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By N. I. Aziz

The importance of using disc cutters for rock excavation is reflected by their wide application in hard rock cutting machines such as tunnel boring machines and raise borers. The forces involved in the cutting process are those due mainly to thrust and rolling forces and are greater than that required by cutting picks. An interesting feature of cutting with discs is the formation of surface crushing, surface and sub-surface chipping and primary crack formation. Experimental, as well as analytical, work has been carried out to determine the optimum spacing between the disc cutters to control primary crack orientation. Wedge bit indenters were used to simulate disc cutters. The paper concludes by proposing a new approach to rock excavation by hybrid cutting based on controlling the primary crack orientation.

Jan 1, 1992

The presence of gold or tin in a particular place in payable quantities may be suspected from geological and prospE;cting reports. It behoves the engineer by judiciously spaced boreholes or pits to establish whether the place is exploitable with profit, and it is the purpose of this paper to set out the ways in which this is done. The various types of deposit to be considered occur in Malaya, Thafland and Borneo, in which countries the writer spent four years in estimating alluvials.The methods described were used in actual practice both by the writer and previous engineers for the same company. The subsequent exploitation of the alluvials evaluated by the methods given below shows that the recovery was as good as, and sometimes higher than, expected. No claims are made to the originality of the methods, but it is 'felt that they may be new to some engineers and< interesting to others contemplating alluvial testing.

Jan 1, 1942

By J. W. Thompson

LIMESTONE DEPOSITS. Limestone deposits that have not been demonstrated to be of such quality as to give them any substantial value over other limestone deposits of the same region, are not regarded as minerals. Gray Trust Co., In re, 47 Land Decisions 18, p. 20. OIL AS A MINERAL. Oil is a mineral substance and its removal will greatly impair the value of the land from which it is removed. Texas & Pacific Coal & Oil Co. v. Howard. Southwestern 735, p. 737. Tex. Clv. App. 212 OIL AND GAS AS MINERALS OWNERSHIP. Oil and gas are minerals and so long as they remain in place they belong to the owner of the land under which they are found and such owner has the right to explore for the oil and gas on or under his land and when found to remove and possess the same. Kimbley v. Luckey, Okla. - 179 Pacific 928, p. 831. OWNERSHIP OF MINERALS LACHES NO BAR. The owner of minerals in land can not be barred by laches for failing to assert his ownership where his title had not been ques- tioned and his right invaded. No lapse of time bars one's right to property and it is only in case his right has been invaded that it can be barred by laches.

Jan 1, 1920

By R. Fuenzalida

Since 2007, a number of Multivariable Predictive Control (MPC) Applications have been implemented on SAG mills, among others, within the Kairos Mining Concentrator Automation Program using ?Profit Controller?? and other tools comprising the ?Profit Suite??. Along this journey, several interesting and challenging issues related to SAG mill operation and control have been faced, which are relevant to be shared with the Mineral Processing community. These advanced control applications have an operational objective whose goal is to increase marginal profit on the concentrator, together with increasing mill stability. In regard to this objective, the issues to be presented and described are in direct relationship with ?Profit Controller? features and the SAG role; they are also stated and linked to get the most of the mill. Some conclusions and findings are also presented, leading to recommended practices on how to use the controller. These findings have also lead us to decide further actions to be taken on new applications to deploy and also on devising and implementing some complementary components to increase robustness of the overall automation solution, as well as reducing the need for operator intervention.

Jan 1, 2012

By Pat McLaughlin

Blast design in the construction industry has often been based on past practice or powder factors. This is to some extent understandable, since construction projects do not have the longevity of mining or quarrying operations and therefore have less opportunity to pursue potential improvements. The main concern of the operator is whether or not the technique will work, and at what cost to the downstream processes. Time, not long term savings, is of the essence.

