Investigation of the effect of agglomeration time, pH and various salts on the cleaning of Zonguldak bituminous coal by oil agglomeration

In this study, the effects of bridging liquid concentration, agglomeration time, pH and various salts on the combustible recovery and ash contents of the agglomerated products have been investigated. Kerosene was used as bridging liquid. The optimum values of kerosene concentration, pH and agglomeration time have been determined as 20 wt%, 7.5 and 15 min, respectively. Metallic salts, such as FeSO₄, NaCl, FeCl₃, Al₂(SO₄)₃ were used in the experiments in which the effects of salts were investigated. While the combustible recovery slightly increased depending on the increase in the concentration of NaCl, very small decreases have been recorded in the recoveries depending on the increase in the concentration of the FeCl₃. A considerable reduction occurs in the agglomeration recovery with the increasing concentration of FeSO₄, while the combustible recovery slightly decreases at low concentration of Al₂(SO₄)₃.     

Optimization of experimental conditions for recovery of coking coal fines by oil agglomeration technique

The significance of coking coal in the metallurgical sector as well as the meager coking coal reserves across the globe increase the necessity to recover coking coal fines from the fine coking coal slurries generated from coal preparation and utilization activities. Oil agglomeration studies were carried out by varying the experimental conditions for maximum recovery of coking coal fines i.e., yield of the agglomerates. The various operational parameters studied were oil dosage, agitation speed, agglomeration time and pulp density. By using Taguchi experimental design, oil dosage (20%), agitation speed (1100 rpm), agglomeration time (3 min) and pulp density (4.5%) were identified as the optimized conditions. A confirmation experiment has also been carried out at the optimized conditions. The percentage contribution of each parameter on agglomerate yield was analyzed by adopting analysis of variance (ANOVA) statistical method as well as multiple linear regression analysis. The order of influence of the parameters on the agglomerate yield is of the following order: pulp density > oil dosage > agitation speed > agglomeration time. A mathematical model was developed to fit the set of experimental conditions with the yield obtained at each test run and also at the optimized conditions. The experimentally obtained yield was compared with the predicted yield of the model and the results indicate a maximum error of 5% between the two. A maximum yield of 90.42% predicted at the optimized conditions appeared to be in close agreement with the experimental yield thus indicating the accuracy of the model in predicting the results.     

Multi-response optimization of oil agglomeration with multiple performance characteristics

In this paper, the multi-response optimization of grade and recovery simultaneously using Taguchi quality loss function has been done for Zonguldak/Turkey bituminous coal by oil agglomeration. The controllable factors selected in this investigation are solid content, amount of oil, agitation time and agitation rate. The percentage contribution of each controllable factor has been determined on the performance of oil agglomeration. The amount of oil has been found as the most effective factor and its contribution is 65.42% on multiple quality characteristics. The confirmation experiment has also been carried out according to the optimum conditions predicted. The grade and recovery have been increased up to 0.565% and 93.04%, respectively against the initial value of grade and recovery as 0.436% and 75.08%, respectively. The results show considerable improvement in both the quality characteristics such as grade and recovery with the multi-response optimization used, as compared the initial value of grade and recovery.     

Application of the Box-Wilson experimental design method for the spherical oil agglomeration of coal

In this study, the Box-Wilson statistical experimental design method was employed to evaluate the effects of important variables such as bridging liquid (oil) concentration, salt (CaCl₂·2H₂O) concentration and stirring speed on the agglomeration of bituminous coal. Response function coefficients were determined by the regression analysis of experimental data and the predictions were found to be in good agreement with the experimental results. The optimum kerosene concentration, CaCl₂·2H₂O concentration and stirring speed were determined as 30 wt%, 1 M and 1683 rpm, respectively, when considering combustible recovery and ash content.In addition, contact angle and solution surface tension measurements were carried out to evaluate of agglomeration success with the contact angle values and surface tension values. The surface tension of CaCl₂ 2H₂O solutions and the average contact angle increased with increasing CaCl₂·2H₂O concentration.     

