Topic 8: Energy, power and climate change Flashcards
1
Q
How is thermal energy converted to work?
A
In principle, thermal energy can be completely converted to work in a single process, but the continuous conversion of this energy into work implies the use of machines that are continuously repeating their actions in a fixed cycle. Any cyclical process must involve the transfer of some energy from the system to the surroundings that is no longer available to perform useful work.
2
Q
Explain what is meant by degraded energy.
A
Energy that is unavailable to a system because it has been transferred to the surroundings.
3
Q
What happens to energy that is transferred to the surroundings?
A
It is no longer available to do work.
4
Q
What is a Sankey diagram?
A
A diagram used to represent energy conversions.
5
Q
In what direction should the main arrow in a Sankey diagram be drawn?
A
From left to right.
6
Q
What does the main arrow in a Sankey diagram represent?
A
The energy changes taking place.
7
Q
What does the width of the arrow in a Sankey diagram represent?
A
The power or energy involved at a given stage.
8
Q
What does the arrow drawn up or down in a Sankey diagram represent?
A
Degraded energy.
9
Q
Outline the principle mechanisms involved in the production of electrical power. (5)
A
- A fuel is used to release thermal energy 2. Thermal energy is used to boil water to make steam 3. Steam is used to turn turbines 4. Motion of the turbines is used to generate electrical energy by rotating coils in a magnetic field 5. Transformers alter the potential difference
10
Q
Identify different world energy sources.
A
In most instances, the Sun is the prime energy source for world energy. Other cases: - gravitational energy of the Sun and the Moon - nuclear energy stored within atoms - the Earth’s internal heat energy
11
Q
What are six renewable energy sources?
A
- hydroelectric
- photovoltaic cells
- active solar heaters
- wind
- biofuels
- geothermal
12
Q
What are four non-renewable energy sources?
A
- oil
- natural gas
- coal
- nuclear
13
Q
Which four energy sources emit carbon dioxide?
A
- coal
- natural gas
- oil
- biofuels
14
Q
Define: renewable energy source
A
Energy that comes from resources which are naturally replenished on a human time scale
15
Q
Define: non-renewable energy source
A
A resource that cannot be replaced when it is used up.
16
Q
Define: energy density
A
energy density = (energy released by fuel) / (mass of fuel consumed)
17
Q
What is the standard index measurement for energy density?
A
J kg-1
18
Q
Discuss how choice of fuel is influenced by its energy density.
A
When the fuel needs to be transported: the greater the mass of fuel that needs to be transported, the greater the cost.
19
Q
What is the energy density of coal?
A
3.3 X 107J kg-1
20
Q
What is the energy density of oil?
A
4.2 X 107J kg-1
21
Q
What is the energy density of natural gas?
A
5.4 X 107J kg-1
22
Q
What was the world’s proportional energy consumption of oil in 2003?
A
38%
23
Q
What was the world’s proportional energy consumption of natural gas in 2003?
A
24%
24
Q
What was the world’s proportional energy consumption of coal in 2003?
A
24%
25
What was the world's proportional energy consumption of nuclear in 2003?
6%
26
What was the world's proportional energy consumption of other resources in 2003?
8%
27
Advantages of nuclear power.
1. Extremely high energy density – a great deal of energy is released from a very small mass of uranium
2. Reserves of uranium are large compared to oil
3. Do not produce carbon dioxide
28
Disadvantages of nuclear power.
1. Process produces radioactive nuclear waste that is currently just stored
2. Larger possible risk if anything should go wrong
3. Non-renewable (but should last a long time)
29
Advantages of wind energy
1. Very clean production – no harmful chemical by-products
2. Renewable source of energy
3. Source of energy is free
30
Disadvantages of wind energy.
1. Source of energy is unreliable – could be a day without wind
2. Low energy density – a very large area would be need to be covered for a significant amount of energy
3. Some consider large wind generators to spoil the countryside because they are ugly and produce a lot of noise
31
Advantages of water energy.
