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Techno-economic analysis of using corn stover to supply heatand power to a corn ethanol plant – Part 1: Cost of feedstocksupply logistics

S. Sokhansanj a, S. Mani b,*, S. Tagore c, A.F. Turhollow a

a Environmental Sciences Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831, USAb Biological and Agricultural Engineering, Driftmier Engineering Center, University of Georgia, Athens, GA 30602, USAc Office of Biomass Program, US Department of Energy, Washington, DC 20585, USA

a r t i c l e i n f o

Article history:

Received 31 August 2009

Received in revised form

29 September 2009

Accepted 6 October 2009

Available online xxx

Keywords:

IBSAL model

Corn stover

Collection cost

Pelleting cost

Transportation cost

Fuel preparation cost

* Corresponding author. Tel.: þ1 706 542 235E-mail address: smani@engr.uga.edu (S.

0961-9534/$ – see front matter ª 2009 Elsevidoi:10.1016/j.biombioe.2009.10.001

Please cite this article in press as: Sokhanto a corn ethanol plant – Part 1: Cj.biombioe.2009.10.001

a b s t r a c t

Supply of corn stover to produce heat and power for a typical 170 dam3 dry mill ethanol

plant is proposed. The corn ethanol plant requires 5.6 MW of electricity and 52.3 MW of

process heat, which creates the annual stover demand of as much as 140 Gg. The corn

stover supply system consists of collection, pre-processing, transportation and on-site fuel

storage and preparation to produce heat and power for the ethanol plant. Economics of the

entire supply system was conducted using the Integrated Biomass Supply Analysis and

Logistics (IBSAL) simulation model. Corn stover was delivered in three formats (square

bales, dry chops and pellets) to the combined heat and power plant. Delivered cost of

biomass ready to be burned was calculated at 73 $ Mg�1 for bales, 86 $ Mg�1 for pellets and

84 $ Mg�1 for field chopped biomass. Among the three formats of stover supply systems,

delivered cost of pelleted biomass was the highest due to high pelleting cost. Bulk transport

of biomass in the form of chops and pellets can provide a promising future biomass supply

logistic system in the US, if the costs of pelleting and transport are minimized.

ª 2009 Elsevier Ltd. All rights reserved.

1. Introduction 75 hm3 from corn grain. Therefore, it is important to develop

Ethanol plants in the US use corn grain as the feedstock for

producing nearly 18 hm3 of ethanol [1]. Most of the ethanol

produced is blended with gasoline. The ethanol represents

roughly 1.5% of the current annual volume of petroleum

consumption of 1.15 km3 [2]. National plans call for increasing

ethanol production to levels that would offset at least 30% of

the annual transportation fuel volume within the next 20–

30 years. It is forecasted that the current and projected

increase in corn grain may support starch-based ethanol

production up to 75 hm3 of ethanol. Lignocellulosic biomass

feedstock can further support ethanol production beyond the

8; fax: þ1 706 542 8806.Mani).er Ltd. All rights reserved

sanj S et al., Techno-ecoost of feedstock supp

secure sources of biomass and supply infrastructure to

support the projected growth of bioenergy.

A typical ethanol plant requires 9.67 MJ of process heat and

0.288 kWh of electricity to produce 1 l of ethanol. Most of the

existing ethanol plants in the US use natural gas as the source

of process heat and electricity from the electric grid [1,2].

Prices for natural gas and electricity have increased in recent

years making ethanol production economics less attractive.

To offset this issue, some plants have or are planning to use

coal [3] and that has created a negative impact on public

acceptance of ethanol as a ‘‘green or clean fuel’’. The tech-

nology of producing process heat and electricity from direct

.

nomic analysis of using corn stover to supply heat and powerly logistics, Biomass and Bioenergy (2009), doi:10.1016/

b i o m a s s a n d b i o e n e r g y x x x ( 2 0 0 9 ) 1 – 72

ARTICLE IN PRESS

combustion of biomass is now well developed [4,5]. Biomass

can provide heat and power to the existing and future starch-

based ethanol plants.

