Performance prediction and optimisation of spiral wound modules

The work deals with the modelling and optimisation of reverse osmosis (RO) spiral wound elements. It is aimed at improving areas of uncertainty and possible limitations which remain with current published predictive schemes. These were compromised mainly by the lack of adequate experimental data representative of actual operating conditions. Two different mathematical models, termed the `Slit' and the `Spiral' model, were developed. These models differ on the geometrical idealisation of a spiral wound element as indicated by their names. The Solution Diffusion model is used to describe water and salt transport across the membrane. The differential equations governing the process were solved numerically using a finite difference method. The resulting computer programs enable concentrations, pressures and flow rates in the brine and permeate channels to be obtained at any point in the module. The investigation covered a wide range of feed conditions by using experimental data provided from two different types of commercial spiral wound modules. These were the ROGA-4160HR [29] and the Filmtec FT30SW2540 [28] modules. The former type dealt with data typical of brackish water desalination whereas the second type provided data typically encountered in sea-water desalination. The required intrinsic membrane characteristics were determined experimentally using small samples of membrane in a test cell in a closed loop system. For both models, the predictions agree very well with the experimental data over the entire range of operating conditions:- with the exception of some few cases, typical deviations were of the order of 6% for the module productivity and of about 10% for the permeate quality. In addition, parametric studies were performed to establish the programs consistency and the results were in accordance with the theory