Modified oil agglomeration process for coal beneficiation. II. Simultaneous grinding and oil agglomeration

The spherical oil agglomeration technique developed at the National Research Council of Canada (NRC) for cleaning and recovering very small coal particles can be simplified by combining the grinding and agglomeration steps such that the excess energy expended while grinding is used for mixing and agglomeration. Experiments with the Szego mill, which is able to handle the pasty agglomerates, have shown that ash removal from Minto (New Brunswick) coal is comparable to that obtained with the usual NRC process. The generally flaky products of the Szego mill allow better ash liberation, and the presence of oil enhances grinding performance. Favourable oil-coal-water ratios have been established. Major savings in equipment and operating costs are possible with the combined process.     

The investigation of coal-pyrite/lignite concentration and their separation in the artificial mixture by oil agglomeration

In this study, the concentration of coal-pyrite and lignite taken from Yozgat-Ayridam (Turkey) Coal Management was investigated by oil agglomeration.In the previous studies, the agglomeration of coal-pyrite was investigated using different bridging liquids (fuel oil, diesel oil and kerosene) and the combination of reagent (KEX, Acorga M5397)+kerosene. When using only bridging liquids, the agglomeration recovery of pyrite was very low. To increase the hydrophobicity of pyrite, KEX was used. However, the pyrite was not agglomerated with an acceptable recovery. But when using Acorga M5397, which is a chelating reagent, the agglomeration recovery of pyrite was increased. The pyrite was agglomerated with a recovery of 76.70 wt% by single-stage agglomeration.In the optimum conditions which were determined for coal-pyrite, the agglomeration recovery of lignite was investigated. It was found that the lignite could not be agglomerated with an acceptable recovery.To investigate the separation of coal-pyrite and lignite, the artificial mixture of coal-pyrite and lignite was prepared with the weight ratio of 1/4 of coal-pyrite and lignite. It was found that the pyrite could be agglomerated at a recovery of 96.54% with three-stage agglomeration process. The lignite concentrate was produced with a recovery of 73.96 wt% and the pyrite content of 0.86 wt%.These findings showed that the coal-pyrite and lignite could be separated by oil agglomeration using appropriate reagent and bridging liquid.     

Modified oil agglomeration process for coal beneficiation. III. Grinding and agglomeration using different szego mill designs

The simultaneous grinding/agglormeration process has been used to beneficiate Minto coal. Experiments with the Szego Mill, a planetary ring-roller mill with grooved rollers, have given good results. Different roller ridge/groove sizes have been tested and favourable oil-coal-water ratios established. Ash removal is closely related to grinding performance. Very short mill residence times, of the order of 10 seconds, are sufficient for microagglomerate formation. Considerable equipment and operating cost savings are possible with the modified process.     

Microbial desulfurization of coal and oil

Biotreatment of fossil fuels may be regarded as suitable technology for the desulfurization of oil and coal before combustion, especially for small-scale combustion plants where flue gas cleaning is too expensive.

Although several patents, especially on the field of biodesulfurization of oil, already exist, successful application in a large scale could not be demonstrated until now. “Organic sulfur” is characterized by covalent C-S bonds and can be regarded as an element which is integrated in the macromolecular matrix of coal and in organic sulfur compounds present in oil. As for the results of more semi-empirical approaches no reproducibility and transferability to other oil qualities could be demonstrated when model compounds representing the organic sulfur species were used.

This research strategy resulted in a number of promising biochemical pathways for the degradation and/or desulfurization of such compounds. However, up to now the use of microorganisms able to degrade model compounds in a biotechnological process for coal or oil desulfurization does not meet the expectations.

Thus, it has to be concluded that additional research is needed which should be focussed on the development of biocatalysts with a broad substrate specificity and on methods to improve the availability of the organically bound sulfur in the molecular structure of oil and coal.     

Biological production of methane from bituminous coal

Biogasification of coal offers significant economic and environmental benefits for the continued utilization of coal resources. Several consortia from various natural sources associated with coal have been shown to produce methane from media containing only coal as the organic carbon source. Methane production of these samples has continued to increase with time. The cultures have remained viable and have continued to produce methane after 5 successive transfers to media containing coal as the sole carbon source. Methane quantities of 4 and 5 volume percent methane (0.03 and 0.04 mmol per tube) have been observed from Pittsburgh and Wyodak coals. Serum tube experiments were scaled to larger column experiments that also indicated that methane is produced from medium containing coal as the only carbon source.     

