Solubilities of fatty acids (myristic acid, palmitic acid and stearic acid) and higher alcohols (cetyl alcohol, stearyl alcohol and arachidyl alcohol) in supercritical CO2, and the entrainer effect (ethanol or octane) on their solubilities, are correlated by the Soave-Redlich-Kwong equation of state with an association model. It is assumed that the system consists of supercritical CO2, solute monomer, solute dimer, hydrogen bonding species between solute monomer and entrainer, and entrainer. The mole fractions of these species are determined by the equilibrium constants for dimerization of palmitic acid, and those for hydrogen bonding species between palmitic acid and ethanol obtained from FTIR spectroscopic study. The calculated results agreed with the experimental data.
The composition and cage-occupancy of guest species in a CO2-methane mixed hydrate system are investigated by use of Raman spectroscopy. A single crystal of mixed gas hydrate shows the homogeneous mole fraction in equilibrium. The CO2 molecule is entrapped into the M-cage prior to the S-cage comparing to methane. The relative cage-occupancy of CO2 and methane in the structure-I hydrate lattice is scarcely affected by pressure condition.
The short dwell coater has been used extensively in paper coating technology for the past decade. The short dwell coater is employed to apply a lightweight coated layer of 4–6 lb/3300 ft2 at high coating speed of 5000 ft/min. The coating color in the short dwell coater passes through different stages of wide shear rate of 0–106 s−1. Therefore it is necessary to study the effect of shear rate on the coating color behavior over this range. Previous work was done using three or four different rheometers to cover this wide range of shear rates. The rheological properties of pigment coating color with concentration range 30–72.9% over a shear rate of 10–106 s−1 are measured using one system of capillary viscometer. The rheological behavior of the pigment coating color depends significantly on the pigment concentration. The concentration up to 62.9% of china clay shows slight shear thickening, whereas, 72.9% shows strong pseudoplastic behavior. This study investigates the presence of sodium chloride and glycerol on the flow behavior of the coating color. The different diameters of the pigment particles show significant influence on their solution viscosity.
Mixing-effective motions are both numerically and experimentally studied for a very viscous fluid around a rotating elliptic cylinder installed in a cylindrical vessel. A two-dimensional direct numerical simulation was conducted in an elliptic boundary-fitted curvilinear coordinate system rotating at the same angular velocity as the elliptic cylinder. Time-dependent streamlines and streaklines were observed with the aid of visualization technique. It is found that a mixing-effective (folding) motion actually occurs in the vicinity of the edges of the elliptic cylinder, and that such a motion may result from the unstableness of hyperbolic fixed points on an integrable two-dimensional heteroclinic orbit due to experimentally unavoidable three-dimensional disturbances.
A method to draw power consumption diagrams (Np-Re diagram) for kneader mixers dealing with wet particles which have a high particle content and a flow curve showing plastic fluid characteristics are proposed. The method requires only power consumption measurement of kneader mixers. Rheological properties measured with a rheometer are unnecessary. The proposed method was developed based on Nagata’s method, which was designed to draw Np-Re diagrams using the Metzner-Otto concept for mixing vessels containing a low-particle content. For drawing Np-Re diagrams, we used Casson equations and the Metzner-Otto method to represent the relationship between apparent viscosities and shear rate. The procedure of the present method is as follows. Firstly Np-Re diagrams for Newtonian fluids are made. Secondly, mixing power consumption is measured for wet particles by varying rotational speeds. Then ratios of yield stresses to the specific equipment factor of the kneader mixer, τc/B, and Casson viscosity, μc, are estimated. Finally Np-Re diagrams can be obtained using corrected Bingham numbers and impeller Reynolds numbers based on Casson viscosities. Then, we ascertained that an Np-Re diagram is determined solely by Reynolds numbers based on apparent viscosities, and the Np-Re diagrams drawn by the method in this study are independent of the kind of wet particles and the scale-up ratio of the kneader mixer.
A laminar counterflow mass exchange device is an open duct divided into two subchannels of uniform wall concentration by inserting a permeable barrier, in which only the composition of the flow stream varies along the channels. Efficiency improvement in mass transfer has been investigated analytically by using an eigenfunction expansion in power series. The results of enhancement in mass-transfer efficiency are represented graphically and compared with those in a single-flow device (without a permeable barrier inserted). Analytical results show that suitable adjustment of the permeable-barrier position can effectively enhance the mass transfer efficiency compared with the efficiency in single-flow operations.
