Interaction mechanism of flocculants with coal waste slurry

Coal tailings are the inevitable by-product of coal mining and preparation plants, and often are problematic in terms of dewatering and solid-liquid separation. The interaction of multi-component fine coal tailings with various coagulants and flocculants are important in dewatering processes. Tunçbilek coal preparation plant wastes are composed of 81% inorganic solids with negative surface charges dominating at all pHs. The highest settling rate and turbidity values without flocculant are obtained at natural pH of 8.3 due to the presence of inorganic ions in the suspension particularly Mg²⁺and Ca²⁺that act as natural coagulants. Additon of medium and low charge density anionic flocculants with high molecular weight at natural pH produced higher settling rates at lower dosages than nonionic and cationic flocculants. It shown that the charge density of anionic flocculants has a significant effect on both settling rate and supernatant turbidity, also the settling rate increases with increasing the degree of anionicity. Anionic flocculants having high molecular weight and high anione charge density produced flocs at sufficient size necessary for settling conditions, yet anionic flocculants having low charge density were more effective in the clarification of suspensions containing clay minerals of high stability. The multivalent ions act as a bridge between negatively charged coal, quartz and clay minerals with anionic groups (-CH₂-(CH-CO)-COO groups) of the polymer. Non-ionic flocculants required higher dosages than other flocculants to achieve equivalent settling rates; though excellent turbidity values were obtained in most common pH values. Cationic flocculants of higher charge densities (%70) achieved good settling rates and low supernatant turbidities (9.9 NTU) at natural pH for a dosage of 119.7 g/t-solids flocculant. An interaction mechanism of each polymer type with different components of the tailings is proposed.     

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 (R² 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.     

Clean fuel-magnesia bonded coal briquetting

Benefaction from coal fines as solid fuel in Turkey is very much important for economical development. Beneficiation from washed coal fines in the industry using solid fuel at lump size and in the municipal areas as an household solid fuel may be only provided by hot briquetting of the coal fines. The most practical common way of that benefication from coal fines in our country have been hot binding by sulfite liquor–sulfite liquor-melas and lime mixtures. Harmful the flue content of sulfite liquor-melas may only be eliminated by lime, a type of solid additive. However, cold bonded briquettes produced from coal fines are environmentally free. Just ash contents of these briquettes increase at a certain degree and heat content of them decrease at a certain extent. By using magnesia binder showed in this study, Tunçbilek lignite fines have been briquetted by cold and hot briquetting techniques. The qualities of briquettes produced by cold binders were compared with to those produced by other hot binding methods As a result, magnesia binder showed the similar characteristics with those of the briquettes produced by only cold bonded gypsum. Use of magnesite mixture and gypsum just as only cold binder was not suitable for the requirements from the coal briquettes to be used as solid fuels, particularly from household fuels, but just only as cold additive should be used.     

Demineralisation of lignites by single and successive pretreatment

In this study, two Turkish lignites (Bolu-Mengen, Kütahya-Tunçbilek) were treated under atmospheric and reflux conditions with 10-30% NaOH, 10% HCl and 10% H₂SO₄ solutions, singly and/or successive treatments to determine the effects of this treatment on the mineral matter and acidic functional groups. Characterisation of the treated and untreated samples was by Fourier transform infrared spectroscopy. The process of successive pretreatment was found to be more effective than single steps in terms of demineralisation and removal of carboxylate structures. During NaOH treatment, the first of successive steps, salts soluble in acid but not in water were determined. In successive demineralisation steps with 30% NaOH and 10% HCl, a low level of 3.3% ash was obtained for the Tunçbilek lignite. In addition, during the pretreatment, most of the Ca and K were exchanged with Na.     

