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By B. P. Watson

The Bushveld platinum group metal deposits are two distinct, shallow-dipping stratiform tabular orebodies and strike for many hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2 000 m. The mining method is a variation of planar open stoping. Pillars are widely used to support the openstopes. Little work has been done in the past to determine pillar strength and pillars have been designed using experience and formulae developed for other hard-rock mines. This has led to oversize pillars with consequential loss of ore or undersize pillars resulting in potential collapses or pillar bursts. This paper describes a back-analysis of pillar failures at Impala Platinum, just north of Rustenburg, and provides insights into pillar behaviour. Strength formulae are presented for Merensky Reef pillars at Impala. These formulae may be used cautiously on other platinum mines with similar geotechnical and geomechanical conditions.

Jan 1, 2008

By J. Kortnik

Mining has always been, and still is, an activity which is vital for the development of mankind. This is because a predominant proportion of industrial products and energy is produced from raw materials that are excavated using mining methods. The need for environmental protection and the close proximity of urban settlements and mines in Slovenia have necessitated ever stricter requirements for the excavation of raw materials and introduction of more environmentally-friendly mining methods. This is achieved by implementing a closed eco-technological cycle of raw material excavation within the scope of mining methods. In surface mines, this means prompt reclamation of the degraded surfaces, and in underground mines the use of methods with minimized impact on the surface and on underground water. In underground mines, mining methods with backfilling installed according to the multi-barrier disposal system are the only ones that allow the possibility of implementing a closed eco-technological cycle of excavating raw materials. Various industrial waste materials are also included in the backfilling material in order to improve its strength properties. Backfilling consisting of several different waste materials is produced in the form of a composite. Before backfilling consisting of waste material composites can even begin to be used in mines, an environmental impact assessment of its suitability for mines needs to be made. In order to make such an assessment, a pressure leaching cell and an open diffusion cell were made, i.e. a pressure leachate test and a sorption test were developed. The two cells and the developed tests will enable the study of the influence of backfilling on the environment if installed in an underground mine. The pressure leachate test performed with the use of the pressure leaching cell simulates leaching from a consolidated backfill during the seeping of underground water into the backfilling material under pressure. The sorption test performed in an open diffusion cell simulates the flow of eluate leached from the backfilling material through the rock/geotechnical barrier. The two tests were developed in such a manner that they are performed either in succession immediately after one another, but they can also be performed separately at a certain time interval. The paper presents an assessment of the suitability of backfilling made of different waste material composites. Keywords: environmental impact assessment, multi-barrier disposal system, waste material composites, pressure leachate test, sorption test, pressure leaching cell, open diffusion cell, eco-technological cycle, mining methods with backfilling.

Jan 1, 2003

By P. Mokwena

Paper written on project work carried out in partial fulfilment of BSc (Hons) in Chemical Engineering Diamond synthesis has attracted a great deal of interest because of its exceptional properties and various applications. In this study, the chemical catalytic vapour deposition (CCVD) method was used to synthesize diamond films using acetylene as carbon source and hydrogen as carrier gas at a temperature of 1000°C, and their thermodynamic stability was studied. Photographic analysis revealed that these products are diamond films, Ramman spectroscopy confirmed that they are graphitic while confocal laser scanning microscopic image analyses proved that these diamonds films have structural defects due to iron impurity from the catalyst precursor. The quantity of diamonds films produced is also proportional to the acetylene to hydrogen ratio but these films are larger in size at lower acetylene to hydrogen ratio. Thermogravimetric analyses showed that transformation of these materials begins at 25°C but could not be used to determine if a temperature range below 25°C exists. The stability of these CCVD-synthesized diamonds also increases below 25°C when stored at different temperatures.

