Clean Coal Ash Research Articles

A Techno-Economic Analysis Method to Determine Yield and Ash of Coal Preparation Products

A techno-economic optimization-oriented analysis method was proposed to determine the optimal yield and ash of coal flotation concentrate, thus maximizing the economic benefits. With the kerosene and No. 2 fuel oil used as flotation agents and lots of flotation tests done, the allowable dosage ranges of the two agents were determined, then two regression models were developed through orthogonal tests to determine the ash and yield of clean coal by using the software of MATLAB. According to the relation between price and concentrate ash, an optimization model was developed and, as a result, the software of LINGO was used to determine the optimal clean ash and yield, that is, 9.93% and 79.91%, respectively, by which the max income of per 100 t of raw fine coal came up to 106,221 RMB. Exemplification results showed that the method proposed is simple and practical.

Effects of preparation conditions on performance of discarded biological oil as coal flotation collectors

Discarded biological oil was modified under various preparation conditions to produce coal flotation collectors to replace traditional petroleum flotation collectors. Effect of alcohol-oil molar ratio, catalyst dosage, reaction temperature and reaction time on clean coal yield was investigated. The results showed that the flotation collectors made from discarded biological had higher clean coal yield. Through orthogonal and single-factor tests, the best modified parameters were obtained, at a temperature of 50°C, an alcohol-oil molar ratio of 8:1, a potassium hydroxide (KOH) catalyst of 0.5% and a reaction time of 2.5 h. The alcohol-oil molar ratio and catalyst dosage were the most important factors to influence the performance of the flotation collectors. Under optimal conditions, the coal flotation collectors had higher clean coal yield than ordinary diesel oil or kerosene, and clean coal ash was also lower. Coal ash and clean coal yield were 7.93% and 58.54% under biological oil flotation collectors, while coal ash and clean coal yield were 8.29% and 57.65% under diesel flotation collectors. [Received: February 7, 2013; Accepted: December 31, 2013]

Effect of elevated temperature and pressure on the leaching characteristics of Indian coals

The Indian coal washing circuits are cursed with the availability of high ash coals having poor liberation characteristics as feed material. This result in unacceptably very low product yield (i.e. 10–15%) when aspiring for low ash clean coal (around 8–10%) for efficiently utilising it in iron making process in the form of coke. In this context, a chemical beneficiation route has been explored for demineralising high ash Indian coals. In this work, the effect of aqueous alkali leaching followed by acid washing on the removal of mineral matter from two different captive coals of Tata Steel at elevated temperature and pressure have been explored. The research study revealed that it is possible to reduce the ash content up to 70% by this method. The effect of process conditions such as alkali concentration, temperature and pressure upon the demineralisation kinetics have been investigated. The alkali content of the product coal does not increase whereas the silica and alumina content reduces by nearly 51.3% and 58.8% respectively. Significant reduction in the phosphorus content is observed after the acid treatment. The process does not significantly affect the crucible swelling number index for coking property of coal.

Improved Collector for Beneficiation of Low-Volatile Medium Ash Clean Coal Fines by Froth Flotation

Froth flotation has emerged as an effective and useful technique for separation of low volatile medium ash clean coal fines. The traditional flotation collector is diesel oil. However, this collector often gives lower concentrate yields. In the present article, an improved collector derived from coal tar, that is, a particular coal tar distillate fraction, in combination with methyl isobutyl carbinol (MIBC) as frother has been successfully used, whereby about 83% of coal fines can be effectively retrieved with a low-ash yield (16%). In this way, a higher yield of coal fines has been successfully obtained in comparison with other collectors. To illustrate the point, compared to our improved collector, the yields with diesel and N-Dodecane as collectors were only 71.4% and 66.7%, respectively. Using the actual experimental results, a mathematical model has been developed using response surface methodology taking into account collector dose, frother dose, and pulp density. The quadratic model developed is in good agreement and effectively validating the experimental results of froth flotation process.

