Biofuels, Solar and Wind as Renewable Energy Systems_Benefits and Risks Episode 2 Part 5 pdf

13 Bio-Ethanol Production in Brazil 339

Buildings are regarded as having a useful life of 50 years and a maintenance en￾ergy cost of 4% per yr (Macedo, 1997). As the greatest energy input is in cement the

energy value of this material is used. As fuel costs are such a large part of manufac￾turing costs, most cement companies have aggressive energy conservation programs

and according to the International Energy Program (IEA, 1999) new manufacturing

plants have reduced energy use by between 25 and 40% compared to 10–15 years

ago. The report by the IEA (1999) gives a value of 6.61 GJ for the energy required

to produced 1 Mg of cement, and other recent reports (Young et al., 2002 and Wor￾rell and Galitsky, 2004) give somewhat lower values of 4.35 and 6.1 GJ Mg−1. We

use the former higher value of 6.61 GJ Mg−1. So allowing for a 4% annual main￾tenance cost the total embodied energy for all buildings over a 50 year period is

(1,600 + (0.04 × 50 × 1,600)) U 6.61 GJ which becomes 31,730 MJ or 634.6 MJ yr ´ −1.

As we assume that the mill serves to grind one third of 2 million Mg of cane per year,

this becomes 0.952 MJ Mg cane milled, or 75.9 MJ ha−1 yr−1 (Table 13.7).

For the mild steel in the mill/distillery we have assumed that one third is in

light equipment and thus subject to more wear and will have a lower useful life

Table 13.7 Energy in the buildings and construction of a standard mill/distillery. Design capacity

2 million Mg year, running at 33% capacity. Methodology for the calculation of the fossil, energy

inputs follows that of Pimentel (2007)

Mass a Useful

lifeb

Including

maintenancec

Including

on-site

energy

utilisationd

per year kg/ha/

year

Total

energy

Mg yr Mg Mg kg kg MJ/ha/yr

Cement in buildings 1600 50 4800.0 5000.0 100000 11.49 75.9

Mild steel

(structural)

2873 25 5746.0 6105.1 244205 28.06 841.8

Mild steel in light

equipment

1437 10 2011.8 2191.4 201180 23.12 693.5

Stainless steel 410 25 820.0 871.3 34850 4.00 287.1

1898.3

Basic data on standard cane Factory

Mg cane harvested by factory 666667 yr−1

Area harvested by factory 8703.2 ha

Energy in cement (MJ/kg)e 6.61

Energy in Steel (MJ/kg)f 30.0

Energy in stainless steel (MJ/kg)g 71.7

a Data from Dedini S.A.. Piracicaba. Sao Paulo. ˜ b According to Macedo et al. (2003).

c Maintenance energy cost of 4% per year.

d 12.5% of mass of each component (Hannon et al. 1978).

e From IEA (1999).

f From Worrel et al. (1997).

g Embodied energy in stainless steel = 2.39 × energy in mild steel

(Pimentel and Patzek, 2007).

340 R.M. Boddey et al.

(10 yrs – Macedo, 1997). The remaining two thirds is considered to be in the struc￾ture of the mill, equipment and distillery, and thus will have a longer useful life

(25 years). The same calculations have been made in the same way as for the cement

in buildings but the embodied energy in mild steel was considered to be 30 MJ kg−1

as justified in Section 13.3.1.4 above.

The data for the standard mill provided by Dedini S.A. show that 410 Mg of stain￾less steel was used, mainly in the distillery columns. Pimentel and Patzek (2007)

give the embodied energy in stainless steel to be 2.39 times that in mild steel, so the

value of 71.7 MJ kg−1 was used for this material. The useful life of this material was

assumed to be 25 years. The energy input for stainless steel in the factory was again

calculated using the same procedure as for cement (Table 13.7).

Finally to account for on-site energy utilised in the construction, all values were

increased by 12.5% as suggested by Hannon et al. (1978). The total energy require￾ment for factory buildings and equipment totalled 1898 MJ ha−1 yr−1 (Table 13.7).

13.3.1.7 Energy Balance

The details of all fossil energy inputs calculated as described in Sections 13.3.1.1–

13.3.1.6 above, are displayed in Table 13.4. The total energy yield of the annual

mean per ha ethanol yield of 6,281 L, becomes 134,815 MJ ha−1 (1 L of ethanol

yields 21.46 MJ L−1 – Pimentel, 1980).

Within the fossil energy inputs in the agricultural operations, fertilisers, espe￾cially N fertiliser, are responsible for the largest contributions. The fact that in Brazil

N fertiliser use is far lower than in just about any other cane growing area in the

world, makes an important economy. If for example 150 kg N ha−1 yr−1 (typical of

most other countries) were used instead of the estimated 56.7 kg, the energy input

would rise from 3060 to 8100 MJ ha−1 yr−1 increasing the total energy input in agri￾cultural operations (including transport of cane and consumables) by 43%.

Because of their complicated synthesis herbicides are extremely energy intensive

and even though only a mean of 3.2 kg a.i. ha−1 yr−1 are applied, this is the second

most important consumables input after fertilisers.

Brazil is fortunate in that most of the country has over 1,000 mm of rainfall a

year, and the most productive cane-growing areas have over 1,300 mm of rain. For

this reason only a very small area is irrigated so that there is effectively no energy

input for irrigation.

The comparatively large input of fossil energy in the manufacture of agricultural

machinery, and to a lesser extent, of human labour, show the importance of includ￾ing these inputs, which is not universal practice in computing such balances (e.g.

Sheehan et al., 1998; Shapouri et al., 2002)

As all factory energy is supplied by bagasse, the main fossil energy input (es￾timated to be ∼1,900 MJ ha−1 yr−1) is in the infrastructure of the construction and

maintenance of structure and equipment of the factory. All factories are built near

abundant water supplies (usually rivers) and pumping comes from electricity gener￾ated from bagasse, and thus involves minimal fossil energy inputs.