Jan 1, 2007

By S. Lubbe

South Africa and Australia are the biggest suppliers of zircon sand to the international zirconium industry. However neither South Africa nor Australia is well known for zircon beneficiation. Geratech Zirconium Beneficiation Ltd (GZB) continued with additional research on sodium hydroxide (NaOH) cracking of zircon sand during 2002-2003. In 2003 GZB started extracting zirconium from zircon sand by means of NaOH cracking on a commercial scale. Experience has shown that temperature profile and atmospheric control inside the furnace is crucial for the beneficiation of zircon sand. Silica carryover to zirconium chemicals could result if a high temperature is used. Once the sodium silicate is extracted from the sodium zirconate and dissolved in hydrochloric acid, two distinct routes can be followed to precipitate various zirconium chemicals. The most common route is to precipitate zirconium oxychloride crystals (ZOC), with subsequent purification from all contaminants (crystal route). Less known is the process (liquid route) that involves the direct precipitation of zirconium basic sulphate (ZBS). This route will yield a less pure product, with contaminants such as silica and titanium. An important factor in this route is the prevention of silica gel formation, which could hamper final product filtration. For applications like paint drying (zirconium octoate) or antiperspirants (zirconium hydroxychloride) low levels of contaminants have no effect on the final product. The advantage of the liquid route is fewer production stages compared to the crystal route. The disadvantage of the liquid route is that the market for the products will be significantly smaller. The optimum solution could be a plant design that could cater for both routes. Another example of an application of zirconium chemicals is the use of ammonium zirconium carbonate (AZC) in the paper industry. Zirconium basic carbonate (ZBC) is dissolved in ammonium carbonate to produce AZC solution. AZC is used mainly in European countries in the paper industry. For example, carton boxes were initially produced with formaldehyde as the binder, however, it has now been replaced with AZC since formaldehyde is considered toxic. AZC reacts with the cellulose fibres in the paper to act as the binder. The resulting product is not toxic, and printing ink dries very quickly due to the porous paper structure. Other applications of zirconium chemicals involve the use of acid zirconium sulphate tetrahydrate (AZST), zirconium orthosulphate (ZOS), potassium zirconium carbonate (KZC), and zirconium hydrous oxide (ZHO). Fluoride-based zirconium chemicals like zirconium tetra-fluoride (ZrF4) and hexafluoro-zirconic acid (H2ZrF6) are used in the aluminium industry. Zirconium oxide (Zr02) can be produced from any of the abovementioned precipitated chemicals via a high-temperature decomposition process. The physical properties of such oxides can differ tremendously, depending on the final application. The fired density of sanitaryware is typically 5.8 g/cm3, compared to milling media at >6.1 g/cm3. The required fired density is achieved by controlling the precipitation and decomposition conditions for these two oxides. The same applies to stabilized and mixed oxides, for example where zirconium oxide acts as an oxygen carrier in fuel cells.

Jan 1, 2012

By C. Steve

ABSTRACT: In this paper, the stability evaluation and bifurcation criteria are presented for the Jinping arch dam structure. The bifurcation models in failure status of the arch dam are derived from the uniqueness of the controlling equation of dam behaviours, and the relative phenomena between positive definition of dam structural tangent stiffness and bifurcation are given in the paper. Then the structural collapse criteria for arch dam are discussed based on the energy mode. A stability criterion of dam based on the connection of yield zones is proposed according to the implementation of elasto-plastic FEM (finite element method) numerical analysis. In accordance with this judging method, nonlinear FEM analysis is used for Jinping arch dam. The failure process of the Jinping dam was simulated and yield zones were found under the overloading condition. Keywords: Stability evaluation, bifurcation, failure process, Jinping arch dam ZUSAMMENFASSUNG: In der Verliegenden Arbeit wird ein integrater geomechanisch Modellversuch fuer Jinping Bogenstaumauer Vorgesstellt. Die Bogenstaumauer liegt aut der komplizerten felsformationen. Der Zerstoerungsmechanismus, die Stabilitaetsfaktoren und die Interaktion zwischen der Bogenstaumauer und den Seiltichen. In der Vorliegenden Arbeit wird eine dreidimensionale finite element analyse fuer die seitlichen. Gestein sauflager mittels dem Bruchmodell Vorgestellt, da fuer Jiniping Bogenstaumauer angewandet wird. Ein Bruch mechanismus model einschliesslich der statistischen parameter der Gesteinfes tigkeit wird entauckeit. RÉSUMÉ: Das ce documènt a été faite une analyse d’elemt limité de trois dimensions dn fondement de construction de roche faisant appel au modéle de l’endommagemnet à fracture, analyse appliquée an fondement du bar ragevoute de Jinping. Ce documènt décrit le test de modéle géomecanique intégral pour le barrage-voûte de Jinping L’ampleur du modéle en question constitute l’une de plus importantes en China. Ils correspondent par faitement anx calculs des résultats.

