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Option F :Fuels and Energy

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1 Option F :Fuels and Energy
The developments of human society has been directly related to the ability to use and manipulate fuels for energy production. This option considers the chemical principles and environmental issues associated with the use of fossil fuels, and nuclear and solar energy.

2 Desirable characteristics of energy sources.
These include energy released at reasonable rates (neither too fast nor too slow) and minimal pollution.

3 Current and potential energy sources.
fossil fuels, nuclear (fission and fusion), electrochemical cells, solar energy alternative sources (eg wind, tidal, geothermal).

4 Fossil Fuels Fossil fuels originated from the decay of living organisms millions of years ago, and account for about 80% of the energy generated in the U.S. The fossil fuels used in energy generation are: Natural gas, which is % methane (CH4). Liquid hydrocarbons obtained from the distillation of petroleum. Coal - a solid mixture of large molecules with a H/C ratio of about 1.

5 Coal: Supply and Demand
Coal exists in many forms therefore a chemical formula cannot be written for it. Peat- Low carbon content, heat High Moisture Lignite- 40% moisture low energy value Sub-bituminous- 30% moisture used for heat Bituminous-86% Carbon industrial/domestic use Anthracite- 98% Carbon, burns with blue flame

6 Sources of Coal

7 Problems with Fossil Fuels
Fossil fuels are nonrenewable resources. At projected consumption rates, natural gas and petroleum will be depleted before the end of the 21st century. Impurities in fossil fuels are a major source of pollution. Burning fossil fuels produce large amounts of CO2, which contributes to global warming.

8 Describe how the burning of fossil fuels produces pollutants.
The primary pollutants are CO, CO2, SO2, NOx, particulates (fly ash) and hydrocarbons.

9 Coal Cleaning Gasification - Coal is converted to synthetic gas. It is carried out in 4 steps: devolatilization, steam-carbon reaction, CO-shift reaction, and catalytic methanation. Devolatilization - Coal is exposed to high temperatures and the volatile matter is released and decomposes to methane and char. Steam-Carbon Reaction - Addition of hydrogen in the form of water (steam) reacts with the char. C + H2O  CO + H2

10 Coal Cleaning CO-Shift Reaction - Some of the carbon monoxide is reacted with more steam, to form more hydrogen. CO + H2O  CO2 + H2 Catalytic Methanation - The additional hydrogen is then caused to react with the remaining carbon monoxide. CO H2  H2O + CH4

11 FeO is regenerated by the process.
Coal Cleaning Claus Process - During gasification sulfur is leaves the system as H2S gas. It is converted to free sulfur, S, which can be sold as a by-product. (1) H2S + FeO  FeS + H2O (2) 2 FeS O2  2 FeO SO2 (3) 2 H2S + SO2  2 H2O S Net: 2 H2S + O2  2 H2O S FeO is regenerated by the process.

12 Coal Cleaning Liquefaction - The products from gasification, CO and H2, are further reacted to form the liquid compounds, formaldehyde (H2C=O) and methanol (CH3OH). Scrubbers - flue-gas desulfurization devices. These devices remove SO2 from combustion gases. One important scrubber is limestone (CaCO3). CaCO3 + SO2  CaSO3 + CO2

13 Products of Oil Distillation

14 Petroleum Fractions Fraction BP (oC) Composition Use Gas 0–20
CH4-C4H10 Fuel Pet ether 20-70 C5H12,C6H14 Solvent Petrol 70-180 C6H14-C10H22 Kerosene C11H24,C12H36 Jet fuel LG Oil C13H28-C17 Diesel HG Oil C18 – C25 Powerplant Lubricant Higher C Grease Solids Pitch

15 Octane Rating Petrol fraction consists of straight-chain alkanes
Fuel burns before ignition by the spark plug – knock – loss of power, damage to engine 2,2,4-trimethylpentane: Octane =100 N-heptane: Octane = 0

16 Octane Rating Can increase octane rating for petrol fraction from 50 to 90 by 3 methods: Cracking Catalytic reforming Addition of octane enhancers like TEL, methanol, ethanol and MTBE

17 Nuclear Energy

18 Electricity - Nuclear Fusion ?

19 Distinguish between nuclear reactions and chemical reactions.
Emphasize that in nuclear reactions nuclei are converted to other nuclei, while in chemical reactions only valence electrons are involved and atoms do not change into other atoms.

