Research Paper
Energy intensity and energy ratio in producing
willow chips as feedstock for an integrated
biorefinery
Mariusz J. Stolarski
, Michał Krzy
_zaniak
, Jo´zef Tworkowski
Stefan Szczukowski
, Janusz Gołaszewski
University of Warmia and Mazury in Olsztyn, Faculty of Environmental Management and Agriculture, Department
of Plant Breeding and Seed Production, Plac Ło´dzki 3/420, 10-724 Olsztyn, Poland
a r t i c l e i n f o
Article history:
Received 20 November 2013
Received in revised form
5 March 2014
Accepted 28 April 2014
Published online
Keywords:
Willow
Energy inputs
Diesel consumption
Energy intensity
Energy ratio
This study examined the production of willow at a commercial plantation with an area of
10.5 ha, situated in north-eastern Poland. Its aim was to evaluate the energy intensity and
energy ratio of the production of chips of new willow cultivars as feedstock for an inte-
grated biorefinery. This study emphasises the key importance of the selection of a willow
cultivar for the production of willow chips and the transport distance to a biorefinery for
the energy intensity of the production process and the energy ratio of the supplied
biomass. The lowest energy intensity for willow chip production was achieved for the
plantation of the highest-yielding cultivar (UWM 006). When the yield exceeded 86 t ha
1
of
fresh biomass, the energy intensity was 0.35 GJ t
1
of fresh matter (f.m.). The energy ratio
for the product at the farm gate varied depending on the cultivar and ranged from 23.9 to
10.2, for UWM 006 and UWM 155 cultivars, respectively. The distance of biomass transport
to a biorefinery significantly affected the energy ratio. When chips were transported for
25 km, the energy intensity for the production of 1 t of chips increased by 3
e7% compared
to its value at the farm gate. The energy intensity for the longest of the analysed transport
distances increased by 23
e53%. The energy ratio for each cultivar decreased significantly
by 3
e35% with increasing transport distance. The values of energy intensity and energy
ratio for UWM 006 and UWM 043 were better than those achieved in other studies.
ª 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Bio-based industry and renewable energy are one of the new
research and development directions supported in Europe by
the European Commission and by other countries around the
world (
Bridge 2020, 2014; European Commission, 2012
). Until
recently, biomass was perceived as feedstock mainly for heat
and power production, while its use for other purposes was
regarded as a niche activity. A huge part of the energy and
* Corresponding author. Tel.:
þ48 895234838; fax: þ48 895234880.
E-mail addresses:
(M.J. Stolarski),
(M. Krzy
_zaniak),
(J. Tworkowski),
(S. Szczukowski),
(J. Gołaszewski).
1
Tel./fax:
þ48 895234880.
Available online at
ScienceDirect
journal homepa ge: www .e lsev ie r.com/locate/issn/153 75110
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
http://dx.doi.org/10.1016/j.biosystemseng.2014.04.011
1537-5110/
ª 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
chemical industry base their production on fossil feedstock
(non-renewable). The continuous increase in consumption of
fossil feedstocks has led to their depletion and to price in-
creases. Moreover, their mining and consumption is accom-
panied by the emission of greenhouse gases and, in
consequence, an escalation of the greenhouse effect (
). As a result, the status of biomass may
change from the “fuel of the poor” to a component of many
biorefinery industry products.
Willow biomass is used in the production of heat, power
and biofuels (
Carroll & Finnan, 2013, 2012; Stolarski,
Krzyzaniak, et al., 2013; Stolarski, Szczukowski, Tworkowski,
& Klasa, 2013; Wang, Dunn, & Wang, 2012
). However, ulti-
mately, willow biomass can be one of the potential lignocel-
lulose feedstocks for integrated multi-product biorefineries.
The EuroBioRef project will develop a new highly-integrated
and diversified concept, including multiple feedstocks
(including
lignocellulosic
biomass),
multiple
processes
(chemical, biochemical, thermochemical) and multiple prod-
ucts (aviation fuels and chemicals). A flexible approach will
widen bio-refinery implementation to the full geographical
range of Europe and will offer opportunities to export bio-
refinery technology packages to more local markets and
feedstock hotspots. The ambitious objectives of the Euro-
BioRef project seek a decrease in energy consumption by 30%
for a final product and at least 10% lower raw material con-
sumption (
). Willow, as a lignocellulose
biomass, is proposed as the feedstock in two value chains: VC
3
e alcohols to fuels and VC 5 e syngas-based products.
Perennial energy crops, including willow, should be char-
acterised by high productivity and the biomass produced from
them should have high calorific value. This would produce
considerable amounts of energy and would result in a high
energy ratio of biomass production. Only if this is achieved
will further stages of biomass conversion to secondary energy
carriers and bioproducts be justified as an environmentally-
friendly and sustainable solution. Short-rotation willow
output achieved in experiments conducted in Poland has
reached 30 t dry matter (d.m.) ha
1
year
1
. The average yield
has usually ranged from 10 to 12 t d.m. ha
1
year
1
Szczukowski, Tworkowski, Wroblewska, & Krzyzaniak, 2011;
Tworkowski, Szczukowski, & Stolarski, 2006
). On the other
hand, the willow yield on large (70
e300 ha) commercial
plantations was usually much lower than that in experiments
and typically amounted to 4
e10 t d.m. ha
1
year
1
. Such a low
yield was achieved on commercial plantations because of
difficulties with the right choice and preparation of the field,
errors in setting up plantations, ineffective weed control,
wrong fertilisation and using clones with low efficiency
(
s, Szczukowski, & Stolarski, 2010
). Therefore,
it is very important from a practical point of view that the yield
obtained in experiments should be verified in professional
commercial production. Further development of this type of
production requires an analysis of the relationship between
the effectiveness of different cultivars and clones of willow on
commercial plantations and environmental and agrotechnical
procedures. An evaluation of the energy intensity (the ratio of
the total energy use per t of fresh matter yield) and energy
ratio (the energy value of yield divided by the total energy
input) in willow chip production for industrial or energy
feedstock is also necessary.
