131 |
Electrostatic charging of water sprays by corona and induction for dust suppressionXiao, Fuchun, Safety Science, Faculty of Science, UNSW January 2000 (has links)
Dust control is a very significant issue in underground coal mining. The benefits of reducing dust levels will be a lesser risk of lung disease to coal miners, improved working conditions and a reduced risk of dust explosions. Coal dust is commonly suppressed by water sprays but suppression efficiency is not high because dust tends to travel in the air flow round the water droplets rather than being captured by them. If water sprays are electrostatically charged, then a significant improvement in dust suppression efficiency may be achieved. Of the three principal droplet charging mechanisms, i.e. corona charging, induction charging and contact charging, corona charging is the most widely used in many industrial fields including dust suppression, However, it requires a high applied voltage, ranging from thousands to more than a hundred thousand volts, depending on the geometry of the charging equipment. Induction charging has been used in agricultural spraying since Law (1978) developed an embedded-electrode induction charging spraying nozzle. This nozzle provides a compact, inexpensively fabricated droplet charger and, reduces design requirements on size and output voltage (of the order of 1000 volts). It also reduces the potential for mechanical damage, misalignment and personnel hazard. In order to evaluate the effectiveness of dust suppression, either the charge on individual droplets or the charge-to-mass ratio of water sprays needs to be known. However, the parameters which control the charge applied to water and the charging rate have been unsolved theoretically for any charging mechanism. The existing theories for the induction-charged and air-atomising a liquid jet have been found to be inadequate. And there is no theory available for corona charging of the droplets produced with a pneumatic nozzle in order to predict the spray charge level or the spray charge-to-mass ratio. In view of this situation, mathematical models have been developed in this thesis for both the corona and induction charging mechanisms. During the development of the theories, it has been assumed that for corona charging, that the jet is disintegrated into droplets and the droplets are then charged; for induction charging, that the jet is first charged and the charged jet is then disintegrated into charged droplets. The Sauter mean diameter of the sprays, D32 , plays an important role in linking the individual droplet charge to the spray charge-to-mass ratio for both charging mechanisms. The developed theories are general models suitable for any liquid with both corona and induction charging. Theoretical calculations for the spray charge-to-mass ratio, individual droplet charge and the ratio of droplet charge to the Rayleigh charge limit have been presented for almost all of the influencing electrical and mechanical parameters such as applied voltage, air flowrate, liquid flowrate, liquid conductivity, liquid dielectric constant, nozzle dimensions, cylindrical electrode dimensions, and fluid parameters, for example, density, viscosity and surface tension. In the calculation for corona charging of droplets, the effect of the droplets on corona current and corona-onset voltage has been assessed for first time. The introduction of the Sauter mean diameter of the sprays, D32 , makes the assessment possible. Theoretical calculations for induction charging of liquid jets have shown that provided liquids have a conductivity value higher than the critical value, s = - 10 4 S/m, then they can be charged satisfactorily by the induction charging method. Among all of the influencing parameters, the electrical and mechanical parameters determine the charging rate and the water spray charge level. The suitability of employing these two charging mechanisms to dust suppression in coal mine has been evaluated based on the spray charge level, safety issues and the simplicity or otherwise of the equipment. The induction charging method was considered to have advantages over its corona charging counterpart, and has been chosen for charging the water sprays in the experiment program. Water has a conductivity of s = - 10 2 S/m, higher than the critical value, s = - 10 4 S/m. Based upon theoretical considerations, it is concluded that water is an appropriate liquid for corona charging, based on its dielectric constant, and for induction charging, based on its conductivity. In order to facilitate the testing of electrostatically charged water spray cloud parameters, a spray charger/collector was designed and constructed by others and a computerised data acquisition system has been employed. According to the theory developed for induction charging, the optimum length of the charging electrode has been analysed based upon the assumption that water jet is first charged and then the charged jet is disintegrated into charged droplets by the high pressure air. An experimental program examined the dependence of spray current upon four parameters: air flowrate, water flowrate, applied voltage and jet diameter. The experiments have shown that the induction-charged air-atomising nozzle used in the experiment is able to impart a significant charge into the water sprays. The spray charge-to-mass ratio calculated based upon the measured spray current demonstrates the same characteristics as predicted by theory: increasing with air flowrate, decreasing with water flowrate, increasing with applied voltage to a peak value then decreasing with further increase in the voltage, and increasing with jet diameter. A successful interpretation of an important phenomenon in the inductioncharged air-atomising a water jet, that spray charge-to-mass ratio and spray current increase with air pressure (or air flowrate) and decrease with increasing water flowrate, has been achieved based on the theories developed in this thesis. This phenomenon occurs because increasing air flowrate and/or decreasing water flowrate leads to a higher velocity of jet flowing through the induction electrode. However, when water flowrate becomes very small, a decrease in spray current with increasing air pressure (or flowrate) may be caused both by jet breakup inside the electrode and by contraction of the jet. In order to verify the theory, a preliminary comparison of experimental data with theoretical predictions employing a constant kic in the air-jet interaction coefficient a which was assumed to be 0.7 has shown a general agreement. However, the value of kic appears to be related to jet diameter, air/water mass ratio and applied voltage. An empirical equation for kic has then been formulated based on the experimental data for the spray charge-to-mass ratio. Finally a comparison of experimental results with theoretical predictions using the formulated kic shows an improved agreement. It is concluded that the induction-charged air-atomising nozzle has a potential application in dust suppression in coal mines, as the voltage required to charge water sprays is only 1000 ~ 1200 volts, and that the theory developed for induction charging of water sprays can be used to guide laboratory investigations and design processes for dust suppression and other industrial applications which might employ the electrostatic charging of liquid sprays.
