Environmental concerns sulfur dioxide emissions

Concern for the environment has resulted in moves to significantly reduce the noxious components in emissions when fuel oils are burned. Attempts are being made to minimize sulfur dioxide emissions and, as a consequence, a strategy to minimize the sulfur content of fuel oils has been implemented. Although typical diesel fuel oils have, in the past, contained 1 % or more of sulfur (expressed as elemental sulfur) by weight, environmental legislation in the United States has required that sulfur content of diesel fuel be less than 0.05% (11). These levels will be reduced to 15 ppm or less to protect new exhaust catalyst after-treatment devices. In Europe, various jurisdictions have moved to lower sulfur content. In Sweden, for example, taxation of higher sulfur, lower cetane fuels is elevated to reflect to their respective environmental cost (93). 

Concerns about the environmental effects of emissions resulting from the combustion of fossil fuels, particularly coal, continue to increase as the utilization of these fuels grows. The large amounts of sulfur dioxide and nitrogen oxides emitted into the atmosphere and the attempts to tie these fossil-fuel-derived pollutants directly to the undeniably difficult problem of acid rain have caused heated debates, numerous research studies, government actions, and serious efforts to reduce pollution. The issues are extremely complex, and our understanding of the origin, properties, behavior, and effects of these pollutants is incomplete. Often, theories are contradictory. 

A second concern was that under some conditions sulfur dioxide in exhaust could be emitted as sulfuric acid as a result of catalytic oxidation over the noble metal catalyst. To answer this concern General Motors conducted a 350-car test designed to simulate sulfate emissions on a busy expressway. The U.S. Environmental Protection Agency, other vehicle manufacturers, and several independent environmental monitoring organizations participated in the experiment. This experiment showed conclusively that ambient levels of sulfuric acid under this worse-case simulated exposure situation were far below threshold levels known to produce adverse health effects. 

The inorganic constituents of coal are often expressed in the form of ash yield and sulfur content. It is, however, often necessary to express an inorganic constituent relative to environmental emissions, such as the amount of sulfur dioxide produced during combustion (Chapters 14 and 15). Furthermore, many of the elements that may be of environmental concern occur in the fly ash after coal combustion (Chapter 14) and, in the case of power plants using flue gas desulphurization (FGD) systens, in the FGD (or scrubber) by-products (Chapter 15). 

Environmental concerns and strict pollution legislation prompted action in the construction of up to date coal-fired boilers and adaptation of existing plants. At the present time, flue gas desulfurization is the only conventional method employed on a commercial scale for reducing sulfur emissions after coal combustion. Over 90% reduction of sulfur dioxide in flue gases can be achieved by this process. Combustion control techniques of the flames will effectively reduce oxides of nitrogen emissions into the atmosphere. 

Copper manufacture during the last part of the 20 century was influenced by an ever-increasing concern for the environment. The most significant release of pollutants in the pyrometallurgy of sulfide ores is related to atmospheric emissions of sulfur dioxide and particulate matter containing heavy metals. If not captured, some sulfur dioxide reacts with water vapor in the atmosphere to form sulfuric acid, which returns to earth in acid rain. All the effects of acidic deposition on soils, vegetation, wildlife and man-made structures are well documented. With new techniques sulfur dioxide is transformed to sulfuric acid. A must from the environmental viewpoint may thus - as is often the case - be profitable. 

The emission of sulfur dioxide into the atmosphere by the combustion of high sulfur fossil fuels has been recognized as a serious environmental and health hazard. Sulfur, leaving smokestacks in the form of sulfur dioxide is generally returned to the earth as sulfuric acid and sulfate ions. Consequently, the control of SO2 emissions has become an increasing concern all over the world. 

In order to address environmental concerns, however, efficient scrubbing systems have to be employed to clean up the emissions (e.g., sulfur dioxide) from these types of plant so that their stack emissions meet the local environmental regulations that are in place. 

---