Handbook Of Pollution Control And Waste Minimization - Chapter 7 doc

7 Energy Conservation K. A. Strevett, C. Evenson, and L. Wolf University of Oklahoma, Norman, Oklahoma 1 INTRODUCTION A large proportion of our current pollution problems is the result of energy technologies that rely on combustion of carbon-based fuels. Included in these problems are emissions of greenhouse gases, acid rain precursors (oxides of sulfur and nitrogen), and carbon monoxide; formation of photochemical oxidants; releases to the biosphere of raw and refined petroleum products; and mining- related pollution. Obviously, then, decreasing our consumption of carbon-based energy will result in decreases in the amounts of these pollutants entering the biosphere. Global warming poses the threat of an environmental impact that is global and, at least on a time scale of centuries, irreversible. Over the very long term of two to three centuries, temperatures could rise by as much as 10 to 18˚C. While it is impossible at this point to predict accurately all the effects of global warming, its consequences are potentially so threatening to human and ecosystem health that humans have an ethical obligation to do something about it (1). It is obvious that strategies for reducing consumption of energy derived from combustion of carbon-based fuels are among the most important means of preventing global pollution. After a look at energy demands, this chapter dis- cusses several such energy conservation strategies, the fuels currently being used Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. to supply these demands, and a survey of the environmental impacts of some of the pollutants produced by these fuels. 2 ENERGY SUPPLIES AND DEMANDS Coal, oil, and natural gas supply about 95% of global energy. Coal dominates energy markets, accounting for about 44% of fossil energy consumption. Oil accounts for about 32% of fossil fuel supply, while natural gas contributes 24% (Figure 1). Coal is the most abundant fossil fuel worldwide, with current reserves expected to last more than 200 years. “Conventional” oil production is expected to peak between 2010 and 2020, resulting in a switch to “unconventional”* sources and a possible increase in price (2). The total ultimately recoverable natural gas resources in the world are estimated to amount to about 80% as much energy as the recoverable reserves of crude oil. At current usage rates, gas reserves represent approximately a 60-year supply (3). Although developed countries account for less than 20% of the world’s population, these countries use more than two-thirds of the commercial energy supply, consuming 78% of the natural gas, 65% of the oil, and about 50% of the coal produced each year (Figure 2). The United States and Canada, for example, account for only about 5% of the world’s population, but consume about one-quarter of the available energy (3). Carlsmith et al. (1990, as cited in Ref. 4) estimated that 36% of U.S. energy consumption is in commercial and residential buildings; industry accounts for another 36% and transportation for the remaining 28%. *Oil is considered unconventional if it is not produced from underground hydrocarbon reservoirs by means of production wells, and/or it requires additional processing to produce synthetic crude. It includes such sources as oil shales, oil sands-based synthetic crudes and derivative products, and liquid supplies derived from coal, biomass, or gas (2). Coal 44% Natural Gas 24% Oil 32% FIGURE 1 Percent contribution of coal, oil, and natural gas to global energy markets. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. In November 1998, the World Energy Outlook (2) predicted 65% growth in world energy demand and 70% growth in CO 2 emissions between 1995 and 2020, without policy changes. The Outlook estimates that fossil fuels will meet 95% of additional global energy between 1995 and 2020 and that two-thirds of the increase in energy demand and energy-related CO 2 emissions over this period could occur in China and other developing countries. The market share of gas is expected to increase, while that of oil will decline slightly and the share of coal will remain stable. By 2020, global electricity generation is predicted to have increased by nearly 88% over 1995 rates. While electricity generation from energy sources other than carbon-based fuels and hydropower is growing fast, it is expected to represent less than 1% of world electricity generation by 2020 without policy changes. 