Full-paper template – The International Symposium on Agricultural and Biosystem Engineering (ISABE) 2013
Potential production of agricultural byproducts and the economic
feasibility of rice straw as a feedstock for bioethanol in Korea
Yeonghwan Bae1 Kidong Park1 and Keum Joo Park1
1
Department of Industrial Machinery Engineering, Sunchon National University,
Suncheon 540-950 Korea, E-mail: yhbae@sunchon.ac.kr
Abstract
The interest in producing bioethanol from agricultural byproducts has grown due to
the rise of oil prices and the depletion of natural resources. This research was performed as an
effort to figure out the availability and feasibility of bioethanol production from agricultural
byproducts in Korea. According to government statistics, rice straw was the most prevailing
agricultural byproduct with an annual production of approximately 5.5 million tonnes (t).
Most of rice straw was collected, baled, and lapped in cylindrical bales weighing around 300
kg (50% w.b.) each. To allocate potential bioenergy facilities and to analyze transportation
cost, Goheung-gun County in Geollanam-do Province was selected as a study area. By using
Geographic Information System (GIS) tools, rice-growing fields were extracted from digital
maps, and the transportation cost to each potential bioenergy plant site was estimated by
using a digital road network map. Optimum locations of potential bioenergy facilities with a
capacity of 20,000 tonnes of dry rice straw annually were determined based on the marginal
costs of transportation. The analysis showed an average delivered feedstock cost of 220,526
Korean won per dry tonne.
Keywords: rice straw, bioethanol, logistics, delivered cost, transportation cost
Introduction
Increase in greenhouse gas emissions and high fuel prices have brought interests in
the use of biofuels including bioethanol and biodiesel. Bioethanol is produced by
fermentation, mostly from starchy or sugar crops such as corn or sugarcane. Biodiesel is
produced from vegetable oils and animal fats. Both bioethanol and biodiesel can be used as a
fuel for vehicles in their pure forms or as fuel additives. Bioethanol produced from grains has
a drawback of raising world food prices. Therefore, recent interests are focused on
transforming cheap raw materials like corn stover, wheat straw, rice straw, switchgrass, wood
chips and sugarcane bagasse into fuel (Sreeharsha, 2013).
To convert agricultural byproducts such as rice straw or corn stover into cellulosic
ethanol, the feedstock has to be collected in the field, densified, and transported to a
bioenergy facility. The economic feasibility of such factory would depend on the year-round
availability and cost of feedstock. In the United States of America production of agricultural
byproducts amounted to 194 Mt (dry weight) annually and corn stover alone comprised 75
Mt (Kim and Gorman, 2007). A case study of rice straw production in Sacramento Valley,
USA illustrated that 550 dry t/day of straw can be accessed at an estimated net delivered cost
of about US$20/t (Kadam et al., 2000). A study on corn stover estimated a marginal
feedstock cost of US$60/t for a facility producing 0.189 hm3/yr of ethanol where the stover to
ethanol conversion rate was assumed to be 0.292 m3/t (Petrolia, 2008). Another study on
switchgrass in USA indicated delivered feedstock costs ranging from US$33 to US$55 per
dry tonne to supply a facility requiring 0.1 Mt a year (Graham et al., 2000).
Full-paper template – The International Symposium on Agricultural and Biosystem Engineering (ISABE) 2013
GIS technologies have been utilized by many researchers to identify potential
locations for collection and storage of biomass feedstock. Haddad and Anderson (2008)
developed spatial location models to identify potential collection sites for corn stover along
an existing railroad in Midwestern region of USA. Perpiñá et al. (2009) developed a GISbased methodology which provided information on the spatial distribution of biomass
residues and mapped potential sites for bioenergy plants by evaluating the time, distance, and
transport costs involved in the road transportation of biomass.
The objectives of this study were to investigate the annual production of agricultural
byproducts and its potential for bioethanol, to estimate the cost of collecting rice straw as a
feedstock for biofuel, and to determine locations of potential bioethanol facilities by
analyzing transportation costs.
