Cationic polyelectrolyte flocculated sewage sludge flocs were hung on an elastic nylon stick, and then subjected to a uniform water flow. Their consequent displacements were then measured. The hydrodynamic drag force on the polyelectrolyte flocculated flocs was estimated from the measured displacement and the elasticity constant of the stick. These measured results compared favorably with the numerical results yielded using a three-dimensional pore structured model based on real waste activated sludge floc.
A relation of the friction factor cf to the Reynolds number Re, cfRe = 24, in mesh-type wicks has been deduced on the basis of a capillary bundle model, using the modified j-function of single-layer polyethylene mesh wicks measured by an electric resistance method. Correlation of the capillary drain height and the capillary drain number has yielded the tortuosity as a function only of the porosity. The cf and Re values calculated using the estimated tortuosity have proved the relation cfRe = 24 to be applicable to plain-woven stainless meshes as well as plain-woven and knitted-type polyethylene meshes, irrespective of the mesh number and the number of mesh layers constituting the wick. The results for the multi-layer mesh wicks have also reasonably supported that the modified j-function would be available even for the mesh wicks where the porosity increases by 12% or decreases by 14% compared to those of the single-layer mesh wicks.
Hydrofluoroethers have been applied as diluent for phosphorus acid extractants in the solvent extraction of zinc(II). They are promising alternatives to conventional organic diluents because of their non-flammability, chemical stability and non-toxicity. Hydrofluoroethers used in this study are a mixture of ethylperfluorobutylether and ethylperfluoroisobutylether and a mixture of methylperfluorobutylether and methylperfluoroisobutylether (HFE-7100). Among the extractants examined, two phosphorus acid extractants, di-(2-ethylhexyl)phosphoric acid (D2EHPA) and 2-ehtylhexyl phosphoric acid mono-2-ethylhexyl ester (EHPNA) were soluble in both hydrofluoroethers. Because of the high specific gravity of hydrofluoroethers and their low solubility in water, phase-separation was rapid and the resulting phases were clear. In the extraction of zinc(II) using the phosphorus acids, the system with D2EHPA gave higher extraction than that with EHPNA, while there was little difference in the extraction behavior between the two hydrofluoroethers. The effects of the equilibrium solution pH and the extractant concentration on the zinc extraction were examined, and the stoichiometric relationship for the extraction was proposed. The extraction equilibrium constants for zinc(II) were found to be higher than those with conventional chlorinated organic solvents such as chloroform and carbon tetrachloride. The backward extraction of zinc(II) was satisfactorily attained with a dilute acid solution, and the separation of several heavy metals was also demonstrated. Moreover, the elution of the extractants and hydrofluoroethers into the aqueous phase was very low, and this makes the present system more attractive.
As the second step to clarify the synergistic extraction mechanism of gallium with the mixed extractant of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and 5-chloro-8-hydroxyquinoline, the initial extraction rate of gallium with EHPNA alone was measured using a stirred transfer cell. First, the aggregation state of EHPNA in the organic solvent, toluene, and the adsorption characteristics at the interface between the aqueous and organic phases were examined. EHPNA was found to exist mainly as dimers in the organic solvent and to adsorb the interface. By considering that the interface is a site for metal-complex formation, the extraction mechanism constructed with the three processes, a mass transfer of metal ions to the interface, an extraction reaction at the interface based on the Eigen mechanism, and a mass transfer of the metal-complex to the bulk organic phase, was proposed to analyze the experimental results.
Catalytic combustion of volatile organic compounds (VOCs) benefits from a low oxidation temperature due to less energy consumption. It is widely applied in industry. A novel technique of Pt/Al2O3/Al catalyst preparation is presented in this paper. Al2O3 film was formed on an Al plate by anodic oxidation in 4% oxalic acid solution at 50 A·m–2 current density. After anodic oxidation, Pt was supported on the oxidized plate utilizing an electrolysis supporting method with an alternating current in an aqueous solution of chloroplatinic acid hexahydrate under both high and low voltages. Catalytic activity was evaluated by both toluene and benzene combustion. Dispersion of platinum in developed catalysts was about 20%, measured by CO pulse adsorption. In the activity test, toluene or benzene was mixed with air and then toluene–air and benzene–air mixtures combusted on the developed catalysts. It is shown that a catalyst prepared under a high voltage has a higher reaction rate than that one prepared under low voltage. This may be explained by that large platinum particles were formed on the film by high voltage. In the running time of 140 hours duration, there exists an induction process of about 10 hours for fresh catalysts, in which, the conversion of toluene was promoted by up to about 8%, and with no obvious change in the reactions that follow. Experimental results indicated that electrolysis impregnation can be regarded as a short-time supporting method for preparing catalyst.