|
132 |
Patrick Edward Connor, "father" of Utah miningFox, William. January 1966 (has links)
Thesis (M.A.)--Brigham Young University, Dept. of History. / Electronic thesis. Also available in print ed.
|
133 |
Magnesium city : transformation and shifting resources on the periphery of Dashiqiao Liaoning, ChinaHe, Liu, River, 何鏐 January 2014 (has links)
With the increasing numbers of resource-dying cities in China, the conflict between city’s sustainable development and basic mining industry has been more and more sharp. It is emergency to find a suitable way of future for those cities in danger. This study is based on a special resources - magnesium. By analyzing the magnesium city, Dashiqiao, it is possible to generate a workable future direction for this city and a prompt for other resource-based cities in China.
The focus lies in the transformation of the city, and also the transformation of magnesium mining industry. Because the city’s developing is quite relevant to its supporting industry, the magnesium industry in the city is largely influenced the step of urbanization. As we all known that the mining industry caused serious environmental pollution, which restrict the possible land use in those preindustrial land. In another word, the mining industry now is restricting the urbanization. To make sure the transformation happened smoothly, it is important to ease the restrict. And it is where this study started with.
Through the study of magnesium industry, it is possible to adapt industrial transformation with city’s urbanization by exploring ignored resources buried in old mining industry, at the meanwhile, reducing the pollution of existing magnesium industry. With the new resources and better environmental condition, the city have a much wider choice for its further development. According to the research of Dashiqiao city’s development, it is now the best time to make a transformation of magnesium industry otherwise it would be late and causes more time and resource to keep the city alive. This study is providing a much more flexible future. / published_or_final_version / Architecture / Master / Master of Landscape Architecture
|
134 |
Methods and environmental factors in the production of thorium from vein depositsCummings, Robert Adams January 1979 (has links)
No description available.
|
135 |
The economics of a one-industry townLeonard, John Wallace, 1919- January 1954 (has links)
No description available.
|
136 |
The development of a method for the determination of the optimum replacement time for surface mining equipmentBarkdoll, Ivan Harry, 1915- January 1961 (has links)
No description available.
|
137 |
Isolation and its effect on employment practices of mining cmpanies in ArizonaEconomidis, Peter, 1934- January 1963 (has links)
No description available.
|
138 |
The mining industry and its contribution to the economic development of Québec.Paquette, Pierre, 1947- January 1971 (has links)
No description available.
|
139 |
The nature and extent of non-financial disclosure in the South African mining industry.Adagish, Kibra Fitwi. January 2009 (has links)
Non-financial disclosures are of considerable interest and importance to the reporting
world and decision making. However, many companies fail to disclose adequate
information on their non-financial matters. The lack of internationally accepted
requirements for the presentation of non-financial disclosures is one reason for inadequate
reporting of non-financial matters and the reporting differences among companies.
The aim of this dissertation was to explore the nature and extent of non-financial disclosure
in South African mining companies listed on the JSE Securities Exchange. This sector was
chosen because of its high risky nature and its significant role in the South African
economy. The data were collected from 22 South African mining companies‘ websites and
related to the 2004, 2005 and 2006 annual reports.
