An ion-exchange process with thermal regeneration VIII. Preliminary pilot plant results for the partial demineralisation of brackish waters

✍ Scribed by H.A.J. Battaerd; N.V. Blesing; B.A. Bolto; A.F.G. Cope; G.K. Stephens; D.E. Weiss; D. Willis; J.C. Worboys

• Publisher: Elsevier Science
• Year: 1973
• Tongue: English
• Weight: 817 KB
• Volume: 12
• Category: Article
• ISSN: 0011-9164
• DOI: 10.1016/s0011-9164(00)82074-3

✦ Synopsis

Significant advances have been made in the development of the "Sirotherm" process which should pave the way for the commercial utilisation of the process for the desalination of brackish water resources, for municipal, boiler-feed and industrial water supply purposes . These advances include the synthesis of new, thermally-regenerable. ion-exchange resins having practical working capacities and fast adsorption rates .

The resin has been made successfully in pilot batches and is being tested in standard pilot-scale ion-exchange equipment . Field trials are showing considerable promise and are continuing on this resin with surface and underground waters . Some pretreatment will be necessary for most natural waters . Resin-life studies are so far promising and are continuing . Additional attractions of this process for desalination are the highly reliable and well-tested technology already developed for conventional ion-exchange, and ease of upscaling .

Further potential exists for increasing the performance of the resin and for broadening the application of the process to a wider range of waters and needs ; to these ends, research continues which backs up the current process-development and field-trial program .

1 . INTRODUCTION

The research and development project to be described in this report has as its objective the development of the "Sirotherm" process for the partial de-• Based on a contribution to the Fifth Federal Convention, Australian Water and Wastewater Association, Adelaide, South Australia, May 31-June 2.1972. Part VII, Desalination, 8 (1970) 21 . H . A. J . BATTAERD et al.

mineralisation of brackish waters . This process is novel and utilises a mixed bed of ion-exchange resins which is regenerated with hot water rather than with acid and alkali .

As described elsewhere (1), such a process has important, long-term fundamental advantages, not all of which are possessed by other desalination processes . These assume increasing significance as the state of development of a process increases since fundamental limitations eventually prevent further improvement . Avoidance of phase changes and latent heat recovery_ the large surface area which is readily available in an adsorbent bed . and extraction of salt from water rather than water from salt, assist reduction of capital costs in the "Sirothcrm" process . The ability to use a small driving force, as a consequence of the large interfacial area between the resin and water. and the use of energy in its cheapest form-low grade sensible heat-favour reduced energy costs. The engineering principles involved in adsorption plants are simple, highly developed and versatile ; they are used in both very large and small-scale plants for sand filtration and in conventional ion-exchange softening and demineralisation processes . Consequently the development, and application, of a thermally regenerated ion-exchange process can proceed rapidly once an adsorbent with the requisite properties becomes available.

The first phase of the project terminated with the discovery of ion-exchange resins with an ability to adsorb sodium chloride and magnesium sulphate to an extent which decreases markedly with rising temperature (2-5) . Extensive studies were made of the relationship between the chemical structure, acidity, basicity and thermal stability of ion-exchange resins of the weak-electrolyte type . The basic principles, elucidated in this way, are a guide to resin selection and to the understanding of the complex equilibria involved .

The next phase involved making a two order of magnitude improvement to the kinetic performance of "Sirotherm"-type resins : this necessitated furher synthetic studies and the elucidation of kinetic mechanisms (7, 8,14) .

Once a practical resin became available in substantial amounts, pilot-plant investigations of the process itself were able to begin in January 1970 . These commenced with the study in Adelaide of simulated bore waters in a fixed-bed unit and were followed later in that year in Melbourne with an investigation of the performance of a larger commercially available unit on simulated bore waters . More recently pilot-plant field trials have begun in Perth and Adelaide . The Perth trials, in collaboration with the local water authorities, are aimed initially at producing a municipal water from a 1000-201x1 ppm bore water . The trials in Adelaide are more complex and aim at producing from a 200-500 ppm tap water a partially demineralised and completely softened water (50-100 ppm) suitable for passage through a conventional mixed-bed ion-exchange plant so as to produce a boiler-grade water.

This paper touches on the basic features of the process but is concerned