Similar studies on energy yield and energy ratio of biomass
production can be found in scientific literature. For instance,
Boehmel, Lewandowski, and Claupein (2008)
compare energy
yield and primary net energy yield (the difference between the
primary energy yield and the energy consumption) of peren-
nial (SRC willow, miscanthus) and annual (maize, rape) plants.
Vande Walle, Van Camp, Van de Casteele, Verheyen, and
Lemeur (2007)
studied the utilisation potential of birch,
maple, poplar and willow as feedstock for the production of
renewable power in Flanders (Belgium). On the other hand,
modelled the energy and carbon budgets of
wood fuel coppice systems, to study the energy and carbon
budgets of biofuel production systems. The above-mentioned
studies, as well as those recently conducted in Italy with
poplar cultivated in a 6-year harvest cycle (
), prove the high energy ratio of
both the cultivation and acquisition of perennial plants.
The advantage of the present study was the possibility of
using varieties offering the lowest willow chip production
energy intensity. This further reduced this indicator for the
final product in the biorefinery. Therefore, the aim of this
study was to evaluate the energy intensity and energy ratio of
the production of chips of seven new willow cultivars har-
vested in a three-year rotation as feedstock for an integrated
biorefinery, depending on the transport distance.
2.
Materials
This study was conducted on a commercial willow plantation
with an area of 10.5 ha, set up in mid-April 2010 at the Didactic
and Research Station in Łe˛
_zany, owned by the University of
Warmia and Mazury in Olsztyn. It is located in the north-east
of Poland, on land of the village of Samławki (53
59
0
N, 21
05
0
E). The area on which the plantation was situated is undu-
lating and very diverse in elevation. Low quality soil (mainly
on soil created from slightly loamy sand and light loamy sand)
that was of limited use for typical annual crops was selected
for the plantation. Generally, the land in the elevated areas
had a groundwater level far below 1.50 m so the soil was
permanently dry. By selecting a relatively poor soil site it was
possible to evaluate the willow yield potential in areas of little
use for food or feed crops. Three cultivars and four clones of
willow were planted on the plantation; for this study they
were regarded as cultivars and all had been bred at the
Department of Plant Breeding and Seed Production of the
University of Warmia and Mazury in Olsztyn. Start, Tur,
Turbo, UWM 006, UWM 043 were of the species Salix viminalis,
UWM 035 was of the species Salix pentandra and UWM 155 was
of the species Salix dasyclados.
Willows were planted at a density of 18
10
3
ha
1
. Willow
cuttings were planted in strips, with two rows in a strip spaced
every 0.75 m, with 1.5 m of space separating the next 2 rows in
a strip with 0.75 m space between them, etc., with plants in a
row spaced every 0.5 m.
Triticale was sown as the previous crop. The following
procedures were carried out in order to prepare the site:
spraying with glyphosate to eliminate weeds (Roundup
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
20
4 l ha
1
), disking (
2), winter ploughing, fertilisation with PRP
Sol (300 kg ha
1
), harrowing (
2), mechanical planting of
willow cuttings with a step planter, spraying with a soil her-
bicide (Guardian CompleteMix 664 SE 3.5 l ha
1
), mechanical
weeding (
2), spraying with a herbicide against mono-
cotyledon weeds (Targa Super 2.5 l ha
1
).
According to our 20-year experience, which involved willow
cultivation as an energy crop, and to the principles of the Euro-
bioref project, no top dressing was applied in the first year of the
willow vegetation. However, before the beginning of the second
year of vegetation, i.e. in spring 2011, mineral fertilisation was
performed at: N 90 kg ha
1
; P
2
O
5
30 kg ha
1
, K
2
O 60 kg ha
1
.
Phosphorus was applied as triple superphosphate and potas-
sium as potassium salt. Nitrogen was applied in two doses as
ammonium nitrate. The first dose of 50 kg ha
1
was applied
immediately before the start of the plant growth, and the
remaining dose (40 kg ha
1
) was applied at the end of May 2011.
In the second year of vegetation, the plantation was sprayed with
a herbicide against monocotyledons (Targa Super 2.5 l ha
1
).
After the third year of growth, in December 2012, three-
year-old willows were harvested with a Claas Jaguar 830
harvester. Chips were collected from the harvester with three
units, each one consisting of New Holland TM 130 tractors and
T 169/2 transport trailers. Subsequently, the trailers with
chips produced from different cultivars were weighed and the
fresh biomass yield in t ha
1
was determined. Further ana-
lyses took into account the transport of chips to a biorefinery
over one of four distances; 25, 50, 100 and 200 km. Professional
containers with a capacity of 80 m
3
of chips each were used for
biomass transport, which totalled about 25 t of fresh chips per
run.
3.