Table 1 lists the current and an estimated future number of

ethanol plants in the US [1]. The list includes an estimate of

the required grain (corn) as feedstock and the amount of

process heat and electrical energy required to keep the plants

running. An estimate of the required grain and stover and the

amount of co-product, distillers dried grain (DDG) is also

presented in Table 1. The last two rows are an estimate of net

energy input to the plants for process heat and electricity.

Assuming that 287 plants become operational in the next 5–

7 years, there will be a production of roughly 48 hm3 of

ethanol from corn. Roughly 48 Tg of biomass is required to

heat and power these plants if all these plants use biomass as

a fuel source.

Typical energy balance studies of corn ethanol show that

the energy balance (defined in terms of renewable energy in

the ethanol product over all non-renewable energy inputs

from seed to product) ranges from 1.1 to 1.3 [4–7]. There are

high energy demands in the provision of fertilizer and crop

management as well as in the demand for heat and electricity

in the process plant. Improvements in process plant effi-

ciency, and the use of renewable energy inputs for electricity

and heat could make the overall renewable energy balance>2.

Morey et al. [4] proposed the use of DDG or corn stover for

heat and electricity generation for the ethanol plants and

found that there was a significant annual energy cost savings

for the 170 dam3 ethanol plant. Use of DDG for power and heat

generation may not be the best option due to its high nutri-

tional value as a choice source of protein and fiber for animal

feed (>80 $ Mg�1). In order to compare and make corn stover

competitive to the existing heating fuels, a techno-economic

analysis of using biomass to supply heat and power systems

should be investigated. Any biomass-based heat and power

Table 1 – Overall ethanol production statistics in the US for the cethanol plants [1,4].

Description Unit For a typical plant No. of

Number of plants – 1

Volume of ethanol hm3 0.169

Mass of grain

as feedstocka

Tg 0.411

Mass of DDG co-product producedb Tg 0.129

Process heat

inputc

PJ 1.632

Electricity energy

inputd

PJ 0.175

Gross energy

requiremente

PJ 2.759

Natural gasf km3 0.073

Biomassg Tg 0.167

a A conversion efficiency of 0.41 l of ethanol per kg of corn [4].

b 0.313 kg of DDG per kg of corn processed.

c 9.67 MJ of process heat per liter of ethanol.

d 0.288 kWh of electricity per liter of ethanol.

e Conversion efficiency of combustion to heat as 80% and conversion ef

f Conversion factor of 38 MJ m�3 for natural gas.

g Conversion factor of 16.5 GJ Mg�1 for stover.

Please cite this article in press as: Sokhansanj S et al., Techno-ecoto a corn ethanol plant – Part 1: Cost of feedstock suppj.biombioe.2009.10.001

production system relies mainly on the continuous and cheap

supply of biomass delivered to the plant. Our main objectives

of this paper were to estimate the cost of supplying corn

stover to the existing dry mill ethanol plants using the Inte-

grated Biomass Supply Analysis and Logistics (IBSAL) model to

produce heat and/or power and to calculate the cost of on-site

fuel preparation for delivering it to the burner.

2. Description of IBSAL model

The Integrated Biomass Supply Analysis and Logistics (IBSAL)

is a dynamic simulation model developed by Oak Ridge

National Laboratory (ORNL) to estimate the delivered biomass

cost, energy input and carbon emissions for various logistic

options [8]. IBSAL consists of different sub-modules for har-

vesting, processing, pre-processing (grinding, pelleting),

storage and transportation. Model input data include: local

weather data; average net yield of biomass; crop harvest

progress data (including start and end dates of harvest); dry

matter loss with time in storage; moisture content of plant at

the time of harvest; operating parameters of equipment; and

cost of machinery in dollars per hour. The model was built on

the EXTENDSIM� platform [9]. Main outputs of the model

include: delivered cost of biomass ($ Mg�1); carbon emission

(kg Mg�1) and energy consumption (GJ Mg�1). IBSAL also

calculates dry matter losses of biomass using the limited data

available for storing biomass bales and handling hay.

Complete information about the model can be found in

Sokhansanj et al. [10] and Sokhansanj and Mani [11].