Jan 1, 2003

By F. Essrich

A quantitative rockburst hazard assessment procedure was introduced on Elandsrand Gold Mine at the end of 1994. It is currently used to evaluate the seismicity-related risk in production areas on the mine. Six parameters related to seismicity, geology, mining layout, and production are rated and results are used as a planning tool on a regular basis. The applied assessment can be considered successful in that it promotes awareness of the seismic hazard and provides an opportunity to address seismicity-related mining problems. A comparison between high risk panels and those working areas with rockburst incidents showed that high hazard ratings reliably forecast the occurrence of larger events in the following month but they do not necessarily predict those working places with rockburst-related accidents. From this one may conclude that high levels of seismicity do not coincide with high rockburst rates.

Jan 1, 1997

By J. Daraisme

Société le Nickel (SLN) exploits the Dôme lateritic nickel orebody at its Tiébaghi operations in New Caledonia. The site geology has an obvious bearing on recovery and metallurgical performance, and the controls are extremely complex at all scales: lithology, oxidation-reduction conditions, mineralogy, and multivariate geochemistry. In that context, establishing an adapted recoverable resource estimation method that is efficient and transparent proves an interesting challenge. The method must address the key notions of: ? Support effect: the exploration data-set can only warrant the estimation of large panels 20×20×3 m3, which are much larger than the selective mining units (SMUs) of 5×5×3 m3 ? Information effect: the selection at production stage uses estimates based on information much denser than that available for mine planning. The problem is rendered more complex in this type of deposit by the fact that the additive variables used for any estimation process (metal accumulation and ore tonnage) are not the ones used to establish the selection at mining stage (i.e. the nickel grade of SMUs, which is the ratio of accumulation on tonnage). Eventually, the selection criteria involve not only Ni grades but also other constituents such as Al2O3, Fe2O3, MgO, and SiO2. The solution presented in this paper is the construction of a platform of SMU multivariate simulations in the saprolitic horizon, together with efficient post-processing aimed at producing the multivariate recoverable resource estimates. The efficiency constraints imposed by the number of blocks to be simulated (1.5 million) lead to resorting to direct block simulations. The underlying multivariate discrete Gaussian model (DGM), the validity of which is tested beforehand, is put to good use to mimic the selection process at the mining stage, by offering the ability to simulate in each block a composite value located at random within the block. Finally, the paper presents the application of a scenario reduction algorithm to pick a representative subset of a few simulations to help appraise the risk attached to the downstream phases (reserve optimization, mine sequencing) of the project. The implementation presented here is for the first generation of the Scenario Reduction plugin built in Isatis software, where measuring the distance between the initial set of scenarios and the reduced set is based on Ni quantities only. Research is under way to adapt the measure to the true multivariate nature of the problem.

Jan 1, 2014

By L Singheiser, W. Willenborg, M. Mueller, K. Hilpert

The limitation of fossil fuel resources and the necessity of reducing CO2emission require an increase of the efficiency of power plants by using combined cycle power systems. Pressurized Pulverized Coal Combustion (PPCC) is a potential concept to realise these objectives. The direct use of hot flue gas for driving a gas turbine requires a hot gas cleanup to achieve corrosion prevention of the turbine blading. One of the main problems is the alkali release during the coal combustion process. Molten coal ash slag has a high potential for alkali retention which depend son the alkali oxide activity in the slag. Knudsen Effusion Mass Spectrometry (KEMS) was used to determine thermodynamic data of alkali gas species over molten coal ash slags and of alkali oxides in molten coal ash slags. The main interest of the investigations focused on the structural dependence of the thermodynamic properties of the alkalis. It was found that there is a strong correlation between the thermodynamic properties and the ratio of nonbridging oxygen to tetrahedral oxygen (NBO/T). An increase of the polymerization of the slag results in a decrease of the alkali oxide activity in the slag and thus a decrease of the alkali partial pressure over the slag. Keywords: coal ash slag, structure, alkali oxide activity, alkali vapour pressure, PPCC, KEMS.