Jan 1, 1994

By Jack Zhang, Yunguo Tang, Baodong Zhao

"Rare earth elements (REEs) have numerous key applications in both traditional and advanced technologies. A shortage of some critical REEs is expected due to the discrepancy between the REE abundance in REE deposits and the REE demand from the market. For example, Neodymium, Europium, Terbium, Dysprosium, Erbium and Yttrium are expected to be in short supply. REE recovery and separation from secondary resources such as uranium wastes, heavy mineral sands, and recycled materials can balance the shortfall in a cost effective way.The Saskatchewan Research Council (SRC) is engaged in the development and commercialization of complete REE recovery and separation technologies in Canada. One of SRC’s newest developments is the design and commissioning of a heavy rare earth (HREE) separation pilot plant. The pilot plant uses hundreds of stages of solvent extraction (SX) to produce high purity individual HREEs from both primary and secondary resources.This paper presents the design of an HREE recovery process for the particular case of uranium processing wastes. The separation results of a group separation are reported and discussed, as well as the issues and the challenges of the development, commissioning and operation of the continuous SX pilot plant.IntroductionSignificant amounts of strategic specialty heavy rare earth elements (HREEs) are found in uranium wastes in Saskatchewan. It estimated that about 47 tonne/a of heavy rare earth element oxides (HREO) including 27 tonne/a of Y2O3, plus 6 tonne/a of Sc2O3 are in the raffinate of every uranium mill for potential recovery. Since the HREEs are already in the raffinate, cost effective HREE production is promising in Saskatchewan.Selective precipitation including nutraulization, oxalate and double-salts precipitation, as well as sulfide precipitation, ion exchange (IX) and SX are commonly used technologies for the recovery and purification of REE solution. REE oxalate precipitation is an effective technology to remove Fe, Al, Ca, Si and other impurities by taking the advantages of the solubility difference between oxalates of REEs and impurities in acidic solution (Xu, 2005)."

Jan 1, 2017

By Hayel M. El-Naggar, Sherif A. Akl

Although grouted piles have been used for several decades since the idea was proposed in the 1970s, their design is mostly based on experience and unpublished proprietary methods. There is little research on grouting drilled shaft tips and even less on grouting shaft sides. This paper presents the analysis of 4 instrumented pile loads tests on base and shaft grouted piles from different sites in Egypt; with emphasis on one of the tests, to demonstrate the analysis process. The data from the tests are analyzed to model the development of unit side friction (USF) with relative displacement. A numerical model using the finite element software PLAXIS is used to investigate the effect of grouting on the surrounding soil stress state. The paper combines the observations from full scale pile load tests and results from the numerical model to suggest an idealized behavior of side friction development with relative displacement of the grouted part of the shaft. The suggested model considers an envelope of Unit Side Friction (USF) with relative displacement, initially dominated by the grout resistance then at higher relative displacements, the friction with radially pressured soil takes over. The grout provides very high USF values up to a relative displacement of 2mm. Then, the USF drops to a typical pile soil side friction behavior; however, this friction is affected by the contact stress between pile and soil, which significantly increases due to compaction grouting. INTRODUCTION Base and shaft pile grouting has been significantly developing in recent years to accommodate the unfavorable conditions in major projects such as the high loads in high rise building and founding on problematic soil formations. Grouting aims to decrease settlements and increase the capacity of the pile under axial load. The technique is first introduced by Kraft (1974) but gained popularity in the 1980s. Typically there are two types of grouting; compaction, and permeation. Compaction grouting is more common in pile foundations practice, and many researchers have provided case histories of pile load tests on base grouted piles and base and shaft grouted piles (Gouvenot and Gabaix,1975; Stocker, 1983; Ghazali et al., 1988; Fleming, 1993; Kusakabe et al., 1994; Robson and Wahby,1994; Joer and Randolph, 1998; Hamza and Leoni, 1998; Mullins et al. 2000; Littlechild et al., 2000; Suckling and Eager, 2001; Dapp and Mullins, 2002; Ho, 2003; Fu and Zhou, 2003; Brettmann and NeSmith, 2005; Ruiz, 2005; Mullins, 2006; Dapp and Brown, 2010; Beadman et al., 2012; Nguyen et al., 2013; Miller et al., 2013; Sinnreich and Simpson, 2015; Hui and Lin, 2015). Compaction grouting is meant to densify the soil around the pile and below the base rather than permeate this soil and increase its cohesion. Research showed that grouting increases the capacity of the piles by a factor of 2~5. The variation in capacity increase depends on pile type, grouting process, and especially grouting pressure. Although there are many case histories of pile load tests on grouted piles but there is no well-defined agreed-upon method to predict grouted pile capacity as typically done in ungrouted piles. Few lab experiments discussed the shaft grouting effects on the soil especially the compaction grouting. The experiments concluded that the compaction grouting forms a homogeneous layer between the pile and the soil, and a residual effective stress is achieved simultaneously with a significant densification of the soil around the pile with noticeable decreasing in void ratio. (Fattahpour et al., 2015; Wang et al., 2015). Recently, studies used numerical analysis to investigate the behavior of the grouted piles and the changes in the surrounding soil (Chiang et al., 2013). That study presents a simulation of the base pressure grouting with a simple FE model and predicts the reduction of the pile settlement by 10 to 20%. Another numerical study using a complex model conducted by Zhou et al. (2017), pr

