A simple and direct method for processing residence time distribution (RTD) signals from conductivity data was developed for a spiral wound membrane reverse osmosis (RO) system. Two models were tested: axial dispersion (AD) model and exponentially modified Gaussian (EMG) model. The results show that the present method provides a simple, fast and accurate RTD data reduction. The presence of fouling in the small laboratory RO module increased the axial dispersion coefficient, indicating that fouling in the membrane channel augments the axial dispersion extent, thus resulting in the deviation of flow pattern from ideal plug flow. The dead volumes gradually decreased with increasing Reynolds number for the worn industrial module, while there was no dead volume for the new industrial module. As a result, the membrane wearing-out could increase the dead zones in the industrial spiral wound module.
Reverse osmosis (RO) concentrates containing high amounts of dissolved salts and anti-scalants are commonly discharged directly. Considerable economic and environmental benefits could be achieved by extending current water recovery limits. One way for reuse of concentrates and thus increasing the water recovery is to recycle part of the brine concentrate to the feed, after precipitating the scaling salts such as CaSO4/CaCO3 held in solution by anti-scalants. In the present study, scaling salt removal was carried out from RO CaSO4 concentrate in the presence of four anti-scalants via addition of six kinds of inorganic particles. Analyses of the kinetics of gypsum removal and the morphologies of CaSO4 crystals were performed. The results show that the method was effective for the removal of scaling salt. After the precipitation removal reactions, the test solutions reached thermodynamic equilibrium. Furthermore, the precipitated gypsum appeared shorter and broader crystal forms. The economic analysis shows the method is feasible.
The reuse of reverse osmosis (RO) concentrates generally involves the removal of scaling salts such as CaSO4/CaCO3, and then the recycle part of the treated concentrate to the feed. By this method, the water recovery can be remarkably increased. However, the time necessary for precipitating the scaling components may extend to a few days, especially in the presence of antiscalants. In the present study, CaCO3 scaling salt removal was carried out from RO concentrates in the presence of three antiscalants by accelerating precipitation approaches. Three methods were adopted, including the air-blow method, inorganic inducer addition, and the combinative method of air-blow and inorganic inducer addition. Calcium ion concentration, pH and antiscalant concentration of the test solutions were monitored. Morphologies of the precipitated CaCO3 were observed by scanning electron microscopy (SEM). These methods were found to be effective, reaching a calcium removal ratio as high as 50–80%. The removal of scaling salt was always accompanied by the adsorption precipitation of antiscalants. In the presence of antiscalants, saw-toothed growth edges and holes on the precipitated CaCO3 surfaces were found. Moreover, fragmented small particles were also observed. The economic analysis shows that the methods are feasible.
The oxidative decomposition of dichlorodifluoromethane (CFC-12) over tungsten(VI) oxide-loaded alumina–zirconia at low temperature has been investigated. Oxidative decomposition in air was found achieve higher initial CFC-12 conversion rates than hydrolysis and oxidative decomposition in the presence of water or butane, although the conversion rate decreased markedly with time on stream. Loading the alumina–zirconia support with platinum-group metals results in higher sustained activity, and the addition of platinum in particular allows the initial conversion rate to be maintained for at least 4 h on stream.
This paper presents a fault detection methodology based on the Fisher discriminant analysis (FDA) and individuals control charts (XmR control charts). As the first step, FDA is used to find the optimal discriminant direction between the normal operation data and the fault data. In the next step, XmR control charts on the discriminant direction are used to monitor the process. To reduce the amount of false alarms, we also used a variable selection technique based on the contribution plot of FDA. The performance of the proposed technique is demonstrated through application to the monitoring of the Tennessee Eastman challenge process.
A new nonlinear process monitoring and quality prediction technique based on kernel partial least squares (PLS) has been developed and applied to a biological wastewater treatment system. The calculation step that makes kernel PLS (KPLS) different from other linear and non-linear PLS techniques is the mapping of the data set from its original space into a hyper-dimensional space before the extraction of the principal components in the feature space. Suggestions are provided for a nonlinear monitoring measure on the KPLS space, as well as guidelines to select the number of eigenvalues in the feature space. Eleven process and manipulated variables (X-block) were used to model three process output variables (Y-block) in the industrial plant: the sludge volume index, cyanide reduction and COD reduction. The prediction results show that the KPLS-based model is superior to other models: it has the smallest mean squared error (MSE) of 5.04% while other PLS models (linear PLS, quadratic PLS, spline PLS) of the input space, as well as the other kernel regression methods, such as the kernel principal component regression and ridge regression, have relatively large modeling error values between 5.8 and 8.5%. Additionally, KPLS gives better fault detection performance when compared to other linear and nonlinear methods, where abnormal process variations are relevant to the microbial treatment and to the settling capability, which affect sludge volume index (SVI), chemical oxygen demand (COD), and cyanide (CN) reduction. These results indicate that the KPLS technique is able to accurately model the nonlinear processes under complex operating conditions, and can supervise process faults in industrial plants, since it can effectively capture the nonlinear causal relationships in the treatment process.
The static contact angle of a liquid on a solid surface submerged in a second liquid is important because the attractive force of a liquid binder in wet agglomeration, the detergency process of a solid surface in liquid and the production of crude oil from porous subsurface rock by water displacement are affected by the wettability of the liquid to the solid surface in the second liquid, that is, mainly by the static contact angle of the liquid on the solid surface in the second liquid. It is known that the contact angle shows hysteresis and therefore differs depending on the measurement method. We experimentally investigated the hysteresis of the static contact angle of a polymer solid–water–liquid system. The hysteresis was evaluated by the difference between an advanced contact angle and a receded contact angle. The contact angle hysteresis of a polymer solid–water–liquid system became greater than that of a polymer solid–vapor–liquid system. The measurements of contact angle were compared with the values calculated by the use of extended Fowkes equation and Young–Dupré equation. Empirical equations showing contact angle hysteresis were obtained.