Techno-economic assessment of the effect of torrefaction on fast pyrolysis of pine
Supplementary Information
The present document is prepared to complement the manuscript and provide additional
information. The features of interest include the process description of other unit operations
and the flow diagrams of the scenarios described in the manuscript.
Section A. MODEL DESCRIPTION OF SOME UNIT OPERATIONS
A.1 Drying
Biomass inherently contains moisture and it is assumed here that the delivered pine wood has a
moisture content of about 25% which will be dried to about 7% which is recommended for fast
pyrolysis. The set-up in this study has the drying step prior to size reduction for a couple of reasons
that includes being able to gain the benefit of reduced energy requirement as a result of a
torrefaction pre-treatment step as well as the fact that moisture content higher than 15% may affect
the size reduction step due to plugging or blinding of the small diameter screen openings that
would be employed to attain the desired particle size. The drying step will be modeled in Aspen
Plus using a stoichiometric reactor and a STEAM thermodynamic package, this calculates the
energy required for drying by estimating the specific energy required to raise the temperature of
the biomass and its inherent moisture to the target temperature and also the latent heat required to
vaporize the moisture in the biomass.
A.2 Size Reduction
The correlation obtained from literature given as follows for pine was used in evaluating the
reduction in energy consumption to attain required size to effect fast pyrolysis.(1)
𝐸𝑔 = −0.756𝑇 + 260.0
(1)
where Eg is specific energy consumption for grinding in kW-hr/ton, T is Temperature in oC
The size reduction step was then modeled in Aspen Plus® as a hammer mill with the estimated
specific energy consumed for grinding estimated at different torrefaction temperatures while the
untreated raw pine’s energy was estimated using ambient temperature of 25oC. The work index
required for grinding was also calculated using
𝐸𝑔 = 10 ∗ 𝑊𝑖 ∗ (
1
√𝑃
−
1
√𝐹
)
(2)
where Eg Specific energy consumption for grinding in kW-hr/ton, Wi is work index in kWhr/ton, P is final particle size in microns and F is Initial particle size in microns
A.3 Combustion
Combustion of products when considered in this study was not modeled using the process
simulation software, however the heat released during combustion were estimated from
correlations obtained from literature as shown below:
A.3.1 Combustion of char
Heat released from the combustion of char was evaluated based on the lower heating value of
char, which was estimated from its higher heating value based on correlation from literature given
below:(2)
𝑤
𝑤
ℎ
𝐿𝐻𝑉 = 𝐻𝐻𝑉 (1 − 100) − 2.444 ∗ 100 − 2.444 ∗ 100 ∗ 8.936 (1 −
Where
𝑤
𝑀𝐽
) [ 𝑘𝑔 , 𝑤. 𝑏. ]
100
(3)
2.444 = enthalpy difference between gaseous and liquid water at 25oC
8.936 = MH2O/MH2; i.e. the molecular mass ratio between H2O and H2
LHV = lower heating value
HHV = higher heating value
w = moisture content of the fuel in wt% (w.b.)
h = concentration of hydrogen in wt% (d.b.)
The higher value utilized in equation above was also estimated from empirical formula as well as
shown below.(3)
𝑀𝐽
𝐻𝐻𝑉 = 0.3491𝑋𝐶 + 1.1783𝑋𝐻 + 0.1005𝑋𝑆 − 0.0151𝑋𝑁 − 0.1034𝑋𝑂 − 0.0211𝑋𝑎𝑠ℎ [ 𝑘𝑔 , 𝑑. 𝑏. ]
(4)
Where Xi is the content of carbon (C), hydrogen (H), etc. from the ultimate analysis of the solid
fuel.
