VTechWorks Repository :: Browsing by Author "Luttrell, Gerald H."

Browsing by Author "Luttrell, Gerald H."

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Advanced Chemical-Mechanical Dewatering of Fine Particles
Asmatulu, Ramazan (Virginia Tech, 2001-03-12)
In the present work, novel dewatering aids and a novel centrifuge configuration were developed and applied for the purpose of dewatering fine particles. Three different types dewatering reagents were tested in different filtration and centrifugation units. These chemicals included low-HLB surfactants, naturally occurring lipids, and modified lipids. Most of these reagents are insoluble in water; therefore, they were used in solutions of appropriate solvents, such as light hydrocarbon oils and short-chain alcohols. The role of these reagents was to increase the hydrophobicity of the coal and selected mineral particles (chalcopyrite, sphalerite, galena, talc, clay, phosphate, PCC and silica) for the dewatering. In the presence of these reagents, the water contact angles on the coal samples were increased up to 90o. According to the Laplace equation, an increase in contact angle with the surfactant addition should decrease the capillary pressure in a filter cake, which should in turn increase the rate of dewatering and help reduce the cake moisture. The use of the novel dewatering aids causes a decrease in the surface tension of water and an increase in the porosity of the cake, both of which also contribute to improved dewatering. A series of batch-scale dewatering tests were conducted on a variety of the coal and mineral samples using the novel dewatering aids. The results obtained with a Buchner funnel and air pressure filters showed that cake moistures could be reduced substantially, the extent of which depends on the particle size, cake thickness, drying time, reagent dosage, conditioning time, reagent type, sample aging, water chemistry, etc. It was determined that use of the novel dewatering aids could reduce the cake formation time by a significant degree due to the increased kinetics of dewatering. At the same time, the use of the dewatering aids reduced the cake moistures by allowing the water trapped in smaller capillaries of the filter cake. It was found that final cake moistures could be reduced by 50% of what can be normally achieved without using the reagents. However, the moisture reduction becomes difficult with increasing cake thickness. This problem can be minimized by applying a mechanical vibration to the cake, spraying a short-chain alcohol on the cake and by adding a small amount of an appropriate coagulant, such as alum and CaCl2 to the coal and mineral slurries. The novel dewatering aids were also tested using several different continuous filters, including a drum filter, disc filter and horizontal belt filter (HBF). The results obtained with these continuous filtration devices were consistent with those obtained from the batch filters. Depending on the coal and mineral samples and the type of the reagent, 40 to 60% reductions in moisture were readily achieved. When using vacuum disc filters, the cake thickness increased substantially in the presence of the novel dewatering aids, which could be attributed to the increased kinetics of dewatering. A dual vacuum system was developed in the present work in order to be able to control the cake thickness, which was necessary to achieve lower cake moistures. It was based on using a lower vacuum pressure during the cake formation time, while a full vacuum pressure was used during the drying cycle time. Thus, use of the dual vacuum system allowed the disc filter to be used in conjunction with the novel dewatering aids. Its performance was similar to that of HBF, which is designed to control cake thickness and cake formation time independently. The effectiveness of using the novel dewatering aids were also tested in a full-continuous pilot plant, in which coal samples were cleaned by a flotation column before the flotation product was subjected to the disc filter. The tests were conducted with and without using novel dewatering aids. These results were consistent with those obtained from the laboratory and batch-scale tests. The novel centrifuge developed in the present work was a unit, which combined a gravity force and air pressure. The new centrifuge was based on increasing the pressure drop across the filter cake formed on the surface of the medium (centrifuge wall). This provision made it possible to take advantage of Darcy s law and improve the removal of capillary water, which should help lower the cake moisture. A series of tests were conducted on several fine coal and mineral particles and obtained more than 50% moisture reduction even at very fine particle size (2 mm x 0). Based on the test results obtained in the present work, two proof-of-concept (POC) plants have been designed. The first was for the recovery of cyclone overflows that are currently being discarded in Virginia, and the other was for the recovery of fines from a pond in southern West Virginia. The former was designed based on the results of the plant tests conducted in the present work. Cost vs. benefit analyses were conducted on the two POC plants. The results showed very favorable internal rates of return when using the novel dewatering aids. Surface chemistry studies were conducted on the coal samples based on the results obtained in the present investigation. These consisted mainly of the surface characterization of the coal samples (surface mineral composition, surface area, zeta potential, x-ray photoelectron microscopy (XPS)), acid-base interactions of the solids and liquids, dewatering kinetic tests, contact angle measurements of the coal samples and surface force measurements using AFM. In addition, carbon coating on a silica plate using palsed laser deposition (PLD) and Langmuir-Blodgett (LB) film deposition tests were conducted on the sample to better understand the surfactant adsorption and dewatering processes. The test results showed that the moisture reductions on the fine particles agree well with the surface chemistry results.
