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By D. S. Choi

Underground production of coal by longwall methods has increased significantly in the last few years and will very likely continue to: increase. There are several reasons for this. First, as mining moves into seams having greater overburden, roof exposure must be reduced since support will become' increasingly expensive. Secondly, the growing demand for coal has forced the coal industry to seek alternative, more productive, coal mining methods. In addition, the longwall method greatly simplifies the underground ventilation network. This paper addresses itself to the design of longwall development headings, particularly to those of the United States where multiple development headings are required by law. The most burdensome problem encountered in many longwall mining installations is deterioration of the tailgate due to the combined effect from, the active longwall gob and the old gob made by mining the previous panel.1 Portions of the tailgate entry are sometimes closed to such a degree that extensive repair work is necessary to keep the entry in usable condition. The purpose of this paper is to present the result of a study in progress which combines field measurements with numerical model analysis to reduce the cost of maintaining tailgate entries in longwall mining systems.

Jan 1, 1975

By J. S. Aronofsky, R. Jenkins

A simple means of predicting the flowing well pressure history in a natural gas reservoir has been developed. The differential equation for unsteady radial flow of gases through porous media was solved by numerical methods using electronic punch card machines. The results obtained from these calculations are presented in a generalized form which is believed to be most convenient for engineering use. These results are compared with those presented in a paper by Bruce, et al4. An effective radius of drainage has been defined which permits the equation of steady state gas flow to be used easily to predict well pressures in gas reservoir depletion. An equivalent effective radius of drainage is defined for liquid flow systems and a comparison is made of the gas solution to the liquid solutions. INTRODUCTION This paper presents a numerical method for describing the transient flow of gases radially through a porous medium from which the production rate is specified. The results obtained from these calculations are presented in a generalized form which is believed to be the most convenient for engineering use. The principal application of these calculations should be to flow in natural gas reservoirs, in the interpretation of pressure drawdown tests, in the estimation of reserves, and in calculation of injection pressures required in gas injection and cycling operations. The evaluation of natural gas wells is based upon back-pressure tests in which measurements of production rate and flowing well pressure are made for periods of one, two, or more days. The flow is assumed to have stabilized at this time, and the observed values of pressure and production rate are used with standardized formulae to determine the well's allowable production rate. Furthermore, the results obtained from such a test of short time duration are extrapolated in such a manner to allow a prediction of what the well pressure will be at some future time for a specified (but possibly untested) flow rate. The manner of conducting such back-pressure tests suggests several questions as follows: 1. 'What is the definition of stabilized flow and what factors determine the length of time required for the flow to become stabilized? 2. How may the recorded values of pressure and rate be utilized? 3. As the well is produced and the reservoir pressure falls, how will the flowing well pressure change? Can this flowing well pressure be predicted from the back-pressure test? 4. Are the results obtainable from the test influenced by a particular procedure used in obtaining the results? 5. Is it possible to estimate the gross reservoir permeability from back-pressure data? It is not within the scope of this paper to provide solutions Or even to discuss adequately all the above questions. However. in considering such matters, the

Jan 1, 1955

By Michael Arnold, Jonathan Delgado

In 2017, Bauer Foundation Corp. (BFC) was awarded the contract to install the deep foundations for the new 17-story Hotel Tower and the Low Rise Casino Expansion at the Seminole Hard Rock Hotel and Casino in Tampa, Florida. The site was underlain by extremely challenging Florida Limestone geology and surrounded by occupied existing buildings and infrastructure. To overcome the challenges of the difficult subsurface conditions, and to successfully complete the foundation installation without impact to the surrounding buildings and casino operation, Langan Engineering (EOR) and BFC were required to modify both the design and installation techniques during construction. The scope of work included 147 temporarily cased drilled shafts to depths up to 230 ft (70 m) below ground surface (BGS), 76 permanently cased micropiles up to 200 ft (61 m) BGS, and more than 300 augered-cast-in-place (ACIP) piles up to 125 ft (38 m) BGS. Voids and zones of high permeability in the limestone created many challenges for execution of the foundation scope including ACIP piles overbreaks of more than 400% above neatline volume, and construction induced ground subsidence/collapses adjacent to structures supported on shallow foundations. This paper will discuss site limitations, design and construction challenges, difficult geology, varied soil conditions, and lessons learned. PROJECT The project is located at Seminole Hard Rock Hotel and Casino Tampa, Florida, as shown in Fig. 1. Seminole Tribe, the owner, started the construction of a new 17-story Hotel Tower and the Low-Rise Casino Expansion at the beginning of 2017.

