Quite literally, it can be said that natural gas is being turned into food.
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