Sulfur dioxide emission reduction

Air Pollution. Particulates and sulfur dioxide emissions from commercial oil shale operations would require proper control technology. Compliance monitoring carried out at the Unocal Parachute Creek Project for respirable particulates, oxides of nitrogen, and sulfur dioxide from 1986 to 1990 indicate a +99% reduction in sulfur emissions at the retort and shale oil upgrading faciUties. No violations for unauthorized air emissions were issued by the U.S. Environmental Protection Agency during this time (62). 

The 1990 Amendments to the U.S. Clean Air Act require a 50% reduction of sulfur dioxide emissions by the year 2000. Electric power stations are beheved to be the source of 70% of all sulfur dioxide emissions (see Power generation). As of the mid-1990s, no utiUties were recovering commercial quantities of elemental sulfur ia the United States. Two projects had been aimounced Tampa Electric Company s plan to recover 75,000—90,000 metric tons of sulfuric acid (25,000—30,000 metric tons sulfur equivalent) aimuaHy at its power plant ia Polk County, Elorida, and a full-scale sulfur recovery system to be iastaHed at PSl Energy s Wabash River generating station ia Terre Haute, Indiana. Completed ia 1995, the Terre Haute plant should recover about 14,000 t/yr of elemental sulfur. 

A variety of models have been developed to study acid deposition. Sulfuric acid is formed relatively slowly in the atmosphere, so its concentrations are beUeved to be more uniform than o2one, especially in and around cities. Also, the impacts are viewed as more regional in nature. This allows an even coarser hori2ontal resolution, on the order of 80 to 100 km, to be used in acid deposition models. Atmospheric models of acid deposition have been used to determine where reductions in sulfur dioxide emissions would be most effective. Many of the ecosystems that are most sensitive to damage from acid deposition are located in the northeastern United States and southeastern Canada. Early acid deposition models helped to estabUsh that sulfuric acid and its precursors are transported over long distances, eg, from the Ohio River Valley to New England (86—88). Models have also been used to show that sulfuric acid deposition is nearly linear in response to changing levels of emissions of sulfur dioxide (89). 

For example, sulfur emissions from utility power plants in the United States are subject to an emissions cap and an allowance-trading system established under the Clean Air Act. An effective cap on annual sulfur dioxide emissions took effect in 2000, so no more than 8.95 million tons of SO can be emitted annually. Utilities that want to build another coal plant must purchase sulfur emission allowances from others who do not need them. This system provides a market incentive for utilities to reduce their sulfur emissions as long as the cost of such reductions is less than the price of purchasing the allowances. 

Silveston, P. L and Hudgins, R. R., Reduction of sulfur dioxide emissions from a sulfuric acid plant by means of feed modulation. Environ. Sci. Technol. 15, 419-422 (1981). 

Source Potential SO2 in Raw Coal, lb/S02/10 Btu Reduction Required, % Sulfur Dioxide Emission Limits lb SO2/IO6 Btu... 

While the development of flue gas clean-up processes has been progressing for many years, a satisfactory process is not yet available. Lime/limestone wet flue gas desulfurization (FGD) scrubber is the most widely used process in the utility industry at present, owing to the fact that it is the most technically developed and generally the most economically attractive. In spite of this, it is expensive and accounts for about 25-35% of the capital and operating costs of a power plant. Techniques for the post combustion control of nitrogen oxides emissions have not been developed as extensively as those for control of sulfur dioxide emissions. Several approaches have been proposed. Among these, ammonia-based selective catalytic reduction (SCR) has received the most attention. But, SCR may not be suitable for U.S. coal-fired power plants because of reliability concerns and other unresolved technical issues (1). These include uncertain catalyst life, water disposal requirements, and the effects of ammonia by-products on plant components downstream from the reactor. The sensitivity of SCR processes to the cost of NH3 is also the subject of some concern. 

In view of the considerable interest in sulfur dioxide reduction to sulfur both in this country and abroad, Allied Chemical extended the use of this technology to control sulfur dioxide emissions from other metallurgical operations as well as from fossil fuel combustion. The experience gained in design, construction, and operation of the large Canadian facility provided the perspective for continuing process research and parallel engineering development. 