1. Very clean production – no harmful chemical by-products
2. Renewable source of energy
3. Source of energy is free
32
Disadvantages of water energy
1. It has been difficult to scale up the designs for wave machines to produce large amounts of electricity.
2. Tidal barrages destroy the habitat of estuary species, including wading birds.
3. Construction of dam will involve land being buried under water and the rotting vegetation underwater releases methane, which is a greenhouse gas.
33
Advatages of solar power
1. Very clean production – no harmful chemical by-products
2. Renewable source of energy
3. Source of energy is free
34
Disadvantages of solar power.
1. Can only be utilised during the day
2. Source of energy is unreliable – could be a cloudy day
3. Low energy density – a very large area would be needed for a significant amount of energy
35
Outline the historical and geographical reasons for the widespread use of fossil fuels.
1. Industrial Revolution in Western Europe in the late 18th and 19th Centuries involved the development of large-scale manufacturing industries and the introduction of the factory as a place of work
2. Machines were designed and built, replacing manual labour
3. The industrial growth of towns and regions in the UK started a process that spread throughout the world
4. As the industrial revolution spread, the rate of energy usage increased and industry tended to develop near to existing deposits of fossil fuels
5. Once factories were established, people seeking work would tend to migrate towards the cities
6. In addition, infrastructure was created to allow coal and other fossil fuels to be transported as the higher rates of energy usage demanded the use of fuels with a high energy density
7. This encouraged the growth of industries located near the raw materials
36
Discuss the energy density of fossil fuels with respect to the demands of power stations.
Higher rates of energy usage demanded the use of fuels with a high energy density.
37
Calculate the rate of fuel consumption by a 500 MW coal power station.
1. Electrical power supply:
1. = 500MW = 5 X 108 J s-1
2. Power released from fuel
1. = (5 X 108) / (efficiency)
2. = (5 X 108 ) / (0.35)
3. = 1.43 X 109 J s-1
3. Rate of consumption of coal
1. = (1.32 X 109) / (energy density) kg s-1
2. = (1.43 X 109) / (3.3 X 107) kg s-1
3. = 43.3 kg s-1
4. = 43.3 X 60 X 60 kg hr-1
5. = 1.56 X 105 kg hr-1
6. = 160 tonnes hr-1
38
Calculate the rate of fuel consumption by a 500 MW oil power station.
1. Electrical power supply
1. = 500 MW = 5 X 108 J s-1
2. Power released from fuel
1. = (5 X 108) / (efficiency)
2. = (5 X 108) / 0.38
3. = (1.32 X 109) J s-1
3. Rate of consumption of coal
1. = (1.32 X 109) / (energy density) kg s-1
2. = (1.32 X 109) / (4.2 X 107) kg s-1
3. = 31.4 kg s-1
4. = 31.4 X 60 X 60 kg hr-1
5. = 1.13 X 105 kg hr-1
6. = 113 tonnes hr-1
39
Calculate the rate of fuel consumption by a 500 MW natural gas power station.
1. Electrical power supply
1. = 500 MW = 5 X 108 J s-1
2. Power released from fuel
1. = (5 X 108) / efficiency
2. = (5 X 108) / 0.45
3. = (1.11 X 109) J s-1
3. Rate of consumption of coal
1. = (1.11 X 109) / energy density kg s-1
2. = (1.11 X 109) / (5.4 X 107) kg s-1
3. = 20.6 kg s-1
4. = 20.6 X 60 X 60 kg hr-1
5. = 7.40 X 104 kg hr-1
6. = 74 tonnes hr-1
40
Advantages of fossil fuels (5)
1. Very high energy density – a great deal of energy is released from a small mass of fossil fuel
2. Fossil fuels are relatively easy to transport
3. Still cheap when compared to other sources of energy
4. Can be built anywhere with good transport links and water availability
5. Can be used directly in the home to provide heating
41
Disadvantages of fossil fuels (5)
1. Combustion products can produce pollution, notably acid rain
2. Combustion products contain greenhouse gases
3. Extraction of fossil fuels can damage the environment
4. Non-renewable
5. Coal-fired power stations need large amounts of fuel
42
Efficiency of coal
35%
43
Efficiency of natural gas
45%
44
Efficiency of oil
38%
45
Describe the environmental problems associated with the recovery of fossil fuels and their use in power stations.
