Clean Coal Ash Content Research Articles

アジア大での環境負荷軽減と石炭需給の安定化 ジグ制御システムの開発とインドネシアのオンビリン炭鉱への適用

In this study, a control system incorporating the know-how of the skilled operators using fuzzy logic is applied by using on-line ash monitors conventionally employed for product coal quality control as a jig control system sensor to a coal preparation plant of the Ombilin Mine in Indonesia. The computer simulation experiments demonstrate that the response can be improved by means of modification of the fuzzy rules. Based on the results of the simulation experiments, it is clear that the present proportional/integral-operation fuzzy control system is effective in mitigating the large dead times of 60 seconds due to the sampling interval of the ash monitor, and also in mitigating the parameter variations due to the properties of raw coal. The experimental results show that the coal washery jig control system developed with the use of the PI fuzzy control system is capable of controlling the clean coal ash content to within a ± 3% range of the target ash content of the clean coal.

Application of response surface methodology and central composite rotatable design for modeling the influence of some operating variables of a Multi-Gravity Separator for coal cleaning

In this study, the application of response surface methodology (RSM) and central composite rotatable design (CCRD) for modeling the influence of some operating variables on the performance of a Multi-Gravity Separator (MGS) for coal cleaning was discussed. Four operating variables of MGS, namely drum speed, tilt angle, wash water and feed solids were changed during the tests based on the CCRD. In order to produce clean coal with MGS, mathematical model equations were derived by computer simulation programming applying least squares method using MATLAB 7.1. These equations that are second-order response functions representing ash content and combustible recovery of clean coal were expressed as functions of four operating parameters of MGS. Predicted values were found to be in good agreement with experimental values ( R 2 values of 0.84 and 0.93 for ash content and combustible recovery of clean coal, respectively). This study has shown that the CCRD and RSM could efficiently be applied for the modeling of MGS for coal and it is economical way of obtaining the maximum amount of information in a short period of time and with the fewest number of experiments.

Effect of operating variables on the performance of dense-media cyclone — a critical study

In a coal washery, two or more dense-media cyclones (DMCs) are normally connected in parallel to form a bank sharing a common feed pipe. Depending on the operating and design variables and on the wear and tear of the equipment, the efficiency of the cyclones would vary. Efforts were made at Tata Steel’s R&D Dept. to evaluate the efficiency of a bank of cyclones at one of its washeries. A mathematical model for the cyclones was developed using the generalized distribution curve. Co-relationships were then developed relating the coefficient of separation (showing the separation efficiency) and the Ep to the design and operating variables of the cyclones. Lower feed rates and smaller spigot diameters were found to improve the separation efficiency of the cyclone. This paper discusses the modeling and optimization studies carried out with the cyclones and the recommendations made for subsequent improvement. On implementation of the recommendation, the clean coal yield improved by 2% for the same ash content in clean coal.

Development of a new coal washability index

A new coal washability index, termed as ‘near gravity material index (NGMI)’, has been developed based on the sink-float data. This new index incorporates the effect of ash distribution in the near gravity material at various specific gravities of separation. The optimum specific gravity of separation of a particular coal may be determined by plotting NGMI as a function of various specific gravities of separation or the desired clean coal ash content. The concept and the method of calculation of this index have been discussed in detail. Using some published float-sink analytical data, a quick comparison of the washability characteristics of several different coals is demonstrated utilizing the NGMI curves for these coals.

Behavior of Coal Particles in Column Flotation.

The behavior of Datong coal particles in a flotation column was investigated in a batchwise operation using a gas distributor evolving uniform bubbles by varying the superficial gas velocity and column height. The value of superficial gas velocity was controlled at 0.66 or 1.99 cm s–1.The time course of ash content in floats was measured when column height was 1.85 m. The ash content in clean coal was larger for higher superficial gas velocity. The hydrophobicity of coal particles recovered from the top of the column was evaluated by means of a film flotation method. Hydrophilic particles having the critical wetting surface tension of particles, γc, greater than 60 mN m–1 floated well for higher superficial gas velocity. The weight percent of fractions having γc above 60 mN m–1 was 29.5, 31.9 and 40.5% for 0.25, 2.00 and 4.25 min, respectively. These values increased with sampling time, and were much greater than those for the lower superficial gas velocity. At lower superficial gas velocity, the hydrophobic coal particles seem to be selectively floated by colliding and attaching to the bubble surfaces. On the other hand, at higher superficial gas velocity, hydrophilic particles that are difficult to attach to bubbles seem to be entrained in the turbulent wake of bubble swarms and float.The grade of clean coal was better for the lower superficial gas velocity, however, carbonaceous materials recovery was lower than that for higher superficial gas velocity. Carbonaceous materials recovery was improved by increasing the recovery zone height.

5314073 Phosphate flotation using sulfo-polyesters: Mahendra Sharma, George J O'Neill, Brij Moudgil assigned to Eastman Kodak Company

Associated minerals in the raw coal increase the energy consumption and abrasion of grinding media of vertical spindle pulverizer (VSP). Moreover, the low separating efficiency of classifier in VSP leads to the return of fines to grinding table, worsens the grinding phenomenon and make the energy-size reduction of coal complex. Beneficiation of fines rejected by classifier is helpful to save energy and decreases the air pollution caused by the combustion of minerals in fines. Aiming to evaluate the potential for beneficiating the circulating loads, multi-analytical techniques are utilized to the raw coal and ground products. Phase composition analyses of raw coal show that kaolinite is the main mineral. Comparison of scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX) of coal before and after comminution illustrates the liberation of kaolinite from coal substance, and the measurement of charge-mass ratios indicates the opposite polarity of tribocharge between coal and minerals, which indicates the separating possibility based on difference in the electric physics. Removal results of minerals from circulating loads by the triboelectrostatic separator vary with product fineness and liberation degrees. The best separation result is obtained on the finest progenies produced with the yield and ash content of clean coal at 61.95% and 18.92%, respectively.

