Fossil fuel power plant
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A fossil fuel power plant is a system of devices for the conversion of fossil fuel energy to mechanical work or electric energy. The main systems are the steam cycle and the gas turbine cycle. The steam cycle relies on the Rankine cycle in which high pressure and high temperature steam raised in a boiler is expanded through a steam turbine that drives an electric generator. The steam gives up its heat of condensation in a condenser to a heat sink such as water from a river or a lake, and the condensate can then be pumped back into the boiler to repeat the cycle. The heat taken up by the cooling water in the condenser is dissipated mostly through cooling towers into the atmosphere.
Fossil fuel plants are divided into very different types of energy generation, classified by fuel type: natural gas, petroleum and coal. Not only are the respective different processes, but also generate very different atmospheric emission levels.
The gas turbine cycle relies on the Brayton cycle in which air compressed to high pressure, and heated to high temperature by the combustion of natural gas or light fuel oil, is the working fluid that expands in the turbine to provide the torque for driving both a compressor and the electric generator. The gas turbine demands clean fuels such as natural gas or light fuel oil. Combustion is the prevailing fuel utilization technology in both the above cycles. Coal is the preferred fuel for the steam cycle because of its low cost and broad and secure availability worldwide.
Combustion-generated pollutants, such as oxides of nitrogen (NO,x), of sulfur (SOx), and particulates, if uncontrolled and emitted into the atmosphere represent environmental and health hazards, such as acid rain. Environmental regulations supported by intensive research and developments have reduced pollutant emissions significantly. Improvements in efficiency and emissions come by increasing steam pressure and temperature in the steam cycle, and by increased turbine inlet temperature in the gas turbine cycle. Coal gasification produces a fuel gas that is capable of being used in the gas turbine. By integrating coal gasification with gas turbine and steam cycles, advantage can be taken of high efficiency and low pollutant emission while using coal, an inexpensive, secure and indigenous fuel in many countries throughout the world. A potential additional advantage of the Integrated Gasification Combined Cycle (IGCC) is the capability of capturing carbon dioxide (CO2) from the fuel gas and making it ready for high-pressure pipeline transportation to a carbon sequestration site. This will be key to the commercial and clean co-production of electricity and hydrogen from coal.
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Natural Gas Plants
Natural gas generating plants produce the lowest atmospheric emissions of any fossil fuel; for example, carbon dioxide emissions are .91 pounds per kilowatt hour as of 2020. In the USA natural gas production accounts for almost one half of all fossil fuel plant production of electricity. This rate of CO2 generation is about four times that compared to the amortised value of solar panel manufacture per kilowatt hour, based upon US based manufacture; however, since most panels are made in China, it is about 1.7 times the value of solar manufacture.
Petroleum Plants
Petroleum plants that produce electricity have lower emissions than coal; namely carbon dioxide emissions are 2.13 pounds per kilowatt hour as of 2020. Of all fossil fuel sources, oil has the advantages of easy transportation especially using pipelines, and easier storage than natural gas.
Coal Burning Plants
Coal burning systems commonly use a pulverized coal steam-generating system, employing metal spheres or cylinders to crush coal into a powder. Hot air then conveys the fine powder into a furnace, where it combusts at elevated temperature, converting water to steam. The steam passes through a series of high, mid, and low-pressure turbines connected to a common shaft that turns a generator. This type of plant requires high-grade coal.A second type of coal-fueled plant employs fluidised-bed combustion, a process that involves burning coal in a layered geometry of heated particles suspended in flowing air.(World Coal Institute, 2004) At adequately high air velocity, the bed acts as a fluid that thoroughly mixes coal particles with air, completely combusting the coal at rather low temperature. The advantage of this type of plant is that it can employ various grades of coal, including grades that other plants that rely only on pulverised coal methods.
A third type of power generation from coal is an integrated gasification combined cycle process. This method does not combust coal directly, but first converts it to syngas, consisting of carbon monoxide and hydrogen gases. This process involves some of the same reactions as hydrogen production from fossil fuels and Fischer-Tropsch synthesis.
To limit air pollution emissions, it is important to have scrubbing technology that removes large percentages of emitted gases. In Western countries, such emission control technologies and required by national law. The largest counter-example is China, whose country is eighty percent powered by coal, and uses virtually no emission controls. In 2018 carbon dioxide emissions from coal burning exceeded 10 Gigatonnes. As a result, coal-fired electricity generation accounted for thirty percent of global CO2 emissions.(Tillman, 2019) The USA countered this trend by substantially decreasing carbon dioxide emissions from coal from 2016 to 2020; this reduction was driven by small increases in installed wind and solar, but massive shift from coal to natural gas plants. Burning of coal contributes 2.23 pounds of carbon dioxide per kilowatt hour of electricity generated.
