Issue Date: February 11, 2013
The Future Of Coal
I enjoyed Marc S. Reisch’s highly informative cover story, “Coal’s Enduring Power” (C&EN, Nov. 19, 2012, page 12). The bar graph showing yearly trends in coal’s market share as a source of energy for electrical utilities, however, contains a common error in the heading “U.S. electricity generation, millions of megawatts per day” (page 16).
I bring this error to your attention because it may be more than merely a typographical mistake; megawatt-hours is what was meant.
For the past decade, U.S. generation of electrical energy consistently has been about 4 billion megawatt-hours (14.4 trillion megajoules) per year, according to the U.S. Energy Information Administration. By dividing 4 billion MWh by the number of days in a year, we arrive at 11 million MWh per day, the intended height of the bars in the graph.
In addition, the error reflects the frequent confusion between power (a rate) and energy (a quantity). Watts measure power, the rate at which energy is generated or expended over time (1 W = 1 J per second). Watt-hours, which is power multiplied by time, measure energy.
The kilowatt-hour is a common billing unit for energy delivered to consumers by electric utilities, but two levels of obfuscation accompany its use. First, this multiplicative approach to quantifying energy is like billing the quantity of gasoline purchased at the gas station not in gallons, but as the flow rate through the nozzle multiplied by the pumping time. Second, because the units of time used to measure the rate and the duration differ, watt-hours introduce the irrelevant factor of the number of seconds in an hour (1 Wh = 3,600 J).
Reisch took upon himself the daunting task of expressing time in seconds, hours, days, and years all in one graph. He could have avoided the first two by using joules, a fundamental unit of energy.
J. Dirk Nies
Reisch has written a good summary about coal. As a Ph.D. chemical engineer, I have been involved with coal processing for 60 years. I have the following comments:
1. Gasification of coal to produce synthesis gas: All current processes have too small annual coal-processing capacity, thereby making the capital cost per ton of coal too high. We need to modify the existing technology to process at least 2 million tons of coal per year in a single train.
2. Combustion of coal: We have been burning coal for several centuries. We have retrofitted existing plants every time new regulations become law, installing scrubbers for particulates and SO2 and processes to remove NOx and now mercury. These unit processes have been piled on to the existing boilers, creating a very high cost chemical operation. We need to reexamine the technology needed to extract the energy content of coal from a fresh viewpoint.
Jagdish C. ( Jay) Agarwal
Chestnut Hill, Mass.
Much progress has been made in the use of coal to generate electricity. Has there been much progress in the mining process? The safety, health, and environmental costs of coal do not appear to be of much concern in the declarations of “clean coal,” but they are of huge negative potential.
Although I appreciate the effort of President Barack Obama’s Administration to make the U.S. energy independent through use of renewable energy sources, this policy has placed both coal and nuclear energy at a disadvantage.
Severe restrictions on the burning of coal and failure to endorse a national site for the disposal of nuclear waste have hampered the continuing use of these two sources of energy. Unfortunately, these actions have been coupled with limited permits for oil drilling and excessive questioning of environmental impacts of fracturing shale to obtain gas, thereby hindering the possibility of the U.S. becoming energy independent in the near future.
In the long term, wind power, hydroelectric power, and biodiesel could help reduce the need for coal, nuclear energy, oil, and natural gas, but they are not sufficient for our present energy needs. The Administration should be reluctant to hamper the conventional sources of our energy requirements.
Silver Spring, Md.
“Coal’s Enduring Power” suggests several emerging technologies to help coal remain a player in the power generation field while becoming a cleaner and more environmentally compliant fuel. Certainly coal is going to have a significant role in electric power generation for decades to come. As a society, we simply cannot afford to shutter all of the coal plants and build replacement natural gas or nuclear facilities overnight.
In the long term, however, probably past midcentury, the real future of coal lies not in power generation but in its value as a feedstock for carbon materials and chemicals. Coal can be converted into graphites, activated carbons, and other value-added forms of carbon. Coal can also be a source of chemical products, such as naphthalene derivatives.
The future will not be based on the coal tar chemistry of the pre-1950s era but rather will need new reactions and processes, hopefully developed within the tenets of green chemistry. Splendid opportunities exist in materials chemistry, organic process development chemistry, molecular structural modeling, polymer chemistry, and allied fields.
University Park, Pa.
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © American Chemical Society