Advancement of the Hydrophobic-Hydrophilic Separation Process
Jones, Alan Wayne III (Virginia Tech, 2019-04-19)
Froth flotation has long been regarded as the best available technology for ultrafine particles separation. However, froth flotation has extreme deficiencies for recovering ultrafine particles that are less than 30-50 μm in size for coal and 10-20 μm for minerals. Furthermore, dewatering of flotation products is difficult and costly using currently available technologies. Due to these problems, coal and mineral fines are either lost to tailings streams inadvertently or discarded purposely prior to flotation. In light of this, researchers at Virginia Tech have developed a process called hydrophobic-hydrophilic separation (HHS), which is based originally on a concept known as dewatering by displacement (DbD). The process uses non-polar solvents (usually short-chain alkanes) to selectively displace water from particle surfaces and to agglomerate fine coal particles. The resulting agglomerates are subsequently broken (or destabilized) mechanically in the next stage of the process, whereby hydrophobic particles are dispersed in the oil phase and water droplets entrapped within the agglomerates coalesce and exit by gravity along with the hydrophilic particles dispersed in them. In the present work, further laboratory-scale tests have been conducted on various coal samples with the objective of commercial deployment of the HHS process. Test work has also been conducted to explore the possibility of using this process for the recovery of ultrafine minerals such as copper and rare earth minerals. Ultrafine streams produced less than 10% ash and moisture consistently, while coarse coal feed had no observable degradation to the HHS process. Middling coal samples were upgraded to high-value coal products when micronized by grinding. All coal samples performed better with the HHS process than with flotation in terms of separation efficiency. High-grade rare earth mineral concentrates were produced with the HHS process ranging from 600-2100 ppm of total rare earth elements, depending on the method and reagent. Additionally, the HHS process produced copper concentrates assaying greater than 30% Cu for both artificial and real feed samples, as well as, between 10-20% Cu for waste samples, which all performed better than flotation.
Analysis and optimization of coalbed methane gas well production
Holman, Travis Scott (Virginia Tech, 1996-07-15)
Coalbed methane wells have been used for many years as a viable means of extracting quantities of methane gas for use as a clean and efficient energy source. However, there is a limited understanding of many of the factors involved during the extraction process. As the more easily attainable reservoirs are depleted, it is imperative to gain a greater comprehension of these factors in order to develop techniques to efficiently collect economical quantities of methane gas in the future. For this investigation, an extensive database was compiled, consisting of a large set of parameters pertaining to the development of coalbed methane gas wells. Using the information contained in this database, a statistical analysis was performed in order to gain a better understanding of the relationships between the many factors involved in extracting quantities of methane gas from the ground. The results of this analysis showed that the majority of the parameters shown to have the greatest impact on methane production were heavily dependent upon the geology of the region. As a result, any attempt to exploit them for optimization exercises would be extremely difficult. Of the parameters shown to have the least dependence on naturally occurring phenomena, the amount of proppant sand used to hold fractures open within the well system after stimulation was shown to have the most impact During the well stimulation procedure, the proppant sand is carried into the fractures in the strata by a foam fracturing fluid. The sand acts to support the fracture system, increasing the permeability of formation, and allowing the methane gas to flow to the wellbore. By treating the sand particles with certain reagents, it is possible to render them hydrophobic, making it possible for them to stick to the bubbles within the foam and be carried deeper into the formation. Results of an investigation of sands treated to different degrees of hydrophobicity have shown that such treatments significantly increase the amount of sand distributed over a greater distance.
