Cutting the carbon

The world relies on electricity, but this has to be generated from other forms of energy. Currently most of it is produced by burning fossil fuels, which releases greenhouse gases. Luckily there are ways of reducing these emissions. Natural gas is cleaner than coal, so using it instead of coal can help. Converting coal into gas turns it into a more efficient fuel. Carbon dioxide can also be removed from fossil fuels before or after they are burned, and stored underground.

THE COAL PROBLEM

Coal generates about two-thirds of the world's electricity. This is partly because it is a very abundant resource, especially in the United States and China. But burning coal produces far more carbon dioxide than using natural gas. Coal-fired power plants are also relatively inefficient, turning less than 40 percent of their fuel energy into electricity. Altogether, coal accounts for more than a quarter of global carbon dioxide emissions. Yet the US is likely to burn 40 percent more coal by 2025, and China intends to triple the energy that it produces from coal by 2020.

THE PRICE OF COAL

Even if coal could be burned cleanly, coal mining is dangerous and often destructive. Deep coal mines are notorious for deadly collapses and explosions. During 2006, when this photograph was taken in Sichuan, China, at least 5,986 Chinese workers were killed in mining accidents. Surface mines are safer, but they leave huge scars on the landscape.

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CARBON CAPTURE AND STORAGE

One way of cleaning up coal-fired power plants is by bubbling their exhaust gases through chemicals called ethanolamines, which absorb 82 to 99 percent of the carbon dioxide. The chemicals are piped away and heated to release the gas, which is collected and pumped underground for storage in old oil wells, coal mines, and reserves of salty water call saline aquifers. The carbon dioxide can also be used to help force oil out of oilfields, and to displace methane from old coal mines so that it can be used as a fuel. In theory, this technology could be used to virtually eliminate the carbon emissions from coal-fired power plants, and it is already being used in many countries.

7. Carbon dioxide stripped from harvested gas

9. Gas is used to generate electricity

1. Gasifier plant pumps air and steam underground

7. Carbon dioxide stripped from harvested gas

9. Gas is used to generate electricity

1. Gasifier plant pumps air and steam underground

8. Carbon dioxide stored underground in depleted coal seams

6. Gas forced to surface up production well

5. Pressure of groundwater contains the gas

3. Gas mixture ignited to generate heat

8. Carbon dioxide stored underground in depleted coal seams

6. Gas forced to surface up production well

5. Pressure of groundwater contains the gas

More gas is released from coal seam by heat

3. Gas mixture ignited to generate heat

Power Station

Power Station

UNDERGROUND COAL GASIFICATION

Instead of mining coal, it is possible to turn it into gas while it is still underground, and use the gas as a much more efficient fuel. Air and steam are pumped into a coal seam, which releases hydrogen, methane, and carbon dioxide. The gas mixture is ignited to generate heat, which turns more of the coal into gas. This is contained by the pressure of groundwater, and forced up a collection pipe to the surface. Here the carbon dioxide can be stripped out of the mixture and pumped back underground, and the gas can be used to generate electricity.

2. Air and steam mix with gas from coal seam

NATURAL GAS

Burning natural gas instead of coal to generate power releases about 40 percent less carbon doxide for each watt of electricity. It is also much cleaner in other ways, since it does not produce soot or sulfur compounds. So although gas is a fossil fuel, simply switching from coal to gas can dramatically reduce carbon dioxide emissions. However, the unburned gas is mostly methane, which is a far more powerful greenhouse gas than carbon dioxide. So any gas leaks, perhaps from pipelines like this one in Canada, can wipe out any advantage that gas has over coal.

2. Air and steam mix with gas from coal seam

Model of an LNG tanker

Model of an LNG tanker

LIQUID FUEL

Natural gas can now be shipped all over the world in special gas tankers that transport it as liquefied natural gas (LNG). The liquefying process uses energy, making LNG up to 30 percent less efficient as a fuel than ordinary natural gas—but it is much more efficient than coal. LNG is highly explosive, so finding suitable sites for gas terminals can be a problem. Since many of the world's gas reserves are now almost exhausted, carrying gas around the globe in LNG tankers may soon be essential if we are to avoid relying on coal.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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