Methods
The energy intensity and energy ratio of the production of
chips from the willow cultivars under study was analysed
based on the fresh biomass yield obtained in the first three-
year harvest cycle. The total input was divided into three
stages. The first one involved setting up a plantation and its
liquidation and the second one involved its operation. The
third stage was transport to a biorefinery. The input for
setting up and running a plantation in the first year of
growth and for its future liquidation is presented here in
whole and was allocated across each of the 21 years of its
operations.
The analysis of materials and energy, incurred for setting
up the plantation and the production of willow chips,
covered separate streams of energy: direct energy carriers
(diesel fuel); utilisation of fixed assets (tractors, machines,
equipment); consumption of materials (mineral fertilisers,
agrochemicals, willow cuttings) and human labour. The total
energy input for the willow cultivation, production and
transport of chips to a biorefinery was calculated based on
the indexes shown in
. The types of equipment used
in field operations and the maximum power of the tractors
and those used in different procedures are shown in
The total power of the Claas Jaguar harvester was 236.0 kW
and the power used was 212.4 kW. The field transport of
willow chips used a tractor with a maximum power of
95.6 kW and the power used was 47.8 kW. The technical and
operational parameters adopted for analyses were based on
the data contained in the paper by
in the catalogue of agricultural machines (
) and in materials published by manufacturers of trac-
tors and machines.
The yield energy value was calculated as the product of
fresh biomass yield and its lower heating value.
Y
ev
¼ Y
b
$Q
r
i
(1)
where Y
ev
is the biomass yield energy value (GJ ha
1
), Y
b
is the
biomass yield (t f.m. ha
1
), and Q
r
i
is the biomass lower heating
value (GJ t
1
).
Accumulated energy gain at the farm gate is the difference
between the yield energy value and the total input for its
production at the farm gate:
E
g
¼ Y
ev
I
fg
(2)
where E
g
is the accumulated energy gain at the farm gate
(GJ ha
1
), Y
ev
is the biomass yield energy value (GJ ha
1
), and I
fg
e total energy input at the farm gate (GJ ha
1
).
Energy intensity is the energy consumption per tonne of
fresh chips, which is the ratio of total energy input to the yield:
EI
¼ E
i
=Y
b
(3)
where EI is the energy intensity (GJ t
1
f.m.), E
i
is the energy
input (GJ ha
1
) and Y
b
e biomass yield (t f.m. ha
1
).
Table 1
e Energy conversion coefficients used to calculate the energy intensity of willow production.
Item
Unit
Energy conversion
coefficient (MJ)
Source
Fuel oil
1 kg
43.1
Nitrogen fertilisers
1 kg N
48.99
Phosphorus fertilisers
1 kg P
2
O
3
15.23
Potassium fertilisers
1 kg K
2
O
9.68
Other fertilisers, e.g. PRP sol
1 kg of fertiliser
15.23
Pesticides
1 kg of active substance
268.4
Cuttings
1 kg or 1 cutting
3.04 or 0.057
This research
Tractors, vehicles, self-propelled machines
1 kg
125
Szeptycki and Wo´jcicki (2003)
Agricultural machines and equipment
1 kg
110
Szeptycki and Wo´jcicki (2003)
Human labour
1 h
60
Szeptycki and Wo´jcicki (2003)
Transport of biomass
1 t d.m. km
1
0.94
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
21
Diesel fuel consumption per tonne of fresh or dry willow
chips is the ratio of the diesel fuel consumption and the wil-
low yield:
D
¼ F
c
=Y
b
(4)
where D is the diesel fuel consumption (kg t
1
f.m. or d.m.), F
c
is the fuel consumption (kg ha
1
) and Y
b
is the biomass yield
(t f.m. or d.m ha
1
).
The energy ratio of willow chips production is the ratio of
the yield energy value (energy output) and the accumulated
material and energy input for its production:
ER
¼ E
o
=E
i
(5)
where ER is the energy ratio, E
o
is the energy output, and E
i
e
energy input.
4.
Results and discussion
4.1.
Accumulated material and energy inputs
The accumulated material and energy inputs for setting up
and running 1 ha of a plantation of willow coppice during the
first year of growth and its liquidation after its exploitation
was completed, amounted to 20.37 GJ ha
1
(
). Con-
verted to one year of plantation exploitation (assuming that
the plantation will be used for 21 years), it amounts to
0.97 GJ ha
1
. The input structure was dominated by the
plantation liquidation (36.3%). This was followed by fertilisa-
tion and planting of willow cuttings. On the other hand, the
energy stream was dominated by direct energy carriers, i.e.
diesel fuel (45.9%), followed by materials (32.6%). The energy
Table 2
e Data for field operations.
