Sulfur reduction cleaning

Conventional coal cleaning processes can remove about 50% of pyritic sulfur and 30% of total sulfur. For northern Appalachian region coals it has been shown that a greater sulfur reduction can be achieved by applying physical coal cleaning to finer size coals (Table 3) (8). 

Table 3. Effects of Physical Cleaning on Sulfur Reduction in Coal ...

There have been several assessments of the potential of physical coal cleaning for reducing SO2 emissions (29-31). Maronde and Deurbrouck ( 1) estimated the maximum potential sulfur reduction that could be achieved through extensive cleaning of coals from the Northern Appalachian Region Maryland, Ohio,... 

Table V presents sulfur reduction data for two of the major coal seams in the region the Pittsburgh Seam and the Lower Kittanning Seam. Laboratory washability (float-and-sink) analyses of representative samples of these coals were used to determine potential sulfur reductions at various levels of cleaning. To assess the impact on regional SO2 emissions, sulfur reduction potentials were estimated for only those coals both produced and utilized in the Northern Appalachian Region. The "Present Level" of cleaning shown in the table represents estimated base-line values for the amount of sulfur in the coal product. These values take into consideration any coal cleaning that occurred, and are compared to coal sulfur contents that would result from more intense levels of cleaning. Each of the 11 major coal-producing seams in the region were evaluated in this manner.

Table V. Theoretical Effects of Coal Cleaning on Sulfur Reduction for Two Northern Appalachian Coals Mined in 1982...

Level of Cleaning Clean Coal Product - Thousands Sulfur of Tons - Sulfur Reduction (Percent) Mining Requirement, Thousands of Tons... 

Table VI. Sulfur Reduction and Btu Recovery by Coal Cleaning...

The removal of both mineral matter and sulfur species to very low values would provide premium solid fuels and possibly new chemical feedstocks. Several techniques are being explored to achieve these goals. The mineral matter in a physically cleaned coal can be further reduced by the solubilization of the aluminosilicate minerals. This can technically be accomplished with the use of alkaline and then acid treatments. A variety of studies are under way to define the conditions required for effective removal of the mineral matter and establish the amount of sulfur reduction that can be accomplished. Others involve the use of fine grinding to liberate the coal from the mineral matter. Then an agglomerant is used to separate the coal matter from the aqueous phase containing suspended mineral matter. A new approach uses microwave energy to selectively decompose the clays into species that can be solubilized and removed. Still another technique involves treatment with carbon dioxide to reduce the particle size and permit the liberation of the mineral matter. Over the next few years these will be studied further and it is hoped that coal will become available in a form with less of these interesting, but not entirely desirable mineral species. 

The Wellman-Lord process can be a significant factor in helping domestic power plants to meet the air pollution abatement requirements of the Clean Air Act of 1970. To show its applicability to the utilities industry, Davy Powergas Inc. is building a demonstration installation at the Dean H. Mitchell Station of Northern Indiana Public Service Co. in Gary, Ind. When completed, it will consist of a Wellman—Lord sulfur dioxide recovery unit connected to an Allied Chemical Co. sulfur dioxide-to-sulfur reduction process to produce elemental sulfur. Davy Powergas guarantees emissions of 200 ppm by volume or less of sulfur dioxide at this facility. 

Conventional coal cleaning plants are quite efficient for Btu recovery, as well as for ash and pyritic sulfur reduction. Btu recovery is generally between 85% and 90% and the ash reductions on a lb of ash/MM Btu basis are usually in the 70%-80% range for Pittsburgh seam coals, and in the 85%-90% range for Illinois and central Appalachian coals (Rosendale et al., 1993). 

The off-gas from each furnace is cooled in an evaporative gas cooler and cleaned in a reverse pulse baghouse before being either vented to atmosphere or used in manufacturing sulfuric acid. The baghouse dust from both the smelting and reduction furnaces is combined and recycled through the smelting furnace. 

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. 

The new Clean Air Act will result in a permanent 10 million ton reduction in sulfur dioxide (SOj) emissions from 1980 levels. To achieve this, EPA will allocate allowances of one ton of sulfur dioxide in two phases, The first phase, effective January 1, 1995, requires 110 powerplants to reduce their emissions to a level equivalent to the product of an emissions rate = (2,5 lbs of S02/mm Btu) x (the average mm Btu of their 1985-1987 fuel use). Plants that use certain control technologies to meet their Phase 1 reduction requirements may receive a two year extension of compliance until 1997. The new law also allows for a special allocation of 200,000 annual allowances per year each of the 5 years of Phase 1 to powerplants in Illinois, Indiana and Ohio. 

The reduction of atmospheric concentrations of the sulfur and nitrogen oxides blamed for acid rain was a major issue in the debate that led to the 1990 Clean Ail-Act Amendments (CAAA). The final legislative action is one of the most complex and comprehensive pieces of environmental legislation ever written. 

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. 

Smooth polycrystalline Au, Pt and Ir thin-layer electrodes were utilized (10-11). Electrodes were cleaned between trials by sequential electrochemical oxidation above 1.2 V [Ag/AgCl (1 M Cl-) reference] and reduction below -0.2 V in 1 M H2SO4 surface cleanliness was verified with the aid of cyclic voltammetry in the same molar sulfuric acid solution. Experiments were carried out in 1 M H2SO4, 1 M NaC104 buffered at pH 7 and 10, and in 1 M NaOH solutions were prepared with pyrolytically triply distilled water (12). Surface reagents employed were iodide, hydroquinone (HQ), 2,5-dihydroxythiophenol [DHT (13)1. and 3,6-dihydroxypyridazine (DHPz). 

By 2010, Tier 2 standards should further reduce vehicle emissions by extending regulations to larger SUVs and passenger vans. The use of gasoline with a lower sulfur content will also reduce emissions and it also makes it easier to build cars that can achieve further reductions. These standards should allow new U.S. cars to be extremely free of air pollutants. But, the Clean Air Act does not cover vehicle C02 emissions. Many new cars are called near zero emissions by their manufacturers and may have tailpipe emissions cleaner than some urban air. Hydrogen fuel cell vehicles will have almost no emissions besides some water vapor and would be much cleaner. 

A different approach to the stereospecific synthesis of sulfinamides described by Johnson (117,118) is based on the conversion of suitable chiral tetracoordinate sulfur compounds into sulfinamides. It was shown (117) that optically active methyl phenyl sulfoximide undergoes a clean and stereospecific reduction to the corresponding sulfinamide by means of aluminum amalgam. On the other hand,... 

---