Minimum fluidization velocity at elevated temperatures and pressures

A procedure based on the Ergun equation to predict the minimum fluidization velocity at elevated temperatures and pressures and for different gaseous fluidizing agents has been discussed and shown to be applicable for practical purposes.     

An investigation of the viscosity of dry air at elevated pressures and temperatures using a steady-flow capillary viscosimeter

A steady-flow capillary viscosimeter, using dry air as the test gas, has been demonstrated at 150, 230, 330 and 430° Centigrade and over a pressure range of 35–150 atmospheres. Measured viscosities showed a maximum isothermal increase of about 4%. An extrapolation procedure was used to correct for flow and temperature discrepancies and a modified Hagen-Poiiseuille equation, using variables evaluated at the mean capillary temperature, was applied to those data taken under nonisothermal conditions. The overall assembly and technique are capable of relative viscosity measurements having a standard deviation within 11/2% in the cited ranges.     

Minimum fluidization velocity at elevated temperature in tapered fluidized bed

Very little data of minimum fluidization velocity at elevated temperatures of tapered bed are available in the literature. This study was undertaken to provide some data under elevated temperature conditions in tapered bed. Data on minimum fluidization velocity have been obtained experimentally for temperature up to 800 °C in case of 0.5 mm diameter of sand particles and up to 500 °C in case of 1 mm diameter of glass beads in tapered bed. An equation valid for the bed has been developed in terms of Archimedes number and Reynolds number. The experimental values for minimum fluidization velocity at elevated temperatures have been compared with the calculated values obtained from present equation and from earlier equations developed by other authors for ambient conditions in conventional (cylindrical) bed and tapered bed. Fairly good agreement was found to exist between the calculated (from present equation) and the experimental values.     

An experimental study of non-newtonian fluid flow in fluidized beds: minimum fluidization velocity and bed expansion characteristics

In this work, new experimental measurements of the minimum fluidization velocity and velocity-voidage characteristics are reported for a variety of liquid-particle systems in glass columns of two different diameters. Three types of liquids, namely, Newtonian, visco-inelastic, and visco-elastic fluids, were used to fluidize the beds of glass particles of four different sizes (1.27–15.8 mm). The results obtained with Newtonian liquids conform to the expected behaviour. The applicability of a variety of equations has been examined with a view to predicting the values of the minimum fluidization velocity and fluidization index for non-Newtonian systems. The experimental results reported herein embrace the following ranges of conditions: 1.27 < D_p < 15.8 mm; D_T = 50.8 and 101.6 mm, and 0.382 n 1.00.     

Prediction of minimum fluidization velocity for vibrated fluidized bed

The prediction of minimum fluidization velocity for vibrated fluidized bed was performed. The Geldart group A and C particles were used as the fluidizing particles. The method based on Ergun equation was used to predict the minimum fluidization velocity. The calculated results were compared with the experimental data.The calculated results of minimum fluidization velocity are in good agreement with experimental data for Geldart group A particles. For group C particles, the difference between the calculated results and experimental data is large because of the formation of agglomerates. In this case, the determination of agglomerate diameter is considered to be necessary to predict the minimum fluidization velocity.     

Determination of minimum fluidization velocity by pressure fluctuation measurement

Using the standard deviation of pressure fluctuations to find the minimum fluidization velocity, U_mf, avoids the need to de-fluidize the bed so U_mf, can be found for operational bubbling fluidized beds without disrupting the process provided only that the superficial velocity may be altered and that the bed remains in the bubbling fluidized state. This investigation has concentrated on two distinct aspects of the pressure fluctuation method for U_mf determination: (1) the minimum number of pressure measurements required to obtain reliable estimates of standard deviation has been identified as about 10000 and (2) pressure fluctuation measurements in the plenum below the gas distributor are suitable for U_mf determination so the problems of pressure probe clogging and erosion by bed particles may be avoided.     