Operation
Tractor/Harvester
Machinery
Operating period
Comments
Name
Mass
(kg)
Power (kW)
(max/used)
Utilisation
of the
power
capacity
(%)
Name
Mass
(kg)
(h ha
1
)
Spraying
New Holland
TM 130 HP
5465
95.6/47.8
50
Krukowiak sprayer,
working width 18 m
2110
0.2
Glyphosate, Roundup
360 SL, 4 l ha
1
Disking
New Holland
TM 130 HP
5465
95.6/60.2
63
Kverneland disk
harrow, working
width 4 m
1160
1.4
2
coverage
Winter
ploughing
New Holland
TM 175 HP
7150
128.6/90.0
70
Kverneland PG 100
plough, working
width 2 m
1120
1.5
5-ridge plough,
ploughing depth 30 cm
Fertilisation
New Holland
TM 130 HP
5465
95.6/47.8
50
Rauch 3,0 t spreader,
working width 18 m
350
0.4
PRP Sol fertiliser, dose
300 kg ha
1
Harrowing
New Holland
TM 130 HP
5465
95.6/52.6
55
Harrow, working
width 6 m
530
1.0
2
coverage
Mechanical
planting of
cuttings
New Holland
TM 130 HP
5465
95.6/62.1
65
4-row step planter
2800
1.3
18,000 cuttings per ha
Spraying
New Holland
TM 130 HP
5465
95.6/47.8
50
Krukowiak sprayer,
working width 18 m
2110
0.2
Soil-applied herbicide,
Guardian CompleteMix
664 SE, 3.5 l ha
1
Weeding
New Holland
TM 90 HP
4410
66.0/33.0
50
Mechanical weeder P
430/2, working width
3 m
340
2.0
2
coverage
Spraying
New Holland
TM 130 HP
5465
95.6/47.8
50
Krukowiak sprayer,
working width 18 m
2110
0.2
Herbicide against
monocotyledon weeds,
Targa Super 05 EC,
2.5 l ha
1
Fertilisation
New Holland
TM 130 HP
5465
95.6/47.8
50
Rauch 3,0 t spreader,
working width 18 m
350
1.3
Mineral fertilisation in
spring 2011, N
e 90; P
2
O
5
e 30; K
2
O
e 60 kg ha
-
Liquidation of
plantation
New Holland
TM 175 HP
7150
128.6/90.0
70
Rototiller FV 4088,
working width 40 cm
1160
6.0
Breaking up larger
rootstocks along rows
Harvesting
Claas Jaguar
830
10,150 236.0/212.4
90
e
e
1
e4*
*Depending on the yield
of a given cultivar,
average productivity of
harvester 20 ton of chips
per hour
Field transport New Holland
TM 130 HP
5465
95.6/47.8
50
T 169/2 tractor
trailer, loading
capacity: 4 tons of
chips
1940
1
e4*
*To ensure continuity of
receipt of chips 3
transportation units
were used
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
22
inputs related to the use of machines, human labour and
tractors accounted for smaller parts of the energy stream.
The accumulated material and energy input for production
of willow chips in a three-year harvest cycle, including setting
up and liquidating the plantation, NPK fertilisation and the
application of herbicide against monocotyledons, were the
same for each cultivar (
). The largest amounts of en-
ergy were consumed for mineral fertilisation (6.21 GJ ha
1
).
The range of values for energy input across cultivars resulted
from the plant harvest with a Claas Jaguar 830 harvester and
the field transport of the chips. The differences between the
cultivars were associated with their differing yields and the
Table 3
e Time and accumulated material and energy input for setting up and running a willow plantation (per ha) in the
first year of vegetation and for its liquidation.
Operation
Labour
Machinery
Tractors
Diesel fuel
Materials
Total
Input structure
Hour
MJ
Hour
MJ
Hour
MJ
kg
MJ
kg
MJ
MJ
%
Spraying (glyphosate)
0.3
18.0
0.2
46.4
0.2
11.4
2.04
87.8
4.00
386.50 550.07
2.7
Disking (2
)
1.6
96.0
1.4
111.7
1.4
79.7
17.96
774.1
e
e
1061.4
5.2
Winter ploughing
1.7
102.0
1.5
154.0
1.5
111.7
29.30 1262.9
e
e
1630.6
8.0
Fertilisation
0.5
30.0
0.4
9.1
0.4
22.8
4.07
175.5
300.0
4569.0
4806.4
23.6
Harrowing (2
)
1.2
72.0
1.0
34.3
1.0
56.9
11.20
482.7
e
e
645.9
3.2
Mechanical planting of cuttings
5.2
312.0
1.3
235.5
1.3
74.0
17.21
741.6
337.5
1026.0
2389.1
11.7
Spraying (soil-applied herbicide)
0.3
18.0
0.2
46.4
0.2
11.4
2.04
87.8
3.5
617.3
780.9
3.8
Weeding (2
)
2.2
132.0
2.0
74.8
2.0
91.9
14.06
605.9
e
e
904.6
4.4
Spraying with herbicide
against monocotyledon weeds
0.3
18.0
0.2
46.4
0.2
11.4
2.04
87.8
2.50
33.55 197.12
1.0
Liquidation of plantation
6.2
372.0
6.0
1531.2
6.0
446.9
117.21 5051.6
e
e
7401.7
36.3
Total
19.5
1170.0
14.2
2289.8
14.2
918.0
217.1
9357.6
647.50 6632.37 20,367.8
100.0
Per year of plantation
cultivation 1/21
S
0.93
55.71
0.68
109.04
0.68
43.72
10.34
445.60
30.83
315.83 969.9
e
Input structure (%)
e
5.74
e
11.24
e
4.51
e
45.94
e
32.56 100.00
e
Table 4
e Time and accumulated material and energy input for production of willow chips (per ha) in a three-year harvest
rotation depending on the cultivar, at the farm gate.