The choices of particular size and operating conditions are

based on three objectives: (1) the latest model of equipment

that is commercially available for harvest, (2) the typical

operational performance data that are available in the ASAE

D497 standard [12] or from manufacturer’s literature, and

urrent, under construction, and planned corn starch-based

current plants Under construction In planning stage Total

97 40 150 287

16.4 6.8 25.3 48.4

39.9 16.5 61.7 118.1

12.5 5.2 19.3 37.0

158.3 65.3 244.8 468.3

17.0 7.0 26.2 50.2

267.6 110.4 413.8 791.8

7.1 2.9 11.0 20.8

16.2 6.7 25.1 48.0

ficiency to electricity as 30%.

nomic analysis of using corn stover to supply heat and powerly logistics, Biomass and Bioenergy (2009), doi:10.1016/

Combine grain Store on farm

Square Bale

Pellets

Corn crop

Corn crop

Grain Elevator

Store

Dry Chop

Integrated Combined Heat and

Power (CHP) & Ethanol

Plant

Corn grain

Corn stover

Fig. 1 – The co-flow paths for corn grain and stover to an

ethanol plant.

b i o m a s s a n d b i o e n e r g y x x x ( 2 0 0 9 ) 1 – 7 3

ARTICLE IN PRESS

(3) limited equipment performance data published for corn

stover elsewhere. Hourly costs are calculated using the

procedure and data described in Sokhansanj and Turhollow

[13]. The rates represent the sum of fixed and variable costs.

The hourly rates for the pull-type equipment (for example,

baler) are the sum of the hourly rate for the implement and the

power equipment (for example, tractor).

3. Economics of corn stover supply to theethanol plant

Almost all of the present ethanol plants in the US use corn

grain as a source of feedstock. The concept is to integrate the

harvest and supply of corn stover with the well-developed

grain harvest and delivery system as outlined in Fig. 1. The

grain is combined and stored on the farm or sent directly to

a central depot (country elevator). The grain is transported to

the ethanol plant either directly from the farm store or from

the depot. Similar to grain that is combined and stored in the

steel bins, corn stover is baled and stacked on the farm or

transported to a larger storage area (depot). The supply of

biomass to the ethanol plant will be in one of the three forms:

(1) baled, (2) chopped/ground, or (3) pelletized. We assume

a 170 dam3 ethanol plant for the analysis. The power rating of

the plant is estimated to be 5.6 MW of power and 52.3 MW of

process heat. The ethanol plant requires as much as 140 Gg of

stover annually. All the cost data in the paper are reported

based in year 2006 US dollars.

Stacking/storage DestringingBale

retrieving

Dry chop storage

Chopretrievin

Pellet storage

Pellet retrievin

Biomass receiving station

Square bales

Dry chop

Pellets

Fig. 2 – On-site biomass storage and fu

Please cite this article in press as: Sokhansanj S et al., Techno-ecoto a corn ethanol plant – Part 1: Cost of feedstock suppj.biombioe.2009.10.001

3.1. Stover collection

We define collection as operations for picking up the biomass,

packaging, and transporting to a nearby site for temporary

storage. The most conventional method for collecting biomass

is baling [14]. Bales are in the form of either rounds or squares.

Limited experience with using round bales for biomass

applications indicates that round bales are not suitable for

large scale biomass handling [15,16]. Because of their round

shape, round bales tend to deform under static loads in

a stack. Bales that are not perfectly round cannot be loaded

onto trucks to form a transportable load over open roads.

Therefore, square baling operation was considered in this

study. The Integrated Biomass Supply Analysis and Logistics

(IBSAL) model [8,11] was used to estimate the resource

requirement and cost of biomass collection. We used a net

stover yield of 5.7 Mg ha�1, a typical stover current yield in the

US Midwest [13,17]. The collection sequence consists of

shredding and baling it into large rectangular bales

1.2 � 1.2 � 2.4 m. The bales are collected using a truck

mounted bale collector [18]. The Stinger transports the

collected biomass to the side of the farm and stacks it in rows

four bales high (4.8 m high).

