Water Journal : Water Journal September 2015
water september 2015 46 Feature article I ncorporating membranes into a concept process design for water treatment plants is time consuming. Once a concept involving membranes has been established, designs have to be configured on a single train basis using vendor software. Each membrane vendor offers different parameters and functional constraints, which makes concept design an iterative process. But what if there was a better way? The five largest Reverse Osmosis (RO) and Nanofiltration (NF) membrane manufacturers have six different modelling software packages. Each package limits the user to a single train design configuration for every model run. Only a limited set of feedwater quality parameters can be modelled without considering the influence of all the other technologies in the process. This can be an issue for designers, particularly when there are recycle streams that can influence performance. Each platform has a different user interface, leaving designers with a number of pain points including: • Learning numerous software types; • Inability to directly compare different design and membrane configurations; and • Inability to collaborate on one platform with other team members to test or review membrane performance prior to selection. The conventional design approach is best suited to detailed design, once the feedwater envelope at the RO feed has been established and negotiations with the membrane vendor begin. Many of the better detailed projection software packages don’t reflect membrane market share, so a generic approach to concept design configuration and membrane selection has merit. MeMbrane desIgn software Currently, designers download and install multiple software packages, with inconsistent configuration parameters such as salt passage increase (SPI), fouling factor (FF) and a limited set of ions. These packages do not consider soluble gases, trace metals, heavy metals or pre- and post-treatment processes, although some have recently incorporated Ultrafiltration (UF) modules and chemical dosing parameters to their platforms. Designers lean on their experience with membrane product properties or vendor representatives to help guide selection of the best membranes based on application and configuration of each RO or NF train. Understanding the RO feedwater quality and how non-modelled parameters might affect performance is crucial. Open systems such as ponds and lakes can influence results where the water quality during process commissioning and operation can look quite different compared with a functional specification. These variables and predicting their impacts are based on the designer’s experience, as this information is not provided in vendor-specific projection software. The Reverse Osmosis System Analysis (ROSA) platform by DOW Corporation is considered the most ubiquitous tool in membrane modelling for detailed design. Many water professionals use the term ‘ROSA’ interchangeably with ‘RO projection software’, having been introduced to ROSA and the DOW Technical Manual as a guide for modelling membrane processes as young engineers. ROSA is a relatively easy to use platform that provides a small set of ions designed for configuring DOW’s FILMTEC membranes. However, it does not include all membrane parameters that may affect permeate quality over time, and is limited to modelling DOW membranes. Other membrane manufacturers continually add features to their projection software to increase membrane sales. However, these additions usually increase software complexity and discourage learning and market uptake. Table 1 outlines a comparison of common vendor projection software packages currently available. The objectives for using RO projection software are different for professionals engaged in commercial, front-end applications and consulting activities compared to detail designers engaged on a membrane project. Commercial developers, applications engineers and consultants require projection software for optioneering, concept design and writing functional specifications. For these users, a platform that is easy to use, fast and reliable in its projections and outputs is a key driver. Comparatively, process engineers engaged in developing the detailed design require vendor-specific, accurate and robust modelling software that can simulate all conditions that might trigger a contract performance clause or a membrane warranty. Hydranautics, GE and Toray have come a long way in improving their projection software. Today, these platforms allow single train model configurations to be run with additional ions in the RO feed, the addition of pre- and post-treatment processes (UF or degassing), and even incorporate anti-scalants. These software packages are ideal for detailed design, but are also more laborious so are not suited to concept design. This is especially true in concept design activities where the entire integrated process needs to be considered in a timely fashion, including the influence of upstream processes and recycle streams on RO feed quality, and the impact of membrane type and array configuration on specific ions in the treated water. Process ModellIng software Approximately 50 different modelling software packages for various aspects of process design are currently available for download. Of these, Aspen is considered the most respected deterministic mass and energy balance software producer, covering many industrial processes. Most of these platforms are focused on chemical, hydrocarbon and thermal modelling for industrial processes and are prohibitively expensive for many users, costing tens of thousands of dollars per licence. PROCESS MODELLING FOR MEMBRANE SYSTEMS Darren Szczepanski and Matthew Brannock from Salt Water look at the various options available in design software.
Water Journal August 2015
Water Journal November 2015