Jan 1, 2018

By William H. Baer, George M. Carlton, Blake M. Loring

IT is a well known fact that age-hardening alloys remain in a supersaturated, or partially supersaturated, condition only for limited periods of time at temperatures below the solvus. In order to develop optimum properties by subjecting the quenched alloy to precipitation or age-hardening treatment at a specified temperature, it is necessary that the cooling rate be sufficiently high to maintain the required degree of supersaturation of the solid solution. In practical applications the size and shape of the specimens obviously have considerable influence on the rate of cooling and there is need for more information on the effects of various rates of cooling. Cooling rates of quenched aluminum alloys generally have been established by the type of quenching medium, the temperature of the medium and the dimensions of the specimen.1,2,3 Except for the work of Roth3 little quantitative information is available on the measurement of cooling rates of aluminum alloys and the significance of the influence of various cooling rates upon the mechanical properties. The purpose of the present investigation was to study the use of the Jominy test for aluminum alloys (Table I). EXPERIMENTAL PROCEDURE The material for this investigation consisted of extruded rods 1 ¼ to 1 ½ in. in diam. The chemical compositions were as follows: [ ] The modified L-type Jominy specimen with dimensions shown in Fig I was selected as the most convenient means for obtaining a wide range of cooling rates. The standard Jominy specimen was not satisfactory because its cooling rate was not sufficiently high. The four flat surfaces machined at right angles along the length of the L-type specimen to a depth of 0-015 in. facilitated the hardness measurements. The specimens were machined from the extruded stock with no intermediate forging. New specimens were used for each aging experiment. The specimens were given solution treatments of 2 hr duration at recommended temperatures in a Hoskins furnace (Table 2). The temperature of the furnace was maintained constant to ±3°C. No protective atmosphere was necessary because the thin film of oxide that formed on the surface of the specimens had no effect on the hardness measurements.

Jan 1, 1948

By K. S. Liddell

The Kell Process has been developed for the extraction of platinum group metals (PGMs) and base metals from sulphide flotation concentrates. The process has been successfully tested on several different sulphide flotation concentrates, including those from the UG2 chromitite horizon and the Platreef mafic/ultramafic layer. It has been shown to provide high (>95 per cent) and selective extraction efficiencies for the key valuable metals, i.e. Pt, Pd, Rh, Au, Ni, Co, and Cu. The Kell Process consists of several commercially proven unit operations. S, Ni, Co, and Cu are first selectively removed by use of a pressure oxidation step during which the dissolution of PGMs is minimized. The residue from pressure oxidation is subjected to a thermal treatment to ensure efficient PGM recovery by subsequent chlorination. All the core steps are very similar to well-proven conventional unit operations in common use, as are the subsequent metal recovery steps to provide marketable end products. Typical metallurgical responses of flotation concentrates from UG2 and Platreef to the Kell Process are provided, and key outcomes of an energy comparison study with smelting are summarized in this paper. Kell presents a potentially substantial improvement in PGM concentrate processing technology, in terms of economics via much-reduced power costs, ease of processing, and various environmental benefits. It allows for the treatment of high-chromium low-grade 'dirty' concentrates, such as secondary concentrates from the platinum industry's 'mill-float-mill-float' (MF2) flotation circuits and concentrates from retreatment of tailings. It allows greater concentrate mass pulls, has higher tolerance to gangue intergrowths in concentrates, and its use can provide substantial increases in overall PGM recovery. Its adoption would be a step change in the platinum industry, and given the commercially proven unit operations embodied in the Kell Process, at much-reduced risk compared with other more experimental technologies. Since the initial process development work, significant improvements and refinements have been introduced as a result of further compre¬hensive testing and process modelling. Pilot-scale testing and engineering study work is in progress for several selected sites.