20 Write balanced nuclear equations.
Both the atomic number and mass number must be balanced.

21 Describe the nature of a , b and g radiation.
Compare the charge, mass, penetrating power and behaviour in an electric field.

22 Types of Radiation alpha, beta or gamma Alpha
a = 42He2+ or 42He or 42a least penetrating can be stopped by aluminum foil > 10-3 cm, paper, skin least harmful most massive

23 Types of Radiation Beta b = 0-1e-
high energy electrons (e-) or positrons (e+) more penetrating stopped by cm of aluminum travel 10 ft through air commonly emitted by TV sets electron: 0-1b- or 0-1e- or e- positron: 0+1b- or 0+1e+ or e+

24 Types of Radiation Gamma g = energy with no mass or charge
Most penetrating radiation Stopped by cm of aluminum or thick layer of concrete or lead Lead is commonly used to enclose radioactive materials because radiation does not penetrate readily In the 1950s, it was common to build thick concrete bomb shelters

25 Types of Radiation Other particles: proton (p+ or 11p or 11H)
neutron (n or 10n) neutrino (00n) and antineutrino (00n), which have no mass or charge and accompany emission of beta particles; these are generally ignored by chemists

26 F.3.4 State the concept of half-life.
Half-life is independent of the amount of a radioactive sample.

27 F.3.5 Apply the concept of half-life in calculations.
Restrict this to whole number of half-lives.

28 F.3.6 Compare nuclear fission and nuclear fusion.

29 F.3.7     Explain the functions of the main components of a nuclear power plant.                    
Include the fuel, moderator, control rods, coolant and shielding. The materials used for the different components should be considered.

30 Reactor core We use B or Cd control rods.
105B + 10n --> 73Li + 42He

31 Diagram of Nuclear Reactor

32 Discuss the differences between conventional power generation and nuclear reactors.

33 Discuss the concerns about safety in nuclear power plants.

34 Solar Energy: The Ultimate Renewable Resource

35 What is Solar Energy? Originates with the thermonuclear fusion reactions occurring in the sun. Represents the entire electromagnetic radiation (visible light, infrared, ultraviolet, x-rays, and radio waves).

36 Advantages and Disadvantages
All chemical and radioactive polluting byproducts of the thermonuclear reactions remain behind on the sun, while only pure radiant energy reaches the Earth. Energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth have the energy equivalent of the total of all the planet’s fossil fuels, both used and unused! Disadvantages Sun does not shine consistently. Solar energy is a diffuse source. To harness it, we must concentrate it into an amount and form that we can use, such as heat and electricity. Addressed by approaching the problem through: 1) collection, 2) conversion, 3) storage.

37 Electricity - Solar Cells

38 How much solar energy? The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.

39 Putting Solar Energy to Use: Heating Water
Two methods of heating water: passive (no moving parts) and active (pumps). In both, a flat-plate collector is used to absorb the sun’s energy to heat the water. The water circulates throughout the closed system due to convection currents. Tanks of hot water are used as storage.

40 Heating Water: Active System
Active System uses antifreeze so that the liquid does not freeze if outside temp. drops below freezing.

41 Heating Living Spaces Passive Solar Trombe Wall
Passively heated home in Colorado

42 Heating Living Spaces A passively heated home uses about 60-75% of the solar energy that hits its walls and windows. The Center for Renewable Resources estimates that in almost any climate, a well-designed passive solar home can reduce energy bills by 75% with an added construction cost of only 5-10%. About 25% of energy is used for water and space heating. Major factor discouraging solar heating is low energy prices.

43 Power Towers Power tower in Barstow, California.

44 Parabolic Dishes and Troughs
Collectors in southern CA. Because they work best under direct sunlight, parabolic dishes and troughs must be steered throughout the day in the direction of the sun.

45 Direct Conversion into Electricity
Photovoltaic cells are capable of directly converting sunlight into electricity. A simple wafer of silicon with wires attached to the layers. Current is produced based on types of silicon (n- and p-types) used for the layers. Each cell=0.5 volts. Battery needed as storage No moving partsdo no wear out, but because they are exposed to the weather, their lifespan is about 20 years.

46 State how solar energy can be converted to other forms of energy.
Include chemical energy (biomass), thermal energy (passive and active methods) and electricity generation (direct and indirect methods).

47 Describe the role of photosynthesis in converting solar energy to other forms of energy.                    
Products of photosynthesis are used for food, primary fuels and conversion to other fuels, eg. ethanol. The equation for photosynthesis is required.

