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4 Electricity Generation and Storage

# 4 Electricity Generation and Storage

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15

Energy Basics

It was the French physicist Charles Augustin Coulomb (1736–1806) who recognized the nature of the electrostatic force between charged particles and showed

that the force between them is proportional to the product of their charges (and

inversely proportional to the distance between them), as shown by Coulomb’s law

(Equation  1.4, where q designates charge in the units of coulombs, F is the force

in newtons, r is the distance between the two charges in meters, and k is a constant

equal to 8.99 × 109 N ⋅ m2/C2).

F =

kq1q2

r2

(1.4)

Just as a mass at some height has a potential energy due to gravitational forces, so

does a charged particle in an electromagnetic field: a charged particle (e.g., an electron)

will be forced to move by being either attracted or repulsed by the field, depending

upon the nature of the charges involved. This electrical potential energy (or electromotive force, EMF) has the units of volts, where a volt is equivalent to joule/coulomb.

Thus, when some material (e.g., a coil of wire in a generator) is moved through a magnetic field, the electrons in the material can be forced to move, generating electricity.

Obviously, moving the coil of wire through the magnetic field is work that requires

some source of energy, as in the raw energy of a fossil fuel. In a typical coal-fired

power plant, combustion of coal provides the thermal energy to generate high-pressure

steam, which turns a steam turbine coupled to a generator: voilá—electricity!

In the United States, the percentage use of natural gas for electrical generation is

approaching that of coal (see Figure 1.10), with hydroelectric and renewable electricity

The U.S. electrical generation by source, 2012

1,200,000

Thousand megawatthours

1,000,000

800,000

600,000

400,000

200,000

0

Coal

Natural

gas

Nuclear Hydroelectric

Other

Other

renewables

FIGURE 1.10  U.S. electrical generation by fuel type (%), 2011. (Adapted from U.S. Energy

Information Administration, 2013b. Net Generation by Energy Source: Total (All Sectors).

Retrieved 19 April 2013, from http://www.eia.gov/electricity/data.cfm#generation.)

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Chemistry of Sustainable Energy

generation making up almost 12% of the total (U.S. Energy Information Administration

2013b). Many U.S. natural gas and coal-fired power plants have generating capacities

of well over 1000 MW, with operating efficiencies limited to 30–40% as a result of

the laws of thermodynamics, which we will turn to in Chapter 3. The largest nuclear

power plants in the United States are rated at a capacity of around 1300 MW (the net

total MWh used in the United States in 2011, for comparison, was 4,100,656 thousand

MWh (U.S. Energy Information Administration 2011)). There are other cleaner ways

of generating electricity: wind turbines (Chapter 4), fuel cells (Chapter 6), and solar

photovoltaics (Chapter 7). While these are very promising sources of electrical energy,

recall the terawatt level of consumption noted above. The comparisons listed below

demonstrate quite bluntly why the matter of scale will be a constant reminder as we

contemplate the chemistry of sustainable energy (Kirubakaran et al. 2009).

Capacity (range)

Efficiency (%)

Turbine

Generator

500 kW to

25 MW

29–42

Photovoltaics

1 kW to 1 MW

6–19

Wind

Turbine

10 kW to

1 MW

25

Fuel Cells

200 kW to

2 MW

40–60

The huge scale required for electricity generation and the variability of sustainable

sources of electricity such as solar and wind raise additional concerns. How useful is

wind energy when the wind is not blowing? How can photovoltaics provide power for

us when the sun is not shining? These concerns are the driving force for the development of a so-called smart grid and efforts to develop effective, large-scale modes of

storing electricity. While weaving together a smart grid is all about digital technology

(and thus not the purview of this text), electrical energy storage (EES) is strongly

embedded in the area of chemistry and materials science. Storage of electricity as

some other form of energy that can be converted back into electricity, possibly at a

moment’s notice, can even out the variability of a wind- or light-driven electricity

supply. There are several approaches to stationary EES systems, including supercapacitors that store electricity in electrical charges or flywheels that convert kinetic

energy back into electrical energy. Potential energy can be used to store electrical

energy, for example, by pumping large volumes of water into a raised reservoir where

it can reside until it is freed to pass through a hydroelectric generating plant. The EES

most relevant to this text is electrochemical energy storage, a.k.a. batteries. Because

the research progress associated with the development of large-scale EES is closely

related to that of fuel cells, this topic will be covered in some detail in Chapter 6.

OTHER RESOURCES

Books

Letcher, T.M. 2008. Future Energy. Oxford, U.K.: Elsevier.

McElroy, M.B. 2010. Energy: Perspectives, Problems & Prospects. New York: Oxford

University Press.

National Research Council. 2010. Electricity from Renewable Resources: Status, Prospects,

and Impediments. Washington, D.C.: National Academies Press.