Modified oil agglomeration process for coal beneficiation. iv. pilot-plant demonstration of the simultaneous grinding-agglomeration process

Simultaneous grinding and agglomeration (SGA) in the novel Szego Mill allows significant simplifications and energy savings. The excess grinding energy is used for mixing and agglomerate formation. Results are reported over a range of operating conditions. The SGA process has been demonstrated in the laboratory and in a 12 tonnes/day pilot plant with satisfactory results. The economics of coal beneficiation for slurry fuel preparation is considered.     

Modified oil agglomeration process for coal beneficiation. I. Mineral matter liberation by fine grinding with the szego mill

The spherical oil agglomeration technique developed at the National Research Council of Canada (NRC) is an excellent method for cleaning and recovering very small coal particles. The finely ground coal, dispersed in water, is contacted with oil by intensive mixing. The hydrophobic coal particles collect onto the oil droplets to form the agglomerates which are then separated from the aqueous phase by screening. A Szego Mill was used to wet grind Minto (New Brunswick) coal which was then subjected to laboratory agglomeration by the NRC procedure. A comparison with coal ground in a ball mill indicated superior ash rejection. The improved performance is attributed to better mineral liberation which is enhanced by the more flaky particles produced in the Szego Mill.     

Effects of operational parameters on emission performance and combustion efficiency in small-scale CFBCs

A well-designed CFBC can burn coal with high efficiency and within acceptable levels of gaseous emissions. In this theoretical study effects of operational parameters on combustion efficiency and the pollutants emitted have been estimated using a developed dynamic 2D (two-dimensional) model for CFBCs. Model simulations have been carried out to examine the effect of different operational parameters such as excess air and gas inlet pressure and coal particle size on bed temperature, the overall CO, NO_x and SO₂ emissions and combustion efficiency from a small-scale CFBC. It has been observed that increasing excess air ratio causes fluidized bed temperature decrease and CO emission increase. Coal particle size has more significant effect on CO emissions than the gas inlet pressure at the entrance to fluidized bed. Increasing excess air ratio leads to decreasing SO₂ and NO_x emissions. The gas inlet pressure at the entrance to fluidized bed has a more significant effect on NO_x emission than the coal particle size. Increasing excess air causes decreasing combustion efficiency. The gas inlet pressure has more pronounced effect on combustion efficiency than the coal particle size, particularly at higher excess air ratios. The developed model is also validated in terms of combustion efficiency with experimental literature data obtained from 300 kW laboratory scale test unit. The present theoretical study also confirms that CFB combustion allows clean and efficient combustion of coal.     

分散剂在尾煤选择性聚团脱灰中的应用

利用选择性聚团法对平顶山尾煤进行脱灰分选 ,加入分散剂后 ,在一定程度上可降低超细精煤的灰分。选择六偏磷酸钠、硅酸钠、腐植酸钠、木素磺酸钙、碳酸钠、糊精 6种分散剂进行了应用实验 ;并通过测量矿浆的ZETA电位分析了这些分散剂的作用机理。     

Steam gasification of an australian bituminous coal in a fluidized bed

To produce low calorific value gas, Australian coal has been gasified with air and steam in a fluidized bed reactor (0.1 m-I.Dx1.6 m-high) at atmospheric pressure. The effects of fluidizing gas velocity (2–5 U_f/U_mf), reaction temperature (750–900 °C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63–1.26) on gas composition, gas yield, gas calorific value of the product gas and carbon conversion have been determined. The calorific value and yield of the product gas, cold gas efficiency, and carbon conversion increase with increasing fluidization gas velocity and reaction temperature. With increasing air/coal ratio, carbon conversion, cold gas efficiency and yield of the product gas increase, but the calorific value of the product gas decreases. When steam/coal ratio is increased, cold gas efficiency, yield and calorific value of the product gas increase, but carbon conversion is little changed. Unburned carbon fraction of cyclone fine decreases with increasing fluidization gas velocity, reaction temperature and air/coal ratio, but is nearly constant with increasing steam/coal ratio. Overall carbon conversion decreases with increasing fluidization velocity and air/ coal ratio, but increases with increasing reaction temperature. The particle entrainment rate increases with increasing fluidization velocity, but decreases with increasing reaction temperature. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

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.     

