Exercise 4.1
Assume that your
friend living in California has just ordered a gold wedding ring weighing 6 g.
Since it is the week before the wedding(!), the ring must be flown 10,000 km by
plane from the Netherlands (where it was made) to California. The manufacturing
of the ring requires an electricity consumption of 2 kWh per kilogram of gold
and it will eventually be buried (equivalent to being landfilled for this example).
Assuming an FU of one ring over the course of one marriage, calculate the
reference flows, nonrenewable energy use, and CO2 emissions over the whole life
cycle. Fill in all missing values in Table 4.14.
Life Cycle Stage
|
Process
|
Unit
|
Energy (MJ/unit)
|
CO2 (kg/unit)
|
Reference Flow
(unit/FU)
|
Energy (MJ/FU)
|
CO2 (kg/FU)
|
Raw materials extraction
|
Gold
|
kg
|
269000
|
16500
|
0,006
|
1614
|
99
|
Fabrication
|
Electricity
|
kWh
|
10,71
|
0,66
|
0,012
|
0,12852
|
0,00792
|
Transport
|
By airplane
|
ton-km
|
16,23
|
1,06
|
0,06
|
0,9738
|
0,0636
|
Elimination
|
Landfill
|
kg
|
0,2
|
0,01
|
0,006
|
0,0012
|
0,00006
|
Total
|
1615,10352
|
99,07158
|
Exercise 4.3
Consider
the hand-drying scenarios discussed in Chapter 3. Use the reference flows and
flowchart from Exercise 3.2 and the emission factors from Table 4.15. Assume that
the manufacturing energy for both devices accounts for less than 1% of total
life cycle energy consumption and emissions.
1.
Using Table 4.15, estimate the
nonrenewable primary energy used and the CO2 emissions due to each hand-dryer
scenario (fill in Table 4.16).
2.
For each process and for the sum of all
processes, calculate the rasio of CO2 emissions to nonrenewable primary energy.
Check if the values obtained for each ratio are consistent with typical values
shown in Figure 4.2.
3.
Now assume that the wastepaper towels,
when incinerated, produce 18 MJ of energy per kilogram burned, 20% of which is
recovered as usable electricity. Calculate how much nonrenewable primary energy
you avoid per kilogram of paper burned, and use this to calculate the avoided
energy per FU in the table.
4.
Which scenario is better for energy and
CO2? Which stages of the life cycle and which components are most important?
What is the importance of the paper towel dispenser or of the electric dryed compared
with the other life cycle stages?
Exercise 3.2: Paper Towels or
Hot-Air Dryer?
Use
LCA to compare the use of paper towels in a public restroom with that of a
hot-air dryer. Many key assumptions and parameter values are provided as bullet
points and in Table 3.6. Use the forms IV.2 through IV.4 in Appendix IV to
a.
Describe the function and any secondary functions of the system.
b.
Choose an FU that represents the function of the system.
c.
For each case, list the reference flows and key parameters corresponding to the
selected FU.
d.
System boundary.
i.
Starting from the FU and the reference
flows, draw the flowchart and system boundary for each scenario; you may want
to stop when you link to the process of an existing database.
ii.
For each scenario, find a secondary
function that may save energy and draw it on the diagram.
iii.
Based on the masses of the various reference
flows involved, decide whether the transportation of the paper towel dispenser
should be included in the system boundary, and explain.
Assume
the following:
·
Fifty uses per day for both scenarios.
·
The hot-air hand-dryer device is made out
of cast iron. It is activated by a button that blows hot air for 30 s.
·
On average, 1.5 paper towels are used for
each pair of hands.
·
Manufacturing energy for towels, towel
dispenser, and air-dryer device are negligible.
