Keith Prisbrey

Prediction of rock hardness and drillability using acoustic emission signatures during indentation

This paper reports rock indentation tests which indicated that there was a certain relation between the indentation hardness of rock and the AE parameters, such as accumulated number of events, peak RMS and integrated RMS. Among the above-mentioned AE parameters, the correlation of RMS of AE events with indentation hardness is pronounced and more than ever the integrated RMS is the best index to correlate with the indentation hardness of rock. It represents the sum of amplitudes of AE varied during all the indentation process and reflects the size of AE energy released in the time period of indentation. Indentation hardness corresponds well to peak RMS value for different rock types. The onset of significant AE activity appears at about 40% peak indentation load, and intense AE activity corresponding to fracture propagation and chipping initiates at about 80-90% of peak indentation load. The peak RMS and integrated RMS may be recommended as the indexes to express rock hardness and may be further employed to predict rock drillability using these indexes in association with penetration rate of drilling.

Influence of preheating on grindability of coal

Abstract Enormous quantities of coal must be ground as feed to power generation facilities. The energy cost of grinding is significant at 5 to 15 kWh/ton. If grindability could be increased by preheating the coal with waste heat, energy costs could be reduced. The objective of this work was to determine how grindability was affected by preheating. The method was to use population balance grinding models to interpret results of grinding coal before and after a heat treatment. Simulation of locked cycle tests gave a 40% increase in grindability. Approximately 40% grinding energy saving can be expected. By using waste heat for coal treatment, the targeted energy savings would be maintained.

Effect of microstructure on the size and shape of coal particles during comminution

Coal samples were comminuted in a ball mill under controlled temperature (20°C), in helium. Microstructural analyses of the coal particles before ball milling and at various times during milling showed relationships between the microstructure and the size and shapes of the resulting particles. During milling, fracture lines tended to proceed through pores and cracks and organic-to-organic and mineral-to-organic interfaces, and thus these features greatly influenced the size and shapes of particles produced. In the early stages of milling, a porous component of lignite produced needle-like or plate-shaped particles that were later broken into blocky and rounded particles. Another less porous component of lignite produced blocky and rounded particles during all stages of milling.

Convection and diffusion limited aeration during biooxidation of shallow ore heaps

Biooxidation of an ore heap containing only a few percent of sulfide minerals requires insertion of a very large amount of oxygen either by natural air convection, forced air ventilation or gaseous diffusion. While shallow heaps, those with large areas relative to their height, are of great interest for many gold and copper heaped ore processing operations, natural convection is often ineffective for oxidizing them because of inadequate lateral flow to the heaps interior. However, even in the absence of airflow, oxygen can diffuse into a shallow heap from its upper, horizontal surface in contact with air. Oxygen diffuses through the air-filled void space within the heap, driven by the oxygen concentration gradient resulting from internal oxygen depletion caused by mineral oxidation. Oxygen diffusion, coupled with the chemical reaction kinetics oxidizing the sulfide minerals, is analyzed for typical ore heap biooxidation parameters. Practical limits on both natural convection and gaseous diffusion for effective biooxidation of the sulfide minerals in shallow ore heaps are discussed.

NEURAL NETWORK PATTERN RECOGNITION OF BLAST FRAGMENT SIZE DISTRIBUTIONS

ABSTRACT Neural networks have considerable potential for applications in particulate image analysis. An area of great current interest is to use image analysis techniques to characterize particle size distributions in video images of blasted rock. A simulated neural network was trained to recognize fragmented rock size classes taken from images of blasted ore in a large open pit mining operation. Size distributions were assigned to categories such as 40% and 60% minus six inches. Pattern recognition features were extracted from digitized images using two-dimensional Fourier transforms. These features were then used as a training set to enable the neural network to recognize the size category of subsequent images of blasted rock taken from the mining operation. Training sets were developed for a back propagation algorithm by hand sorting and sizing the blast fragments from photographed piles. Within the limits of this experiment, the trained network consistently recognized the size distribution categories....

Solid-state diffusion-based processing kinetics for uniaxial self-propagating high-temperature synthesis of MoSi2

An analysis is presented for self-propagating, high-temperature synthesis (SHS) of MoSi2 from a mixture of silicon and molybdenum powders compacted into a semi-infinite, uniaxial bar and ignited at one end. The kinetics of reacting molybdenum grains are controlled by solid-state diffusion through the interposing product shell of MoSi2 that surrounds each shrinking molybdenum grain. The previously determined temperature-dependent microkinetics of this solid particle reaction are coupled with one-dimensional (1-D) heat transfer and storage to describe the time-dependent macrokinetics of the synthesis reaction sequencing through a perfectly insulated bar. The resulting equations are solved numerically to provide computed results of temperature and conversion as a function of time and distance. Preignition time, propagation velocity, and thickness of the reaction front are also determined. Results depend primarily on the initial temperature at the end of the bar, which affects preignition time, and the molybdenum grain radius. The perfectly insulated model was relaxed by limiting the maximum temperature to arbitrary values corresponding with lateral heat dissipation, and these results compare favorably with experimentally measured propagation velocities and maximum temperatures during SHS of MoSi2. The model presented, with MoSi2 as the prototype, is expected to be applicable to the SHS of many other refractory materials.

FOURIER SHAPE DESCRIPTORS AND PARTICLE BREAKAGE ENERGY

ABSTRACT Non linearities in population balance grinding equations can seriously decrease Che accuracy of the simulation, scale-up, or design of grinding circuits. A solution to this problem may be to incorporate particle shape in the grinding equations, provided that particle shapes change during grinding. In two examples of single particle crushing, unique particle shapes were produced by each level of energy input. In a third grinding example, observed nonlinear grinding kinetics of coal in a dry batch ball mill coincided with changes in particle shape. Fourier shape descriptors were used to detect the differences in shape, and can become an important tool in improving population balance models.

Practical assessment of a Solvay-type heat amplifying pump

Abstract The advantages of Solvay-type heat pumps include potentially high prime heat amplification factors. Our research took a theoretical approach to determining how good the amplification factors are. The process involved investigating a method used for selecting potential chemical reactions, such methods being an examination of chemical data-bases for good amplifying factors and good waste heat temperature boosts using graph theory algorithms. It appeared that Solvay heat pumps could be found to match a variety of industrial operating temperatures and waste heat availability with promising heat amplification. Assessment was made regarding the practicality of implementing real systems in general, including chemical product separation problems and reaction extent.

Fourier Bessel Characterization of Polished Metal Surfaces

The amount of information available from metallographic cross sections about material properties remains only subjectively accessible via trained metallurgical experts. Image analysis has not fulfilled the promise to quantify, standardize, or transmit this subjective information. Our solution is to describe different alloys with Luerkens-Beddow style Bessel Fourier descriptors. When AISI-SAE 1035, 1045, and 1060 steels undergo spheroidizing or normalizing heat treatments, the relative amounts and morphology of pearlite, bainite, and other phases, which determine material properties, change even more. The Bessel Fourier descriptors enable accurate classification (up to 93% accuracy) according to heat treatment history and alloy composition, indicating their superior ability to describe metallographic surfaces.

PARTICLE SHAPE AND HYOROCYCLONE EFFICIENCY

ABSTRACT Particles that are size classified in a hydrocyclone experience a complex force environment which includes forces proportional to size, shape, and specific gravity. Inefficient size classification occurs if particles of the same size and specific gravity appear both in the overflow and underflow streams. Fourier shape discriptors were used to show that the variation of drag forces due to particle shape was a significant factor in this inefficiency, thus providing a tool for better hydrocyclone design.