Transcript Electricity
Electricity Part 5: Coal Power Plants, Particulate Mater, Flue Gases, Carbon Capture and Storage Typical Coal Fired Power Plant Coal-fired power plants will be eliminated in the U.S. by 1. 2020 2. 2025 3. 2050 4. 2065 25% 1 25% 2 25% 3 25% 4 CO2 emissions from coal-fired plants will double by 2030 1. True 2. False 100% 0% 1 2 Stationary Source Air Pollution Control 1/3 energy in U.S. used to generate electricity 70% of electricity in U.S. generated by fossil fuels 45% generated by coal Coal has the most emissions of any fossil fuel Emissions from Coal-Fired Plants Gases CO2 SO2 NOx Particulates Soot & Fly ash Mercury Thorium Emissions from Coal-Fired Plants Different means needed to remove various types of pollutants. Particulates The majority of particles are very small with sizes < 0.1 m ~ 95% of the mass is made up by larger particles Sizes of various “particles” Particulates The rate at which particles precipitate (fall) out of atmosphere depends on size. Smaller particles fall more slowly. This allows them to travel long distances Old Pollution Control Build a tall chimney to get broad dispersal. Old Pollution Control Atmospheric temperature inversion makes a barrier. Old Pollution Control Prevailing Winds Can Take Pollution Thousands of Miles This tends to make it Someone Else’s Problem Particulate Control Devices Gravitational Collector Cyclonic Collector Electrostatic Precipitator Mechanical Filters Gravitational Collector Works for Particles > 50m Cyclonic Collector Works for particles down to 5m Electrostatic Precipitator: Works for particles down to 1m Collects 99% of the total mass but only 5% of total number of particles Uses about 50,000 Volts Mechanical Filters Can use fabric filters to remove particles smaller than 1m. Similar to a filter on a vacuum cleaner Removes up to 99.9% of particles Effective for particles down to 0.1m. Should the EPA have the authority to regulate particulate emissions from power plants 1. Yes 2. No 100% 0% 1 2 Other Air Pollution Sulfur Dioxide Acid Rain Carbon Dioxide Greenhouse gas Nitrogen Oxides Respiratory Diseases Sulfur Dioxide 32 30 tons of SO 2 28 26 24 22 20 18 1940 1950 1960 1970 year 1980 1990 2000 Acid Rain H2O (l) + CO2 (g) → H2CO3 (aq) In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction: SO2 + OH· → HOSO2· which is followed by: HOSO2· + O2 → HO2· + SO3 In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid: SO3 (g) + H2O (l) → H2SO4 (l) Also Nitrogen dioxide reacts with OH to form nitric acid: NO2 + OH· → HNO3 Effects of Acid Rain pH Tolerance of Aquatic Animals Sulfur Dioxide Use Smoke Stack Scrubbers to remove. Gases pass through a water solution spray and SO2 reacts with calcium carbonate (Limestone) to form Calcium Sulfate and Caron dioxide. (Flue Gas Desulfurization) SO2 + CaCO3 CaSO3 + CO2 Removes 98% of SO2. Gas is reheated to regain buoyancy. A 1000 MW power plant burning 10,000 tons of coal per day can generate 4000 tons per day of concentrated aqueous waste. Big disposal problem. But Aerobic oxidation of the CaSO3 gives CaSO4, gypsum. Most gypsum sold in Europe comes from flue gas desulfurization Flue gas desulfurization accounts for 1015% of construction costs in new power plants. Energy required is 3-7% of plant output. As of 2006, China is the world's largest sulfur dioxide polluter, with 2005 emissions estimated to be 25.49 million tons. Comparable with U.S. in 1980. Output dropping since then world's largest sulfur dioxide polluter, with 2010 emissions estimated to be 21.85 million tons. Fluidized Bed Combustion Sulfur is “removed” during the actual combustion. Old technology but just now making its way into power industry. Could signal a rebirth of use in high sulfur coal. Should the EPA be able to regulate sulfur dioxide emissions from power plants? 