There is, however, some success to note in the reduction of sulfur emissions from industrial operations in some developed countries. The European Union, for example, expect a decrease in sulfur dioxide emissions from 1990 to 2010, ranging from 11 to 47% in its individual member states (Anonymous 1999, see also Part I, Chapter 3). However, significant problems persist with regard to air pollution by SO2 (see the following paragraph). 

Anonymous (1999) Reduction of sulfur dioxide emissions in the EU 2010 vs. 1990. International Institute of Applied Systems Analysis. 

Reduction of annual sulfur dioxide emissions by approximately 10 million tons from 1980 levels in accordance with Title IV of the Clean Air Act i.e., reduction of annual sulfur dioxide emissions to approximately 10 million tons below 1980 levels by 2000 (with the exception of sources repowering with qualifying clean coal technology in accordance with section 409 of the Clean Air Act, and sources receiving bonus allowances in accordance with section 405(a)(2) and (3) of the Clean Air Act.). 

Reduction of sulfur dioxide emissions in the seven easternmost Provinces to 2.3 million tonnes per year by 1994 and the achievement of a cap on sulfur dioxide emissions in the seven easternmost Provinces at 2.3 million tonnes per year from 1995 through December 31, 1999. 

By most measures, the Acid Rain Program has been a model for successful emission trading systems. Allowances in Phase I sold for approximately 100 per ton of SOj, well under half of what had been forecast (about 250/ton.). Since 1994, allowances have cost 65 to 210 per ton as scrubber technology has become cheaper, and it has become less expensive to switch to low-sulfur coal. Sulfur dioxide emissions declined faster than anticipated and the market has now reached a value of 2 billion/year. Twenty-seven units added scrubbers accounting for 45% of the reductions in 1995-96. Seven large units accounted for two-thirds of this amount. Many units also switched fuels - almost all from high to lower sulfur coal. ... 

Lake ecosystems are also complex, but they sometimes respond more quickly than do forest ecosystems to reductions in sulfur dioxide emissions. In many lakes, however, the decline in sulfate concentrations is less than expected given the drop in atmospheric sulfur dioxide deposition, and the pH shows surprisingly little change. As Peter Dillon et al. describe in Chapter 4, water quality in lakes in Ontario improved very little despite a major reduction in atmospheric acid deposition because sulfates are carried into the lakes from the surrounding watershed in stream water, especially following drought years. Sulfur dioxide emissions will need to be lowered even more before accumulated sulfates are removed from this system. 

Although reduction of sulfur dioxide emissions has not been sufficient to solve the problem of acidification of lakes and forests, it is a necessary step. The rapid progress in reducing these emissions in both North America and Europe is therefore promising, and provides a good model for regions in eastern Asia where sulfur dioxide deposition is a growing problem. 

Fujita, S., Y Ichikawa and R. K Kawaratan (1991) Preliminary inventory of sulfur dioxide emissions in East Asia. Atmospheric Environment 25A, 1409-1411 Fujita, E. (1999) Photochemical carbon dioxide reduction with metal complexes. Coordination Chemistry Review 185-186, 372-384... 

The total acidity in the years around 1966 was the highest in the world for this country. Increased energy requirements combined with a change from pit coal to oil resulted in the increased sulfur dioxide emissions. The reduction after 1967 was then credited to a large conversion to gas when the largest coherent natural gas field in the world was found in the province of Groningen. Because of a prior commitment for the exportation of much of this gas, the domestic use will be reduced until the year 2000. In the meantime a reconversion to oil and coal will be necessary to satisfy the energy requirements, and the SO2 emissions accompanied by increased acid deposition are expected to rise. 

As a result of this lower temperature, the nitrogen oxide levels in the flue gas are reduced considerably. In addition, a reduction in sulfur dioxide emissions can also be achieved by mixing the coal with limestone (or dolomite). At the temperature of the bed, the carbonate is converted to the oxide that reacts with any sulfur dioxide to give calcium (or magnesium) sulfate ... 

Precombustion cleaning involves the removal of any, or at least of a part, of pollution-generating impnrities from coal by physical, chemical, or biological means. A substantial amount of the coal nsed in ntility boilers does receive some form of cleaning before it is burned. The major objective of many of the precombustion cleaning processes is the reduction of the sulfur content (usually pyritic, FeS2, sulfur). The wider use of conventional coal-cleaning processes will allow the sulfur dioxide emissions to be reduced markedly. 

---