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By Fuqiang Zheng, Yufeng Guo, Guanzhou Qiu, Tao Jiang, Xiaoming Qu

MxTi3-xO5 is the main titanium-bearing mineral in the titanium-bearing electric furnace slag (TEFS), which is produced by direct reduction-electric furnace smelting process with vanadium titanomagnetite concentrate in Panzhihua-Xichang region of China. In order to effectively utilize the titanium resource in TEFS, the thermomechanical analysis and conditions for the growing up of MxTi3-xO5 grain were investigated, which emphasized on the effects of CaF2 and cooling rate on the crystallization of MxTi3-xO5 in the melting process. The mineral phase and morphology of titanium-bearing slag were determined by XRD and electron microscope technique, respectively. The results indicated that the average grain size of MxTi3-xO5 grown up from 30 to 92 lm and the area fraction of MxTi3-xO5 reached about 66% from 61% under the conditions of 5 wt% CaF2 and cooling rate at 1 °C/min.

Mar 1, 2017

By G. W. Jones

During the course of an investigation by the Bureau of Mines into the causes, behavior, and control of anthracite-mine fires, it was observed that the carbon monoxide disappeared from a sealed fire area much more rapidly than could be explained on the basis of leakage of gases. Two suggestions were offered for this high rate of disappearance: (1) That the carbon monoxide, was oxidized at temperatures below 150° C. by either the anthracite or its ash (tests on many anthracites have shown that at temperatures above 150° C. carbon monoxide is liberated in the oxidation products when air is passed through it); (2) that the carbon monoxide was oxidized by micro-organisms present in the sealed area.

Jan 1, 1939

By D. J. MacKinnon

Smooth, compact, dendrite-free, 24-h zinc deposits have been electrowon from zinc chloride electrolyte using a diaphragm cell. The cell consisted of sealed anode compartment con- taining DSA anodes which were separated from an open cathode compartment by Dynel cloth membranes. Fresh electrolyte was fed to the cathode compartment where zinc deposition onto an aluminum cathode was aided by air-sparging. The catholyte passed through the diaphragm into the anode compartment from which chlorine gas and spent anolyte were withdram.

Jan 1, 1980

By H. Staton, N. Michaelson

"INTRODUCTION Lundin Mining’s Eagle Operation, located in Marquette County, upper Michigan consists of a mine and concentrator that process a Ni-Cu-(PGE) ore. The mine itself is an underground operation and the ore is trucked from the Eagle mine site 66 miles to the Humboldt mill where both nickel and copper concentrates are produced. Operations began in 2014 and continued with an average production of approximately 23,000 tonnes of Ni and 20,000 tonnes of Cu per year for the first three years of operation. The Humboldt Mill, currently operated by Lundin Mining, processes the nickel/copper ore from Eagle Mine and performs the concentration through several stages of flotation. Originally built in 1954, the Humboldt Mill began operations as an Iron Ore processing facility, and was converted to a gold processing plant during the 1980s. Various groups owned the site after closure of the gold operation. Eagle purchased the Mill in 2008 and invested more than $280 million to clean up historic mine waste and refurbish the plant (see flowsheet in APPENDIX). This paper will overview the ramp-up of the operation, and discuss some specific areas that went well and some that could have gone better during the design phase. HIGH LEVEL DESIGN CRITERIA Coarse ore arrives from the mine and is stored in a building with a capacity of 10,000 tonnes. Ore is crushed in three stages to a final product size of 100% Passing 12mm. Crushed ore is conveyed to the mass flow fine ore bins, which have a live capacity of 3000 tonnes. Crushed ore is fed to two parallel 900 HP ball mills, charged with 3” high chrome grinding media, and ground, in closed circuit with hydrocyclones, to a p80 of 110 microns in the flotation feed. Soda ash is added to the mills based on process water hardness. Cyclone overflow passes to the bulk conditioner where Sodium Isopropyl Xanthate (SIPX) and Methyl Isobutyl Carbinol (MIBC) are added. The slurry is pumped to the rougher bank for bulk flotation. Rougher concentrate is fed to a 500HP vertically stirred regrind mill and is ground to a p80 of 50 microns, using 5/8” high chrome balls. Rougher tailings report to the tailings thickener. The regrind cyclone overflow is sent to the single stage cleaner bank followed by two scavenger banks. The cleaner concentrate is pumped to the copper-nickel separation circuit. Cleaner tailings report to the tailings thickener. In the copper-nickel separation circuit, the pH is raised to 11.5 and a copper concentrate is recovered from the bulk cleaner concentrate in two stages, namely the copper roughers and the copper cleaner columns. The concentrate from the copper flotation columns is the final copper concentrate. The tailings from the columns return to the head of the copper-nickel separation. The nickel concentrate is the copper rougher tailings stream."