The photo-induced reduction rate of m-nitroacetophenone (NAP) in the presence of TiO2 powder (anatase and rutile forms) is obtained by measuring the time-courses of the concentration of a product, m-aminoacetophenone (AAP). This photo-induced overall reaction in the ethanol is expressed as
The photo-induced reduction rate of NAP is dependent on the TiO2 and initial NAP concentrations. The time courses of the AAP concentration normalized by the initial NAP concentration decrease with increasing initial NAP concentration. These characteristics can be interpreted by the non-linear differential equation as follows,
d[AAP]/dt = k([NAP]0 − [AAP])(2k0t − 6[AAP])
where [NAP]0 is the initial NAP concentration. The rate constants, k0 and k, express the oxidation rate of ethanol and the reduction rate of NAP, respectively. The value of k0 is dependent on the initial NAP and TiO2 concentrations. It takes a maximum value of 4.0 g/dm3 for anatase and 1.0 g/dm3 for rutile when the initial NAP concentration is about 1.0 mmol/dm3. Then, the maximum value for anatase is 11.1 times that of rutile. The value of k0 decreases with increasing initial NAP concentration. The k value is independent of the TiO2 and initial NAP concentrations, and the same value for both anatase and rutile forms is obtained.
For a bubble column with draft tube sparging gas into the annulus, the effects of equipment dimensions and liquid properties on the circulation flow rates of liquid and gas are experimentally studied. The gas circulation flow rate is estimated by comparing gas holdup in the downcomer with that in a gas-liquid cocurrent downflow bubble column. The liquid circulation flow rate becomes higher as the distance between the upper end of draft tube and the liquid surface at aeration lengthens, and it remains unchanged when the distance is beyond double the column diameter. It increases with increasing draft tube diameter and with increasing bubble size. The gas circulation flow rate is strongly governed by the liquid circulation flow rate. The driving force for gas circulation is the difference between the descending velocity of liquid and the rising velocity of bubble swarm in the downcomer. Based on the energy balance, an empirical equation of the loss coefficient in the zone above the upper end of the draft tube is obtained. The circulation flow rates of liquid and gas calculated by using the energy balance and correlations, agree with the measured data within an error of ±30%.
The kinetics of oxidation of carbon monoxide on Pd-supported catalysts are determined at low temperature and under typical conditions of atmospheric pollution (a few ppm of CO in air). The nature (silica, alumina, silica-alumina) as well as the geometry (beads, fibers, powder) of the support were varied, the latter to change the mass-transfer resistance. The nature of the support has no influence on the kinetics. With powder or fiber as the supports, the catalyst operates without mass transfer limitation, and the kinetics is of negative order with respect to CO, of positive order with respect to oxygen. The energy of activation is about 85 kJ/mol. This corresponds to the regime of CO-inhibition, never reported at so high O2 to CO ratio (75–104). The surface is dominated by adsorbed carbon monoxide, and the reaction rate is limited by oxygen adsorption. With beads as the support, the orders in CO and in oxygen are both positive and the energy of activation is 42 kJ/mol. This kinetics law is attributed to mass transfer limitation.
Oleic acid oxidation experiments were conducted under various temperature conditions, and the time courses of the concentrations of oleic acid, hydroperoxide and dissolved oxygen (DO) were measured. A novel kinetic model was constructed on the basis of an autocatalytic free-radical chain reaction mechanism, in which two kinds of initiation reactions due to hydroperoxide decomposition, the reaction to generate a secondary product, and the consecutive reaction of the secondary product with oxygen were involved. There were seven unknown constants, two constants for gas-liquid mass transfer, and five constants for chemical reaction in the model. In order to estimate the constants for the gas-liquid mass transfer, gas absorption experiments were conducted using oleic acid with antioxidant. The chemical kinetic constants were estimated by fitting the model equations with the results for the concentrations of the oleic acid, the hydroperoxide and the dissolved oxygen obtained experimentally. The fitted results were in good agreement with the experimental data over a wide range of temperatures. The validity of activation energies in the kinetic constants was verified by comparison with the previously reported literature values. Furthermore, the variation of the oxidized oleic acid composition was simulated by the model.