Jan 1, 2018

By C A. Heinrich, J L. Walshe, V J. Wall

The Porgera Gold Mine, located in the highlands of Papua New Guinea, has produced over 5 million ounces of Au, since its opening in late 1990. The deposit is located within Upper Cretaceous Papuan Platform sediments approximately 25 km south of the Lagaip Fault, and is spatially and temporally associated with the 6 Ma alkaline Porgera Intrusive Complex.

Jan 1, 1995

By George L. Gates

[When clays e.re mixe~ "Jith "~later to nake mud fluids f'ol' use in :irilling ','Iells "for oil and gar: h;:r vue :;'0 tary me thee. t 18 liquid mij~ tUl"es have certair.. phypicr..l characteri.",t.ics that vary ",dth t e Qlldlltit.y find]

Jan 1, 1941

By Josh Johnson, Stephen Tadolini, Mark Ferster, Curt Jacobs

"Stillwater Mining Company is the only U.S. producer of platinum group metals (PGMs) and the largest producer outside of South Africa and Russia. The Company controls a considerable portion of the J-M Reef and is currently developing the ""Blitz Project,"" which will provide a main haulage level, ore pass systems, backfill plants, and flow-through ventilation to increase production and ensure sustainable extraction of this critical strategic mineral. While driving two sub-parallel footwall laterals to about 8,125 m (26,000 ft) long, one of the development drifts experienced a massive fall in a geologically disturbed area created by a dike intrusion. Combinations of a void fill material (Tekseal), polyurethane injection, fore poling coupled with steel arches, and supplemental bolting allow safe and efficient advance through this geologically disturbed zone. This paper presents the details of this project.INTRODUCTIONStillwater Mining Company is the only U.S. producer of platinum group metals (PGMs) and the largest producer outside of South Africa and Russia. The Company controls a considerable portion of the J-M Reef and is currently developing the ""Blitz Project,"" which will provide a main haulage level, ore pass systems, backfill plants, and flow-through ventilation to increase production and ensure sustainable extraction of this critical strategic mineral.Tunnel Boring Machines (TBMs), shown in Figure 1, have been used extensively at both the Stillwater Mine and the East Boulder Mine to develop access to the J-M Reef. The J-M Reef is a PGMbearing reef deposit located in the Stillwater Complex near NyeMontana. The mining property and location are shown in Figure 2.The Blitz Project is named after the Blitz mining claims and is developing the Eastern extent of the J-M Reef Project., This consists of a 5.5 m (18 ft) diameter TBM drive on the SOE (1,562 m (5,000 ft) above sea level and east of the shaft collar) and a 4.7 x 4.7 m (15 x 15 ft) drill and blast heading on the 5,600E (1,750 m (5,600 ft) above sea level and east of the shaft collar). The Benbow Decline will be completed running perpendicular to the TBM by drilling and blasting methods. The TBM drift will be used for exploration drilling, ventilation, and will serve as the main haulage level. The 56E will be used for ventilation and exploration drilling. The Benbow decline will serve as the exhaust drift."

Jan 1, 2016

By M. Kuchta, A. Newman

LKAB’s Kiruna Mine, located in northern Sweden, produces about 24 Mton of iron ore yearly using sublevel caving. For efficiency, the mine must deliver planned quantities of three ore products. We use mixed integer programming to schedule Kiruna’s operations, specifically, which production blocks should be mined, and when they should be mined to minimize deviations from planned production quantities while adhering to mining restrictions (e.g., sequencing). A new production block database and a well-formulated mixed integer programming model dramatically reduce the size of the original problem; in less than ten minutes we generate five-year schedules with time fidelity of months.