Analytical and Numerical Techniques for the Optimal Design of Mineral Separation Circuits
Noble, Christopher Aaron (Virginia Tech, 2013-06-13)
The design of mineral processing circuits is a complex, open-ended process. While several tools and methodologies are available, extensive data collection accompanied with trial-and-error simulation are often the predominant technical measures utilized throughout the process. Unfortunately, this approach often produces sub-optimal solutions, while squandering time and financial resources. This work proposes several new and refined methodologies intended to assist during all stages of circuit design. First, an algorithm has been developed to automatically determine circuit analytical solutions from a user-defined circuit configuration. This analytical solution may then be used to rank circuits by traditional derivative-based linear circuit analysis or one of several newly proposed objective functions, including a yield indicator (the yield score) or a value-based indicator (the moment of inertia). Second, this work presents a four-reactor flotation model which considers both process kinetics and machine carrying capacity. The simulator is suitable for scaling laboratory data to predict full-scale performance. By first using circuit analysis to reduce the number of design alternatives, experimental and simulation efforts may be focused to those configurations which have the best likelihood of enhanced performance while meeting secondary process objectives. Finally, this work verifies the circuit analysis methodology through a virtual experimental analysis of 17 circuit configurations. A hypothetical electrostatic separator was implemented into a dynamic physics-based discrete element modeling environment. The virtual experiment was used to quantify the selectivity of each circuit configuration, and the final results validate the initial circuit analysis projections.
Apparatus and process for the separation of hydrophobic and hydrophilic particles using microbubble column flotation together with a process and apparatus for generation of microbubbles
(United States Patent and Trademark Office, 1992-12-01)
A method and apparatus are disclosed for the microbubble flotation separation of very fine and coarse particles, especially coal and minerals, so as to produce high purity and high recovery efficiency. This is accomplished through the use of a flotation column, microbubbles, recycling of the flotation pulp, and countercurrent wash water to gently wash the froth. Also disclosed are unique processes and apparatus for generating microbubbles for flotation in a highly efficient and inexpensive manner using either a porous tube or in-line static generators.
Apparatus and process for the separation of hydrophobic and hydrophilic particles using microbubble column flotation together with a process and apparatus for generation of microbubbles
(United States Patent and Trademark Office, 1998-09-29)
A method and apparatus are disclosed for the microbubble flotation separation of very fine and coarse particles, especially coal and minerals, so as to produce high purity and high recovery efficiency. This is accomplished through the use of a flotation column, microbubbles, recycling of the flotation pulp, and countercurrent wash water to gently wash the froth. Also disclosed are unique processes and apparatus for generating microbubbles for flotation in a highly efficient and inexpensive manner using either a porous tube or in-line static generators.
Apparatus for dewatering and demineralization of fine particles
(United States Patent and Trademark Office, 2020-02-18)
Hydrophobic particles such as coal and hydrophobized mineral fines can be readily separated from hydrophilic impurities by forming agglomerates in water using a hydrophobic liquids such as oil. The agglomerates of hydrophobic particles usually entrap large amounts of water, causing the moisture of the recovered hydrophobic particles to be excessively high. This problem can be overcome by dispersing the hydrophobic agglomerates in a hydrophobic liquid that can be readily recycled. The dispersion can be achieved using specially designed apparatus and methods that can create a turbulence that can help destabilize the agglomerates in a recyclable hydrophobic liquid and facilitate the dispersion.
Apparatus for improved ash and sulfur rejection
(United States Patent and Trademark Office, 1996-06-04)
An apparatus for separating impurities from coal, includes a device for removing a predetermined amount of ash-forming substances from the coal and a device for removing a predetermined amount of high specific gravity (e.g., pyrite) from the coal having been processed by the ash-forming substance removing device. The ash-forming substance removing device and the high specific gravity material removing device each possess characteristics that allow them to more efficiently reject different types of mineral impurities from coal.
Apparatus for the separation of hydrophobic and hydrophilic particles using microbubble column flotation together with a process and apparatus for generation of microbubbles
(United States Patent and Trademark Office, 1995-03-14)
An apparatus is disclosed for the microbubble flotation separation of very fine and coarse particles, especially coal, and minerals so as to produce high purity and high recovery efficiency. This is accomplished through the use of a flotation column, microbubbles, recycling of the flotation pulp, and countercurrent wash water to gently wash the froth. Also disclosed are unique processes and apparatus for generating microbubbles for flotation in a highly efficient and inexpensive manner using either a porous tube or in-line static generators.