An enhanced-gravity method to recover ultra-fine coal from tailings: Falcon concentrator

The Falcon concentrator is an enhanced-gravity separator used for the concentration of fine and ultra-fine minerals. This study was conducted to evaluate the effects of different process variables on the performance of the Falcon SB-40 concentrator for beneficiation of tailings to recover ultra-fine coal. Various operating and design conditions such as bowl speed (G force), water pressure, pulp solid ratio and pulp feed rate were investigated. A hydrocyclone was used for pre-enrichment with the Falcon concentrator. Operation parameters of the hydrocyclone, namely feed solids, inlet pressure, vortex finder and apex diameters were investigated. In order to produce fine coal concentrates, regression equations were derived by applying the least squares method using Minitab 15 software. Response functions were produced for the ash content and the recovery of the clean coal concentrates for the performance of the hydrocyclone and Falcon concentrator under different operating conditions. Predicted values were found with the experimental values giving R² values of between 0.73 and 0.58 for ash content and between 0.65 and 0.39 for recovery of the clean coal. It was shown that under optimized conditions the Falcon concentrator can produce a clean coal with an ash value of 36% from a feed coal of about 66% ash.     

Clean Chromite Production from Fine Chromite Tailings by Combination of Multi Gravity Separator and Hydrocyclone

Chromite is an important mineral used in the metallurgy, chemistry, and refractory industries. For this reason, beneficiation of chromite tailings is very important. In this study, the possibility of beneficiation of chromite tailings in the Uckopru/Fethiye-Turkey region by Hydrocyclone and Multi Gravity Separator (MGS) combination was investigated. The two signification operational parameters of hydrocyclone, which were diameter of apex and diameter of vortex, and the three signification operational parameters of MGS, which were drum speed, tilt angle, and wash water, were varied and the results were evaluated with the Central Composite Rotatable Design. The results of beneficiation studies showed that commercial concentrate containing 48.18% Cr₂O₃ was obtainable with a 69.79% rate of recovery.     

Process development studies on recovery of clean coal from ultra fine hardcoal tailings using enhanced gravity separator

In this study, we report the experimental results with respect to the beneficiation of fine hardcoal from the Çatala?z? Coal Preparation site tailings containing about 90% (by weight) of ?600 µm size particles. These tailings contain 28.41% ash. The coal sample was subjected to a two‐stage concentration process. The underflow product of hydrocyclone under optimized conditions was further processed in Mozley Multi‐Gravity Separator to reduce the ash content of the coal. The results showed that a coal product containing 6.98% ash was obtainable with recovery of 61.73% by this two‐stage concentration process.     

Investigation of co-combustion of coal and olive cake in a bubbling fluidized bed with secondary air injection

In this study, a bubbling fluidized bed of 102 mm inside diameter and 900 mm height was used to burn olive cake and coal mixtures. Tunçbilek lignite coal was used together with olive cake for the co-combustion tests. Combustion performances and emission characteristics of olive cake and coal mixtures were investigated. Various co-combustion tests of coal with olive cake were conducted with mixing ratios of 25%, 50%, and 75% of olive cake by weight in the mixture. Operational parameters (excess air ratio, secondary air injection) were changed and variation of pollutant concentrations and combustion efficiency with these operational parameters were studied. The results were compared with that of the combustion of olive cake and coal. Flue gas concentrations of O₂, CO, SO₂, NO_x, and total hydrocarbons (C_mH_n) were measured during combustion tests.For the setup used in this study, the optimum operating conditions with respect to NO_x and SO₂ emissions were found to be 1.35 for excess air ratio, and 30 L/min for secondary air flowrate for the combustion of 75 wt% olive cake and 25 wt% coal mixture. The highest combustion efficiency of 99.8% was obtained with an excess air ratio of 1.7, secondary air flow rate of 40 L/min for the combustion of 25 wt% olive cake and 75 wt% coal mixture.     

