Energy Chapter 13
Three big ideas • Energy resources should be evaluated by… potential supplies, net energy they provide, and their environmental impacts. • Using a mix of renewable energy sources can drastically reduce pollution, greenhouse gas emissions, and biodiversity losses. • A sustainable energy future will require sharply reducing energy waste, using a mix of environmentally friendly renewable energy resources, and including the harmful environmental costs of energy resources in their market prices.
Section 13-1 What is net energy and why is it important?
Basic science: Net energy is the only energy that really counts • The usable amount of high-quality energy available from a given quantity of an energy resource is its net energy yield: the total amount of useful energy available from an energy resource minus the energy needed to make it available to consumers. • We can express net energy as the ratio of energy produced to the energy used to produce it. As the ratio increases, the net energy also rises. When the ratio is less than 1, there is a net energy loss.
Net energy ratios for various energy systems over their estimated lifetimes differ widely
Energy resources with low or negative net energy need help to compete in the marketplace • Any energy resource with a low or negative net energy ratio cannot compete in the open marketplace with other energy alternatives with higher net energy ratios unless it receives financial support from the government (taxpayers) or other outside sources of funding. • For example, the low net energy yield for the nuclear power fuel cycle is one reason why many governments throughout the world must heavily support nuclear power financially to make it available to consumers at an affordable price.
Section 13-2 What are the advantages and disadvantages of fossil fuels?
Fossil fuels supply most of our commercial energy • The direct input of solar energy produces several other forms of renewable energy resources that: wind, flowing water, and biomass. • Most commercial energy comes from extracting and burning nonrenewable energy resources obtained from the earth’s crust. • 87% from carbon-containing fossil fuels (oil, natural gas, and coal). • 6% from nuclear power. • 8% from renewable energy resources—biomass, hydropower, geothermal, wind, and solar energy.
We depend heavily on oil • Crude oil (petroleum), is a black, gooey liquid consisting of hundreds of different combustible hydrocarbons along with small amounts of sulfur, oxygen, and nitrogen impurities. • Also known as conventional oil and as light or sweet crude oil. • Oil, coal, and natural gas are called fossil fuels because they were formed from the decaying remains (fossils) of organisms that lived millions of years ago. • When the rate of crude oil production starts declining it is referred to as peak production for the well.
We depend heavily on oil • Global peak production is the point in time when we reach the maximum overall rate of crude oil production for the whole world. • After extraction, crude oil is transported to a refinery by pipeline, truck, or ship (oil tanker). • Crude oil is heated to different boiling points in a complex process called refining to separate it into different layers, such as petrochemicals.
When crude oil is refined, many of its components are removed at various levels
How long might supplies of conventional crude oil last? • Crude oil is now the single largest source of commercial energy in the world. • Proven oil reserves are identified deposits from which conventional crude oil can be extracted profitably at current prices with current technology. • Geologists project that known and projected global reserves of conventional crude oil will be 80% depleted sometime between 2050 and 2100. The remaining 20% will likely be too costly to remove.
How long might supplies of conventional crude oil last? • Options include: • look for more oil. • use less oil. • waste less oil. • use other energy resources.
OPEC controls most of the world’s crude oil supplies • 13 countries make up the Organization of Petroleum Exporting Countries (OPEC). • In 2010, OPEC holds about 77% of the world’s proven crude oil reserves. • OPEC’s members are Algeria, Angola, Ecuador, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. • The U.S. has only about 2% of the world’s proven oil reserves. China has only 1.1%, India has 0.4%, and Japan has no oil reserves.
OPEC controls most of the world’s crude oil supplies • Currently, the world’s largest producers of oil are, in order, Russia, Saudi Arabia, and the U.S. Energy experts project that by about 2020, Iraq will become the world’s third largest oil producer. • Since 1984, production of conventional crude oil from proven reserves has exceeded new oil discoveries. Since 2005, global crude oil production has generally leveled off. Of the world’s 64 major oil fields, 54 are now in decline.
OPEC controls most of the world’s crude oil supplies • According to some analysts, in order to keep using conventional oil at the projected increasing rate of consumption, we must discover proven reserves of conventional oil equivalent to the current Saudi Arabian supply every 5 years. Most oil geologists say this is highly unlikely.
