Environmental Engineering Reference
In-Depth Information
P
¼
4
p
R
2
s
SB
T
4
, where the Stefan
-
Boltzmann constant
s
SB
¼
5.67
10
8
W/ m
2
K
4
.
This is evaluated as
10
27
W
P
¼
1
:
47
:
In the simplest view, this suggests that the original heat energy could be radiated
away in about 42 h, since 42
U. But the radiative cooling quickly slows
as the temperature falls, and the linear approach fails. At present, the inner core
temperature has been estimated as 5700 K, while lava (magma) at temperatures
3600
P
¼
1500 K is present at some locations as close as 10 km to the earths surface. The
remaining heat energy in the earths core is, of course, enormous and certainly can be
regarded as a renewable resource.
Practical extraction of the earths heat is accomplished at locations where molten
lava extends close to the surface, providing regions of hot rock that are used to heat
injected water to produce steam. U.S. capacity of this type is 3.09 GW, with the largest
facility at The Geysers
field (http://www.gwpc.org/meetings/forum/2007/proceed-
ings/Papers/Khan,%20Ali%20Paper.pdf.) in CA. Iceland has exploited its geother-
mal energy to a great extent. A map (http://www.magma-power.com/pages/mag-
ma_power_plant.html.) of locations in the United States where magma exists within
10 km of the surface reveals sites concentrated in western states and along the
Aleutian Islands. While plant designs have been offered for tapping directly into a
lava field, this has not been accomplished.
1.1.3.3 The Earth
s Deuterium and its Potential
Fusion of light elements to release energy is the heating mechanism of the sun. A
good starting point for fusion is the deuteron, two of which can fuse tomake
4
He with
release of nearly 24MeV of energy. The most likely products for DD fusion are
actually a triton plus a proton, with 4MeV; or
3
He plus a neutron, with 3.27MeV, so
that the average energy release per DD fusion is 3.7MeV. The deuteron fusion
reactions are considered important because D particles, Deuterons, are present on
earth, notably in seawater. Wherever protons occur, there is about 1/6400 chance of
finding instead a Deuteron. Heavy water HDO, therefore, occurs as 1/3200
0.031%
of all water. There is enough in the ocean that this is considered a sustainable or
renewable energy source. The problem is that at present there is no practical process
using Deuterons to actually release energy by the fusion reactions.
If we take the ocean mass as 1.37
¼
10
21
kg, comparing it with the mass per water
10
27
kg, we
nd that there are N
10
46
watermolecules
molecule, 18
1.67
¼
4.6
10
46
H atoms, and therefore there are
in the ocean. This means there are 9.2
10
43
deuterons. The energy release, if all of these deuterons were fused at the
average energy release of 3.7MeV, is therefore 1.42
1.42
10
43
10
6
3.27
1.6
10
19
J
10
30
J. If the present energy consumption is 14.7 TW, so that one
years energy consumption is 4.63
¼
7.45
10
20
J, the deuteron-based energy would last for
10
10
years. So, wemay say that the deuteriumin the ocean, if it can be converted,
is a renewable resource. InChapter 4 of the topic, we will look into the possibilities for
achieving this release of energy.
1.6
