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Sea: Pollution
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Water Resources and Hydrological Systems, 2020
The ocean waters absorb carbon dioxide (CO2), sulfur dioxide (SO2) and trioxide (SO3), and nitrogen oxides (NxOy) from the atmosphere. Because the atmospheric concentrations of these gaseous oxides are increasing, the oceans are becoming more acidic.[35] The potential consequences of ocean acidification are not fully understood; however, there are concerns that structures made of calcium carbonate may become vulnerable to dissolution, affecting corals and the ability of shellfish to form shells.[36,37] Oceans and coastal ecosystems play an important role in the global carbon cycle and have removed about 25% of the carbon dioxide emitted by human activities between 2000 and 2007. Rising ocean temperatures and ocean acidification means that the capacity of the ocean carbon sink will gradually become weaker. Also, the methane clathrate reservoirs, containing large amounts of the greenhouse gas methane, under sediments on the ocean floors, can potentially release the methane when oceanic water becomes warm. In 2004, the global inventory of ocean methane clathrates was estimated to occupy between 1 and 5 million cubic kilometers. This estimate corresponds to 500–2500 gigatonnes carbon (Gt C), and can be compared with the 5000 Gt C estimated for all other fossil fuel reserves.[38]
Nonrenewable Energy Sources
Published in John C. Ayers, Sustainability, 2017
Unconventional natural gas is obtained from sources other than oil fields. Unlike oil, natural gas is not restricted in depth to a “window,” so deeper drilling can uncover new reserves of unconventional natural gas. Unconventional natural gas can also be produced by biofuel production methods that transform biomass to natural gas through bacteria-mediated anaerobic decay. The same processes occur in swamps and landfills, where bacteria obtain energy by catalyzing the breakdown of heavy hydrocarbons to form methane (swamp gas). Decomposition of organic material in landfills and sewage also produces methane. Landfills used to burn off produced methane to prevent explosions, but it is becoming more common for landfills to recover it for use as a fuel. Similarly, sewer treatment plants in large cities such as Los Angeles and New York City are starting to recover methane and use it to produce electricity. Another unconventional natural gas source is methane clathrates or “methane ice” stored in sediments on the continental shelf. Methane clathrates may store more energy than all of the other fossil fuels combined (Lavelle 2012). However, we have yet to develop a safe method for extracting natural gas from these deposits.
Methane from Gas Hydrates
Published in Yatish T. Shah, Water for Energy and Fuel Production, 2014
Methane clathrates (hydrates) are commonly formed during natural gas production operations, when liquid water is condensed in the presence of methane at high pressure. It is known that larger hydrocarbon molecules such as ethane and propane can also form hydrates, although these are not as stable as methane hydrates. Once formed, hydrates can block pipeline and processing equipment. They are generally removed by (1) reduction of the pressure, (2) addition of heat, or (3) dissolving them using chemicals such as methanol and ethylene glycol. Care must be taken to ensure that the removal of the hydrates is carefully controlled, because as the hydrate undergoes phase transition, the release of water and methane can occur at very high rates. The rapid release of methane gas in a closed system can result in a rapid increase in pressure [104,105], which can be harmful to the drilling operation. In recent years, hydrate formation during drilling operation is controlled with the use of kinetic hydrate inhibitors [96–99,113–116], which dramatically slow the rate of hydrate formation and anti-agglomerates, which prevent hydrates from sticking together to block pipes and other parts of equipment.
Hydrogen-/propane-hydrate decomposition: thermodynamic and kinetic analysis
Published in Molecular Physics, 2019
Mohammad Reza Ghaani, Niall J. English
Dissociation had an Arrhenius temperature dependence; activation energies increased in going from a semi-planar (X) to a planar interface (T). This is in accord with the previous findings of English and Phelan comparing spherical nano-clusters and planar surfaces for methane clathrate [27].