物理的選別法による石炭の脱灰性に関する研究 （第３報） 微粉炭の脱灰試験法と脱灰性評価

Release analysis (RA) and oil agglomeration (OA) procedures were investigated to determine a standard testing method for de-ashing of fine (>10μm) and ultra-fine (<10μm) coal. The results indicated that OA was suitable for both fine and ultra-fine coal, but RA only for fine coal. Oil agglomeration tests were carried out for Datong, Wandoan and Illinois coals of different sizes. Based on the liberation model previously proposed by the authors and the removal characteristics of mineral matter by the oil agglomeration, a new simulation method was developed to predict the amount of minerals and ash content of clean coal. There was good agreement between experimental and calculated results for the clean coal of agglomerates.

Fine Coal Cleaning by Spiral and Water Washing Cyclone

The performance of three different types of spirals and a 200 mm diameter water washing cyclone have been assessed in open-circuit on-site testwork at the Norwich Park preparation plant on nominally 500 µ x 75 µm sized coal. The study is part of a program investigating alternative methods to heavy media cyclones and froth flotation for removing ash from fine coal from Central Queensland mines in the nominally 3 mm x 75 µm size range. The two spirals specifically developed for treating fine coal showed better cleaning efficiencies than the water washing cyclone on the +75 µm size fraction in the feed (essentially 1 mm top size). Their single start capacity was about half that of the water washing cyclone for the same clean coal ash content. The spirals readily produced a high ash reject (> 81%) in a single stage and, with the appropriate splitter configuration, a small middlings suitable for retreatment. Middlings splitter setting and vortex finder position (for the water washing cyclone) both provided reasonable control of clean ash at intermediate solids feed rates. For the spirals there was a strong correlation between solids feed rate and both clean coal ash content and yield at constant middlings splitter setting. For small cuts to middlings, separation efficiency remained relatively constant over the full range of feed rates. Relative density partition data indicated that less size classification took place in the spirals although the efficiency of both processes decreased sharply below about 125 µm. For a given clean coal ash the capacity and/or recovery of the spirals and water washing cyclone depended on tshe proportion of -75 µm high ash slimes in the feed.

Selective agglomeration: An interlaboratory test program

Among advanced coal preparation processes, various approaches to selective agglomeration have been recognized to have enormous potential in terms of producing a superclean fuel from coal. In order to compare and contrast the performance of different processes that have been developed within the generic area of selective agglomeration, the Department of Energy's Pittsburgh Energy Technology Center (PETC) conducted an interlaboratory test program in 1988. Organizations that agreed to participate received carefully split samples of three bituminous coals with the goal of obtaining the maximum Btu recovery at a clean coal ash content of roughly 2%. The process developers ground and beneficiated the coal, and returned the products to PETC for analysis. This paper describes the various process schemes that were evaluated and presents an overview of the major findings. 5 refs., 9 figs., 7 tabs.

Computational Techniques for Coal Washery Optimization - Parallel Gravity and Flotation Separation

To carry out washery optimization calculations in a digital computer, both the raw coal feed characteristics and separator efficiency performance must be reduced to a form that is both accurate and easv to translate into code. A systematic analysis has been made of mathematical representation for partition curves and separation characteristics for froth flotation machines. A number of representations of the partition curves have been found to be useful. The programs developed accept conventional partition data or modelled partition curve parameters. Flotation performance is specified according to a two-rate constant kinetic model. Feed coal characteristics used are typical for coal preparations plants in China. Optimization of the process is carried out by maximization of yield, and three programs have been developed for the purpose. The programs can deal with any one of seven plant flowsheets commonly used in China. One program can be applied to determine the optimal ash content of clean coal for either each category of separator or each coal feed group. The other two programs are very useful to determine the optimal cut points of separators being installed in a plant. The computing techniques applied in both the programs are the Rosenbrock pattern search and the so-called “Replacement Method”. The cubic spline interpolation techniques have been applied in a number of calculations with success. All the programs have been proved to be effective and convenient tools for the design and operation of coal preparation plants.

Cleaning tests of central Illinois coal

The fluidization of Geldart B particles commonly falls under the bubbling fluidization category, where the coalescence of bubbles is the dominant phenomenon. If the diameter of bubbles becomes too large, the fluidization quality will deteriorate and lead to significant maldistribution of bed density. In this study, a pronation-grille baffle was introduced into a gas-solid dense phase fluidized bed (GDPFB) in order to improve fluidization quality. This was termed as a pronation-grille baffle dense phase medium fluidized bed (PGBFB). The inhibitory effect of the pronation-grille baffle on the coalescence of bubbles and the large-scale particles back mixing, as well as the collaborative optimization of the baffle placing height and operating gas velocity were investigated. The density standard deviation (Sδ) and density skewness (SKδ) were employed to evaluate the uniformity and stability of the bed density distribution. According to the experimental results, the Sδ of a PGBFB was substantially reduced by 83.7%, compared to a GDPFB, and the lowest SKδ value was decreased to −0.0106, significantly improving the uniformity and stability of the bed density. Additionally, the beneficiation experiments were performed on a 1–6 mm raw coal in a PGBFB. The beneficiation results showed that the probable error, E, was 0.091 g/cm3 and the ash content of clean coal was 16.63%, being reduced by 21.76%, compared to the ash content of the raw coal. This indicates that fine coal beneficiation using a PGBFB can provide a simple and efficient way for coal cleaning in arid and cold regions.