Study on Energy Consumption in Fine Coal Flotation

Energy is of crucial importance in coal flotation. In the present study, a torque sensor was used to measure the energy consumed during flotation experiments carried out using the optimal reagents dosages and concentration. During flotation, with an increase in flotation time, the clean coal ash gradually increased, the flotation rate constant k values decreased, and the energy required to recover a unit mass of clean coal became greater. With higher agitation speed, the amount of energy consumed also increased. A model of combustible recovery and flotation energy was established. The flotation behavior of narrow size particle agreed with the unclassified size. The flotation rate order of narrow size was as follows: −250 to +125 μm > −500 to +250 μm > −125 to +75 μm > −75 μm.

Study on Drainage Oil to Prepare Collectors of Coal Flotation

At present, kerosene is one of the most widely used non-polar hydrocarbon oil collector agent in coal flotation in China, kerosene is difficult to dissolve in water, with good collector, but the dosage is comparatively large in the actual production.The drainage oil is from the dining recycled goods and the waste of animal flesh, can be used for preparation of fatty acid collector, which not only to reduce environmental pollution,but also to reduce the risk of food safety. At the same time, if drainage oil can replace the kerosene in coal collection, it will improve the coal preparation plant efficiency and solve the problem of shortage of national resources. In this study, we use Huangling coal as raw material for flotation experiment, use kerosene, diesel, drainage oil and emulsified drainage oil as collectors. Adding different collectors in the same flotation conditions to research the yield of clean coal, the clean coal ash and the yield of tailings by changing the dosage of collectors. The results show when adding to OP emulsifier and the proportion of water and oil is 6:4, flotation effects is the best, the yield of clean coal is 88.67%, the ash of clean coal is from 9.16% down to 8.63%, the yield of tailings is 11.32% .

Study on Coal Separability for Wangcun Inclined Shaft in Chenghe

On the basis of the coal quality characteristics, the screening and drifting tests have been carried out to investigate the separability of the coals in the inclined shaft coal samples of Chenghe Wangcun coal mine. The results showed that the mine raw coal seams are medium ash, high sulfur and medium volatile coals. The screening test results showed that the water content and sulfur content of coals samples in each grade after sieving essentially remained the row coal characteristic. Heating value increased with the decrease of particle size, but ash content decreased with the particle size. The float-and-sink tests showed that when the given clean coal ash content was 10%13% and 15% respectively, the coal samples were in the extremely difficult degree, medium separability degree and medium separability degree respectively.

Study of Flotation Effect of ST-1 Complex Reagent

There are lots of problems in coal flotation reagents. For example, it is difficult to disperse in coal pulp, it needs a large consumption, and its selectivity is poor. So this paper refers that kerosene can be made into compound kerosene by using different chemical products and surfactants, and then used for coal flotation. Tests proved that when the ST-1 Complex Reagent dosage is 500g/t, kerosene dosage is 900g/t, clean coal ash consistent is the same, and clean coal yield is closed, collector dosage saved 44.44%, and the fastest floating speed of clean coal is 99.3g/min, 4.8g/min fast than kerosene, Zeta potential is-28.9409mv after kerosene effect, Zeta potential is -13.2555mv after ST-1 Complex Reagent effect.

Effect of the column height on the performance of liquid–solid fluidized bed for the separation of coarse slime

A liquid–solid fluidized bed separator, used for the separation of coarse slime, was developed. Test particles sized in the range from 0.25 to 0.5, 0.5 to 1.0, and 0.25 to 1.0mm were separated in the liquid–solid fluidized bed. Beds with column heights of 1200, 1500, and 1800mm were tried. The clean coal and the tailings were subsequently analyzed by float–sink testing. The results showed that the ash and yield of clean coal both decreased with increasing column height, for all three size fractions, and that the ash of the clean coal obtained from tests on the broader size fraction was less than that from the narrower sized fractions. The separation density decreased with increasing column height. The lowest E value was seen for a column height of 1500mm, for which conditions the separation density was 1.45g/cm3. The E value was 0.084 for the 0.25–0.5mm fraction but the corresponding separation density was 1.48g/cm3, and the E value 0.089, for the broader 0.25–1.0mm fraction.

