Population, Fossil Fuel, and Food
Richard D. Schwartz
The World's looming energy crisis can be tied directly to the exploding world population and the attendant needs for expanded energy resources. A key to population growth in the past 80 years has been the increased production of food supplies. Perhaps one of the most important factors behind the increase in food supplies is the Haber process (developed by Fritz Haber in 1909) for the production of anhydrous ammonia. As a widely applied fertilizer,anhydrous ammonia has increased crop yields by a factor of two to three times over that which existed on a wide scale prior to the introduction of the fertilizer. Aside from the expansion of agricultural lands, the introduction of anhydrous ammonia is arguably the most important development of the 20th Century which has promoted world population growth from about 1.5 billion persons in 1920 to about 6 billion in 2000.
When addressing the issue of fossil fuel consumption as it relates to food production, one automatically thinks of the intense use of machinery in modern agriculture. Obviously, significant amounts of fuel are consumed in tilling, planting, harvesting, processing, and transport to markets and consumer outlets. When it is stated that "modern agricultural is the process whereby fossil fuels are turned into food", our first thoughts are of the immense fuel consumption involved. However, a primary constituent in the production of anhydrous ammonia is natural gas. PERHAPS AS MUCH AS HALF OF THE BIOMASS IN OUR FOODS TODAY IS DERIVED FROM THE USE OF ANHYDROUS AMMONIA WHICH IS PRODUCED DIRECTLY FROM NATURAL GAS. Quite literally, it can be said that natural gas is being turned into food.
An important process for the production of anhydrous ammonia is the conventional steam reforming process wherein high temperatures (450-600K) and high pressures (100-200 bar) are employed. The production proceeds via the following steps:
(0.88) Methane + (1.26) Air + (1.24) Water
yields (0.88) Carbon Dioxide + (1.0) Molecular Nitrogen + (3) Molecular Hydrogen
(1.0) Molecular Nitrogen + (3) Molecular Hydrogen
yields (2) Ammonia Molecules
The latter reaction involves use of a catalyst. A complete discussion of this process is available on the website of the European Fertiliser Manufacturer's Association at www.efma.org/publications/ (see publication1 on the Production of Ammonia, section 04). For a typical natural gas feedstock plant, about 22 GJ of feedstock are required to produce one metric tonne (t) of ammonia. In addition, about 8 GJ of fuel (usually natural gas) is required to power the process, leading to the use of about 30 GJ per tonne of ammonia produced. In 1997, North American nitrogen fertilizer production was about 13 Mt. Thus about 3.9E17 J was required. The energy content of natural gas is about 1.05 MJ per cubic ft (cf), so this translates to the use of about 0.372 tcf of natural gas. The natural gas production in North America was about 18 tcf in 1997 (Ristinen and Kraushaar1999, Energy and the Environment (John Wiley: New York), p. 48). Thus about 2.1% of the natural gas produced was used in the production of ammonia fertilizer.
Worldwide, about 85 Mt of ammonia fertilizer was produced in 1997. Whereas ammonia production has seen small increases in developed nations in the decade of the 1990s, developing countries increased ammonia output from 42 Mt to 51 Mt from 1991 to 1997, more or less tracking the population increase in these countries. It is likely that a much higher percentage of domestic natural gas is used to produce fertilizer in developing countries (such as China) than in developed countries. As the world population continues to increase and natural gas production rates peak and go into decline (pending potential development of a fundamentally new natural gas resource such as the sea floor methane ices), an increasing percentage of natural gas will be used for fertilizer production, obviously at increasing costs. Coal gasification can also provide feedstock for ammonia production, but the present production cost per tonne is about 1.7 times greater than for ammonia production from natural gas. In coming decades, pressures will build for the construction of coal gasification plants.
Perhaps a more important delimiter for population growth will be the lack of additional agricultural land and fresh water supplies, as well as the degradation of present irrigated lands. Modern agriculture has benefited from extensive irrigation of dry land (e.g., the high plains of the U.S.), but at the cost of depleting aquifers which cannot last for more than a few decades at present extraction rates. Moreover, extensive fertilization with anhydrous ammonia has produced copious quantities of soil nitrates, many of which have leached into groundwater supplies and polluted the drinking water of a large area of the Central U.S.
The bottom line would appear to be that the end of exponentiating population and food supplies is in sight. If a Herculean effort at worldwide birth control is not successfully launched within this decade, nature will undoubtedly level the playing field with a combination of malevolent acts, not the least of which will be mass starvation and wars over the world's resources. Some would argue that, given world events, we have already stepped over that precipice.