A.3.2 Combustion of condensates from torrefaction
Energy released from the combustion of condensates from torrefaction when such step takes place
in this study was estimated by obtaining from literature the lower heating value of the individual
components in the condensates.(4) Based on the lower heating value of the individual components
and their weight fraction in the liquid, the lower heating value of the liquid was estimated. For
high molecular compounds produced from either the torrefaction or pyrolysis step whose lower
heating values were not found in literature, their lower heating values were estimated using
correlation obtained from literature as shown below:(5)
For compounds containing only carbon, hydrogen and oxygen, general combustion reaction was
given as
𝐶𝑎 𝐻𝑏 𝑂𝑐 + (𝑎 +
𝑏 𝑐
𝑏
− ) 𝑂2 → 𝑎𝐶𝑂2 (𝑔) + 𝐻2 𝑂 (𝑙)
4 2
2
(5)
The standard heat of combustion is then given as
∆𝑐 𝐻 ° = −𝑎∆𝑓 𝐻 ° (𝐶𝑂2 , 𝑔) −
1
2
𝑏∆𝑓 𝐻 ° (𝐻2 𝑂, 𝑙) + ∆𝑓 𝐻 ° (𝐶𝑎 𝐻𝑏 𝑂𝑐 )
= 393.51𝑎 + 142.915𝑏 + ∆𝑓 𝐻 ° (𝐶𝑎 𝐻𝑏 𝑂𝑐 )
(6)
(7)
Where ∆𝑓 𝐻 ° is the enthalpy of formation. When the heat of formation is not available from
literature, it was estimated based on the structure of the component by using the Joback method
which is based on group contribution.(4, 6)
A.3.3 Combustion of non-condensable gas from torrefaction
Heat generated from combustion of non-condensable gas from torrefaction was estimated using
the lower heating value of the components present in the non-condensable gas phase. Severity of
torrefaction usually determines the components contained in the non-condensable gas, however
for this study, the components were assumed to be essentially CO2 and CO in a 80 to 20 ratio
hence heat released from combustion is due to the CO component only, this assumption is
supported by the report of Tumuluru et al which showed energy released from the combustion of
volatiles from torrefaction is mainly from CO.(7)
A.3.4 Bioe correlation for heat of combustion estimation
One of the correlation used in Aspen Plus® to estimate the heat of combustion of unconventional
solids such as biomass based on the ultimate analysis is as shown:
𝑑𝑚
𝑑𝑚
𝑑𝑚
𝑑𝑚
𝑑𝑚
∆𝑐 ℎ𝑖𝑑𝑚 = [𝑎1𝑖 𝑤𝐶,𝑖
+ 𝑎2𝑖 𝑤𝐻,𝑖
+ 𝑎3𝑖 𝑤𝑆,𝑖
+ 𝑎4𝑖 𝑤𝑂,𝑖
+ 𝑎5𝑖 𝑤𝑁,𝑖
]102 + 𝑎6𝑖
(8)
Where wC,i dm is the weight fraction of carbon.
Values of the parameters as given by Aspen Plu® are as follows(8)
a1i = 151.2, a2i = 499.77, a3i = 45.0, a4i = -47.7, a5i = 27.0 and a6i = -189
A.4 Conveyance
Biomass movement across the plant is assumed to be carried out using conveyor belts, and the
energy required for this conveyance was estimated by firstly using the guidelines by CEMA as
shown by Couper et al.(9, 10) The conveyance is assumed to be carried out using a 24 inch, 45o
troughed belt conveyor of length, 33.5m and up a longitudinal incline of 22o. The running angle
of repose of the woodchips is taken to be about 30o and the required power is estimated by using
equation 7.
𝑃𝑜𝑤𝑒𝑟 (ℎ𝑝) = 𝑃ℎ𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 + 𝑃𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 + 𝑃𝑒𝑚𝑝𝑡𝑦
(9)
Where Phorizontal = (0.4+L/300)(W/100), Pvertical = 0.001HW, and Pempty obtained based on desired
conveyor length from literature.(10)
A.5 Energy Return on Energy Invested (EROEI)
𝐸𝑅𝑂𝐸𝐼 =
𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡
𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛
=𝐸
𝐸𝑏𝑜 + 𝐸𝑐ℎ𝑎𝑟
𝑡ℎ𝑒𝑟𝑚𝑎𝑙 +𝐸𝑒𝑙𝑒𝑡𝑟𝑖𝑐𝑖𝑡𝑦
=
𝑚̇𝑏𝑜 𝐿𝐻𝑉𝑏𝑜 +𝑚̇𝑐ℎ𝑎𝑟 𝐿𝐻𝑉𝑐ℎ𝑎𝑟
𝐸𝑡ℎ𝑒𝑟𝑚𝑎𝑙 +𝐸𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦
(10)
Where Ebo is the energy obtainable from bio-oil estimated based on its lower heating value (LHV),
Echar is the energy obtainable from char also obtained from its lower heating value. 𝑚̇ is the mass
flowrate while Ethermal is the required process heat required over the whole process and Eelectricity is
the energy associated with size reduction and conveyance across the process. Energy due to
electricity was converted to thermal assuming an efficiency of about 35% for the conversion of
steam to electricity.