Application of Extended DLVO Theory: Modeling of Flotation and Hydrophobicity of Dodecane
Mao, Laiqun (Virginia Tech, 1998-05-23)
The extended DLVO theory was used to develop a flotation model by considering both hydrodynamic and surface forces involved in the process. A stream function was used to estimate the kinetic energies for thinning the water films between bubbles and particles, which were compared with the energy barriers, created by surface forces, to determine the probability of adhesion. A general expression for the probability of detachment was derived from similar mechanism for chemical reaction, and the kinetic energy for detachment was estimated with French and Wilson's model. The hydrophobic force parameter (K132) calculated from the rate constants of single bubble flotation tests showed that, K132 for bubble-particle interaction were close to the geometric means of K131 for particle-particle interactions and K232 for bubble-bubble interaction, indicating that the combining rules developed for dispersion forces may be useful for hydrophobic forces. The model was used to predict flotation results as functions of several important parameters such as contact angle, double-layer potentials, particle size, bubble size, etc. The predictions were consistent with experience, and could be explained in view of the various subprocesses considered in the model development. Furthermore, the model suggested optimum conditions for achieving the maximum separation efficiency. The extended DLVO theory was also used to determine the hydrophobic force between two oil/solution interfaces from the equilibrium film thicknesses of dodecylammonium chloride (RNH3Cl) solutions obtained using Thin Film Balance (TFB) technique. The results showed that, the oil droplets were inherently hydrophobic, and the hydrophobic force played an important role in the stability of emulsions. This force decreased with increasing surfactant concentration, and also changed with pH and the addition of electrolyte. The interfacial area occupied by molecules indicated that, the dodecane molecules might present between two surfactant ions at interface, thus the hydrophobicity of oil/solution interface was less sensitive to the addition of the surfactant than that of air/solution interface. Thermodynamic analysis suggested that, there might exist a relationship between the interfacial hydrophobicity and the interfacial tension.
The Application of Mineral Processing Techniques to the Scrap Recycling Industry
Koermer, Scott Carl (Virginia Tech, 2015-11-09)
The scrap metal recycling industry is a growing industry that plays an important role in the sustainability of a large global metal supply. Unfortunately, recycling lacks many standards, and test procedures in place for mineral processing. These standards and practices, if used in recycling, could aid recyclers in determining and achieving optimal separations for their plant.. New regulations for scrap imports into China make it difficult to obtain the metal recoveries that have been achieved in the past. In order to help scrap yards adhere to the new regulations the Eriez RCS eddy current separator system was tested in full scale. The principles this system uses, called circuit analysis, have been used by the mining industry for years, and can be used with any separation system. The Eriez RCS system surpassed the requirements of the Chinese regulations, while simultaneously increasing the recovery of metals. In order to further analyze eddy current separator circuits, tree analysis was attempted for single eddy current separators, as well as more complex circuits mimicked using locked cycle tests. The circuits used in the locked cycle test were a rougher-cleaner, a rougher-scavenger, and a rougher-cleaner-scavenger. It was found that it is possible to use tree analysis to compare different eddy current separator circuits using the same settings, however standards for this practice need to be established for it to be useful. Using the data analysis methods developed for this particular tree analysis, the rougher-cleaner-scavenger test had the best performance overall. This is the same result as the full scale testing done on the Eriez RCS system, but more testing should be conducted to confirm the data analysis techniques of calculating theoretical efficiency, recovery efficiency, and rejection efficiency.
Applications of Queuing Theory for Open-Pit Truck/Shovel Haulage Systems
May, Meredith Augusta (Virginia Tech, 2013-01-29)
Surface mining is the most common mining method worldwide, and open pit mining accounts for more than 60% of all surface output. Haulage costs account for as much as 60% of the total operating cost for these types of mines, so it is desirable to maintain an efficient haulage system. As the size of the haulage fleet being used increases, shovel productivity increases and truck productivity decreases, so an effective fleet size must be chosen that will effectively utilize all pieces of equipment. One method of fleet selection involves the application of queuing theory to the haul cycle. Queuing theory was developed to model systems that provide service for randomly arising demands and predict the behavior of such systems. A queuing system is one in which customers arrive for service, wait for service if it is not immediately available, and move on to the next server or exit the system once they have been serviced. Most mining haul routes consist of four main components: loading, loaded hauling, dumping, and unloaded hauling to return to the loader. These components can be modeled together as servers in one cyclic queuing network, or independently as individual service channels. Data from a large open pit gold mine are analyzed and applied to a multichannel queuing model representative of the loading process of the haul cycle. The outputs of the model are compared against the actual truck data to evaluate the validity of the queuing model developed.