Jan 1, 2004

By A. P. Squelch

The question of what stress condition exists in the hangingwall of tabular stopes remains topical and largely unanswered. Limited field data exist to quantify the situation and provide calibration for investigative computer modelling exercises. Work conducted in1989 and 1990 under a Chamber of Mines Research Organization (now the CSIR: Division of Mining Technology) programme of research into the behaviour and benefits of backfill may assist with this situation. The original work was motivated by the premise that the improved hangingwall stability in backfilled panels (identified by rockfall accident analyses) is due to a change in the hangingwall stress regime. Current, largely theoretical, studies into mechanisms of stope hangingwall behaviour and support interaction could benefit from considering these data. Keywords: Backfill, horizontal stress, stope hangingwall, hangingwall stability, support interaction.

Jan 1, 2002

By J. Utt

Recent developments in circulating fluidized bed (CFB) once-through supercritical technology (OTSC) have enabled this technology to be offered as a utility-scale alternative competing head-to-head with pulverized fuel (PF) OTSC offerings. One clear example is the CFB supercritical unit at the Lagisza Power Plant in Poland, owned by PoludniowyKoncernEnergetyczny SA (PKE). This unit has now been in commercial operation for three full years, exhibiting very good performance, and has validated Foster Wheeler?s performance model at this utility scale as well as for units in the 600 MWe and 800 MWe size ranges offering net efficiency of ~43 per cent (LHV basis). This operating unit has also proven the use of the world?s first FW/BENSON? vertical-tube OTSC low mass flux technology. Since the Lagisza original international tender specified OTSC PF technology, it is important to note that the alternative selection of CFB OTSC technology over conventional PF technology is of historic significance, not only for the validation of the CFB supercritical platform as a viable alternative to conventional PF technology, but it also positions the CFB OTSC with fuel flexibility for offering of sizes up to and including 800 MWe units. This paper explores the differences between CFB OTSC technology and standard PF OTSC in utility power generation. Selection criteria, fuel burning range in both technologies, and other selection drivers are discussed. Economic analysis of both technologies, based on existing cases, is also provided. Also discussed are the technical advantages and uses of each technology. Foster Wheeler has recently been awarded a contract for four units of CFB OTSC technology, which utilizes a 2 on 1 configuration of two 550 MWe CFB OTSC boilers on two single 1000 MWe turbines. Essentially this provides a fuel-flexible low-emissions alternative to a 2 × 1000 MWe solid fuel power block.

Jan 1, 2012

By I. C. Spangenberg

The status of sampling practices in the gold mining industry in Africa was determined as an initial step in a process to standardize sampling practices in the mining industry. Twenty-one gold mines, twenty metallurgical plants, and thirteen laboratories were rated for the potential influence of the relevant sampling errors on each component of the particular sampling system. The findings of the study on the status of equipment, standards, procedures, and management principles were presented in a dissertation (Spangenberg, 20121) and are now used by AngloGold Ashanti?s mines in the quest for correct sampling practices. The information is also used to compile a guideline on leading practice procedures for sampling methods in gold mining. This article is an overview of sampling best practice found in African mining Keywords theory of sampling, best practise, sampling errors, sampling standards.