Cultivar
Operation
Human labour
Machinery
Tractors
Diesel
Materials
Total
Hour
MJ
Hour
MJ
Hour
MJ
kg
MJ
kg
MJ
MJ
For each
cultivar
Setting up and
liquidation of
plantation
2.8
167.1
2.0
327.1
2.0
131.1
31.0
1336.8
92.5
947.5
2909.7
NPK fertilisation
1.5
90.0
1.3
29.4
1.3
74.0
13.24
570.5
425.5
5446.8
6210.7
Spraying with
herbicide against
monocotyledon
weeds
0.3
18.0
0.2
46.4
0.2
11.4
2.04
87.8
2.5
33.6
197.1
Start
Harvesting
2.1
123.7
2.1
1743.3
e
e
105.1
4528.2
e
e
6395.1
Field transport
6.2
371.0
6.2
219.9
6.2
352.0
63.0
2713.2
e
e
3656.1
Total
12.8
769.8
11.8
2366.1
9.7
568.5
214.3
9236.4
520.5
6427.8
19,368.7
Tur
Harvesting
1.0
62.8
1.0
884.7
e
e
53.3
2298.1
3245.6
Field transport
3.1
188.3
3.1
111.6
3.1
178.6
31.9
1377.0
1855.5
Total
8.8
526.2
7.7
1399.3
6.7
395.2
131.6
5670.2
520.5
6427.8
14,418.7
Turbo
Harvesting
2.1
128.0
2.1
1803.7
e
e
108.7
4685.2
6616.9
Field transport
6.4
383.9
6.4
227.5
6.4
364.2
65.1
2807.3
3782.9
Total
13.1
786.9
12.1
2434.3
9.9
580.7
220.1
9487.6
520.5
6427.8
19,717.4
UWM 006
Harvesting
4.3
259.1
4.3
3652.7
e
e
220.1
9488.0
13,399.9
Field transport
13.0
777.3
13.0
460.8
13.0
737.5
131.9
5685.1
7660.7
Total
21.9
1311.6
20.8
4516.5
16.5
954.1
398.3
17,168.2
520.5
6427.8
30,378.1
UWM 035
Harvesting
1.5
89.9
1.5
1267.1
e
e
76.4
3291.2
4648.1
Field transport
4.5
269.6
4.5
159.8
4.5
255.8
45.8
1972.0
2657.4
Total
10.6
634.7
9.5
1829.9
8.0
472.4
168.4
7258.3
520.5
6427.8
16,623.0
UWM 043
Harvesting
3.5
210.6
3.5
2969.3
e
e
179.0
7712.8
10,892.7
Field transport
10.5
631.9
10.5
374.6
10.5
599.5
107.2
4621.4
6227.4
Total
18.6
1117.7
17.6
3746.8
14.1
816.1
332.5
14,329.2
520.5
6427.8
26,437.6
UWM 155
Harvesting
0.9
53.6
0.9
755.8
e
e
45.5
1963.1
2772.4
Field transport
2.7
160.8
2.7
95.3
2.7
152.6
27.3
1176.3
1585.0
Total
8.2
489.6
7.1
1254.1
6.2
369.1
119.1
5134.4
520.5
6427.8
13,675.0
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
23
consequent time of work of the harvester and the ancillary
equipment. Therefore, the total energy input in the three-year
cycle of the willow harvest ranged from 13.68 GJ ha
1
to
30.38 GJ ha
1
, for the UWM 155 and UWM 006 cultivars,
respectively. This can be compared to the energy input in the
extensive cultivation of willow as an energy crop without
fertilisation, weed control or irrigation, which was estimated
as 14.14 GJ ha
1
by
. Energy inputs in
the production of poplar biomass were 14.2 GJ ha
1
year
1
for
Manzone, Airoldi, and Balsari (2009)
, while those in the pro-
duction of miscanthus biomass, depending on the level of
nitrogen fertilisation, ranged from 17.82 to 27.39 GJ ha
1
year
1
for
The structure of the energy stream for production opera-
tions in the highest-yielding cultivars (UWM 006 and UWM
043) was dominated (over 60%) by the total input attributable
to harvesting and field transport (
). On the other hand,
the largest part of the energy input for the lowest-yielding
cultivars (UWM 155 and Tur) was mineral fertilisation (over
40%). Similar relationships were observed in the energy
stream structure for these cultivars, which was dominated by
the inputs into fertilisers (42
e45%).
This part decreased in the highest-yielding cultivars and
was replaced by inputs of energy resulting from the con-
sumption of diesel fuel and the use of machines. A higher
yield required more intensive use of equipment and con-
sumption of fuel. For example for UWM 006 cultivar, the en-
ergy input of diesel fuel consumption accounted for 56.5% of
the total input and that of machines accounted for 14.9% of
the total input. The corresponding values for the UWM 043
cultivar were 54.2% and 14.2%. Also, the input of fertiliser use
was large and accounted for 20
e30% of the total input. In a
different study conducted by the present authors, the energy
stream in the production of willow chips was dominated by
the input of mineral fertilisation and fuels (
).
Moreover,
Heller, Keoleian, and Volk (2003)
reported that the
structure of energy carriers in production of willow biomass
was dominated by fuels (46%), followed by fertilisation (37%).
Therefore, replacement of mineral fertilisation by wastewater
sludge from local wastewater treatment stations and
introducing liquid renewable fuels, such as biodiesel, to the
process of willow biomass production could reduce the energy
input, resulting in an increase in the energy ratio of the pro-
duction of fuel from the plant species by as much as 40%
(
Heller et al., 2003; Keoleian & Volk, 2005
The total diesel fuel consumption (398.3 kg ha
1
) in the
process of willow chip production was the highest in the UWM
006 cultivar, whose yield amounted to 86 t f.m. ha
1
).
