Processing Sweet Sorghum For a Dual Feedstock Bioenergy System Dani Bellmer, Professor Biosystems & Agricultural Engineering Food and Agricultural Products Center Oklahoma State University
Feb 04, 2016
Processing Sweet Sorghum For a Dual Feedstock Bioenergy
System
Dani Bellmer, ProfessorBiosystems & Agricultural Engineering Food and Agricultural Products Center
Oklahoma State University
Why I Love Sweet Sorghum
• Versatility– Can be grown in temperate climates
– Adapts well to adverse environments (hot, dry, high salinity)
• Relatively low input requirements
• High carbohydrate production (in both the sugar & lignocellulosic fractions)
Feedstock Yield Potential
Liquid Sugar
Biomass
Starch
HugeBiofuel Potenti
al
Lignocellulosic Feedstock Yield Comparison
Crop Location
1Dry Yield(Mg/ha)
2 EthanolYield(L/ha)
Corn Stover U.S.A 12 3516
Switchgrass U.S.A 13 3809
Miscanthus U.S.A 17 4981
Mixed Prairie Grass U.S.A 6.7 1963
Woody Crops U.S.A 11 3223
Energy Cane U.S.A 26 7618
Sweet Sorghum Bagasse U.S.A 22 6446
1Source: DOE Update to the Billion Ton Sudy (2011)2Ethanol yield assumes that 50% of d.m. can be converted to sugars
Feedstock Yield Potential
Sugar Biomas
s
LargeBiofuel
Potential
Sw. Sorghum: 3800 + 6446 10,246 L/ha
Sweet Sorghum Processing Options: Scale Matters
Scenario #1: 10,000 contiguous acres in a tropical climate
Use a System that Mimics Sugarcane Processing (large press roll train)
Scenario #2: Smaller acreage in a temperate climate
Best Processing Options are Not So Clear
Low Hanging Fruit for Biofuel Production:
Immediate Uses for Sweet Sorghum Juice:
• As a low-cost seasonal feedstock in existing ethanol plants
• As a complementary feedstock during sugarcane processing (4-5 months when harvestable cane is not available)
Considerations for the South Central U.S.
• Short sorghum harvest window (3-4 months), juice is unstable
• A dual feedstock system would improve process economics
• Sugar beets could be alternated
• Ideally, a similar process could be used for both feedstocks
Sugar Beet Processing
Beets are sliced into cossettes and then put
through a diffuser system to extract
the sugar
Dual Feedstock Process
Sweet Sorghum
Sugar Beets
MillingDiffusion
Counter Current Diffusion Process
Diffusion Studies with SS• Seydelman bowl chopper to
generate 2 particle sizes
• Batch process to simulate counter current diffusion
• Tested effects of particle size, temp (60, 70, 80oC), L/S ratio (0.5, 1.0, 1.5)
Simulation of Counter
Current Diffusion
Process in a 4-Stage
Batch System
Diffusion Studies
0
10
20
30
40
50
60
70
80
90
100
0.50 0.75 1.00 1.25 1.50 1.75
Ma
xim
um
Th
eo
reti
ca
l Yie
ld (
% M
TY
)
L/S Ratio
60 oC
Fine Coarse
0
10
20
30
40
50
60
70
80
90
100
0.50 0.75 1.00 1.25 1.50 1.75
Max
imu
m T
heo
reti
cal Y
ield
(% M
TY
)
L/S Ratio
70 oC
Fine Coarse
0
10
20
30
40
50
60
70
80
90
100
0.50 0.75 1.00 1.25 1.50 1.75
Ma
xim
um
Th
eo
reti
ca
l Yie
ld (
% M
TY
)
L/S Ratio
80 oC
Fine Coarse
Diffusion Results
• Sugar extraction ranged from 45% to 91% of theoretical maximum yield
• L/S Ratio had a significant effect on sugar extraction
• Trend toward higher sugar extraction with fine particle size, but not significant
• No significant differences with temperature
Would it be more efficient to process the whole stalk, and take advantage of the
starch and cellulose present?
Liquid Sugar BiomassStarch
Proposed Dual Feedstock Process for Whole Stalks
Twin Screw Press for Milling and
Juice Extraction
Counter Current Diffusion Process
Sweet Sorghum
Sugar Beets
+ Cellulases & Amylases
Twin Screw Press• Interrupted flight design, which
generates multiple stages of compression in overlapping screws, resulting in very high shearing action.
• Shear forces may provide enough fiber development for either partial or complete cellulose hydrolysis
• In addition, juice is extracted
What can we learn from the pulp & paper industry?
• Thermomechanical refining is a common method of fiber development for separation of lignin, cellulose and hemicelluloses.
• Physical pretreatment with refiners rather than chemical treatment
Whole Stalk ProcessingFuture Goals
• Utilize a twin screw press for whole stalk processing and evaluate the extent of fiber pretreatment
• Simultaneously hydrolyze starch and cellulose in an attempt to maximize carbohydrate production.
• Evaluate the use of a mechanical refiner for stalk fiber pretreatment
Sweet Sorghum Has Tremendous Untapped
Potential
• Can be used in both the sugar and cellulose arenas
• A dual feedstock process with sugar beets may be advantageous
Liquid Sugar BiomassStarch
Acknowledgements
• Sorghum Checkoff Program
• South Central Sun Grant Program
• Robert M. Kerr Food and Agricultural Products Center
Questions ?
Thank You
Sweet Sorghum Yields
Location
Year(s)
Wet (Green)
Yield (Mg/ha)
Dry Biomass
Yield (Mg/ha)
Source
United States: Ames, IA 1988-1992 ----- 15.3-20.7 Hallam et al, 2001 Ft. Collins, CO 1984-85 89.2-90.7 ----- Smith & Buxton, 1993 Stillwater, OK 2007 65-81 ----- Bellmer & Huhnke, 2008 Salinas, CA 1981-83 82.6 ----- Hills et al., 1990 Riley County, KS 2009 ----- 24.4 Wu et al, 2009 Whiteville, TN 2009 46.7-90 ----- Powell, 2010 Salisbury, MD 2009 35-65 ----- Benner, 2010 Weslaco, TX 1991-93 ------ 17.2-18.4 Bennett & Annex, 2007 St. Gabriel, LA 1979 58-94 ----- Ricaud et al, 1980 Brazil: EMBRAPA 2008-2009 32-52 ----- Schaffert, 2010 India: Patancheru 2006 35-57 ----- Dar, 2006 Italy: Rutigliano, Bari 1990-1993 ----- 22-32 Mastrorilli et al., 1995 Spain Madrid 1991-1992 ----- 18-48 Curt et al., 1995 1
Energy Feedstock Yield Comparison
Crop Location Crop Yield
(Mg/ha)
BiofuelBiofuelYield(L/ha)
Maize U.S.A 9.4 Ethanol 3751
Sugarcane Brazil 73.5 Ethanol 5476
Sugar Beet
Global 46.0 Ethanol 5060
Cassava Global 12.0 Ethanol 2070
Soybean U.S.A. 2.7 Biodiesel 552
Palm Oil Indonesia 17.8 Biodiesel 4092
Starch, Sugar, and Oilseeds
*Source: FAO, The State of Food and Agriculture. Biofuels: Prospects Risks and Opportunities (2008)
Potential Ethanol Yield (gal/acre)
from Sweet Sorghum Juice
Biomass Yield
(t/acre)
Juice Sugar Content (%) 13 15
17
25 250 288 326
35 351 404 457
45 451 518 586
Assumes .55 juice expression ratio and 90% fermentation efficiency