Heat into electricity
The combustion of coal has been used to generate electricity since early in the industrial era. Heat produced by burning coal is used to drive a heat engine, which usually utilizes steam to drive electric turbines1 . Since humans first began to use coal to produce electricity we have developed much more efficient steam powered heat engines. This has helped to continually increase the efficiency of coal-fired electricity. Coal is used to produce more electricity than any other fuel source. Coal is the primary source of baseload power in the world. Coal power plants are most cost effective when they are run at full capacity all the time, with the exception of planned maintenance down times or emergencies.
The efficiency at which coal can be converted into electricity varies with the thermal efficiency of the plant and the quality of coal used. Using a reasonable set of assumptions, one can state that approximately 2.0 kilowatt-hours (kwh) of electricity are generated from the burning of one kilogram of coal. If a kilowatt-hour is not a meaningful unit to you, please see our Energy: Terms and Definitions article.
Using the value of 1995 billion kWh of coal power generated in the US, also generating 129 million tons of fly ash we can estimate a fly ash contribution of 58.6 grams/kWh on average. Using the 2008 average electricity use per US household of 11,040 kWh/year, a household powered by coal-fired electricity is responsible for the generation of approximately 647 kg of fly ash per year. This is significant since almost half of the electric power produced in the United States is from coal2 .
More efficient coal-fired power plant designs have been developed over the last century. These designs have improved efficiency as well as reduced the emitted gaseous pollutants. These designs have been adopted thanks to both government regulation and technological developments.
The average thermal efficiency of coal power plants in the world is 28%3 with designs existing with efficiencies as high as 48%4 . This means that on average a coal plant today turns thermal energy into electric energy with an efficiency of 28%.
Government requirements to reduce emissions have driven down the nitrous oxide, sulphur oxide, particulate matter, and fly ash emissions of coal power dramatically over the past 40 years. However, this reduction is not enough, since these reduced emissions still pose a serious human health concern. Cost effective scrubber and electrostatic precipitator technologies have yielded these benefits without significantly increasing the cost of coal electricity.
Further technological development will be necessary to meet pending pollution standards. Taxes on carbon emission are especially relevant to coal-fired electricity. These taxes are seeing increased implementation around the world in recent years5 . High carbon dioxide emissions may make coal power significantly more expensive if carbon capture and sequestration technology is not rapidly and cost-effectively developed.
Burning coal releases heat energy, but it also releases many other products. Combustion products such as carbon dioxide, water vapour, nitrous oxides, sulphur oxides, particulate matter, and fly ash are also produced in varying amounts. Before it became a regulated waste, fly ash was mostly released into the atmosphere along with the other combustion products.
In the past 45 years coal plants have been required by regulation to capture increasing fractions of their fly ash rather than expelling it into the atmosphere. In most developed countries, over 99% of the fly ash is captured and stored. However, this has created a large waste disposal issue that we will discuss in more detail later in this article.
Of these byproducts, only water vapor is not considered a pollutant. The effects of these products on humans and the environment will be discussed in more detail later in this article. Additionally, coal-fired power plants need a constant and consistent supply of cooling water. The exhaust of heated water represents the introduction of thermal pollution to the body of water used for cooling.
Health and environmental effects
Some negative externalities arise from the use of coal as a primary electricity source. Negative health effects on the nearby human population, plant life, and wildlife have been hard to quantify precisely and thoroughly, and are generally not included in the cost of coal power to the consumer.
The developed world currently has comparatively high standards for some forms of coal emissions, but this does not avoid all loss of life in these places. We may not remain so lucky, as there are ongoing struggles between industry lobbies and environmental groups for the attention of governments to consider loosening environmental regulations, as occurred under the “Clear Skys Act“.
Some developing nations are not so forward-looking on this issue, choosing to allow the industry to emit toxins unhindered because that is the cheaper alternative. It is hard to blame the poorest nations for their relative lack of environmental standards because they are doing the best they can to advance to a better standard of living. However, it is possible to advance towards more healthy energy sources without sacrificing very much wealth. If the developed world aided impoverished nations more, this problem could be alleviated to some extent.
