Separation and concentration of coal macerals by flotation

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Characterization and non-isothermal decomposition kinetics of some Turkish bituminous coals by thermal analysis

The thermal behavior of five bituminous coal samples was investigated in non-isothermal condition by thermal analysis. The integral method was used in the analysis of TGA data in order to determine the decomposition kinetics. The main region of the sample's weight loss, arising from the conversion of organic matter to gas, occurred within the temperature range 400-600 °C. The thermal parameters derived from TG and DTG curves were correlated with petrographic, proximate and ultimate analyses data. The results indicated that H/C ratio, fuel ratio, mean vitrinite reflectance and petrofactor could be qualitatively used in the prediction of the TG and burning behavior of various rank bituminous coals. © 2003 Elsevier B.V. All rights reserved

Ash melting behaviour with respect to VM content of coal

Traditional way for energy production is coal fired power plants. Ultimate product of coal fired power plants is ash. Coal ash is valuable for operations like cement production and in future it might get more importance. Ash properties changes with parent coal and operational parameters. Change in ash properties results in slagging or fouling problems inside the boiler. High temperature of combustion and low melting point of ash are the main reason of these problems. In this study 3 coal samples with moderate to high VM (volatile matter) content are observed in terms of ash melting behaviors. Lower VM content of coal resulted as lower initial ash deformation point. With the increase of VM content, increase in the slagging factor was observed. As temperature inside the boiler increases slagging is more likely to happen, since ash is molt at high temperatures. High VM content of coal is a reason for the accelerated temperature increase inside boiler. Slagging and fouling potential of the ashes of these 3 pattern coal are obtained with different indexes. Ash fusion temperature index of slagging and fouling potential resulted as “low to medium” potential for lower VM content of coal, and “high to severe” for higher VM content coals. © Springer International Publishing Switzerland 2016

Modeling of unburned carbon in fly ash and importance of size parameters

Unburned carbon (UBC) percentage in coal ash can be considered as an economic and environmental constraint since it is not only an important characteristic in terms of combustion efficiency but also it becomes more of an issue of further utilization of ash. In this study, particle size distribution (PSD) effect on UBC in fly ash (FA) was discussed and efficient size parameter of PSD in terms of UBC formation was determined. At the first stage of the study, regarding ash formation, percentage of any set of coal particles which are more likely to form fly ash (FA) was theoretically determined. For this purpose, a formulation including the size parameters was proposed. Secondly, with the help of a 3-day long systematical control of power, the effect of size distribution on UBC was obtained. The size distributions of these samples showed that an increase in D32 size parameter causes an increase in the amount of UBC as well. Relationships between the amount of UBC and mean values of size parameters (D10, D50, D90, D32, D43)were all statisticallymeaningful for both units of power plant concerned but D32 size parameter has a better fit among all the size parameters. In summary, D32 & UBC have a regression coefficient of 0.90 (R2 ~ 0.9),while other size parameters (D10, D50, D90, D43) & UBC have regression coefficients of 0.2 (R2 ~ 0.2) for both units. Finally, a model including these size parameters was proposed to predict UBC in FA. The model proposed was in good agreement with the measured UBC in FA. © 2015 Elsevier B.V

Coal floatability characterization by film flotation

This study covers film flotation data conducted on a bituminous coal of -850 + 425 µm, -425 + 300 µm, -300 + 212 µm, -212 + 150 µm, and -150 + 63 µm size fractions. Separation medium was prepared at various methanol-water mixtures to give different surface tensions. The float and sink fractions obtained by the tests were subjected to ash analyses. Calculated contact angle values were related with weight distribution and ash contents of floats. A contact angle distribution was observed in all size fractions. Inorganic materials were observed to be placed usually in vitrinite group macerals. It was concluded that distribution of contact angle resulted mostly from the distribution of organic constituents (maceral groups) within particles and selective breakage occurred during the comminution. The highest value of contact angle, 77.03°, was determined for -850 + 425 µm and the lowest one, 67.82°, was determined for -150 + 63 µm size fraction where some degree of inorganic liberation and/or selective accumulation was obtained. Copyright © Taylor & Francis Group, LLC

Stirred grinding of coal bottom ash to be evaluated as a cement additive

By-product generation from coal combustion in coal-fired thermal power plants has been increasing worldwide and reached to 125 million tons in the U.S. and 100 million tons in Europe. Coal-fired thermal power plants have a share of about 20% in Turkey's electricity production. Almost 57 million tons of coal with varying ash content of 20-55% was consumed in those plants. Uranium and thorium radioactivity of ashes of low rank coals limits the use of ashes. Consuming local bituminous coals, Catalagzi Thermal Power Station has been producing 0.65 million tons of ash including fly ash (80%) and bottom ash (20%), which have a potential use in civil engineering. The majority of the fly ash has already been used in cement or directly in concrete mortars. This study was aimed to evaluate the bottom ash of the CATES. For this purpose, bottom ash was ground in a pilot scale set including a vertical stirring mill. The set had the controlled feeding, separation, and collection facilities to represent industrial scale grinding. Compressive strength tests were carried out on the ground bottom ash samples by mixing in varying amounts of Portland cement for curing times of 2, 7, 28, and 90 days. It was found that with a 25% ash containing cement a strength value of 48.86 Mpa which corresponds to 93.82% of strength of reference was obtained at 90 days curing time. © 2010 Taylor & Francis Group, LLC

