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By Hajime Kitamura, Nobuharu Isago, Yuta Yamanishi, Kosuke Kawata, Hiroshi Yagi, Akira Matsuoka

Mountain tunnels are generally considered to be stable during earthquakes, however, it is known that the portal areas are prone to seismic damages. Characteristics in portals such as the location of the slope, modulus of ground deformation, and the change of overburden are different for each tunnel, and damage degrees are unclear. In this study, we reproduced the seismic behavior to investigate the effect on the tunnel portal by considering some parameters above, using simple static model tests and numerical analysis. As a result, the conditions of the slope condition and minimum distance from slope was confirmed to influence on the mechanical behavior of the tunnel portal during earthquakes.

Dec 1, 2022

By Dominique Francois-Bongarcon

The rational and optimal determination of the design of a mining exploitation is a very intricate and difficult problem : the parameters are numerous, some technical, some economic or technico-economic which cannot be fully controlled; beside, deposits are estimated from very limited information and the choice criteria are not always quantitative, the economic context has to be anticipated by several years, and even the technological limits can change tomorrow. So, although very clever and performing numerical algorithms have been developed in recent years for open-pit design, we consider that this problem has not really been solved satisfactorily until now. The reasons are that people have concentrated their efforts on informatical algorithmical problems, and have assumed that the technical and economical data are well defined at the time of the study, which is generally not true. In particular, the mere fact of assigning dollar- values to blocks in order to maximize the total cash-flow is generally unrealistic because of the uncertainty of the data used. Consequently, the significance of the unique pit obtained as a result of these algorithms is questionable.

Jan 1, 1981

By Harry E. Holzschuh

The two Agrico Chemical Company self unloading Phosphate Rock barges put into service in 1976 operate at over their design carrying capacity. Each barge now carries 26,000 short ton instead of the planned 25,000 short ton at 32 foot of draft. They are in service between Agrico's Tampa, Florida Terminal and the Donaldsonville, Louisiana Fertilizer Complex, moving a total of 2,500,000 short tons each year. This was the first use of the Parascrew design for a marine application. The barges, with their 3,000 STPH unloading and matching loading rate is the vital link in this total transportation and handling system. Rock is moved from the Pierce, Florida Mines through the Tampa Big Bend Terminal, across the Gulf of Mexico, and up the Mississippi to the Agrico Faustina Phosphoric Acid Plant 30 miles below Bacon Rouge, Louisiana. The trip from the terminal to the plant is 600 miles and the turnaround time is just about six days. Seven years operating experience has proved that the system works. Fittingly, the two barges are named the "Faustina" and the "Pierce". They have a beam of 85-feet and are 495 feet long. folded depth is 43 feet, with a ballasted light draft of 19 feet and a typical loaded draft of 32 feet. There are four separated holds with the machinery room located forward of 101 hold. Each hold is 51 feet wide at the coamings with an 18 foot straight section on the side, and a 24 foot long, 600 slope sheet for a 23 foot clear reclaim width at the bottom. The Parascrew in each of the holds is 37 feet long between the bearings and is supported on a 14 inch diameter hollow shaft. The screw pitch varies and the diameter of the flights step up from l'-9" diameter to 2'-6" diameter on the discharge end. By sloping the centerline, a minimum four inch bottom clearance is maintained across the hold. Some bending of the tube does take place.

Jan 1, 1983

By Wolfgang Gütter

India is targeting to boost its electrical capacity from 100 GW to 200 GW within the next 10 years. The National Hydroelectric Power Corporation (NHPC) has decided in2001 to take execution of the 800 MW Stage-II of the prestigious 2,051 MW Parbatihydrol electric project in Kulu district of the northern province Himachal Pradesh. Two parallel 30° inclined underground pressure shafts of 1.542m in length each will be excavated in different geological formations and lined with hexagonal concrete segments by a hard rock double shield TBM. That kind of heading will be a novelty to India and an innovative method for inclined pressure shafts. The 4.88m Mitsubishi DSTBM will be assembled underground on a swivelling steel platform especially designed for the launching as well as for the acceptance of the TBM in the upper cavern of each shaft. The hexagonal segmental lining system causes a significant higher job safety than an open TBM with conventional support. Each ring consists of four honeycomb segments with 20 cm thickness. After finalisation of the excavation a steel liner will be installed and concreted. The Joint Venture Jäger-Seli will perform the two pressure shafts as a sub-contractor for the Indian company Gammon India Ltd.

