Solid–liquid phase equilibrium data for binary (l-arabinose–water) and (d-xylose–water) systems at temperatures from (269.85–298.05) K and ternary (l-arabinose–d-xylose–water) system at temperatures of 273.85 K, 278.85 K and 284.45 K were measured at atmospheric pressure. The ternary phase diagrams of the systems were constructed on the base of the measured solubility. Two pure solid phases were formed at given temperatures, including pure l-arabinose and pure d-xylose, which were confirmed and determined by the method of Schreinemakers' wet residue. At the same temperature, the crystallization region of l-arabinose was larger than d-xylose's. The acquired solubility data were then correlated using the NRTL model, Wilson model and Xu model. The calculated solubility with the three models agreed well with the experimental values.

Vapor–liquid equilibrium (VLE) data are reported for mixed electrolyte solution systems containing NaCl + KCl + H2O, K2SO4 + MgSO4 + H2O and NaCl + CaCl2 + H2O. The measurements were carried out with a pressure between 6.3 and 101.3 kPa in a computer-controlled glass apparatus. A modified NRTL model based on the hypothesis of hydration was used in this paper. Literature data for electrolyte solutions, with temperature spanning from 273.15 to 415.85 K, were successfully correlated using the model. Meanwhile, the model was also successfully applied to predict the VLE data in mixed electrolyte solution systems with the binary parameters.

The design of various multistage RO systems under different feed concentration and product specification is presented in this work. An optimization method using the process synthesis approach to design an RO system has been developed. First, a simplified superstructure that contains all the feasible design in present desalination process has been presented. It offers extensive flexibility towards optimizing various types of RO system and thus may be used for the selection of the optimal structural and operating schemes. A pressure vessel model that takes into account the pressure drop and concentration changes in the membrane channel has also been given to simulate multi-element performance in the pressure vessel. Then the cost equation relating the capital and operating cost to the design variables, as well as the structural variables of the designed system have been introduced in the objective function. Finally the optimum design problem can be formulated as a mixed-integer nonlinear programming (MINLP) problem, which minimizes the total annualized cost. The solution to the problem includes optimal arrangement of the RO modules, pumps, energy recovery devices, the optimal operating conditions, and the optimal selection of types and number of membrane elements. The effectiveness of this design methodology has been demonstrated by solving several seawater desalination cases. Some of the trends of the optimum RO system design have been presented.

The seawater reverse osmosis (RO) desalination is an attractive and viable method for the production of fresh water in many areas. This paper addresses the optimal design of RO desalination system considering membrane cleaning and replacing during the 5-year maintenance period, and only a single stage configuration with pressure exchanger is analyzed. A mathematical model for the prediction of the performance of RO process is presented in detail. Simultaneously, this paper also addresses the new fouling model and the criterion of cleaning and replacing. Then the relevant economic models to the RO desalination process are developed, which relate the cost of investment and operation with the design variables, the structural variable, as well as the binary variable that determine the membrane regeneration. The optimum design problem can be formulated as a mixed-integer non-linear programming (MINLP) problem, which minimizes the total annualized cost. The mathematical programming problem is solved with GAMS software. As a result, the optimal operational parameters and the optimal cleaning and replacing scheduling are given. According to this model, one example is solved to illustrate the advantage and effectiveness of the suggested method.

In order to improve the energy efficiency, reduce the CO2 emission and decrease the cost, a cogeneration system for desalination water, heat and power production was studied in this paper. The superstructure of the cogeneration system consisted of a coal-based thermal power plant (TPP), a multi-stage flash desalination (MSF) module and reverse osmosis desalination (RO) module. For different demands of water, heat and power production, the corresponding optimal production structure was different. After reasonable simplification, the process model of each unit was built. The economical model, including the unit investment, and operation and maintenance cost, was presented. By solving this non-linear programming (NLP) model, whose objective is to minimize the annual cost, an optimal cogeneration system can be obtained. Compared to separate production systems, the optimal system can reduce 16.1%-21.7% of the total annual cost, showing this design method was effective.

In this work, a new activity coefficient model was deduced for the correlation of solid–liquid equilibrium (SLE) in electrolyte solutions. The new excess Gibbs energy equation for SLE contains two parts: the single electrolyte item and the mixed electrolyte item. Then a new hypothesis for the reference state of activity coefficients was proposed in the work. Literature data for single electrolyte solution and mixed electrolyte solution systems, with temperature spanning from 273.15 to 373.15 K, were successfully correlated using the developed model.A new activity coefficient model was deduced for the correlation of solid–liquid equilibrium in electrolyte solutions. Literature data for single electrolyte solution and mixed electrolyte solution systems, with temperature spanning from 273.15 to 373.15 K, were successfully correlated using the developed model.Download high-res image (113KB)Download full-size image