1.4 This test method was tested on reagent water only. Unreactive silica or non-reactive silica is a polymeric form of silica; thermally unstable which reverts to normal silica when heated. Colloidal silica is not retained by the ion exchangers and is hydrolyzed into soluble silica in the boiler. As a result, it can cause problems with deposits being formed as well as scaling. as small suspended silicate particles (colloidal silica). Chemicals to react with feedwater hardness 2. •SILICA -- coming thru the makeup water to the feedwater that may be used for attemperation can cause problems in the turbine area. The documents listed below are referenced within the subject standard but are not provided as part of the standard. Both dissolved and total … It can cause undesirable scale formation in boilers and cooling towers, can clog pores of adsorption media. Many plants unfortunately fail on providing correct pre oxidation. The silica particles are suspended in the stream and cannot be easily settled out from the liquid component. So limiting criteria are designed for total silica, as follows - Boiler Pressure (psig) SiO 2 Tolerance in Feed Water … In many cases there is also seen a significant pH depression, due to formation of organic acids from the colloid. Based on the above, there could be a situation where the demineralized water from an ion exchange system may have residual reactive silica below 10 ppb, which is a good number, but there could be some colloidal silica which is not measured neither by the lab testing or the on-line silica analyzer. 1.2 This test method is applicable in the range from 25 to 250 μg/L of silica as SiO2. We and third parties such as our customers, partners, and service providers use cookies and similar technologies ("cookies") to provide and secure our Services, to understand and improve their performance, and to serve relevant ads (including job ads) on and off LinkedIn. Other plants fail on allowing floc passage from the settlers and/or filters. the source of the problem was colloidal silica in the form of fine mud in the boiler feed water. Volatilization and carryover of silica with the steam may cause hard, glassy siliceous deposits to form on turbine blades that reduce turbine efficiency. The surface of colloidal silica in … 1.6 This standard does not purport to address the safety concerns, if any, associated with its use. •Recommend maintaining close limits of allowable silica in the boiler water to keep sat steam silica … Boiler scale is caused by impurities being precipitated out of the water directly on heat transfer surfaces or by suspended matter in water settling out on the metal and becoming hard and adherent. 1.5 The values stated in SI units are to be regarded as standard. For water treatment, silica can foul reverse osmosis (RO) membranes under some conditions. by subtracting the value for reactive silica from the total silica value. Silica is the only boiler water salt that vaporizes at pressures below 2400 psig. Ensure good pre oxidation in the clarification process. Unreactive silica is polymerized or colloidal silica… Reactive silica, though it has anionic characteristics, is not counted as an anion in terms of balancing a water analysis but it is counted as a part of total TDS. 1.3 This test method determines total silica, and does not distinguish between soluble and insoluble forms. The immediate result is a sudden raise in silica concentration in the boiler water. Good operation of settling/filtering in order to not allow floc leakage. Ion exchange will remove this as long as … It is important to control the external water … Due to the extremely tight filtration of the R.O. Hence, the name non-reactive silica to refer to all other forms of silica which do not readily react with the molybdate reagent. Schematic representation of the silica gel surface. Higher concentrations may be determined by decreasing the aliquot volume (see Note 6). A colloidal silica slip will significantly increase the SiO2 levels in the boiler water, well above typical values of 2-20 ppm (for pressures > 900 psig). D1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits, D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water, D3370 Practices for Sampling Water from Closed Conduits, D3919 Practice for Measuring Trace Elements in Water by Graphite Furnace Atomic Absorption Spectrophotometry, D4453 Practice for Handling of High Purity Water Samples, D5810 Guide for Spiking into Aqueous Samples, D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis, ASTM D4517-15, Standard Test Method for Low-Level Total Silica in High-Purity Water by Flameless Atomic Absorption Spectroscopy, ASTM International, West Conshohocken, PA, 2015, www.astm.org. The … reactive silica is present in the range from 1 to 2.8.. 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Carryover of silica in water Active ( this link will always route to the extremely tight filtration of small. Installed, choose a ultrafiltration process as a result, it can contribute the... Components in feedwater–steam circuit the temperature and pressure are increased, more silica becomes in.

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