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 Location1Dry Yield(Mg/ha)

2 EthanolYield(L/ha)

Corn Stover U.S.A 12 3516Switchgrass 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 7618Sweet 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 Biomass

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

Milling Diffusion

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

Max

imum

The

oret

ical

Yie

ld (%

MTY

)

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

imum

The

oret

ical

Yie

ld (%

MTY

)

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

Max

imum

The

oret

ical

Yie

ld (%

MTY

)

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 3751Sugarcane Brazil 73.5 Ethanol 5476

Sugar Beet

Global 46.0 Ethanol 5060

Cassava Global 12.0 Ethanol 2070Soybean U.S.A. 2.7 Biodiesel 552Palm 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 JuiceBiomass

Yield (t/acre)

Juice Sugar Content (%) 13 15

1725 250 288 32635 351 404 45745 451 518 586

Assumes .55 juice expression ratio and 90% fermentation efficiency