1. Coal can be obtained through underground mines (tunneling) or open cut or strip mining.
1. Mines must be ventilated so that poisonous and flammable gases can escape
2. Particulate matter has to be pumped to the surface
3. Cave-ins in discontinued mines have caused hazards to land and surface structures above the mines
2. Environment damage can still be caused by oil blowouts when the pressure of reservoir exceeds the pressure of the drill hole.
3. The key problem with the burning of fossil fuels is the release of pollutants. Carbon dioxide and carbon monoxide are major pollutants introduced by fossil-fueled power stations. Carbon monoxide is a poisonous gas that reduces the blood’s capability of transporting Oxygen. Carbon Dioxide is a greenhouse gas that contributes to global warming. Other major pollutants are sulfur dioxide and oxides of nitrogen. Power stations can reduce emissions in the form of silica and metallic oxides, silicates, and sulfates.
46
Define: nuclear fission
The nuclear reaction whereby large nuclei are induced to break up into smaller nuclei and release energy in the process. It is the reaction that is used in nuclear reactors and atomic bombs.
47
Describe how neutrons produced in a fission reaction may be used to initiate further fission reactions (chain reaction).
1. A typical single reaction might involve bombarding a uranium nucleus with a neutron
2. This can cause the uranium nucleus to break up into two smaller nuclei
3. Since the original neutron causing the reaction has resulted in the production of three neutrons, there is the possibility of a chain reaction occurring
4. These three neutrons that have been produced will then go on to bombard a further three uranium nuclei
48
What does the chance that a given neutron will go on to cause a fission reaction depend on?
1. The number of potential nuclei in the way
2. The energy of the neutrons; only low-energy neutrons (≈ 1 eV) favour nuclear fission.
3. When a critical mass of fuel has been assembled, a chain reaction can occur.
49
Distinguish between controlled nuclear fission (power production) and uncontrolled nuclear fission (nuclear weapons).
1. A nuclear reactor controls the fission process, ensuring that only one neutron from each reaction goes on to initiate a further reaction. If more reactions took place, the number of reactions would increase all the time and the chain reaction would go out of control. If fewer reactions took place, the number of reactions would decrease and the fission process would stop
2. A nuclear power station involves controlled nuclear fission, whereas an uncontrolled nuclear fission produces the huge amount of energy released in nuclear weapons. Weapons have been designed using both uranium and plutonium as the fuel.
50
Outline issues associated with nuclear warfare
1. Aggression associated with warfare - nuclear weapons have such destructive capability that since the Second World War the threat of their deployment has been used as a deterrent to prevent non-nuclear aggressive acts against the possessors of nuclear capability
2. Potential for nuclear holocaust- has forced many countries to agree to non-proliferation treaties, which attempt to limit nuclear power technologies to a small number of nations
3. By product of peaceful use of uranium for energy production is plutonium-239 - could be used for the production of nuclear weapons
51
Define: fuel enrichment
The process by which the percentage composition of uranium-235 in naturally occurring uranium (1%) is increased to make nuclear fission more likely.
52
Describe the main energy transformations that take place in a nuclear power station.
nuclear energy → thermal energy → kinetic energy (→ thermal energy dissipated) → electrical energy
53
Discuss the role of the moderator in the production of controlled fission in a thermal fission reactor.
Collisions between the neutrons and the nuclei of the moderator slow them down and allow further reactions to take place.
54
Discuss the role of the control rods in the production of controlled fission in a thermal fission reactor.
Moveable rods that readily absorb neutrons. Can be introduced or removed from the reaction chamber in order to control the chain reaction.
55
Discuss the role of the heat exchanger in a fission reactor.
Allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. The reactions increase the temperature in the core. This thermal energy is transferred to heat water and the steam that is produced turns the turbines.
56
Describe how neutron capture by a nucleus of uranium-238 (238U) results in the production of a nucleus of plutonium-239 (239Pu).
1. Plutonium-239 is capable of sustaining fission reactions.
2. Is formed as a by-product of a conventional nuclear reactor.
3. A uranium-238 nucleus can capture fast moving neutrons to form uranium-239, which undergoes β-decay to neptunium-239.
4. This then undergoes further β-decay to form plutonium-239:
1. 23892U + 10n → 23992U
2. 23992U → 23993Np + 0-1β + ν
3. 23993Np → 23994Pu + 0-1β + v
57
Describe the importance of plutonium-239 (239Pu) as a nuclear fuel.
Reprocessing involves treating used fuel waste from nuclear reactors to recover uranium and plutonium and to deal with other waste products.
Plutonium-239 is used in other types of reactors. A fast breeder reactor is one design that utilises plutonium-239.
58
Discuss safety issues and risks concerning nuclear power
1. The possibility of thermal meltdown - If the control rods were all removed, the reaction would rapidly increase its rate of production. Completely uncontrolled nuclear fission would cause an explosion and thermal meltdown of the core. The radioactive material in the reactor could be distributed around the surrounding area, causing many fatalities
2. Problems associated with nuclear waste - Much of this waste is of a low level risk and will radioactively decay within decades. However, a significant amount of material is produced that ill remain dangerously radioactive for millions of years. The current solution is to bury this waste in geologically secure sites
3. Problems associated with the mining of uranium - Uranium fuel is mined from underground and any mining operation involves significant risk. The ore is also radioactive so extra precautions are necessary to protect the workers involved in uranium mines
4. The possibility that a nuclear power programme may be used as a means to produce nuclear weapons
5. Maintaining and confining a high-temperature, high-density plasma - Temperature and density must be high enough to ionise atomic hydrogen into a plasma state where electrons and protons are not bound by atoms, but move independently
59
Define: photovoltaic cell
Converts a portion of the radiated energy directly into a potential difference. Uses a piece of semiconductor to do this. A typical photovoltaic cell produces a very small voltage and it is not able to provide much current. Using them in series would generate higher voltages and several in parallel can provide a higher current.
60
Uses of photovoltaic cells.
To run electrical devices that do not require a great deal of energy.
61
Energy transfers in a photovoltaic cell.
solar energy –photovoltaic cell→ electrical energy
62
Define: active solar heater
Designed to capture as much thermal energy as possible. Uses thermal energy to heat water directly.
63
Uses of solar heating panels
Hot water produced can be used domestically and would save on the use of electrical energy.
64
Energy transfers in solar heating panels
solar energy –solar heating panel→ thermal energy in water
65
Outline reasons for seasonal and regional variations in the solar power incident per unit area of the Earth's surface.
1. Weather conditions – affect scattering and absorption of rays
2. Differences in latitude – different latitudes receive different amounts of solar radiation
3. Seasons – affect how spread out the rays that are incident on Earth become
66
What is the source of energy in hydroelectric power?
The gravitational potential energy of water. If water is allowed to move downhill, the flowing water can be used to generate electrical energy.
67
How does water in a hydroelectric power station gain energy?
1. As part of the water cycle, water can fall as rain. It can be stored in large reservoirs as high up as is feasible
2. Tidal power schemes trap water at high tides and release it during a low tide
3. Water can be pumped from a low reservoir to a high reservoir. Although the energy used to do this pumping must be more than the energy gained when the water flows back down hill, this pumped storage system provides one of the few large scale methods of storing energy
68
What are different hydroelectric schemes based on?
* water storage in lakes
* tidal water storage
* pump storage
69
Describe the main energy transformations that take place in hydroelectric schemes.
gravitational potential energy of water → kinetic energy of water → kinetic energy of turbines → electrical energy
70
Outline the basic features of a wind generator.