1. Yes 2. No 98% 2% 1 2 Carbon Dioxide Naturally occurring gas in the atmosphere but recent significant increase due to human activity. A greenhouse gas. Greenhouse Effect Prevents infrared light given off by the Earth from escaping into space Greenhouse Effect Solar radiation heats the Earth’s crust. The Earth gives off infrared radiation Black Body (Thermal) Radiation Solar radiation heats the Earth’s crust. The Earth gives off infrared radiation Black Body (Thermal) Radiation Any object above absolute zero gives off em radiation lmaxT = 2.898 x 10-3 m·K Black Body (Thermal) Radiation Any object above absolute zero gives off em radiation lmaxT = 2.898 x 10-3 m·K Human skin temperature ~35°C What wavelength of light is given off? Black Body (Thermal) Radiation Any object above absolute zero gives off em radiation lmaxT = 2.898 x 10-3 m·K Human skin temperature ~35°C lmax = 2.898 x 10-3 m·K/308 K lmax = 9.4 x 10-6 m (9.4 m, IR) Greenhouse Gases Primary greenhouse gases (GHG) Water vapor Carbon dioxide Methane Nitrous oxide ozone Carbon Dioxide Naturally occurring gas in the atmosphere but recent significant increase due to human activity. A greenhouse gas. Counted as a pollutant since 2009. Current atmospheric concentration ~383 ppm, up from ~280 ppm before industrial revolution. Contributor to global climate change. Should all greenhouse gases be eliminated from the atmosphere? 1. Yes 2. No 98% 2% 1 2 Oceans have absorbed ~50% of carbon released from burning fossil fuels. Caused a pH decrease in the ocean of ~0.1 The rate at which reef-building corals produce their skeletons decreases. The ability of marine algae and free-swimming zooplankton to maintain protective shells is reduced. The survival of larval marine species, including commercial fish and shellfish, is reduced." Carbon Capture and Storage Underground/water Storage Pump pressurized gas into deep, permanent storage locations. In deep ocean, pressure is high enough that CO2 is a liquid that is denser than water. Should stay there, …but will it? Contributes to acidification of oceans.\ Will CO2 find ways to escape from deep well storage? Cracks in rocks. Lake Nyos Cameroon Over 1700 people killed by sudden release of CO2 from lake. Potential uses for captured Carbon Dioxide Convert it into hydrocarbons where it can be stored or reused as fuel or to make plastics. Stimulate growth of algae to produce biodiesel. Enhanced production of conventional oil. Enhanced coal bed methane production A one-year study by the National Research Council looked at many costs of energy production and the use of fossil fuels that aren't reflected in the price of energy. The $120 billion sum was the cost to human health from U.S. electricity production, transportation and heating in 2005, the latest year with full data. The report also looks at other hidden costs from climate change, hazardous air pollutants such as mercury, harm to ecosystems and risks to national security, but it doesn't put a dollar value on them. Coal-fired power and motor-vehicle transportation accounted for roughly 99 percent of those costs The report looks at the sulfur dioxide, nitrogen oxide and particulate emissions from 406 coal-fired plants in the lower 48 states, which produce 95 percent of the nation's coal-generated electricity. There were wide differences among plants in the amount of pollution each produced. The estimated health damages ranged from less than half a cent per kilowatt hour to more than 12 cents. The average was 3.2 cents per kilowatt hour. Read more: http://www.mcclatchydc.com/2009/10/19/77423/report-looks-athidden-health.html#ixzz0idRmBTdQ Should the EPA have the authority to regulate carbon dioxide emissions? 1. Yes 2. No 91% 9% 1 2 Usually use multiple stages of pollution control Methods really are effective Cleaner Coal Technology Syngas Rather than burning coal directly, gasification (a thermo-chemical process) breaks down coal - or virtually any carbonbased feedstock - into its basic chemical constituents. The environmental benefits of gasification stem from the capability to achieve extremely low SOx, NOx and particulate emissions from burning coal-derived gases. A coal gasification power plant gets dual duty from the gases it produces. First, the coal gases, are fired in a gas turbine to generate one source of electricity. Second, the hot exhaust of the gas turbine, and heat generated in the gasification process, are used to generate steam for use in a steam turbinegenerator. The efficiency of a coal gasification power plant can potentially be boosted to ~50%.