Morey-Co-generation at Ethanol Plants 2-22-12 - For Your Information

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www.biomassCHPethanol.umn.edu

Co-generation Opportunities at Ethanol Plants

Vance [email protected]

ProfessorBioproducts and Biosystems Engineering

50th Annual Rural Energy ConferenceLa Crosse, Wisconsin

March 1, 2012


Project SupportXcel Energy Renewable Development Fund

University of MinnesotaInitiative for Renewable Energy and the Environment

Project CooperatorsAMEC E&C Services Inc.LLS Resources, LLC

DOE Feedstock Logistics Program


Biomass for Electricity and Process Heat at Ethanol Plants



Motivations for Using Biomass

• Reduce fossil energy inputs, i.e. improve energy balance

• Reduce natural gas costs

• Decrease net greenhouse gas emissions

• Generate renewable, dependable (base load) power that complements power from renewable sources that are variable such as wind and solar


Conventional Dry-grind Ethanol Process

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Energy Ratio: 1.7


Energy Ratio: 1.7


Combined Heat and Power (CHP) Concept

• Simultaneous production of two or more types of usable energy from a single energy source (also called “Cogeneration”)

• Use of waste heat from power generation equipment


Biomass Technology Options

• Process heat for the ethanol plant• Combined heat and power (CHP) – process

heat plus generate electricity with a back pressure turbine

• CHP plus grid – process heat plus generate electricity with an extraction turbine and condensing turbine

• Biomass integrated gasification combined cycle (BIGCC) – process heat plus generate electricity with gas turbine and steam turbine.


Biomass Sources• Ethanol coproducts

– DDGS – distillers dried grain with solubles

– “syrup” – solubles

• Corn stover

• Corn cobs


Biomass Fuel Properties

TypeHeating val.(dry),

Btu/lb

Ash

%

Nitrogen

%

Sulfur

%

Chlorine

%

DDGS 9350 4 4.8 0.8 0.2 - 0.3

Syrup* 8500 7 2.6 1.0 0.35

Corn stover 7700 6 - 8 0.7 0.04 0.1 - 0.2

Corn cobs 7900 1.5 0.4 0.04 0.1 - 0.2

Wood8400 -8900

0.5 - 1.5 <0.2 0.02 0.05

*Syrup moisture 67%; other fuels 10 - 15%

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Fluidized Bed Combustion

www.tekes.fi/opet/chp.htm

• Limestone bed material for reducing emissions

• Flexible for different types of fuels


Rentech-SilvaGas Process

• Steam blown gasifier, atmospheric pressure• Medium energy value synthesis gas• Char combusted in combustor• Gasifier heated by hot sand from combustor


Emissions Control• Dryer volatile organic compounds (VOC)

• Route dryer exhaust air through combustor

• Particulate matter• Cyclones• Baghouse

• Sulfur and chlorine emissions• Limestone sorbent bed material• Flue gas semi-dry scrubbing

• NOx emissions• Selective non-catalytic reduction (SNCR)


ASPEN Plus Modeling• Started with USDA model of a dry-grind fuel

ethanol plant• Used this model to understand the ethanol

process and its energy requirements• Added components to the model

– Biomass conversion (fluidized bed combustion or gasification)

– Electricity generation– Emissions control (NOx, SOx, Chlorine)– Modified drying system to use process steam (steam

tube dryer)


Steam Tube DryersUsed for drying co-products and biomass fuel

Davenport Dryer Co. http://bcgcommunications.com/


Electricity Generation – Steam Turbine

• Back-pressure Turbine• Constant steam pressure at outlet• Should use all outlet steam for process needs

• Extraction Turbine• Extract steam at constant pressure for process• Condense excess steam at low pressure

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Electricity Generation – Combined Cycle


Corn Stover Combustion: CHP + Grid


Integrated Gasification Combined Cycle


Heat and Power using Stover at a Corn Ethanol Plant

• 100 million gallons ethanol per year

• 800 to 1200 tons per day of stover– 32 to 48 truckloads (25 tons each) of

compacted bulk biomass per day or

– 1280 to 1920 bales (1250 lbs each) per day

• 120 truckloads of corn per day

• 40 truckloads of DDGS per day


Agricultural to Industrial System

Agricultural –One harvest per year

Industrial –Requires supply throughout the year


Agricultural vs Industrial

Agricultural Scale System – Biomass Source

(Harvest 4-6 weeks in fall)

Collection / Transport to Local Storage

Shredding and raking Baling (round bales) Bale storage near field Nutrient replacement

Industrial Scale System – Biomass User

(Supply throughout the year)

Processing (Bale to Bulk)/Truck Transport from Local Storage

Tub (coarse) grinding (portable unit)Roll-press compaction (portable unit)Truck transport in 25-ton loads to

users (15 lb/ft3 bulk density)

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Harvesting/Transport to Local Storage


Local Storage Cost and Storage Loss Assumptions

• Bales stored in rows end to end in a north-south orientation, 3 ft between rows of bales

• Storage cost – 33¢/ton based on $200/acre land rent

• Storage loss – 5% average assumed for all storage (1 to 11 months). Equivalent to assuming 5% more stover delivered to storage than is removed .