Demineralization of a UK bituminous coal using HF and ferric ions

A UK bituminous coal has been used to study demineralization by two-stage chemical leaching. The first-stage uses hydrofluoric acid (HF) at 65 °C and reduces the ash content from 5.30 wt% to 1.37 wt% by mainly removing Al and Si containing minerals. Subsequent leaching by ferric ions decreases the ash content further to 990 ppm by removing most of the pyrite and fluorides formed during the HF leaching. Calorific value of the coal shows no change following leaching, which suggests no oxidation is occurring to the coal carbonaceous matrix. The mercury and sulfur contents after the two-stage leaching sequence decrease by 40% and 26%, respectively.     

附聚胶乳附聚作用的研究

本文研究了一种胶乳对另一种胶乳的附聚作用。研究了附聚过程的基本规律,发现存在两个附聚峰。在水溶性大分子附聚胶乳机理的基础上,探讨了附聚胶乳附聚作用的机理。     

Prediction of economic operating conditions for Indian coal preparation plants

The most important optimization concept, which, has long been recognized in coal preparation with multiple cleaning circuits, is the constant incremental quality approach. However, this approach maximizes the overall plant yield for a targeted product quality, without putting any emphasis on coal value/price. So, sometimes confusion arises in the determination of the overall plant yield that would more than offset the price due to lower quality of product. In this paper a method is presented to maximize the coal value by considering the equal incremental quality approach as well. Here the predicted yield of composite coal has been calculated by using a designed probable error value, then the value of a particular coal is maximized. A case study with six different coals of different characteristics is presented to ascertain the merit of this approach. This technique offers the coal preparation engineer an effective and straight forward method for determining the optimum cut points of separation for different coals to achieve maximum economic gain.     

On the effects of firing semi-anthracite and bituminous coal under oxy-fuel firing conditions

Traditional wisdom has lead to the design of a boiler being dictated by its fuel. Typically, lignite requires a large boiler to accommodate the moisture content and ash behaviour and anthracite needs a design with a long residence time to allow for complete combustion. Thus the result is that different boiler designs are required for different fuel types. This work demonstrates that it is possible to fire under oxy-fuel firing conditions different fuels in potentially a single combustion environment. In the present work a short series of scoping tests firing Russian semi-anthracite under air and oxy-fuel firing conditions on the RWEnpower Combustion Test Facility (CTF) have been performed and result compared to firing a South African bituminous coal. An IFRF swirl burner was used. The purpose behind this work was to determine whether oxy-fuel firing offered the potential for firing a wider range of coal qualities on a swirl stabilised burner than is conventional showing that stable combustion can be achieved with semi-anthracite as with bituminous coal. In this short communication, it is shown that this is possible. Flame photographs of the Russian semi-anthracite coal fired on air and under oxy-fuel firing conditions at recycle ratios of 75%, 72% and 68% were taken. The air firing condition produced a non-luminous flame in the near burner region. For oxy-fuel firing at 75% recycle ratio, the flame is also non-luminous and more so that the air firing case. When the recycle ratio is reduced from 75% to 68% the flame becomes increasingly luminous and at 68% an intense flame was observed well anchored into the burner quarl. Radiative heat flux measurements were taken with the Russian semi-anthracite coal at 68% recycle ratio and compared to the South African bituminous coal at 68% recycle ratio and on air. In general the peak in radiative heat flux for the Russian semi-anthracite at 68% recycle ratio compared to the South African bituminous coal on air is slightly higher reflecting the effect of oxygen enrichment and the higher calorific value of the semi-anthracite. It can also be observed that the location of the peak in radiative heat flux with Russian semi-anthracite coal at 68% recycle is displaced downstream. In the near burner region, the radiation intensity is lower for the Russian semi-anthracite at 68% recycle ratio compare to South African bituminous coal at 68% recycle ratio and on air reflecting the lower (but not insignificant) intensity of combustion in this region for the Russian semi-anthracite coal.