2002 Volume 56 Issue 3 Pages 247-255
Reverse osmosis membrane processes are effecient in terms of energy and widely used in the desalination field. Recently, a new scheme of reverse osmosis seawater desalination, which is called a brine conversion twostage process, was proposed by Toray Industries, Inc. In this process, a second stage is added to a conventional RO unit, and the concentrated brine from the unit is further desalinated at the second stage to increase the water recovery ratio over 40% to 60%. The recovered energy from the first stage brine is used to pump the feed to the second stage up to approximately 10 MPa. For this purpose, a new membrane, UTC-80BCM, has been developed besides the conventional UTC-80. A test plant based on this scheme (210m3/day) was built at Ehime factory, Toray, Inc. and was operated under a wide range of conditions.
The purpose of this work is to establish the calculation method for RO process for seawater desalination. In this research, first, we measured the membrane properties and the mass transfer coefficients of each spiral-type element, SU-820 and SU-820BCM, which use UTC-80 and UTC-80BCM. Next, we developed a computer program based on the concentration polarization model. In this calculation, we consider the change of the membrane itself in terms of operating conditions, the temperature, and the pressure, whose corrections are determined from the laboratory experiments. Finally, the test plant data under the various operating conditions were taken and a calculation method was successfully verified.
As a result, this method enables us to obtain membrane transport parameters from running plant data to find the causes of membrane fouling under various operationg conditions, and to predict the plant performance, which is necessary for us to design the process.