Using crude oil has advantages and disadvantages • Extraction, processing, and burning of nonrenewable oil and other fossil fuels have severe environmental impacts. • Land disruption. • Air pollution. • Greenhouse gas emissions. • Water pollution. • Loss of biodiversity.
Using crude oil has advantages and disadvantages • Oil spills cause catastrophic damage. • In 2010, the BP Company’s Deepwater Horizon oil-drilling rig exploded, spilling an estimated 679 million liters (180million gallons) of crude oil into U.S. Gulf Coast waters. • In 1989, the oil tanker Exxon Valdez ran aground and spilled 42 million liters (11 million gallons) of oil into Alaskan waters. • More than 2.5 times the estimated amount of crude oil spilled in the 2010 Gulf Coast disaster has been spilled from off the coast of Nigeria with little media attention.
Will heavy oil be a useful resource? • Oil shale is rock that contains a solid combustible mixture of hydrocarbons called kerogen which can be processed to produce shale oil. • Producing shale oil requires large amounts of water and has a low net energy and a very high environmental impact. • Estimated potential global supplies of unconventional shale oil are about 240 times larger than estimated global supplies of conventional crude oil. • Shale has a low net energy yield so would require subsidies to compete on the open market, and shale extraction would have a high environmental impact, causing severe land disruption, high water use, and high CO2 emissions when produced and burned.
Using heavy oil from oil shale and tar sands as energy source has advantages and disadvantages
Natural gas is a useful and clean-burning fossil fuel • Natural gas is a mixture of gases of which 50–90% is methane (CH4). • Has high net energy. • Versatile fuel that can be burned to heat indoor space and water, propel vehicles and produce electricity. • Lies above most reservoirs of crude oil. • When a natural gas field is tapped, propane and butane gases are liquefied and removed as liquefied petroleum gas (LPG). • Cleanest-burning among the fossil fuels, releasing much less CO2 per unit of energy than coal, crude oil, and synthetic crude oil from tar sands and oil shale.
Using conventional natural gas has advantages and disadvantages
Use of fracking to extract natural gas is controversial • Hydraulic fracturing, or fracking, pumps water mixed with sand and some toxic chemicals underground to fracture deep rock and free up natural gas stored there. • The gas flows out, along with a toxic slurry of water, salts, toxic heavy metals, and naturally occurring radioactive materials that is stored in tanks and holding ponds. • Drillers maintain that fracking is necessary for exploiting this reserve at a reasonably low cost, and they argue that no groundwater contamination directly due to fracking has ever been recorded.
Use of fracking to extract natural gas is controversial • Scientists and citizens point out that there is no guarantee that sharply increasing use of the process will not contaminate groundwater or that holding ponds and tanks used to store the toxic slurry will not leak and pollute rivers and streams. • People who rely on aquifers and streams in these areas for their drinking water have little protection from pollution of their water supplies that might result from natural gas drilling.
Use of fracking to extract natural gas is controversial • Natural gas can be transported as liquefied natural gas (LNG). However, LNG has a low net energy yield, as more than a third of its energy content is used to process it and to deliver it to users. • The long-term global outlook for conventional natural gas supplies is better than for crude oil. • Potential sources of unconventional natural gas include coal bed methane gas and methane hydrate, but environmental impacts and cost may limit their use.
Coal is a plentiful but dirty fuel • Coal is a solid fossil fuel formed from the remains of land plants that were buried 300–400 million years ago and exposed to intense heat and pressure over those millions of years. • Coal is burned in power plants to generate about 42% of the world’s electricity, and burned in industrial plants to make steel, cement, and other products. • The three largest coal-burning countries are China, the U.S., and India. • Coal is plentiful and cheap.