SECTION B. INPUT DATA TABLES USED IN MODELING
Table 1a. Torrefation component distribution (wt % organics) of organics from torrefaction of pine at different
torrefaction temperatures.
Component (wt/wt organics)
Acetic Acid
Propionic Acid
Acetol
Fufural
2-Furanmethanol
5-(hydroxymethyl)-2-furancarboxaldehyde
Levoglucosan
Xylose
Hydrolysable Oligomers(cellobiose)
Glucose
Isoeugenol
Eugenol
Vanillin
2-methoxy-4-vinylphenol(p-vinylguaiacol)
Catechol(benze-1,2-diol)
Phenol
2-methoxyphenol (guaiacol)
4-methylphenol(p-cresol)
3-methylphenol (m-cresol)
4-ethylphenol
2-methoxy-4-methylphenol (creosol)
Low MW Lignin Derived Compound
A(Dimethoxy stilbenzene)
Low MW Lignin Derived Compound B
(Dibenzofuran)
High MW Lignin Derived Compound A
High MW Lignin Derived Compound B
290oC
8.01
0.25
2.47
1.01
0.09
0.00
0.40
0.40
0.00
0.10
0.33
0.05
0.21
0.00
0.00
0.00
0.49
0.00
0.00
0.00
0.00
0.95
Torrefaction temperature
310oC
330oC
11.92
13.09
0.42
0.48
5.08
6.43
1.26
1.95
0.11
0.21
0.00
0.00
2.43
3.00
1.22
1.32
0.15
0.36
0.61
0.60
0.76
1.83
0.13
0.27
0.32
0.31
0.00
0.00
0.00
0.00
0.00
0.00
0.83
1.48
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1.24
1.87
0.19
0.25
0.38
0.79
0.17
1.04
0.23
1.56
0.34
Table 2a. Ultimate analysis data (wt %) for torrefied pine chips at different torrefaction temperatures.
Torrefaction Temperature
Component
Ash
Carbon
Hydrogen
Chlorine
Nitrogen
Sulfur
Oxygen
290oC
0.6
55.05
5.94
0.11
38.3
310oC
Wt %
0.6
57.27
5.79
0.14
36.0
330oC
0.8
65.75
4.87
0.28
27.6
Table 3a. Proximate analysis data (wt %) for torrefied pine chips at different torrefaction temperatures.
Torrefaction Temperature
Component
Ash
Moisture Content
Volatile Matter
Fixed Carbon
290oC
0.60
0
78.6
20.8
310oC
Wt %
0.80
0
76.4
22.8
330oC
1.4
0
60
38.6
Table 4a. Pyrolysis component distribution of organics (wt/wt organics) for one step and two step pyrolysis of pine.
One Step
Component
Two Step
290oC
310oC
330oC
7.59
3.69
3.11
1.00
0.12
0.23
4.42
0.00
3.28
0.29
0.07
0.28
2.96
0.00
2.39
0.15
0.04
0.15
1.11
0.00
0.85
0.38
0.11
0.45
7.24
2.19
3.29
1.10
0.54
0.12
0.42
0.79
2.53
0.19
0.46
0.06
0.02
0.07
0.46
7.11
7.91
2.05
5.28
1.17
0.58
0.36
0.14
0.37
4.88
0.33
0.46
0.12
0.06
0.14
0.85
6.50
6.04
1.01
4.70
0.34
0.58
0.20
0.15
0.25
2.32
0.24
0.37
0.10
0.13
0.05
0.50
6.00
8.45
0.94
0.00
0.00
0.50
0.17
0.12
0.21
2.08
0.23
0.30
0.06
0.09
0.07
0.59
3.05
1.43
1.31
1.21
0.62
5.94
1.30
5.43
1.18
5.02
1.10
2.55
0.56
Torrefaction temperature
(wt %)
Acetic Acid
Propionic Acid
Acetol
Fufural
2-Furanmethanol
5-(hydroxymethyl)-2furancarboxaldehyde
Levoglucosan
Xylose
Cellobiose
Glucose
Isoeugenol
Eugenol
Vanillin
P-vinylguaiacol
Catechol
Phenol
Guaiacol
P-cresol
M-cresol
4-ethylphenol
Creosol
Low MW Lignin Derived Compound
A(Dimethoxy stilbenzene)
Low MW Lignin Derived Compound B
(Dibenzofuran)
High MW Lignin Derived Compound A
High MW Lignin Derived Compound B
Table 5a. Ultimate and proximate data (wt %) for char obtained after pyrolysis.