Jan 1, 2014

By M. Nduna

Surface properties of metal sulphides have a great significance in various areas of engineering and science, such as acid mine drainage, contaminant sorption, and metal separation. In various attempts at producing metal sulphide particles from synthetic solutions, prodigious quantities of nuclei that grow only to colloidal dimensions have been frequently reported. This copious nucleation is promoted by the high levels of supersaturation that characterize most precipitation reactions. Colloidal particle formation in precipi¬tation-based separation processes results in sub-optimal solid-liquid separation, which is alleviated by the production of more highly crystalline particles or agglomerates. The current work approaches this challenge from an electrochemistry perspective, by measuring surface charge potential of precipitant particles during metal sulphide precipitation with respect to the concentration of metal sulphide lattice ions in solution. Electrophoresis was used to measure the metal sulphide particle zeta potential and the settling properties were obtained by performing settleability measurements using an Imhoff settling cone. A suspension of copper sulphide particles was precipitated from synthetic solutions of copper and sulphide ions at equimolar concentrations. Immediately after precipitation the copper sulphide particles had a zeta potential of -50 mV and a settleability of about 7 ml.l-1. With the addition of copper ions the settleability increased by a factor of nearly three times and the zeta potential also increased to a maximum of -40 mV. A decrease in zeta potential to a minimum of -60 mV was observed after the addition of sulphide ions and this was associated with a settleability of 0 ml.l-1.

Jan 1, 2013

By Z. van Zyl

The southern African coal industry is facing the reality that coal reserves are becoming deeper and harder to mine than before. Alternative visions need to be considered to offset the impact of these challenges on productivity, cost, and profitability. One of the main challenges is to maintain current production levels under more difficult conditions, and improve productivity where conditions allow. There is a need to move from the reactive event-based management system towards the more adaptable and flexible process-based management system. This paper focuses on underground coal mining, but the principles are also applicable to other commodities and mining methods. This paper is based on research undertaken by the personnel from Mining Consultancy Services Pty Ltd (MCS) on trends in the underground coal mining sector, as well as practical experience over a period of 16 years in the field of electronic monitoring of mining machinery and productivity optimization.

Jan 1, 2015

By E. Demir

Transportation cost is the dominant cost and accounts for almost half of the total mining cost in surface mining. Therefore, determining transportation cost is critically important for the economic feasibility of mining projects. Turkey produces around 85 million tons of lignite per annum. The biggest state-owned company, Turkish Coal Enterprises (TKI), accounts for 43 per cent of the country?s total lignite production. Around 85 per cent of the produced lignite is used in power plants for electricity generation and 15 per cent is used for domestic heating in cities and urban areas. On behalf of the Turkish government, TKI distributes around 2 Mt of lignite annually, at no cost to poor needy families countrywide in accordance with Social Assistance and Solidarity Funding aid. Subcontractors are utilized for lignite transportation, and conflicts arise due to the different transportation cost calculations at different mines. A robust model that provides unbiased cost estimations is therefore of paramount importance. This paper presents the transportation cost estimation software, NAKMAL, that has been developed for estimating the transportation cost of lignite from the mine face, including excavation and loading, to various final destination points through five different transportation scenarios. NAKMAL was designed using VisualStudio.NET, validated using field data and some case studies, and it is currently being used by TKI for calculation of transportation cost country-wide.

