Analytical Instrumentation

A Fast Method for Determining PCB/Chlorine Contamination in Transformer Oils by Monochromatic X-Ray Fluorescence (MCXRF)

Mar 22 2010 Read 10645 Times

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On an annual basis, millions of electrical transformers are removed from service in the global power grid. This activity generates many tons of solid waste and hundreds of millions of gallons of dielectric fluid / coolant (transformer oil) that can be recycled or must be incinerated as a hazardous waste. Although many chemical analysis criteria are utilised to determine the fate of both the solid and liquid reclaimed materials, the need to demonstrate regulatory compliance and control reclamation processes make testing for the presence of polychlorinated biphenyls (PCBs) contamination in used transformer oil absolutely essential.

Introduction / Abstract
Polychlorinated biphenyls (PCBs) are a liquid mixture of chemically stable chlorine containing compounds. They were widely used in the twentieth century for many electrical applications because of their excellent heat
resistance and electrical insulation (dielectric) characteristics. Beginning in the late 1970’s, production of high purity PCBs-based transformer oil material ceased in the United States and was eventually banned in most
countries because of evidence they build up in the environment and can cause harmful health effects.

Today PCBs contamination in transformer oil is measured and controlled as millions of gallons of various
dielectric/transformer oil materials are produced, recycled and traded on a global basis. Most analysis techniques take advantage of the high chlorine content in the individual compounds that comprise PCBs mixtures and measurement of specific PCBs compounds can readily be accomplished by a variety of analytical techniques, such as gas chromatography and mass spectrometry. However, analysis for the specific compounds that make up a PCBs mixture is not always practical or necessary, particularly when large number of individual samples must be characterised.

As indicated above, measurement of chlorine can be an excellent predictor for actual PCB contamination in transformer oil and other fluids of interest. X-Ray fluorescence (XRF) technology provides a reliable, fast and easy-to-use chlorine measurement methodology. The proven technique has been used for decades for primary measurement and most importantly for screening applications that reduce the need to analyse large numbers of materials with more expensive and time consuming analytical techniques.

The following describes the findings of a thorough examination of a new bench-top Monochromatic Energy Dispersive X-Ray Fluorescence (MCXRF) spectrometer. The compact (13”Wx 20”D x 16”H ) and lightweight (30 lbs) analyser was found to be able to readily measure chlorine content in transformer oils to part per million levels, in duplicate, in six minutes. The analyser’s performance characteristics easily meet transformer oil recycling industry requirements whenever rapid reliable chlorine measurement is essential to routine screening and process feed control activities.

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