Jan 1, 2012

By Jan Pan, Deqing Zhu, Xianlin Zhou, Yanhong Luo, Zixing Xue

"Magnetic roasting process, aiming at obtaining magnetite concentrate, is the principle method of exploiting siderite as a raw material in iron and steel industry. Study on preparing DRI from siderite through coal based reduction technology is sporadic. To make the process of how siderite is reduced to iron clear, roasted ore reduced from siderite by lignite under different time periods were analyzed. The results indicated that: at the temperature of 1050°C, siderite was rapidly decomposed into magnetite, and further reduced as Fe30r?FeO?Fe, the later step was slower than the previous one. A fracture of particles was found during the process of thermal decomposition and the reduction of newly formed magnetite. As the reduction proceeded, metallization rate of products increased, and the iron grain grew along with time.IntroductionWith the rapid development of economy, China demands more and more iron ores for the iron and steel industry. China has rich iron ore resources, but 97% of them are below 30% in iron grade, many are refractory and unutilized [1], therefore large quantities of imported iron ores are in a desperate need. China imported 686 million tons of iron ore in 2011 (data from the China Customs), accounting for nearly 60% of the total consumption. To guarantee the healthy development of iron and steel industry, domestic refractory iron ores have to be utilized both economically and environmentally."

Jan 1, 2013

The Thermo-MIE personal DataRAM dust monitor (pDR) is a light-scattering instrument approved for use in gassy underground mines by the U.S. Mine Safety and Health Administration (MSHA). However, the use of light-scattering monitors has been inhibited by concerns about inaccurate readings resulting from changes in dust size distribution and composition, as well as concerns about the impact of moisture in the mine air. Because of this concern, the National Institute for Occupational Safety and Health (NIOSH) evaluated the pDR using available data from laboratory tests and mine surveys. The data show that accuracy can vary widely from test to test and mine to mine. In most cases, the results can be improved by using a companion gravimetric measurement to adjust the pDR data.