An integrated approach for coal tailings management

A detailed study on an integrated process featuring three distinct mechanisms (i.e., hydrophobic extraction, coagulation and flocculation) is presented. In this process, fine coals in the tailings stream are extracted into a mineral oil by hydrophobic extraction, while coagulant and flocculant are used to aid effluent clarification by coagulation/flocculation. With a single stage process, a coal‐in‐oil mixture is produced as a potential fuel, while clarifying the water for recycling. The hydrophobicity of coal is found to be a key parameter in coal extraction. The addition of mineral oil prior to flocculant and coagulant, especially in the presence of fine clays, is beneficial for recovering weakly hydrophobic fine coals. Fine clays are found to stabilize coal‐rich oil droplets, reducing coal recovery. The presence of hydrophobic coal enhances droplet coalescence and improves process performance. In a case study using a tailings stream from OBED coal preparation plant, it was found that re‐grinding of original tailings is necessary to expose fresh hydrophobic surfaces. Applying this single stage unit operation to a tailings containing 52% ash, a combustible recovery greater than 85% in the form of coal‐in‐oil mixture at product ash content less than 14 wt% was achieved.     

屯兰选煤厂浮选系统改造可行性分析

为了提高屯兰选煤厂浮选系统的分选效果,提高精煤回收率,减少因煤泥灰分高而造成煤炭资源的浪费,通过对选煤厂浮选系统中存在的浮选尾煤灰分低,分选效率低,浮选药耗高和浮选精煤池消泡困难的问题进行分析,提出了更新改造工程方案,并对方案进行了预测及论证。结果表明,通过对XJM-12浮选机进行更新改造,可以有效提高浮选精煤产率及浮选尾煤灰分,同时节省浮选药耗及电耗,节约选煤成本,年增加经济效益4208.96万元。     

Desulphurization of some low-rank Turkish lignites with crude laccase produced from Trametes versicolor ATCC 200801

In this paper, data obtained during the oxidative desulphurization of some low-rank Turkish lignites with crude laccase enzyme produced from Trametes versicolor ATCC 200801 are presented. In order to optimize desulphurization conditions, effects of incubation time, pulp density, incubation temperature, medium pH, and also lignite source on the desulphurization have been examined. The values for incubation period, pulp density, temperature and pH in optimum incubation condition were found as 30 min, 5%, 35 °C, and pH 5.0, respectively. Under optimum conditions, treatment of coal samples with crude laccase has caused nearly 29% reduction in their total sulphur content. During the study, the rate of desulphurization of coal sample provided from Tunçbilek with crude laccase was found to be relatively higher than the other examined coal samples. Results of analytical assays have indicated that the treatment of coals with crude laccase has caused no change in their calorific values but reduced their sulphur emissions. 35%, 13%, and 25% reductions of pyritic sulphur, sulphate and organic sulphur in a period of 30 min were achieved, for a particle size of 200 μm under optimal conditions with enzymatic desulphurization. Also, statistical analyses such as Tukey Multiple Comparison tests and ANOVA were performed.     

Application of response surface methodology and central composite rotatable design for modeling and optimization of a multi-gravity separator for chromite concentration

In this study, the application of response surface methodology (RSM) and central composite rotatable design (CCRD) for modeling and optimization of the influence of some operating variables on the performance of a multi-gravity separator (MGS) for chromite concentration is discussed. Three MGS operating variables, namely drum speed, tilt angle, and wash water flow rate were changed during the concentration tests based on CCRD. The range of values of the MGS variables used in the design were a drum speed of 133-217 rpm, tilt angle of 1.6°-8.4°, and wash water flow rate of 1.3-4.7 lpm. A total of 20 concentration tests were conducted using MGS on chromite ore obtained from Kangal/Eskikoy—Turkey.In order to optimize chromite concentration 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 concentrate grade and recovery were expressed as functions of three operating parameters of MGS. Predicted values were found to be in good agreement with experimental values (R² values of 0.96 and 0.98 for concentrate grade and recovery, respectively). In order to gain a better understanding of the three variables for optimal MGS performance, the models were presented as 3-D response surface graphs. This study has shown that the RSM and CCRD could efficiently be applied for the modeling of MGS for chromite concentration and it is an economical way of obtaining the maximum amount of information in a short period of time and with the fewest number of experiments.     