Increasing heat and carbon content Increasing moisture content Anthracite (hard coal) Lignite (brown coal) Peat (not a coal) Bituminous (soft coal) Heat Heat Heat Pressure Pressure Pressure Partially decayed plant matter in swamps and bogs; low heat content Low heat content; low sulfur content; limited supplies in most areas Extensively used as a fuel because of its high heat content and large supplies; normally has a high sulfur content Highly desirable fuel because of its high heat content and low sulfur content; supplies are limited in most areas Stepped Art Fig. 13-12, p. 310
Coal is a plentiful but dirty fuel • Mining and burning coal have severe impacts on the earth’s air, water, land, climate, and human health. • Coal-burning power and industrial plants are among the largest emitters of the greenhouse gas CO2. • Coal burning emits trace amounts of toxic and radioactive materials. • Burning coal produces a highly toxic ash that must be safely stored, essentially forever. • China uses three times as much coal as the U.S. and it has become the world’s leading emitter of CO2 and of sulfur dioxide.
This power plant burns pulverized coal to boil water and produce steam that spins a turbine to produce electricity.
Coal is a plentiful but dirty fuel • Coal is cheap but most of the harmful environmental and health costs are not included in the price. • The clean coal campaign. • Powerful U.S. coal companies and utilities oppose measures. • Publicity campaign built around the misleading notion of clean coal. • Burn coal more cleanly by adding costly air pollution control devices. • There is no such thing as clean coal.
Section 13-3 What are the advantages and disadvantages of nuclear energy?
How does a nuclear fission reactor work? • Nuclear power plant is a highly complex and costly system designed to perform a relatively simple task: to boil water to produce steam that spins a turbine and generates electricity. • A controlled nuclear fission reaction is used to provide the heat. • The fission reaction takes place in a reactor. • Light-water reactors (LWRs) produce 85% of the world’s nuclear-generated electricity (100% in the U.S.). • The fuel for a reactor is made from uranium ore mined from the earth’s crust, then enriched and processed into pellets of uranium dioxide.
How does a nuclear fission reactor work? • Pellets are packed into fuel rods which are then grouped into fuel assemblies and placed in the core of a reactor. • Control rods are moved in and out of the reactor core to regulate the amount of power produced. • A coolant, usually water, circulates through the reactor’s core to remove heat, which keeps fuel rods and other materials from melting and releasing massive amounts of radioactivity into the environment.
How does a nuclear fission reactor work? • A containment shell surrounds the reactor core to keep radioactive materials from escaping into the environment in case there is an internal explosion or a melting of the reactor’s core. • Light water reactors are highly inefficient; the net energy loss is about 82%, without taking into account the energy needed to dismantle a plant at the end of its life and transport and store its radioactive materials for thousands of years.
Small amounts of radioactive gases Uranium fuel input (reactor core) Control rods Containment shell Waste heat Heat exchanger Steam Turbine Generator Hot coolant Useful electrical energy about 25% Hot water output Pump Pump Coolant Pump Pump Waste heat Cool water input Moderator Shielding Pressure vessel Coolant passage Water Condenser Periodic removal and storage of radioactive wastes and spent fuel assemblies Periodic removal and storage of radioactive liquid wastes Water source (river, lake, ocean) Fig. 13-17a, p. 314
What is the nuclear fuel cycle? • A nuclear power plant is only one part of the nuclear fuel cycle, which also includes the mining of uranium, processing and enriching the uranium to make fuel, using it in the reactor, safely storing the resulting highly radioactive wastes for thousands of years until their radioactivity falls to safe levels, and retiring the highly radioactive plant by taking it apart and storing its high- and moderate-level radioactive material safely for thousands of years.
What is the nuclear fuel cycle? • In addition to a nuclear power plant, the nuclear fuel cycle includes: • mining uranium. • processing and enriching the uranium to make fuel. • using it in the reactor. • safely storing the resulting highly radioactive wastes for thousands of years until their radioactivity falls to safe levels. • retiring the highly radioactive plant by taking it apart. • storing its high- and moderate-level radioactive material safely for thousands of years.
Decommissioning of reactor Fuel assemblies Reactor Enrichment of UF6 Fuel fabrication (conversion of enriched UF 6 to UO2 and fabrication of fuel assemblies) Temporary storage of spent fuel assemblies underwater or in dry casks Uranium-235 as UF6 Plutonium-239 as PuO2 Conversion of U3O8 to UF6 Spent fuel reprocessing Low-level radiation with long half-life Geologic disposal of moderate- and high-level radioactive wastes Mining uranium ore (U3O8) Open fuel cycle today Recycling of nuclear fuel Fig. 13-18, p. 315