Yield estimates of agricultural byproducts in Korea and the potential of
bioethanol production
The data on crop coverage and the yield of principal products for some major crops
cultivated in Korea were obtained through the homepage of Statistics Korea. The amount of
byproducts for the crops was estimated by applying residue coefficients published by the
Rural Development Administration, Korea. Table 1 lists the acreage and estimated amount of
byproducts for several staple crops. Rice straw was the top agricultural byproduct yielding
5.5 Mt/yr, followed by rice husk and the residues of red pepper.
Table 1. Estimated production of agricultural byproducts in Korea (year 2009)
Rice
917,990
4,898,725
Barley
23,447
71,662
Corn
15,326
76,975
Soybean
70,265
139,251
Potato
21,396
590,375
Byproduct
Ratio (%)
Amount (t)
112.7 (straw)
5,518,552
42.2 (husk)
2,067,262
9.8 (bran)
480,075
119.7 (straw)
85,779
31.7 (bran)
22,717
164.1 (stalk)
126,316
118.9 (stalk)
165,569
50.4 (hull)
70,183
80
472,300
Red pepper
50,521
350,436
217.9
Crop
Acreage (ha)
Amount of principal
product (t)
763,600
A chemical analysis showed that cellulose accounts for 36.4% of rice straw by weight.
By applying maximum saccharification efficiency of 0.90, theoretical ethanol yield from
reducing sugar of 0.511, and maximum fermentation efficiency of 0.81 (Bae et al., 2010), the
total amount of annual rice-straw production can be converted to 0.746 Mt/yr of cellulosic
ethanol.
Determination of rice straw production per unit area
The characteristics and production of rice straw were investigated for two varieties of
rice such as Hwanggeum Nuri (short-stem class) and Asahi (long-stem class) at Jukam farm
in Goheung-gun County. After hand harvesting the rice within 1 m2 area at 10 cm above the
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ground, the weights of grain and straw and the length and moisture content of straw were
measured. Dry weight yield of rice straw was 438.9 g/m2 for the short-stem class and 461.4
g/m2 for the long-stem class resulting in a mean value of 450.2 g/m2 (Table 2).
Table 2. Characteristics of rice straw harvested at Jukam farm
Variety
Hwanggeum
Nuri
Asahi
Mean
Straw
Grain
(g/m2)
Length
(mm)
Weight
(g/m2)
Dry weight
(g/m2)
(kg/ha)
Moisture
content (%)
640.7
759.9
1254.1
65.0
438.9
4389
718.0
679.4
973.8
866.9
1415.3
1334.7
67.4
66.2
461.4
450.2
4614
4502
Collection system and collection cost of rice straw
Collection system of rice straw
In Korea rice straw is generally collected in two types: round bale or square bale.
Round baling operation is composed of harvesting by combine, raking, baling, lapping and
transportation in the field. The size of a round bale is 1.0-1.25 m in diameter, 1.0-1.4 m in
height and weighs 300-400 kg. About 30 round bales of rice straw are produced per hectare
(ha) of paddy field. The primary use of rice straw is as a feed for beef cattle.
After bailing operation rice straw bales are transported from the field to a destination
by 1 tonne or 4.5 tonne trucks. An excavator is used to load round bales from the field to a
truck, and a loader attached to a tractor or an exclusive loader is used to unload bales from
the truck at a destination (Fig. 1). The collection period of rice straw is usually consistent
with rice harvesting period. Rice harvesting period is around 60 days from late September to
middle November.
Figure 1. Rice straw collection and baling operations
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Collection cost of rice straw
The capacity and field efficiency of machines involved in raking, baling, lapping,
transporting in the field, loading and unloading were estimated on the basis of 3,000 m2
paddy field. A total of 63 minutes was required to accomplish a series work including raking,
baling, lapping, loading and unloading bales within 3,000 m2 by the machines used at Jukam
farm without including road transport.
Because the field capacity of the baler was 9,000 m2/hr, showing the lowest value
among the machines, the effective field capacity of the collection system was assumed to be
9,000 m2/hr. Since the field efficiency was measured considering field capacity, field
efficiency was assumed to be 100%. Actual working time ratio and workable day ratio were
assumed to be 62% and 78.7%, respectively, to get the capacity of the bale collection system.
The effective field capacity of the rice-straw collection and baling system, determined by Eq.
1, turned out to be 211 ha/yr.
A=
1
𝑒
104 𝑓
1
𝑒𝑢 𝑒𝑑 𝐴ℎ 𝑈 𝐷
(1)
= 104 × 1.00 × 0.62 × 0.787 × 9,000 × 8 × 60 = 211 ha/yr
where
A = effective field capacity per year (ha/yr)
𝐴ℎ = effective field capacity per hour (9,000 m2/hr)
U = work hours per day (8 hr/day)
D = harvest period (60 day/yr)
𝑒𝑓 = field efficiency (1.0)
𝑒𝑢 = actual working time ratio (0.62)
𝑒𝑑 = workable day ratio (0.787)
The costs associated with machinery depreciation, fuel, lubricant, labor, rice straw
itself and lapping material to produce bales from 211 ha of paddy field were evaluated to
obtain production cost per bale. Annual fixed costs were assumed to be 23% of purchase
price. Since general purpose machinery such as tractor, excavator and exclusive loader can be
used for other works and their working periods are around 8 months a year including baling
operation, the annual fixed costs can be reduced to one-fourth of 23%. Fuel cost was
estimated by multiplying fuel price (1,100 won (₩) per liter (L), tax free for farm machinery),
fuel consumption (0.2 L/ps·hr), and annual input power (75% of rated power × working time).