Jan 1, 2006

By R. I. Jaffee, C. M. Craighead, G. A. Lenning

The effects of increasing hydrogen content, introducing a notch, and changing the strain rate on properties of titanium and one of its alloys were investigated over a range of testing temperatures from —196° to 200°C. Both high purity and commercial purity A-55 titanium were used as representative a materials, while a commercial Ti-8 pct Mn alloy was used for an a-P alloy. It was found possible to analyze the data, using the ductile-to-brittle transition temperature concept. Increasing hydrogen, the presence of a notch, and increasing the testing speed raised the transition temperature for the a materials. The presence of hydrogen and notches raised the transition temperature of the a-B alloy also. However, increasing the testing speed generally decreased the transition temperature of the a-p alloy. IN previous papers, the authors have shown that hydrogen is most detrimental to the notch-bend impact toughness of a-titanium' and to the tensile ductility of a-B titanium alloys.' These general effects have been confirmed by Kessler and co-workers," and by Kotfila and Erbin." Kessler showed that the slower strain rate in notch-rupture tests was a more sensitive measure of hydrogen embrittle-ment of a-B alloys than the tensile test. In the present paper the authors cover, with tensile and notch-bend tests, the effect of testing speed, notches, and testing temperature on hydrogen em-brittlement. High purity and commercial purity titanium, examples of u materials, and a commercial a-,f3 Ti-8 pct Mn alloy were investigated. The purpose of the investigation was to correlate the factors producing embrittlement. Materials The high purity titanium for this investigation was obtained by arc-melting crystal bar from Foote Mineral Co. into 1 Ib ingots. As-cast hardnesses for these ingots ranged from 60 to 90 Brinell. The arc-melted ingots were forged to % in. diam rods at 1470°F. These rods were swaged to & in. diam at room temperature prior to machining of the specimens for hydrogenation and testing. The commercial A-55 titanium and the Ti-8 pct Mn alloy were obtained from Rem-Cru Titanium Inc., as % in. diam rod. The A-55 titanium was hot swaged to 1/4 in. diam at 1300°F prior to machining of the specimens for hydrogenation and testing. The a-p C-11OM alloy was hydrogenated prior to hot swaging to 1/4 in. roc1 at 1300°F. Hydrogenation prior to fabrication permitted testing of the a-P alloy in the equilibrated and stabilized condition. The equilibration and stabilization treatment used was an air anneal for 1 hr at 1300°F, followed by furnace cooling to 1100°F and then air cooling. Hydrogenation was done in a Sieverts apparatus described previously.' The hydrogenation treatment consisted of heating for 1/4 to 1/2 hr at 820 °C in purified hydrogen, slow cooling to 680"C, holding 1 hr for homogenization, and rapid cooling to room temperature. Intended hydrogen levels for the a-tita-nium materials were 0.05, 0.5, 1.0, 1.5, and 2.0 atomic pct—about 15 to 430 ppm. For the Ti-8 pct Mn alloy, the intended hydrogen levels were 0.05, 0.5, 1.0, 2.5, and 5.0 atomic pct—about 15 to 1100 ppm. The material for the 0.5 atomic pct level of hydrogen was vacuum annealed prior to hydrogenation to increase the accuracy of the addition. Vacuum annealing to remove hydrogen consisted of heating for 6 hr at 820°C, and resulted in a hydrogen content of about 10 to 15 ppm. When hydrogen contents were above 0.5 atomic pct—100 ppm—the hydrogen was added without prior vacuum annealing.

Jan 1, 1957

By Fred H. Lippold, Wm. H. Wolf

Methods of fair payment for excavating, supporting, and concrete lining tunnels have been sought by various owners for years. Tunneling techniques have changed with the development of equipment-from the hand-mucking operation to the machine mucker and, most recently, to machine-boring; from tunnel supports using timber sets to steel sets to rock bolts and, most recently, to shotcrete support; and from hand-placing the concrete lining using wooden forms to pumping or pneumatic placing using steel forms. As tunnel construction techniques advanced, so did methods for payment for the work performed. The recent development of tunnel-boring machines, or "moles," is precipitating another change. These changes have led to some difficulty in providing proper payment for the various items of work for different types of tunnels. As a major construction agency engaged in water-resources development in the western states, the U.S. Bureau of Reclamation has long been aware of the need for clarification of payment provisions in tunnel construction. The Bureau has some 150 miles of tunnels completed on its projects and about 50 miles of tunnels under construction. In this construction, the Bureau has benefited by the advance made by contractors in improving the techniques of tunnel excavation. To assure that the Bureau has an up-to-date approach to payment provisions, the Chief Engineer recently established a "standard" method of payment for all types of tunnels. It is believed that this new method of payment will be equitable for all contractors bidding on various types of tunnels using the diversity of methods of excavation now available to them. These payment provisions provide for different quantities for excavated tunnels using the blasting technique or using machine-boring techniques. In this way, the contractors have a choice in excavation methods and an equal opportunity to be low in their bids. We believe this will be an incentive to all contractors to be as progressive as the development of new equipment economically allows.