3.2. Pre-processing

Pre-processing of biomass may consist only of grinding. Loose

cut biomass has a low bulk density ranging from 50 to 120 kg

m�3 depending on the particle size. The ground biomass of

less than 6 mm could have a bulk density of 160 kg m�3 in the

truck box [17,19]. This density may be suitable for short hauls.

To process biomass bales into chopped form, a mobile

shredder/grinder is used to chop the biomass. The machine is

similar to an agricultural tub grinder and can be transported to

the stacks. A bale is placed on the grinder/shredder; the

ground biomass is then transferred to a weighing truck box

using an attached belt conveyor. The cost of the biomass

chopping process was estimated using the IBSAL simulation

model.

For longer hauls and long term storage, denser biomass in

the form of pellets or cubes may be desired. The bulk density

of pellets can be as high as 700 kg m�3 and cubes as high as

500 kg m�3[20]. To make pellets, the baled biomass is chopped

using a tub grinder, fine ground using a hammer mill, and

extruded using a pellet mill. The pellets are cooled and stored.

The pellets will have a bulk density of 600–700 kg m�3. Corn

Debaling/chopping

g

Fine grinding

Pneumatic conveying

g

Combined Heat &

Power Plant

el preparation for use in the boiler.

nomic analysis of using corn stover to supply heat and powerly logistics, Biomass and Bioenergy (2009), doi:10.1016/

Table 2 – Completion date, cost, energy input, emissions and dry matter for a conventional baling system for corn stover ata yield of 5.7 Mg haL1.

Operationa Date completedb Mass (Mg) Cost ($ Mg�1) Energy input(MJ Mg�1)

Carbon emission(kg Mg�1)

Payment to producer 10.00

Shredding Dec 10 141550 4.11 47.4 1.0

Balingc Dec 13 140359 12.36 136.9 2.9

Stacking Dec 16 139819 7.89 123.5 2.7

Profit (15% of the collection costs) 3.65

Overall 38.01 313.7 6.7

a No. of equipment: combines, 48; grain trucks, 16; shredders, 22; balers, 36; stackers, 6.

b Start of harvest is September 15.

c Large rectangular baler

b i o m a s s a n d b i o e n e r g y x x x ( 2 0 0 9 ) 1 – 74

ARTICLE IN PRESS

stover can be easily compacted into pellets for easy transport

and storage [21,22]. Economics and energy input to the pel-

leting operation were obtained from Mani et al. [23].

3.3. Stover transport

Stover in the form of bales, chops and pellets are usually

transported by trucks. Bales are transported using flatbed

trucks. The ground (chopped) and pelletized biomass is

transported using truck boxes. In our analysis, the biomass is

loaded onto trucks and transported to an integrated combined

heat and power (CHP) and ethanol plant daily throughout the

year. For bale transport, bales are stacked on a flatbed trailer

to the maximum height of 4 m (above ground). Roughly 36

rectangular bales (1.2 � 1.2 � 2.4 m) are placed on a 14.6 m

long flat bed. Larger trailers with more axles are available

when allowed by local transport regulations. For bale loading

and unloading, loaders equipped with bale grabbers were

used. The bale grabbers remove one or two bales from the

stack at a time and place them on the deck of the trailer. A full

bale load weighs roughly 18 Mg assuming 0.5 Mg per bale on

dry basis (0% moisture content).

The truck box is 2.4 m wide � 2.4 m high � 12.6 m long

with a capacity of roughly 70 m3. Tests with grinders have

shown that grinding biomass to a size less than 5 mm can

result in a bulk density of about 160 kg m�3[21]. This will yield

a load of roughly 11 Mg per truck box. The pellets can be

Table 3 – Cost and energy analyses of biomass pelletingprocess [23].

Processes Cost ($ Mg�1) Energy (GJ Mg�1)

Bale tub grindinga 5.72 0.15

Hammer mill 0.95 0.59

Pellet mill 3.31 0.31

Pellet cooler 0.34 0.46

Screens 0.16 0.07

Miscellaneous equipment 2.77 0.08

Labor 12.74 0.18

Land and building use 0.26

Sub-total 26.25 1.84

Total (plus 15% profit) 30.19

a Data obtained from Wright et al. [19].