The reaction progress in supercritical water oxidation (SCWO) of methanol is simulated in terms of a detailed chemical kinetics model for the two ideal reactors, plug flow reactor (PFR) and continuous stirred tank reactor (CSTR). The reaction has an induction time and a character of first order reaction against the methanol concentration in PFR. The reaction does not appreciably depend on the oxygen concentration as far as the methanol conversion is concerned. In CSTR, the dependence of methanol conversion X on residence time t can be described using a simple first order relation applicable to CSTR, taking into account the induction time τ phenomenologically, that is, X/(1 − X) = k(t − τ). Conversion in the CSTR increases very rapidly against the residence time, compared with that in the PFR, and correspondingly the induction time is much shorter. The dependence of concentrations of intermediates, i.e., CH2O and CO, against the residence time in CSTR is weaker than that in PFR, which is also the case for radical species, in particular, HO2 and OH. Relevant elementary reactions are discussed.
In the present study, heat regeneration of spent bleaching clay was conducted in a box furnace with air flowing through it. The regenerated clay was then employed for bleaching peanut oil. Red color indices of bleached and unbleached peanut oils were determined to calculate regeneration efficiency. Experimental results indicate that the regeneration rate can be increased by increasing the temperature between 573 and 773 K. However, above 773 K, the regeneration rate is reduced due to sintering of the clay. The rate expression for regeneration is determined to be
The performance of three catalysts, namely Pt/γ-Al2O3, Pt-Sn/γ-Al2O3 and Pt-Sn-K/γ-Al2O3 for dehydrogenation of propane is discussed. All catalysts are found to be highly selective towards propene. Pt-Sn-K/γ-Al2O3 appears to be the most stable and suitable catalyst for the dehydrogenation of propane. Pt-Sn/γ-Al2O3 is also found to be superior to Pt/γ-Al2O3. In the kinetic study, the reaction rate constants based on the number of active sites are calculated from the apparent reaction rate constants and the number of metal active sites. The reaction rate constants for Pt/γ-Al2O3, Pt-Sn/γ-Al2O3 and Pt-Sn-K/γ-Al2O3 catalysts at 773 K are 0.48 × 10−28, 0.67 × 10−28 and 2.98 × 10−28 mol/(site·s·Pa), respectively. In addition, for Pt-Sn-K/γ-Al2O3, the frequency factor and the activation energy are 6.14 × 10−24 mol/(site·s·Pa) and 62.7 kJ/mol, respectively.
An experimental study on the devolatilizing performances of screw elements with different screw geometries in an intermeshing co-rotating twin-screw extruder (ICoTSE) was conducted using a polystyrene/ethylbenzene (PS/EB) system. The experimental devolatilization (DV) data and literature data obtained in the same type of ICoTSE with a different screw diameter for the same PS/EB system are correlated by the proposed model, where the effect of differences in screw geometries, screw diameters, degree of filling, and fully-filled length in the screw channels as well as changes in the operating temperature caused by the shear heat on DV are taken into account. Furthermore, the difference in the description of the surface renewal DV in a screw extruder between the proposed model and Latinen-type models in the case of ignoring the backmixing of axial dispersion is compared and discussed.
To concentrate sea water, it is necessary to develop a high pressure reverse osmosis system. First, the effect of applied pressure and feed concentration on flux and rejection was measured using a commercially available membrane. Secondly, the experimental data were analyzed by Spiegler-Kedem equations. The equations are also confirmed to be effective in high pressure reverse osmosis system. The membrane shows high rejection under applied pressure of 20 MPa with feed solute concentration of 12 wt% NaCl, insuring a good stability of the dense layer to pressure and to feed concentration. On the other hand, the support layer is compacted under 20 MPa, which marks the onset of the resistance to permeation.
