Yazar "Ceylan, K" seçeneğine göre listele
Listeleniyor 1 - 18 / 18
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Catalytic dissolution of two Turkish lignites in tetralin under nitrogen atmosphere: effects of the extraction parameters on the conversion(Elsevier Sci Ltd, 2001) Karaca, H; Ceylan, K; Olcay, ATwo Turkish lignites were extracted with tetralin in a batch autoclave under nitrogen atmosphere. Fe2O3, Mo(CO)(6), MoO3 or Al2O3 were used as the added catalyst. The isothermal extraction temperatures ranged from 325 to 425 degreesC, the starting nitrogen pressure ranged from atmospheric to 5 MPa, the isothermal extraction periods ranged from 0 to 120 min. After removal of char and solvent, the remaining products were separated into three fractions: preasphaltenes (benzene insolubles), asphaltenes (benzene soluble, n-pentane insolubles) and oils (n-pentane solubles) by successive extractions with benzene and n-pentane. The variations in the conversions and soluble product compositions were investigated with respect to the extraction conditions. The results indicate that the conversions of the lignites are low below 350 degreesC but high over 375 degreesC. The catalysts enhance mainly the oil formation, and the catalytic activities of Mo(CO)(6) and Fe2O3 are higher than the others. Lignite-impregnated catalysts show higher reactivity than the physically mixed catalysts. Increasing the extraction time and temperature affects the total conversion and soluble product composition. The gaseous product formation increases with the time at temperatures of 400 degreesC and above. (C) 2001 Elsevier Science Ltd. All rights reserved.Öğe Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide(Elsevier Science Bv, 1997) Karaca, H; Ceylan, KTwo Turkish lignites (Beypazari and Tuncbilek) were leached with the solutions of hydrogen peroxide in water or in 0.1 N H2SO4. The effects of some process parameters, such as concentration, time and temperature, on the removal of ash and sulphur have been investigated. The rate of ash and sulphur removal are relatively high in the first 30 min, but slow after 60 min of the reaction time. Depending on the type of lignite, the maximum reductions ranged from 30 to 70% in ash, from 70 to 95% in pyritic sulphur, and from 42 to 58% in total sulphur. A relatively small reduction (a maximum of 25%) was estimated for organic sulphur. The optimum process conditions were established as a hydrogen peroxide concentration of 15 wt.%, a temperature of 30 degrees C and a leaching time of 60 min. High peroxide concentration or high temperature did not result in an appreciable further reduction in ash and sulphur. Due to partial dissolution or oxidation of the lignites, some organic material losses occurred but no heating value loss was estimated. An overall kinetic approach was also applied for pyritic sulphur removal and the conversion data were analyzed by using both homogenous and heterogeneous reaction models.Öğe Eddy diffusivity of particles in turbulent flow in rough channels(Elsevier Sci Ltd, 2002) Altunbas, A; Kelbaliyev, G; Ceylan, KThe eddy diffusivity coefficient of particles depends on the flow characteristics and on the physical properties of the particles. Experimental data and theoretical considerations suggest that the ratio of the eddy diffusion coefficient of particles (D-TP) to the eddy diffusion coefficient of fluid (D-T) is dependent mainly on the friction velocity of fluid (U-*), the sedimentation velocity of the particles (V-s), the Reynolds number (Re) of the flow and also the relative roughness of channel.(epsilon/D). It is shown here that this relation among these parameters may be represented as D-TP/D-T = mu(R) proportional to (U-*(m)/V-S)(n), where m and n are empirical constants. Some new empirical relationships are proposed for the eddy diffusion coefficient of particles in the turbulent flow in vertical or horizontal channels. The results compare favorably with experimental data from the literature. (C) 2002 Elsevier Science Ltd. All rights reserved.Öğe Effectiveness of the dense medium and the froth flotation methods in cleaning some Turkish lignites(Pergamon-Elsevier Science Ltd, 2004) Ceylan, K; Kücük, MZThe feasibility of cleaning three Turkish lignites (Beypazari, Golbasi and Kangal lignites) by the dense medium separation or the froth flotation method has been investigated. Solutions of zinc chloride (ZnCl2) with specific gravities ranging from 1.1 to 1.75 have been used as the dense medium. In the case of froth flotation, methyl isobutyl carbinol (MIBC), diethyl isohexanol (DEH) and sodium dodesyl sulphonate (SIDS) were used as the frother and kerosene was used as the collector. In both methods, each lignite sample was separated into two sub-fractions: the lignite rich part and the mineral matter rich part. The results indicate that the effectiveness of the methods in ash and sulphur removal is appreciably different for the different lignites. An effective pyritic sulphur removal (over 90%) was obtained for Beypazari or Golbasi lignites by the dense medium separation. The effectiveness of the froth flotation was relatively different depending on both the lignite and frother type. The recovery is generally low and changes considerably depending on the frother type and particle size. (C) 2003 Elsevier Ltd. All rights reserved.