Discussion

Exercise 2.6

1. If there is no «away», why isn't the world filled with waste matter?

2. Use the second law of energy to explain why a barrel of oil can be used as a fuel only once.

3. Imagine that you have the power to violate the law of conservation of energy (the first law of energy) for 1 day. What are the 3 most important things you would do with this power?

4. Imagine that you have the power to violate the second law of energy for 1 day. What are the three most important things you would do with this power?

Unit 3 resources What keeps us alive?

Energy from the sun and natural resources support and sustain all life and all economies on the earth.

What is a resource? From the human standpoint, a resource is anything obtained from the environment to meet human needs and wants. On our short human time scale, we classify the material resources we get from the environment as perpetual, renewable and nonrenewable.

A renewable resource can be replenished fairly rapidly (hours to several decades) through natural processes as long as it is not used up faster than it is replaced. Examples are forests, grassland, wild animals, fresh water, fresh air, and fertile soil. If we exceed a resource natural replacement rate, the available supply begins to shrink, a process known as environmental degradation. Examples of such degradation include urbanization of productive land, water logging and salt buildup in soils, topsoil erosion, deforestation, and pollution.

Resources, which exist in a fixed quantity or stock in the earth’s crust, are called nonrenewable resources. These exhaustible resources include energy resources (coal, oil, natural gas, which cannot be recycled), metallic mineral resources (such as iron, copper, and aluminum, which can be recycled), and nonmetallic mineral resources (such as salt, clay, sand and phosphates, which are difficult or too costly to recycle). We know how to find and extract more than 100 nonrenewable minerals from the earth's crust. We convert these raw materials into many everyday items and then we discard, reuse or recycle them. When we almost completely exhaust a mineral resource, we have six choices: 1) try to find more, 2) recycle or reuse existing supplies, 3) waste less, 4) use less, 5) try to develop a substitute, 6) wait millions of years for more to be produced by nature.

Major types of material resources. This scheme is not fixed; renew-able resources can become nonrenewable.

Recycling involves collecting and reprocessing a resource into new products. For example, glass bottles can be crushed and melted to make new bottles or other glass items. Recycling metallic resources takes much less energy, water and other resources and produces much less pollution than exploiting virgin metallic resources. Reuse involves using a resource over and over in the same form. For example, glass bottles can be collected, washed and refilled many times.

What types of energy do we use?

Some 99% of the energy used to heat the earth and all of our buildings come directly from the sun. Without this direct input of essentially inexhaustible solar energy, the earth's average temperature would be -240 ^оC. This direct input of solar energy also produces several other indirect forms of renewable solar energy: wind, falling and flowing water (hydropower), and biomass (solar energy converted to chemical energy stored in chemical bonds of organic compounds in trees and other plants).

Commercial energy makes up the remaining 1% of the energy we use. Most commercial energy (81%) comes from extracting and burning nonrenewable mineral resources: 75% from fossil fuels and 6% from nuclear power. During the 20^th century there were major shifts in the world's major sources of energy: the use of coal dropped from 55% to 22%, oil increased from 2% to 33%, natural gas from 1% to 23%, nuclear energy increased from 0% to 6%, and renewable energy (mostly wood and flowing water) decreased from 42% to 19%. The United States is the world's largest energy user: with only 4% of the population it uses 24% of the world's commercial energy.

The world's current dependence on nonrenewable fossil fuels is the primary cause of air and water pollution, land disruption, and greenhouse gas emission. Affordable oil may be economically depleted within 42  93 years and gradually replaced by other energy resources. What is our best immediate energy option? The general consensus is to cut out unnecessary energy waste by improving energy efficiency. There is disagreement about our next best energy option. Some say we should get much more energy from renewable sources such as sun, wind, hydropower, biomass, hydrogen gas, geothermal energy. Others say we should burn more coal and synthetic liquid and gaseous fuels made from coal because it is our most plentiful energy resource. Some think we can find more oil. Many believe that fairly abundant and clean-burning natural gas is the answer. Some think nuclear power is the answer.

Experience shows that it usually takes at least 50 years and huge investments to phase in new energy alternatives to the point where they provide 10  20% of total energy use. To choose the best alternative we should answer the following questions:

• How much of the energy source will be available in the near future (the next 15  25 years) and in the long term (the next 25 -50 years)

• What is this source net energy yield?

• How much will it cost to develop, phase in and use this energy resource?

• How will extracting, transporting, and using the energy resource affect the environment, human health, and the earth's climate?

What is net energy? It is the only energy that really counts, as it takes energy to get energy. For example, oil must be 1) found, 2) pumped out from beneath the ground or ocean floor, 3) transferred to a refinery and converted to useful fuels (such as gasoline, diesel fuel and heating oil), 4) transported to users, 5) burned in furnaces and cars before it is useful for us. Each of these steps uses energy, and the second law of energy tells us, that each time we use energy to perform a task; some of it is wasted and degraded to low-quality energy. We can express net energy as the ratio of total energy produced to the energy used to produce it. Currently, oil has a high net energy ratio because much of it comes from large, accessible deposits such as those in the Middle East. When those sources are depleted, the net energy ratio of oil will decline and prices will rise. Conventional nuclear energy has a low net energy ratio because large amounts of energy are needed to 1) extract and process uranium ore, 2) convert it into a usable nuclear fuel, 3) build and operate nuclear power plants, 4) dismantle the highly radioactive plants after their 15  40 years of useful life, and 5) store the resulting highly radioactive wastes for thousands of years.