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Biomass gasification: Improving yield and quality of producer gas
Ajay KumarAssistant Professor
Biosystems and Agricultural Engineering DepartmentBiobased Products and Energy Center (BioPEC)
Oklahoma State University
Sep 15, 20101
Thermochemical conversion
Energy conversion pathways
Source Conversion techniques
Products orintermediate
products
agricultural residues,perennial crops,forestry residue,animal waste,municipal wastes, etc.
Biochemical conversion Ethanol
Synthesis gas (syngas)/ producer gas
(38-50% cellulose, 25-32% hemicellulose,
15-25% lignin)
lignin & hemicellulose
Biomass
2
Bio-oil
2
Thermochemical Conversions
Pyrolysis
Gasification Gas
Char
Ash
Bio-oilBiomass
Air
Steam
Combustion Heat
Tar
Byproduct 3
Gasification process
• Required: high temperature & oxidizing agent
• biomass + air + H2O C (char)+ CH4+ CO + H2 + + CO2 + N2 + H2O (unreacted steam) + ash + tar
4
Biomass
Air
Gas
Char
Ash
Tar
Steam
Sorghum Switchgrass
Gasification process - factorsHeating,
Chemical reactions,
catalysis
•Particle size•Bulk density•Proximate analysis•Elemental analysis•Energy content•Cellulose, hemicelluloses &Lignin contents
•Syngas composition•Syngas energy•Carbon conversion efficiency•Energy conversion efficiency•Overall energy efficiency•Amount of tar•Amount of char
•Biomass flow rate•Temperature profile•Flow rates of oxidizing agents (equivalence ratio (ER), steam to biomass ratio, (SBR))•Amount and type of catalyst
Gasification
Biomass properties
Operating conditions
Product properties
5
Gasification: technical challenges
• Experimental challenge– Understand and predict the effects of gasification conditions and biomass
properties on yield and composition of product
– Reduce amounts of tar and impurities in the producer gas• Optimize gasification operating conditions & gasifier design
• Improve cold gas cleaning technique
• Improve hot gas cleaning technique
– Increase percentage compositions of CO and H2
– Increase net energy efficiency
– Obtain data for developing gasification reaction kinetics for a wide variety of feedstock
• Computational challenge– Develop gasification reaction kinetics
– Incorporate reaction kinetics into gasification model to reliably predict gas yield and composition 6
Ongoing projects
1. Design, development and performance evaluation of lab-scale fluidized-bed gasifier (FBG)
2. Evaluate effectiveness of commercial reforming catalysts to crack tar
3. Investigate gasification reaction kinetics using TG-FTIR
4. Gasification of a wide variety of biomass in a downdraft gasifier
7
1. Design, development and performance evaluation of lab-scale fluidized-bed gasifier (FBG)
•Biomass feedrate : 3-6 kg/h
Objectives
• Design a new lab-scale FBG with instruments to control and monitor process conditions
• Evaluate performance of the gasifier
• Improve the system components so that it can run continuously for longer duration8
9
Gasifier components
Factor considered while designing
Biomass feed rate Physical characteristics of biomass Test duration Equivalence ratio Superficial velocity
Biomass hopper Screw feederGasifier
Fluidized bed
reactor
HopperCyclone
Separators
Orificeplate
Fig. Fluidized bed gasifier set up 10
Gasifier temperature profile with time
11
Effect of equivalence ratio (ER) on gasifier temperature
12
775
800
825
850
875
900
925
0.15 0.25 0.35 0.45 0.55
Tem
pera
ture
(C
)
Equivalence ratio ( Ø )
Avg. reactor bed temperature
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4.0
4.5
5.0
5.5
6.0
6.5
0.00
1.00
2.00
3.00
4.00
0.15 0.25 0.35 0.45 0.55
HH
V (
MJ/
Nm
3 )
Dry
gas
yie
ld
(Nm
3 /Kg
of b
iom
ass)
Equivalence ratio (Ø)
Dry gas yield
HHV of dry gas
Effect of ER on yield and higher heating value (HHV) of producer gas
14
0
10
20
30
40
50
60
0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55
% v
/v
Equivalence ratio (Ø)
CO
H2
CH4
CO2
N2
C2H2
C2H4
C2H6
Effect of ER on producer gas composition
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Effect of ER on gasifier efficiencies
30
40
50
60
70
80
90
100
0.15 0.25 0.35 0.45 0.55
Effi
cien
cies
(%)
Equivalence ratio (Ø)
Carbon conversion efficiency
Hot gas efficiency
Cold gas efficiency
16
Conclusions:
A lab-scale fluidized bed gasifier was designed and developed. The gasifier performance was evaluated for switchgrass as a feedstock
by varying equivalence ratio (Ø) from 0.18 to 0.51 At equivalence ratio of 0.32,
The highest gas heating value was 6.17 MJ/Nm3 (db) , The maximum cold gas efficiency was 80% and The maximum hot gas efficiency was 84%.