3 NONRENEWABLE ENERGY SOURCES 3.1 Coal Coal is fossilized plant material preserved by burial in sediments and altered by geological forces that compact and condense it into a carbon-rich fuel. Its advantage lies in its abundance of supply. The environmental effects of burning all the remaining coal, however, could be catastrophic. Coal is the worst offender among fossil fuels in terms of CO 2 per unit of energy generated. The supply of coal is enough to permit atmospheric carbon buildup of severalfold (4). In addition, the burning of coal is a primary source of acid rain precursors. Pollution associated with the mining of coal is discussed later. Industrialized countries generate between 20% and 30% of their energy from coal; in the case of China, the figure is nearly 75% (5). In the United States, the relative contribution of coal declined from a peak of about 75% of total energy Developed Underdeveloped Coal 50% 50% Oil 65% 35% Natural Gas 78% 22% FIGURE 2 Comparison of coal, oil, and natural gas consumption in developed and less developed countries. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. supply in 1910 to about 17% in 1973 and increased again to about 23% in 1989. In 1989, about 86% of domestic coal consumption was accounted for in electric power production (6). 3.2 Petroleum Petroleum, like coal, is derived from organic molecules created by living organ- isms millions of years ago and buried in sediments where high pressures and temperatures concentrated and transformed them into energy-rich compounds. Petroleum has represented a relatively inexpensive source of fuel for transporta- tion and provides the chemical industry with feedstocks, e.g., for the production of plastics. However, its use results in emissions of carbon dioxide, carbon monoxide, and acid rain precursors, and in the formation of photochemical oxidants. In addition, aquatic and terrestrial systems may become polluted by unintentional releases of raw and refined petroleum. 3.3 Natural Gas Natural gas is a combustible mixture of methane (CH 4 ) and other hydrocarbons formed during the anaerobic decomposition of organic matter. It is the least polluting of the fossil fuels, releasing only a little more than half as much CO 2 as coal. Important disadvantages of natural gas are its limited supply, difficulty of storage in large quantities, and difficulty of transport across oceans. It can be transported across land via pipelines; however, leaks of methane from these pipelines represent a significant contribution to global warming. Furthermore, such pipeline networks are prohibitively expensive for developing countries. As a result, much of the natural gas produced in conjunction with oil pumping is simply burned (flared off), representing a terrible waste of a valuable resource (3). 4 SOURCES AND ENVIRONMENTAL IMPACTS OF POLLUTANTS The production and/or consumption of carbon-derived energy result in release to the biosphere of a variety of pollutants. These include gaseous pollutants [carbon dioxide, acid rain precursors (nitrogen oxides and sulfur dioxide), and carbon monoxide], photochemical oxidants, unintentional releases of raw and refined petroleum, mining-related pollution (i.e., acid mine drainage), methane, and thermal pollution. 4.1 Gaseous Pollutants 4.1.1 Carbon Dioxide Carbon dioxide is responsible for 55% of global warming. The two primary anthropogenic sources of atmospheric CO 2 are fossil fuel burning (~77%) and Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. deforestation (~23%). Cline (4) has estimated that if human sources of atmo- spheric carbon were immediately reduced by about 43%, warming could be held to about 2.5˚C. Atmospheric CO 2 concentration was more or less stable near 280 ppm for thousands of years until about 1850, and has increased significantly since then (Figure 3) (Schimel et al., 1995, as cited in Ref. 7). Since the beginning of the industrial era, about 40% of all CO 2 released through the burning of fossil fuel has been absorbed by sinks; the remainder has remained in the atmosphere (1). The human-caused increase in atmospheric CO 2 already represents nearly a 30% change relative to the preindustrial era (7); annual global emissions of CO 2 have increased 10 times this century (8). At the current rate of increase in concentra- tions of CO 2 and other heat-trapping gases in the atmosphere, greenhouse gas concentrations will be equivalent to double the preindustrial CO 2 concentration by 2050 (National Academy of Sciences, 1992, as cited in Ref. 1). Ultimately, this could increase the average global temperature by about 1–5˚C, with a likely figure of 2.5˚C. According to Cline (4), we are already committed to about 1.7˚C of warming from the existing accumulation of greenhouse gases, and warming could increase by 10˚C or more if nothing is done to alter likely fossil fuel consumption patterns. The historic record suggests that the average global surface temperature has already risen approximately 0.3–0.6˚C since the nineteenth century (1). Natural gas releases slightly less than half the amount of CO 2 released during the combustion of coal, with petroleum in between. Coal and natural gas each accounts for about 27% of U.S. fossil fuel supply, but coal accounts for about 275 300 325 350 375 1700 1750 1800 1850 1900 1950 2000 Atm. CO 2 Conc. (ppm) FIGURE 3 Historical increase in global CO 2 emissions. (Sources: Refs. 35–37.) Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. one-third of U.S. CO 2 emissions. In the United States, electric utilities account for about one-third of all CO 2 releases, with transportation activities adding approximately an additional third. Globally, oil consumption accounts for nearly half of total CO 2 emissions and much of its air pollution (6). 4.1.2 Nitrogen Oxides Nitrogen oxides (NO x ) are responsible for about 35% of acid rain, and are a precursor of O 3 pollution (Figure 4). Of all U.S. air pollutants, oxides of nitrogen have been the most difficult to control. They are formed when ambient diatomic nitrogen (N 2 ) is heated to temperatures > 1200˚F, and their dominant sources are the internal combustion engine and power plants (Figure 5) (1). The 900 million tons of coal burned annually in the United States are responsible for about one-third of all this country’s NO x emissions (3). 2NO + O 2 → 2NO 2 2NO 2 + H 2 O → HNO 2 + HNO 3 There are various ways of reducing nitrogen oxide emissions including combustion control and the use of catalysts (9). Our best option for reducing this pollutant, however, is through reduced burning of fossil fuels and forests. 4.1.3 Sulfur Dioxide Sulfur dioxide (SO 2 ) is responsible for about 60% of acid rain (Figure 4). At least two-thirds of the sulfur oxides in the United States are emitted from coal-fired power plants. Much of the coal burned in the United States has a high sulfur content—2% or more. Most of the remaining SO 2 emissions are accounted for by industrial fuel combustion and industrial processes such as petroleum refining, sulfuric acid manufacturing, and smelting of nonferrous metals (Figure 5) (10). 4.1.4 Carbon Monoxide Carbon monoxide (CO) is the result of incomplete combustion. CO inhibits respiration in animals by binding irreversibly to hemoglobin. About half the CO released to the atmosphere each year is the result of human activities. In the United States, two-thirds of the CO emissions are created by internal combustion engines in transportation (3). 4.2 Photochemical Oxidants Photochemical oxidants are products of secondary atmospheric reactions driven by solar energy—e.g., splitting of an O 2 or NO 2 molecule, freeing an oxygen atom which reacts with another O 2 to form ozone (O 3 ). O 3 is the result of atmospheric chemistry involving two precursors, nonmethane hydrocarbons (HCs) and NO x , which react in the presence of heat and sunlight (Figure 6) (11). Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. SO 2 NO x Acid Rain Atmospheric mixing yields sulfuric and nitric acids Dry deposition of acidic compounds Vehicular emissions Burning of fossil fuels yields SO 2 and NO x FIGURE 4 NO x and SO 2 contributions to acid rain formation. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. This ground-level O 3 is a pollutant that can have harmful effects on human health, while O 3 present in the upper atmosphere protects the earth from harmful ultraviolet radiation. Figure 6 demonstrates the dynamic interactions between HCs and NO x , which are produced from combustion, and atmospheric oxygen. In addition to forming O 3 , NO x can also remove ground-level O 3 . This removal is often temporary, however, as O 3 is re-formed through other reactions. Ground-level O 3 is a respiratory irritant that causes health concerns at very low concentrations because its very low solubility in water means it tends not to be removed by the mucous in the upper respiratory tract and penetrates deeper into the lungs. There is evidence that exposure to O 3 accelerates the aging of lung tissue and increases susceptibility to respiratory pathogens. Human exposure to O 3 can produce shortness of breath and, over time, permanent lung damage (12). Costs of the health effects of O 3 in the United States are estimated to be about $50 billion per year. In addition, O 3 causes more damage to plants than any other pollutant (1). O 3 concentrations rise with temperature and are therefore expected to be exacerbated by global warming. If cloud cover decreases as a result of global SO 2 Emissions Other Combustion 3% Industrial Combustion 12% Ind/Mfg Processes 13% Transport. 