Pavel Ditl

Suspension of Solid Particles

Abstract This paper deals with the prediction of the impeller speed required for complete suspension of solid particles. Based on the inspection analysis of the governing equations, the dimensionless equation expressing such impeller speed was proposed. The specific forms of this equation were determined experimentally for a six-pitched blade turbine for solid concentrations of 2.5 and 10% by volume. Four different hydrodynamic regimes were observed depending on the relative particle size and Reynolds number values. In view of our results the weaknesses of existing theories and correlations were shown and discussed.

Comparison of three methods for natural gas dehydration

Abstract This paper compares three methods for natural gas dehydration that are widely applied in industry: (1) absorption by triethylene glycol, (2) adsorption on solid desiccants and (3) condensation. A comparison is made according to their energy demand and suitability for use. The energy calculations are performed on a model where 10 5 Nm 3 /h water saturated natural gas is processed at 30 °C. The pressure of the gas varies from 7 to 20 MPa. The required outlet concentration of water in natural gas is equivalent to the dew point temperature of – 10 C at gas pressure of 4 MPa.

Vortex depth in mixed unbaffled vessels

Abstract An experimental investigation of vortex depth in an unbaffled cylindrical vessel with co-axial agitation was made. Five types of impellers: standard six-blade disc turbine, flat six-blade turbine, pitched six-blade turbine, pitched three-blade turbine and anchor agitator were tested. Turbine impellers were investigated in two positions ( H 2 = d and H 2 = d /3). On the basis of theoretical analysis, the dimensionless vortex depth was statistically correlated as a function of Froude and Galileo numbers and a relative impeller size. Liquid viscosity and impeller size variations were reflected in the value of the Galileo number which was within the range 4 × 10 5 – 5 × 10 10 . The vessel diameters used in the experiments were, D = 0.15, 0.20, 0.30, 0.40 and 0.64 m.

Recovering copper from electric cable wastes using a particle shape separation technique

A particle shape separation technique was used to recover copper from electric cable wastes used in computer devices from the point of view of resource recycling. After the electric cables were crushed by a cutter mill, small pieces of the cables were impact milled for the purpose of liberating the copper wire from the plastic covering. The shape of the copper wires was prepared for separation by shape at the same time. By impact milling, the copper wires were twined and became pill-like particles. However, the shape of the plastic covering was irregular. An inclined conveyor and an inclined vibrating plate were used as the particle shape separator, and the most effective operating conditions for these apparatus were experimentally investigated. As a result, it was possible to separate copper from the plastic covering with high efficiency.

Solids concentration distribution in slurry reactors stirred with multiple axial impellers

Abstract The solids concentration distribution in solid—liquid suspensions in batch, mechanically stirred, vessels was investigated. The vessels were characterized by a high aspect ratio and were stirred with various combinations of multiple axial impellers. The suspensions were made of glass beads of various sizes in water and aqueous solutions of polyvinylpyrrolidone (PVP). The solids concentration was measured along the vertical axis of the vessel by means of an optical technique. The suspension efficiency of the impellers was compared on the basis of the departure of the solids concentration from suspension homogeneity (given as the variance of the solids concentration along the axis with respect to the mean) versus power consumption per unit mass. The solids concentration profiles were also modelled with the one-dimensional sedimentation—dispersion model having the Peclet number as a single adjustable parameter. For each geometrical configuration the Peclet number was correlated with the ratio of the tip speed to particle settling velocity and a Reynolds number based on the Kolmogorov theory. Once the difference in aspect ratio is taken into account, a single correlation for all the geometrical configurations could be obtained.

Natural Gas Dehydration

The theme of natural gas (NG) dehydration is closely linked with storage of natural gas. There are two basic reasons why NG storage is important. Firstly, it can reduce dependency on NG supply. With this in mind, national strategic reserves are created. Secondly, NG storage enables the maximum capacity of distribution lines to be exploited. NG is stored in summer periods, when there is lower demand for it, and is withdrawn in the winter periods, when significant amounts of NG are used for heating. Reserves smooth seasonal peaks and also short-term peaks of NG consumption. Underground Gas Storages (UGS) are the most advantageous option for storing large volumes of gas. Nowadays there are approximately 135 UGSs inside the European Union. Their total maximum technical storage capacity is around 109 ms3. According to the latest update, over 0,7∙109 ms3 of additional storage capacity will come on stream in Europe by 2020 [1]. There are three types of UGSs: (1) Aquifers, (2) Depleted oil/gas fields, and (3) Cavern reservoirs (salt or hard rock). Each of these types possesses distinct physical characteristics. The important parameters describing the appropriateness of UGS use are storage capacity, maximum injection/withdrawal performance, and gas contamination during storage. Generally, the allowable pressure of stored gas inside a UGS is up to 20 MPa. The pressure inside increases as the gas is being injected, and decreases when gas is withdrawn. The output gas pressure depends on further distribution. Distribution sites from UGS normally begin at 7 MPa. The temperature of the gas usually ranges from 20 35°C. The exact temperature varies with the location of the UGS and with the time of year.