Lubricant cost was assumed to be 10% of fuel cost. Thus, the annual cost of the collection
and baling system was determined by Eq. 2.
𝐶 = 𝐹𝑐 𝐶𝑖 + 𝐻(𝐹 + 𝑂 + 𝐿)
where
C = annual cost (₩/yr)
𝐹𝑐 = annual fixed cost ratio (0.23/yr for implements, 0.23×0.25/yr for tractor,
excavator and exclusive loader)
𝐶𝑖 = purchase price (₩)
H = hours used per year (hr/yr)
F = fuel cost (₩/hr)
O = lubricant cost (10% of fuel cost, ₩/hr)
L = labor cost (15,000 ₩/hr)
(2)
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A field survey indicated that the price of uncollected rice straw and lapping material
were 400,000 ₩/ha and 4,000 ₩/bale, respectively. The collecting system was constructed
on the basis of the effective field capacity of 211 ha. Table 3 shows the costs of collecting
round bales from an area of 211 ha. From this area, 6,330 round bales would be produced
amounting to 950 tonnes of dry rice straw. As shown in Table 3, the total collection cost of
rice straw from 211 ha was about 177 million won which corresponds to 27,978 won per bale.
Table 3. Collection costs of rice straw (based on a field capacity of 211 ha)
Work
stage
Raking
Collection system
tractor A (60 ps)
+ rake 1 set
Baling
tractor B (100 ps)
+ bale 1 set
Lapping
tractor C (80 ps)
+ lapper 1 set
Transport tractor A (60 ps)
in field
+ loader 1 set
Loading
excavator 1 set
Unloading exclusive loader
1 set
Sum
Rice straw
Lapping material
Field
Tractor Machinery Working Collection
capacity
price
price
time
cost
2
3
3
(m /hr) (10 won) (10 won)
(hr)
(103 won)
12,000
32,000
7,000
284
10,512
9,000
48,000
60,000
378
28,471
12,000
41,000
22,000
284
15,415
36,000
6,000
95
3,734
50,000
50,000
70,000
30,000
68
68
5,944
3,308
3
67,384
84,400
25,320
400,000 won/ha×211 ha=84,400×10 won
4,000 won/bale×6,330 bale=25,320×103
won
Total cost
Cost per bale
* 1 US $ corresponds to about 1,100 Korean won (₩)
177,104
27.978
Case study: Estimation of production distribution and delivered cost of rice
straw in Goheung-gun County
To investigate the economic feasibility of utilizing rice straw as a feedstock for
bioenergy facility, Goheung-gun County in Geollanam-do Province was selected as a study
area. Geollanam-do is the largest rice-producing province in Korea, and the province and
Goheung-gun County account for 20.3% and 1.6% of national rice straw production,
respectively.
A total of 135 digital maps, each covering 2.75 km × 2.2 km area, was purchased
from the National Geographic Information Institute to cover the entire inland area of
Goheung-gun (698 km2) excluding mountainous areas. Each digital map contains 33 layers
including vegetation, water systems, road boundaries, buildings, etc. A country-level digital
road network map, produced by the Korea Transport Institute, was also utilized which
contains 45 layers representing distance between nodes, number of lanes, road names, speed
limits, road types and so on.
The area of paddy field layer was extracted from each digital map and was
accumulated to the entire inland area of Goheung-gun County. There existed an average
discrepancy of 9% between the rice cultivation areas estimated from the digital maps and the
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statistical data provided by the county office. Therefore, the extracted paddy field area from
the digital maps was corrected to correspond with the statistical data for each of thirteen subcounty level municipalities.
To simplify the analysis of transportation cost of rice-straw feedstock, Goheung-gun
County region was divided into cells of 1 km × 1 km each, and an assumption was made such
that the total production of rice-straw bales in each cell was concentrated at the centroid of
the paddy field area within each cell (Graham et al., 2000) as shown in Fig. 2. Therefore,
each centroid possessed the number of round-bale production as an attribute. The estimated
number of round bales produced at each centroid was determined by Eq. 3.