The fuel consumption for the UWM 043 cultivar was lower by
nearly 66 kg ha
1
, with a yield of 70 t f.m. ha
1
. On the other
hand, the lowest consumption of diesel of 119 kg ha
1
was
recorded for the lowest-yielding cultivar, UWM 155.
4.2.
Energy ratio
The yield energy value at the farm gate in a three-year willow
harvest cycle ranged widely, from 138.8 GJ ha
1
in UWM 155 to
727.4 GJ ha
1
in UWM 006 (
) and the energy gain at the
farm gate ranged from 125.2 to 697 GJ ha
1
, respectively. When
calculated per year of plantation use, it amounted to 41.7 and
232.3 GJ ha
1
year
1
, respectively. A high energy gain was also
achieved for the UWM 043 cultivar (186.3 GJ ha
1
year
1
). Ac-
cording to
, the mean net energy from willow
plantations in Sweden is approximately 170 GJ ha
1
year
1
.
This can be increased to over 200 GJ ha
1
year
1
by using
wastewater for irrigation of a plantation of willow (
). In another study, the energy value of the
yield obtained in two-year harvest cycle for Salix viminalis
ranged from 73 to 290 GJ ha
1
year
1
with the sludge dose of
0 and 300 kg N ha
1
, respectively (
reported that the energy
value of willow biomass in a three-year harvest rotation
amounted to 226 GJ ha
1
year
1
. On the other hand, the energy
value of poplar yield was 188 GJ ha
1
year
1
(
) and that of the miscanthus biomass, depending on the
level
of
nitrogen
fertilisation,
ranged
from
approx.
210
e231 GJ ha
1
year
1
The energy input and the yield significantly differentiate
the energy intensity of production per tonne of willow
biomass from different cultivars. It has been shown in this
Table 5
e Structure of accumulated material and energy input for production of willow chips in a three-year harvest
rotation, depending on cultivar, at the farm gate (%).
Item
Start
Tur
Turbo
UWM 006
UWM 035
UWM 043
UWM 155
By production operations
Setting up and liquidation of plantation
15.0
20.2
14.8
9.6
17.5
11.0
21.3
NPK fertilisation
32.1
43.1
31.5
20.4
37.4
23.5
45.4
Weed control
1.0
1.4
1.0
0.6
1.2
0.7
1.4
Harvest
33.0
22.5
33.6
44.1
28.0
41.2
20.3
Field transport
18.9
12.9
19.2
25.2
16.0
23.6
11.6
By energy stream
Human labour
4.0
3.6
4.0
4.3
3.8
4.2
3.6
Machinery
12.2
9.7
12.3
14.9
11.0
14.2
9.2
Tractors
2.9
2.7
2.9
3.1
2.8
3.1
2.7
Diesel fuel
47.7
39.3
48.1
56.5
43.7
54.2
37.5
Materials, including:
33.2
44.6
32.6
21.2
38.7
24.3
47.0
Seedlings
0.8
1.0
0.7
0.5
0.9
0.6
1.1
Pesticides
0.9
1.3
0.9
0.6
1.1
0.7
1.3
Fertilisers
31.5
42.3
30.9
20.1
36.7
23.1
44.6
Total
100.0
100.0
100.0
100.0
100.0
100.0
100.0
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
24
study that the lowest consumption of diesel fuel for the pro-
duction of 1 tonne of fresh chips at the farm gate was recorded
in the production of the UWM 006 cultivar (4.6 kg t
1
f.m.),
which amounted to 9.3 kg t
1
d.m. Consumption of diesel fuel
per tonne of dry matter of the UWM 043 cultivar was higher by
3%. The value was higher by 14% and 53% for the Start and
UWM 155 cultivars, respectively. The consumption of diesel
fuel per tonne of willow chips in this study was higher than
has been found in other studies. Very low fuel consumption
(3.0 l t
1
of willow chips) was achieved by
. In a study conducted by
and by
Gonza´lez-Garcı´a, Mola-Yudego, Dimitriou, Aronsson, and
Murphy (2012)
consumption of fuel for willow chip production
amounted to 3.6 and 4.1 l t
1
, respectively. On the other hand,
the consumption of fuel in the production of chips from
poplar trees ranged from 6.4 to 7.5 l t
1
The energy intensity per tonne of fresh willow chips at the
farm gate was the lowest for the UWM 006 cultivar and it
amounted to 0.35 GJ t
1
f.m (
). This value was only
around 0.03 GJ t
1
f.m. higher for the production of the UWM
043 cultivar. On the other hand, it was twice as great for the
low-yielding cultivars: UWM 155 and Tur. In different studies,
the energy intensity of willow chip production in a three-year
harvest cycle ranged from 0.30 to 0.61 GJ t
1
f.m. (
). Much lower energy intensity was
achieved in harvesting 5-year-old poplar trees (
Schweier, & De Francesco, 2012
).
The energy ratio in the process of production of willow
chips at the farm gate varied depending on the cultivar (
). It was the highest in UWM 006 (at 23.9), followed by UWM
043, Start, Turbo, UWM 035, Tur and was lowest for UWM 155
(10.2). The energy ratios of willow production found in other
studies have covered a wide range, from about 12 to over 50
(
Heller et al., 2003; Matthews, 2001; Stolarski, 2009
). Varied
levels of energy ratio in the production of willow biomass
result from differences in the preparation of the production
site and the use of mineral fertilisers and pesticides. Other
important factors include cultivars, planting density, the
harvest cycle and its technology, as well as the biomass yield.