Prediction of minimum fluidization velocity for fine tailings materials

The suitability of several minimum fluidization velocity correlations has been investigated for fine zinc slime, iron ore tailings, both pre and post hydro-cyclone uranium tailings, and a relatively coarse grade of fly ash. It has been found that most of the published correlations significantly underestimate the value of minimum fluidization velocity for the four different tailings materials. Predictions due to Van Heerden et al. (1951) [45], Noda et al. (1986) [76], Coltters and Rivas (2004) [39], and Xu and Zhu (2009) [93], agree reasonably with the experimental data, whereas the fly ash, which belongs to Geldart Group B materials, has shown a large deviation. Thus these correlations could be used for the fine tailings materials that comprise a variety of constituents and possess a degree of cohesiveness. A modification of Coltters and Rivas correlation has also been suggested to assess the combined effect of particle size and density on minimum fluidization velocity.     

Hydrogen mass transfer in liquid hydrocarbons at elevated temperatures and pressures

The mass transfer rate of hydrogen in tetralin and hydrogenated SRC II liquid was studied in a stirred vessel at 606–684 K and 7.0–13.5 MPa. Experiments were carried out using a newly developed in-situ hydrogen probe made of semi-permeable nickel membrane. The effects of stirrer speed, liquid height to vessel diameter ratio, temperature and pressure on mass transfer rate coefficients were investigated. The experimentally determined $\text{K}{}_{\mathrm{<mtext>l</mtext>}}\text{a}$ values were correlated in terms of power input per unit volume of liquid and liquid height to vessel diameter ratio as follows: $\text{k}{}_{\mathrm{<mtext>L</mtext>}}\text{a = 3.43 × 10}{}^{\mathrm{?4}}\text{(}\text{P}\text{V}\text{)}{}^{0.8}\text{(}\text{H}\text{D}{}_{\mathrm{<mtext>T</mtext>}}\text{)}{}^{\mathrm{?1.9}}$ Furthermore, the liquid-phase mass transfer coefficient, $\text{k}{}_{\mathrm{<mtext>l</mtext>}}$, was found to be of the order of 10^?5 m s^?1 for low agitator speeds.     

Liquid hold-up and minimum fluidization velocity in a turbulent contactor

Transient-response experiments have been performed in conjunction with bed expansion measurements to determine liquid hold-ups and minimum fluidization velocities in a 12-in. turbulent-bed gas-liquid contactor. The amount of liquid hold-up was found to be independent of gas velocity, but dependent upon both liquid rate and packing diameter in the same manner as reported for conventional fixed-bed absorbers. The data on minimum fluidization velocity, G_mf, which was interpreted in the present study as the maximum gas mass velocity at which the bed maintained its static height, showed a considerable variation with packing diameter, d_p and liquid flow rate, L. A correlation of G_mf with d_p and L was presented.     

Viscosity of organic liquids at elevated temperatures and the corresponding vapour pressures

This work involved the measurement of the viscosities of pure organic liquids at temperatures ranging from 353.15 K to 463.15 K and at the corresponding vapour pressures. A rolling ball viscometer was used where considerable emphasis was given to achieve simplicity and rapidity in obtaining results, without sacrificing the accuracy. Considering the forces affecting the motion of the ball inside the viscometer tube, an equation for the calibration of the viscometer at the same working temperature was derived. The constants of this equation were determined using benzene as the reference liquid, and the dependency of the constants on the temperature was also established. Comparing the derived equation with published ones demonstrated its adequacy in both the streamline and transition flow conditions. The liquids studied were toluene, methanol and n-hexane. In some cases, the results compared reasonably well with published data while in others, deviations of up to 15% were found. Nine equations were tested with the experimental results for the prediction of the viscosity of these liquids. It was found that the 3-constant Agrawal and Thodos empirical equation gave the least average deviation.     