Jan 1, 1970

By C. O. Aksoy

Operating the underground marble quarries effectively, it is important to evaluate the deposit blocks economically which are affected by the suitability of the topography and configuration of bedding. The joint sets within the deposit and the spacing between these discontinuties are also of great importance. In this study, the marble deposits that could be geomechanically eligible for underground excavation have been selected throughout Turkey and these selected reserves have been classified accordingly by Q-Rating System. These classified marble deposits that forms groups of 1,2, and 3 (groups were determined by evaluating the O-rating, topography, quarry situation, cracks, joints etc.) are convenient for this type of production. Nevertheless, when the auxiliary factors (topography, location, production method etc.) regarding the deposit have also been investigated, the most convenient sub-group of deposits (Afyon Tiger Skin, Burdur Beige, Diyarbakir Pink and Mugla White) have emerged. The sizing of the pillars have been performed utilising Bieniawski?s stress profile. The LAMODEL software, developed by National Institute for Occupational Safety and Health (NIOSH), USA and run under the laminated displacement discontinuity method, has been used to size the pillars. This work brings in a novel opportunity to Turkey, in which no underground marble quarry has been attempted up-to-date similar to its several examples in Italy, USA, etc. This study serves as a reference for the marble operators and for the pioneering application of laminated displacement discontinuity method in hard rocks.

Apr 1, 2005

By Jack Elorenta

We often hear that, "Blasting was an art, but now blasting is now a science". 'Scientific' blasting implies that we have quantified and reproducible measurements of the feedstock and product of the blasting process. However, the industry's reluctance to adopt two key technologies, drill monitoring and optical size analyzers, sheds doubt on the claims of scientific blasting.

Jan 1, 2003

By C. Arson

"Optimizing hydraulic fracture injection parameters in order to maximize hydrocarbon extraction and to avoid extensive borehole spalling is still an open issue. In this paper, the Differential Stress Induced Damage (DSID) model is employed to simulate the anisotropic damage distribution around pressurized boreholes drilled in fractured shale. The loading path is purely mechanical: excavation and fluid injection are simulated by stress relaxation followed by pressurization. We investigate the effect of pre-existing fracture orientation, in-situ stress and injection pressure on the propagation of anisotropic damage during pressurization. Finite Element results indicate that (1) damage initiates and develops when the ratio of two in-situ stress component deviates from 1, and the magnitude of damage is proportional to this stress deviation; (2) For a given in-situ stress field, damage initiates for a certain threshold of injection pressure, and the damage zone extends as the injection pressure increases; (3) A pre-existing fracture only affects the damage zone locally; the orientation of that fracture does not affect the damaged zone, which is controlled by in situ stress and injection pressure.INTRODUCTIONHydraulic fracturing is used to increase shale permeability and to enhance hydrocarbon extraction. In order to maximize the extraction ratio and to avoid wellbore spalling and clogging during fluid injection, the parameters related to injection for each particular site need to be optimized. Therefore, it is necessary to clearly understand how shale responses upon excavation and pressurization.It is well known that breakouts grow in the direction of minimum compression and that plastic deformation around wellbores tends to arrest breakouts (Zoback et al., 1985). Laboratory acoustic emission tests revealed that fractures propagate along the direction of maximum compression stress, and fractures (breakouts) are surrounded by the Excavation Damaged Zone (EDZ), in which rock properties are weakened by the presence of micro cracks (Eberhardt et al., 1999; Martino et al., 2004). The anisotropy from orientated foliations and cracks may influence the development and propagation of fractures and breakouts (Everitt et al., 2004). Sonic televiewer logs proved that during hydraulic fracturing, fluid injection further alters the stress distribution (Evans et al., 2005). Shale natural fabric strongly affects the evolution of the EDZ around boreholes."

