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By Kenneth L. Rubow, Virgil A. Marple, Ye Tao

Techniques are being developed for measuring the mass concentration of respirable diesel exhaust particles found in underground coal mines. Studies have been conducted over the past five years to investigate size selective sampling techniques to measure the respirable mass concentrations of diesel exhaust and mine dust aerosol particles in underground coal mines. Results from these studies have been used to develop design and performance criteria for a personal diesel exhaust aerosol sampler. Three personal diesel exhaust aerosol samplers have subsequently been designed and evaluated in both laboratory and field settings. These samplers use size selective classifiers for the determination of the respirable mass concentrations of mineral dust and diesel exhaust particles. Their designs are based on the premise that diesel exhaust particles are predominantly less than 0.8µm while mineral dust is greater than 0.8 µm. One design, selected for field evaluation, consists of a 10 mm nylon respirable dust cyclone followed by a 0.8 µm cutpoint impactor and afterfilter. The cyclone removes the large nonrespirable particles while the inertial impactor stage, collects the mineral dust on an impaction plate and allows the diesel particles to penetrate to an afterfilter. The two sample fractions of the respirable particles (<0.8 µm and >0.8 µm) are gravimetrically analyzed to determine the concentrations of the diesel and mineral dust portions in the respirable coal mine aerosol.

Jan 1, 1991

By John A. L. Dr. Campbell, James W. Haskew, F. Hoy Lee, Elliott P. Dr. Doane

Emissions of particulates, unburned hydrocarbons, nitrogen oxides (NO[ ]) and carbon monoxide (CO) from diesel engines are of concern in mines, particularly underground mines. All these undesirable products except NOx are the result of incomplete combustion in the cylinders. Various approaches to achieving more complete combustion in diesel engines have included different fuel compositions, use of catalysts, fuel additives, engine modifications, and oxygen-enriched intake air. The present study shows that injecting minute quantities of primarily platinum group metal catalysts into the intake air of a Deutz/MWM D916-6 mine diesel engine substantially reduces emissions in the exhaust. The catalyst injection system, which was developed by National Fuelsaver Corporation (Robin. 1981), transfers catalyst compounds in solution to a stream of air bubbles by a process called Bubble Fractionation (Lemlich et al.. 1966, 1968. 1970). The amounts are so minute that concentrations in the engine exhaust should be well below OSHA/NIOSH Time Weighted Average (TWA) exposure limits at steady state, a fact that was confirmed by analysis of collected particulates in the exhaust. When the catalyst injection was used along with a pleated paper filter to remove exhaust particulates, the filter operating life was shortened greatly. Therefore, this system is not recommended for use on diesel engines equipped with a water scrubber and a filter. It does offer a practical and relatively economical way of reducing exhaust emissions from other diesel engines, such as those in outby mine service

Jan 1, 1995

By G. Fehr, B. B. Panda, R. Bansberg, K. Arnold, T. Freiman

To evaluate the potential for process solutions to contaminate groundwater outside of the area of the Oxide Pit, it is necessary to predict the ultimate maximum pit lake elevation once pit-related mining activities have ceased. A water balance model was developed based on the existing pit geometry, the groundwater flow equation, and assumed hydrologic input parameters. The model assumed that at any point in time, total inflow into the system (i.e., direct precipitation, surface water and groundwater) minus outflow from the system (evaporation from the lake surface) was equal to the change in the pit water volume. The pit lake depth over time was predicted by assuming a succession of steady- state water balance conditions over short time increments. An analytical method using a spreadsheet and computer model was employed in this study to model the filling of the lake in the Oxide Pit. A sensitivity analysis was performed to evaluate uncertainty associated with the input parameters in the model. The sensitivity analysis indicated that the model was most sensitive to values of precipitation and evaporation and to the static water table.

Jan 1, 2003

By F. Michael Wahl

With the exception of reports on commercial deposits of kaolin, fuller&apos;s earth, and other specialty type clays, there is little published information on the extent, properties, and potential uses of the clay resources of Florida. Recent studies by the Florida Bureau of Geology in cooperation with the University of Florida and the U.S. Bureau of Mines have proven the existence of two extensive Miocene clay deposits, one in peninsular Pinellas County and the other in southeastern Charlotte County. Drilling and subsequent testing of the clays from these deposits indicate their potential for economic development. Both deposits consist of montmorillonite type clays, have an average thickness of 25 to 35 feet, and are overlain by unconsolidated Pleistocene sediments. Preliminary firing tests indicate that the clays from Pinellas County are a potential raw material for lightweight aggregate production. The clay has good bloating characteristics across an acceptable temperature range with a resultant aggregate density of less than 1.00 specific gravity. The clays from Charlotte County have poorer natural bloating characteristics but might well be used after treatment or with additives. The economic potential and locations of both deposits emphasize the need for locating similar clay resources in the state that might have economic potential so that land use planning and subsequent urbanization will not prohibit their development.

