Consequences of Carbon Management: Addressing Greenhouse Gases for Energy Nitrogen and Sulfur
If the energy system of the world remains based on fossil fuels throughout the 21st century and little is done to target the atmospheric emissions of CO2, it is plausible that the atmospheric CO2 concentration may triple its “preindustrial’’ concentration of approximately 280 parts per million by the year 2100. Strategies to slow the rate of buildup of atmospheric CO2 are being developed worldwide, and all appear to have a positive effect of reducing the production of energy nitrogen and sulfur. First among these strategies is an increase in the efficiency of energy use throughout the global economy, resulting in less energy required to meet the variety of amenities that energy provides (e. g., mobility, comfort, lighting, and material goods). Greater energy efficiency directly decreases energy nitrogen and sulfur.
Other CO2 emission-reduction strategies address the composition of energy supply. First, nuclear energy and renewable energy are nonfossil alternatives, resulting in CO2 emissions only to the extent that fossil fuels are used to produce the nonfossil energy production facilities. Neither nuclear nor renewable energy sources produce energy nitrogen and sulfur, but nuclear waste is another source of concern.
Second, the mix of coal, oil, and natural gas in the energy supply affects CO2 emissions because they have different carbon intensities (carbon content per unit of thermal energy). Specifically, coal has the highest and natural gas the lowest carbon intensity so that shifts from coal to oil or natural gas and shifts from oil to natural gas, other factors held constant, reduce the greenhouse effect of the fossil fuel system. The nitrogen and sulfur intensity of fossil fuels (nitrogen and sulfur content per unit of thermal energy) differ in the same way (i. e., on average, the intensity of coal is highest and the intensity of natural gas is lowest). Thus, fuel shifts within the fossil fuel system that reduce greenhouse effects will also reduce fossil nitrogen and sulfur.
Third, many countries throughout the world are investing in research, development, and demonstration projects that explore the various forms of capturing carbon from combustion processes before it reaches the atmosphere and sequestering it on site or off. Several available technologies can be used to separate and capture CO2 from fossil-fueled power plant flue gases, from effluents of industrial processes such as iron, steel, and cement production, and from hydrogen production by reforming natural gas. CO2 can be absorbed from gas streams by contact with amine-based solvents or cold methanol. It can be removed by absorption on activated carbon or other materials or by passing the gas through special membranes. However, these technologies have not been applied at the scale required to use them as part of a CO2 emissions mitigation strategy. The goal is to sequester the carbon in a cost-effective way, for example, as CO2 injected deep below ground in saline aquifers. This is a relatively new area of research and development, and little attention has been given to the consequences of fossil carbon sequestration for energy nitrogen and sulfur, but decreases are a likely result. For example, to capture and sequester the carbon in coal will require the gasification of coal and the subsequent production of hydrogen and a CO2 gas stream. Coal nitrogen or sulfur should be amenable to independent management, with results that include extraction as a saleable product or cosequestration below ground with CO2. The first of these results is one of many “polygeneration’’ strategies for coal, in which products may include electricity, hydrogen, process heat, hydrocarbons, dimethyl ether, and nitrogen. The long-term goal is to run the economy on noncarbon secondary energy sources, specifically electricity and hydrogen, while sequestering emissions of CO2.
2. CONCLUSION
The atmosphere functions as a pool and chemical reaction vessel for a host of substances. Many of the most important ones (e. g., oxygen, carbon dioxide, nitrogen, and sulfur compounds) are released by the activity of organisms. Often with the help of the water cycle, they pass through the atmosphere and are eventually taken up again into soil, surface water, and organic matter. Through technology related to energy production and use, humans have added enormously to the atmospheric burden of some of these substances, with far-reaching consequences for life and the environment. The evidence is clearest in the case of acid deposition: gases, particles, and precipitation depositing to the surface causing acidification.
In North America and in some European nations, public concern regarding the effects of acid rain has been transformed into regulations restricting the amount of SO2 and NOx released by electric utilities and industries. The result has been a decrease in annual acidic deposition in some areas, especially due to the reduction in sulfates. There is also evidence that when acid deposition is reduced, ecosystems can recover. The chemistry of several lakes has improved during the past 20 years, but full biological recovery has not been observed. Nitrogen has become the main concern because emissions have been reduced much less than those of SO2. In the future, it will be very important for the industrialized world to transfer its technology and experience to the developing world in order to ensure that the same acid rain problems do not occur as these countries consume more energy during the process of industrialization. Whereas in the past few years the acid deposition decreased in Europe and the United States, an increase has been observed in Asia. It is essential to establish or optimize monitoring programs aimed at following the trends in acid deposition and recovery.
The acid deposition levels in the industrialized areas of the world are well above the critical thresholds of different ecosystems. Because energy emissions are the largest source for acid deposition, abatement is necessary. Multipollutant-multieffect approaches are necessary to ensure that measures are cost-effective and do not create problems for other areas. It has to be determined which effects limit the emissions in different areas most: Is it because of the air quality and the effects on humans, or is it the ecosystem loading? In this way, regional emissions can be optimized and caps can be set to prevent any effects. Furthermore, it is probably most effective to follow CO2 emission reduction options and to then consider SO2 and NOx, instead of the reverse. In most cases, when CO2 emission is decreased, SO2 and NOx are also decreased, whereas if measures to reduce SO2 and NOx are taken first, CO2 is increased because of the energy penalty or additional energy use of abatement options.
