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.

Table 13.7 Emission sources in bioethanol production (Bauen, 2005)

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)

Typical Gasoline Co2

0 100 200 300 400 500 600 GHG emission (kg CO2eq./t)

Figure 13.9 Typical GHG emissions for bioethanol from wheat (Bauen, 2005)

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