Estimating the local turbulent energy dissipation rate using 2-D PIV measurements and a 1-D energy spectrum function

A simple method for estimating the local turbulent energy dissipation rate for a non-isotropic state is proposed. The proposed method is based on an estimation of the isotropic dissipation rate under the assumption of local isotropy, which is subsequently corrected for the actual conditions. The level of anisotropy is characterized by the fluctuation velocity components. The isotropic dissipation rates are obtained by energy spectrum function fitting. A data block averaging technique is used to smooth the spectrum. The effect of the data number within block on the calculated turbulent energy dissipation rate is taken into account. The proposed method has been tested on data obtained by a 2-D time-resolved PIV method. The effect of the spatial resolution of PIV on the estimation of the dissipation rate is also taken into account, using the correction proposed by Delafosse et al. (2011). The estimate of the local turbulent energy dissipation was found to be the same irrespective of the fluctuation velocity component that was taken for calculating the energy spectrum. This accords with the scalar character of the dissipation rate. The method also enables an estimate to be made of the integral length scale components.

Effect of pressure profile on evaluation of volumetric mass transfer coefficient in kLa bioreactors

Abstract The volumetric mass transfer coefficient k L a is a very important parameter that plays an important role in bioreactor design. Numerous authors have reported that the use of simple models not taking into account the dispersion effects in the gas and/or liquid phase may cause a large error in k L a estimation. We have analysed the effect of another factor on k L a determination, namely, the effect of the pressure profile along the vessel height. We propose a two-phase dispersion model which takes into account the pressure profile. We studied the sensitivity of various parameters to error caused by neglecting the pressure profile. It was found that even when applying an experimental technique that eliminates dispersion effects, the existence of the pressure profile needs to be taken into account, especially in large volume tanks with a non-ideal flow pattern in the liquid phase. We propose a simple correlation describing the error caused by neglecting the pressure profile. The proposed procedure can be used to correct all mass transfer coefficients evaluated by a model not taking into account the pressure profile.

Helax—a new type of static mixer—operation characteristics and comparison with other types

Each element of the new static mixer, Helax, is comprised of the helical surfaces of a twisted prismatic body whose diagonal base dimension equals the tube diameter D. The mixer is very efficient with a low pressure drop. The main operating characteristics λSM versus Re and LSM/D versus Re were determined experimentally on two tubes of diameters D = 16 and 25 mm. The pressure drop of the Helax static mixer was correlated by the equation λSM = 0.775 + 805/Re valid in the range 0.5 < Re < 10 000. Homogenization measurements in the range 8 < Re < 20 000 were correlated using LSM/D = 2.5 + [0.103 + 0.0032(log Re)2 + 4.9727 × 10−9(log Re)15]−sol43 The advantage of Helax static mixers is the extremely low pressure drop in the turbulent regime, low energy requirements for homogenization, and a low shear stress. The Helax mixer can be used advantageously in many industrial applications (e.g. in polymer engineering and bioengineering).

OPTIMIZATION OF PRESSURE SWING ADSORPTION EQUIPMENT PART II OPTIMIZATION OF TWO BED OXYGEN GENERATORS

Local equilibrium model described in Part I is used to stimulate both, the steady state operation conditions and transient regime after the start of PSA equipment. The effect of axial dispersion, adsorption isotherm nonlinearity and high pressure level is simulated. On the basis of numerical analysis, the operation of a classical two-bed oxygen generator is compared with two configurations having pressure equalizing step. The optimization strategy of the given PSA equipment has been proposed and the procedure is demonstrated on an example. The scaling-up condition for PSA equipments which can be described by local equilibrium model has been proposed on the basis of the theoretical analysis.