Jan 1, 1972

By J. Peck, M. J. Scoble, C. Hendricks

This paper is based on field studies in North American surface mines. The work involved the adaptation of microprocessor-based instrumentation to monitor various operating parameters on-board rotary blasthole drills and mining shovels. Following a review of instrumentation and monitoring methodology - drawing on experience gained under field conditions-the paper will focus on the application of monitoring technology within the framework of an Integrated Equipment Monitoring System. Such a system will permit real-time performance evaluation of key equipment involved in surface mine production. Drill performance monitoring has been demonstrated through work to date, to provide significant input into blast design, reserve estimation, mine planning and production control processes, through an improved facility for ground characterization. Monitoring excavation equipment has been proven valuable in assessing how effectively the input from drill monitored data has been used in the evolution of blast designs. This specifically refers to assessing blast efficiency through measuring associated levels of excavator performance in relation to muckpile characteristics. The medium-term goal of equipment instrumentation and monitoring has been to assist mines in optimizing the overall rock breakage and handling process. Based on the reported results, this has been accomplished. Long-term efforts now concern using a greater understanding of equipment performance and response to varying operating conditions as a foundation for the implementation of mining automation.

Jan 1, 1993

By H. Wilcox, M. Prichard, Y. P. Chugh

Environmental considerations related to the disposal of coal combustion byproducts (CCBs) and the impacts of deforestation associated with the harvesting of timber for utilization as roof supports in mines should become more severe in the future, as landfill space and suitable timber reserves become more scarce. To help address these concerns, lightweight artificial supports, such as post and crib elements, that use large percentages of coal combustion byproducts as aggregate have been developed for use in underground mines. These structural products show equal or better engineering characteristics than timber, and they have the potential to replace timber support in underground mines. CCB-based ultralight structural material (ULSM) has also been developed and commercialized for use in the construction of ventilation stoppings in underground mines. The bulk densities of these blocks range from 0.40 to 0.64 g/cm3 (25 to 40 lb per cu ft) with more than 75% CCBs. Efforts are also given to develop and demonstrate large volume CCB-based subgrade improvement technique for road construction. Soil treated with SIUC fluidized-bed combustion (FBC) fly ash developed an immediate bearing value exceeding 25% with a swelling strain of less than I %, which is greater than untreated soils, and met Illinois Department of Transportation (IDOT) standard specifications. In this paper, development procedures, engineering characteristics and beneficial uses of CCB-based structural products are given.

Jan 1, 2002

By Steven H. Brown

Ore bodies which were once uneconomical to mine by conventional methods such as tunneling or open pits, have become attractive due to the development of nonconventional techniques, involving considerably less capital expenditure. Technologies such as uranium solution mining or in-situ leaching, have enabled commercial scale mining and milling of relatively small ore pockets of lower grade, and may make a significant contribution to overall U.S. uranium supplies during the next 20 years. Commercial size solution mining production facilities have operated since late 1975. Solution mining involves the pumping of ground water, fortified with oxidizing and complexing agents into an ore body, leaching and solubilizing the uranium in-situ, and then pumping the solutions to the surface where they are fed to a processing plant. Processing involves ion exchange, precipitation, calcining, and packaging operations. This paper presents an overview of the solution mining process and the health physics monitoring programs developed over the last four years at several production facilities as a result of the radiological character of these processes. Although many radiological aspects of the process are similar to that of conventional mills, conventional-type tailings as such are not generated. Some special monitoring considerations are presented which are required due to the manner in which radon gas is evolved in the process and the unique aspects of controlling solution flow patterns underground. An overview of the major aspects of the health physics compliance and monitoring programs that have been developed are discussed.