Willow biomass yield may be diverse in successive harvest
rotations.
report that subsequent harvest
rotations of willow biomass will give a higher yield by as
much as 30
e40% compared to the first harvest. However, our
multi-year studies have shown that this depends on multiple
factors and, in agricultural practice, an increase in yield is
indeed achieved in the second and third rotation of willow
harvest. However, the yield may decrease in subsequent
(4
e7) harvest rotations due to accumulation of diseases, pests
and plant loss; therefore, such a large increase is not always
achieved in subsequent harvest rotations. In consequence, it
was assumed in this study that mean biomass yield in sub-
sequent harvest rotations would be similar to the first har-
vest rotation, which is achievable in agricultural practice.
Obviously, any higher yield would result in better energy
intensity and energy ratio values. This study focused mainly
on an assessment of the effect of the choice of a cultivar on
these indexes and it showed that the effect of cultivar can be
very important, because the energy ratio at the farm gate in
the production of willow chips of the UWM 006 cultivar was
2.3 times higher than in the UWM 155 cultivar. Much higher
levels of energy ratio were achieved when harvesting 5-year-
old poplar trees (
). On the other hand, in
the studies by
, the energy ratio in
poplar production was 13, while in the production of mis-
canthus biomass this ratio was ranged from 7.72 to 11.79, at
200 and 0 kg ha
1
N of nitrogen fertilisation, respectively
Selected production effectiveness ratios for willow chips
at the biorefinery gate are shown in
. Obviously, they
strongly depended on the distance that had to be covered in
biomass transport between the plantation and the bio-
refinery. The parameters were worse with increasing
transport distance. The total accumulated material and
energy input at the biorefinery gate ranged from 14.1 GJ ha
1
for UWM 155 cultivar at a distance of 25 km to 46.4 GJ ha
1
when chips of the UWM 006 are transported a distance of
Table 6
e The yield of fresh and dry matter and consumption of diesel fuel for the production of willow chips in a three-year
harvest rotation at the farm gate.
Item
Start
Tur
Turbo
UWM 006
UWM 035
UWM 043
UWM 155
Diesel fuel consumption (kg ha
1
)
214.3
131.6
220.1
398.3
168.4
332.5
119.1
Yield (t f.m. ha
1
)
41.2
4.4
c
20.9
1.6
e
42.7
4.9
c
86.4
4.9
a
30.0
4.2
d
70.2
8.7
b
17.9
0.8
e
Yield (t d.m. ha
1
)
20.3
2.5
c
11.0
0.9
e
20.3
2.5
c
42.7
2.5
a
15.1
2.2
d
34.5
4.3
b
8.4
0.4
e
Standard deviation;
a, b, c
.
Homogenous groups.
Table 7
e Selected efficiency indexes in the production of willow chips of different cultivars in a three-year harvest rotation,
at the farm gate.
Item
Start
Tur
Turbo
UWM 006
UWM 035
UWM 043
UWM 155
Energy inputs (GJ ha
1
)
19.4
14.4
19.7
30.4
16.6
26.4
13.7
Energy value of yield (GJ ha
1
)
344.6
191.6
341.5
727.4
259.7
585.4
138.8
Energy gain (GJ ha
1
)
325.2
177.2
321.8
697.0
243.0
559.0
125.2
Diesel fuel consumption (kg t
1
f.m.)
5.2
6.3
5.2
4.6
5.6
4.7
6.7
Diesel fuel consumption (kg t
1
d.m.)
10.6
11.9
10.8
9.3
11.1
9.6
14.2
Energy intensity (GJ t
1
f.m.)
0.47
0.69
0.46
0.35
0.56
0.38
0.77
Energy ratio
17.8
13.3
17.3
23.9
15.6
22.1
10.2
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
25
200 km. Therefore, in the last case, the biomass transport
consumed about 16 GJ ha
1
.
An increase in the transport distance resulted in an increase
in the energy intensity per tonne of chips (
). When chips
were transported for 25 km, the energy intensity increased by
3
e7% compared to its value at the farm gate. A further increase
in the distance to 50 km meant an increase in the index by
7
e13%. When biomass was transported a distance of 100 km,
the increase ranged from 14 to 26%. The energy intensity in the
option with a transport distance of 200 km increased by 23
e53%
compared to its level at the farm gate.
Furthermore, the energy ratio for each cultivar decreased
significantly for each cultivar with increasing transport dis-
tance. When chips were transported the shortest distance, the
ratio decreased by 3
e6%. On the other hand, it decreased by
19
e35% with the longest transport distance (
also found the transport dis-
tance to be one of the most important factors affecting the
energy ratio. They showed that when chips were transported
up to 38 km, the energy ratio decreased by less than 8.3%.
When chips were transported for over 38 km, the ratio
decreased significantly (25.9%). A decrease in energy ratio with
increasing transport distance was also found by
. Another important factor pointed out in other research
is the effect of the willow yield on the energy contained in the
yield and energy ratio (
). With a yield of
10 t ha
1
, the energy ratio was 19.3, whereas with a yield of
14 t ha
1
it was 23.5. In our research we also found that the
choice of a cultivar for chip production is significant for the
amount of energy produced and the final energy effectiveness
of its production. The energy ratio for the highest-yielding
UWM 006 cultivar was 2.2 times higher on average than the
lowest-yielding UWM 155 cultivar.