Öğe Effects of the reaction conditions on the distribution of sulphur among the products of the catalytic dissolution of Turkish lignites(Elsevier Sci Ltd, 2002) Karaca, H; Ceylan, KEffects of the process parameter on the distribution of the inherent sulphur among the products of the catalytic liquefaction of two Turkish lignites have been investigated. The dissolution reactions were carried out in tetralin at 350-425 degreesC under nitrogen atmosphere. Fe2O3, MO(CO)(6), MoO3 or Al2O3 were used as the added catalysts. The starting nitrogen pressure ranged front atmospheric to 5 MPa. the isothermal extraction periods ranged from 0 to 120 min, solvent/lignite ratio ranged from 1/1 to 6/1. After drying in vacuum, the char and the Soluble products were analyzed for their sulphur contents. The results indicate that the sulphur content of the Soluble products were generally lower than 1% and only a small portion (approximate to0.5-7%) of the initial total sulphur passed to the Soluble product. Most of the Sulphur was remained in the char or passed into the gaseous products. Besides the process conditions, the structures of sulphur in the original lignites strongly affect the partitioning of the sulphur among the products. (C) 2002 Elsevier Science Ltd. All rights reserved.Öğe Estimation of optimum fluid velocity in high gradient magnetic filtration(Taylor & Francis Inc, 1998) Abbasov, T; Ceylan, KA high gradient magnetic cleaning process is favored by several branches of industry for the high purification of various technological fluids involving magnetic(ferro, para, or diamagnetic) particles. This paper presents a theoretical study about the effects of the parameters of a magnetic filtration system on the fluid velocity to be chosen. A model is presented to estimate the optimum filtration velocity needed to satisfy a predefined filter performance. The model is applicable for magnetic filter systems with packing fractions of up to 0.62 and for fluids containing magnetic particles. It is essentially based on the balance of moments acting on particles captured and accumulated in the magnetic filter. The boundary layer approach is used in the development of the model. The results indicate that the optimum filtration velocity depends on the properties of the fluid and on the parameters of the filter system. Model predictions and experimental data given in the literature are in a good agreement.Öğe Estimation of the maximum stable drop sizes, coalescence frequencies and the size distributions in isotropic turbulent dispersions(Elsevier, 2003) Ceylan, S; Kelbaliyev, G; Ceylan, KThe process of coalescence or breakup of drops in turbulent flow is of importance in many technical applications. A new size distribution takes place due to the coalescence or the breakup of the drops during the motion of a dispersed system. Based on the experimental data given in the literature, some new empirical relationships are developed in this paper to evaluate the maximum stable drop sizes, the coalescence frequencies and the drop size distribution in an isotropic turbulent flow. The relationships are developed essentially in terms of the particle Reynolds number or of the physical properties of the system. The Focker-Planck equation is used to estimate the particle size distribution. The model predictions are compared with the experimental data given in the literature. The results indicated that the predicted values and the experimental data are in a good agreement. (C) 2002 Elsevier Science B.V. All rights reserved.Öğe Estimation of the minimum stable drop sizes, break-up frequencies, and size distributions in turbulent dispersions(Taylor & Francis Inc, 2005) Kelbaliyev, G; Ceylan, KThe breakage of drops or bubbles in isotropic turbulent dispersions has been investigated. Based on the experimental data given in the literature, some new empirical relationships are derived to evaluate the minimum stable drop sizes, the breakup frequencies, and the drop size distribution in turbulent dispersions. The solutions of the stochastic Focker-Planck equation are used to estimate the particle size distribution. The relationships are expressed essentially in terms of the system properties. In addition, a new relationship was proposed to estimate the ranges of Reynolds, Weber, or Morton number, at which the drag coefficient is minimum. The model predictions are compared with the experimental data given in the literature.Öğe Filter performance and velocity distribution relation in magnetic filtration of non-Newtonian liquids(Marcel Dekker Inc, 1999) Abbasov, T; Ceylan, KFluid flow regime and the velocity distribution are effective parameters for systems in which various transport phenomena take place. Besides the properties of the contaminating particles and filter system in the case of high gradient magnetic filtration, the theological properties of the fluid are also important for both design and efficiency of the process. This paper presents a theoretical study about estimation of the velocity distribution in a magnetic filter and the dependence of filter performance on this distribution. A model is presented to estimate the velocity distribution and filter performance in magnetic filtration of Newtonian or weak non-Newtonian liquids. The model is essentially based on the balance of forces acting on particles captured and accumulated in the filter. Model predictions and experimental data given in the literature for Newtonian liquids are in a good agreement.