Jan 1, 2018

By Joseph T. Coe, Alireza Kordjazi, Michael Afanasiev

Cross-hole sonic logging (CSL) is a common quality assurance measure for the evaluation of the structural integrity of drilled shafts. The results of CSL can be supplemented by a set of tomographic images generated by cross-hole tomography (CT). Although the same access tubes, sources and receivers are used in both methods, CT has the advantage of providing a higher quality image of the possible anomalies in drilled shafts. Nevertheless, it has been reported in literature that the CSL and CT miss anomalies with sizes of smaller than 10 percent of the cross sectional area of the drilled shaft. This implies poor resolution despite the high-frequency of the stress waves utilized in these methods. This issue with resolution can be at least partially attributable to the fact that CT relies entirely on the inversion of the first time of arrival and ignores the information embedded in the rest of the recorded traces. This study examines the application of full waveform inversion (FWI) to generate a higher resolution image of the possible defects in drilled shafts from the same data used for cross-hole tomography. FWI is a wave-field method that aims to directly match the recorded traces with traces obtained from a numerical model of the domain. This has the benefit of avoiding the selection of the first time of arrival, along with increasing the resolution of the final image due to extracting more information out of the traces. Through a series of numerical simulations, synthetic traces were generated from a drilled shaft with defects of known mechanical properties, dimensions, and location. These traces were then inverted to evaluate the performance of FWI for structural integrity testing of the drilled shafts. INTRODUCTION The presence of construction defects can compromise the structural integrity of drilled shafts and negatively affect their performance (O’Neil 1991; Sarhan et al. 2002; O’Neil et al. 2003; Poulos 2005). Several non- destructive testing (NDT) methods exist that are currently used for the evaluation of the structural integrity of drilled shafts. Cross-hole sonic logging (CSL), cross-hole sonic tomography (CT), and thermal integrity profiling (TIP) are well-established and documented in the industry and practical manuals (Brown et al. 2010). NDT methods prevent the need for coring and excavation and are relatively fast and cost effective. Successful implementation of these techniques has also been reported in the literature (Branagan et al. 2000; Iskander et al. 2001; Mullin 2010; Johnson 2016).

Jan 1, 2019

By S. J. Page, W. E. Wallace, P. Bolsaitis, D. Eppelsheimer, M. J. Keane, J. Poston, J. Harrison