Optimization of Solvent Extraction Process Parameters of Indian Coal

Medium coking coals from West Bokaro coalfield, India, were extracted with N-methyl-2-pyrrolidone (NMP) and ethylenediamine (EDA) under reflux condition at atmospheric pressure. The objective of the study was to maximize the clean coal yield maintaining the specified clean coal ash content. Experimentations using three level full factorial designs were carried out to elucidate the importance of variables such as extraction time, coal to solvent ratio, and filtration mesh size upon solvent extraction of coal. To determine the significance of the effects, Pareto chart, residual analysis, and surface plots were used. It was found that the maximum extraction yield was obtained for 1 h extraction time and 1:12 coal to solvent ratio. Finer mesh (0.025 mm) size in filtration was found favorable in producing low ash clean coal (CC). Under optimum conditions it was possible to produce clean coal with 6% ash and 55% yield for coals having about 29% ash.

The influence of discharge style on the separation of coarse coal slime by a hindered fluidized bed

Two kinds of liquid distributor, a central discharge or a peripheral discharge, were designed into a hindered fluidized bed separator. The beneficiation performance of the fluidized bed was investigated using 0.25∼1.00 mm coarse coal slime and the two different distributors. The experimental results show that the heterogeneity of axial particle velocity in the radial direction of the bed can be reduced by a distributor that has a central discharge. The beneficiation performance for this distributor is improved relative to the distributor with the peripheral discharge. This indicates that it is necessary to eliminate or suppress the core-annulus structure within a hindered fluidized bed. Increasing superficial water velocity causes the clean coal ash content, the tailings ash content, and the combustible recovery to increase. Additionally, increasing the bed height decreases all of these three indexes. The optimum superficial water velocity and bed height for a 0.25∼1.00 mm coal feed were determined to be 3 mm/s and 800 mm, respectively. This work provides a foundation for the scale-up of the bed.

Study on flotation properties of emulsified diesel oil

A new emulsified floatation agent with a compound of diesel, surfactant and water with a percentage of 27:3:70 was applied to the research on the floatation test with two coal samples of Guandi coal and Xingtai coal to solve the problem of low efficiency and high oil consumption of traditional floatation which used diesel itself to serve as the collector. The results showed that the floatation agent was good in performance and reliability, high in selection, and has improved the floatation performances. Based on the clean coal ash remaining unchanged, in comparison with the diesel, when EDO was applied as the collector of Guandi coal, the diesel oil could be saved about 73%, meanwhile, the clean coal production could be increased by around 3%. When EDO was applied as the collector of Xingtai coal, the diesel oil could be saved about 46%, meanwhile the clean coal production could be increased by 7% or thereabouts.

Coal flotation using wash oil as a new type of collector

The use of wash oil as a coal collector is proposed to overcome the disadvantages of regular collectors in coal slime flotation. These disadvantages include high price, limited sources and high consumption. The effect of additives on flotation was studied and an innovative “one rough separation—one cleaning separation” flotation technology was developed. The experimental results show that the clean coal ash content decreases by about 1.36% and the clean coal yield declines by around 10% with the application of the depressant. There is an increase of 3.76% in the yield of clean coal and a decrease of 0.40% in the ash content caused by utilizing a dispersant. An ultimate product having an ash content of 10.78% and yield of 70.12% can be attained using a combination of dispersant and depressant. The use of this new technology decreases the ash content by 1.21%, decreases the yield by 2.80% and an increases the coal flotation perfect index by 2.03%. Compared to common flotation, the utilization of the new technology reduces ash by 0.17%, increases yield by 5.3% and increases perfect index by 4.18%.