4% Utilities 68% NO x Emissions Ind/Mfg Processes 5% Other 1% Other Combustion 4% Transport. 42% Industrial Combustion 16% Utilities 32% FIGURE 5 Percent contribution to SO 2 and NO x emissions in the United States of various industries. (Source: Ref. 34.) Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. warming, thus permitting increased penetration of sunlight, O 3 concentrations will be further increased. 4.3 Raw and Refined Petroleum Spills and Leaks Crude oil spills such as that of the Exxon Valdez are probably the most widely known examples of this type of energy-related pollution. In addition, it has been estimated that about 11 million gallons of gasoline are lost each year by leaking underground storage tanks (3). 4.4 Mining-Related Pollution Acid mine drainage is one of the most common and damaging problems in the aquatic environment. Many waters flowing from coal mines and draining from the waste piles that result from coal processing and washing have low microbial H OH H 2 O O 2 O 2 HO NO O NO 2 hv λ=0.39µ m O 2 OO 3 O 2 O 2 H O 3 O O 2 hv λ=0.39µ m NO 2 NO OH FIGURE 6 The release of hydrocarbons and NO during combustion results in the conversion of NO to NO 2 . Increased formation of NO 2 increases the production of O 3 . Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. densities due to the highly acidic nature of these waters. Acidic mine water results from the presence of sulfuric acid produced in a series of microbially mediated reactions that begin with the oxidation of pyrite, FeS 2 (13). Often, mining operations result in surface waters infiltrating into the subsurface voids, especially after the mine is exhausted and pumping ceases. In some areas of Appalachia, large underground impoundments of water have filtered into coal mines. These waters have become very acidic and, when they are returned to the surface via pumping or by subsurface flows, their low pH value devastates the aquatic systems they infiltrate (14). Another impact of underground mining is the waste materials that are a by-product of any mining operation. Gaining access to the vein or seam of coal, as well as transporting the coal to the surface, requires large amounts of waste materials to be removed to the surface. These waste materials, or tailings, are often piled up in large mounds in close proximity to the mine. The composition of many tailings can contain toxic minerals such as mercury, lead, or iron sulfide. Water percolating through these waste materials often produces water quality problems downstream from the tailings similar to those associated with subsur- face water flows from within the mines. In addition to the sterile conditions on tailings mounds themselves, rain water running off the tailings often is so acidic as to kill both the vegetation in the immediately affected lands and the aquatic life in streams and rivers receiving these waters. Many lands and streams within the Appalachian coalfield areas of western Pennsylvania, West Virginia, eastern Kentucky, and eastern Ohio are devastated by the acidic waters resulting from coal mining operations. The enactment of environmental legislation limits the damage associated with active mining operations, but the land degradation associated with past mining has left a filthy legacy of degraded landscapes (14). Surface mining is usually favored over underground mining for primarily economic reasons. It is virtually impossible to prevent land degradation when surface mining occurs. First, in some operations, huge depressions result. Second, the overburden (extracted soil, subsoil, and unconsolidated earth and rocks) must be stored and then replaced systematically in their original order after the mineral is removed. Even under optimal conditions, which rarely occur, restoration usually results in a landscape that is less productive than it was prior to mining. Subsurface groundwater flow is always disturbed, and revegetation is often slow. Restoration is further complicated when toxic materials are leached from the overburden during its storage. These conditions often occur in coal mining operations, which have disturbed about 2.3 million acres in the United States (14). The area affected by mining can be three to five times more widespread than the area actually exploited (15). Even when increased acidity is not consid- ered, mining-related soil erosion alone can impact natural waters significantly. Added nutrients may increase aquatic productivity, resulting in eutrophication. Lower levels of dissolved oxygen associated with eutrophication may render the Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. [...]