Jan 1, 2012

By T. H. Yang, K. K. Lee, Z. Z. Liang, C. A. Tang, L. C. Li, Y. Tsui, L. G. Tham

Abstract: A series of numerical tests of hydraulic fracturing in heterogeneous rocks were performed to investigate the influence of pore pressure magnitude and gradient on initiation and propagation of tensile fractures. The numerical tests were run with a Rock Failure Process Analysis code, F-RFPA2D, incorporated with a Flow-Stress-Damage coupling model (FSD). To investigate the influence of pore pressure magnitude on fracture behaviour, “pinch-off” breaking tests, originally employed by Bridgeman to investigate the effective stress law for tensile fracture in a uniform pore pressure field, were numerically modelled. In another numerical test, a double-notched sample, with fluid pressure in one notch while keeping the other one open to the atmosphere, is numerically extended to investigate how the fluid flow direction or the pore pressure gradient will influence the fracture behaviour. The simulation results show that fracture is strongly influenced by both pore pressure magnitude and pore pressure gradient. Keywords: seepage mechanics; heterogeneous; pore pressure; numerical simulation; failure process ZUSAMMENFASSUNG: Um den Einfluss der Wasserdruckgroesse der Oeffnung und der Porisitaet auf den Bruchentstanden und Verbreiten der Tension von Gebirgen zu beurteilen, wurde viele nummerische Pruefungen auf den hydraulischen Bruch in dem Gebirgen aufgenommen. Diese Pruefungen wurden mittels der Analyse- Software F-RFPA2D und Flow-stress-Damage Coupling model ( FSD) durchgefuehrt. Um den Einfluess der Wasserdruckgroesse der Oeffnung auf den Bruch zu beurteilen, wurden auch Bruchpruefung und nummerische Analogexperimenten gemacht, und dadurch wurde die ganze Phase der Bruchentstanden und Verbreiten wiedergezeigt, und die Ergebnissen ergeben sich, dass die Wasserdruckgroesse der Oeffnung und der Porisitaet sehr viel auf den Bruchentstanden und Verbreiten der Tension von Gebirgen beeinfluessen. Schluesselwoerter: Durchlaessigkeit , ungeleichmaessig, Wasserdruck der Oeffnung, nummerische Analog, Zerstoerungspahse Résumé : Une série de simulations numériques a été ménée pour analyser l’influence de la grandeur de la pression de pore et du gradient sur la naissance et la propagation des fractures de tensions par le biais de la simulation numérique des fractures hydroliques dans des rochers hétérogènes . Le logiciel F-RFPA (Rock Failure Process Analysis code ) intégrant FSD ( Flow-Stress-Damage coupling model ) y a été employé. Les résultats des simultations montrent tout le processus de la naissance et de la propagation des fractures sous la pression de pore. Ces résultats nous ont permis de constater que la grandeur de la pression de pore et le gradient exercent une influence importante sur la naissance des fractures dans les rochers et sur leur mode de propagation . Mots de clé : le mécanisme de transfusion ; l’hétéogénéité ; la pression de pore ; la simultation numérique ; le processus destructif

Jan 1, 2003

By A. E. Lewis

Particle morphology is a term that is used to describe the overall external shape and appearance of particulate solids. From the physical point of view, a precipitated solid is characterized primarily by the size and morphology of the particles (Sohnel andGarside, 1992). If the morphology of the crystal structures is to be related to the processing conditions, then the morphologies need to be quantified in some way. This can be achieved by using surface area measurements as well as fractal dimensions. The key idea is that rugged and indeterminate systems can be described by using a fractional number that describes the ruggedness of the system (Kaye, 1989). In other words, when the complexity of a structure, such as an agglomerate, increases with increasing magnification, it is useful to employ fractal dimensions to describe the structure. Fractal geometry proposes that, instead of attempting to measure the length of an irregular boundary, the rate at which the length of the boundary approaches infinity with increasing resolution should be calculated. Cross-sectional profiles of rugged particles can thus be quantified using the fractal dimension, and a measurement of the ruggedness of the morphology obtained. One of the additional uses of measuring the fractal dimension is that the measured value can be related to the physical properties and formation characteristics of the particle (Kaye and Trottier,1995). The morphology of nickel crystals was quantified with fractal dimension calculations of particle cross-sections. Particle cross-sections were obtained by mounting the particles in resin and polishing back. These were then photographed using Scanning Electron Microscopy and the resulting profiles analysed using the structured walk technique.