Jan 1, 2002

By Enrique Touceda

FOR a number of years prior to the world war, the firm of Geo. H. Thacher & Co., of Albany, N. Y., was engaged in the manufacture of marine and other gray-iron castings. At -the outbreak of the war the firm decided to specialize in the manufacture f propeller wheels. It attacked the problem, therefore, from a foundry point of view, seeking to produce a casting that would be so accurate that no subsequent machining would be required on the blades, also from the point of view of the ship builder. There were two general methods f manufacture, the shortcomings of which have been freely acknowledged. In the sweep method, the nowel, or bottom half-mold, for each blade is swept up by a spindle beam and pitch race, while the top half-mold for each blade is built up individually. In the pattern method one individual blade, with the hub or hub portion, is mounted on a spindle and the individual -blade mold formed, the pattern is then rotated on the spindle to the position- for the next blade, etc. In rare cases wheels were made from a solid pattern. Owing to the cost of the pattern, its failure in many instances to be correctly made, and (when made of wood) its early and sure distortion the disadvantage of this practice is obvious, while metal patterns in most instances were prohibitive in cost. In these methods both green-sand and loam molding was practiced. The casting produced by either method can be considered only as a blank from which the propeller must be machined. The back surface f each blade must be chipped too the templet and through this procedure chipped to such accuracy, as will be required for a static balance. Inasmuch as the' work done by the machine tool is confined to the driving face of the blades, not only is perfection most difficult, but corrosion will be greater because of the removal of the dense skin f the casting and the local strains set up by the pneumatic tool in chipping. To produce a finished 9-ft. propeller for a Navy destroyer required from 8 to 21 days f foundry work and about the same length of, time for the machining. Through the use f the Thacher process, only as many hours are required, besides it is possible to produce a finished casting in perfect conformity, with any particular propeller-wheel design,

Jan 4, 1921

By O. Mejia, J. Drozdiak

"This paper summarizes a comprehensive energy and cost study comparing an existing SAG mill based circuit at Huckleberry Mine with two proposed circuits involving comminution technologies which are associated with energy efficiency: high pressure grinding rolls (HPGR) and high speed stirred mills. The specific energy requirements expressed as kWh/t for the proposed circuits were determined from pilotscale HPGR and stirred mill testing conducted at the University of British Columbia. Samples and operating data were collected from Huckleberry’s copper-molybdenum concentrator to evaluate current mill performance for comparison. To support the base case, the SABC circuit was modeled using JK SimMet® software. The main comparison focused on the complete energy requirements for each circuit, including materials handling equipment such as conveyors, screens, feeders and pumps. This paper also provides capital and operating cost estimates for each of the comminution circuits. The results showed that the HPGR - ball mill circuit achieved a 21% reduction in energy consumption over the existing SAG - ball mill circuit at the same P80 grind size of 160 µm. At a grind of 80% passing 75 µm, the HPGR - stirred mill circuit showed a 34% reduction in energy compared to the base case. It was concluded that the energy reduction for the new flowsheets significantly improved the economics of the Huckleberry comminution duty.INTRODUCTIONUp until now, tumbling mills such as AG/SAG mills and ball mills have had a dominant bearing on the design and economics of comminution circuits. However, it is commonly agreed that the majority of employed comminution processes are energy intensive and energy inefficient, accounting for up to 80% of overall process plant energy consumption and having an efficiency of as low as 1% (Abouzeid and Fuerstenau, 2009; Fuerstenau and Abouzeid, 2002). The U.S. department of energy reported that there is a potential to reduce energy consumption in the metals industry by up to 61% from current practice to bestestimated practical minimum energy consumption; suggestions included the implementation of best practices and the adoption of energy efficient mining and mineral processing technologies such as advanced blasting techniques, high pressure grinding rolls (HPGR) and stirred mills (U.S. DOE, 2007)."