"Respirable-sized dust particles from a clay mine and mill were examined for aluminium and silicon content by scanning electron microscopy-energy dispersive X-ray analysis at incident electron energies of 5--20 keV. Most of the high silica content particles, those which had a silicon to silicon plus aluminium signal fraction, measured at 20 ke V, of0.9 or greater, showed a decrease in the silicon fraction of signal with decreasing incident electron energy, down to values of between 0.6 and 0,8 at 5 keV: this decrease was a function of particle size and composition. Simple models for silicon fractiol) of signal vs incident electron voltage suggest this behavour is due to a heterogeneous particle structure in which an aluminosilicate coating occludes the surface of a silica particle core. The coating survives incubation in a major component of pulmonary surfactant.INTRODUCTIONMINING and some other dusty workplace atmospheres are monitored for respirable dust and quartz dust for purposes of occupational health protection, respirable quartz dust being a known cause of pulmonary disease. Respirable quartz exposure data are acquired also for epidemiological research on the correlation of pulmonary disease prevalence with respirable dust composition and concentration. For these purposes quartz content often is measured on collected dust samples by X-ray diffraction or in spectroscopy. Scanning electron microscopy-energy dispersive X-ray analysis spectrometry (SEM-EDX) is also used. The first two methods measure the bulk composition of a multi-particle dust sample; SEM-EDX measures the elemental composition of single ·particles. These methods as typically applied, including SEM-EDX with a 20-30 kilo-electron volt (keV) electron beam accelerating potential, do not distinguish homogeneous distribution of impurities in a particle from possible heterogeneous surface distribution. These measurements of quartz content are not always accurate predictors of the prevalence of dust-induced disease (ROBOCK and BAUER, 1990), which implies that the biologically available quartz surface may not be equivalent to conventionally measured quartz content of respirable dust in some exposure settings. Using a minor modification of conventional scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) protocols on samples of settled and airborne dust from a clay mine and mill we have detected heterogeneity with depth for aluminium impurity in high silica content particles, indicating that some of the quartz or 'free silica' respirable particles of the dust are aluminosilicate occluded. Coatings were not removed by incubation of the dust in a surrogate pulmonary hypophase surfactant fluid."

Jan 1, 1990

By O Salisbury

Ingress of air into the longwall goaf environment needs to be managed appropriately to reduce the risk of creating a spontaneous combustion event. The maingate goaf edge is an area of particular concern in this respect, as air often penetrates for some distance into the goaf along this region inbye of the longwall face. Since the flow rate in this part of the goaf is also quite low, an opportunity exists to disrupt the air pathway by implementing a barrier to the airflow. Previous attempts using plugs made from an assortment of materials have resulted in varying degrees of success. More recently, Narrabri Coal Operations (NCO) has introduced the use of a chemical foam that is mixed with nitrogen to produce a standing barrier with the consistency of shaving cream. The implementation of this practice has consistently proven to be very effective for reducing the oxygen concentration along the maingate goaf edge by systematically retreating the foaming unit with the longwall. This paper presents how the foam is applied in the underground goaf environment to prevent oxygen ingress and uses results from gas monitoring to confirm the foam effectiveness.

Oct 12, 2022

By Gordon G. Bentle, W. P. Fishel

GREINER, Marsh, and Stoughton1 have reviewed the literature in a monograph on the iron-silicon system. The lack of agreement among the various studies may be due to the difference in the purity of materials in some cases. The results of the X-ray method indicate only a general rather than a specific limit of the y loop. The iron-titanium system was investigated by Roe and Fishel,' whose results are used in determining the iron-silicon-titanium y loop. The literature indicates that no study has been made thus far of the iron-silicon-titanium system in the y loop region. Experimental Procedure The alloys were made from Armco iron, 99.86 pct Si, and 98.5 pct Ti. The titanium contains 1.07 pct Fe. The Armco iron contains 0.01 pct C, 0.005 pct Si, 0.02 pct Mn, 0.006 pct P, 0.01 pct S, and 0.04 pct Cu. A dilatation sample of Armco iron was prepared in the same manner as were the other samples. Several dilatation runs indicated that Ac3 begins at 905°C and ends at 910°C, which compares favorably with the study of Wells, Ackley, and Mehl' employing specially purified iron. All alloys were melted in an induction furnace in Alundum crucibles and were top poured into baked core sand molds. The ingots weighed about 600 g as cast. Dilatation samples of 4 in. by % in. diam were taken from the bottom end of the ingot, from which turnings for analysis were taken. Turnings from each end of two of the samples indicated that the alloys possessed uniform silicon content. A hole was drilled halfway through each end of a 4 in, dilatation sample. A chromel-alumel thermocouple was inserted in each hole and the surrounding metal peened in to hold the thermocouple in place. Fig. 1 represents the dilatation apparatus. The heating unit is an Alundum tube wound with resistance wire; the dilatation tube is a McDanel combustion tube; the push rod is zircon; the dial gage is graduated in 0.0001 in. and was vibrated to prevent sticking. A blank run over the temperature range of interest gave no significant dilatation. The thermocouples were attached to a multiple recording micromax which indicated the temperature at each end of the sample at 35 sec intervals. A Lindberg control unit governed the rate of heating of the furnace, and lowering or raising the