Approaches and Barriers to Incorporating Sustainable Development Into Coal Mine Design
Craynon, John Raymond (Virginia Tech, 2011-07-27)
It is widely recognized that coal is and will continue to be a crucial element in a modern, balanced energy portfolio, providing a bridge to the future as an important low-cost and secure energy solution to sustainability challenges. The designer of coal mining operations needs to simultaneously consider legal, environmental, and sustainability goals, along with traditional mining engineering parameters, as integral parts of the design process. However, traditional coal mining planning seldom considers key “sustainability factors” such as societal impacts; dislocation of towns and residences; physical and economic impact on neighboring communities and individuals; infrastructure concerns; post-mining land use habitat disruption and reconstruction; and long-term community benefit. This work demonstrates the advantage of using a systems engineering approach based on the premise that systems can only be optimized if all factors are considered at one time. Utilizing systems engineering and optimization approaches allows for the incorporation of regulatory and sustainability factors into coal mine design. Graphical approaches, based on the use of GIS tools, are shown as examples of the development of models for the positive and negative impacts of coal mining operations. However, this work also revealed that there are significant challenges inherent in optimizing the design of large-scale surface coal mining operations in Appalachia. Regulatory and permitting programs in the United States, which give conflicting and ill-defined responsibilities to a variety of federal and state agencies, often focus on single parameters, rather than the full suite of desirable outcomes for sustainability, and serve as barriers to innovation. Sustainable development requires a delicate balance between competing economic, environmental and social interests. In the context of coal mining in the U.S., the current regulatory frameworks and policy-guidance vehicles impede this balance. To address this problem, and thus effectively and efficiently provide energy resources while protecting the communities and environments, the U.S. will likely need to fundamentally restructure regulatory programs. Ideally, revisions should be based upon the key concepts of public ecology and allow for a systems engineering approach to coal mine design.
Approaches to Simulation of an Underground Longwall Mine and Implications for Ventilation System Analysis
Zhang, Hongbin (Virginia Tech, 2015-06-19)
Carefully engineered mine ventilation is critical to the safe operation of underground longwall mines. Currently, there are several options for simulation of mine ventilation. This research was conducted to rapidly simulate an underground longwall mine, especially for the use of tracer gas in an emergency situation. In an emergency situation, limited information about the state of mine ventilation system is known, and it is difficult to make informed decisions about safety of the mine for rescue personnel. With careful planning, tracer gases can be used to remotely ascertain changes in the ventilation system. In the meantime, simulation of the tracer gas can be conducted to understand the airflow behavior for improvements during normal operation. Better informed decisions can be made with the help of both tracer gas technique and different modeling approaches. This research was made up of two main parts. One was a field study conducted in an underground longwall mine in the western U.S. The other one was a simulation of the underground longwall mine with different approaches, such as network modeling and Computational Fluid Dynamics (CFD) models. Networking modeling is the most prevalent modeling technique in the mining industry. However, a gob area, which is a void zone filled with broken rocks after the longwall mining, cannot be simulated in an accurate way with networking modeling. CFD is a powerful tool for modeling different kinds of flows under various situations. However, it requires a significant time investment for the expert user as well as considerable computing power. To take advantage of both network modeling and CFD, the hybrid approach, which is a combination of network modeling and CFD was established. Since tracer gas was released and collected in the field study, the tracer gas concentration profile was separately simulated in network modeling, CFD model, and hybrid model in this study. The simulated results of airflow and tracer gas flow were analyzed and compared with the experimental results from the field study. Two commercial network modeling software packages were analyzed in this study. One of the network modeling software also has the capability to couple with CFD. A two-dimensional (2D) CFD model without gob was built to first analyze the accuracy of CFD. More 2D CFD models with gob were generated to determine how much detail was necessary for the gob model. Several three-dimensional (3D) CFD models with gob were then created. A mesh independence study and a sensitivity study for the porosity and permeability values were created to determine the optimal mesh size, porosity and permeability values for the 3D CFD model, and steady-state simulation and transient simulations were conducted in the 3D CFD models. In the steady-state simulation, a comparison was made between the 3D CFD models with and without taking the diffusivity of SF6 in air into account. Finally, the different simulation techniques were compared to measured field data, and assessed to determine if the hybrid approach was considerably simpler, while also providing results superior to a simple network model.