The maximum carbon conversion efficiency of 95.95% was observed at Ø value of 0.51.
Near pilot-scale FBG
•Biomass feedrate: 15-30 kg/h
•Fluidized-bed Gasifier (FBG)
•Gas scrubbing system
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2. Evaluate effectiveness of commercial reforming catalysts to crack tar
• Two stage evaluation– 1st stage: Test catalysts using toluene as a model
tar
– 2nd Stage: Test catalysts using real producer gas with tar
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1st Stage: Evaluation of catalysts to crack toluene as a model tar
Objectives• Evaluate selected commercially available catalysts (Cerium-Zirconium-Platinum, Hifuel R110
and Reformax 250) for their effectiveness in cracking toluene as a model tar• Study effects of reaction conditions such as temperature, catalyst particle size, and steam to
carbon ratio on tar degradation
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Effect of space time (catalyst weight)
Figure Captions :a) Cerium Zirconium Platinum
catalyst powder.
b) Hifuel R110 catalyst powder.
c) Reformax 250 catalyst powder.
50
60
70
80
90
100
110
0 100 200 300
% T
olue
ne C
onve
rsio
n
Time on stream (minutes) 0.25g 0.15g
a)
50
60
70
80
90
100
110
0 50 100 150 200 250 300
% T
olue
ne C
onve
rsio
n
Time on stream (minutes) 0.25g 0.15g
b)
50
60
70
80
90
100
110
0 50 100 150 200 250 300
% T
olue
ne C
onve
rsio
n
Time on stream (minutes) 0.25g 0.15g
c)
20
Effect of temperature on Cerium-Zirconium-Platinum catalyst
Weight of catalyst tested-0.15g, Steam to Carbon ratio-2.
0
20
40
60
80
100
120
0 50 100 150 200 250 300
% T
olue
ne C
onve
rsio
n
Time on stream (minutes)
21
Other Gas Compositions
(Experimental conditions :T=700°C, S/C ratio=2, weight of catalyst =0.25g.)
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0 50 100 150 200 250 300Time on stream (minutes)
H2
Conc
entr
atio
n (g
L-1
)
0
0.05
0.1
0.15
0.2
0.25
0.3
0 50 100 150 200 250 300
CO2
Conc
entr
atio
n (g
L-1
)
Time on stream (minutes)
0
0.02
0.04
0.06
0.08
0.1
0.12
0 50 100 150 200 250 300
CO C
once
ntra
tion
(g L
-1)
Time on stream (minutes)
22
Other Gas Compositions (Contd.)
(Experimental conditions :T=700°C, S/C ratio=2,Weight of catalyst =0.25g.)
0
0.005
0.01
0.015
0.02
0.025
0 50 100 150 200 250 300
CH4
Conc
entr
atio
n (g
L-1
)
Time on stream (minutes)
23
Conclusions from Bench Scale System
• Cerium Zirconium Platinum , Hifuel R110 and Reformax 250- successfully reduced amount of toluene
• Higher catalyst weight (Space time)- Higher toluene conversion.
• Higher catalyst bed temperature - Higher the conversion .
• Gas Compositions:
For all three catalysts increase in H2, CO2, and decrease in CO and CH4 concentration.
• Overall reaction:
C7H8+H20+H2+CO2+CO+CH4+N2= C7H8+ H20+ H2+ CO2+ CO+ CH4+N2 + C2-C6 HC
• Catalyst Deactivation
Cerium Zirconium Platinum > Hifuel R110 > Reformax 250. Powder > Pellets.
For Cerium Zirconium Platinum catalyst - 600 > 800°C.
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2nd Stage: New catalytic reactor for hot gas cleaning
Objectives
• Design a catalytic reactor to evaluate catalysts in cracking real tar
• Study effects of operating condition of catalytic cracker (air and steam flowrate, temperature, residence time) and various steam reforming catalysts on tar level and gas composition
To FlareAir
H2O (HPLC)
Syngas w/ tar
Gas sampling GuardBed
Tar sampling
Catalytic Bed
Heated gas line
Stop valve
Mass flow controller
To Flare
Gas sampling
Tar sampling
DPI
TITI
TI
TI
TI
D
TI
TI
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3. Investigate gasification reaction kinetics using TG-FTIR
Objectives• Investigate the effects of oxidizing atmosphere, temperature and heating rate on
rate of weight loss, gas and tar composition• Derive volatization kinetics of various feedstocks• Incorporate the kinetic parameter into gasification model to predict producer gas
yield and composition
TGA
GC
FTIR
GC-MS
BiomassEvolved gas
Ash and partial char
Nitrogen or air
0
20
40
60
80
100
120
0 100 200 300 400 500 600 700 800 900
Temperature (°C)
Res
idua
l wei
ght (
%)
(TG
A)
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
DTG
(%/°
C)TGA (%) DTG (%/°C)
ash +
fixed carbon
Stage IDehydration
volatiles
Stage IIActive pyrolysis
Stage IIIPassive pyrolysis
Kumar et al., 2008. Biomass and Bioenergy.