This study deals with the effect of an exponential-decay flux of ultrafiltration on the mass transfer rate of solute for dialysis in cross-flow membrane modules. The numerical method of orthogonal collocation was used to solve this problem. The calculated results of solute concentrations and separation efficiencies were analyzed under various operating conditions and decay coefficients of flux in ultrafiltration. The mass transfer rate is usually enhanced by the addition of the effect of ultrafiltration, but this effect decreases as the decay coefficient increases. A significant influence of the decay coefficient on the mass transfer rate appears when the solute transport is dominated by the effect of ultrafiltration, i.e. the conditions of lower dialysate flow rate, lower solute sieving coefficient, or lower overall mass transfer coefficient.
The effective interfacial area for chemical absorption in a laboratory column has been reported to be a function of liquid viscosity and gas superficial velocity. In this study, liquid viscosity was varied in the range of 0.95 × 10−3 to 4.5 × 10−3 Pa·s, while gas superficial velocity encompassed the range of 48.0 × 10−3 to 173.0 × 10−3 m/s. A transition in the formation of the effective interfacial area was observed and related to the interaction between liquid viscosity and gas flow conditions. A correlation effectively predicting this transition behavior is developed on the basis of the liquid phase capillary number and the gas phase Reynolds number.
Porous quicklime powder is produced from 5 μm limestone particles in a Powder-Particle Fluidized Bed (PPFB). PPFB is a new fluidization technique in which agglomerative fine particles adhere onto the surface of the fluidized coarse particles, and are co-fluidized in the bed. For 5-μm limestone calcined with dry air at 1073 to 1223 K, the PPFB yields the lime powder with BET specific surface areas of 15 to 60 m2/g, depending on the residence time of gas in the PPFB. Measurement of the total pore volume of produced lime reveals a maximum value of 0.178 cm3/g, which is much higher than those obtained by conventional methods. However, the pore volume of the lime produced at 1173 K with gas containing CO2 is almost constant, regardless of the residence time of gas. This can be caused from the fact that the CO2 effect on mild sintering surpasses the temperature-promoted sintering. From this study, the lime powder that has very large BET specific surface and large pore volume can be produced by this method.
The Sedimentation balance type particle size analyzer is improved. The slurry supply device was automated and the height of peripheral wall of the detective tray was raised. As a result we can acquire data of the sedimentation mass change accurately. Moreover, the ratio of measured total sedimentation mass to the theoretical total sedimentation mass was kept constant ranging from 1.00 to 1.02 independent of particle size. By the above improvement, we can develop a more precious sedimentation balance. Twomey’s non-linear iteration method was applied to retrieve a particle size distribution from the sedimentation curve measured with a sedimentation balance method. It is found that the non-linear iteration method can calculate size distributions accurately. Furthermore, the influence of the thickness at the base of the detective tray on the sedimentation distance was also investigated. As a result, it is clarified that the change in detected mass did not depend on thickness at the base of the tray. Therefore, it is concluded that the sedimentation distance in the sedimentation balance method should be defined as the distance between the lower surface of the base of the tray and suspension surface.
The particle formation mechanism during hydrolysis and condensation of tetraethyl orthosilicate (TEOS) was studied with in-situ measurements of particle size distribution, electric surface potential and electric conductivity in the absence and in the presence of electrolytes, KCl and LiCl. Experiments were performed at a TEOS concentration of 0.4 mol/dm3, a water concentration of 11 mol/dm3 and an ammonium concentration of 1 mol/dm3. The addition of KCl has a greater effect on the particle sizes than that of LiCl. The average particle size attained 1 μm at a KCl concentration of 4 mmol/dm3 maintaining high monodispersity in particle sizes. Measurements of surface potential and electric conductivity show that the increase in particle size by the addition of the electrolytes is caused by both a reduction in the surface potential and an increase in the ionic strength. The effect of the electrolytes was also examined in seeded growth experiments. Addition of KCl to the system suppresses the generation of new particles and enables the growth of seed particles by as much as fifty-fold in volume. Our experimental results show that electrostatic interaction between the particles is the dominant factor in controlling particle size distributions.