Jan 1, 2015

By A Horeth, E Duggan, B Versiani, A Gooch

Iron ore screening plant productivity is strongly affected by the performance of the shuttle operation, with the control system robustness and associated strategies having a direct impact on utilisation and throughput rates. A number of aspects intrinsic to the methods and technologies traditionally applied on the motion control of shuttles are often observed to decrease the efficiency of the ore distribution process across multiple screening modules, which ultimately impacts the plant’s production. Those include the number of operational scenarios that are unmanaged by conventional discrete control logics which may intermittently lead to undesired events, such as ‘high level alarms’ and ‘low level interlocks’ in the screening bins. This outcome usually demands excessive manual intervention by Control Room Operators. A Reinforcement Learning (RL) Artificial Intelligence (AI) solution was deployed to control the motion operation of the scalping and products screening shuttles in an iron ore handling plant. The RL algorithm was trained in advance to handle multiple operational scenarios and generate optimised outputs. In nominal operation, the shuttles are moved in a modulating and highly predictive fashion over the whole range of safely reachable bins. When the need occurs, the AI control agent deviates from that modulation behaviour, limiting its travel range or moving to other groups or clusters of available bins by employing ‘bin jumping’ or ‘ore break’ strategies. The RL platform capabilities include the ability to learn in real time to account for and auto-adapt to new operational patterns and process changes whilst applying improved strategies for shuttle dwelling times, target setting and speed control. The deployed Reinforcement Learning AI solution has better managed the existing challenges associated with the shuttle operation and control, and resulted in a more efficient ore delivery process, superior operations stability and increased production rates.

Nov 8, 2021

By P. C. Parsons, G. C. Milligan

"IN FIELD WORK in the Cape Breton Highlands, which are heavily covered with vegetation, it is necessary to run traverses along the valleys of small brooks. We encountered difficulty in closing such traverses, and the following technique was developed to solve this problem. It has been tested in the field for four seasons by several people, and found to be simple, efficient and more accurate than any other compass-and-pace system of which we are aware. So far as we can find, the technique has not been described previously. It may be of use to others.The Cape Breton Highlands of Nova Scotia consist of hills of old intrusive and metamorphosed sedimentary rocks protruding up to 1,000 feet above the general level of the younger sediments which underlie the valleys. The flat hill-tops are the remnants of a plateau; drainage off the edge of this plateau has produced many small steep brooks. They occupy valleys which are up to 800 feet deep, and V-shaped in cross section, with steep sides covered by mixed conifers and hardwoods. The stream at the bottom is rarely more than a few feet wide, with a negligible meander belt, but with many bends, rapids and falls. Visibility along the stream, in consequence, is rarely more than a few hundred feet, and in many places much less.It was found impractical to map the streams by the method of meander lines, as described in many standard surveying texts and hand-books. The limited visibility, and the numerous bends of the brooks, necessitated many corners. Every corner introduces errors. To 'close' a survey with 40 or 50 such corners proved either very time-consuming or impossible. In most cases, however, the general direction of a valley may be obtained from an aerial photograph, or by direct observation, and this became the basis of the method adopted."

Jan 1, 1971

By Takanori Kokubo, Kenta Suzuki, Tomohiro Sasaki, Toshiya Anami

"Previous work has shown that the strengthening Al-Mn alloys with copper leads to the formation of an undesirable reduction in recrystallized grain size. In this study the mechanisms of strengthening and recrystallization behavior in a continuously cast automotive heat exchanger fin stockof Al-1.1wt%Mn-0.5wt%Fe-0.3wt%Si with a0.3wt%Cu addition were investigated. Metallurgical analysis revealed that the Cu strengthening was dominated by the formation of dispersoid particles, while solid solution strengthening decreased with the Cu additions. This result is attributed to the decrease in the amount of Mn solid solution. The post brazing recrystallized grain size was reduced compared to that not containing Cu. It is postulated that the Cu addition leads to a decrease in the amount of Mn in solid solution which leads to a finer grain size. This effect is attributed to Mn in the aluminum matrix inhibiting boundary migration but allowing other grains to grow during heat treatment. The results are rationalized based on particle stimulated nucleation (PSN), wherein dispersoid particles are more likely to become active recrystallization nuclei during the heat treatment. The increase in the number of active dispersoid particles with Cu addition is correlated to the recrystallized grain structure.INTRODUCTIONImprovements in properties such as strength, braze ability and corrosion resistance in thermal fin stock alloys are all means to gain improved efficiency in heat exchangers particularly in automotive applications. While Al-Mn alloys dominate automotive heat exchanger fin stock alloy, even small chemical compositional changes can profoundly influence these properties (Kawaharaet al., 2004; Yoshino et al., 2009). The microstructure (particularly the grain size and shape) also plays a key role in determining the product performance and hence the thermo-mechanical processing (TMP) must also be considered. The casting method (typically conventional direct chill, DC, or continuous casting) significantly influences the properties in no small part due to the very different TMP routes that are used. Continuous casting is generally favored for fin stock applications as its higher cooling rate (which can be 2 to 3 orders of magnitude higher than DC casting) leads to finer as-solidified intermetallic particles and an increase in super-saturated solid solution elements (such as Mn)that are known to improve fin stock performance such as strength, braze ability(Okiet al., 2008)."