... drowned out some of the most beautiful stretches of American rivers, flooded agricultural lands, forests, and areas of historical and geological value, and resulted in the dislocation of communities and loss of wildlife (6) Dam failure can cause catastrophic floods and thousands of deaths Sedimentation often fills reservoirs rapidly and reduces the usefulness of the dam for either irrigation or hydropower... Inefficient and incomplete burning of wood in stoves and fireplaces produces smoke laden with fine ash and soot and hazardous amounts of carbon monoxide and hydrocarbons The U.S Environmental Protection Agency (EPA) ranks wood burners high on a list of health risks to the general population, and standards are being considered to regulate the use of woodstoves nationwide Highly efficient and clean-burning... decomposition of organic matter in landfills However, leaks in natural gas pipelines contribute about 21% of anthropogenic methane, and the burning of coal adds an additional 6% Other energy-related sources of methane include coal mines, natural gas leaks, gas associated with oil production, and the creation of new wetlands when forests are flooded following construction of hydroelectric dams 4.6 Thermal Pollution. .. lands devoted to croplands, or the 31% to pastures Moreover, many of the solar cells could be placed on the walls and roofs of existing structures, reducing the area of land needed (6) If the entire present U.S electrical output came from central tower solar steam generators, 78 0 square miles of collectors would be needed This is less land, however, than would be strip-mined in a 30-year period if all... Dams As of 19 87, hydroelectric dams in the United States provided the energy equivalent of about 71 large power plants, about 10–14% of U.S electricity, or about 3% of total energy supply, depending on year-to-year rainfall patterns Of the pollutants associated with fossil fuel energy, methane is the only one that results from the damming of rivers However, large dams have drowned out some of the most... Transportation Transport activities account for about 30% of the energy used by final consumers, and about 20% of the gross energy produced (9) About 98% of the total comes from petroleum products refined into liquid fuels, and the remaining 2% is provided by natural gas and electricity (3) Movement of people takes about 70 % of the total, and movement of freight about 30% Within this sector, road transport... 20% of the greenhouse effect, and concentrations have already risen to more than double preindustrial estimations Concentrations continue to rise at about 0.9% annually (4) The majority of anthropogenic methane is the result of non-energy-related human activities such as ruminant livestock and cultivation of rice (from which about half the world’s population derive about 70 % of their calories), and. .. Challenge of Change In J Byrne and D Rich (eds.), Energy and Environment: The Policy Challenge, New Brunswick, NJ: Transaction, 1992 7 P M Vitousek, H A Mooney, J Lubchenco, and J M Melillo, Human Domination of Earth’s Ecosystems Science, vol 277 , pp 494–499, 19 97 8 A Whyte, The Human Context In H Coward (ed.), Population, Consumption and the Environment, pp 41–59 Albany: State University of New York... energy, and large-scale hydropower for another 30% (9) About half of all wood harvested in the world annually is used for fuelwood; many countries use fuelwood (including charcoal) for more than 75 % of their nonmuscle energy About 40% of the world’s total population depend on firewood and charcoal as their primary energy source In some African countries, such as Rwanda and Sudan, firewood demand is... 1% of energy in the United States, but in many of the world’s poorer countries, wood and other biomass fuels provide up to 95% of all energy consumed Approximately half of all wood harvested annually is for fuel About 40% of the world’s population depend on firewood and charcoal as their primary energy source; however, about three-fourths of these lack an adequate, affordable supply (3) In wood-burning . these demands, and a survey of the environmental impacts of some of the pollutants produced by these fuels. 2 ENERGY SUPPLIES AND DEMANDS Coal, oil, and natural gas supply about 95% of global. consumption of energy derived from combustion of carbon-based fuels are among the most important means of preventing global pollution. After a look at energy demands, this chapter dis- cusses several. biosphere of raw and refined petroleum products; and mining- related pollution. Obviously, then, decreasing our consumption of carbon-based energy will result in decreases in the amounts of these