48 Outline the principles of using solar energy for space heating.
Example should include storage of heat by water and rocks.

49 F.4.5     Discuss the methods for converting solar energy into electricity.                    
Include parabolic mirrors and photovoltaic cells. Consider the advantages and disadvantages of each method.

50 Discuss how biomass can be converted to energy. Include :

51 Electrochemical Energy

52 Explain the workings of lead-acid storage batteries and dry cell (zinc- carbon and alkaline) batteries. Include the relevant half-equations.

53 Electrochemical Cell

54 The Alkaline Dry Cell

55 “Dry” Cell Battery Leclanche cell: anode: Zn(s) + 2e-  Zn2+(aq) + 2e-
cathode: 2NH4+(aq) + 2MnO2(s) + 2e-  Mn2O3(s) + 2NH3(aq) + H2O(l) overall: Zn(s) + 2NH4+ (aq) +MnO2(s)  Zn2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l) supplies 1.5V new; not rechargeable; voltage decreases on use (why?) Advantages and disadvantages?

56 Dry Cell Why?

57 Mercury Battery Zn(Hg)+ HgO(s)  ZnO(s) + Hg(l)

58 Fuel Cells Fuel cells :“Non-polluting” energy source (vs fossil fuels as CH4, gasoline) CH4 + 2O2(g)  CO2(g) + 2H2O(l) +energy (40% of chem energy converted into electricity)

59 Explain how a hydrogen-oxygen fuel cell works.
Include the relevant half-equations.

60 Hydrogen-Oxygen Fuel Cell

61 Cathodic Protection

62 Identify the factors that affect the voltage and power available from a battery.                    
Voltage depends primarily on the nature of the materials used while power depends on their quantity.

63 Storage of Energy and Limits of Efficiency

64 Advantages and disadvantages of energy storage schemes.
Include both pumped storage and conversion to hydrogen.

65 Electricity Main way to produce electricity now is coal.
Alternative ways to produce electricity: 1. Hydroelectric power - (falling water) - it is a renewable resource and nonpolluting however, dams are expensive, environmental and political problems. 2. Geothermal energy - (heat energy) - it is a renewable resource however, it is a very limited source, only used in Ca, and it releases some polluting chemicals.

66 Electricity 3. Wind Power - It is a primary renewable resource, however it is unreliable and intermittent. Can be used as a supplemental energy source for example to pump water up a hill into a reservoir. Then use hydroelectric power to produce electricity. 4. Tidal Power - (changing tides) - uses variations in water levels. One in France, 40 feet tides, twice a day, 5 hours each.

67 Solar Energy Ultimate energy resource is the sun. Problems include the intermittency of sunlight, available at high intensity for only 6 to 8 hours a day and only on sunny days. Solar Thermal Energy - collect the rays of the sun on a solar collector, a black absorbing surface, where it is transformed into heat energy or infrared radiation.

68 Solar Energy Photovoltaic Energy Conversion - convert solar energy directly into electricity without intermediate conversion to heat. Chief components of the cells are semiconductors, wafers of silicon with gallium or arsenic. Passive Solar Heating - space heating using solar collectors is called active solar heating. South facing windows and skylights fall under passive solar heating. Natural convection in the home circulates the heat. Na2SO4•10 H2O; CaCl2•6 H2O - melt and absorbs heat then gives off heat as it cools.

69 Solar Energy Ocean Thermal Energy Conversion - sun causes water near the surface of a body of water to be warmer, it may be possible to take advantage of the temperature difference to generate electricity. A fluid (liquid ammonia or propane) circulating in a conversion system could be alternately vaporized (absorb) and condensed (give off). Solar Power Satellite - a satellite in space that would collect solar energy. The collecting would be continuous and at higher intensity.

70 Energy Storage Pumped storage - Uses off-peak electric power for pumping water uphill to a reservoir so it can be used to generate hydroelectric power. Batteries - electrochemical cells - dry cells -batteries are used to power flashlights, etc.. Alkaline battery - zinc-alkaline-manganese dioxide battery. Major competitor of dry cell. Storage Batteries - can be recharged - lead-acid battery.

71  How Hydropower Works The Hydrologic Cycle: Water constantly moves through a vast global cycle, in which it evaporates from lakes and oceans, forms clouds, precipitates as rain or snow, then flows back to the ocean. The energy of this water cycle, which is driven by the sun, it tapped most efficiently with hydropower. 



74 The End

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