Jan 1, 2001

By H. Yavuz

Physical modelling is one of the research tools in the understanding of the failure mechanisms and the deformations likely to be experienced by the strata during mining operations. Success of the physical models to predict the strata behaviour depends on satisfaction of the scaling requirements in modelling material used. This paper gives results from a laboratory work carried out into the factors influencing the strength and elastic properties of a physical model material to satisfy the scaling requirements determined from application of dimensional analysis to the pertinent variables affecting the deformation and failure of the underground structures. It was found that the conditions for preparing the material over its composition had a great influence on the final properties. The effect of different water quantities, sand size and mixing time upon the properties of modelling material was studied and water requirement for different proportions of sand/plaster to prepare the material was optimized. Various sand/plaster ratios of compositions were cured at three different levels of oven temperatures. Curing at low temperature produced material within the average modulus ratios ranging from 290 to 432, which are common to most rock types according to Deere?s rock classification, whilst curing at high temperature produced material within the low modulus ratios ranging from 64 to 140 depending on its composition. A combination of low and high temperature curing resulted with an increase in modulus ratio compared to high temperature curing. Curing the material at low temperature compared to other curing temperatures provided a satisfactory range of strength ratio. It has been shown that the relative amount of filler to plaster in the mix controls the frictional properties of the material and results with an increase in strength and modulus ratio of the material provided that suggested preparation and curing conditions were applied. Model material developed by curing at low temperature simulated modulus ranging from 241 to 343 and strength ratios ranging from 11.6 to14.8 of a coal mine rocks, satisfactorily.

Jan 1, 2003

By L. A. Matthews

The embrittlement of the Ti-6Al-4V alloy by hydrogen dosing at elevated temperature has been investigated. Metal coupons were subjected to isothermal treatments in a partial hydrogen atmosphere in the temperature range from 650ºC?950ºC and the degree of embrittlement after treatment was determined by drop-weight impact testing. Embrittlement was found to be inversely related to reaction temperature as a result of the combined effects of greater hydrogen absorption and titanium hydride precipitation at the lower isothermal temperatures. Keywords Titanium, hydrogen embrittlement, impact energy

Jan 1, 2011

By J. Utt

Recent developments in circulating fluidized bed (CFB) once-through supercritical technology (OTSC) have enabled this technology to be offered as a utility-scale alternative competing head-to-head with pulverized fuel (PF) OTSC offerings. One clear example is the CFB supercritical unit at the Lagisza Power Plant in Poland, owned by PoludniowyKoncernEnergetyczny SA (PKE). This unit has now been in commercial operation for three full years, exhibiting very good performance, and has validated Foster Wheeler's performance model at this utility scale as well as for units in the 600 MWe and 800 MWe size ranges offering net efficiency of -43 per cent (LHV basis). This operating unit has also proven the use of the world's first FW/BENSONTM vertical-tube OTSC low mass flux technology. Since the Lagisza original international tender specified OTSC PF technology, it is important to note that the alternative selection of CFB OTSC technology over conventional PF technology is of historic significance, not only for the validation of the CFB supercritical platform as a viable alternative to conventional PF technology, but it also positions the CFB OTSC with fuel flexibility for offering of sizes up to and including 800 MWe units. This paper explores the differences between CFB OTSC technology and standard PF OTSC in utility power generation. Selection criteria, fuel burning range in both technologies, and other selection drivers are discussed. Economic analysis of both technologies, based on existing cases, is also provided. Also discussed are the technical advantages and uses of each technology. Foster Wheeler has recently been awarded a contract for four units of CFB OTSC technology, which utilizes a 2 on 1 configuration of two 550 MWe CFB OTSC boilers on two single 1000 MWe turbines. Essentially this provides a fuel-flexible low-emissions alternative to a 2 x 1000 MWe solid fuel power block.

Jan 1, 2012

By A. Kapito

The formation of bainite in steel is dependent on the size of the casting, the heat treatment, and the alloying elements. It is difficult to obtain a fully bainitic microstructure in steels during heat treatment because of its close proximity to the martensite (a?) reaction. The ferrite (a) and pearlite reactions in steels are also rapid and shield the bainite reaction. Alloying elements therefore need to be added to separate the bainite reaction. Boron (B) and molybdenum (Mo) are key elements added to bainitic steels because of their ability to retard the a reaction. Other elements used in the production of bainitic steels are silicon (Si), chromium (Cr), manganese (Mn), and titanium (Ti). In this paper we investigate the effect of alloying elements on the bainite reaction through the use of dilatometry. Dilatometry is a technique that determines phase transformations in the steel and through which continuous cooling transformation (CCT) curves can then be developed. Some initial results are presented of an ongoing study on the development of bainitic steels for railway wheel applications.

Jan 1, 2013