A disclosure index was developed to investigate the extent and nature of non-financial
disclosure in the South African mining companies with regards to environmental, social,
corporate governance, forward-looking information and Management Discussion and
Analysis (MD&A), and the extent of non-financial disclosure with the JSE Securities
Exchange reporting requirements; that is, the King II and the JSE SRI Index. Thereafter, a
content analysis of the companies‘ annual reports was carried out using the disclosure
index developed for this study.
The study found that the non-financial disclosure for all 22 mining companies showed an
increasing trend over the years studied. Mining companies were disclosing environmental
issues more than any of the other non-financial disclosure items. However, more than half
of the companies did not provide information with regard to their non-compliance issues.
Generally this means that, although the mining companies face obvious risks, they are better
at disclosing positive rather than negative information. The main reason for the increase in
the companies‘ adoption of Global Reporting Initiative (GRI) as a non-financial reporting
guideline is King II. The study demonstrates that there was not 100% compliance level of
adherence with the reporting requirements of the JSE Securities Exchange on corporate
governance and integrated sustainability reporting.
Keywords: Non-financial disclosures, mining companies, South Africa, JSE Securities
Exchange, environmental, social, corporate governance, forward-looking, MD&A. / Thesis (M.Acc.)-University of KwaZulu-Natal, 2009.
|
140 |
An investigation into the effects of UG2 Ore variability on froth flotation.Ramlall, Nigel Valentino. 23 September 2014 (has links)
South Africa is the world’s largest producer of platinum group elements (PGEs). Mining
takes place in the Bushveld Complex, and recent statistics, (Mudd, 2010), showed that the
UG2 reef is the main source of production, accounting for approximately 60% of world
mining production. However, recovery by flotation is complicated by variations in the
mineral composition, the need to grind fine and entrainment of chromite, which has an
adverse effect on the subsequent smelting of the concentrate. The recovery of PGEs is
variable, and it is influenced by PGE feed properties such as degree of liberation, mineral
type and grain size. Conventional rougher batch flotation tests on drill core samples do not
provide sufficient information for predicting plant performance.
The aim of this research was to develop a rigorous method for the testing of UG2 drill core
samples. A rougher-cleaner flotation test procedure was developed, and statistical tests were
applied to select an appropriate model, which included entrainment of hydrophilic minerals.
Fifty UG2 samples from across the Bushveld were milled at a fixed energy input, and the
new test procedure was applied to derive model parameters for all samples. There was a
significant variability in the PGE recovery, and typical feed characteristics such as PGE feed
grade and grind did not show a clear link to the PGE recovery. This was due to the complex
mineralogy of the PGE minerals and variations in ore hardness. Hence, a statistical modelling
algorithm was used to determine the factors affecting PGE recovery, and an empirical model
was developed, which relates the PGE recovery to feed properties. The model can be used to
estimate PGE recovery based on feed properties. Samples which had a high base metal
content (e.g. high nickel to iron ratio) had a high PGE recovery, and samples which were
altered (e.g. high Rb/Sr ratio and loss on ignition) had a low PGE recovery.
Depressant addition is used in PGE flotation to control the recovery of gangue, but it also
affects the flotation of composite PGE/gangue particles. Seven of the fifty UG2 samples were
selected for a more detailed investigation, using a more advanced batch flotation test and a
mineralogical liberation analysis. The advanced batch flotation test was a new development,
in which flotation model parameters were derived simultaneously for flotation after two
stages of grinding and a combined cleaning stage. The effect of a range of depressant
additions was also modelled. The floatable PGE fraction, determined from batch modelling,
was linked to the mineralogical liberation analysis of the feed. The model is the first of its
kind, and it makes it possible to predict the mineralogical characteristics of the feed from
flotation data.
A spread-sheet simulator was developed, to demonstrate how batch data (from the advanced
flotation test) could be used to predict plant performance. Scale-up parameters were derived
by using pilot-plant data for one of the ores. The spread-sheet was then used to optimise the
plant design and depressant addition for an ore, while constraining, the mass of concentrate
and the chromite content. The example showed that there was an optimum depressant
addition and rougher-cleaner volume capacity for an ore.
The gambit of this study was the linking of feed chemical assay and mineralogical properties
to PGE recovery. The application of mineralogical tests and modelling of data from the
advanced flotation test has demonstrated that the link is relatively complex. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.
|
Page generated in 0.1003 seconds