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.

Desirable characteristics of energy sources.       

• These include energy released at reasonable rates (neither too fast nor too slow) and minimal pollution.

Current and potential energy sources.         

• fossil fuels,

• nuclear (fission and fusion),

• electrochemical cells,

• solar energy

• alternative sources (eg wind, tidal, geothermal).

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 70 - 80% 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.

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

Sources of Coal

World Coal Reserves

25%

2%6%

9%29%

29%

North America

Latin America

Africa

Western Europe

Asia and Australia

Central Europe

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.

Describe how the burning of fossil fuels produces pollutants.

                   

• The primary pollutants are CO, CO2, SO2, NOx, particulates (fly ash) and hydrocarbons.

Coal Cleaning• GasificationGasification - Coal is converted to synthetic gas.

It is carried out in 4 steps: devolatilization, steam-carbon reaction, CO-shift reaction, and catalytic methanation.

• DevolatilizationDevolatilization - Coal is exposed to high temperatures and the volatile matter is released and decomposes to methane and char.

• Steam-Carbon ReactionSteam-Carbon Reaction - Addition of hydrogen in the form of water (steam) reacts with the char.

• C + H2O CO + H2

• CO-Shift ReactionCO-Shift Reaction - Some of the carbon monoxide is reacted with more steam, to form more hydrogen.

• CO + H2O CO2 + H2

• Catalytic MethanationCatalytic Methanation - The additional hydrogen is then caused to react with the remaining carbon monoxide.

• CO + 3 H2 H2O + CH4

Coal Cleaning

• Claus ProcessClaus 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 + 3 O2 2 FeO + 2 SO2

• (3) 2 H2S + SO2 2 H2O + 3 S

• Net: 2 H2S + O2 2 H2O + 2 S

FeO is regenerated by the process.FeO is regenerated by the process.

Coal Cleaning

• Liquefaction Liquefaction - The products from gasification, CO and H2, are further reacted to form the liquid compounds, formaldehyde (H2C=O) and methanol (CH3OH).

• ScrubbersScrubbers - flue-gas desulfurization devices. These devices remove SO2 from combustion gases. One important scrubber is limestone (CaCO3).

• CaCO3 + SO2 CaSO3 + CO2

Coal Cleaning

Products of Oil Distillation

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 Fuel

Kerosene 180-230 C11H24,C12H36 Jet fuel

LG Oil 230-305 C13H28-C17 Diesel

HG Oil 305-405 C18 – C25 Powerplant

Lubricant 405-515 Higher C Grease

Solids Pitch

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

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

Nuclear Energy

Electricity - Nuclear Fusion ?

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.

Write balanced nuclear equations.                    

• Both the atomic number and mass number must be balanced.

Describe the nature of , and radiation.                    

• Compare the charge, mass, penetrating power and behaviour in an electric field.

Types of Radiation

• alpha, beta or gamma• Alpha = 4

2He2+ or 42He or 4

2

• least penetrating• can be stopped by aluminum foil > 10-3 cm, paper,

skin• least harmful• most massive

Types of Radiation

• Beta = 0

-1e- • high energy electrons (e-) or positrons (e+)• more penetrating• stopped by 0.05 - 0.1 cm of aluminum• travel 10 ft through air• commonly emitted by TV sets• electron: 0

-1- or 0-1e- or e-

• positron: 0+1- or 0

+1e+ or e+

Types of Radiation• Gamma = energy with no mass or charge• Most penetrating radiation• Stopped by 5 - 11 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

Types of Radiation

• Other particles:

– proton (p+ or 11p or 1

1H)

– neutron (n or 10n)

– neutrino (00) and antineutrino (0

0), which have no mass or charge and accompany emission of beta particles; these are generally ignored by chemists

F.3.4     State the concept of half-life.                    

• Half-life is independent of the amount of a radioactive sample.

F.3.5     Apply the concept of half-life in calculations.                    

• Restrict this to whole number of half-lives.

F.3.6     Compare nuclear fission and nuclear fusion.

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.

Reactor core

• We use B or Cd control rods.

• 105B + 1

0n --> 73Li + 4

2He

Diagram of Nuclear Reactor

Discuss the differences between conventional power generation and nuclear reactors.

Discuss the concerns about safety in nuclear power plants.                    

Solar Energy: The Ultimate Renewable Resource

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).

Advantages and Disadvantages

• Advantages• 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.

Electricity - Solar Cells

How much solar energy?

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

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.

Heating Water: Active System

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

Heating Living Spaces

Passive Solar

Trombe WallPassively heated home in Colorado

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.

Power Towers

Power tower in Barstow, California.

Parabolic Dishes and Troughs

Because they work best under direct sunlight, parabolic dishes and troughs must be steered throughout the day in the direction of the sun.

Collectors in southern CA.

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 partsdo no wear out,

but because they are exposed to the weather, their lifespan is about 20 years.

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).

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.

Outline the principles of using solar energy for space heating.                    

• Example should include storage of heat by water and rocks.

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.

Discuss how biomass can be converted to energy.  

            Include :  

Electrochemical Energy

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

Electrochemical Cell

The Alkaline Dry Cell

“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?

Why?

Dry Cell

•Zn(Hg)+ HgO(s) ZnO(s) + Hg(l)

Mercury Battery

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)

Explain how a hydrogen-oxygen fuel cell works.                    

• Include the relevant half-equations.

Hydrogen-Oxygen Fuel Cell

Cathodic Protection

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.

Storage of Energy and Limits of Efficiency

Advantages and disadvantages of energy storage schemes.                

• Include both pumped storage and conversion to hydrogen.

Electricity• Main way to produce electricity now is coal.• Alternative ways to produce electricity:• 1. Hydroelectric powerHydroelectric power - (falling water) - it is

a renewable resource and nonpolluting however, dams are expensive, environmental and political problems.

• 2. Geothermal energyGeothermal 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.

Electricity

• 3. Wind PowerWind 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 PowerTidal Power - (changing tides) - uses variations in water levels. One in France, 40 feet tides, twice a day, 5 hours each.

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 EnergySolar 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.

Solar Energy• Photovoltaic Energy ConversionPhotovoltaic 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 HeatingPassive 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.

Solar Energy• Ocean Thermal Energy ConversionOcean 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 SatelliteSolar Power Satellite - a satellite in space that would collect solar energy. The collecting would be continuous and at higher intensity.

Energy Storage• Pumped storagePumped storage - Uses off-peak electric power for

pumping water uphill to a reservoir so it can be used to generate hydroelectric power.

• BatteriesBatteries - electrochemical cells - dry cellsdry cells -batteries are used to power flashlights, etc..

• Alkaline batteryAlkaline battery - zinc-alkaline-manganese dioxide battery. Major competitor of dry cell.

• Storage BatteriesStorage Batteries - can be recharged - lead-acid battery.

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. 

The End