Öğe Kinetic rate models for dissolution of Turkish lignites in tetralin under nitrogen or hydrogen atmospheres(Elsevier Science Bv, 1998) Ceylan, K; Olcay, AThe reaction kinetics of the dissolution of two Turkish lignites have been investigated. The dissolution products were separated into pseudo-components such as preasphaltenes, asphaltenes and oils by successive solvent extractions. Reaction mechanisms have been proposed and tested to estimate the rates of formation of these products. The proposed mechanisms are based on the assumptions that the reactions are irreversible, pseudo-first order with respect to the reacting species, and their rate constants obey linear Arrhenius behavior. The product distributions data have been assessed by a simple simulation program, The results indicated that certain simple kinetic models represent the data well and the prevailing mechanism changes slightly with temperature. The estimated energy of activation for dissolution changes from 54 kJ/gmol to 185 kJ/gmol depending on the lignite and the suggested reaction model. The results suggest that conversions of lignites to preasphaltenes and gases are slower than the conversion of preasphaltenes and asphaltenes to oils. Published by Elsevier Science B.V.Öğe Kinetic study of the thermal decomposition of (2-phenyl-1,3-dioxolane-4-yl) methyl methacrylate and 2-hydroxyethyl methacrylate copolymers(John Wiley & Sons Inc, 2005) Ceylan, NN; Ilter, Z; Ceylan, KThe kinetics of nonisothermal decomposition of (2-phenyl-1,3-dioxolane-4-yl) methyl methacrylate (PDMMA), 2-hydroxyethyl methacrylate (HEMA), and vinyl-pyrrolidone (VPy) copolymers were investigated by thermogravimetry (TG) and differential thermal analysis (DTA). The data indicated that the major weight loss occurs in the range of 270 to 450degreesC. The decomposition characteristics showed essentially two regimes and varied depending on the temperature and the copolymer composition. The apparent kinetic parameters of the decompositions were estimated from both TG and DTA data by using the alternative calculation methods. The results suggest that the weight loss rates may be represented, depending on the type of sample, by a reaction model of overall order 1.0 to 1.6, with an activation energy of approximately 65-95 kJ mol(-1). The DTA data estimated considerably higher values for the overall activation energies, around 198-240 kJ mol(-1). (C) 2005 Wiley Periodicals, Inc.Öğe Low temperature extractability and solvent swelling of Turkish lignites(Elsevier Science Bv, 1997) Onal, Y; Ceylan, KSix Turkish lignites have been pretreated with the solutions of HCl or sodium ethanolate at room temperature or at 150 degrees C. The volumetric swelling of the raw or pretreated lignites have been investigated by using 13 solvents at room temperature. These lignites have been subjected to Soxhlet extractions in the same solvents and in the linear alkylamines. The solubility of the samples in toluene under supercritical conditions were also tested. The effect of solvent on swelling ratio and on the extraction yields of the raw or pretreated lignites have been examined. The results have indicated that both swelling and extraction yields generally increased after the pretreatments and the increments are higher with hydrogen bonding solvents. Especially, sodium ethanolate pretreatment increases the solubility in toluene under supercritical conditions, The results suggest that solvent solubility parameter and electron donor number are effective in both swelling and solubility. A qualitative information regarding the structural characteristics of extracts was obtained by UV and NMR analysis. (C) 1997 Elsevier Science B.V.Öğe A new model for estimation of drag force in the flow of Newtonian fluids around rigid or deformable particles(Elsevier Science Sa, 2001) Ceylan, K; Altunbas, A; Kelbaliyev, GA number of relationships are given in the literature for estimation of the drag coefficients; however, most of these are applicable only for a narrow range of Reynolds number (Re). Some new empirical relationships are proposed in this study to estimate the drag coefficients in the flow of Newtonian liquids around the solid spherical or cylindrical particles and the deformable particles. An approximation series approach is used to develop these empirical relationships. It is shown that the proposed relationships can be applicable for the solid spherical or cylindrical particles in the range of 0.1 > Re > 10(6), and for the deformable particles (drops and bubbles) in the range of 0.1 > Re > 10(4). The predicted coefficients are in a good agreement with the experimental data given in the literature. (C) 2001 Elsevier Science B.V. All rights reserved.