Essam El-Sayed

Performance evaluation of two RO membrane configurations in a MSF/RO hybrid system

Abstract Although integration between multistage flash distillation (MSF) and reverse osmosis (RO) in hybrid desalination systems has been long discussed in the literature, and has been shown to be technically and economically superior to nonintegrated MSF and RO systems, no serious attempts have yet been made to adopt or implement such an approach in the design or construction of new desalination plants. This, perhaps to some extent, may be attributed to the real need first for some tangible experience on an acceptable scale and to the lack of experimental data on the performance of RO membranes in MSF/RO hybrid systems. Hence, this paper attempts to fill in this gap by presenting: operational experience using reasonably-sized RO production plants, a large body of experimental data on RO membrane performance in a simple MSF/RO hybrid model, and an overall evaluation of the performance of the RO membranes operating under the given conditions. The work represents the second phase of an experimental investigation of MSF/RO hybrid systems. In this phase the performances of two types of RO membranes operating in a simple easy-to-implement MSF/RO hybrid model were measured and evaluated. The experiments were carried out at the Doha Desalination Research Plant (DRP) using two RO units linked with the nearby MSF unit A-1 of the Doha East Distillation Plant via one common feed water header and pretreatment unt. The common feed water system, however, does not prevent either of the two RO units from being operated independently from each other. The RO units are of the spiral-wound and the hollow-fiber twin seawater RO membrane configurations, each of 300 m3/d nominal production capacity. Descriptions of the MSF/pretreatment/RO experimental model, measurements of performance data, analytical procedures, and discussions of the results obtained are presented. The results indicate that the two tested types of membranes behave in a very similar fashion, both qualitatively and quantitatively. RO product water recovery under hybrid operation is significantly higher than under isolated surface seawater operation. Up to a 43% increase in the RO product water recovery was realized when data under hybrid operation were compared with those under isolated surface seawater operation and similar feed pressures. The average change in RO product water recovery was almost linearly related to the change in feed water temperature at an average rate of 2.2% 1° C change in feed water temperature.

Pilot study of MSFRO hybrid systems

Abstract Evaluation of the reverse osmosis (RO) process performance in an multistage/reverse osmosis ( MSF RO ) hybrid system is of particular interest due to the obvious advantages of hybrid desalination plants over isolated ones. Meaningful evaluation of the RO process performance in a hybrid model requires continuous monitoring of an RO test unit for an appreciable period of time during the winter season when the ambient seawater temperature is low. The primary objective of this study was to systematically confirm possible gains in the RO product water flow rate and to examine the overall performance of an RO plant operating in a hybrid environment. Experiments were carried out at the Doha Desalination Research Plant (DRP) using a carefully designed and equipped 20 m3/d RO test unit linked with the nearby MSF unit A-1 of the Doha East Distillation Plant. Actual hybrid testing of the RO unit started during the cold season and continued for about 1,800 h. The temperature of the RO seawater feed withdrawn from the MSF reject stream ranged from 24 to 31°C. Operating data collected from the RO test unit included temperature, pressure, flow rate, concentration, silt density index (SDI), and pH according to the function of each stream. A description of the experimental model, including the MSF RO arrangement, performance data, and a discussion of the results obtained are included in the course of this paper. It was shown that an increase of up to 49% in the RO product water recovery was realized when data from before and after hybridization were compared. Also, a 42–48% gain in RO product water recovery was estimated for a seawater feed temperature of 33°C as compared to an isolated RO plant using surface seawater at a temperature of 15°C and at a reference feed pressure of 55 bar. Higher SDI values, increased frequency of backwash and chemical dosing, and loss of the membranes salt rejection were also encountered during the hybrid testing.

Fifteen years of R&D program in seawater desalination at KISR part II. RO system performance

Kuwait Institute for Scientific Research (KISR) and the Ministry of Electricity and Water (MEW) collaborated over the past 15 years in developing and adapting the seawater reverse osmosis (RO) technology to the Gulf seawater conditions (one and half time the salinity of open seas and large temperature variations between summer and winter in the range of 35°C and 10°C, respectively). The development process went through several stages involving performance evaluation of three types of membrane configurations under various operating conditions and using different types of feed water pretreatment techniques. It went also through the evaluation of various commercially available energy recovery systems and the development of a new system. During this period, the RO research program evaluated the performance of ten different seawater membranes, cleaning and restoration techniques and procedures, using various potential agents. Furthermore, computer aided design program and process design and optimization procedures were developed specifically for Gulf seawater conditions. The studies also involved two-phase evaluation of multistage flash/reverse osmosis (MSF/RO) hybrid systems. Cost assessment of product water from RO under different operating conditions and various system configurations was always an important integrated part of each research project.

On performance measures of reverse osmosis plants

This analysis presented in this paper assesses the difference in the performance measures due to the inclusion of an energy recovery system into a small reverse osmosis (RO) in terms of plant availability. The failure behavior of an RO plant including an energy recovery Pelton wheel turbine is analyzed along with its operational time. The plant is divided into main subsystems and the availability/unavailability of each subsystem is derived. the overall availability of the RO plant with and without the energy recovery turbine are derived from the performance of its subsystems and were compared. Assessment of the operational time of the plant was considered to be more appropriate than other performance measures since the plant was designed for continuous operation. The plant subjective assessment of failure probabilities of subsystems was made wherever detailed data were not available.

Prediction of RO membrane performance for Arabian Gulf seawater

Arabian Gulf seawater is characterized by its high average seasonal temperatures, silt density index (SDI), and total dissolved solids (TDS), in addition to other parameters such as level of pollution and type and magnitude of marine microorganisms. The overall effect of these on RO membrane performance is very significant and complex as well. Hence, the primary objective of this paper is to present a mathematical model for the prediction of RO membrane performance for Arabian Gulf seawater under the prevailing local conditions. A complete system of equations that can be used for the prediction of product water flow rate and separation of ions present in seawater for a given RO membrane was obtained on the basis of the Kimura-Sourirajan analysis. Solution of this system for the purpose of performance prediction requires prior knowledge of certain parameters that are specific to the RO membrane under consideration and pertinent to the ions present in the seawater. A computer program has been developed to evaluate such parameters, solve the obtained system of equations, and process the performance predictions utilizing experimental data available from the operation of two RO membrane systems, spiral wound and hollow fiber, at the Doha Desalination Research Plant (DRP). Comparisons between predicted and experimental data at standard conditions have shown reasonable agreement for product flow rates and very good agreement for the rejection of total salts and ions present in the seawater.