This paper describes the analysis of behavior of powder being compressed and sheared by a rotor in a high-speed elliptical-rotor-type powder mixer (HEM). Two kinds of two-dimensional simplified dynamics models are proposed to analyze the powder behavior under conditions in which the maximum external force acts on the powders. Each of these models express the phenomena in which the powder layer slides on the vessel wall after it causes plastic deformation, and the rotor compresses the powder layer dynamically. The model equations contain both the operating conditions of HEM and the physical properties of powder as parameters, and are used to estimate the stresses acting on the powders while the HEM is operated. Good agreement between the experimental data and the calculated value of the torque acting on the rotor shaft during the mixing operation is obtained. It is clarified from the calculation that the powder layer is compressed dynamically in the minimum clearance region, and the powder layer in the other region is forced out of the minimum clearance region. The results obtained in this study indicate that adequate selection of the operating conditions of HEM enable achievement of precise control of stress acting on a powder of arbitrary physical properties.
Fluidized bed coaters or granulators with spray nozzles are used to produce coating particles, granules and agglomerates in various industrial fields. When the binder liquid containing fine particles is sprayed into a hot fluidized bed, the fluidizing particles grow in size by agglomeration due to the particles colliding with the spray droplets that first form liquid and then solid bridges between particles. This phenomenon causes unstable coating or granulating and ill-balanced products. The question then arises about mono-core coating with finer particles. We investigated the characteristics of the mono-core coating using a draft-tube spouted-bed coater, applying the separation force due to the high-speed gas from the inlet nozzle. As a result, it is found that mono-core coating could be achieved due to the shear force and the external solid circulating system. It is shown that the coating ratio can be controlled by selecting the coating operation time and the concentration of binder liquid. Also, it is found that choking of the draft-tube can be delayed by increasing the inlet gas velocity and the bed temperature.
In this paper, a simple independent design method for multi-loop controllers is proposed which exploits process interactions for the improvement of loop performance. Unlike many other methods that emphasize suppression of interactions for decoupling purposes, our method is developed to channel the effect of interactions to individual loops for speeding up loop responses. This is achieved by regarding each loop together with its corresponding interactions from all other loops as an equivalent single-input single-output (SISO) plant, and designing an independent SISO controller for it. Once an objective transfer function is specified for each of these equivalent processes, a set of simultaneous equations is formed and separated into independent ones, each of which contains one controller element only. They are then solved to obtain exact solutions, which are usually irrational. The exact solutions can be well approximated by rational functions. The popular multi-loop PID controllers can naturally be obtained as a special case of rational approximation, and they give a reasonable trade-off between loop and decoupling performance. Simulation examples are provided to show the effectiveness of the proposed method, and comparisons are made with the BLT method.
New differential equations are derived for optimal control of a consecutive reaction system in a batch reactor. These equations can be solved easily with a one-dimensional optimum search technique in terms of the initial concentrations of each component. The computations are readily carried out on-line in real time, and the optimal temperature profile can be calculated at each time-step based on the current values of the states. Optimization is considered in terms of the temperature, but also in terms of an operation variable. For a consecutive reaction system, the optimal equations are formulated and optimal profiles are numerically calculated.
Optimal multiperiod planning methodology for utility systems is proposed considering internal energy demand, which is formulated as a mixed integer nonlinear programming (MINLP) problem. The problem is decomposed into two levels: the energy distribution network level as a mixed integer linear programming (MILP) problem, and the steam generation unit as a nonlinear programming (NLP) one. The internal steam demand is calculated from the first principle model, and the internal electricity demand is obtained from design data. For multiperiod operation with varying demand as a series of piecewise constant for utilities, the optimal configurations of utility pumps (UP) are determined. The objective function is comprised of the operational costs for each period, transition costs and switch costs between periods. Total cost obtained from the proposed planning methodology has been reduced by 2.34% compared with the planning result without considering switch costs between periods and 3.15–9.14% compared with the result by Lee et al. (1998).
This paper describes a qualitative interpretation method, which is used for extracting qualitative information from numeric sensor data. Firstly, whether any change has occurred in chemical process data is determined by using the CUSUM (CUmulative SUMmation) test. From the sign of the first derivatives of the process variables, sensor patterns can be classified into the seven primitives. Secondly, extraction of the trends of the data employing the modified scale-space filtering is performed. The recursive form reduces the calculation cost of the real-time scale-space filtering and solves the endpoint problem. The proposed method was tested for artificial patterns and the simulated data of a evaporator process, and produced good results.
