Semester

Summer

Date of Graduation

2010

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Eric Johnson.

Abstract

Liquid water (moisture) in coal causes a number of economic and environmental issues for the mining and electrical power generation industries. Coal preparation plants utilize large amounts of water for cleaning coal and removing unwanted materials such as clay, sulfur, pyrite and mercury. After the cleaning process, it is necessary to separate as much of the water from the coal as possible. Unfortunately, current dewatering techniques are not effective with particle sizes below 150 microm, which compromises 6--8% of the total energy found in mined coal. In most cases, these fine coal particles end up in slurry waste ponds. Additionally, coal-fired power plants typically purchase coal on a per btu of heating value basis. In many cases, coal can re-absorb moisture during transportation from mine to power plant, and some pulverized coal plants operate with moisture contents as high as 40%. It has been shown previously that a 1% reduction in the moisture content of coal leads to approximately a 0.1% increase in the heating value of coal.;To address this issue, two two-stage, variable-area fluidized bed prototypes have been constructed. The first bed is a steam-jacketed warm-air dryer for fine particles (WADFP) with a lower riser stage bed diameter of 5" and an upper riser stage bed diameter of 8". The second is a half-scale transparent model. One of the primary objectives of this study is to utilize the scale-model fluidized bed to study the unique fluidization characteristics of a large scale fluidized bed consisting of a lower small-diameter riser stage and an upper large-diameter riser stage with secondary air injection. The second objective of this study is to develop a simplified set of scaling relationships that allow for the scaling of fluidization regime transition velocities between different fluidized beds. The final objective of this study is to perform a thermodynamic exergy analysis on the fluidized bed drying process.;Preliminary test results show a similar trend of secondary air injection being the controlling factor of fluidization regime determination for both the large scale dryer and the small scale model riser. A proposed scaling method using riser area-normalized mass flow rates resulted in good matching between the two systems. Experiments with fluidizing wet coal also resulted in significant reductions in the moisture content of coal after drying.

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