Water. Desalination + reuse
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water.desalination+reuse December 2016 SPONSORED ARTICLE Challenge: Flux decline, increase in pres- sure drop and salt passage Silica scaling on membranes used in the desalination process is a major problem if water that passes through a desalination plant has high silica concentration. Scaling causes a flux decline and increases pressure difference and salt passage. Silica scaling happens when the con- centration of dissolved silica exceeds the solubility limit at the temperature and pH of solution. This is a major problem at Reverse Osmosis plants where silica concentration in feed water is at elevated range (e.g. 25 ppm) and recovery is high (e.g. more than 80%). At these levels, the silica in concentrate stream precipitates out of the aqueous phase. Solution: Kemira's new antiscalant to control silica scaling Kemira KemGuard™ PB-20412 antiscalant prevents scale formation by controlling the scaling environment in the Reverse Osmosis process, promoting conditions where scale will not form. We ran a pilot trial at a desalination plant with a capacity of 110 000 m3/day. The feed analysis. A'er performance testing, the membrane autopsy was closely studied. Results: Silica scaling of membranes suc- cessfully inhibited Based on the performance data (flux, pres- sure difference, and salt passage), Kemira's antiscalant product performed well and prevented silica scale formation efficiently. A close study of the membrane used in the pilot shows absence of silica both in amor- phous and crystalline form. Silica scale for- mation on the membrane was inhibited as scale was dispersed in the aqueous phase. The pressure difference over the mem- brane was not changed during the pilot trial. This also shows that the membrane was not blocked or fouled by silica scale i.e. the Kemira antiscalant performed effectively. Key benefits: • prevents scale formation • improves desalination process efficiency • reduces frequency of membrane change needs • reduces frequency of cleaning • lowers energy consumption References Gill, J.S., Inhibition of silica-silicate deposit in indus- trial waters, Colloids and surfaces A: physicochemical and engineering Aspects, 74 (1993) 101-106 Mickley, Michael C.; Straley, Martin; Coury and Asso- ciates, Glenn, An experimental project to determine the parameters of silica scaling in reverse osmosis systems: technical completion report, United States, Office of Water Research and Technology, National government publication, 1982. Reducing silica scaling on membranes at desalination plants Silica scaling is a major problem when water has high silica concentration. THE BIG IDEA SPONSORED ARTICLE water for the plant is mainly surface water and hot spring water. The plant has a high concentration of silica in the feed (20–25 ppm) and high recovery (85-90%). Before Reverse Osmosis, water goes through coagu- lation, flocculation, sand filter, and cartridge filter. The Reverse Osmosis unit itself has three stages. The pilot plant, where the antiscalant was used, simulated the last of these stages. Feed water flow rate to the pilot was 1.2 m3/h, inlet pressure 23 bar and recovery for a single 8-inch membrane was about 90%. The performance of the antiscalant was monitored for a month. Permeate flow, pres- sure difference, silica concentration, and conductivity of permeate and concentrate were monitored and collected for further To see and extended version of this article, visit Desalination.biz www.kemira.com water@kemira.com