Jan 1, 1981

By D. Raicevic

The presence of residual uranium and other radionuclides in the uranium mill tailings are posing a continuous health concern to the surrounding environment. The slow generation of sulphuric acid from residual sulphide minerals is the cause of persistant dissolution and discharge of many metallic components of the tailings. The most effective long term solution to these problems would seem to be to produce chemically stable tailings. This paper describes two possible answers to the objective: (1) Removal of radionuclides and pyrite from tailings by mineral dressing techniques; some 60 - 68% of the residual uranium, 70 - 75% of the radium, 60 - 65% of the thorium and 95 - 98% of the pyrite have been rejected from the Elliot Lake tailings. The decontaminated tailings contained 0.003% uranium, 50 - 60 pCi/g radium226, 0.01% thorium and less than 0.1% sulphur as pyrite. (2) Preconcentration of radionuclides and pyrite by beneficiation from Elliot Lake ores prior to leaching; applying this approach about 97% of the uranium, 95% of the radium, 92% of the thorium and 98.5% of the sulphides were concentrated in a radionuclide and pyrite concentrates comprising 25% and 8% of the ore, respectively. The preconcentration tailings (waste) produced contained 0.004% uranium, 20 - 25 pCi/g radium226, 0.005% thorium and less than 0.1% sulphur as pyrite. Economic and environmental advantages of both approaches and the leaching of the concentrates are also discussed.

Jan 1, 1980

By Greg R. Wheeler

Few members of the general public have a clear understanding of mineral resources. Most people do not know how minerals are mined or why they must be extracted from many diverse locations. Many people acquire knowledge of mineral development from mass media sources with incomplete details or obvious anti-mining bias. The California Mineral Education Foundation was formed in 1991 to provide educational opportunities for the public and industry. There have been major changes in earth science teaching requirements for kindergarten through 12th grade (K-12) curricula since the passage of California Senate Bill 813 in 1983. Model graduation standards, curriculum standards and the state science framework mandate substantial coverage of geoscience topics. The California State Commission on Teacher Credentialing has completed changes in multiple subject and single subject science credentials which will require more geoscience preparation for all teachers. The need for pre-service and in-service education in geoscience is at an all time high. Teachers must have continuing education to maintain their credentials and many are now seeking information in geoscience. The California Mineral Education Foundation designed and conducted the California Mineral Education Conferences held in August 1991 and 1992. The conferences involved lectures and field trips on mining geology, environmental problems and political concerns. Master teachers were employed to share how they get across mineral resource concepts in the classroom. Ninety-six percent of the participants stated that they had changed to a more positive perception of mining after taking the three day course.

Jan 1, 1995

By Frank F. Aplan, Edward C. Dowling, Richard R. Klimpel

Several series of time-instantaneous samples were taken on a cell-by-cell basis in the flotation circuits of the Pinto Valley, AZ copper concentrator. These samples were used to calculate mass flow rates throughout the circuit using standard, deterministic metallurgical formulae and also a variety of more statistically oriented techniques. Because of the magnitude of the errors associated with the individual cell samples, the standard metallurgical formulae are not sufficient. Consequently, it is necessary to utilize some type of statistical technique capable of distributing the individual cell sample errors in such a way so as to provide a physically useful mass balance for the entire circuit. This paper explores the use of linear and least squares programming as one technique to providing credible mass balance calculations. For linear programming this was done by distributing the error using two different criteria involving specific linear programming formulations: least absolute sum minimization (which assumes an underlying double exponential distribution error structure) and minimax (which minimizes the maximum absolute deviation and assumes an underlying rectangular distribution error structure). These results were then compared to the more standard formulation of minimization of the sum of least squares which assumes an underlying normal distribution error structure. The least absolute sum approach was particularly attractive due to its simplicity of use and the ease in which repetitive calculations can be done with no user intervention.

Jan 1, 1990

By S. K. Das

A detailed strata-mechanics investigation and examination was carried out in the E2 Panel (ML-II/7) of the XVI Bottom coal seam, which is located in the Moonidih Colliery of B.C.C.L., Jharia coalfield, India. Above this panel, the XVI Top coal seam was previously worked out by a longwall panel. Based on intensive field study and on experiments in a number of longwall panels located within various Indian coal mines, the actual behavior of the coal roof strata was evaluated and new strata-mechanics concepts around the longwall panels were developed. These concepts resulted in new methodologies concerning the behavior of roof rocks, caving characteristics, etc. within longwall panels and in the area of strata mechanics. Based on these new strata-mechanics concepts, a very simple, but realistic, model was developed to determine the optimum capacity of the powered supports. This model considered the combined loads resulting from the detachment of strata and composite layer blocks from the face and, also, loads due to the deflection of strata and composite layers situated above the detached roof rockmass. This formula, along with the other related formulas by the author, prompted the determination of the optimum capacity requirement for the powered supports to be used in the XVI Bottom coal seam, located under the worked out area. This new concept in strata mechanics and capacity requirements of the powered supports in a longwall face may be an aid to Mining Engineers.

