Environmental Problems, Their Causes, and Sustainability 1

17-4 COALWhat Is Coal, and How Is It Extracted?A Mostly Carbon FuelCoal, which can be extracted by surface andunderground mining, consists mostly of carbonplus small amounts of sulfur and trace amounts ofmercury and radioactive material.Coal is a solid fossil fuel formed in several stages asburied remains of land plants that lived 300–400 millionyears ago were subjected to intense heat and pressureover many millions of years (Figure 17-20). Coal ismostly carbon and contains small amounts of sulfur,released into the atmosphere as SO 2 when coal isburned. Burning coal also releases trace amounts oftoxic mercury and radioactive materials.Anthracite (which is about 98% carbon) is themost desirable type of coal because of its high heatcontent and low sulfur content. However, because ittakes much longer to form, it is less common andtherefore more expensive than other types of coal.Some coal is extracted underground by minersworking in tunnels and shafts (Figure 16-12, p. 342).This is one of the world’s most dangerous occupationsbecause of accidents and black lung disease caused byprolonged inhalation of coal dust particles. Area stripmining (Figure 16-11c, p. 341) is used to extract coalfound close to the earth’s surface on flat terrain, andcontour strip mining (Figure 16-11d) is used on hilly ormountainous terrain. In some cases, entire mountaintopsare removed and dumped into the valleys belowto expose seams of coal. The scarred land from thesurface mining of coal is not restored in most countriesand only partially restored in parts of the UnitedStates.Fly over parts of West Virginia and you will seesome mountains looking as if their tops had beensliced off with a machete and others so deeply minedthat they look like ugly miniatureGrand Canyons. Enormousslurry ponds containing miningwaste are sandwiched betweenthe remains of these mountains.Mountaintop mining has pollutedsome 760 kilometers (470Peat(not a coal)miles) of West Virginia’s streams and displaced thousandsof families.After coal is removed, trains usually transport it toa processing plant, where it is broken up, crushed, andwashed to remove impurities. After the coal is dried itis shipped (again usually by train) to users, mostlypower plants and industrial plants.How Is Coal Used, and How Long WillSupplies Last?Coal is burned mostly to produce electricity and steel,and reserves in the United States, Russia, and Chinacould last hundreds to thousands of years.Coal is burned to generate 62% of the world’s electricity(52% in the United States) and make three-fourthsof its steel. Coal is by far the world’s most abundantfossil fuel, with deposits containing ten times more energythan oil and natural gas resources combined. Accordingto the U.S. Geological Survey, identified andunidentified supplies of coal could last the world for214–1,125 years, depending on the rate of usage.The United States has one-fourth of the world’sproven coal reserves. Russia has 16% and China 12%. In2002, just over half of global coal consumption was splitalmost evenly between China and the United States.China has enough proven coal reserves to last 300years at its current rate of consumption. According tothe U.S. Geological Survey, identified U.S. coal reservesshould also last about 300 years at the currentconsumption rate, and unidentified U.S. coal resourcescould extend those supplies for perhaps another 100years, at a higher cost. However, if U.S. coal use shouldincrease by 4% a year—as the coal industry projects—the country’s proven coal reserves would last only 64years.Figure 17-21 lists the advantages and disadvantagesof using coal as an energy resource. Bottom line.Increasing moisture contentLignite(brown coal)Increasing heat and carbon contentBituminous Coal(soft coal)Anthracite(hard coal)HeatHeatHeatFigure 17-20 Natural capital:stages in coal formation over millionsof years. Peat is a soil material madeof moist, partially decomposed organicmatter. Lignite and bituminouscoal are sedimentary rocks, whereasanthracite is a metamorphic rock(Figure 16-9, p. 339).Partially decayedplant matter in swampsand bogs; low heatcontentPressureLow heat content;low sulfur content;limited supplies inmost areasPressurePressureExtensively usedas a fuel becauseof its high heat contentand large supplies;normally has ahigh sulfur contentHighly desirable fuelbecause of its highheat content andlow sulfur content;supplies are limitedin most areas364 CHAPTER 17 Nonrenewable Energy Resources