Öğe The roughness effects on friction and heat transfer in the fully developed turbulent flow in pipes(Pergamon-Elsevier Science Ltd, 2003) Ceylan, K; Kelbaliyev, GConvective heat transfer coefficient is strongly influenced by the mechanism of flow during forced convection. In this paper, the effect of pipe roughness on friction factor and convective heat transfer in fully developed turbulent flow are briefly discussed. A correlation for the friction factor applicable in the region of transition to the fully developed turbulent flow regime is proposed. Using this relationship, some new approximation formulae are proposed to predict the convective heat transfer coefficients in the pipes with a relative roughness of epsilon/D less than or equal to 0.05. The effectiveness parameter. for the heat transfer is investigated as a function of the pipe roughness, Reynolds number and Prandtl number. The effect of fouling is also briefly discussed. The: predictions of the proposed correlations are compared with the experimental data and with some other previous correlations given in the literature. (C) 2002 Elsevier Science Ltd. All rights reserved.Öğe Stochastical modeling of the granule size distribution in the agglomeration processes of powdered materials(Elsevier Science Sa, 2001) Ceylan, K; Kelbaliyev, GPowders with the correct amount of a liquid binder can be formed into agglomerates by vibrating, shaking or paddle mixing. Rotating drums or disks are commonly used in industry. The break-up process of the drops of the binding liquid and the kinetics of the powder agglomeration affect the granule size distribution in the agglomerate. Generally, mathematical procedures are required to estimate such size distributions. A theoretical model is presented in this study to emphasize the major system parameters affecting the particle size distribution during agglomeration. First, an analytical relationship is derived to represent the changes in the droplet volume with time. Then, Focker-Planck equation is used to predict the granule size distribution in an agglomeration process. The model predictions are compared with the experimental data, The results indicated that the model predictions and the experimental data are in a good agreement. (C) 2001 Elsevier Science B.V. All rights reserved.Öğe A theoretical model for estimation of drag force in the flow of non-newtonian fluids around spherical solid particles(Elsevier Science Sa, 1999) Ceylan, K; Herdem, S; Abbasov, TA theoretical approach for estimation of the drag correlation coefficients in the flow of Newtonian or weak non-Newtonian liquids around spherical solid particles is presented. Some new analytical relations are derived by using a stream function and the energy dissipation equation to approximate the drag coefficients to the experimental data. It is shown that these relationships can be applicable in a wide range of Reynolds number, Re, up to Re < 1000 for the liquids with a flow behavior index, n, in the range of 0.5 < n < 1. The predicted coefficients from these relationships are in very good agreement with the experimental data given in the literature. (C) 1999 Elsevier Science S.A. All rights reserved.Öğe A theoretical model for the particle distribution in a polydispersed solid mixture under hydrodynamic and gravitational effects(Elsevier Science Sa, 2001) Kelbaliyev, G; Ceylan, KThe particle size distribution in a polydispersed mixture significantly affects the technological behaviour of the mixture. Generally, mathematical procedures are required to estimate the particle size distribution or concentration distribution in a sorting process of such a mixture. A theoretical model is presented in this study to emphasize the major system parameters affecting the particle size distribution under hydrodynamic and gravitational effects. First, an analytical relationship is derived to represent the concentration profile in a sorting column during the classification of polydispersed mixtures. Then, the Focker-Planck equation is used to obtain the distribution function depending on the particle size. Some of the parameters of these analytical relationships are evaluated by comparing the equations with experimental data. The results indicated that the model predictions and the experimental data are in good agreement. (C) 2001 Elsevier Science B.V. All rights reserved.Öğe Thermogravimetric analysis of pretreated Turkish lignites(Elsevier Sci Ltd, 1999) Ceylan, K; Karaca, H; Önal, YThe kinetics of nonisothermal pyrolysis of raw, demineralized or oxidized Turkish lignites have been investigated by thermogravimetry, differential thermal analysis and differential scanning calorimetry. The analyses were carried out in an inert atmosphere or in air atmosphere. The weight loss data indicate that pyrolysis characteristics of the lignites and the prevailing kinetic mechanism vary depending on temperature. The weight loss rates show essentially two regimes, and the major weight loss occurs in the range of 300 degrees C-650 degrees C. The results for the low temperature region (T < 200 degrees C) suggest that the weight loss may be represented by 1.2-1.4-th order of reaction with an activation energy of approximately 15-35 kJ mol(-1). The differential thermal analysis and the differential scanning calorimetry data gave similar values for the overall reaction order and activation energies for this temperature region. At the higher temperature region (T > 300 degrees C), 1.2-1.8-th order of reaction shows a good fit with the weight loss data. The values of the estimated activation energies for this region vary from approximately 40 to 85 kJ mol(-1) depending on the type of sample. However, the differential thermal analysis data suggest that the overall reaction order is around 1.0-1.2 and the effective activation energies vary approximately from 170 to 250 kJ mol(-1). (C) 1999 Elsevier Science Ltd. All rights reserved.
