SUITABILITY EVALUATION OF EMERGING DRYING TECHNOLOGIES FOR FINE CLEAN COAL DRYING

Author

Xinbo Yang, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2015

Degree Name

Master of Science

Department

Mining Engineering

First Advisor

Mohanty, Manoj

Abstract

The selling price of coal product in the market depends on the heating value or BTU content of coal, which is a function of both ash and moisture content. Typically the ash content of fine coal and coarse coal reporting to the clean coal belt of a coal preparation plant are relatively similar from each other, however, the moisture content of fine coal is much higher, i.e., 2 to 3 times that of the coarse coal. In that case, although the fine coal proportion of the total clean coal tonnage produced from a plant is in the 10 to 15% range, as much as 33% of the total moisture content in the clean coal product is contributed by the fine coal fraction. A simple analysis indicates that if the moisture content of the fine coal fraction can be substantially reduced by 50% or more, the density-cut of the coarse coal cleaning circuit can be increased and higher overall plant yield can be obtained while satisfying the overall product heating value specification. To achieve this improvement, the use of a suitable drying technology for fine coal is required. The conventional thermal dryer using convective heating mechanism is an expensive option because of the inherent inefficiencies and safety issues in its operations. The major goal of this study was to evaluate two emerging coal drying technologies, the Nano Drying Technology (NDT) and the Parsepco Drying Technology (PDT), for further reducing moisture content of fine clean coal generating from coal preparation plants in Illinois. The Nano Drying Technology, developed by Nano Drying Technologies, LLC. in West Virginia, makes use of molecular sieves to extract residual moisture from mechanically dewatered coal. In this study, mechanically dewatered fine clean coal collected from Prairie Eagle coal preparation plant, IL and Kepler coal preparation plant, WV were used for the NDT system evaluation. The laboratory experimental results showed that the NDT is able to reduce the moisture content of Illinois fine clean coal from over 20% to less than 10%. Pilot-scale experiments were conducted at NDT LLC's pilot-scale facility in Beckley, WV to evaluate and optimize the system's performance. A parametric study conducted using the Box-Behnken experimental design showed that the mass ratio of molecular sieves to coal feed was the most significant factor for the NDT coal moisture reduction process. An optimal product moisture content of 7.3% was achieved for the IL No. 6 seam coal. The Parsepco Drying Technology is provided by Particle Separation System (PSS) Ltd. in South Africa, which utilizes medium wave infrared radiation to remove the moisture from dewatered fine clean coal. Pilot-scale tests were conducted in Illinois Coal Development Park with IL fine clean coal collected from Prairie Eagle coal preparation plant. Product moisture of 5.3% was achieved with production of 22.8 lb/hr. An optimization analysis on the preliminary tests results was then carried out using Historical Data Respond Surface Method in Design Expert software. The medium-wave infrared radiative (MIR) intensity at 60% of its full power was concluded to be the optimal condition for fine clean coal drying. Feed rate and retention time of drying controlled by coal depth and speed of belt were significant on production. The optimized condition predicted a coal product moisture of 9.5% with production of 57.7 lb/hr. An economic analysis of the plant yield improvement and the resulting revenue gain achievable in a coal preparation plant flow sheet was conducted for Prairie Eagle coal processing plant in Illinois which produces 88 tph mechanically dewatered fine clean coal with average moisture content of 19.66%. The increased coal production of the plant with introducing fine coal drying technology was estimated based on the feed washability data of Knight Hawk coal. Both NDT and PDT are able to reduce the fine coal product moisture to be less than 10%, however, the nanotechnology was proved to be more safety and economical for fine clean coal drying.