Kadim Ceylan

Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide

Two 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 °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.

Effects of treatments on the mineral matter and acidic functional group contents of Turkish lignites

Six Turkish lignites were treated with solutions of HCl or EtONa at ambient temperature or at 150°C. The proximate analysis, forms of sulfur, acidic functional groups and calcium contents of the raw and treated lignites were determined. The solutions after treatment were analysed for calcium. The effects of the treatment on certain structural components of the lignites varied from one lignitie to another. HCl treatment was effective in ash reduction and in the transformation of carboxylate species to carboxylic acids, but not in desulfurization. The ash reduction was accompanied by an increase in combustible sulfur. EtONa treatment was effective in desulfurization but not in ash reduction or in the removal of chelate- or salt-forming cations. The results suggested that this treatment promoted selective cleavage of certain chemical bonds, such as ester, ether or carbon-sulfur bonds, resulting in an increase in acidic functional groups of the lignites, desulfurization and partial dissolution. FT-i.r. spectroscopy and X-ray diffractometry provided some additional evidence regarding the changes in lignite structure due to the treatments.

DEVELOPMENT OF NEW EMPIRICAL EQUATIONS FOR ESTIMATION OF DRAG COEFFICIENT, SHAPE DEFORMATION, AND RISING VELOCITY OF GAS BUBBLES OR LIQUID DROPS

Some new correlations are derived to estimate the drag coefficient, the shape deformation, and the rising velocity of particles moving in an infinite liquid medium. The correlations are derived in terms of the dimensionless groups such as Reynolds number (Re), Morton number (Mo), and Weber number (We). The derivations are based on the experimental data or some other correlations given in the literature. A single statement is proposed to estimate the drag coefficient for the spherical solid particles that may be applicable in the range of 0.5 < Re < 105. Similarly, some other equations are also derived to estimate the drag coefficient, the shape deformation, or the rising velocity for gas bubbles or liquid drops. The drag equation is applicable in the range of 0.5 < Re < 100 and 9 × 10−7 ≤ Mo ≤ 7; the shape deformation equation is applicable in the range of 0.5 < Re < 100 and 1.1 × 10−5 ≤ Mo ≤ 7; and the rising velocity equation is applicable in the range of 0.1 < Re < 100 and 9 × 10−7 ≤ Mo ≤ 80. The model predictions are compared with the experimental data and with the other correlations given in the literature. The results indicated that the model predictions are in a good agreement with the literature data.

A theoretical model for estimation of drag force in the flow of non-newtonian fluids around spherical solid particles

A 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.

A new model for estimation of drag force in the flow of Newtonian fluids around rigid or deformable particles

Abstract A 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.

Dissolution of two Turkish lignites in tetralin under hydrogen or nitrogen : effects of the extraction parameters on the conversion

Abstract Two Turkish lignites were extracted with tetralin in a batch autoclave under nitrogen or hydrogen atmosphere. The isothermal extraction temperatures ranged from 325 to 425 °C at 25 °C intervals and the isothermal extraction periods were 0, 30, 60 and 120 min. After removal of char and solvent, the remaining products, which were completely soluble in tetrahydrofuran, 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 coal conversion and soluble product composition were investigated with respect to the extraction conditions. The conversion was low below 350 °C but high above 375 °C. As the conversion of the lignites increases, transformation of tetralin to naphthalene also increases. An increase in extraction period affects the product composition but not the percentage conversion, at temperatures of 400 °C and above. In general, the effect of type of gaseous atmosphere on the total conversion was minor. Depending on the extraction conditions, however, the gaseous atmosphere affected the soluble product composition.

The roughness effects on friction and heat transfer in the fully developed turbulent flow in pipes

Convective 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 e/D⩽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.

Eddy diffusivity of particles in turbulent flow in rough channels

Abstract The 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 ( e / D ). It is shown here that this relation among these parameters may be represented as D TP /D T = μ R ∝(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.

Estimation of the maximum stable drop sizes, coalescence frequencies and the size distributions in isotropic turbulent dispersions

Abstract The 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.

Reductive leaching of pyrolusite ore by using sawdust for production of manganese sulfate

Manganese compounds, such as manganese sulfate, can be obtained from pyrolusite, a manganese ore. Low-grade manganese ores is usually treated by hydrometallurgical methods. In this study, the leaching and recovery of manganese from pyrolusite ore in sulfuric acid solutions containing sawdust as reducing agent was investigated. The effects of experimental parameters, such as sulfuric acid concentration, sawdust amount, solid-to-liquid ratio, stirring speed, particle size, reaction temperature, and leaching time, on the manganese extraction from ore were examined. The results showed that the leaching rate of pyrolusite ore increased with an increasing sulfuric acid concentration, sawdust amount, stirring speed, reaction temperature and leaching time, and decreasing in solid to liquid ratio and particle size. The kinetic analysis of leaching process was carried out, and it was determined that the reaction rate was controlled by diffusion through the product layer under the experimental conditions in this work. The activation energy was found to be 22.35 kJ mol−1. Manganese can be recovered as manganese sulfate by the evaporative crystallization of the purified leach liquor.