NRM = APF × RC / WB
(3)
where
NRM = number of round bales per cell
APF = corrected area of paddy field in the cell (ha)
RC = residue coefficient (4.5 dry t/ha)
WB = weight of a bale (0.15 dry t/bale)
Figure 2. Centroids of the paddy fields within
each cell of 1 km × 1 km area
Figure 3. Buffer zones created to restrict the
placement of bioenergy facilities
Buffer zones were created to restrict the placement of a bioenergy facility due to some
environmental constraints such as rivers, streams, high slope regions, etc. (Perpiñá et al.,
2009) as illustrated in Fig. 3. Transportation of rice straw was assumed to be accomplished
by 4.5-tonne trucks which could carry 15 round bales. The parameters related to truck
transport are listed in Table 4.
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Table 4. Parameters related to truck transport of round rice-straw bales
Parameter
Capacity of truck
Fuel consumption of truck
Fuel price
Labor cost of truck driver
Purchase price of truck
Annual fixed cost ratio of truck
Annual use of truck
Value
4.5 t
4.5 km/L (full load)
5.6 km/L (empty)
1,806 ₩/L (diesel)
15,000 ₩/hr
₩52,400,000
23%
1920 hr
A round-trip cost of truck transport was calculated as the sum of fixed cost, labor cost
of driver, and fuel and lubrication costs (Eq. 4). The lubricant cost was assumed to be 10% of
fuel cost.
TCRT = TT × HRE + LUN
(4)
where
TCRT = Transportation cost per round trip (₩)
TT = travel time (hr) = round-trip distance (km) / average speed (km/hr)
HRE = hourly expenses (₩/hr)
= fixed costs (6,277 ₩/hr) + labor cost of driver (15,000 ₩/hr) + FLC
FLC = fuel and lubricant costs (₩/hr)
= [fuel price (₩/L) × average speed (km/hr) / fuel efficiency (km/L)] × 1.1
LUN = labor cost of truck driver while loading and unloading 15 bales (₩)
To locate potential bioethanol facilities in Goheung-gun County, the capacity of each
facility was assumed to be 20,000 dry t/yr of rice straw feedstock. The Network Analyst
toolbox of ArcGIS 10.0 (ESRI, UAS) was utilized to evaluate the distance between source
and destination cells and corresponding travel time. Potential locations of the facilities,
determined by the marginal cost of feedstock (Graham et al., 2000), are shown in Fig. 4. The
estimated delivered costs of rice–straw feedstock are summarized in Table 5.
Table 5. Characteristics of proposed locations and delivered costs of rice-straw feedstock
Item
Coverage area of paddy fields (ha)
Number of round bales collected
Dry weight of collected bales (tonne)
Average one-way travel distance (km)
Maximum one-way travel distance (km)
Marginal cost of transportation (₩/bale)
Mean delivered cost of feedstock (₩/bale)
A
4531
135,926
20,389
9.9
17.7
5501
32,809
Proposed location
B
4485
134,539
20,181
9.5
15.6
5469
32,859
C
4553
136,594
20,489
11.6
18.1
5624
33,570
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Figure 4. Proposed locations of bioenergy facilities
The results indicated that the average delivered costs of rice-straw feedstock ranged
from 32,809 won to 33,570 won per bale depending on site location. Since the average dry
weight of a round bale is 0.15 tonne, the overall average delivered cost turned out to be
220,526 ₩/dry tonne (approximately 200.5 US$/dry tonne). Considering that Korean beef
cattle farmers pay 40,000 to 47,000 won for a round rice-straw bale, the estimated figure of
the delivered cost seems to be not far from actual value. Actual delivered cost of rice-straw
feedstock to a bioenergy facility would vary with the combination and the effective field
efficiency of engaged machinery system, the capacity of bioenergy facility, competition
among rice-straw feedstock demands such as for animal feed, and the practical removal rate
of straw residues considering the maintenance of soil fertility level. The estimated delivered
cost of rice straw is almost ten times the cost of US rice-straw feedstock estimated by Kadam
et al. (2000). This makes the economic feasibility of using rice straw as a feedstock for
bioethanol in Korea very questionable.
References
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Biomass and Bioenergy 18: 309-329.
Full-paper template – The International Symposium on Agricultural and Biosystem Engineering (ISABE) 2013
3. Haddad, M. A. and Anderson, P. F. (2008). A GIS methodology to identify potential corn
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