Presentation on theme: "Option F :Fuels and Energy"— Presentation transcript:
1Option 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.
2Desirable characteristics of energy sources. These include energy released at reasonable rates (neither too fast nor too slow) and minimal pollution.
3Current and potential energy sources. fossil fuels,nuclear (fission and fusion),electrochemical cells,solar energyalternative sources (eg wind, tidal, geothermal).
4Fossil FuelsFossil 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.
5Coal: Supply and Demand Coal exists in many forms therefore a chemical formula cannot be written for it.Peat- Low carbon content, heat High MoistureLignite- 40% moisture low energy valueSub-bituminous- 30% moisture used for heatBituminous-86% Carbon industrial/domestic useAnthracite- 98% Carbon, burns with blue flame
7Problems 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.
8Describe how the burning of fossil fuels produces pollutants. The primary pollutants are CO, CO2, SO2, NOx, particulates (fly ash) and hydrocarbons.
9Coal CleaningGasification - 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
10Coal CleaningCO-Shift Reaction - Some of the carbon monoxide is reacted with more steam, to form more hydrogen.CO + H2O CO2 + H2Catalytic Methanation - The additional hydrogen is then caused to react with the remaining carbon monoxide.CO H2 H2O + CH4
11FeO is regenerated by the process. Coal CleaningClaus 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 SNet: 2 H2S + O2 2 H2O SFeO is regenerated by the process.
12Coal CleaningLiquefaction - 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
14Petroleum Fractions Fraction BP (oC) Composition Use Gas 0–20 CH4-C4H10FuelPet ether20-70C5H12,C6H14SolventPetrol70-180C6H14-C10H22KeroseneC11H24,C12H36Jet fuelLG OilC13H28-C17DieselHG OilC18 – C25PowerplantLubricantHigher CGreaseSolidsPitch
15Octane Rating Petrol fraction consists of straight-chain alkanes Fuel burns before ignition by the spark plug – knock – loss of power, damage to engine2,2,4-trimethylpentane: Octane =100N-heptane: Octane = 0
16Octane RatingCan increase octane rating for petrol fraction from 50 to 90 by 3 methods:CrackingCatalytic reformingAddition of octane enhancers like TEL, methanol, ethanol and MTBE
19Distinguish 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.
20Write balanced nuclear equations. Both the atomic number and mass number must be balanced.
21Describe the nature of a , b and g radiation. Compare the charge, mass, penetrating power and behaviour in an electric field.
22Types of Radiation alpha, beta or gamma Alpha a = 42He2+ or 42He or 42aleast penetratingcan be stopped by aluminum foil > 10-3 cm, paper, skinleast harmfulmost massive
23Types of Radiation Beta b = 0-1e- high energy electrons (e-) or positrons (e+)more penetratingstopped by cm of aluminumtravel 10 ft through aircommonly emitted by TV setselectron: 0-1b- or 0-1e- or e-positron: 0+1b- or 0+1e+ or e+
24Types of Radiation Gamma g = energy with no mass or charge Most penetrating radiationStopped by cm of aluminum or thick layer of concrete or leadLead is commonly used to enclose radioactive materials because radiation does not penetrate readilyIn the 1950s, it was common to build thick concrete bomb shelters
25Types 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
26F.3.4 State the concept of half-life. Half-life is independent of the amount of a radioactive sample.
27F.3.5 Apply the concept of half-life in calculations. Restrict this to whole number of half-lives.
28F.3.6 Compare nuclear fission and nuclear fusion.
29F.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.
30Reactor core We use B or Cd control rods. 105B + 10n --> 73Li + 42He
35What 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).
36Advantages 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!DisadvantagesSun 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.
38How much solar energy?The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.
39Putting 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.
40Heating Water: Active System Active System uses antifreeze so that the liquid does not freeze if outside temp. drops below freezing.
41Heating Living Spaces Passive Solar Trombe Wall Passively heated home in Colorado
42Heating Living SpacesA 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.
44Parabolic 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.
45Direct 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 storageNo moving partsdo no wear out, but because they are exposed to the weather, their lifespan is about 20 years.
46State 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).
47Describe 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.
48Outline the principles of using solar energy for space heating. Example should include storage of heat by water and rocks.
49F.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.
50Discuss how biomass can be converted to energy. Include :
64Advantages and disadvantages of energy storage schemes. Include both pumped storage and conversion to hydrogen.
65Electricity 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.
66Electricity3. 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.
67Solar EnergyUltimate 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.
68Solar EnergyPhotovoltaic 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.
69Solar EnergyOcean 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.
70Energy StoragePumped 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 WorksThe 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.