A simple method is proposed for PID controller settings for an integrating plus dead-time system and a stable FOPTD system with an integrator. The method is based on matching the coefficients of corresponding powers of s, s2, s3 in the numerator to α1, α2, and α2 times that in the denominator of the closed-loop transfer function, respectively, for the servo problem. Here α1 and α2 are tuning parameters, and α1 is greater than 1. It is found by simulation on various transfer function models that the use of α2 = 0.6α1 gives good results. The robustness of the controller is evaluated theoretically by Kharitonov’s theorem. The method is used to design a PID controller for an isothermal continuous copolymerization reactor, and the performance of the controller designed by the present method is compared with a modified gain margin method (Luyben, 1996). The method is extended to design a PID controller for a stable FOPTD system with an integrator. The performance of the method is better than the method proposed by Zhang et al. (1999) for the servo problem, and it is superior to their method for the regulatory problem.
In this study a model for the drying process in paper production plants was developed based on the mass and heat balances around drying cycles. Relationships for the heat transfer coefficients between the web and the air as well as between the drying cylinder and the web were extracted from the closed-loop plant operation data. It was found that the heat transfer coefficients could be represented effectively in terms of moisture content, basis weight and reel velocity. The effectiveness of the proposed model was illustrated through numerical simulations. From the comparison with the operation data, the proposed model represents the paper plant being considered with sufficient accuracy.
By combining chemical reaction and multi-stage distillation in one column, a reactive distillation (RD) column can significantly save capital investment and make chemical conversion reach a much higher level. In a previous study, an optimal steady state design for the production of ethyl acetate (EtAc), consisting of two columns (one for RD and one for stripping column) and an overhead decanter, was reported. As a continuous study to that previous work, four alternative plant-wide control strategies for this designed process are studied in this paper. Feed compositions of both Acetic acid (HAc) and ethanol (EtOH) streams are treated as disturbances. These disturbances are used to test the closed-loop performance of each control scheme. It is found that control of the product qualities by modulating two tray temperatures in the RD column and one tray temperature in the stripper is most appropriate. By this control scheme, both of HAc and EtOH impurities in the product stream can be kept effectively within the acceptable product specifications.
In this work, an auto-tuning PID controller based on the generalized predictive control (GPC) method is proposed for on-line tuning of the controller parameters due to the changes in operating conditions. The proposed scheme is applied to the control of a distillation column, with identification of the parameters of an ARMAX model determined from the operating data of an industrial column. An evaluation of the maximum likelihood (ML) and Kalman filter (KF) methods of identification showed that at a 10-second sample interval, reliable model parameters could be predicted using either the ML or KF method. However, at a 60-second sample interval simulation results showed that only the KF method generated reliable parameters. Column control was studied for an objective of maintaining constant liquid temperature on an intermediate tray, in the presence of a disturbance in the feed flow rate, with the top product flow rate being a manipulated variable. The simulation results for the auto-tuning PID control scheme using the GPC formulation are compared to the control performance which was obtained using a tuned conventional PID controller and also GPC, at a 60-second sample interval.
Development of a new processing method for the effective use of rice-Shochu distillation remnants is an important subject for the reduction of environmental pollution. In this study, inhibitory effects on the growth of human stomach tumor cells along with the induction of apoptosis were obtained for powder treated with ethanol from freeze-dried supernatant of rice-Shochu distillation remnants in vitro. Futhermore, the powder obtained from rice-Shochu distillation remnants showed no toxicity to normal rats in vivo experiments. These results suggest that rice-Shochu distillation remnants might be effectively used not only as medicine but also as food supplements for health.
A novel pulping method without generating pollutants consists of a sodium hydroxide (NaOH) treatment followed by steam explosion was proposed and evaluated in this investigation. The cellulose component (degree of glucose polymerization: about 500) from Eucalyptus globlus chips treated with 10 g·dm–3 NaOH and then exploded with steam at 2.5 MPa for a steaming time of 5 min, was converted into pulp with physical properties almost the same as those of conventional hardwood pulp.