Environmental Engineering Reference
In-Depth Information
Table 1.10
Efficiencies for Biomass Production
Oceans
0.07%
Woods
0.55%
Fresh water
0.50%
Maize
3.2%
Man-made landscape
0.30%
Sugarcane
4.8%
Grassland
0.30%
Sugar beet
5.4%
H
2
O
+
O
2
+
metabolic
+
CO
2
+
substances
+
+
H
2
O
∆
E
C
k
H
m
O
n
products
Biomass
(1.7)
Dyes such as chlorophyll split water molecules H
2
O using the energy
E
of
the visible sunlight. The hydrogen H and the carbon dioxide CO
2
taken from
the air form biomass C
k
H
m
O
n
. Oxygen O
2
is emitted during that process.
Biomass can be used for energy in various ways. Such use converts biomass
back again to CO
2
and H
2
O. However, this conversion emits as much CO
2
as
the plant had absorbed from the atmosphere while it was growing. Biomass is
a carbon dioxide-neutral renewable energy source as long as the resource is
managed sustainably.
A comparison of biomass production with other energy conversion
processes is based on the estimated efficiencies of various plants. This efficiency
describes what percentage of solar energy is converted to biomass. The average
efficiency of global biomass production is about 0.14 per cent.
Table 1.10 shows some specific efficiencies of different methods of biomass
production. The efficiency is calculated based on the calorific values given in
Table 1.11 of the biomass grown in a certain area over a given time, which is
then divided by the solar energy incident in this area during the same period of
time.
Biomass usage can be classified as use of organic waste or agricultural
residues and the cultivation of purpose-grown energy plants. Biomass can be
used, for instance, in combustion engines, typically combined heat and power
(CHP) plants. These CHP plants are usually smaller than large conventional
coal or gas power plants, because it is important to minimize biomass
transportation distances. Therefore, these power plants usually have a capacity
of a few MW. Figure 1.18 shows a power station that is fired with residues
from olive oil production.
Table 1.11
Calorific Values of Various Biomass Fuels
Fuel (anhydrous)
Lower calorific value (LCV)
Fuel (anhydrous)
LCV
Straw (wheat)
17.3 MJ/kg
China reed
17.4 MJ/kg
Non-flowering
Colza oil
37.1 MJ/kg
plants (wheat)
17.5 MJ/kg
Ethanol
26.9 MJ/kg
Wood without bark
18.5 MJ/kg
Methanol
19.5 MJ/kg
Bark
19.5 MJ/kg
Petrol (for comparison) 43.5 MJ/kg
Wood with bark
18.7 MJ/kg
