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GE Water & Process Technologies, a unit of General Electric Co., provides an antiscalant technology program, GE Betz HT15/PDC9323, to Water en Energiebedrijf (WEB) Aruba N.V., which provides power and water to the island of Aruba. GE’s antiscalant technology program is a scale inhibitor for use in Multi-stage Flash (MSF) plant evaporators using steam to drive the desalination process to obtain potable water.
The GE technology was used in WEB Aruba’s Aquachem 5 (AC-5) MSF plant, which has 40 stages, 36 recovery and four reject, enclosed in seven vessels and a capacity of 600m3 per day. Prior to using the GE Betz HT15/PDC9323 program, sulfuric acid was injected into the makeup line prior to the dearator. GE’s antiscalant technology was added in two places: downstream of the brine recirculation pumps and at the entrance to the warmest stages.
The antiscalant program at WEB Aruba’s AC-5 MSF plant was monitored for a six-month period. Results of the program were a success, meeting all of WEB Aruba’s goals. GE Betz HT15/PDC9323 effectively controlled scale at a TBT of 110°C, without acid addition at a concentration factor of 1.5 cycles. In addition, the plant’s Gained Output Ratio was maintained, and the new technology had little or no adverse effect on plant corrosion. Brine heaters were extremely clean after the six-month period, and no deposits typically found when the plant is acid-dosed were present.
MSF plants use thermal technologies in the desalination process. To increase heat transfer efficiency, steam is used to heat the influent seawater and sequential chambers. While most substances are easily dissolved in higher temperatures, calcium and magnesium salts naturally contained in seawater exhibit retrograde solubility. As brine temperatures increase, the solubility of the mineral compounds decrease. The resulting scale accumulates on heated surfaces and disrupts heat transfer. Scale control in high temperature desalination processes is primarily achieved by acid dosing, or with addition of antiscalant chemicals and ball cleaners.