Hot Air Hand Dryer
|
|||||||
Life Cycle Stage
|
Process (unit)
|
Quantity per FU (unit
per FU)
|
Energy per Unit
(MJ/unit)
|
Energy per FU (MJ/FU)
|
Emissions per Unit
(kgCO2/unit)
|
Emissions per FU
(kgCO2/FU)
|
Check (gCO2/MJ)
|
Materials
|
Steel (kg)
|
4
|
24,6
|
98,4
|
1,51
|
6,04
|
61,38211382
|
Iron (kg)
|
8
|
64,3
|
514,4
|
3,9
|
31,2
|
60,65318818
|
|
Fabrication
|
cast iron (kg)
|
-
|
|||||
Transport
|
ton-km
|
1,2
|
3,7
|
4,44
|
0,215
|
0,258
|
58,10810811
|
Use
|
kWh
|
5475
|
12,4
|
67890
|
0,703
|
3848,925
|
56,69354839
|
Elimination
|
kg
|
4
|
0,204
|
0,816
|
0,007
|
0,028
|
34,31372549
|
Avoided energy
|
kWh
|
-
|
|||||
Total
|
68508,056
|
3886,451
|
|||||
Paper Towel
|
|||||||
Life Cycle Stage
|
Process (unit)
|
Quantity per FU (unit
per FU)
|
Energy per Unit
(MJ/unit)
|
Energy per FU (MJ/FU)
|
Emissions per Unit
(kgCO2/unit)
|
Emissions per FU
(kgCO2/FU)
|
Check (gCO2/MJ)
|
Materials
|
kg
|
6
|
97,5
|
585
|
3,11
|
18,66
|
31,897436
|
Fabrication
|
kg
|
-
|
|||||
Transport
|
ton-km
|
0,6
|
3,7
|
2,22
|
0,215
|
0,129
|
58,108108
|
Use
|
kg
|
1960,05
|
17,2
|
33712,86
|
0,86
|
1685,643
|
50
|
Elimination
|
paper landfilled (kg)
|
1960,05
|
0,447
|
876,1424
|
0,015
|
29,40075
|
33,557047
|
PP landfilled (kg)
|
6
|
0,33
|
1,98
|
0,03
|
0,18
|
90,909091
|
|
Avoided energy
|
-
|
||||||
Total
|
35178,20235
|
1734,0128
|
|||||
Paper Towel (Incinerated Paper)
|
|||||||
Life Cycle Stage
|
Process (unit)
|
Quantity per FU (unit
per FU)
|
Energy per Unit
(MJ/unit)
|
Energy per FU (MJ/FU)
|
Emissions per Unit
(kgCO2/unit)
|
Emissions per FU
(kgCO2/FU)
|
Check (gCO2/MJ)
|
Materials
|
kg
|
6
|
97,5
|
585
|
3,11
|
18,66
|
31,897436
|
Fabrication
|
kg
|
-
|
|||||
Transport
|
ton-km
|
0,6
|
3,7
|
2,22
|
0,215
|
0,129
|
58,108108
|
Use
|
kg
|
1960,05
|
17,2
|
33712,86
|
0,86
|
1685,643
|
50
|
Elimination
|
incinerated paper (kg)
|
1960,05
|
0,292
|
572,3346
|
0,018
|
35,2809
|
61,643836
|
PP landfilled (kg)
|
6
|
0,33
|
1,98
|
0,03
|
0,18
|
90,909091
|
|
Avoided energy
|
incinerated paper (kg)
|
1960,05
|
-3,6
|
-7056,18
|
|||
Total
|
27818,215
|
1739,8929
|
|||||
Skenario
yang terbaik:
·
Energi : Paper Towel dengan cara eliminasi incinerated paper karena memiliki total pengeluaran energi yang
lebih kecil dibandingkan skenario yang lain.
·
CO2: Skenario paper towel dengan cara eliminasi paper landfilled merupakan skenario
terbaik dilihat dari total pengeluaran CO2 .
Exercise 4.4
Consider
the hand-drying scenarios again, but this time using the LCA I/O approach instead
of the process-based approach. Assume that the consumer prices for hand drying are
•
Paper towels: $0.01/paper towel; $25/plastic dispenser
•
Electric hand-dryer: $0.01/kWh; $350/dryer
Use
the data in Table 4.17 to estimate energy use and CO2 emissions (Table 4.18) for
each scenario. Note that the transportation to final user is not considered
here, but transportation from raw material is included in sector expenses and
impacts of each sector.
Paper towel
|
||||||||
Life Cycle Stage
|
Process (unit)
|
Cost per FU (US$/FU)
|
Energy per $ (MJ/$)
|
Energy per FU (MJ/FU)
|
Emmisions per $
(KGco2/$)
|
Emissions per FU
(KGco2/FU)
|
Check (Gco2/MJ)
|
|
Materials
|
Kg
|
50
|
23
|
1150
|
1
|
50
|
43,47826
|
|
Fabrication
|
unit
|
-
|
||||||
Use
|
Unit
|
5475
|
15
|
82125
|
0,95
|
5201,25
|
63,33333
|
|
Elimination
|
Unit
|
-
|
||||||
Total
|
142350
|
7281,75
|
||||||
Electric hand dryer
|
||||||||
Life Cycle Stage
|
Process (unit)
|
Cost per FU (US$/FU)
|
Energy per $ (MJ/$)
|
Energy per FU (MJ/FU)
|
Emmisions per $
(KGco2/$)
|
Emissions per FU
(KGco2/FU)
|
Check (Gco2/MJ)
|
|
Materials
|
Kg
|
350
|
44
|
15400
|
3
|
1050
|
68,18182
|
|
Fabrication
|
Unit
|
-
|
||||||
Use
|
kWh
|
54,75
|
93
|
5091,75
|
9,9
|
542,025
|
106,4516
|
|
Elimination
|
kg
|
|||||||
Total
|
20491,75
|
1592,025
|
||||||