A simulation study of laboratory scale ball and vertical stirred mills

The aim of this study was to investigate the grindability of solid fossil fuels from a thermal power plant by using a vertical stirred mill and conventional ball mill. The solid fossil fuel sample was obtained from the Zonguldak Catalagzi thermal power plant in Turkey. The sample below 3350µm (d80 = 2100µm) was ground in the laboratory scale stirred mill and ball mill. The d80 sizes of the products at the end of grinding periods of 0.25, 0.50, 1 and 4 min in the stirred mill were determined as 190, 102, 78 and 28µm, respectively. For this purpose, the stirred mill was used at a stirring speed of 360 rpm and with a 6 mm diameter ball. In the ball mill, the d80 sizes of product after 1, 4, 8, 12 and 24 min of grinding were determined as 1802, 1130, 324, 167 and 81µm, respectively. The results indicated that grinding by means of a stirred mill was much more efficient than grinding with a ball mill in terms of size distribution of the products. The energy consumption of the product with d80 = 78µm was obtained as 10.53 kWh/t after 1 min of grinding time in the laboratory scale stirred mill. In the same manner, the energy consumption of product with d80 = 81µm by using the laboratory scale ball mill was 72.73 kWh/t after 24 min of grinding. It can be clearly seen that the d80 size of the fossil fuel reduced from 2100µm to 1130µm after a 4 min grinding period in the ball mill grinding tests. However, the d80 size of the solid fossil fuel reduced to 28µm after the same grinding time in the stirred mill and it was also possible to efficiently obtain size reduction below 100µm. However, the ball mill grinding process cannot provide this efficient size reduction for longer grinding times. The ball mill grinding experimental results and simulation results showed that they were fairly consistent with each other. The simulation of higher speed mills such as pin type stirrers has been extensively investigated for relatively small-scale applications by JKSimMet. In this study, the JKSimMet software package was adapted for a stirred mill with the help of the base model of ball milling. The aim of this study was to investigate the grindability of solid fossil fuels from a thermal power plant by using a vertical stirred mill and conventional ball mill. The time evolution of particle size and the related energy consumption have been determined. Furthermore, a simulation tool was used to describe the observed behavior. Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Petrographic properties with respect to VM content of coal

Petrographic analysis of coal is most critical step that must be taken into consideration regarding pulverized coal combustion. Petrographic constituents of coal play an important role and petrographic constituents have different combustion activeness. VM (volatile matter) content changes with respect to the coal rank. Petrographic composition of coal is also is a function of coal rank. That is why, coal fired power plants not only take proximate analysis of coal on board but also they should conceive the petrographic analysis. In this study, 3 coal samples with different VM content respectively are analyzed in terms of proximate and petrographic analysis. Petrographic analysis resulted as lowest VM content (20.98 %) of coal has the lowest vitrinite percentage (20.8 %). VM content are close for the analyzed two coals (20.98%, 23.38%) and vitrinite composition are close (21% and 32 %) for them. Not only petrographic composition is evaluated but also the reflection measurement of these 3 coals is obtained. In terms of reflection measurement of these coals, two coals with lower VM has the biggest range (0.40-0.94) and the coal with highest VM content has the narrowest range of vitrinite reflection (0.50-0.79) respectively. In addition, microscopic observations are carried out and pictures are provided in the order of better understanding the effect of petrographic composition on combustion. © Springer International Publishing Switzerland 2016

The effect of grinding media shape on the specific rate of breakage

The effect of the shape of grinding media on the breakage parameters of colemanite has been investigated in kinetic studies. In this present research, three different monosize fractions, i.e., -425 + 300 µm, -300 + 212 µm and -212 +150 µm, were used. The grinding media used for the tests were 36.5 × 36.5, 30.1 × 30.1, 25.4 × 25.4, 19.05 × 19.05 and 12.7 × 12.7 mm diameter cylinders, and 36.5, 30.1, 25.4, 19.05 and 12.7 mm diameter balls made from cast iron. The specific rate of breakage (S i) and model parameters (aT, a) were evaluated for the same quantity of cylinders, balls and feed material. The values of Si and the model parameters indicated that a faster breakage rate can be obtained by using cylinders as the grinding media. The size distributions of the products showed that the use of cylinders for grinding offers advantages for relatively coarse feeds. At shorter grinding periods, the product fineness from cylinder grinding was greater than that from ball grinding. However, after progressive grinding, the product fineness of ball grinding eventually exceeded that of cylinder grinding. The overall results indicated that the shape of the grinding media plays a determining role in the overall process. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA

Effect of chemical demineralization on thermal behavior of bituminous coals

Growing environmental concerns and the need for alternatives for oil and natural gas resulted in intensive researches on ultra clean coal (UCC). Therefore, the researches related to practice and application of various methods to produce UCC become more important. Thermal characterization of chemically demineralized coals by thermogravimetric analysis method is presented in this study. The aim of the study is to provide thermal data for HF-HNO3 leaching system used for the production of UCC. Coal samples were first physically enriched by density separation. Then the enriched portion was chemically demineralized by using HF and HNO3, respectively. Ash content of coal samples were reduced to a range of 0.12-0.41% by chemical demineralization process. The petrographic, ultimate and proximate analyses were carried out to determine main features of samples. Physically and chemically enriched coal samples were then analyzed in a TG by two different techniques separately. The first technique covered thermal characterization of samples under non-isothermal conditions. Characteristic temperatures for each sample were obtained from the TG and DTG data. The second technique involved the determination of reactivity of in situ produced chars of each sample. © 2006 Springer-Verlag