Carbon Dioxide Storage in Coal Seams with Enhanced Coalbed Methane Recovery: Geologic Evaluation, Capacity Assessment and Field Validation of the Central Appalachian Basin
Ripepi, Nino Samuel (Virginia Tech, 2009-08-03)
The mitigation of greenhouse gas emissions and enhanced recovery of coalbed methane are benefits to sequestering carbon dioxide in coal seams. This is possible because of the affinity of coal to preferentially adsorb carbon dioxide over methane. Coalbed methane is the most significant natural gas reserve in central Appalachia and currently is economically produced in many fields in the Basin. This thesis documents research that assesses the capacity of coal seams in the Central Appalachian Basin to store carbon dioxide and verifies the assessment through a field validation test. This research allowed for the first detailed assessment of the capacity for coal seams in the Central Appalachian Basin to store carbon dioxide and enhance coalbed methane recovery. This assessment indicates that more than 1.3 billion tons of carbon dioxide can be sequestered, while increasing coalbed methane reserves by as much as 2.5 trillion cubic feet. As many of the coalbed methane fields are approaching maturity, carbon sequestration and enhanced coalbed methane recovery has the potential to add significant recoverable reserves and extend the life of these fields. As part of this research, one thousand tons of carbon dioxide was successfully injected into a coalbed methane well in Russell County, Virginia as the first carbon dioxide injection test in the Appalachian coalfields. Research from the field validation test identified important injection parameters and vital monitoring technologies that will be applicable to commercial-scale deployment. Results from the injection test and subsequently returning the well to production, confirm that fractured coal seams have the potential to sequester carbon dioxide and increase methane production. It was demonstrated through the use of perfluorocarbon tracers that there is a connection through the coal matrix between the injection well and surrounding producing gas wells. This connection is a cause for concern because it is a path for the carbon dioxide to migrate to the producing wells. The thesis concludes by presenting options for mitigating carbon dioxide breakthrough in commercial-scale injection projects.
A Characterization and Determination of the Coal Reserves and Resources of Southwest Virginia
Westman, Erik C. (Virginia Tech, 1999-04-14)
Coal mining and timber are the two primary industries supporting the people of Southwest Virginia. Coal mining has occurred for more than 100 years, but production has dropped since reaching a peak in 1990. In order to properly plan with remaining coal production a study was conducted to characterize and estimate coal resources. Seam thickness was found to be the parameter which most influenced resource levels. An economic model was developed to determine which portion of the reserves could economically be extracted. It was found that 3.95 billion tons, or 14% of the remaining resource, is economic under current mining conditions. More than 60% of these reserves, however, are in deep seams which require shafts to be constructed prior to initiation of mining.
Characterization and scale-up of microbubble generation in column flotation
Davis, Van Leslie (Virginia Tech, 1990-04-05)
Recent hydrodynamic studies suggest that small air bubbles can be used to improve the performance of column flotation. Tests carried out at Virginia Tech during the past several years have shown that various types of inline motionless (or static) mixers can successfully produce microbubbles for column flotation. Unfortunately, few guidelines exist for selecting the proper size and type of motionless mixer for generating microbubbles. In the present work, the mean bubble size produced by various types of in-line motionless mixers has been experimentally determined over a wide range of operating conditions and generator geometries. Test results indicate that generator performance is described by a series of expressions derived from a dimensional analysis. These expressions demonstrate that bubble diameter is primarily determined by the generator geometry and a dimensionless term known as the Weber number. Tests have also been conducted to determine the reduction in the performance of centrifugal pumps under air admitting conditions. A semi-empirical pump model has been utilized which allows the proper size of pump to be selected for microbubble generation. This information should prove useful for the design and operation of microbubble generation circuits on an industrial scale.
