Development of a Novel Dry Coal Processing Technology

The extraction of coal typically results in the recovery of pure rock that ranges from small to very large quantities depending on seam thickness and other characteristics. In some areas of the U.S., large quantities of rock are being extracted in order to recover the coal, which has reportedly resulted in 60%-70% of the raw material being rejected to waste areas. The haulage, processing, pumping and storage of the rock represent significant energy inefficiency and have negative environmental consequences. Ideally, the majority of the pure rock should be removed near the extraction point, thereby, minimizing the negative impacts. Removal of the pure rock using a relatively high separation density of around 2.0 is generally referred to as 'deshaling'. Wet-based separation processes are the most commonly employed cleaning units for removing rock from coal. However, these processes are generally massive and immobile while also requiring water addition and a slurry treatment system. Dry processes are preferable but typically are inefficient in preventing the loss of coal to the reject stream. The proposed deshaling process wiil involve the development of a novel dry, density-based cleaning technology. As part of the proposed project, evaluation of the separation performance provided by the novel deshaling unit will be conducted on iignite, sub-bituminous and bituminous coals being extracted by surface mining operations located throughout the U.S. Based on investigations conducted in China, the novel separator has the potential to provide effective high-density separations for particle sizes up to 80 mm (3 inches). The density-based separation occurs on an aerated table whereby the air fluidizes the fine, heavy particles, thereby creating an autogenous dense medium. As a result, only the heavy particles can pass through the bed and report to the table surface. Vibration of the table provides movement of the material toward the reject discharge port. The light, clean coal particles maintain an elevated position in the fluidized particle bed and eventually reports to the clean coal port. The unit provides a relatively high capacity per unit of floor space and, thus, can be mounted on a skid or crawlers for easy transport at the mining operation. A diverse research team comprised of two major research universities (University of Kentucky and Virginia Tech), a major process equipment manufacturer (Eriez Manufacturing), and three leading coal mining companies (Peabody Energy, Massey Energy and Falkirk Mining/North American Coal) has been assembled to undertake the development of the proposed deshaling system. The three mining companies, which supply about 20% of the U. S. production of coal, wiil provide four-to-five test sites that are located in West Virginia, North Dakota, Texas and New Mexico. Eriez Manufacturing will supply a 10 ton/hr pilot-scale unit of the dry, density based separator and technical assistance in the operation of the unit. The project goals for the 2-year effort are to develop and evaluate a novel, dry deshaling technology that can be integrated into mining operations for the purposes of removing high ash content materiai prior to loading and hauling to further coal cleaning or load-out facilities. Benefits will be realized from the extraction of high-ash content coals in the eastern U. S. and the low rank coals in the western U. S. that require deshaling to meet the required coal quality levels. Tasks include 1) performance of a parametric test program to optimize operating conditions, 2) detailed evaluation of the process efficiency on a particle size-by-size basis, 3) on-line measure of the separation efficiency using the novel 'Smart' tracer technology, 5)development and modification of the unit to improve the desha ling efficiency, 6) increase the effective top size of the unit, 7) evaluation of the unit at two different coal producing operations, 8) performance of an integration plan with the mining operations with an associated economical feasibility and energy efficiency study. Based on a preliminary assessment, deshaling of a surface mine coal that is currently being hauled 20 miles for treatment in a preparation plant will increase annual pre-tax profit by $625,000, which yields a return on investment of around 51%. Significantly greater benefits is realized when the deshaled surface coal is blended with a cleaned underground coal. In this case, the increase in annual profit was projected to be $1.16 million, which results in an payback period of about 1 year and a return on investment of 99%. Nationaily, the implementation of deshaling would enhance energy efficiency associated with material transportation, pumping, processing, waste storage and utilization by about 1.0%, which equates to annual energy savings of 270 trillion Btu with a value estimated to be around $380 million.