Jan 1, 2005

By P. C. Kapur

The hierarchical relationship between three broad kinds of grinding models for a spatially homogeneous, linear, time-invariant batch grinding system are first established. Limiting and asymptotic arguments for arriving at approximate but simpler models are employed in all three cases. These parsimonious models -provide alternate and, in some respects, more incisive and convenient tools for the analyses of grinding processes and simulation of comminution circuits. In the discrete-size, discrete- time class of models, a reduced mill matrix is derived, which is seemingly adequate for those grinding circuits whose identification otherwise is difficult because of limitations on the quantity of data and its quality. In discrete-size, continuous-time types of models, parameter lumping has been employed for obtaining a G-H solution which is quite accurate and exceptionally useful for graphical display of data, model verification, and parameter estimation and simulation. In continuous-size, continuous-time models, a similarity transformation is used for solving the integrodifferential equation of grinding. This solution provides a unified framework for a number of apparently diverse empirical grinding phenomena such as self-preserving behavior of ground particle size distributions and energy laws.

Jan 1, 1987

By Joseph Matoney, B. K. Parekh

INTRODUCTION The term "dewatering" refers to removal of water from coal. Water associated with coal can be categorized as "free or surface" and "inherent or chemically bound" moisture.' The free moisture is found on the surface of coal, in capillaries and small spaces between two or more particles. The inherent or chemically bound water is found in the interior of the coal and as part of coal structure. A significant amount of free moisture can be removed by mechanical dewatering techniques. However, inherent moisture can only be removed by applying energy intensive techniques, e.g., direct or indirect heating. Moisture in the coal offsets some of the benefits of coal cleaning. Extra water in clean coal adds to extra cost in transportation, heat lost during vaporization, and plugging of chutes. From a utility perspective, a 1 % increase in moisture can offset a 4.5% decrease in ash.2 Mechanical dewatering can be classified into two major process categories according to the principles involved, namely, 1. Sedimentation-liquid is constrained and particles move freely. 2. Filtration-particles are constrained by a medium and the liquid flows through. Each of the process categories is composed of various separation techniques shown in Fig. Equipment currently being used by the mechanical dewatering of coal of varying size ranges and final moisture content is illustrated in Fig. 8-2. This figure indicates that sizes larger than 13/, in. (37.5 mm) present no particular dewatering problem. Shaker screens of the very crudest types and designs are capable of producing these sizes at low surface moistures. High-speed vibrators are used for the intermediate sizes and can be used for smaller sizes down to 0.02 in. (0.5 mm) if high moistures (15% surface moisture or greater) can be tolerated in the product. Usually, however, the vibrator is not used below 3/, to 3/, in. (9.5 to 6.3 mm) because of the moisture associated with these fine sizes. At this level, centrifugal force is usually employed to aid dewatering. Centrifuges of various types and designs are used practically

Jan 1, 1991

By Andrew Bursey, Colin Lyons

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Jun 13, 2021

By Sebastian Sucri, Percy Townsend

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Jun 13, 2021

By Dave Dorfman, Ben DiFiore

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Jun 13, 2021

By David Watson, Steve Price

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Jun 13, 2021

By Luis Fernandez-Deza, Kaveh Talebi, Seth Pollak, Soto Vardakos

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Jun 13, 2021

By Anton Hupfauf, Peter Raleigh

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Jun 13, 2021

By Mohamed Younis, Keith Ward

INTRO PAGE

Jun 13, 2021

By Mike Stolkin, Julio Martinez

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Jun 13, 2021

By Aaron McClellan, Eric Levonas

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Jun 13, 2021

By Renee Fippin

INTRO PAGE

Jun 13, 2021

By Randy J. Mikula

Cleaning of low-rank coals can have several meanings, depending upon the definitions of the terms "low rank" and "cleaning." In general, low-rank coals would be lignite or subbituminous according to the ASTM classification. For the purposes of this summary, cleaning is defined to be any process which materially reduces the proportion of inert material in the coal. For low-rank coals, this often means a reduction in moisture content since moisture is the major inert component in these coals. A brief discussion of conventional cleaning processes is included, as is an extensive reference list.