An emphasis on optimum fuel production for Indian coal preparation plants treating multiple coal sources

Optimization of operating parameters of integrated coal washing plants for achieving maximum clean coal yield at any desired clean coal ash level is a major problem. The problem is largely associated with processing of raw coal obtained from different seams/collieries with frequent variations in proportions and characteristics of individual coals. For large number of source coals or washing different size fractions there are no simple methods of optimization. This paper presents a numerical solution to the constrained non-linear optimization of a multivariable objective function utilizing Excel ® spreadsheet. The method is capable of handling any number of source coals with different size fractions. Here the yield is optimized subject to constraints on both ash and specific gravity. It is shown that the operational constraints of different washeries in the integrated plant utilizing gravity separation methods can also be overcome. The method offers the plant operators an easy and straightforward way for determining the optimum cut points of separation for blended coals to produce a maximum overall product yield at specified level of ash content.

Studies on characteristics and flotation of a hard-to-float high-ash fine coal

High-efficiency separation of hard-to-float high-ash fine coals has been a research hotspot in some countries, especially in China. Separation of hard-to-float high-ash fine coals by froth flotation, although considered to be the most effective, remains some challenges to be overcome. In this paper, the mineralogical/petrologic, physical and chemical characteristics of the of a hard-to-float high-ash fine coal collected in Kailuan mining area were studied. The floatability and liberation characteristics of this coal sample and potential separation processes were investigated experimentally. According to the coal characteristics, four separation processes were put forward and evaluated. Experimental results indicated that classified floatation couldn’t effectively improve the fine coal quality, while the processes of fine grinding-recleaning to roughing cleaning coal and selective agglomeration-floatation were suitable for the Kailuan coal. Compared with the original coal flotation process, the processes of fine grinding-recleaning to roughing cleaning coal increased the cumulative yield from 50.87% up to 55.53% while reduced the product ash content from 11.76% down to 10.74%. In the processes of selective agglomeration-floatation, the lowest ash of clean coal is 10.69%, with 58.72% yield, 7.85% higher in yield and 1.07% lower in ash content. The ash contents of the products from the two processes are lower than 11%, which meets the clean coal requirement.

An Evaluation of a Two-Stage Spiral Processing Ultrafine Bituminous Coal

Testing was conducted to evaluate the performance of a multistage Multotec SX7 spiral concentrator treating ultrafine bituminous coal. This spiral mimics a two-stage separation in that the refuse is removed after four turns, and the clean coal and middlings are repulped (without water addition) and then separated in the final three turns. Feed samples were collected from the spiral circuit of a coal cleaning plant located in southwestern Pennsylvania. The samples consisted of undeslimed cyclone feed (nominal − 0.15 mm) and deslimed spiral feed (nominal 0.15 × 0.053 mm). Testing was carried out to investigate the effects of slurry flow rate and solids concentration on spiral performance. Detailed size and ash analyses were performed on the spiral feed and product samples. For selected tests, float-sink and sulfur analyses were performed. In nearly all cases, ash reduction occurred down to approximately 0.025 mm, with some sulfur reduction occurring even in the − 0.025 mm interval. The separation of the + 0.025 mm material was not significantly affected by the presence of the − 0.025 mm material when treating the undeslimed feed. The − 0.025 mm material split in approximately the same ratio as the slurry, and the majority of the water traveled to the clean coal stream. This split ultimately increased the overall clean coal ash value. A statistical analysis determined that both flow rate and solids concentration affected the clean coal ash value and yield, though the flow rate had a greater effect on the separation.

Study of the effect of ultrasonic treatment on the surface composition and the flotation performance of high-sulfur coal

This paper highlighted the use of X-ray diffraction, scanning electron microscopy and X-ray fluorescence spectroscopy to investigate the changes on the surface composition of high-sulfur coal and pyrite before and after ultrasonic conditioning. The results showed that ultrasonic conditioning resulted in a decrease in the contents of iron and sulfur in coal, an increase in the content of element carbon, and an increase in the purity of the coal. Conversely, ultrasonic conditioning led to an increase in the content of iron and sulfur in pyrite, a decrease in the impure content of calcium, and a relative increase in the purity of the pyrite after ultrasonic conditioning. This study verified that on the one hand, ultrasonic conditioning can promote the pyrite separation from the high-sulfur coal, with the separated pyrite taking the form of FeS; on the other hand, it can produce a cleaning effect on the surface of coal and pyrite with the consequent increase both in hydrophobicity of coal and hydrophilicity of pyrite. The paper introduced ultrasonic pre-treatment of the slurry and stepped froth removal tests of high-sulfur coal and the study on the yield, ash and sulfur content of clean coal in different phases. The results gave further evidence of the increases both in the rate and the selectivity of flotation. This study shows that ultrasonic conditioning can enhance the performance of de-sulphurization of high-sulfur coal flotation.