In addition to the direct harm to humans, coal emissions harm our environment as well. The emission of carbon dioxide has received an increasing amount of media attention in the past decade, and for good reason. Emissions of the greenhouse gas carbon dioxide due to human activities, such as coal power, are believed to be a key contributing factor to global warming and climate change by the scientific community.
Rising levels of carbon dioxide in the atmosphere are also believed to be related to increasing acidification of the oceans. Ocean acidification is damaging sensitive sea life and ecosystems as well as human industries dependent on ocean productivity.
The fine particulate matter emitted when coal is burned has the potential to significantly harm human health. These small particles are breathed into the body, damaging lung alveoli or helping to trigger lung cancer. The smallest particles can work their way directly into the blood stream.
These particles can be filtered from emissions to a large extent with today’s technology, but this is not always done. Regulatory requirements vary from nation to nation, and not all have strong emissions standards. Without regulation forcing them to literally ‘clean up their act’, coal power producers have little incentive to spend even the relatively small amount of money necessary to clean up these emissions.
This type of pollution contributes to approximately 24,000 deaths in the USA per year by damaging cardio-respiratory health and triggering lung cancer. The EPA considers the majority of these to be preventable deaths, as emissions reduction technology exists to prevent approximately 90% of these deaths.
Sulphur oxides (SOx)
Unless removed before combustion, the sulphur present in coal will be emitted as sulphur oxides when the coal is burned. In the atmosphere, sulphur oxides are capable of forming sulphuric acid, which damages plants and buildings through the production of acid rain. The concentration of sulphur in coal deposits varies from site to site, but it is known that China has particularly high levels of sulphur in their coal. In China alone, there are approximately 400,000 deaths each year due to sulphur dioxide emissions, the majority of which are emissions from burning coal that has a high sulphur content.
Efforts to control the emissions of sulphur oxides in Europe and North America are a regulatory success story. The intent was to produce a cleaner and healthier environment for us at manageable economic costs. In the US, a cap and trade system was phased in following a major study in 1991. This system contributed to decreasing acid rain levels by 65% compared to 1976 levels. The EPA estimates the cost of the program at 1-2 billion dollars per year, about a quarter of the original cost predictions6 . The EU saw a 70% decrease in acid rain levels over the same time period.
Many plants and animals are sensitive to changes in soil and water pH, so acid rain will have a variable but overall negative effect on ecosystems. The plant and animal species that are particularly sensitive can be put in serious danger by the emissions from coal power plants. Damage to flora and fauna has a significant effect on the balance of the ecosystem.
Additionally, changes in soil pH cause the leaching of base cations such as calcium and magnesium. This causes the soil to become more basic, which will require correction through soil additives to minimize negative effects on life. Applying such additives is only practical for agricultural land, as it can be added like a fertilizer or other crop additive. Wild areas, or those not under cultivation, are unlikely to be able to naturally correct for these effects in a timely manner. Changes in soil pH of this sort tend to reduce the health and quantity of vegetation growth.
Acid rain also causes damage to human construction, including outdoor masonry and art. The acidity dissolves the calcium in marbles and limestone over time. Additionally, acidic solutions increase the corrosion rate of bronze and copper art and architecture. This can cause the degradation and eventual loss of priceless human artifacts7 .
Nitrogen oxides (NOx)
Nitrogen oxides are produced from the oxygen and nitrogen gases present in high-temperature coal combustion. Nitrogen oxides contribute to the greenhouse effect, the formation of acid rain, ground level ozone production, and photochemical smog. Nitrogen oxides can also produce nitric acid when interacting with moisture and other chemicals in places such as the human lungs. Ozone, a product of nitrogen oxide reactions with other pollution and the atmosphere, is a harmful oxidizing agent that damages the lungs. As a result of all of these effects, nitrogen oxides released through the combustion of coal lead to numerous early deaths due to respiratory and heart damage, as well as the aggravation of asthma and bronchial conditions.