Energy Basics

17

Online Resources

Energy Resources Conservation Board (Canada): http://ercb.ca/

International Energy Agency: http://www.iea.org/

United States Energy Information Administration: http://www.eia.gov/

United States Department of Energy: http://www.doe.gov/—National Energy Technology

Laboratory: http://www.netl.doe.gov/index.html—Energy Efficiency and Renewable

Energy: http://www.eere.energy.gov/

United Nations Development Programme, Environment & Energy: http://www.undp.org/content/undp/en/home/librarypage/environment-energy.html

U.S. National Renewable Energy Laboratory: http://www.nrel.gov/

World Energy Council: http://www.worldenergy.org/

REFERENCES

Bauer, D., D. Diamond, J. Li et  al. 2011. Critical Materials Strategy U.S. Department of

Energy. U.S. Department of Energy, http://energy.gov/sites/prod/files/DOE_CMS2011_

FINAL_Full.pdf.

British Petroleum. 2012. World Primary Energy Consumption Grew by 2.5% in 2011, Roughly

in Line with the 10-Year Average. British Petroleum 2012 [cited 1 May 2013]. Available

from http://www.bp.com/extendedsectiongenericarticle.do?categoryId=9041234&cont

entId=7075077.

Boden, T.A., G. Marland, and R.J. Andres. 2010. Global, Regional, and National Fossil-Fuel

CO2 Emissions. Carbon Dioxide Information Analysis Center, Oak Ridge National

Laboratory, U.S. Department of Energy, Oak Ridge, TN, USA.

Boundy, B., S. W. Diegel et al. 2011. Biomass Energy Data Book. U.S. Department of Energy/

Office of the Biomass Program/Energy Efficiency and Renewable Energy.

da Rosa, A.V. 2009. Generalities, Fundamentals of Renewable Energy Processes. Burlington,

Girard, J.E. 2010. Principles of Environmental Chemistry, 2nd ed. Sudbury, MA: Jones &

Bartlett.

IEA/International Energy Agency. 2013. 2013 Key World Energy Statistics. International

Energy Agency. Paris: France.

Kirubakaran, A., S. Jain, and R.K. Nema. 2009. A review on fuel cell technologies and power

electronic interface. Renew. Sustain. Energy Rev. 13:2430–2440.

Knowledge Transfer Network. 2010. Minerals and Elements Review. Chemistry Innovation

Ltd. 2010 [cited 8 May 2013]. Available from http://www.chemistryinnovation.co.uk/

Massefski, A. and K. Capelli. 2012. Dead zone: The source of the Gulf of Mexico’s hypoxia.

In Science Features: USGS.

McElroy, M.B. 2010. Energy: Perspectives, Problems & Prospects. New York: Oxford

University Press.

Milne, J.L. and C.B. Field. 2013. Assessment report from the GCEP workshop on energy

supply with negative carbon emissions. Stanford University Global Climate and Energy

Project.

National Aeronautic and Space Administration. 2013. Earth Observatory Glossary 2013

[cited 2 April 2013].

Olah, G.A., G.K.S. Prakash, and A. Goeppert. 2011. Anthropogenic chemical carbon cycle for

a sustainable future. J. Am. Chem. Soc. 133 (33):12881–12898.

Peter, L. M. 2011. Towards Sustainable Photovoltaics: The Search for New Materials. Philos.

Trans. R. Soc. Lond. A, 369(1942):1840–1856.

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Purves, W.K., D. Sadava, G.H. Orians et al. 2004. Life: The Science of Biology. 7th ed.

Sunderland, MA: Sinauer Associates, Inc.

Reisch, M.C. 2012. Coal’s enduring power. C. & E. News 90 (47):12–17.

Roney, J.M. 2010. Humanity’s Ecological Footprint, 1961–2007, edited by B. Barbeau. Global

Footprint Network. www.earth-policy.org/datacenter/xls/book_wote_ch1_9.xls

Schröder, J.J., D. Cordell, A.L. Smit et al. 2010. Sustainable Use of Phosphorus. Report

357. EU Tender ENV.B.1/ETU/2009/0025. Plant Research International/Business

Unit Agrosystems and Stockholm Environment Institute (SEI). Wageningen, The

Netherlands, DLO Foundation.

Simms, A., V. Johnson, and P. Chowla. 2010. Growth Isn’t Possible. Why We Need a New

Economic Direction. The Great Transition. London, UK: New Economics Foundation.

Sørensen, B. 2007. Renewable Energy Conversion, Transmission & Storage. Burlington, MA:

Sørensen, B., P. Breeze, T. Storvik et al. 2008. Renewable Energy Focus Handbook.

Staffell, I. 2011. The Energy and Fuel Data Sheet. works.bepress.com 2011 [cited 16 April 2013].

Stanier, C. and J. Hutchinson. 2011. A sustainable global society: How can materials chemistry help? A white paper from the chemical sciences and society Summit (CS3) 2010.

Royal Society of Chemistry.

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Atmospheric Administration, Earth System Research Laboratory 2013 [cited 2 April

2013]. Available from http://www.esrl.noaa.gov/gmd/ccgg/trends/mlo.html.

U.N. World Commission on Environment and Development. 1987. Our Common Future. New

York: United Nations.

