02
18.0
30.7
2.4
4.0
9.3
6.7
3.1
3.2
3.7
3.5
Pyrolysis (catalytic upgrading feedstock, no torrefaction)
bPU: Pyrolysis + catalytic Upgrading (no torrefaction)
cTP: Torrefaction + Pyrolysis (catalytic upgrading feedstock)
dTPU: Torrefaction + Pyrolysis + catalytic Upgrading
Torrefaction - Combustion
Comparison of combustion of torrefied
biomass, untreated biomass and coal
1.2
remain
ning frac
ction
1
t225
0.8
t235
t250
0.6
t260
t275
0.4
t285
t300
raw pine
0.2
coal
0
0
1000
2000
Time
3000
4000
Conclusions
„
„
„
Condensable compounds are mainly released from
extractives in the biomass as α, β-pinene, camphene
etc.
t These
Th
compounds
d can be
b redirected
di
t d to
t supply
l
heat energy during torrefaction
During
D
i
torrefaction,
t
f ti
hemi-cellulose
h
i
ll l
iis almost
l
t removed
d
and results in higher energy density product with a
heating value of 10,000
10 000 Btu/lb.
Btu/lb Torrefaction
temperature plays a major role in defining the energy
density
y of biomass and can be optimized
p
for any
y
specific applications.
Torrefaction followed by
y pelleting
p
g costs about $
$30/t of
pellets. Torrefaction process alone costs about $6.5/t.
Conclusions
„
„
„
Biomass torrefaction process can produce high energy
density and consistent feedstock for thermal conversion
technologies (gasification, co
co--firing & pyrolysis)
pyrolysis)
Pelleting of Torrefaction of biomass may be difficult due
to hydrophobic nature of the material and require
additional binders to increase the bulk density
Future research at UGA is focused on optimizing the
best reactor configuration
g
for a torrefaction p
process
and promote its application to co-firing, gasification
and pyrolysis processes
Acknowledgement
„
Financial support from
• University of Georgia Research
Foundation
• State of Georgia – Traditional Industries
Program
• Georgia Power – Southern Company
Thank you
Densification
Direct
combustion
Gasification
Biocoal
Co-firing with
coal
Biomass Torrefaction Technology