This disclosure relates to coal-derived solid hydrocarbon particles and methods of preparing such particles. Coal-derived solid particles include coal-derived carbonaceous matter and coal-derived mineral matter. Coal-derived solid hydrocarbon particles include discrete solid coal-derived carbonaceous matter particles, derived from any coal source, which are milled to a sufficiently small size to be substantially free of inherent or entrained mineral matter. Systems and methods for the separating coal-derived carbonaceous matter particles from coal-derived mineral matter particles are disclosed. The resulting coal-derived solid hydrocarbon particles are substantially free of inherent or entrained coal-derived mineral matter.
Coal is a solid fossil fuel formed from ancient plant materials. Coal contains varying amounts of carbon, hydrogen, nitrogen, oxygen, and sulfur as well as varying amounts of other elements and compounds, including mineral matter. Mined coal rocks are a composite material composed of three general categories of substances: organic carbonaceous matter, including macerals; inorganic mineral matter; and fluids. The carbonaceous matter includes solid hydrocarbons of different molecular weights. The mineral matter includes the ash-forming mineral content of coal. The mineral matter dispersed through the coal-derived solid carbonaceous matrix is referred to as inherent mineral matter or inherent ash. Mineral matter which originates from the inter-seam bands or the roof and floor strata during mining is referred to as extraneous ash. The fluids occur in pores within and between the other two solid constituents. The fluids in coal prior to mining are mainly water and methane. Water typically ranges from 10 to 50 wt. %.
Mined coal is passed through a preparation plant to crush the coal to the proper size for shipment and to remove bulk extraneous ash (inorganic mineral formations layers, nodules, fissures, and rock fragments) associated with mined coal. Additionally, coal rocks with too much inherent ash (disseminated or entrained mineral matter, fine inclusions of mineral matter in the solid hydrocarbon matrix) are also screened out via density separation techniques. The materials removed from mined coal rock in a preparation plant are sent to an impoundment as waste coal refuse.
Coal is one of the most important energy sources in the world. Approximately 1 billion tons of coal are produced in the United States each year. Coal is typically crushed. During the mining and crushing operation, coal waste fines, also known as coal dust, are generated. Furthermore, coal is typically washed prior to transport to remove surface dust. Coal fines are defined as coal that is less than 1 millimeter in size, and coal ultrafines are defined as coal that is less than 500 microns in size. The current industrial process to recover coal particles less than 1 mm in size is more expensive than other coal processing. The smaller the particles, the greater the processing cost. Further, there are no current commercial processes to recover and sell particles less than 100 microns (0.1 mm). Approximately 200 to 300 million tons of coal waste fines are produced and impounded each year in the United States. It is estimated that over 3 billion tons of coal are produced in China each year, and over 500 million tons of associated coal fines are impounded each year.
There are many grades of coal based on the mineral matter ash content, moisture, macerals, hydrocarbon, and volatile matter. Regardless of grade of coal, the energy content of coal is directly correlated to its moisture and ash-forming mineral matter contents. The lower the ash-forming mineral matter and moisture content of the coal, the greater the energy content and the higher the value of the coal. Coal of any grade can be improved through reducing the mineral matter component content of the coal.
While coal fines are the same chemical composition of the larger-size mined coal product, it is considered waste because the conventional coal recovery process is not designed to handle small particles. The waste coal fines are left unused because they are typically too wet to burn, too dirty to be worth drying, and too fine to transport. There are billions of tons of waste coal fines impounded at thousands of coal mines throughout the world. It is estimated there are over 10 billion tons in the United States and China, and billions of additional tons in Australia, India, Indonesia, Russia, Colombia and other countries.
As used herein, coal fines generally contain three components: (1) solid hydrocarbon; (2) solid mineral matter, which includes ash-forming component particles, such as clay, limestone, and sand; and (3) water. These coal fines typically have a mineral matter content of greater than 30%, by weight (about 15% by volume), and a moisture content of greater than 30%, by weight. They are often impounded as environmentally hazardous.
Of particular challenge in the coal industry is the burning of coal with typical ash-forming mineral matter components. The components are the major source of most harmful emissions, such as SOx, and reduce energy value and heat transfer efficiency. Removing or separating the solid mineral matter components from the solid hydrocarbon components would enable the preparation of a cleaner burning coal product and would be a significant advancement in the energy sector. Substantially pure solid hydrocarbon component of coal may also be useful in chemical, industrial, and energy applications that were previously unsuitable for solid coal when it was in the state of coal rock and coal particles.
It would be an advancement in the art to provide methods of obtaining coal-derived solid hydrocarbon particles which are substantially free of coal-derived mineral matter.