Page 250 - Membranes for Industrial Wastewater Recovery and Re-Use

Systt-ni dmign aids 2 19

0 feed or product water quality and quantity.
0 membrane type, which then determines the flux and pressure, and
0 conversion.

All of these parameters must be entered into the design before the array can be
optimised, usually through iteration.
The comprehensiveness, level of sophistication, and user-friendliness of the
design package varies from one manufacturer to the next. However, all these
packages have been developed to help the designer produce an array design as
easily as possible. using the inaniifacturer’s own RO membrane products. Hence the
information pertaining to mass transfer of dissolved solids and water across
the membrane is specific to the membrane products listed within the package.
Apart from the way in which the design information is set out, this is the main
difference between the available packages.
The ROPRO package (Version 7) is the proprietary CAD program produced by
the suppliers of the Fluid Systems RO membranes. ROPRO offers a number of
overall design configurations and options, such as bypass, pre- and post-acid/
base dosing and degassing, and has a comprehensive “help” file. It also has an
ancillary costing facility. Most of the ROPRO features are self-evident from the
main flowsheet schematic, which has active regions for the pre-treatment, array
and post-treatment processes, as well as for the stream compositions. Any of
these can be checked at any point.
The quickest route to designing the plant is as follows:

1. Use the Input Wizard (on the Input menu) to enter all the data (ignoring pre-
dosing for now)
2. Once the array design screen is reached, the Array Wizard should be used
and an estimate of the flux made from the information given for the membrane
element selected.
3. When all the data has been entered, the large GO button on the menu bar
can be clicked to reveal the results.

The next screen informs the user where the design fails, either through figures
shown in red for the scaling indices or through a Warnings prompt in the light
blue box. A further screen appears when the Warnings button is pressed.
Having read the warnings, the array design can be adjusted accordingly.
A few common remedial measures are as follows:

0 RO membranes tcnd to scale-up on thc concentrate side of the membrane.
The only option offered by this package for ameliorating this problem is
acid dosing.
0 The flux chosen is critical. Too high a value causes an overlarge operating
pressure and scaling problems. Too low a flux means that the system is
hydraulically unbalanced and not optimised.
0 The number of elements in each module can be adjusted, but the default
value is normally quite reasonable.