Optimization of Reagents Distribution Down a Coal Flotation Bank to Improve the Recovery of Coarser Particles

Fine coal (− 0.5 mm) is treated in a flotation circuit at Bhelatand washery of Tata Steel. The average ash content of the flotation feed, the fine clean coal, and the tailings of the flotation circuit are 18.5%, 12.5%, and 36%, respectively. The yield of clean coal from the flotation circuit is about 72%. However, the performance of the circuit in terms of clean coal yield is not satisfactory. The feed to the flotation contains 15–20% of oversize (+ 0.5 mm) fraction because of the inefficiency of the desliming screens. These oversize materials, which are of high carbonaceous value, are not efficiently recovered through the flotation process. Hence, the major challenge is to improve the flotation kinetics of the coal fines, especially the oversize particles. The way flotation reagents are distributed down a flotation bank can positively influence the flotation response of oversize particles. Hence, two-stage reagent distribution, with extra amount of reagent in the second stage, was studied in the laboratory. Results of laboratory-scale studies showed an improvement in yield of clean coal of 10–12% with a marginal increase of clean coal ash content. Based on encouraging laboratory findings, the idea was implemented in the plant, which showed a substantial improvement in the yield of clean coal from 74% to 84% with marginal increase in clean coal ash content.

Separation Characteristics of Coal Fines in a Knelson Concentrator – A Hydrodynamic Approach

The Knelson concentrator has found wide acceptance in the gold processing industry to recover fine free gold particles from the milling circuits. Several case studies have recently been reported to extend its applications for processing various mineral fines with limited success. A few empirical models have also been developed, but there has been hardly any attempt to understand the basic particle separation mechanism inside this equipment. An attempt has, therefore, been made to understand the separation characteristics of coal fines in a Knelson concentrator. The entire exercise has revealed that this equipment can produce a clean coal ash content of 17% from a feed coal ash content of around 36%. The hydrodynamic analysis provided will also help in understanding the roles of centrifugal force and the fluidization water to process various other mineral fines using a Knelson concentrator.

Fine coal circuitry considerations in treatment of soft coal with difficult washabilities

A typical process used in Chinese metallurgical coal preparation plants employs heavy-media separation to treat the coal coarser than 0.5 mm. The − 0.5 mm fine coal is treated with froth flotation. A major disadvantage of this process is that a large quantity of fine coal is recycled in the heavy-media cyclone circuit, which results in high magnetite losses. The − 0.5 mm fine coal in the media is a result of poor raw coal deslime screen efficiency and the continuous breakage associated with the processing of soft coal. Another disadvantage of this typical process is that some coarse clean coal particles are lost to the froth flotation tailings. This investigation focuses on the simulation of processing fine soft coal with water-only cyclone (WOC) and spirals. WOCs and spirals have become popular devices for treating fine coal. WOCs can operate at low specific gravity cut points to produce low ash clean coal while spirals tends to operate at high specific gravity cut points and act as a scavenger to rewash the underflow (refuse) from WOCs. The combination of WOCs and spirals can compete with a heavy-media cyclone with respect to both efficiency and clean coal yield when treating 1 mm × 100 Mesh fine coal. This fine coal processing circuit can subsequently increase the bottom size of the heavy-media cyclone feed from 0.5 mm to 1 mm which will reduce the loading of the heavy-media cyclone circuit. This change in circuitry thus reduces magnetite consumption without scarifying separation efficiency of the 1 mm × 0 size fraction. Furthermore, the reduction of the nominal top size of the froth flotation feed from 0.5 mm to 0.15 mm will greatly decrease or eliminate the loss of clean coal to flotation tailings.