Blades, turbine, generator
71
Describe the main energy transformations that take place in wind turbines.
solar energy –heating Earth→ kinetic energy of wind → kinetic energy of turbine → electric energy
72
Determine the power that may be delivered by a wind generator, assuming that the wind kinetic energy is completely converted into mechanical kinetic energy.
The area swept out by the blades of the turbine
= A = π r2
In one second the volume of air that passes the turbine
= v A
So mass of air that passes the turbine in one second
= v A ρ
Kinetic energy available per second
= 12mv2
= 12(vAρ)v2
= 12Aρv3
Power
= Et
= E1
Therefore, the power available
= 12Aρv3
73
Define: oscillating water column
A device built on land. Incoming waves force air in and out of a turbine that generates electrical energy. The design of the Wells turbine means that it generates electrical energy whatever the direction of flow of the air.
74
Describe the principle of operation of an oscillating water column (OWC) ocean-wave energy converter.
1. Wave capture chamber set into a rock face
2. Tidal power forces water into the chamber
3. Air is alternately compressed and decompressed by the oscillating water column
4. Rushes of air drive the Wells turbine, generating electrical power
75
How can energy be extracted by water waves?
* Pelarmis
* Buoys
* Directly to turn turbines
* Oscillating water column
76
Define: albedo
The fraction of the radiation received by a planet that is reflected straight back into space.
77
Symbol for albedo.
The fraction of the radiation received by a planet that is reflected straight back into space.
78
State factors that determine a planet's albedo.
* Season (cloud formations)
* Latitude
79
Compare the albedo of the oceans and snow
Oceans have a low value but snow a high value.
80
What is the global mean albedo on Earth?
The global annual mean albedo is 0.3 (30%) on Earth.
81
Describe the greenhouse effect.
1. Short wavelength radiation is received from the Sun
2. This causes the surface of Earth to warm up
3. Earth will emit infrared radiation
4. Some of this infrared radiation is absorbed by gases in the atmosphere
5. This trapped infrared radiation is then re-radiated in all directions
82
Identify the main greenhouse gases and their sources.
1. Methane, CH4 – principal component of natural gas and product of decay, decomposition and fermentation; livestock and plants produce significant amounts
2. Water vapour, H2O – small amounts in upper atmosphere
3. Carbon dioxide, CO2 – combustion releases carbon dioxide into the atmosphere, which can significantly increase the greenhouse effect
4. Nitrous oxide, N2O – livestock and industries are major sources; can remain in the atmosphere for long periods
83
Explain the molecular mechanisms by which greenhouse gases absorb infrared radiation.
Greenhouse gases absorb infrared radiation as a result of resonance. The natural frequency of oscillation of the bonds within the molecules of the gas is the infrared region. If the driving frequency from the radiation emitted from the Earth is equal to the natural frequency of the molecule, resonance will occur. The amplitude of the molecules' vibrations increases and the temperature will increase. The absorption will take place at specific frequencies depending on the molecular bonds.
84
Define: black body radiation
Radiation from a black-body or perfect emitter.
85
State the Stefan-Boltzmann Law.
total power radiated by a perfect emitter ∝ T4
P=σAT4
Where:
P is total power radiated by a black-body in W
σ is the Stefan-Boltzmann constant = 5.6710-8W m-2 K-4
A is surface area of the emitter in m2
T is absolute temperature of the emitter in K
86
Define: emissivity
The ratio of power radiated per unit area by an object to the power radiated per unit area by a black body at the same temperature. As a ratio it has no units.
87
Symbol for emissivity.
ε
88
Defining equation for emissivity.
ε = (power radiated by object per unit area) / (power radiated per unit area by a perfect emitter at the same temperature)
89
Define surface heat capacity, CS.
The energy required to raise the temperature of unit area of a planet's surface by one degree.
It is measured in J m-2 K-1.