Please cite this article in press as: Sokhansanj S et al., Techno-ecoto a corn ethanol plant – Part 1: Cost of feedstock suppj.biombioe.2009.10.001

loaded onto truck boxes and transported to the ethanol plant.

We assume a bulk density of 560 kg m�3 for pelletized or

cubed stover. A 70 m3 truck box can hold roughly 40 Mg. This

is an efficient way of moving biomass assuming that carrying

heavy loads is permitted on the local roads.

3.4. On-site storage and fuel preparation

For storage, a covered building with a flat floor for bales and

chops is considered. For pellets, we specify steel bins with

a flat floor. The area footprint for three forms of biomass was

2780 m2 for bales, 3870 m2 for ground stover and 348 m2 for

pelletized biomass. The difference in areas was due to bulk

density and the area allowed for movement of handling

equipment. The storage building costs were estimated at 107 $

m�2, 161 $ m�2 and 215 $ m�2, for storing bales, ground

(chops) and pellets. The storage building for chopped biomass

was more than that for bales because retaining walls are

needed to hold the pile of biomass. The most expensive

storage is steel bins with filling and emptying auxiliaries and

aeration equipment.

Solid fuels require on-site preparation to be used in the

boiler. The combustion system for this project will accom-

modate pulverized biomass/solid fuels. Corn stover delivered

to the ethanol plant will be in one of three forms: square bales,

ground chops, or pellets. The aforementioned three forms of

biomass can be easily handled in the existing grain handling

facilities with necessary modifications or additional process-

ing/handling equipment. Ground biomass and square bales

may be stored under cover or in the open sheds. Each of the

biomass formats (Fig. 2) requires different pre-treatment

before it can be fed to the burner. Square bales require de-

stringing, de-baling (primary shredding), fine grinding

(hammer milling) and are then conveyed by a pneumatic

Table 4 – The cost of transporting biomass in three forms.

Mg load�1 No. oftruckloads

Loadsh�1

No. oftrucks

Total($ h�1)

Cost($ Mg�1)

Bales 18 9722 1.16 3.24 249.54 9.98

Chop 11 15909 1.89 5.30 408.33 16.33

Pellet 40 4375 0.52 1.46 112.29 4.49

nomic analysis of using corn stover to supply heat and powerly logistics, Biomass and Bioenergy (2009), doi:10.1016/

Table 5 – Estimated cost of receiving, storing, and preparing biomass for boiler use.

Operations Baled stover Chopped stover Pelletized stover

Explanation Cost ($ Mg�1) Explanation Cost ($ Mg�1) Explanation Cost ($ Mg�1)

Receiving Unload and

stack bales

2.22 Front-end

loader and piler

1.10 Dump in pit, elevatea 0.00

Storing Enclosed, free

standing, stacked

bales

4.77 Enclosed

reinforced

bearing walls

for piled stover

6.62 Steel bin with

overhead distribution

1.27

Reclaiming

biomass

Stacker, belt conveyor,

de-stringer, de-baler

4.34 Front-end loader,

conveyor

1.40 Bin unloader 1.40

Fine grinding Hammer mill 5.41 Hammer mill 5.41 Hammer mill 5.41

Delivery Pneumatic airlock,

blower

2.21 Pneumatic, airlock,

blower

2.21 Pneumatic, airlock,

blower

2.21

Total

(þ30% overhead)

24.64 21.76 13.38

a Use the existing grain pit and elevator.

b i o m a s s a n d b i o e n e r g y x x x ( 2 0 0 9 ) 1 – 7 5

ARTICLE IN PRESS

feeding system to the boiler. To manage dust during fine

grinding, the ground biomass will be collected in the cyclone

system. Dry chops and pelletized biomass require only

a single stage grinding. Ground biomass may not require re-

grinding. A similar type of fuel preparation system is currently

used in the Chariton Valley power generation system [24,25].

4. Results and discussions

4.1. Cost of biomass collection

Table 2 summarizes IBSAL’s output for collection operations

including size, production rate, and number of equipment to

make it possible to complete each operation at a specific date.