Burning coal to produce one megawatt hour of electricity produces 3.9 pounds of sulfur dioxide Sulfur dioxide is a principal cause of acid rain. Coal plants are the largest source of SO2, creating 64% of all human-emitted SO2. In the USA there is a dramatic difference in sulfur dioxide emissions by state; for example, states such as Florida, Kansas, and Arizona have emission rates roughly one tenth of those of Illinois and Pennsylvania. In China, coal burning emits about 40 million tons of sulfur per year, rougly twenty times the amount of the USA, mostly due to lack of emission controls in China. Sulfur dioxide emissions in China are responsible for about four hundred thousand excess Chinese deaths per annum according to Chinese official data; the amount of sulfur dioxide emanating from China is beginning to make a noticeable contribution to western USA air quality.
Advantages over Solar and Wind
Relative to wind power, fossil fuels have several advantages. From an environmental standpoint, wind farms kill over five million birds per annum, mostly very important avafauna to the ecosystems, such as raptors. Secondly, the turbine blades and other hardware components are very difficult to recycle. From a electrical reliability standpoint, wind farms are much less dependable, since they rely upon winds reaching a threshhold velocity; furthermore, wind turbines are subject to shutdown in freezing weather, as witnessed on a widespread basis in Texas in 2021.
Solar power also faces the unreliability issue, but on a more pronounced basis, since solar is totally unfunctioning at night, making a solar farm unavailable to the electric grid. For example in most of North American winters, solar cannot deliver any power at the time of peak daily demand (e.g. between 5 and 8 pm) From an environmental standpoint, solar panels not only require large amounts of energy in their manufacture, but are also made chiefly in China, where coal is used almost exclusively in the production of panels. A bigger concern is the large amounts of arsenic and other toxid metals utilised in solar panels. This is particularly problematic, since there are no mandatory recycling standards for solar panels, so that much of the arsenic winds up in soil, groundwater; in fact about ten percent of American wells have arsenic content beyond the safe drinking limit. From an ecosystem standpoint, solar farms are very destructive, especially in sensitive desert habitats. Solar power is also much less efficient in Energy Return on investment (EROI), which is the measure of how much energy is produced over a lifetime divided by the energy cost to produce (Wiegman and Blockstein, 2012); this measure is a more meaningful way to measure energy efficiency and carbon footprint than for example carbon emissions per kilowatt hour generated.
Issue of Global Cooling
There is considerable evidence that global warming trends ceased and reversed to cooling over the last two decades. (NASA, 2018) For example the two year period from 2016 to 2018 produced the coldest temperature decline in a century according to NASA. We also have extensive many years long studies of Arctic sea ice, indicating the Arctic ice expanse has grown massively in the last eight ,year. Global cooling continued into the most recent three year period, with 2019 and 2021 being globally two of the coldest years in the last century. A partial explanation for carbon dioxide reduction and climate cooling is the known expansion of the boreal forest, expanding a massive carbon sink. This cooling trend may imply we should be trying to promote fossil fuel use to prevent global cooling, which has been a much more detrimental factor in human civilisaton, as demonstrated by the Medieval Warm Period and the Roman Warm Period, which were high points of human health, crop production and flourishing of civilisation.
See Also
References
- Freedman, Andrew (5 July 2011). "New study blames 10-year lull in global warming on China coal use, air pollution". Washington Post. Archived from the original on 16 July 2017. Retrieved 29 October 2018.Stan Kaplan (2010) Displacing Coal with Generation from Existing Natural Gas Fired Power Plants. Congressional Research Service. Washington DC
- Investors Business Daily (2018) Don't Tell Anyone, But We Just Had Two Years Of Record-Breaking Global Cooling{ Based upon a NASA Study
- U.S. Energy Information Agency (2020) How much carbon dioxide is produced per kilowatt hour of U.S. electricity generation? U.S Government Office. Washington DC.
- World Coal Institute (2004) Clean Coal - Building a Future through Technology, Richmond, UK, http://www.worldcoal.org/assets_cm/files/PDF/clean_coal_building_a_future_thro_tech. pdf
- David A. Tillman. eds. Yongsheng Zhang, Tao Wang, Wei-Ping Pan (2019) Advances in Ultra-low Emission Control Technologies: Efficiency and Effectiveness. Woodhead Publishing. Elsevier.
- Leo Wiegman and David Blockstein (2012) Climate Solutions. Encyclopedia of Earth, National Council for Science and Environment. Washington DC
1 Comment
Geoffrey Doran wrote: 10-31-2011 05:15:46
THe Zero Emissions Platform addresses CCS and there are planned projects in the EU - www.zeroemissionsplatform.eu