90
Defining equation for surface heat capacity
CS = energy temperature change of surface × area of surface
91
Describe some possible models of global warming
1. Changes in the composition of greenhouse gases in the atmosphere - could be caused by natural effects or could be caused by human activities
2. Changes in the intensity of the radiation emitted by the Sun linked to, for example, increased solar flare activity
3. Cyclical changes in the Earth’s orbit and volcanic activity
92
Define: enhanced greenhouse effect
An increase in the greenhouse effect caused by human activities
93
What is the likely major cause of the enhanced greenhouse effect?
It is likely that the increased combustion of fossil fuels is the major cause of the enhanced greenhouse effect.
94
Describe the evidence that links global warming to increased levels of greenhouse gases.
Russian Antarctic base at Vostok
* Each year’s new snowfall adds another layer to the ice
* Isotopic analysis allows the temperature to be estimated and air bubbles trapped in the ice cores can be used to measure the atmospheric concentrations of greenhouse gases
* Record provides data from up to 420,000 years to the present
* Variations of temperature and carbon dioxide are very closely correlated
* Produces evidence of atmospheric composition and mean global temperatures
95
Outline some of the mechanisms that may increase the rate of global warming.
1. Global warming reduces ice/snow cover, which in turn reduces the albedo. This will result in an increase in the overall rate of heat absorption
2. Temperature increase reduces the solubility of CO2 in the sea and thus increases atmospheric concentrations
3. Continued global warming will increase both evaporation and the atmosphere’s ability to hold water vapour. Water vapour is a greenhouse gas
4. Regions with frozen subsoil exist (called tundra) that support simple vegetation. An increase in temperature may cause a significant release of trapped CO2
5. Not only does deforestation result in the release of further CO2 into the atmosphere, the reduction in number of trees reduces carbon fixation
96
Define: coefficient of volume expansion
Records the fractional change in volume per degree change in temperature.
97
Defining equation for coefficient of volume expansion.
ɣ=(ΔV) / (V0Δθ)
Where:
ΔV is the increase in volume in m3
Δθ is the increase in temperature in K or °C
V0 is the original volume in m3
ɣ is the coefficient of volume expansion in K-1 or °C-1
98
Reasons for a predicted rise in mean sea level.
* Warming the ocean - thermal expansion
* Loss of ice by melting glaciers and ice sheets
* Reduction of liquid water storage on land
99
Why are precise predictions for rising sea levels are difficult to make?
* anomalous expansion of water
* different effects on ice melting on sea water compared to ice melting on land
100
Identify some possible solutions to reduce the enhanced greenhouse effect.
* Advances in technology could be utilised to ensure:
* greater efficiency of power production
* decarbonising exhaust gases from power plants (carbon dioxide capture and storage
* fusion reactors are made operational
* Reduction of energy requirements by:
* improving thermal insulation in homes
* reducing journeys and using more energy efficient methods of transport such as hybrid vehicles
* use of combined heating and power systems
* Replacing the use of coal and oil:
* with renewable energy sources and/or nuclear power to eliminate emissions
* with natural gas to reduce emissions
* Planting new trees and ensuring existing forests are maintained
101
Discuss the Intergovernmental Panel on Climate Change
The World Meteorological Organisation and the United Nations Environment Programme established the IPCC in 1988. Hundreds of governmental scientific representatives from more than 100 countries regularly assess the up to date evidence from international research into global warming and human induced climate change.
102
Discuss the Kyoto Protocol
This is an amendment to United Nations Framework Convention on Climate Change. By signing the treaty, countries agree to work towards achieving a stipulated reduction in greenhouse gas emissions. Although over 160 countries have ratified the protocol, some significant industrialised nations have not signed, including the United States and Australia. Some other countries such as India and China, which have ratified the protocol, are not currently required to reduce their carbon emissions.
## Footnote
103
Discuss the Asia-Pacific Partnership on Clean Development and Climate
Six countries (Australia, China, Japan, Korea and the USA) that represent approximately 50% of the world’s energy use have agreed to work together and with private sector partners to meet goals for energy security, national air pollution reduction and climate change in ways that promote sustainable economic growth and poverty reduction.
104