Jan 1, 1997

By C. Douglas Lee

This case study describes the work done at the University of Arizona on the development of a computer mine model for an irregularly shaped and spotty ore deposit. The purpose of the work was to develop techniques for modeling any highly irregular deposit, for which the regular 3D fixed block model is not well suited. The deposit contained complex geology consisting of sedimentary beds that had been faulted, thrusted, and intruded by igneous rocks (see Fig. 1). The physical dimensions of the modeled ore body were 1067 m (3500 ft) along the N-S direction and 914 m (3000 ft) along the E-W direction. Topographic relief in the modeled area was approximately 274 m (900 ft). The highest grade of ore was found near the surface with mineralization extending down to approximately 152 m (500 ft) below. Using a fixed bench height of 12 m (40 ft), the model required 25 levels with the highest elevation being at 1286 m (4220 ft). Fig. 2 shows a cross section of the developed computer model of the ore deposit. The particular modeling approach selected for this deposit was the 3D irregular block model.* This meant that only the dimension of bench height was fixed at 12 m (40 ft). Irregular size blocks in the form of polygons were adopted in the model to describe the ore zones and geologic contacts. The following sections of this chapter describe some of the techniques used in modeling.

Jan 1, 1979

By H. Wu, V. Izaxon

Intensive ventilation is required during the excavation of a mine opening and the subsequent exploitation of the mineral resources. The exchange of heat between the ventilation air and the rock mass has a major influence on the thermal regime of a mine, especially in the initial segment of the airway. In frozen ground, heat flow into the rock mass from the ventilation air can result in the eventual thawing of the permafrost, which can result in roof-rock instability. This paper presents a mathematical analysis of the dispersion process of ventilation-induced heat by thermosyphons placed on the surface of the mine. The principal uses of thermosyphons in the Arctic are to reduce the ground temperature to prevent potentially unstable permafrost from thawing and to increase the bearing strength of the material. The mathematical model of the physical problem, generally known as "the Stephan problem," takes into account the varying thermo-physical properties of air and the frozen and thawed rock mass, the thermal properties of the freeing fluid in the thermosyphons and the phase change of water. Finite-difference techniques were employed to determine the temperature isotherms around the thermosyphons. It was found that two rows of thermosyphons on a 10- x 10-m grid provide an acceptable design spacing for reducing the ground temperature around the mine airway.

Jan 1, 1997

By E. C. Grunsky

Spatial auto- and crosscorrelation assessment of variables can be carried out using quadratic function estimates. From the function estimates, multivariate relationships of the variables can be determined in the form of spatial factors. The calculation of the spatial factors requires computation of the corresponding amplitude vectors from the eigenvalue solution. This vector reflects the relative amplitudes by which the variables follow the spatial factors. Instability of some of the eigenvalue solutions requires that caution be used in interpreting the resulting factor pat- terns. A measure of the predictive power of the spatial factors can be determined from the auto- correlation coefficients and squared multiple correlation co-efficients which indicate which of the variables are significant in any given factor. The use of unconditional simulations provides a basis by which geological variables of varying spatial ranges can be modelled using the spatial factor technique. Simulations were generated for a variety of ranges and variables were created that form single or multiple combinations of the spatial patterns. The success of the spatial factor technique depends on the amount of associated noise, and the size of the neighbourhood relative to the spatial range of the variable. The predictive power of the components is dependent on these two factors. Problems with collinearity of variables can result in unrealistic eigenvalues and result in the failure of the method. Application of this method to spatial data in mineral exploration can assist in outlining spatially continuous zones of alteration associated with mineralization.