Jan 1, 2013

The observation of lower-than-predicted Fe/Cu ratios in the cementation of copper on iron in tests at elevated temperatures indicated that some other reaction was contributing to the reduction of cupric sulphate in addition to the reduction by elemental iron. Experiments showed that the copper sponge, which initially formed on the iron, subsequently reduced the cupric sulphate giving the products cuprous oxide and sulphuric acid.Tests were undertaken to determine the rate and equilibrium conditions of the reduction reaction with variations in the types of the reducing agent and solution parameters. The reaction first became apparent at temperatures above 50°C and as it ceased at pH 1·8 it was possible to induce further reaction by alkali addition.

Jan 1, 1974

By Forrest T. Moyer

The overall injury experience, excluding officeworkers, at metal mines and mills during the period 1961-63, reported by operators, was 174 fatal and 11,357 nonfatal disabling work injuries during an aggregate worktime of 451 million man-hours. These injuries occurred at a frequency rate of 25.55 per million man-hours, comprising 0.39 for the fatal and 25.17 for the nonfatal injuries. The combined severity rate of the disabilities was 3,779 days lost or charged per million man- hours, consisting of 2,314 for the fatal and 1,465 for the nonfatal injuries. The average severity of all disabilities during 1961-63, was 148 days per injury. The number of days lost and/or charged, ex- cluding officeworkers, at metal mines and mills during the period 1961-63, was 1,440,000 days charged to fatal injuries and 661,290 days lost from nonfatal injuries. An average of 70,966 men were at work daily. The outstanding cause for fatal injuries was the fall of rock or ore from the back, while most of the nonfatal injuries were caused by handling materials, slips or falls of persons, machinery, falls of rock or ore from back and side, and haulage. Injury experience at primary nonferrous smelters, refineries, and reduction plants during 1961-63, excluding officeworkers, was 23 fatal and 3,214 nonfatal disabling injuries during a total work- time of 277 million man-hours. The injuries occurred at frequency rates of 0.08 per million man-hours for the fatalities and 11.61 for the nonfatal disabilities. The severity rate for all injuries of 1,085 days lost or charged per million man-hours comprised 498 for fatal and 587 for nonfatal injuries. The number of days lost, excluding officeworkers, at primary nonferrous smelters, refineries, and reduction plants during 1961-63 was 138,000 from fatal injuries and 162,385 from nonfatal injuries, An average of 34,938 men were at work daily an active plant days during the three year period. The injury experience for officeworkers at metal mines and mills during the period 1961-63 was 20 nonfatal disabling work injuries, (there were no fatal injuries reported), during an aggregate work-time of 28,694,244 man-hours. These injuries occurred at a frequency rate of 0.70 per million man-hours. There were no fatal injuries reported for officeworkers at non-ferrous smelters, refineries, and reduction plants during 1961-63, but seven nonfatal injuries were reported during an aggregate work-time of 30,814,772 man-hours. The frequency rate for these injuries was 0.23 per million man-hours for this period.

Jan 1, 1967

By Gary E. Sherman

To aid the U.S. Army Corps of Engineers in their Resource Development Navigation Study, the U.S. Bureau of Mines (Bureau) examined the potential for mineral development near ten Alaska port sites. This report presents the results for the following four sites: Balboa Bay, Beluga, Lost River, and Point MacKenzie. There are 579 known deposits within the area considered for these ports. The majority of the deposits are located within a highway/railroad corridor examined for the Point MacKenzie port site. Based on the current level of knowledge, coal deposits near the Beluga and Point MacKenzie port sites are most likely to be developed in the near future. This conclusion is based on the fact that coal projects in these areas are actively being pursued for development. The mineral wealth surrounding the four port sites is substantial. Mine models were used to examine the potential for mining tin, gold, silver, copper, and molybdenum. The models were based on published reserve and grade data and therefore do not include proprietary company data which, if available, would likely change the analysis results. Of the models examined, the tin placer mine model developed for the Lost River port site proved to be closest to being economic.