Jan 1, 1957

By Francisca Tapia, Jorge Blázquez, Paulo Couceiro, Patricio Vergara, Luis Manriquez, Luis Martínez, Juan Navarro

Efficient energy transmission is critical for effective rock fragmentation in open-pit blasting. However, in zones with highly fractured or soft rock, mismatches in acoustic impedance between the explosive and the rock can lead to significant energy loss. These mismatches reduce fragmentation efficiency and, when energy input is increased to compensate, can trigger unintended side effects such as NOx fume generation. This paper presents a novel methodology that integrates the Fragment Size Energy Fan model with acoustic impedance theory to dynamically optimize explosive energy delivery. A redefined impedance formulation captures volumetric energy transfer and enables the calculation of a Rock Impedance Factor (RIF), calibrated through non-linear regression. To operationalize the model, rock impedance is estimated using the X-4Traits Model—a meta-learning algorithm that interprets Measurement While Drilling (MWD) data from both autonomous and manually operated drills to produce high-resolution, spatially distributed impedance maps. The methodology was calibrated and applied at Minera Escondida Limitada (MEL), using data from over 218,447 blastholes and 526 blasts. Two case studies illustrate its application: Expansion 1 demonstrates improved fragmentation consistency and a 10.7% reduction in powder factor by aligning explosive energy with local impedance variations; Expansion 2 highlights the model’s utility in managing NOx emissions in fractured zones by optimizing energy distribution and confinement without compromising fragmentation. This impedance-based framework provides a robust tool for improving fragmentation outcomes, optimizing energy use, and enhancing control in geologically variable blasting environments.

Jan 26, 2026

By J. Griesel, P. H. F. Bouwer, K. Bisaka

Transalloys produces 160 000 tons of SiMn per annum from five AC submerged-arc furnaces. The lime-ore melt from two AC open-arc furnaces is contacted with SiMn to produce 50 000 tons of medium carbon FeMn per annum. Metallics in the slag are reclaimed in a jigging plant, which has been in operation since 1999. The flow of materials between the jigging plant and furnaces has been optimised. The amount of recycle slag in the feed of the SiMn furnaces has been decreased by more than 30% which still provides satisfactory stability of the furnace operation. The jigging plant has absorbed all the additional slag generated, to recover SiMn metal. A review of the raw materials used and operating parameters for SiMn production was also undertaken. Slag to metal ratios were decreased by more than 30% by reducing the slag recycle, removing magnesite from the recipe and introducing high-grade ore. Electrode penetration was improved by reducing coke levels and by utilising more reactive coal. The pitch circle diameter (PCD) was reduced to get a better operating stability on furnace no 5 using the MINSTRAL Control System. Energy consumption on the furnaces improved by more than 15% while SiMn production increased as a result by more than 18%.

Jan 1, 2004

By L. T. Isaacs, W. H. Traves

A numerical model for analysing the drainage of fill in mine stopes has been described. The model can be used to analyse the process of fill drainage in existing and proposed mine stopes. The validity and potential value of the model have been established by experience with a simpler, 2-dimensional numerical model and by testing the new model against the earlier model. The new model is more useful than the 2-dimensional model because it allows for heterogeneity of fill material within the stope - a factor that has been demonstrated to affect drainage characteristics significantly. The 3-dimensional model is also capable of predicting pore pressures and drainage rates at specific locations in the stope without the need to resort to 2-dimensional generalisations. Such information, integrated with relevant field data as they become available, will provide valuable mine planning information for the scheduling of filling operations and design of fill mixes

May 1, 1991

By Mark P. Meyer

During 1991 through 1993, the U.S. Bureau of Mines (Bureau) -Alaska Field Operations Center (AFOC) in cooperation with the Bureau of Land Management (BLM) -Arctic District Office and the State of Alaska, Division of Geological and Geophysical Surveys (ADGGS), conducted exploration, geological, geochemical, geophysical, mineral resource, and mineral potential investigations in the 6.7 million hectare Colville Mining District (CMD) study area. This mining district study area, located in northern Alaska, includes the Colville River drainage basin as well as 0.35 million hectares of the southern part of the National Petroleum Reserve in Alaska (NPRA). This investigation was conducted as part of the Bureau's continuing Mineral Land Assessment (MLA) mining district program. The Bureau's MLA mining district program is designed to provide reliable and comprehensive mineral resource information that supports mineral resource policy and land use decisions made by Congress and Federal land management agencies.