Startup of an ideal heat integrated distillation column (HIDiC) is considered in this paper. A procedure for the startup operation is suggested by taking the special characteristics of the ideal HIDiC into account. An overhead trim-condenser and a bottom trim-reboiler look necessary to be added to the process configuration during this period. However, it is found that the ideal HIDiC can also start smoothly without the presence of the bottom trim-reboiler. The transition from semi-continuous phase to normal operation mode is investigated and compared by employing two control systems. One is a gain-scheduled decentralized PI controller, the other is a nonlinear process model-based one (NPMC). It appears that the ideal HIDiC could start quite smoothly with no special difficulties compared with its conventional counterparts. The NPMC holds more advantages than the gain-scheduled PI controller, since the former provides safer and more economic startup operation of the ideal HIDiC than the latter.
Ash deposition characteristics under high-temperature pulverized coal reaction conditions were studied using a horizontal pulverized coal reactor with pre-combustor to produce high-temperature vitiated air. The ash deposition experiments were performed by inserting a water-cooled tube into the reactor. Burning two types of coal with different melting temperature and ash content, and the ash deposition phenomena were visually and quantitatively elucidated. As a result, the quantity of ash deposition on the tube surface increases with an increase of the surface temperature. This is because the burning particles in the upper stream of the tube are radiatively cooled down under low temperature condition of the tube surface. Both the structure and quantity of ash deposition depend on coal types such as melting temperature and ash content. The deposition rate at the beginning of deposition, obtained by the peripheral width of deposition layer on the tube surface, is correlated as an Arrhenius-type equation since viscosity of the molten ash can be correlated as an Arrhenius-type equation. Hence, it suggests that the ash deposition phenomena may relate to the viscosity of molten ash.
Analysis of behavior of each individual component in extraction is demonstrated from energy and exergy viewpoints. A material-utilization diagram (MUD) for phenomena in which chemical components transfer between two different phases is proposed. The mathematical derivation of exergy loss for extraction suggests two important terms, i.e., njRT0 with dimension of energy and dimensionless term –ln(aj, out/aj, in), for analyzing such phenomena. The MUD is applied to trace of flow rate and concentration change for each component in single stage, 3-stage and 6-stage countercurrent extraction. Characteristic features of transfer of each component in those operations and advantages of multiple stages are represented graphically.
Experimental investigations on the scrubbing of particulates (fly ash) in high-velocity water sprays are reported. Performance characteristics of an atmospheric spray scrubber incorporating high-velocity water sprays using a two-phase atomiser are analysed in terms of various physical and flow parameters of the system, and a simplified correlation has been developed. The efficiency of particulate collection in the scrubber can be well predicted using this correlation.
A multiple-compartment absorber and generator in close-to-equilibrium operation is implemented in a single stage absorption-compression hybrid heat transformer. It is found that by utilization of a multiple-compartment absorber and generator in close-to-equilibrium operation, the high exergy efficiency and wide temperature range of heat source can be obtained. Further, a large amount of electric power can be saved.
Incineration ash was melted using a micro-scale furnace under various temperatures and gas atmospheres. As a result of the elemental composition analysis of the molten slag, it was confirmed that heavy metals with properties of low boiling points were readily emitted during melting treatment. The emission amount is influenced by vitrification behavior of the ash with operating temperature. The emission of lead and zinc under the reducing condition is larger than that under the oxidizing condition. Cadmium is completely vaporized under all conditions examined in the present study.
In the present work, the possibility of continuous O− emission using the YSZ was examined. A simple experimental apparatus incorporating a gap between a YSZ (yttria stabilized zirconia) anode and a stainless steel electrode coated with gold was designed and constructed. By applying a DC voltage of 150 V across the electrode gap, the ion current, consisting of negatively charged species such as O− radical anions, could be detected by using the quadrupole mass spectrometer. The results of the variation of ion current with distance between two electrodes have revealed that the emission of O− and electrons are strongly related to the temperature and electric field. From these results, the activation energy of releasing O− from YSZ anode can be described as: E = E0 – 0.036(V/d) [kJ·mol−1]. Furthermore, the electric field may decrease the activation energy of O− desorption from the YSZ anode.