Jan 1, 1989

By R. F. McFarlin, H. E. El-Shall

Since its inception, the Institute of Phosphate Research has examined every promising proposal in order to find an economical, practical and environmentally sound method of dewatering phosphatic clays. The in-house development of the FIPR/DIPR process (DIPR = Dewatering Instantaneously with Pulp Recycle) would appear to answer that quest. When small amounts of fibrous materials are mixed with clay slurries and flocculent, rapid dewatering occurs. Clay solids contents of 20 to 25% can be attained by simply rolling the clay mass down an inclined screen. Higher solids (>40%) are reached by physically pressing the cake; e.g., with a belt press. Because mechanical pressing devices are too expensive for phosphatic clay treatment, FIPR has developed the "sandwich" method of simultaneously dewatering the phosphatic clays and reclaiming the mine cut, as well as a second alternate, the "median strip" proposal. Economic projections of these bench-scale alternates suggest that the FIPR/DIPR process should be no more costly than present practice, when credit is given for the simultaneous reclamation accomplished.

Jan 1, 1993

By Daryl L. Gusey, John T. Neubert, Matthew A. Sares

The Colorado Geological Survey completed an inventory of environmental degradation associated with abandoned and inactive mines on National Forest System lands in Colorado. In the course of the inventory, areas with naturally occurring acid rock drainage were also noted. Approximately 18,000 abandoned mine- related features were inventoried, including about 900 features that are considered significant enough environmental problems to warrant further investigation. Water quality data, such as pH and conductivity were gathered at all features where water was present, such as draining adits, seepage at the toe of dumps and tailings, and standing water in shafts. Samples were taken where field tests indicated low pH andlor high conductivity, including several areas with naturally occurring acid rock drainage. Samples were analyzed for dissolved and total metals, and for selected anions. All mine locations and data collected by the field geologists were entered on field forms and, subsequently, into a computer database and GIS format. With the information provided by the inventory, the Forest Service, in cooperation with other agencies, has been able to prioritize abandoned mines for reclamation. In most cases, cleanup is approached on a watershed basis. Mines in priority watersheds have been selected for reclamation first. Watersheds where studies prerequisite to cleanup are occurring include the upper Anirnas River, Willow Creek (tributary to the upper Rio Grande), Chalk Creek (tributary to the upper Arkansas River), the Uncompahgre River, and the Alamosa River. During the inventory, evidence of naturally occurring water quality degradation was found in areas where little or no evidence of mining activity exists. These areas include the upper Alamosa River, the Middle Fork of Mineral Creek, Peekaboo Gulch, and Handcart Gulch. Water from these natural sources has been found to significantly exceed Colorado water quality standards for several metals.

Jan 1, 2000

By S. Ostap

INTRODUCTION Paradoxically, it has been found that the people who are the most aware of the origin, mineralogy and composition of bauxite are also the people who are the least aware of how bauxite composition affects its treatment by the Bayer process. These people are the exploration and mining geologists normally associated with aluminum producing companies. The purpose of this paper is to give some idea of how the concentration and physical nature of the different minerals found in bauxites affect the operation of the Bayer process used to extract their alumina content. The bauxites we will consider here will be only the tropical bauxites such as occurring in Jamaica, various countries in South America i.e. Guyana, Surinam, Brazil, African bauxites, Malaysia and in Australia. When we speak of the Bayer process, it will be the North American version of the Bayer process using low caustic concentrations and bauxite digestion temperatures varying between 130° to 250°C. TABLE 1 shows the minerals and elements of interest occurring in tropical bauxites. The minerals and elements listed in the table do not by any means represent all of those identified in bauxites. Using mass spectrographic analysis on six bauxites from different geographic locations, we managed to identify between 50-60 different elements. Fortunately, only about 13-14 of these elements possess the necessary chemical properties to be able to accumulate in caustic Bayer solutions. The remainder are either not attacked, or form insoluble reaction products with some main liquor component, i.e., hydroxide, aluminate or carbonate, or reprecipitate with alumina trihydrate during the precipitation stage.