Jan 1, 2011

By George A. Hill

WE of the oil industry, devoted to freedom of initiative, free competitive enter- prise, and free American institutions, applaud, with one voice, affirmation by the President of the national will and purpose to preserve and to protect, against all aggressors, "our American way of life with our individual and national freedom." We subscribe utterly and completely to this guiding declaration and seek its further definition as applied to the oil industry. Fortunately for all, the policy of the Government, after adequate study and deliberation, has been given precise definition. The National Defense Advisory Commission, with its patriotic, highly qualified, and distinguished personnel, has unanimously agreed to and adopted twelve general principles governing national defense contracts and also fair labor standard requirements. The President of the

Jan 1, 1940

By R. N. Hunt

GEOLOGICAL and exploration work of the United States Smelting Refining and Mining Company are handled by the mines geological and the exploration divisions of a geological department under the direction of the chief geologist. The mines division at present includes, in Utah. a geologist in charge, resident at Bingham, assisted by a geologist stationed at each operation, and a small group of geologists resident at the Bayard unit, in New Mexico. The duties of the mines division include the mapping and delineation of the geology of the mines, direction of sampling and diamond drilling, and the periodic calculation of ore reserves. At Bingham an amount of underground drilling within the limestone and porphyry formations which are hosts to the ore bodies supplements and completes development by mine workings. At Bayard, five to seven drills are kept busy underground, and eight to twelve drills operate on the surface. The mines division men live at the mine and work in close co-operation with mine superintendents and foremen. Development work is discussed, initi-

Jan 1, 1948

By S. Khoshjavan

Separation of refractory rock phosphate (P2O5 = 11.5%) from the Dalir area, Iran, containing quartz, calcite and other impurities, by calcination and flotation processes has been successfully used to upgrade the phosphate values. Petrographic studies of this ore showed that collophanite was the major phosphate mineral and the main gangue minerals were calcite, dolomite and quartz. The results of characterization studies showed that the liberation degree of apatite occurred below the average grain size of 140 µm. Preliminary flotation tests were used to process the phosphate samples. Results of preliminary flotation tests showed that they don?t contain any desirable efficiency (grade or recovery) of P2O5. Calcination was the best process for preconcentration of this ore. In the desliming stage, about 14.4% of total P2O5 was removed. Encouraging concentrate grades were obtained after flotation with anionic and cationic flotation, successively. The reagent schemes that have been used in this study consisted of COCO-amine acetate and fatty acid as silicate and apatite collectors, respectively, as well as fuel oil and anionic poly acryl amid as promoter collectors. The optimum pH values for direct and reverse flotations of phosphate were 11 and 6, respectively. Experiments conducted using d80=140 µm deslimed fractions has yielded an acceptable grade of more than 30% P2O5 with a recovery of more than 62%. Finally, a laboratory flowsheet for the processing of Dalir refractory phosphate ore has been proposed.

Jan 1, 2011

By G. H. Cobb, J. L. Johnson, H. H. Heady

An infrared absorbance technique is described for analyzing anodic gases produced during the electrowinning of uranium , thorium , and rare - earth metals in molten fluorides . Typical components determined qualitatively in a gas sample are CO , CO₂ , CF4 , C₂ Fe , C3F8 , COS , CS₂ , and SiF4 . About 20 minutes are required to record and interpret the spectrogram , and report quantitative results for CO, CO₂ , CF4 , and SiF . The procedure is used for control during electrolysis .

