Maintaining the moisture level of oil to a maximum of content of 15 PPM is a typical requirement. The saturation indicator can be directly related to the equilibrium relative humidity of the fluid (oil). The saturation indicator changes from a blue colour to pink when the silica gel requires reactivation or replacement. The most widely used indicating silica gel was impregnated with cobalt chloride that gives the silica gel its activity saturation indicator changing from a blue colour to pink when a 10-12% moisture loading (by weight) of the desiccant is exceeded.īeaded indicating silica gel is the best material to use in transformer breathers as it provides high resistance to attrition (dusting breakdown) during handling and regular bed packing providing uniform flow rate characteristics. Indicating silica gel is a silica-based material capable of adsorbing 25% of its own weight in moisture. This will depend on several key factors including the environmental conditions during use the reactivation temperature and reactivation procedure.Īlthough this may seem a simple procedure inadequate control and poor process techniques can have a major impact on maintenance schedules by reducing the average time between reactivation and replacement of exhausted indicating silica gel. Indicating silica gel can theoretically be reactivated a number of times. This means it can recovered and used again. One of the principal reasons for the use of indicating silica gel is its ability to release adsorbed moisture when heated to a temperature of over 100 oC.
Indicating silica gel is used throughout the power generation and transmission industry for Transformer Breathers to protect the heat transfer cooling oil from moisture (condensed water) contamination. This article suggests a number of simple improvements to improve the practice and procedures for reactivation of silica gel. The use of valved Transformer Breathers has eliminated the need to maintain the oil seal fluid level and combining this with improved reactivation contributes to further savings by extending the average maintenance period. Shorter maintenance periods have an impact on both time and cost. Ineffective reactivation control can result in Transformer Breathers being maintained by up to three times more than is necessary. See caution note as cobalt chloride impregnated silica gel is now carcinogenic. The indicating property is achieved by impregnation with cobalt chloride salt which is sensitive to water vapour. Silica gel is available in two primary types indicating and non-indicating. The majority of Transformer Breathers used by the power generation industry contain indicating silica gel.
Silica gel is capable of adsorbing up to thirty percent of its own weight of water vapour. Silica gel, or gel packets, are used throughout industry to adsorb moisture and maintain low relative humidity thereby preventing product contamination and degradation.
Silica gel desiccant reactivation is a common operating procedure regularly used and performed to remove moisture from saturated material.
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