Historically, coal mining was a very dangerous undertaking for those involved. Underground coal mines were prone to collapse, with the potential to harm miners. The modernization of the coal mining industry has drastically reduced this risk. It is now the case that in the U.S., only tens of coal miners die per year compared to times in history when yearly coal miner deaths numbered in the hundreds to thousands.8
Most of the ill effects of coal mining today are due to pollutants that are released during the mining process. Most of this pollution is caused by a technique known as mountaintop removal, in which the ‘overburden’ above a coal seam is removed into valleys, along with other waste from the mining process. Mountaintop removal exposes toxic contaminants in the ground that are found along with coal. These toxic materials are often swept into the ecosystem by rain and streams that have been buried in the valleys.
Damage to ecosystem
Deforestation and elimination of streams due to mountaintop removal can have a drastic effect on the ecosystem. In particular, they damage the biodiversity of the local ecosystem by driving out or killing species populations. The current environmental re-mediation efforts are inadequate to replace the ecosystem services that were once provided by the living ecosystems of the regions before they were subjected to mountaintop removal.
Ecosystems that were once largely forested are repopulated with fast growing non-native grasses. Streams which were an integral part of the local ecosystem are filled in with mining waste and rubble. Weak environmental regulations permit this woefully incomplete re-mediation process. If a more thorough ecosystem replacement were required, many mountaintop removal projects would no longer be economically viable.
This land has, however, been found to be appropriate for other uses, such as real estate development, grazing, and the farming of game animals. Additionally, the sale of lumber may provide supplemental income before the mining begins, if it is not simply burned.
One of the starkest and most obvious changes is visible in the deforestation and altered topography of sites that have undergone mountain top removal. To this author, it seems a pity to sacrifice such sites of natural beauty, as well as the health of those fortunate enough to live near them, in order to extract a marginal amount of coal.
Water bodies that are downstream have been found to contain elevated levels of arsenic and other pollutants which can pose a definite human health hazard. Even worse, much of this pollution is in excess of existing regulatory limits that are not being enforced. To combat this, coalitions of environmental activist organizations and locals must often take polluters to court at their own expense.
When warm water used to cool a coal power plant is exhausted into bodies of water that harbor life, it becomes thermal pollution which can have negative effects on the ecosystem. Heating a body of water decreases its dissolved oxygen content, which has the potential to harm animals dependent on it for oxygen. Heating also leads to an increase in the metabolic rate of the organisms living in the body of water, causing them to require more food. Warmer waters can trigger algae blooms, further depriving the water of oxygen.
Some forms of life may benefit from changes to the temperature of water bodies. In particular, the manatee is known to use the thermal output of power plants as a refuge in the winter. However, changes in temperature tend to cause biodiversity in these areas to go down. These local ecosystems are being forcibly moved away from the self directed equilibria in which the diversity of life has established some degree of balance.
What can be done about thermal pollution? Fortunately, there is some hope. The more efficient a thermal power plant is, the less thermal pollution needs to be rejected into the environment to produce the same amount of electricity. The use of cooling ponds and cooling towers reduces the quantity of heat exhausted into the living environment. Both of these techniques use man-made structures to encourage heat dispersal through water evaporation and the heating of the air.
Alternatively, the extra heat can be used for human and industrial needs, such as space heating, district heating, or industrial processes requiring ‘low grade’ heat. ‘Low grade’ heat refers to thermal resources that are at a relatively low temperature by industrial standards, generally below about 130ºC, or 266ºF. The process of utilizing waste heat from a power plant for other uses is known as co-generation.
Fly ash represents the large particulate matter left over after coal is burned. It contains large amounts of silicon and calcium oxides as well as smaller proportions of heavy metals such as mercury and arsenic. Fly ash is a very toxic material. Since the formation of the EPA, stringent emission regulations have required the removal of larger and larger fractions of fly ash from atmospheric emissions. In the western world, it is common for more than 99% of fly ash to be captured at the stack. While this has been a great boon for air quality worldwide, this has created a new form of hazardous waste that we need to deal with.