Jan 1, 1964

By Daniel W. H. Su

A nearly 305-m- (1,000-ft-) wide sandstone channel was projected to run through the mid panel area of a 457-m- (1,500-ft-) wide longwall panel in a southwestern Pennsylvania coal mine. This sandstone channel was known to cause serious longwallface roof control problems in the mine?s B-panel area in 1998 and 1999; and most recently, it induced many large face cavities and caused a substantial production delay in the preceding panel. For the two B panels mined in 1998 and 1999, hydraulic fracturing of the massive sandstone was conducted to facilitate better caving, thus relieving cantilever compressive stress at the longwall face. Vastly improved longwall face condition was observed and four weeks of mining delay due to bad roof conditions were eliminated. The implementation of the hydraulic fracturing technique, results of underground observation and measurement, and results of numerical modeling were summarized in a paper presented in the 20th International Conference on Ground Control (Su et al., 2001). This article is a summary of the activities that took place during a four-month period (October 2011 through February 2012) at a Consol Energy longwall mine southwestern Pennsylvania to improve face conditions and safety of underground personnel during mining of the 457-m- (1,500-ft-) wide longwall panel. The elevated concern for safety was driven by adverse face conditions encountered while mining the preceding longwall panel. Many of the problems were attributed to a thick and massive sandstone channel. A joint task force consisting of coal operations engineering, Pennsylvania operations engineering and CNX Gas personnel was formed in August 2011, which recommended drilling four hydraulic fracturing holes along the center axis of the sandstone channel to reduce pressure and improve face conditions at the longwall face. To further provide detailed monitoring of the longwall face and to evaluate the effectiveness of the hydraulic fracturing program, the Longwall Visual Analysis (LVA) software (Hoyer, 2011) was installed in early December 2011 to track the face pressure and c

Jun 1, 2013

By D. J. Dollhopf

An overburden handling dragline operation was conducted at a strip mine near Colstrip, Montana. The objective of the demonstration was to determine the degree a dragline could mix overburden inhibitory zones during the spoiling process. In order to quantify the mixing process the overburden was: 1) scatter spoiled; 2) dump spoiled; and 3) spoiled in a normal manner. This demonstration was part of an effort to investigate means of reestablishing non-polluted hydrological systems in areas where surface mining directly impacts shallow ground-water resources. When inhibitory material constituted < 5% of the total overburden volume, such material was essentially not detectable in the resultant spoil pile. When inhibitory material exceeded 15% of the overburden volume it was always found in the resultant spoil pile, generally with a smaller extent, indicating partial dilution. Inhibitory overburden zones often reappeared at the base or top of spoil piles in the potential aquifer and root zones suggesting the need for selective placement procedures. Scatter spoiling did not appear to be significantly more effective than normal spoiling, however clump spoiling seemed to produce less mixing of inimical zones. Mining activity has reduced ground-water levels within 1600 m of the active pit. The aquifer which is developing in spoils appears to have similar confinement characteristics as those that existed in the premined aquifer. To date no definite trends have been observed concerning changes in surface or ground-water chemistry associated with mining.

Jan 1, 1978

By Marco A. Vera

"This paper investigates the froth function in flotation and the associated upgrading process. Flotation literature has revealed that one of the main functions of the froth phase is the cleaning of bubble-particle aggregates by rejection of entrained material. The cleaning and transport processes across the froth phase exert straining forces on these aggregates on their way up to the froth surface. These forces will impact on the recovery of bubble-particle aggregates.The grade at the top of the froth (TOF) is a parameter related to the quality of particles collected by bubbles in the pulp zone (true flotation). It has recently been demonstrated that TOF corresponds to the maximum practically attainable grade described by the recovery-grade (or enrichment ratio) curve. TOF lumps all the processes experienced by the bubble-particle aggregates before reaching the launder concentrate. This paper describes a methodology for quantifying flotation performance by means of the top of the froth sample - a touch of froth.INTRODUCTIONFroth flotation may be the most important mineral processing technique, but its theory is complex and is not completely understood even though many aspects have been studied and reviewed (Teague, 1998; Wills, 1992).Two distinct particulate systems prevail in the flotation process: a pulp phase and a froth phase (Figure 1). The pulp zone had been studied extensively; however, it is only recently that techniques to measure the froth zone performance have been developed (Contini et al., 1988; Falutsu and Dobby, 1992; Feteris et al., 1987; Seaman, 2002; Vera et al., 1999b).Flotation involves a number of mass transfer processes, occurring in the pulp phase and the froth phase. The formation of the froth and its subsequent removal are considered to be two important steps of the process. Phenomena that occur in the froth phase are known to affect flotation performance significantly (Cutting et al., 1981).Because the froth has a high free surface energy (as a result of the extensive interfacial surface between liquid and air), it appears thermodynamically unstable. The foaming is a dynamic balance, as new bubbles are added continuously from the pulp, while others disappear from the top. Under steady-state conditions, the volumes of added and subtracted air are equal (Booth, 1953)."

