Climate impacts of bioethanol
For bioethanol, in figure 13.7 five variants of feed-stocks are shown with results ranging from minus 30 to 110 percent. The worst case is corn. Grain and sugar beet follow. Sugar cane and wood are best suited. The positive results using wood as a feedstock are for the gasification of wood and the transformation of the resulting process gas into ethanol by a Fischer-Tropsch synthesis (2nd generation biofuels - see table 13.5). On average about 60 percent as compared with fossil-fuel generated CO2 emissions would result if bioethanol is applied.
120,0
100,0
80,0
60,0
20,0
100,0
80,0
60,0
20,0
- Figure 13.7 GHG effects of biofuel production (Bauen, 2005)
Bioethanol production from corn as a feed-stock is connected with high inputs of agrochemicals and pesticides, but also with high power needs for the production. Wheat and sugar beet are in the medium range.
Sugar cane is the basic feed-stock for the Brazilian Proâlcool bioethanol programme. This is due to favourable cultivation conditions which pre-dominate in the Brazilian climate where a large part of solar radiation is transformed into plant biomass and hence into the energy source of bioethanol production. An energy output of bioethanol of about 85.5 GJ/ha from energy input of nearly 32.7 GJ per hectare (see figure 13.8) was reported in 1990. This is an energy input/energy output ratio of 2.6:1. Recently a much better ratio of 8.3 was documented for Brazil (Szwarc, 2004).
- Figure 13.8 Energy budget of bioethanol in Brazil (in GJ/ha) (Soyez, 1990)
The LCA after a "well-to-wheel" approach indicates that even the GHG efforts for the long distance transport from South America to Europe do not compensate for the positive effects.
A more detailed analysis of the GHG emissions of the bioethanol production from wheat is given in table 13.7. It contains every process step and a range of concrete GHG emission values as well as the key variables which influence the process result.
|
Source of emission |
Emission kg CO2-eq./t bioethanol |
Key variables | |
|
minimal |
maximal | ||
|
Feedstock-production | |||
|
Land use change |
0 |
>1,000 |
Type of vegetation replaced (only significant where deforestation or vegetation changes occur) |
|
Fertilizer manufacture |
0 |
450 |
Type of fertilizer, fertilizing regime, crop yield, co-products |
|
Emissions from soil |
0 |
100 |
Soil conditions, climate, fertilizer applied, co-products |
|
Fossil fuel used for cultivation |
60 |
180 |
Tillage methods, tractor efficiency, co-products |
|
Fossil fuel used for drying and storage |
10 |
100 |
Farm equipment, energy used for drying, co-products |
|
Transportation and processing | |||
|
Fossil fuel for transportation |
20 |
50 |
Distance from farm, mode of transport 0, if renewable fuels are used |
|
Transportation of product (Bioethanol) |
20 |
80 |
Distance from farm to process, mode of transport |
|
Processing | |||
|
Fossil fuel used for processing such as crushing, cleaning, drying |
50 |
250 |
Type of crusher, moisture content, fuel used to power crusher, co-products |
|
Hydrolysis, fermentation, distillation |
-700 |
550 |
Type of process, export of heat and/or electricity |
|
Total range |
-540 |
>2,900 | |
|
Unleaded gasoline |
3,135 | ||
The resulting GHG emissions range from -540 to more than 2,900 kg CO2-eq./t bioethanol produced. Extremes are unlikely but possible. Typical values for bioethanol from wheat under British conditions are given in figure 13.9. They sum up to about 1.250 kg CO2-eq./t which is about 40 percent the value of gasoline.
Fertilizer On-farm fuel use Other cultivation Transport (50 km) Pre-processing Processing Transport to end user (225 km)
Fertilizer On-farm fuel use Other cultivation Transport (50 km) Pre-processing Processing Transport to end user (225 km)
0 100 200 300 400 500 600 GHG emission (kg CO2eq./t)
Figure 13.9 Typical GHG emissions for bioethanol from wheat (Bauen, 2005)
Guide to Alternative Fuels
Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.
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