Richard Dean Schwartz
Dept. of Physics and Astronomy
University of Missouri-St. Louis
Weapons Plutonium Disposition:
MOX Gets Go Ahead; Immobilization Dead in Water
Long a disputed issue, the disposal of excess weapons plutonium seems to be headed for technical resolution in U.S. national policy. In a report posted on the Internet, the National Academy of Sciences Committee on International Security and Arms Control (CISAC) has concluded that irradiating the plutonium in MOX (mixed oxides of uranium and plutonium) in a once-through nuclear reactor fuel cycle would meet its "spent-fuel" standard for resistance to theft and proliferation.
A close look at the report also indicates that previously considered methods of immobilization by underground burial are not now approved or available for weapons plutonium.
Because of the longstanding debate about plutonium disposition, its a little odd that these significant NAS results have not gotten more public attention. Ive been following this issue for years, partly in connection with a book being prepared with some colleagues about Cold-War nuclear arsenals and legacies, yet it was only this year (2001) that I noticed the July 1999 "Interim Report." No final report is available, although it was scheduled for the Fall of 1999.
It seems strange that all three of their significant conclusionsregarding MOX burning, immobilization, and demilitarizationare only published in an unheralded interim report. It is hard not to wonder whether the apparently imminent final report was not issued because it was considered ideologically unacceptable in certain quarters.
CISAC adopted for their 1999 review a systematic methodology to compare options for plutonium disposal. Perhaps because it is only "interim," the 1999 report is difficult to read and understand, with many of its important findings rather obscure or relegated to footnotes. It is not a simple matter to sort through the jargon, but a careful reading indicates that today's state of the art does not permit the spent-fuel standard to be met through immobilization (either by vitrification or can-in-canister).
Those of us who have long been calling attention to the advantages of isotopic "denaturing" of weapons plutonium can find some satisfaction in a footnote (no. 13) in the CISAC report. For the first time in print, the official body explicitly acknowledges that any attempt to insert isotopically demilitarized plutonium in existing weapon configurations would be "likely" to run into an abundance of difficulties, such as "design modifications and . . . new nuclear-explosive tests . . . to confirm that the change in isotopic composition had not unacceptably degraded performance."
The chairperson of CISAC, John Holdren, explained his own views about reactor-grade plutonium in an article he wrote for The Bulletin of the Atomic Scientists in 1997:
. . .because the isotopics are different, weapons using this plutonium would have to be redesigned, which would require nuclear tests. That means the path to reuse of spent fuel would be more difficult technically and politicallyas well as easier to detectthan reusing weapons plutonium extracted from glass.
Thus the Committee has definitively embraced the proposition that demilitarized plutonium is really not useful for making military-quality weapons. This has important implications in evaluating treaty-breakout scenarios for nuclear-weapons states after deep cuts in arsenals have taken place. The report now effectively supports the contention that isotopic demilitarization would make plutonium inherently unsuitable for rapid recovery into weapons. Demilitarized plutonium is more securely protected against reversal into high-quality weapons than is buried "immobilized" plutonium that has not been put through a reactor fuel cycle.
After deciphering the oblique vocabulary of the report, it looks as though the Academy is saying not only that MOX irradiation (which results in chemical, metallurgical, and isotopic demilitarization of plutonium) meets the disposition standard, but that irradiation in reactors is the only practical way currently available to dispose of weapons plutonium.
Am I the only one who has noticed this progress?
Retired from Argonne National Laboratory
21302 W. Monterrey Dr., Plainfield, IL 60544
- Committee on International Security and Arms Control, National Academy of Sciences, "Interim Report for the US Dept. of Energy by the Panel to Review the Spent-Fuel Standard for Disposition of Weapons Plutonium"http://nationalacademies.org (July, 1999).
- A. DeVolpi, V.E. Minkov, V.A. Simonenko and G.S. Stanford, Nuclear Shadowboxing: Myths, Realities, and Legacies of Cold War Weaponry (unpublished).
- J.P. Holdren, "Work with Russia", The Bulletin of the Atomic Scientists (Mar/Apr, 1997).
- A. DeVolpi, "The Physics and Policy of Plutonium Disposition", Physics and Society, Vol. 23, no. 4 (1994), "A Coverup of Nuclear Test Information", Physics and Society (Oct. 1996).