The effect of preswelling and/or pretreatment of some Turkish coals on the supercritical fluid extract yield

The effects of preswelling, and/or pretreatment with 1N HCl of four Turkish coals (Bolu-Göynük, Seyitömer, Tunçbilek and Soma-Merkez) on the supercritical toluene extract yields have been investigated. Methanol, 1,4-dioxane, THF (tetrahydrofuran), pyridine and EDA (ethylenediamine) were used as swelling agents. Solvent swelling and pretreatment with 1N HCl of coals significantly enhanced the liquid yields. The effectiveness of the swelling solvents in enhancing the liquid yield is in the same order as their swelling ratios. Swelling in EDA and pyridine were more effective for the extraction of coals. The highest improved liquid yields in supercritical toluene for each coal was obtained by the combined effects of pretreatment and preswelling of coals. No simple trend in reactivity increment with properties of coals was observed.     

The influence of the binder on the properties of sintered glass-ceramics produced from industrial wastes

Sintered glass-ceramics were produced from coal fly ashes, red mud from aluminum production and silica fume. The capabilities of Tunçbilek fly ash and a mixture of Orhaneli fly ash, red mud and silica fume to be vitrified and devitrified by sintering process were investigated by means of scanning electron microscopy and X-ray diffraction analysis. To determine the effect of binder in the sintering technique, glass powders were pressed without or with the addition of polyvinyl alcohol. Owing to microstructural observations, density and hardness measurements, it can be said that physical properties and the hardness of the produced samples strongly depended on the crystallization degree of the samples. Toxicity characteristic leaching procedure test results showed that glass-ceramic samples produced by using sintering technique could be considered as non-hazardous materials. Chemical durability of the sintered glass-ceramic samples was also good. Microstructural investigations, hardness and physical properties of the samples indicated that the addition of polyvinyl alcohol improved the properties of sintered glass-ceramics obtained from Orhaneli fly ash, red mud and silica fume.     

Split and collectorless flotation to medium coking coal fines for multi-product zero waste concept

The medium coking coal fines of − 0.5 mm from Jharia coal field were taken for this investigation. The release analysis of the composite coal reveals that yield is very low at 10.0% ash, about 25% at 14% ash and 50% at 17% ash level. The low yield is caused by the presence of high ash finer fraction. The size-wise ash analysis of − 0.5 mm coal indicated that − 0.5 + 0.15 mm fraction contains less ash than − 0.15 mm fraction. Thus, the composite feed was split into − 0.5 + 0.15 mm and − 0.15 mm fractions and subjected to flotation separately. The low ash bearing fraction (− 0.5 + 0.15 mm) was subjected to two stages collectorless flotation to achieve the concentrate with 10% ash. The cleaner concentrate (18.9%) with 10% ash was recovered which has an application in metallurgical industries. The concentrate of 30.2% yield with 12.5% ash could be achieved in one stage collectorless flotation which is suitable for use in coke making as sweetener. As the − 0.15 mm fraction contains relatively high ash, collector aided flotation using sodium silicate was performed to get a concentrate of 23.6% yield with about 17% ash. The blending of this product with cleaner tail obtained from − 0.5 + 0.15 mm produces about 35.0% yield with 17% ash and that can be utilized for coke making. The reject from the two fractions can be used for conventional thermal power plant or cement industries using a 23.5% ash after one stage collector aided flotation and the final tailings produced content ash of 61.6% can be used for fluidization combustion bed (FBC). This eventually leads to complete utilization of coal.     

Centrifugal float–sink separation of fine Turkish coals in dense media

Zonguldak bituminous coal, Tunçbilek and Soma–Merkez lignites were each separated into two sub-fractions, coal rich and mineral matter rich, using a centrifugal float–sink separation technique in heavy media. An isopropyl alcohol (IPA)–carbon tetrachloride (CCl₄) mixture and a zinc chloride (ZnCl₂) solution, with a specific gravity of 1.40 g cm⁻³ at 25°C were used as dense medium liquids. The addition of surface active agents (Triton X-100 and Brij-35) to the zinc chloride solution improved the removal of minerals. The recovery and purity of the final product (float) obtained from the heavy media separation depend on such parameters as the density of the medium, rotor speed and centrifugation time. The separation efficiency of each coal differed significantly. Particle size distributions of the coals and their float and sink fractions were analysed using a Laser Particle Size Analyser. A Scanning Electron Microscope (SEM) was used to interpret the liberation of minerals from the coal particles.     