Jan 1, 1991

By Jan Visman, James W. Parkinson

GENERAL INTRODUCTION Sample collection, preparation and analysis are all steps in a single process designed to provide information about a much larger amount of material than the sample itself. For example, information about the ash content of a unit train load of coal may be derived from a single, relatively small sample of perhaps a few hundred pounds (liters) extracted from the entire shipment. These three steps can be thought of as links in a chain, allowing the simple analogy that the strength of the chain, or, in other words, the value of the information is only as strong as the weakest link. Sample collection, discussed in Part 1 of this chapter, is critical because analytical procedures can do no more than reveal the characteristics of the sample presented to the laboratory. If that sample does not properly represent the population to be characterized, neither will the analysis of that sample. Sample preparation is also a critical part of the chain. Any change in the nature of a sample between the time it is collected and the time it is analyzed will appear to reflect the nature of the population. For example, sample preparation procedures that allow air to partially dry the coal sample before reaching the laboratory will cause the sample analysis to indicate a lower moisture content than the sample originally had. Other changes can be more subtle. Second only to moisture loss, oxidation reactions generally cause the greatest problems. Oxidation of a coal sample can alter surface properties, changing flotation response. In extreme cases, combustion parameters, such as caking or agglomerating properties or mineral composition, such as pyrite content, can change. Water samples can also be altered by oxidation. For example, ferrous iron can oxidize to ferric iron, possibly changing water quality parameters such as pH. Sample analysis, the subject of Part 2 of this chapter, is the final link in the chain. Obviously, no laboratory procedure can correct for problems created by improper sample collection and preparation. At the same time, poor analytical techniques will create incorrect information about the total amount of coal from which the sample was extracted (the population) in the same manner as improper sample collection and preparation. The key to gaining correct information about the population is to view these three steps as parts of a single process. Following proper techniques through only one or two steps of the process will not produce accurate information.

Jan 1, 1991

By Peter T. Luckie, Felicia F. Peng

INTRODUCTION The maximum recovery of cleaned coal at the required quality is of major concern to plant operators. However, the quantity and quality of products of coal cleaning, predicted by theoretical calculation based on washability studies and determined in the operation of actual commercial cleaning plants, will be different for each coal. Therefore, during the last half century, coal preparation engineers have repeatedly sought methods for evaluating the technical and economical efficiency of separating coal in coal cleaning equipment and for predicting the quantity and quality of cleaned coal produced, as well as profit- ability for the entire plant. Many formulas have been proposed by investigators to evaluate the efficiency of various coal cleaning operations. Performance criteria in use today are capable of defining all of the important aspects of a given concentrating operation; however, each criterion has certain restrictions or limitations. It is important, therefore, to understand how such formulas can be used and the problems involved in their construction. Technical Measures of Equipment/Plant Performance Conventional measures for evaluating the performance of a preparation plant are generally the same as those used to evaluate equipment performance. Measures involving separation efficiencies are influenced by the following three broadly encompassing primary factors: (1) density composition of the feed coal, (2) design characteristics of the cleaning unit, and (3) relative density of the separation. Since separation efficiencies are dependent on factors involving the nature of the coal, they are termed dependent criteria and represent a very broad technical indicator of an individual process or plant performance. Performance measures known as independent criteria are influenced mainly by quantitative errors inherent in the design and operation of the processing equipment. Economic Measures of Plant Performance True assessment of coal cleaning methods require reference to economic measures such as profitability. During the years in which technical efficiency criteria for characterizing plant performance were being improved, coal preparation engineers were also seeking appropriate economic criteria to assess plant performance. Technical and economic effectiveness of plant performance are important parameters for coal preparation flowsheet design. The relationship of the technical and economic parameters can be formulated in an economic model and mathematical model with the aid of computers. The computerized models

Jan 1, 1991

By Byron C. Hardinge, E. R. Palowitch, Albert W. Deurbrouck, David J. Akers, Edward R. Torak

During 1983, 42.2% of the 686.0 (624.3 Mt) million tons of coal reported, 289.6 (263.5 Mt) million tons were mechanically cleaned, of which 107 (97.4 Mt) million tons were cleaned by dense media (magnetite and sand) processes.' The percentage of bituminous coal and lignite cleaned mechanically by dense medium processes increased from 7 to 38% between 1938 and 1983. The Electric Power Research Institute estimates that 150 million tons (137 Mt) of coal were cleaned by heavy-media processes in 1986, and that this number may increase to 265 million tons (241 Mt) by 1990.2 Dense medium separations include those coal preparation processes that clean raw coal by immersing it in a fluid having a density intermediate between clean coal and reject. As there is a general correlation between ash content and specific gravity, it is possible to achieve the required degree of removal of ash-forming impurities from a raw coal by regulating the specific gravity of the separating fluid. Dense medium processes generally offer the following advantages over other coal cleaning processes: • Ability to make sharp separations at any specific gravity within the range normally required even in the presence of high percentages of raw coal whose specific gravity is near the specific gravity of separation. • Ability to maintain a separating gravity that can be controlled within + 0.005 sp gr units. • Ability to handle a wide range of coal sizes. • Ability to change specific gravity of separation to meet varying market requirements. • Ability to handle fluctuations in feed, in terms of both quantity and quality. Unfortunately, dense medium processes can have the following disadvantages: • Relatively high capital costs caused primarily by the need for equipment to collect and recycle the medium. Relatively high operating costs caused primarily by operation of medium recycle equipment and loss of medium.

Jan 1, 1991