Collection operation requires 20 shredders, 36 balers, and six

bale stackers to complete the collection operations for an

ethanol plant. The output includes completion dates for each

operation. For corn stover, the net amount collected was

1.399 Tg at 38 $ Mg�1 delivered cost using the IBSAL model.

The cost includes $10 payment to the producer and 15% of

total collection costs as profit assuming the work is done by

a custom operator. Table 2 lists the amount of energy input to

Table 6 – Total delivered cost for different form of biomassup to the biomass burner.

Bale($ Mg�1)

Chop($ Mg�1)

Pellet($ Mg�1)

Collection 38.01 38.01 38.01

Pre-process 0.00 8.21 30.19

Transport 9.98 16.33 4.49

Total delivered

cost to the plant

48.35 62.91 72.69

On-site fuel preparation 24.64 21.76 13.80

Total cost 72.63 84.31 86.49

Total cost

($ GJ�1)a4.40 5.12 5.24

a Total delivered cost in $ GJ�1 was calculated by assuming the

heating value of biomass as 16.5 GJ Mg�1.

Please cite this article in press as: Sokhansanj S et al., Techno-ecoto a corn ethanol plant – Part 1: Cost of feedstock suppj.biombioe.2009.10.001

the power equipment due to diesel fuel consumption. All the

mass units are reported throughout on a dry basis (0% mois-

ture content). The input energy required to collect corn stover

is 313.7 MJ Mg�1. To put this energy use in perspective, the

amount of energy in a dry Mg of stover is roughly 17 GJ. The

amount of energy used to power equipment is roughly 2% of

the energy content of biomass. Table 2 also lists the amount of

carbon emission as a result of burning diesel fuels in the

collection machinery.

4.2. Pre-processing cost

The costs for chopping involve a loader with an operator

(1.42 $ Mg�1), and an industrial grinder (5.72 $ Mg�1), for

a total of 7.14 $ Mg�1. We increased the cost by 15% to account

for profit (return on investment) to 8.21 $ Mg�1. Table 3 shows

the breakdown of cost and energy demand for the biomass

pelleting process. The pelleting plant has a production

capacity of 6 Mg h�1 with annual production of 45 Gg [23].

Roughly three pellet mills are needed to process the entire

biomass for the ethanol plant. The pellet plant operates 24 h

for 310 days annually (annual utilization period 85%). The dry

biomass is used as a feedstock for the pellet plant and that

eliminates the drying operation. Total cost of pelleting was

about 30.19 $ Mg�1 of pellets with an energy requirement of

1.84 GJ Mg�1. About 11% of the biomass energy is used to

produce pellets. Cost of pelleting biomass can be further

reduced if a larger capacity pellet plant (12–15 Mg h�1) is

considered [23].

4.3. Transport cost

Transport cost of biomass is one of the major cost compo-

nents in the entire supply system. Biomass transport cost

varies with form of biomass and distances to be transported.

Table 4 summarizes calculations for the cost of transporting

biomass. The table lists Mg per load, total number of truck

loads to transport 140 Gg year�1 and the number of required

loads per hour. Then, the number of truckloads required for

a given average speed of 50 km h�1 and 140 km distance

traveled (70 km each way) is calculated. The total $ h�1 is the

nomic analysis of using corn stover to supply heat and powerly logistics, Biomass and Bioenergy (2009), doi:10.1016/

b i o m a s s a n d b i o e n e r g y x x x ( 2 0 0 9 ) 1 – 76

ARTICLE IN PRESS

product of the number of trucks required by the cost of one

truck load (at 77 $ h�1). Total $ h�1 divided by 25 Mg h�1 gives

the $ Mg�1 that is $10 for transporting bales, $16 for trans-

porting ground biomass and $4.5 for transporting pellets.