Saturated thermodynamic properties for the air-water system at elevated temperatures and pressures

A new thermodynamic model is proposed to calculate the thermodynamic properties for the air-water system in which the dry air was assumed to be a mixture of nitrogen and oxygen with the mole fractions of 0.7812 and 0.2188, respectively. For the vapor phase, fugacity coefficients were calculated with the modified Redlich-Kwong equation of state in which a new interaction parameter of oxygen and water was correlated from the experimental data of oxygen-water system. The dissolved gas followed Henry's law. Henry's constant of nitrogen was calculated with the Helgeson equation of state and that for oxygen was correlated from the experimental data of oxygen-water system. The proposed model was verified by comparing the calculated results with the available experimental data. It is shown that the proposed model is suitable for predicting saturated thermodynamic properties for the air-water system up to 300°C and . Furthermore, the prediction results of the proposed model are better than those calculated with the model of Rabinovich and Beketov (Moist Gases, Thermodynamic Properties. Begell: House, 1995), and the application range is wider than that of the model of Hyland and Wexler (ASHRAE Trans. 89(2A) (1983a, b) 500-519, 520-535) which are among the best of today's models.     

Raman and infrared spectroscopic study of kerogen treated at elevated temperatures and pressures

Kerogen was treated for 24 h at temperatures of 250–700 °C and pressures of 500–1500 bar. Raman spectroscopic study of the run products documented systematic changes in both the first- and second-order spectral features with temperature and pressure. The micro-FTIR analysis of the kerogen treated showed that the presence of hydrogenated functional groups and importance of aromatic rings in the structures of the kerogen increased with temperature. An abrupt change in the chemical composition and structural state of the kerogen treated occurred at ∼500 °C.     

Prediction of minimum velocity and minimum bed pressure drop for gas-solid fluidization in conical conduits

Experimental investigations have been carried out for spherical and non-spherical particles using beds comprised of single-sized particles and mixtures in the size and particle density ranges of 439 to 1524 μm and 1303 to 4948 kg/m³, respectively. Five conical fluidizers with varying apex angles of 8.86, 14.77, 19.60, 32.0 and 43.2 degrees were used. Experimental values of minimum velocity and bed pressure drop with air as the fluidizing medium have been compared with their respective values obtained from different models available in the literature. Deviations for each chosen model have been presented.     

Prediction of minimum bubbling velocity, fluidization index and range of particulate fluidization for gas-solid fluidization in cylindrical and non-cylindrical beds

A uniform fluidization exists between minimum fluidization velocity and minimum bubbling velocity. Experimental investigations have been carried out for determination of minimum bubbling velocity and fluidization index for non-spherical particles in cylindrical and non-cylindrical beds. In the present paper equations have been developed for the prediction of minimum bubbling velocity for gas-solid fluidization in cylindrical and non-cylindrical (viz. semi-cylindrical, hexagonal and square) beds for non-spherical particles fluidized by air at ambient conditions. A fairly good agreement has been obtained between calculated and experimental values. Based on the experimental data it is concluded that under similar operating conditions minimum bubbling velocity and the fluidization index are maximum in case of either semi-cylindrical conduit or hexagonal conduit for most of the operating conditions and minimum in case of square one. It is further observed that the range of uniform (particulate) fluidization is maximum in case of semi-cylindrical bed for identical operating conditions.     

Reduced kinetic mechanism for combustion of synthesis gas at elevated temperatures and pressures

The key combustion reactions of synthesis gas at elevated initial temperatures (T ₀ = 500–700 K) and pressures (p = 10–30 atm) are identified by analyzing the kinetic mechanism. A reduced mechanism of the oxidation reactions of synthesis gas consisting of 14 elementary reactions involving 13 species is proposed which adequately describes the results of experimental data on the burning velocities of mixtures of synthesis gas with oxygen and inert diluents at T ₀ = 300–700 K, p = 10–30 atm, and ratios CO/H₂ = 0.05–0.95, and satisfactorily predicts the flame structure and the dependence of the flammability limits on the initial temperature at atmospheric pressure.