Jan 1, 2011

By David Cole, Paul Cooper, Dale Preece, Jerome Stofleth

The Explosive Destruction System (EDS) has been designed at Sandia National Laboratories for the disposal of chemical munitions (phosgene, mustard gas, sarin etc.), many dating back to World War I. EDS is a portable system that is trailer mounted and consists of a vessel into which a chemical munition can be loaded and opened for neutralization with linear and conical shaped charges. Gases are contained within the sealed chamber. The linear shaped charges split the munition in two and the conical shaped charge (CSC) is aimed at the explosive burster, in each munition, which is detonated by the resulting shaped charge jet, Toxic chemicals remaining in the vessel following detonation are neutralized and disposed of. This paper documents the development of a new CSC needed to reliably detonate explosive bursters in an expanding array of chemical munitions that are beyond what the EDS device was originally designed to eutralize. Design of this new CSC was controlled by the need to deliver energy above the detonation threshold into the explosive after penetrating the outer steel casing, fluid, the burster casing and finally the explosive. Design considerations were driven by jet conditions at the steel/explosive interface inside the burster. Parameters to consider in CSC design include: 1) diameter, 2) liner thickness, 3) liner position in body, 4) explosive weight, and 5) liner shape or interior (apex) angle. The effects of these parameters on final CSC performance are examined in detail. CSC’s that meet the design specifications have been manufactured and tested. The performance of these charges are compared with the original design requirements.

Jan 1, 2002

By B. Clermont

Ball mills are usually the largest consumers of energy within a mineral concentrator. Comminution is responsible for 50% of the total mineral processing cost. In today?s global markets, expanding mining groups are trying to optimize mill performances. Since comminution is concerned with liberating valuable minerals for recovery in the separation process, it is crucial to run the mills at the best operating conditions which lead to good liberation at competitive throughputs with minimum costs (energy and wear). The high availability of the equipment is also essential to maximize production and profit. To reach this key objective, continuous and reliable information about the mill operation is vital. An innovative tool which can deliver information about in-mill dynamics has been developed by Magotteaux. It can provide online and accurate measurements of the degree of grinding ball fill and pulp position for timely decision making and actions. This tool could be used on its own or linked to an automatic grinding ball loading system named Magoload. Therefore, ball load could be kept constant by using direct measurement. This article describes the Sensomag and presents some of the major improvements that can be achieved with it. Some other promising avenues are still to be explored. Keywords: Comminution, process control, process optimization, process instrumentation, online analysis.

Jan 1, 2010

By P. H. Reynolds, S. Liaghat, A. Zarasvandi

"Darreh-Zerreshk and Ali-Abad are two relatively small porphyry copper-type deposits in Yazd Province in central Iran. They are located within the central Iranian volcano-plutonic belt, formed above the collisional convergent margin of the Iranian lithospheric plate from the late Eocene to the Miocene. This paper discusses the geochemical characteristics of the igneous rocks, and 40Ar/39Ar geochronology of plutons and alteration phases associated with the Darreh-Zerreshk and Ali-Abad deposits. The deposits are spatially associated with igneous complexes that consist of older and barren granites intruded by intermediate-composition granitoids, which are the carriers of Cu mineralization. The granites have relatively high content of Nb, Y, and K, a prominent negative Eu anomaly, and were probably derived from melting of, or contamination of mantle-derived magmas by, continental crust. Porphyritic diorites, quartz monzodiorites, and granodiorites show enrichment in light rare earth and large-ion lithophile elements, depletion in middle rare earth elements, and have no negative Eu anomaly. These intermediate-composition granitoids were derived from melting of the upper mantle or lower crust, and their differentiation was controlled partly by fractionation of hornblende. A pilot K/Ar whole-rock dating study suggests that the pre-ore granites were emplaced in the Oligocene. Dating by the 40Ar/39Ar method of nine samples of secondary biotite and sericitized rocks from drillcore within the mineralized and altered zones in both deposits yielded a well-defined age of ca. 16 Ma. This date is interpreted to be the time of hydrothermal alteration and of porphyry copper type mineralization in this part of Iran."