Jan 1, 1984

By R. P. King

INTRODUCTION It is now 21 years since Wiegel and Li published their paper on a random version of Gaudin&apos;s model for the mineral liberation phenomenon (Wiegel and Li, 1967). This paper was to revitalise interest in North America in one of the most fascinating, difficult and important problems in the field of theoretical mineral processing. Gaudin had many years previously (Gaudin, 1939) already presented a penetrating analysis of the problem and Wiegel and Li based their analysis very closely on the Gaudin model but they realised that the indeterminate geometrical structure of mineralogical materials demanded that only probabilistic models could provide the necessary quantitative information when working with real materials. They proposed and solved a randomised version of the Gaudin model but retained the essential geometrical simplicity of cubic mineral grains and a cubic fracture pattern. Although their model met with some limited success it was to be superseded in due course. During the 1940&apos;s and 1950&apos;s the classical field of geometrical probability spawned the mathematical discipline of integral geometry and as early as 1965, Bodziony (1965, a,b) showed that the techniques of integral geometry could accommodate the problems associated with the indeterminate nature of the geometrical mineralogical structure, provided that these were couched in probabilistic terms. In particular he showed that the quantitative description of the comminution process and that of liberation could be decoupled with the resulting economy of effort. This idea has profoundly influenced the course of research in liberation theory and has greatly facilitated its application and the measurement of liberation in a practical way. Bodziony demonstrated also that any theory that required the specification of the mineral "grain

Jan 1, 1989

Stope width was controlled around 3.5 feet for the narrow high grade vein system at Hollister Gold Mine. Without top access, backfill material was pumped from bottom access up into stope through a series of pipes after ore had been slushed out in each mining cycle. Backfill material was changed from one layer of low strength concrete plus one layer of high strength concrete cap to one layer of low strength cellular concrete plus one layer of high strength concrete cap. Backfill cost was cut down to 30 percent during this process. To reduce the steel concrete pipe set up and tear down time which was about 2 to 3 shifts in each mining cycle, steel pipes were left in man-way between mining cycles. Cellular concrete was firstly introduced into backfilling stopes at Hollister mine in Nevada Mining. This process including concrete pump selection, pumping pipe selection, material mixing, material mechanics and quality control were fully covered in this paper. CUT AND FILL MINING CYCLE The most flexible mining method, cut and fill (Figure 1), was used to mine the high grade, narrow steep vein system on this Northern Nevada property which is located eighty miles north east of Winnemucca. Without top access, stopes were accessed through two man-ways on each end, in which people travel ladders and material transport slides were set up (Figure 2). Each mining cycle was called a cut, from 6 to 8 feet high. Overhand sequence was used. Mining cycle started with drill and blast the middle portion of the stope, then expanded towards both ends. Broken ore was slushed into mill hole located at middle of the stope and then mucked out through bottom access into main haulage. Stope length was about 300 feet, which was restricted by slushing distance. Timber man-ways and mill hole would be raised and established for backfill and ready for the next mining cycle.

Jan 1, 2011

By G. H. Lewis, C. L. Krcil, N. S. Harding, D. E. Havekotte

INTRODUCTION Limestone injection work was completed in a 440-kW (1.5-million Btu per hour) pilot-scale combustor in preparation for a 50,000-kg/h (110,000-lb per hour) industrial steam boiler limestone injection test program. The main objectives were to: (1) identify the important variables that affect sulfur capture, (2) determine the maximum SO2 removal, and (3) determine the effect of limestone addition on furnace operability and heat transfer. A more detailed report is given by Lewis et al. (1985). The test program was divided into two phases. The objectives of Phase I were to determine the important variables that affect SO2 reduction and to investigate the effect of limestone addition on combustor operation and heat transfer surfaces. The objective of Phase II was to determine, using only the important variables identified during Phase I, the conditions that resulted in the greatest sulfur dioxide reduction. Phase I Test program Using one limestone, five variables were identified as having an effect on SO2 reduction. These are noted with their respective ranges: heat release rate [103 to 166 kW/m3 (10,000 to 16,000 Btu per hour-cu ft)], Ca/S molar ratio (0 to 3), flue gas oxygen concentration (3% to 5%), additive particle size [90% -150 µm (-100 mesh) and 90% -45 µm (-325 mesh)], and burner stoichiometry (SR = 0.75 and >1.15). A 2.3% sulfur northern West Virginia coal, pulverized to a nominal grind of 70% -75 µm (-200 mesh), was burned for the tests. The limestone used was obtained from a Maysville, KY, quarry and contained 51.75% (wt) CaO. An 11-run statistically designed program (plus three duplicates) was used to screen the five variables. The effect of limestone injection on the combustor heat transfer surfaces was determined by comparing the heat transfer rates through a slag panel and fouling probes during periods with and without limestone injection. Combustor operation was determined by noting any operating problems that occurred during the tests. Test procedure After furnace wall temperatures had stabilized at operating conditions, heat transfer surfaces (slag panel and fouling probes) and the convection section were blown clean, and a four-hour test was begun. The

Jan 1, 1987