Ultimate Analysis
Components
Wt. %
Ash
7.67
Carbon
83.03
Hydrogen
1.14
Nitrogen
1.37
Chlorine
Sulfur
Oxygen
6.56
Proximate Analysis
Components
Wt. %
Ash
4.60
Moisture Content
Volatile matter
7.40
Fixed carbon
88.0
Table 6a. Estimated number of employees and their wages rate.
Employee
Plant/General Manager
Plant Engineer
Maintenance Supervisor
Lab Manager/Chemist
Shift Supervisor
Maintenance Tech
Shift Operators
Admin Assistants
Annual Salary
Number Required
$136,830.00
1
$108,630.00
1
$76,480.00
1
$77,970.00
1
$74,470.00
5
$70,450.00
6
$55,980.00
23
$43,440.00
2
SECTION C. SCHEMATIC DIAGRAMS FOR SCENARIOS 2 & 3 OF THE DESIGN
OBJECTIVES.
Non condensable gases 1
Combustion of gas to offset
natural gas usage
Torrefaction at
temperatures of 290oC ,
310oC and 330oC
Conveyor feed hopper
Woody biomass chips,
25mm
25% MC
Woody biomass chips,
25mm
8% MC
Conveyor
Dryer
Non condensable gases 2
Torrefier
Torrefier feed hopper
Conveyor
Bio-oil condenser
Biocoal chips,
25mm
Bio-Oil
Hammer mill
Cyclone
Condensed
liquid from
torrefaction
added to liquid
from pyrolysis
Combustion of
char to offset
natural gas
Pyrolysis unit feed
hopper
Biocoal chips, 2mm
Biochar
Fast Pyrolysis Unit
Conveyor
Figure c1. Schematic diagram for scenario 2 of a two-step conversion route.
Non condensable gases 1
Combustion of gas to offset
natural gas usage
Torrefaction at
temperatures of 290oC ,
310oC and 330oC
Conveyor feed hopper
Woody biomass chips,
25mm
25% MC
Conveyor
Dryer
Non condensable gases 2
Woody biomass chips,
25mm
8% MC
Torrefier
Torrefier feed hopper
Conveyor
Bio-oil condenser
Biocoal chips,
25mm
Bio-Oil
Hammer mill
Cyclone
Combustion of
some of the
liquid from
torrefaction
Credits for
char sales
Pyrolysis unit feed
hopper
Biocoal chips, 2mm
Biochar
Fast Pyrolysis Unit
Conveyor
Figure c2. Schematic diagram for scenario 3 of a two-step conversion route for pine biomass to bio-oil.
SECTION D.
FIGURES FOR SENSITIVITY ANALYSIS RESULTS.
Figure d1. Sensitivity analysis for scenario 2 of a one-step conversion of pine to bio-oil
Figure d2. Sensitivity analysis for scenario 1 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 290oC.
Figure d3. Sensitivity analysis for scenario 2 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 290oC.
Figure d4. Sensitivity analysis for scenario 3 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 290oC.
Figure d5. Sensitivity analysis for scenario 1 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 310oC.
Figure d6. Sensitivity analysis for scenario 2 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 310oC.
Figure d7. Sensitivity analysis for scenario 3 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 310oC.
Figure d81. Sensitivity analysis for scenario 1 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 330oC.
Figure d9. Sensitivity analysis for scenario 2 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 330oC.
Figure d10. Sensitivity analysis for scenario 3 of a two-step conversion process of pine to bio-oil at torrefaction
temperature of 330oC.
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