Jan 1, 2003

By T. S. Spicer

The relationship of coal characteristics to the principal types of firing equipment has been known to the coal combustion engineer, but is not as familiar a subject for purchasing agents, salesmen, consumers, and executives of coal-producing and consuming companies. This general survey of characteristics determined by standard laboratory tests, of major types of combustion techniques, and of the relationships between the two is directed toward the latter audience. It will also serve as a review for those actively engaged in the combustion of coal. Although the relationship of coal characteristics to the principal types of firing equipment is well known to the experienced coal combustion engineer, apparently there is need for a summary article on this subject. The author has received numerous requests for such a paper from purchasing agents, coal salesmen, coal customers and executives of coal-producing and consuming companies. Consequently, the scope of this paper will be directed to this audience, with the hope that it may serve also as a review to others actively engaged in the combustion of coal. The magnitude of this subject is so great that only a brief general treatise is possible. The author realizes that because there are so many special cases and exceptions to the generalities which follow, he is in jeopardy of contradicting himself. It is the hope, however, that the many references cited will prove valuable to those who wish to study the details excluded by necessity, due to space and time limitations. Hence, the characteristics of coals as determined by standard laboratory tests will be discussed; the major types of combustion techniques reviewed; and then the characteristics and firing will be related. CHARACTERISTICS OF UNITED STATES COALS The coals of the United States range from lignite to anthracite and each has its own general characteristics. The extensive coal fields of the U. S. are shown in Fig. 1 and the estimated reserve according to rank for each state is illustrated in Fig. 2. Coals may be classified according to rank as shown by Table I from the ASTM Standards on Coal and Coke, D-338-38.1 The basis of this classification is ac- cording to fixed carbon and heating value (Btu per pound) calculated to a mineral-matter-free basis. The high-rank coals are classified according to fixed carbon on the dry basis; and the low-rank coals according to Btu on the moist basis. Agglomerating and slacking (weathering) indices are used to differentiate between certain adjacent groups. While rank is not itself a characteristic it does signify certain characteristics that accompany a class of fuel. Anthracite, for example, immediately implies a hard, free-burning, smokeless coal of low volatile matter, usually having an ash of high fusibility. Coals may also be classified according to grade as described by ASTM Designation D-398-37.1 This quality classification is determined by size, calorific value, ash, ash-softening temperature, and sulfur. This type of classification is not used as extensively by the industry as the rank classification. Fig. 3 shows the heat value of different ranks compared to proximate analyses. Coals may also be classified by sizes, as shown in Tables IIA and IIB, and sizes can be on both top and bottom limits. If this is done, then the coal is called double screened; otherwise, either top or bottom sizes can be specified as a limit. Bituminous coal sizing varies from field to field and depends upon the market demand. The common sizes and their main uses are outlined in Table IIA. Anthracite is usually available in many sizes at the colliery, and Table IIB summarizes standard sizes and names. Although rank, grade, and size designations help identify and describe a coal in question, there still remain other characteristics such as indicated by moisture, free swelling index, grindability tests, etc. A bituminous coal information chart Table III) suggested for use in studying the available coals in a region, lists origin and chemical and physical characteristics. Even this more comprehensive list does not completely spell out all the characteristics of a heterogenous material like coal. For example,

Jan 1, 1961