Jan 1, 2007

By N. D. Policow, J. S. Orphanos

D.A. Dahlstrom In the paper, a comparison was made between flowsheets using the screen bowl centrifuge and disc filters, respectively, as the primary dewatering device. The authors very effectively show that by raising feed temperature, mechanical dewatering is enhanced through reduced viscosity of the water. When a final coal moisture of 10% is required, the net effect of heating the feed is a reduction in thermal requirements because of the lower evaporated load on the dryer. The flowsheet comparison on this, however, was not completely correct. Disc filters do not generally utilize enhanced mechanical dewatering through increased temperature. Horizontal belt filters, through the optimal use of steam heating of the filter cake, have shown significant cost reductions over disc filters where steam is not used. In addition, the authors forgot to mention that there is a certain fraction of the feed that is so fine that it cannot be recovered by the centrifuge economically. That is the function of the filtration device shown in Fig. 4. In subbituminous pipeline coals, this fraction represents more than 10% of the feed. Even after flocculation and belt pressing, the moisture content in the fine fraction is 30%-40. Recent tests on a subbituminous pipeline coal slurry, compared an Eimco-Extractor horizontal belt filter with the screen bowl centrifuge flowsheet shown in Fig. 4. Mechanical dewatering was enhanced through the use of a steam dry zone after the initial dewatering zone. Vacuum pump horsepower was reduced by more than 50% through the use of condensors, and heat recovery was utilized to minimize thermal costs. Thermal drying to 10% moisture by weight was required in both flowsheets. The 0.5 wt% fines in the filtrate were flocculated and recycled to the filter, thus eliminating the belt press and solids mixers. When the three major operating costs (which normally account for 50%-75% of the coal operating costs) of steam, electricity, and flocculants at current prices were calculated, the flowsheets utilizing the Eimco-Extractor had cost savings vs the centrifuge flowsheet of 89¢/t (81o; per st) of surface dry coal. This advantage increases with increasing thermal and electricity prices. I congratulate the authors for the strides made with the screen bowl centrifuge. However, filtration flowsheets continue to be improved and their simplicity and low thermal and electrical requirements should not be so quickly dismissed. ? Reply by N.D. Policow From a technical standpoint, a number of extensive test programs have demonstrated that by raising the feed temperature, mechanical dewatering is enhanced whether it be centrifuges or filters performing the separation. Economic constraints usually become the over-riding issue. If an inexpensive source of thermal energy is available, i.e., waste steam, etc., the approach becomes commercially acceptable. For the specific case of coal slurry pipelines, since the dewatering plants will be located close to power generation stations, the preheating approach becomes especially attractive. The cost comparison shown in Fig. 7, which was prepared by a major West Coast engineering firm, contrasted screen bowl centrifuges and disc filters. In both alternatives, a thermal dryer was specified to produce a contract moisture of the final product. Sizing of the thermal dryer on the screen bowl alternative was substantially smaller than that of the filter, since the screen bowl was credited with a four to six percentage point decrease in product moisture compared to the disc. This comparison was made at ambient temperatures and reflected solely the mechanical dewatering capabilities of the two devices. No preheating of the feed was included in this particular comparison. Early generation screen bowl centrifuges operated under the principle of maximum bulk tonnage throughput. Second and third generation machines have followed the trends dictated by the coal industry calling for higher one-pass recoveries than previously demanded. The current generation of high-speed, long-bowl centrifuges permit recoveries of ultrafine solids directly comparable to commercial filter operation. On typical coal preparation plant feeds with nominal 600 E. an X 0 (28 mesh X 0) clean coal, recovery levels in excess of 99% are now obtained. The material that does escape the centrifuge and reports to the main effluent is typically -10 µm, high ash material. We have documented substantial beneficiation effects in screen bowl centrifuge performance with the cake product containing lower ash levels than the feed. On the referenced pipeline, coal tests performed on Western subbituminous coal, we found that the percentage of -10 µm material in the feed was six to eight times greater than normally encountered on eastern Appalachian seams. Our 45-t/h (50-stph) production centrifuge was never set up to maximize recovery. It was used as part of the two-stage dewatering circuit that had been chosen by designers of the proposed pipeline. Recoveries up to 95% were recorded. With field adjustments, that performance could most certainly have been improved. In contrast, manufacturers of the horizontal belt filter provided a small pilot-scale unit that operated on a side stream at the test facility. Numerous combinations of chemical additions were evaluated to determine those that had the best impact on filter performance. Whereas the screen bowl centrifuges operated without chemical addition, producing a dry, fluffy cake, the belt filter required two stages of chemical addition to attain satisfactory performance and high recovery levels. On the two-stage circuit that incorporated a belt press as the secondary

Jan 12, 1983