Water Journal : Water Journal December 2011
conference reviews regular features 50 DECEMBER 2011 water Robert Maliva (US) looked at Injection Well Options for the Sustainable Disposal of Desalination Concentrate (authors: Dr Robert G Maliva, Dr Thomas M Missimer, Russell Fontaine), drawing on the range of options and designs in plants across the US, from beach wells to intake tunnels similar to those common in Australia. Membrane Technology Session Another interesting paper that attracted a sizeable audience was titled Utilising Nanotechnology to Enhance Membrane Performance for Seawater Desalination (authors: Christopher Kurth, Dr Robert Burk, Jeff Green). Beginning with a quick overview of the history of the development of nanotechnology, Christopher Kurth explained the principles behind the operational success that led to the synthesis of the first nano-particulate membranes for RO application. The increased permeability to water that arises with these membranes was found to be associated with the roughness of the nano-particulate surface and is essentially due to the increased surface area available to the water molecules. Delving deeper, a second layer of structure within this roughness was shown to enable the water molecules to travel through. The next step towards developing a commercial product for seawater desalination plants was to produce a nano-composite membrane on top of a supportive polymer layer. Rejection issues and fouling complicated the development of the final product and the team set out to work out where foulants and other particles were lodging in the nano-membrane. Defect channels in the membrane -- areas where nano-particulate aggregate had formed during the initial membrane fabrication -- appear to be the source of the problem. Continuing research in the fabrication process is expected to lead to further improvements to flux and increasing sulphate rejection. Currently the team is targeting the finalisation of their research to bring it to commercial production with field validation via pilot modules, and expanding the product line so that it could yield membranes specifically designed to suit source water and/or product application. Materials Session For those planning, designing, constructing and operating desalination plants, this session provided a list of what to do and not to do when selecting materials and seeking to maintain them in a membrane seawater desalination plant (SWRO) in Australia. Since it was Australia's first plant and has now been operating for five years, a summary of lessons learned from Perth 1 was presented by Tako Heiner (co-author: David Parracinii). He began by stating that the goal of his presentation was to "raise awareness" and for others to learn from the experiences being detailed. While responsibility for Perth material selection tends to be placed ultimately on the designer, the owner is concerned about costs, the operator about functionality, while the constructor has a range of other priorities. For the Perth SWRO, minimising crevice corrosion as occurs with continual exposure to saltwater and air and being equipped to resolve it when it occurs, without loss of production, was a priority in selecting materials and components. Types of failure observed in the five years of operation include: • Seawater intake grille SAF2205, heads of bolts hollowed out; • Non-return valves showed perforation through the body after three years' service; • Non-return spring collapse where the mechanism was found to be galvanic coupling; • Rack inlet valve showed seal faces and stem crevice corrosion. The conclusion: no material is, or is likely to be ideal in seawater because of the inherent variability of the medium in oxygen, salinity and other water quality criteria. A different emphasis, from the Sydney Seawater Desalination Plant, was provided by Andreas Broeckmann (co-authors: Stephen J Roddy, Peter Eccleston). This paper discussed the selection of essential process systems and elements for the plant, rather than the materials components themselves. At Sydney SWRO, elements identified as likely to be the source of problems were seawater, 1st pass concentrate and the permeate. For the intakes, biological growth and dealing with chlorinated seawater were identified as factors in materials selection. For the pre- treatment systems, the issues were again chlorinated seawater, spray and splash, varying fluid levels and aeration. Andreas commented that coatings for concrete structures and metallic equipment may not be as protective against corrosion as just stainless steel. For the RO system, the concerns were rack design, the operational envelope, performance and energy consumption. For critical process components, the use of super duplex steel was deemed essential, despite cost, due to its corrosion resistance and design flexibility. The pumps need hydraulic testing to ensure optimal performance. Vibration and noise continue to be difficult to manage. Other points made included: casting quality is critical and welding needs to be of a high standard; poor work needs to be identified and corrected prior to moving onto the next step to avoid subsequent downstream failures; and tanks for chemicals and for storing treated water, in particular, need quality welding followed by integrity tests and QA. The final point emphasised was the need for robust and careful management, with attention to detail at all stages. Unassigned/General Papers This category captured an eclectic mix of papers that did not fit clearly into other sessions. The most interesting group identified a new market -- the oil industry -- for future application of desalination technology. The first, titled Turning Water into Oil: Desalination a Process to Enhance World Oil Resources, was given by Dale Williams, LoSalTM EOR Facilities Program Manager for BP in the UK. The purpose of Dale's paper was to highlight the existence, nature and potential available to the desalination industry NCEDA researchers at the IDA World Congress.
Water Journal April 2012
Water Journal November 2011