4.4. On-site fuel storage and preparation

Table 5 itemizes the costs of receiving, storing, reclaiming and

final fine grinding of biomass for immediate delivery to the

boiler room. Bales are received at the ethanol plant and will be

stacked under a roof. Chopped (shredded) biomass is received

in silage type truck boxes. The load is dumped on a concrete

floor and piled using a front-end loader. The existing grain pit

and grain elevator legs at the ethanol plant can serve to

unload and distribute pellets to the bin. We assumed 1.5 Gg

storage of biomass will be adequate for 3 days of operation at

500 Mg day�1.

The cost of reclaiming bales is higher than those for chops

and pellets because each bale has to be placed individually on

a conveyor belt. The strings are cut and removed automati-

cally as the bales advance towards a primary shredder

(debaler). These processes are not necessary for the shredded

or pelletized feedstock. The shredded feedstock or pellets are

ground into fine particles in a hammer mill. Table 5 also

estimates the cost of pneumatic conveying of ground biomass

to the burner at 2 $ Mg�1. An overhead of 30% is added to the

costs for contingency, and any extra labor requirement.

4.5. The total cost of biomass fuel delivered to the burner

Table 6 summarizes the total delivered cost of different

biomass formats to the burner. Pelleted biomass has the

highest delivery cost of 86 $ Mg�1 mostly because of the high

cost of making pellets from bales. Next is the delivered cost of

chopped biomass at 84 $ Mg�1. The square bale format has the

lowest delivered cost of 73 $ Mg�1. The delivered cost of

switchgrass in the form of bales was about 81 $ Mg�1 for 10 Mg

ha�1 biomass yield [26]. Biomass can be supplied to produce

heat and power to the ethanol plant at a price lower than the

cost of DDG (100 $ Mg�1) currently sold in the market [4].

A cost difference of 10–20 $ Mg�1 of feedstock would make

a considerable difference in the annual energy saving for the

ethanol plant. Overall, for the scenarios and the distance of

70 km transport, pellets are the most expensive form of

biomass delivered to the burner, followed by chops and

square bales. For corn stover, opportunity still exists for

reducing the delivered cost of stover through single pass

harvesting, compressed bulk transport and granulation of

biomass.

5. Concluding remarks

A systematic cost analysis of corn stover collection, pre-pro-

cessing and transport operations combined estimated as 48,

63 and 73 $ Mg�1 for baled, chopped and pelleted biomass

respectively. An additional 25 $ Mg�1 is required to prepare

baled biomass to make it suitable for a combustion process.

Pelleted biomass has the least fuel preparation cost of 14 $

Mg�1, due to its low on-site storage cost. Collection cost of

Please cite this article in press as: Sokhansanj S et al., Techno-ecoto a corn ethanol plant – Part 1: Cost of feedstock suppj.biombioe.2009.10.001

biomass (38 $ Mg�1) was the largest cost factor in the entire

supply system, which can be further reduced if a whole crop

harvesting system is developed and used. Research work has

already been initiated to estimate the stover collection cost

using a whole crop harvesting system. Transport cost of

chopped biomass was the highest due to low bulk density.

Compaction of chopped biomass in the truck to increase bulk

density may reduce the transport cost further by increasing

the payload per truck. Although the transport cost of pelleted

biomass is less, the pellet production cost is a technical

barrier. Granulation of biomass to increase bulk density may

reduce the cost of pre-processing. Granulation is a process of

increasing the size and bulk density of biomass particles using

limited shear forces and liquid binders. Biomass granulation

will also reduce the on-site fuel preparation cost, as granules

do not require fine grinding and an expensive pneumatic

handling system. Apart from the high cost of compacting

biomass into pellets (30 $ Mg�1), pellets can be easily stored

for long periods, similar to grains, and become an attractive

form of fuel for domestic and central heating applications.

Further reduction in biomass delivered cost is possible if more

efficient collection and transport systems are developed. We

envision that creating demand for biomass will build infra-

structure for biomass fuels, which may further reduce the cost

of biomass. Successful use of biomass in Europe is mainly

because of well established infrastructures to collect, trans-

port and store biomass fuels. For example in Holland,

Denmark and Sweden, the use of waterways to transport bulk

biomass has considerably reduced the cost of biomass

transport.

Acknowledgement

The authors acknowledge Oak Ridge National Laboratory

(ORNL) and Office of Biomass Program, US Department of

Energy (DOE), for providing funding to conduct this research.

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