U.S. Energy Information Administration. 2012. Annual Energy Review, 2011. U.S. Energy

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www.eia.gov/electricity/annual/.

U.S. Energy Information Administration. 2013b. Net Generation by Energy Source: Total (All

Sectors). U.S. Energy Information Administration [cited 19 April 2013]. Available from

http://www.eia.gov/electricity/data.cfm-generation.

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2007.

Waldheim, L. and T. Nilsson. 2001. Heating Value of Gases from Biomass Gasification. TPS01/16. IEA Bioenergy Agreement Subcommittee on Thermal Gasification of Biomass.

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2

Fossil Fuels

Before we can make any progress toward a sustainable energy future, we need to

learn from our past and present. Although proven reserves of fossil fuels may continue to meet our energy needs for some years to come and nonconventional sources

of fossil fuels are pushing back the “end” of oil, there will come an end, particularly

because our reliance on fossil fuels remains great (recall Figure 1.2). The story of

fossil fuels is a fascinating mix of history, politics, and science, with global security,

economics, and most certainly the environment demanding that we begin to phase

out our dependence on fossil fuels. The aim of this chapter is to understand what

fossil fuels are, where they came from, how we got to this point, and where we are

going with respect to finding fossil fuels for the foreseeable future. (N.B. Appendix

IV provides some additional information with respect to units and conversions peculiar to the oil and gas industry.)

2.1  FORMATION OF OIL AND GAS

Contrary to popular belief, deceased and decomposed dinosaurs are not the primary

source of fossil fuels that we use to power our planet. But before we can fully understand the source of petroleum (literally “rock oil”), we need to review a little geology.

Scientists have devised many cycles to explain the processes and conversions of our

planet, such as the carbon cycle to explain the chemical fate of carbon in the environment. The analogous rock cycle explains how rocks (far from sedentary objects) are

moved about by internal and external processes on and in our planet. In this cycle,

igneous, metamorphic, and sedimentary rocks are transformed and transported. We

are most concerned with sedimentary rocks for they are the source of oil and gas.

Produced from sediments deposited either on the land or at the bottom of a body of

water, sedimentary rocks represent only about 5% of Earth’s crust (Skinner and Porter

2000). Sediment—and hence, sedimentary rocks—comes from everywhere and

everything, including rock fragments, chemical precipitates (e.g., calcium carbonate

from bones and shells), long-dead marine organisms, and detritus in general. In the

sedimentation process, various kinds of materials are stratified such that sandy sediments (sandstone) overlay clay sediments (shales), with calcium carbonate-containing

sediments (limestones) at the bottom of the strata. Sediment is buried and compacted

to become sedimentary rock, typically at or near the site at which it was originally

deposited. As a result, oil (which ultimately comes from sedimentary rock, vide infra)

is not widely distributed on the planet, with obvious geopolitical consequences.

Given that sediment comes from everywhere and everything, the fact that a small

portion of sedimentary rocks consists of organic matter is self-evident. Roughly 18%

of the total amount of carbon in Earth’s crust is organic carbon in the form of oil,

gas, and coal (Schidlowski et al. 1974). Living things die and the carbon, hydrogen,

19

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Chemistry of Sustainable Energy

nitrogen, and oxygen that were once a part of living biota become part of the landscape. In an aerobic environment, this organic matter is oxidized, but in an oxygenfree environment (as when trapped in a layer of sediment), oxidation is negligible.

Numerous types of organic compounds, then, are trapped in sedimentary rocks and

converted into crude petroleum and other carbon-rich materials under conditions of

heat and pressure over a geologic timescale.

Fossil fuels, then, are mixtures of hydrocarbons in a low oxidation state, formed

over a period of millions of years and trapped in sediment that makes them fairly inaccessible. What is the chemical composition of these mixtures and what is their origin? Given that ancient crude oil primarily consists of even-numbered carbon chains

and that the material is both optically active and levorotatory, it is widely accepted

that the vast majority of oil is biological in origin (Selley 1998). Decomposition of

this once-living matter into fossil fuels is a process whereby the highly oxygenated

organic matter is reduced to hydrocarbon species.

Lipids and lignins from the original plant or animal material are the primary

organic materials that decay to hydrocarbon fossil fuels. (Ultimately, of course, these

carbon atoms came from carbon dioxide in the process of photosynthesis.) Lignins,

found in all woody plant materials as a very complex polymeric mixture of phenols

and glycerol, are the source of solid fossil fuels such as peat and coal (Figure 2.1).

CH2OH

O

HO

CH2OH

OCH3

O

CH3O

O

HO

HO

CH3O

HO

O

CH2OH

OH

O

OH

CH3O

O

CH3O

O

CH3O

OH

CH2OH

HOCH2

O

O

O

OCH3

OH

H3CO

HOCH2

O

HOCH2

O

OCH3

H

CH3O

O

O

HO

OCH3

OCH3

CH3O

O

FIGURE 2.1  Lignin structure.

OCH3

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