Electricity. Part 5: Coal Power Plants, Particulate Mater, Flue Gasses, Carbon Capture and Storage. Original slides provided by Dr.

Transcription

1 Electricity Part 5: Coal Power Plants, Particulate Mater, Flue Gasses, Carbon Capture and Storage Original slides provided by Dr. Daniel Holland

2 Typical Coal Fired Power Plant Audio Link

3 Stationary Source Air Pollution Control A lot of focus on this since one third of energy is used for electrical generation and a lot of this is from coal, the dirtiest fossil fuel. Use different devices to remove various types of pollutants.

4 Most of the particulate mater is very small i.e. <0.1µm Larger particles account for most of the mass (~95%)

5 Sizes of various particles

6 Rate at which particles fall out of atmosphere depends on size. Smaller particles fall more slowly. This allows them to travel long distances

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8 Old Pollution Control: Build a tall smoke stack and make it someone else s problem

9 Prevailing Winds Can Take Pollution Thousands of Miles

10 Pollution Control Devices Gravitational Collector: Works for Particles >50µm

11 Cyclonic Collector: Works for particles down to 5µ m

12 Electrostatic Precipitator: Works for particles down to 1µm Collects 99% of the total mass but only 5% of total number of particles Uses about 50,000 Volts

13 Can also use fabric filters to remove even smaller particles. Works like a filter on a vacuum cleaner Removes up to 99.9% of particles Effective for particles down to 0.1µm.

14 Other Air Pollution Sulfur Dioxide : Acid Rain Carbon Dioxide Global Warming

15 Sulfur Dioxide tons of SO year

16 Acid Rain H2O (l) + CO2 (g) H2CO3 (aq)

17 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) Nitrogen dioxide reacts with OH to form nitric acid: NO2 + OH HNO3

18 Effects of Acid Rain

19 ph Tolerance of Aquatic Animals

20 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.

21 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 CaSO gives CaSO, 3 4 gypsum. Most gypsum sold in Europe comes from flue gas desulfurization

22 Flue gas desulfurization account for 10-15% 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 million tons, a 27% increase since (Comparable with U.S. in 1980.)

23 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.

24 Carbon Dioxide Naturally occurring gas in the atmosphere but recent significant increase due to human activity. One of many Greenhouse Gasses. Only recently counted as a pollutant. 12/07/2009 WASHINGTON After a thorough examination of the scientific evidence and careful consideration of public comments, the U.S. Environmental Protection Agency (EPA) announced today that greenhouse gases (GHGs) threaten the public health and welfare of the American people.

25 Current atmospheric concentration ~383 ppm, up from ~280 ppm before industrial revolution. Contributor to global climate change. A lot more later.

26 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."

27 Carbon Capture and Storage

28 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.

29 Lake Nyos Cameroon Over 1700 people killed by sudden release of CO2 from lake.

30 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

31 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:

32 Should the EPA have the authority to regulate carbon dioxide emissions? 1. Yes 2. No 50% 1 50% 2

33 Usually use multiple stages of pollution control

34 Methods really are effective

35 Clean(er) Coal Technology Syngas Rather than burning coal directly, gasification (a thermo-chemical process) breaks down coal - or virtually any carbon-based 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.

36 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 turbine-generator. The efficiency of a coal gasification power plant can potentially be boosted to ~50%.

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