Vibroacoustical selective agglomeration of coal slimes

Coal slimes from coking coal with an average ash content of about 45% and difficult separation characteristics have been studied. Investigations have also been carried out on two artificial mixtures of gangue and coal of low ash content. Two kinds of agitation have been tested: mechanical—rotational (with an impeller mixer) and vibroacoustical (with vibrating band) at a frequency of 50 Hz and an amplitude of 1 – 2 mm. Vibroacoustical agitation was much more efficient than mechanical-rotational. Second-degree orthogonal-central-compositional planning was used for studying slimes of appropriate size (−0.063 mm). In the most successful test with natural slimes, an efficiency of separation of 34.41% was obtained with the following technological parameters: yield of concentrate 27.93%, ash content of concentrate 22.00%, yield of refuse 72.07%, ash content of refuse 54.30%, the ash content of the run-of-mine coal being 45.28%. These results are close to the best ones obtained with the same slimes by fractional analysis in a liquid of density 1500 kg/m³. In this case, an efficiency of separation of 39.18% was obtained with yield of concentrate 35.04%, ash content of concentrate 24.01%, yield of refuse 64.96%, and ash content of refuse 56.01%.

The experiments on selective agglomeration have been carried out using kerosene at 14.8% consumption with respect to solids. The investigations are of a preliminary character.     

高挥发分不黏煤作高炉喷吹煤的可行性研究

针对株洲洁净煤公司炼焦煤资源紧张、产品结构单一等问题,在分析原煤性质的基础上,对株洲洁净煤公司选煤工艺进行改造,研究高挥发分不黏煤作高炉喷吹煤的可行性。结果表明：原生煤泥产率和灰分均较低,可采用不脱泥分选;原煤属于极易选煤,-1.80 g/cm^3浮物累计灰分只有4.00%,可将中煤导入精煤输送系统。通过将中煤系统筛上物并入精煤输送系统,矸石水直接导入辐射式浓缩机,在精煤筛增加喷水管道及若干喷嘴,精煤压滤机滤液导入浮选系统,确定浮选复合药剂用量,在尾煤压滤泵前自动加入聚合氯化铝,并添加1套自动加药系统等措施,株洲洁净煤公司介耗降低了0.2 kg/t,水分、灰分分别降低了0.70%和0.32%,精煤产率提高3.50%,尾煤水分降低9.70%,每年增加利润500万～1000万元。株洲洁净煤公司高挥发分不黏煤作高炉喷吹煤可行。     

高硫无烟煤降灰脱硫可行性试验研究

重点分析了王河煤矿高硫无烟煤的煤质特征、可选性及降灰脱硫的可行性。研究表明:简单地利用现有的物理分选方法很难将该矿区高硫无烟煤精煤硫分降到1%以下,而且精煤理论产率很低;如果将精煤硫分控制在1.2%～1.3%,并采用配煤等技术,可使精煤产率达到一个相对合理的水平;可以从高硫煤洗矸中选出硫精矿,实现资源的综合利用;也可考虑发展煤化工项目。     

高性能环保选煤捕收剂N9858和N9836的应用研究

实验对比了N9858、N9836及柴油对不同煤种的浮选效果;对于难选的粗颗粒煤,N9858和N9836均显示出比柴油要优异很多的浮选性能,可燃体回收率提高16%,精煤灰分无变化。对于易选的细颗粒煤,N9858显示出更强的浮选能力,在用量为柴油的50%条件下,与柴油及N9836相比,可燃体回收率分别提高了5.90%和4.04%,精煤灰分无明显变化。N9858及N9836的实际浮选效果比柴油更加贴近理论的分步释放曲线。