Unlike the other pollutants emitted by the burning of coal, which are gaseous or energy, there is a large volume and mass of fly ash that needs to be dealt with. In the US alone, 129 million tons of fly ash are produced each year. While some of this ash is cycled into other uses such as a concrete filler, a significant amount of it remains stored in ash ponds and landfills.
We assert that landfilling fly ash is not a solution; it only creates an ever-growing accident waiting to happen. As the amount of fly ash stored worldwide increases, accidents such as this one in Tennessee will continue to happen at increasing costs to people’s health and pocketbooks, as well as the environment.
If we can produce less fly ash through the burning of less coal, we can move toward the goal of reusing more fly ash than is produced each year. The goal is to decrease the amount of fly ash stored, since it represents a significant danger to human and ecosystem health. Fly ash is considered fit for a variety of uses, from fill material on Portland cement to use as a sewage stabilizer for human waste, to ‘cinder blocks‘ used for construction.
We believe that this aspect of coal pollution warrants more attention than it currently gets. There are a number of interesting and informative articles from other sources to draw upon for more information on this topic, such as this Scientific American article regarding the radioactive content of fly ash, or this lengthly article discussing the aftermath of the Kingston coal ash spill in Tennessee.
Coal industry vs the people
It is in the interest of those profiting from the producing and use of coal power to keep the costs of this damage external, and knowledge of the extent of the damage poorly developed. This means that it is in the economic interests of the coal industry to keep the public ignorant of these negative effects, and thus keep these extra costs from affecting their profits, or knowledge of the damage from hurting their reputation or catalysing the creation of stricter regulations.
It is in the interest of those suffering the ill effects of this damage to ensure that companies and people responsible for producing coal power internalize the costs they have placed on society and the environment. Market goods need to carry their true prices in order for free market economics to function effectively. Coal power should only be used if the benefits outweigh its true costs, and those individuals who are harmed through its use are fairly compensated.
Why do we still do it?
So far, this article has largely been a list of warnings, quantifying the damaging effects of using coal for electrical production. The reader might ask, why then do we still burn coal? Well, for starters, burning coal to make power is cheap. Coal is a fairly inexpensive and abundant fuel source and humanity has had much practice in developing more cost effective and thermally efficient ways of burning it. We have commented in the past that it is difficult to find a cheaper source of power than ‘burning flammable dirt’.
As discussed earlier, many of the costs of burning coal remain unaccounted for in the bills of those using coal power. Some of these costs are born in other ways, such as through lower agricultural productivity and higher health care costs, while other costs will not necessarily be seen immediately or locally.
Many of the institutions of our developed society directly or indirectly benefit from very low electricity costs. For our society to continue functioning as we expect it to, it is transitioning towards electricity sources that can compete with coal in terms of cost. In the past decades we have seen cost-effective power sources from natural gas, hydro, wind, nuclear, biomass and geothermal9 .
Some relatively new forms of electricity such as solar photovoltaics and solar thermal power are also showing great promise. When calculations include the full cost of coal, including the negative effects on the environment and human health, cleaner forms such as wind energy have already taken the lead as the cheapest form of electricity in many areas of the world.
It is also advisable to reduce our electricity use while these new technologies are being refined and implemented. This will extend the lifetime of our existing power infrastructure and reduce the impact that changes in the cost of electricity will have on our lives. Transitioning away from coal-fired electricity will take a lot of time and effort, but technologies exist that can currently be implemented to steadily replace it as our primary source of electrical power. There may be difficulty in this transition, but we can choose an energy path that is less costly to our health and environment.
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- Wikipedia: Carbon Tax. Accessed October 13th, 2010. [↩]
- Wikipedia: History of acid rain in the United States. Accessed October 12th, 2010. [↩]
- Top 5 Endangered Heritage Sites – Acid Rain. CyArk. Accessed October 13th, 2010. [↩]
- Injury Trends in Mining. United States Department of Labor. Accessed October 13th, 2010. [↩]
- Wikipedia: Cost of electricity by source. Accessed October 12th, 2010. [↩]