Environmental Effects of Coal - from Wikipedia

[Systematic Chaos]

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Burning

Combustion of coal, like any other fossil fuel, occurs due to an exothermic reaction between the components of the fuel source, and the components air surrounding it. Coal is made primarily of carbon, but also contains sulfur, oxygen and hydrogen. The reaction between coal and the air surrounding it produces oxides of carbon, usually carbon dioxide (CO2 - a major greenhouse gas) in a complete combustion, along with oxides of sulfur, mainly sulfur dioxide (SO2), and various oxides of nitrogen (NOx). Because of the hydrogen and nitrogen components of air, hydrides and nitrides, of carbon and sulfur, are also produced during the combustion of coal in air. These could include hydrogen cyanide (HCN), sulfur nitrate (SNO3) and many other toxic substances.

Further, acid rain may occur when the sulfur dioxide produced in the combustion of coal, reacts with oxygen to form sulfur trioxide (SO3), which then reacts with water molecules in the atmosphere to form sulfuric acid (see Acid anhydride for more information). The sulfuric acid (H2SO4) is returned to the Earth as acid rain. Flue gas desulfurization scrubbing systems, which use lime to remove the sulfur dioxide can reduce or eliminate the likelihood of acid rain.

However, another form of acid rain is due to the carbon dioxide emissions of a coal plant. When released into the atmosphere, the carbon dioxide molecules react with water molecules, to produce carbonic acid (H2CO3). This, in turn, returns to the earth as a corrosive substance. This cannot be prevented as easily as sulfur dioxide emissions can, because carbon is the main component of coal, and this resultantly means that a person cannot as easily reduce carbon dioxide emissions caused in the oxidation of coal, as they can with the aforementioned use of lime to reduce sulfur dioxide emissions.

Emissions from coal-fired power plants represents one of the two largest sources of carbon dioxide emissions, believed to be the cause of global warming. Coal mining and abandoned mines also emit methane, another purported cause of global warming. Since the carbon content of coal is higher than oil, burning coal is a serious threat to the stability of the global climate, as this carbon forms CO2 when burned. Many other pollutants are present in coal power station emissions, as solid coal is more difficult to clean than oil, which is refined before use. A study commissioned by environmental groups claims that coal power plant emissions are responsible for tens of thousands of premature deaths annually in the United States alone. Modern power plants utilize a variety of techniques to limit the harmfulness of their waste products and improve the efficiency of burning, though these techniques are not subject to standard testing or regulation in the U.S. and are not widely implemented in some countries, as they add to the capital cost of the power plant. To eliminate CO2 emissions from coal plants, carbon capture and storage has been proposed but has yet to be commercially used.

Coal and coal waste products including fly ash, bottom ash, and boiler slag, contain many heavy metals, including arsenic, lead, mercury, nickel, sulphur, vanadium, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, selenium and radium, which are dangerous if released into the environment. Coal also contains low levels of uranium, thorium, and other naturally-occurring radioactive isotopes whose release into the environment may lead to radioactive contamination.<6><7> While these substances are trace impurities, enough coal is burned that significant amounts of these substances are released, resulting in more radioactive waste than nuclear power plants.<8> Mercury emissions from coal burning are concentrated as they work their way up the food chain and converted into methylmercury, a toxic compound<9> that may affect people who frequently consume freshwater fish affected by mercury pollution from nearby coal-fired power plants.<10> Ocean fish account for almost all of most people's exposure to methylmercury;<10> the sources of ocean fish methylmercury are not well understood.

[madokie]

1. Why aren't they using gasifiers?

http://www.fossil.energy.gov/programs/powersystems/gasification/howgasificationworks.html

The heart of gasification-based systems is the gasifier. A gasifier converts hydrocarbon feedstock into gaseous components by applying heat under pressure in the presence of steam.

A gasifier differs from a combustor in that the amount of air or oxygen available inside the gasifier is carefully controlled so that only a relatively small portion of the fuel burns completely. This "partial oxidation" process provides the heat. Rather than burning, most of the carbon-containing feedstock is chemically broken apart by the gasifier's heat and pressure, setting into motion chemical reactions that produce "syngas." Syngas is primarily hydrogen, carbon monoxide and other gaseous constituents; the composition of which can vary depending upon the conditions in the gasifier and the type of feedstock.

Minerals in the fuel (i.e., the rocks, dirt and other impurities which don't gasify like carbon-based constituents) separate and leave the bottom of the gasifier either as an inert glass-like slag or other marketable solid products. Only a small fraction of the mineral matter is blown out of the gasifier as fly ash and requires removal downstream.

Sulfur impurities in the feedstock are converted to hydrogen sulfide and carbonyl sulfide, from which sulfur can be easily extracted, typically as elemental sulfur or sulfuric acid, both valuable byproducts. Nitrogen oxides, another potential pollutant, are not formed in the oxygen-deficient (reducing) environment of the gasifier; instead, ammonia is created by nitrogen-hydrogen reactions. The ammonia can be easily stripped out of the gas stream.

[Systematic Chaos]

2. Once again, from Wikipedia:

A major challenge for waste gasification technologies is to reach an acceptable (positive) gross electric efficiency. The high efficiency of converting syngas to electric power is counteracted by significant power consumption in the waste preprocessing, the consumption of large amounts of pure oxygen (which is often used as gasification agent), and gas cleaning. Another challenge becoming apparent when implementing the processes in real life is to obtain long service intervals in the plants, so that it is not necessary to close down the plant every few months for cleaning the reactor.

Several waste gasification processes have been proposed, but few have yet been built and tested, and only a handful have been implemented as plants processing real waste, and always in combination with fossil fuels<10>.

One plant (in Chiba, Japan using the Thermoselect process<11>) has been processing industrial waste since year 2000, but has not yet documented positive net energy production from the process.

Edit: link here.

[madokie]

3. Waste disposal???

[AndyTiedye]

4. We Need That Coal to Make CARBON FIBER!