Tub-Grinding/Roll-Press CompactionFeed

Roll Roll

Compact


Transport from Local Storage to End User

• Bulk transport in 25-ton truck loads (15 lb/ft3)

• Average round trip distance equals 52 miles – average distance for a maximum radius of 30 miles with 1.3 winding factor

• $6.40/ton average transport cost


Total Cost

$74/ton of corn stover delivered (MC = 15% w.b.)


Life-Cycle Fossil Energy Consumption

1101 MJ/dry tonne (i.e., 7% of dry corn stover energy)

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Life-Cycle GHG Emission

134 kg of CO2e/dry tonne of corn stover(includes combustion emission, but not SOC)


Life-Cycle GHG Emission

8 g of CO2e/MJ of dry corn stover(includes combustion emission, but not SOC)


System Comparisons

• CHP, CHP + Grid, and BIGCC with corn stover and syrup and corn stover as biomass fuels

• Life-cycle GHG analysis for fuel ethanol based on Liska et al. (2009), Plevin (2009), and GREET (2009)

• Life-cycle GHG analysis excludes indirect land use change effects


Power and Efficiency*

SystemFuelInput MWth

PowerTotal (Grid),

MWe

Power Gen. Eff. %

System Therm. Eff.,

%

CHP+G Corn Stover

208 34.8 (21.4) 16.7 63.6

BIGCC Corn Stover

220 67.4 (49.2) 30.6 72.6

NGCC 220 70.4 (60.6) 32.0 77.7

*100 million gallon/yr plant


Conventional Ethanol Plant

U.S. Midwest average corn ethanol (Liska et al., 2009; Plevin, 2009)

-20

0

20

40

60

80

100

Input Output Net Gasoline

g C

O2e/

MJ

Gasoline

Ethanol Net

Coproduct Credit

Biorefinery Other

Denaturant 2%Vol.Fossil Electricity

Natural Gas

Corn Production

Conventional Plant Gasoline


CHP and BIGCC Stover

-80

-60

-40

-20

0

20

40

60

80

100

Input Output Net Input Output Net Gasoline

g C

O2e

/MJ

Gasoline

Ethanol Net

Renewable Elec.Credit

Coproduct Credit

Stover Fuel

Biorefinery Other

Denaturant 2% Vol.

Corn Production

CHP BIGCC Gasoline

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38.9%

91.8%

124.1%

93.4%

0%

20%

40%

60%

80%

100%

120%

140%

Natural GasPlant (Liska)

CHP+GridCorn Stover

BIGCC CornStover

NGCC NaturalGas

GH

G R

edu

ctio

n (

%)

BIGCC & NGCC vs GHG Reduction


Business Model

Power Island• Produce electricity and steam• Sell electricity and steam toethanol plant

• Sell electricity to grid• Purchase fuel – corn stover, syrup from ethanol plant, or natural gas

Ethanol Plant• Buy electricity and steam frompower island

• Possibly sell syrup coproductto power island

• Sell ethanol • Sell distillers grains• Send VOCs to Power Island

www.biomassCHPethanol.umn.edu www.biomassCHPethanol.umn.edu

Capital Costs – 100 MM Gal/Yr PlantEstimated by AMEC E&C Services Inc.

$0

$50,000,000

$100,000,000

$150,000,000

$200,000,000

$250,000,000

Conventional CHP+Grid CornStover

BIGCC CornStover

NGCC NaturalGas

Cap

ital Cost ($)

Power Island

Ethanol Plant


Economic Analysis – Assumptions

• Natural gas – $7/million Btu

• Electricity purchase price – 7¢/kWh

• Electricity sale price – 10¢kWh

• Ethanol – $2.08/gal

• Corn – $4.33/bushel

• DDGS – $141/ton

• Corn stover – $77/ton

• Steam -- $10.66 per 1000lbs


Return on Equity – 100 MM Gal/Yr Plant

0%

5%

10%

15%

20%

25%

Conventional CHP+Grid CornStover

BIGCC CornStover

NGCC NaturalGas

Return on Equity (%

)

Power Island

Ethanol Plant

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Economic Conclusions• Natural gas price is key for attractiveness of

biomass for both ethanol plant and power island

• Biomass becomes attractive for both ethanol plant and power island when natural gas price is greater than about $10/million Btu

• Energy policy which favors low carbon liquid fuels and low carbon electricity is important for both ethanol plant and power island

• Natural gas combined cycle (NGCC) may be an attractive interim option with low NG prices


Electric Power Production Potential in Minnesota

• Approximately 1 billion gallons of annual corn ethanol production capacity

• 500 MW could be produced and sent to grid if biomass power generation were fully implemented at these plants

• Renewable, dependable (base load) power that complements power from renewable sources that are variable such as wind and solar


Questions?

Vance [email protected]

Morey-Co-generation at Ethanol Plants 2-22-12 - For Your Information

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