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Equipment
Coupled TGA-FTIR set-up•Studying reaction kinetics of gasification•Identifying compounds at various reaction conditions Mass Spec with precision sampling system
•Online measurement of gas composition
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TGA profiles of switchgrass for different heating rates in nitrogen atmosphere
28
29
Time (minutes)Time (minutes)
20.020.015.015.0
10.010.05.05.0
Absorbance (Abs)Absorbance (Abs)
0.300.30
0.200.20
0.100.10
-0.00-0.00
Wavenumbers (cm-1)Wavenumbers (cm-1)40004000
30003000
2000200010001000
Online FTIR spectra with varying time (and temperature)
Results and discussion
Figure. TGA profiles of switchgrass at different heating rates in air atmosphere 30
Results and discussion
Figure. DTG profiles of switchgrass at different heating rates in nitrogen atmosphere 31
Results and discussion
Heating rate
(oc/min)
ActivationEnergy (E) in
KJ.mol-1
Frequency factor
(A)
Order of the
reaction (n)
R2
10 99.15 1.91×108 0.39 0.99
30 92.90 1.11×108 0.38 0.99
50 87.85 0.5×108 0.49 0.99
Heating rate
(oc/min)
Activation energy (E )in
KJ.mol-1
Frequency factor
(A)
Order of the
reaction (n)
R2
10 73.12 3.1×105 0.67 0.96
30 68.516 3.09×105 0.74 0.96
50 66.015 2.6×105 0.77 0.96
Table 1. Kinetic parameters during second stage decomposition in air atmosphere
Table 2. Kinetic parameters during second stage decomposition in nitrogen atmosphere
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Results and discussion
33
Figure. TGA plot of switchgrass pyrolysis in nitrogen atmosphere
Weight loss with temperature
34
Rate of weight loss with temperature
35
Products with increase in temperature (detected by FTIR)
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0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
150 250 350 450 550 650 750 850 950
Inte
nsity
Temperature ( C)
CO2 variationCO variationwater variationC=O variationCH4 variation
Observations
• Switchgrass decomposition takes place in three stages
• The significant weight loss was observed corresponding to hemicellulose and cellulose decompositions
• Lignin decomposes slowly over a wide range of temperature
• CO2,CO, water, formaldehyde, methane were observed by FTIR as major products during switchgrass pyrolysis
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4. Gasification of a wide variety of biomass in a downdraft gasifier
Air lock
Biomass hopper
Burner
PropaneAir
Ash
To gas cleanup system
Biomass
Tar & particulate measurement system
38
Temperature profilefor switchgrass gasification
0
200
400
600
800
1000
1200
0 50 100 150 200
Time from start, minutes
Tem
pera
ture
, C
Tar Cracking,CG1
Below Grate
Flame
39
Gas compositionSwitchgrass gasification
0
10
20
30
40
50
60
0 50 100 150 200 250 300 350
Time from start, min
% V
olum
e
COH2CH4CO2N2C2H2C2H4C2H6
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Energy efficiencies
0
10
20
30
40
50
60
70
80
90
450 500 550 600 650 700
Specific air input rate. kg/h-sq. m
Hot
gas
eff
icie
ncy,
%Wood Pellets
Switchgrass
Sweet Sorghum
Forage Sorghum W2
Wood Shavings
Corn fermentation waste
0
10
20
30
40
50
60
70
80
450 500 550 600 650 700
Specific air input rate. kg/h-sq. m
Cold
gas
eff
icie
ncy,
%
Wood Pellets
Switchgrass
Sweet Sorghum
Forage Sorghum W2
Wood Shavings
Corn fermentation waste
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Personnel and Financial SupportPIs:• Ajay Kumar• Krushna Patil• Danielle Bellmer• Raymond HuhnkeGraduate students/Research engineer:
– Ashokkumar Sharma – Design and study of lab-scale FBG– Prakash Bhoi – Study of downdraft gasification– Vamsee Pasangulapati – Thermochemical characterization of biomass– Akshata Modinoor & Pushpak Bhandari– Design and study of a new catalytic tar cracker– Luz Martin & Akshata Modinoor– Characterization and evaluation of selected catalysts for tar
cracking• Financial Support provided by:
– Oklahoma State Regents for Higher Education– NSF OK-EPSCoR– Oklahoma Bioenergy Center– USDA Special Grant– Director of the Oklahoma Agricultural Experiment Station
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Thank you
Questions?
43