Lecture -11: Fossil Fuels and the environment ENV 107: Introduction to Environmental Science Dr. A.K.M. Saiful Islam
16.1 Fossil Fuels Fossil fuels are all forms of stored solar energy. We say because plants are solar energy collectors. They convert solar energy to chemical energy through photosynthesis. The fossil fuel created from incomplete biological decomposition of dead organic matter (mostly plants and marine organisms). When organic matter is buried and escape oxidation, it can be converted by complex chemical reactions in the geologic cycle to hydrocarbons and to fossil fuels. The main fossil fuels are crude oil, natural gas and coal are considered our primary energy sources because on a worldwide basis they provide approximately 90% of the energy consumed.
16.2 Crude oil and natural Gas Crude oil (petroleum) and natural gas are formed primarily along tectonic belts at plate boundaries. Oil and gas are derived from organic materials that were buried with marine or lake sediments in what are known as depositional basins. The elevated temperature and pressure initiated the chemical transformation of the organic material in the sediment into oil and gas. The oil and gas field from which we extract resources are places where the natural upward migration of the oil and gas to the surface is interrupted or blocked by what is known as a trap. The rock that helps form the trap known as cap rock is composed of silt and clay sized particles. Favorable geometry in the rock structure such as anticline (Arcshaped fold) or a fault (fracture in the rock along which displacement has occurred) may form traps.
Petroleum production Primary production involves pumping from the wells under natural pressure in the oil fields which can be high and must be carefully controlled. This method can recover 25% of available petroleum. Secondary recovery or enhanced can recover 60% of available petroleum. In secondary recovery, the pressure in the reservoir is changed by injecting steam, water or chemicals such as carbon dioxide or nitrogen gases into the reservoir to push the oil toward the wells where it can be recovered by pumping.
Environmental Effects of Oil and Natural Gas 1. Recovery Disruption of the land to construction pads for wells, pipelines, or storage tanks and to building a network of roads and other production facilities. Pollution of surface waters and groundwater from runoff and infiltration or leaking from ken pipes or tanks of contaminated surface, waste water or fluids used in secondary recovery. Accidental release of air pollutants, such as hydrocarbons and hydrogen sulfide (in toxic gas). Land subsidence (sinking) as oil and gas are withdrawal. Loss or disruption and damage of fragile ecosystem, such as wetlands or other unique landscapes.
(cont..) 1(b) Additional environmental impacts associated with oil production in the marine environment include: Oil seepages resulting from normal operations or large spills from accidents such as blowouts or pipe ruptures. Release of drilling mud (heavy liquids injected into the bore hole during drilling to keep the hole open) containing heavy metals, such as barium, that might be toxic to marine life. Aesthetic degradation from the presence of offshore oil-drilling platforms, which some people think unsightly.
(cont..) 2. Refining At refiners, crude oil is heated so that its components can be separated and collected. Refiners may accidental spills and slow leakage of gasoline and other products from storage tanks and pipes. Over years of operation, large amounts of liquid hydrocarbons may be released, polluting soil and groundwater resources below the site. The various industrial processes involved have the potential for releasing a variety of pollutants into the environment.
(Cont..) 3. Delivery and Use The most extensive and significant environmental problems associated with oil and gas occur when the fuel is delivered and consumed. Crude oil is mostly transported on land in pipelines or across the ocean by tankers. Both methods have the potential to produce oil spills, however marine oil spills are better known. Marine spills kill thousands of seabirds, temporarily spoiled beaches and caused loss of tourist revenue. Air pollution is perhaps the most familiar from serious environmental impact associated with the use (burning) of oil.
Coal Coal is by far most abundant world s most abundant fossil fuel, with a total recoverable resources of about 1000 billion metric tons.
Coal and the environment Most coal mining in the United States is done by strip mining, surface mining in which the overlying layer of soil and rock is stripped off to reach the coal. The impact of strip mining with abundant rainfall, drainage of acid water from mine sites is a serious problem. Underground coal mining is a dangerous profession; there are always hazards of collapse, explosion, and fire. Respiratory illness are risk, especially black lung disease, which is related to exposure to coal dust and has killed or disabled many miners.
(contd..) Some environmental problems associated with underground mining are listed here: Acid mine drainage from the mines and waste piles has polluted thousands of kilometers of streams. Land subsidence can occur over mines. Vertical subsidence occur when the ground above coal mine tunnels collapses. Coal fires in underground mines may be either naturally caused or deliberately set. The fire may belch smoke and hazardous fumes causing people exposed to them to suffer from a variety of respiratory diseases.