Advanced physical coal cleaning to comply with potential air toxic regulations. Quarterly report, 1 March 1995--31 May 1995

Abstract

Studies have indicated that the potentially hazardous trace elements found in coal have a strong affinity for coal pyrite. Thus, by maximizing the rejection of pyrite, one can minimize the trace element content of a given coal while also reducing sulfur emissions. The pyrite in most Illinois Basin coals, however, is finely disseminated within the coal matrix. Therefore, to remove the pyrite using physical coal cleaning techniques, the pyrite must be liberated by grinding the coal to ultrafine particle sizes. Fortunately, the coals being fed to pulverized coal boilers (PCB) are already ground to a very fine size, Le., 70% passing 200 mesh. Therefore, this research project will investigate the use of advanced fine coal cleaning technologies for cleaning PCB feed as a compliance strategy.Work in this quarter has focused on the processing of a run-of-mine coal sample collected from Amax Coal Company's Delta Coal mine using column flotation and an enhanced gravity separator as separate units and in circuitry arrangements. The -60 mesh run-ofmine sample having an ash content of-about 22 % was cleaned to 6 % while achieving a very high energy recovery of about 87% and.a sulfur rejection value of 53 % in a single stage column flotation operation. Enhanced gravity treatment is believed to be providing excellent total sulfur rejection values, although with inferior ash rejection for the -400 mesh size fraction. The circuitry arrangement with the Falcon concentrator as the primary cleaner followed by the Packed-Column resulted in an excellent ash rejection performance, which out performed the release analysis. Trace element analyses of the samples collected from these tests will be conducted during the next report period. DISTRIBUTION OF THIS DOCUMENT IS U N U M m & r / EXECUTIVE SUMMARYThe Clean Air Act Amendment of 1990 requires U. S . utilities to comply with an increasing variety of environmental regulations. The restrictions on sulfur dioxide emissions in particular have received the most attention due to their impacts on medium and high sulfur coal markets. Another regulation that the Clean Air Act Amendment will impose in 1995 is the limitation of air toxic emissions. It has been estimated that, due to the combustion of over 600 million tons of coal per year, thousands of tons of potentially hazardous trace elements are released into the atmosphere. Thus, it is important to develop a pre-combustion coal cleaning strategy that will effectively reduce the trace element and sulfur contents of Illinois Basin coal.The results of conventional float-sink tests have indicated that most trace elements are largely inorganically associated with the coal matrix, although a few of them, such as boron, beryllium and germanium, are strongly bound to the organic portion of coal and probably present as metal chelates. This conclusion has provided a basis for the reduction of the levels of many trace elements by physical coal cleaning methods. For example, it was found that many elements of environmental concern, including ar...