Jan 1, 2018

By Shimi Tzobery, John E. Shamma, Samuel Swartz, Gary B. Hemphill

The trapezoidal tapered ring method has made significant progress in recent years for shielded-TBM projects, excavating tunnels with high overburden, strict water tightness criteria, and multiple curve alignments. The selection of compatible tapered rings is critical for successful advancement of the tunnel, assuring efficient installation of rings, as well as prevention of ring damage and excessive leakage. Using experience from the Arrowhead Tunnels Project, this paper describes guidelines for ring selection in tunnel curves, geometric analyses that comply with criteria principals, and provides techniques developed to determine the appropriate relative key position.

Jan 1, 2005

By Paul R. Lear

Sustainability continues to be an important aspect of remediation and infrastructure projects. Deep soil mixing (DSM), a common construction and remedial technology, can easily incorporate the following sustainability best management practices (BMPs), including Minimizing Total Energy Use and Maximizing Use of Renewable Energy; Minimizing Air Pollutants and Greenhouse Gas (GHG) Emissions and Maximizing Use of Machinery Equipped with Advanced Emission; Minimizing Water Use and Impacts to Water Resources; Beneficial Reuse of Materials/Reduction of Materials and Waste Reduction; Use of Local Labor and Supplies. This paper focuses on the sustainability of DSM treatment and provide carbon footprint calculations at least one completed DSM project which used these sustainability BMPs to demonstrate the environmental impact of the sustainability.

Sep 8, 2021

By F. W. Jessen, R. W. Durie

The dissolution of salt in the development of salt cavities is controlled by free-convection boundary layer flow along the salt surfaces. It is the purpose of this paper to expand upon results published previously, and primarily to illustrate the influence of surface features on the boundary layer and hence the dissolution process in the development of underground salt cavities. General dissolution equations are presented that apply to a surface inclined to the vertical. A salt surface inclined so as to be overlain by water is dissolved by boundary layer flow, while an inverted surface is dissolved by a combination of boundary layer and cellular flow. Detailed investigation of the boundary layer was limited to laminar free-convection flow. Truly laminar free-convection boundary layer flow may be encountered only in laboratory solution cavities, but the boundary layer will control dissolution even where cavity dimensions are such that free-convection turbulence will occur. The factors found to significantly affect the laminar boundary layer will affect dissolution with a turbulent boundary layer. INTRODUCTION Underground salt cavities have been used extensively for the storage of LPG products, and the use of these cavities is expanding each year. The increasing requirements for such cavities suggest the need for a better understanding of the mechanisms involved, for the purpose of the control of cavity geometry and the most effective use of the injected water. A previous paper outlined a quantitative approach to the determination of salt dissolution rates in the laminar free-convection dissolution of salt. It is the purpose of this paper to expand upon the results previously published and to point out significant factors in the application of these results to the dissolution of field cavities. The dissolution of salt in laboratory scale cavities is controlled by the free-convection boundary layer, which is the region of flow along the salt surface caused by the difference in buoyancy forces resulting from the salt dissolution. The transfer of salt into solution at the salt face causes an increase in salinity, and hence a greater density, in the water at the salt surface. The region of higher density tends to fall through the lighter, less saline water and a flowing boundary layer is the result. The water remains stationary at the contact with the salt surface,l so the resulting velocity profile is such that the influence of gravity is opposed by a viscous shear force at the salt surface. For salt to be transferred into solution from a solid surface to a boundary layer of fluid, it must diffuse through a stationary film of water at the salt contact. According to Fick's first law, the rate of mass transfer by diffusion is the product of the diffusion coefficient and the concentration gradient, with diffusion transfer in the direction of decreasing salinity. Once the salt has passed into the boundary layer, it will be transferred by a combination of molecular diffusion and convection. The convection transfer will in turn affect the rate of dissolution by influencing the gradient of the salt concentration at the surface. In the previous investigation by the authors to determine the basic mechanism of the salt dissolution process, an equation was developed that agreed very well with the experimental rates of free-convection salt dissolution from a smooth vertical surface. The technique was taken from the work of Eckert2 in the analogous heat transfer system and will be referred to as the integral method. The rate of salt transfer from a vertical section of height H was found to be:

Jan 1, 1965

By P. V. Ananthapadmanabhan

Feedstock powders of metals, alloys and ceramics for thermal spray applications have to meet several specifications. Particle shape, size and distribution, powder flow characteristics and density are the important factors that need to be controlled, in order to ensure high spray efficiency and better coating properties. Thermal plasma technology can be effectively utilized to produce metal, alloy and ceramic powders for spray applications. The present paper describes plasma spheroidisation of commercially available aluminium powder and nickel-aluminium powder blend in a plasma reactor. Results show that the processed powder particles bear spherical morphology with excellent flow characteristics, which make them ideal for thermal spray applications.

Jan 1, 1997

By Herman Garlichs

THE development of the extensive Southeast Missouri deposits greatly preceded that of the Iowa and Wisconsin deposits. It began about 1720 at Mine La Motte and other localities, and has continued uninterruptedly to the present time. It is estimated that this district produced about 184,000 tons of lead in the year 1916, having a value of approximately, $25,000,000. This is a new high record. The Southwest Missouri orebodies were hardly known before 1845 and were not extensively developed until 1870: Lead production in South-west Missouri for 1916 was 38,788 tons. Oklahoma produced 14,399 ,tons and Kansas 2,345 tons, making a total for Southwest Missouri, and the adjoining districts in Oklahoma and Kansas, of 55,532 tons of lead. The first metallurgists in Missouri were the Indian and the hunter. The early settler learned to procure his bullets either by melting ore in his camp fire or by throwing pieces of galena on an old stump and depending on the usual roasting and reaction method to obtain the metal. A little more refined method was to arrange two flat stones in the form of a V. Wood and galena were placed in the furnace and ignited. As heat developed, some of the metal was extracted and molded into bullets. The next step in utilizing the lead ores was the log hearth. All lead in Missouri was smelted in this crude affair before 1820. It was built on sloping ground, and consisted of a hearth of stone, surrounded on the front and two sides by a stone wall. The wall was 7 ft. high in front. The top and rear end were left open and in front an arch or opening was made, forming the eye of the furnace. In front of this a pit was dug in the ground, to receive the molten metal. Large logs were rolled in at the back and made to rest upon ledges formed inside, to raise them from the hearth and to give a draft. These logs filled the entire width of the furnace. Small split logs were then set up around the two sides and the front, and the ore was piled on until the furnace was full. Finally, the mass was covered with logs and fuel until the ore was completely surrounded. A gentle heat was started, which was raised very gradually. After 12 hr. the heat was increased and continued for 12 hr. more, 24 hr. being required, for each smelting. The furnace treated about 5,000 lb. per 24 hr. and the ore yielded about 50 per cent. of its metallic lead. A considerable quantity of the ore was not desulphurized, and fell between

Jan 7, 1917