Characterizing Flotation Response: A Theoretical and Experimental Comparison of Techniques
Randolph, John Michael Jr. (Virginia Tech, 1997-09-12)
Over the past 40 years, several procedures have been proposed for characterizing ideal flotation behavior. These procedures, known as release or tree analysis, generally involve multi-stage flotation in batch, laboratory flotation cells using various combinations of rougher, cleaner, and scavenger configurations. Although some of these procedures have been experimentally compared, there remains considerable controversy as to which approach best approximates the ideal flotation response. In this investigation, modeling and simulation techniques are used in conjunction with experimental studies to compare three procedures commonly used for characterizing flotation behavior. These procedures include timed release analysis, simplified release analysis, and tree analysis. Timed release analysis is shown to produce superior results to simplified release analysis and tree analysis; although simplified release analysis appears to be best suited for locating the "elbow" of the grade-recovery curve. In no case, do any of these techniques approximate a perfect separation. A novel technique, known as reverse release analysis, is described and demonstrated to be superior to the other three procedures. Finally, a theoretical methodology for obtaining the true ideal separation curve is presented.
Characterizing Trace Element Associations in the Pittsburgh No. 8, Illinois No. 6 and Coalburg Coal Seams
Conaway, Shawn Michael (Virginia Tech, 2001-07-26)
Coal preparation is widely regarded as a cost effective method for reducing the amounts of potentially hazardous air pollutant precursors (HAPPs) that occur as trace elements in the run-of-mine coals. Unfortunately, many existing coal preparation plants are inefficient in removing trace elements because of poor circuit design and inadequate liberation of coal and mineral matter. These problems are often difficult to correct in the absence of characterization data regarding the mineralogical association and washability of trace elements in run-of-mine coals. Therefore, the first step in removing the trace elements through coal preparation is to characterize the modes of association for trace elements in a coal seam. The purpose of this project was to link the occurrence of specific trace elements to the mineralogy and washability characteristics of different eastern U.S. coal seams. Detailed characterization studies were carried out using scanning electron microscopy (SEM) coupled with automated image analysis (AIA) to establish the association between different trace elements and the various components contained in coal. The first step in this analysis required the preparation of 11 different density fractions from a run-of-mine sample of 65 x 100 mesh Pittsburgh No. 8 coal. The samples were then examined using the scanning electron microscope (SEM) to establish the individual mineral constituents contained within each gravity fraction. For comparison, each gravity fraction was also carefully analyzed for trace element content by atomic adsorption spectroscopy (AA). The contribution of various mineral components to the trace element concentrations was determined in the present work using statistical procedures, i.e., individual linear regression and multiple linear regression. After completing the SEM analyses, washability (float-sink) tests were performed on three different coal seams. In this work, several size fractions from each of three different run-of-mine coals were subjected to float-sink testing and release analysis. Because of the overwhelming amount of data, statistical analyses were conducted to show the key relationships identified by this work. The data collected from this study show that trace elements are primarily associated with the mineral matter present in run-of-mine coal. The washability work also shows that the trace elements are concentrated in the heavier specific gravity classes. The characterization work shows that majority of the trace elements are associated with the ash-forming mineral matter and pyrite. The only element found to have a strong association with organic matter was beryllium. The information obtained from this work suggests that a properly designed coal preparation plant can remove substantial amounts of trace elements prior to coal combustion.
Chemical and Electrochemical Coal Cleaning in acidic medium application and analysis of the process
Dieudonne, Vincent (Virginia Tech, 1988-10-06)
The Chemical and Electrochemical Coal Cleaning (CECC) process, designed to remove mineral matter from coal, has been investigated by treating coal samples in acidified slurries. Various coals, characterized by different maceral structures and mineral matter contents, were subjected to several experimental procedures under mild conditions. Substantial amounts of mineral matter (up to 70%) could be extracted from coals which were resistant to physical cleaning, while 22% of sulfur could be removed from pyritic coals. The operating conditions of the CECC were studied in order to determine their influence on the process efficiency. Analyses conducted on solids and leachates resulting from the tests demonstrated that different mechanisms were achieving demineralization by the CECC. Between 50% and 95% of the feed mineral matter was removed by dissolution, whereas the balance could be ascribed to liberation. The CECC process is suitable for cleaning middlings, as well as for further extracting mineral matter from physically clean coals, especially from pyritic vitrinite and fusinite type coals.

Browsing by Author "Luttrell, Gerald H."

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