5.
Conclusions
These findings clearly show that the choice of willow cultivar
is vitally important from the point of view of its energy in-
tensity and energy ratio in biomass production when pro-
ducing chips as feedstock for an integrated biorefinery. The
energy input at the stage of setting up a plantation and its
potential liquidation was the same for every cultivar. On the
other hand the yield of the cultivars in the three-year harvest
cycle significantly modified the total energy input for pro-
duction of willow chips (13.7
e30.4 GJ ha
1
). This was associ-
ated with the energy use of the harvester and the field
transport of the chips. The energy stream in the lowest-
yielding cultivars was dominated by the cost of fertilisers
(42
e45%) and in the highest-yielding ones it was dominated by
diesel fuel consumption (54
e56%). It was found that the
cultivation of high-yielding willow cultivars can lead to much
lower energy intensity in willow chip production (diesel fuel
consumption, energy intensity) and a higher energy ratio
compared to low-yielding cultivars.
As was expected, the distance of biomass transport to a
biorefinery significantly changed the energy effectiveness for
the production of willow chips. When chips were transported
for 25 km, the energy intensity increased slightly (by 3
e7%)
compared to its value at the farm gate. The energy intensity
for a transport distance of 200 km increased considerably (by
23
e53%) compared to its level at the farm gate. Furthermore,
the energy ratio for each cultivar decreased significantly for
each cultivar with increasing transport distance. When chips
were transported for the shortest distance, the ratio decreased
slightly (by 3
e6%). On the other hand, it decreased by as much
as 19
e35% with the longest transport distance.
Table 8
e Selected efficiency indexes in the production of willow chips of different cultivars in a three-year harvest rotation,
at the biorefinery gate.
Item
Transport distance (km)
Start
Tur
Turbo
UWM 006
UWM 035
UWM 043
UWM 155
Energy inputs (GJ ha
1
)
25
20.3
14.9
20.7
32.4
17.3
28.1
14.1
50
21.3
15.5
21.6
34.4
18.0
29.7
14.5
100
23.2
16.5
23.5
38.4
19.5
32.9
15.2
200
27.0
18.6
27.4
46.4
22.3
39.4
16.8
Energy intensity (GJ t
1
f.m.)
25
0.49
0.71
0.49
0.38
0.58
0.40
0.79
50
0.52
0.74
0.51
0.40
0.60
0.42
0.81
100
0.56
0.79
0.55
0.45
0.65
0.47
0.85
200
0.66
0.89
0.64
0.54
0.75
0.56
0.94
Energy ratio
25
17.0
12.8
16.5
22.5
15.0
20.9
9.9
50
16.2
12.4
15.8
21.2
14.4
19.7
9.6
100
14.9
11.6
14.5
18.9
13.3
17.8
9.1
200
12.8
10.3
12.5
15.7
11.6
14.9
8.3
Table 9
e Changes in the energy ratio (%) depending on the transport distance (0 km [ 100%).
Transport distance (km)
Start
Tur
Turbo
UWM 006
UWM 035
UWM 043
UWM 155
0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
25
95.3
96.5
95.4
93.8
95.9
94.2
97.2
50
91.0
93.3
91.2
88.3
92.1
89.1
94.6
100
83.5
87.4
83.8
79.1
85.4
80.3
89.7
200
71.7
77.7
72.1
65.4
74.5
67.1
81.3
b i o s y s t e m s e n g i n e e r i n g 1 2 3 ( 2 0 1 4 ) 1 9 e2 8
26
One of the project objectives was to achieve a 30% reduc-
tion of energy input in the particular processes. In the present
study, it was demonstrated that the willow cultivar chosen
affects to a very large degree the efficiency indicator values in
the production of lignocellulose biomass for an integrated
biorefinery. Therefore, the application of an appropriate wil-
low cultivar could allow a greater energy ratio of final product
production to be achieved. The results obtained will be helpful
in the assessment of the chip transport distance to a
biorefinery.
These data emphasise the key importance of the selection
of a willow cultivar for the production of willow chips and the
transport distance to a biorefinery for the energy intensity of
the production process and the energy ratio of the biomass
supplied. From a practical point of view, this study suggests
that UWM 006 and UWM 043 cultivars can be the most useful
source of lignocellulosic feedstock for integrated biorefineries.
Moreover, when choosing a location for a biorefinery, one
should take into account the fact that transporting chips to a
biorefinery for a distance of up to 50 km can generate a loss of
up to 10%, whereas when chips have to be transported for
200 km, the decrease in the energy ratio can reach 30%
compared to its level at the farm gate.
It should be emphasised that the obtained results should
be cross-referenced to similar climatic and soil conditions. For
willow plantations situated on better quality soils and fertil-
ised with wastewater sludge or digestate from a biogas plant,
the biomass yields could be higher and lead to potentially
better biomass production efficiency indicators. On the other
hand, willow biomass production on sandy soils with water
deficiencies could result in a reduction in yield and value of
biomass production efficiency indicators.
Acknowledgements
This research received funding from the European Union
Seventh Framework Programme (FP7/2007
e2013) under grant
agreement n
241718 EuroBioRef.
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