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ACS Cobra Energia has installed a Liquidew moisture-in-liquid analyser from Michell to help save time and money on maintenance at the Extresol-1 thermosolar power plant in Extremadura, Spain.

The Liquidew analyser monitors the levels of moisture in the heat transfer fluid, alerting operators when levels of moisture become too high and enabling them to act early to avoid damage to the system.

The Extremadura plant, which generates 50MW, covers 195 hectares and contains 156 mirror arrays, with a total length of tubing of 92km.

Solar thermal power plants, with parabolic trough technology, capture the sun’s heat to drive traditional steam turbines, rather than producing electricity with photovoltaic cells.

The heat is focused using mirrors and generates steam to drive the turbines via a tube filled with a special heat transfer liquid.

The heat transfer liquid is a mixture of biphenyl/diphenyloxide and has a similar appearance and viscosity to water, but with very different characteristics.

It boils at 300C, making it ideal for coping with the high temperatures needed to drive the turbines.

It also has a freezing temperature of 12C and it must be kept above this temperature at all times.

The heat transfer fluid may contain dissolved moisture, which presents a problem at night when the fluid cools, as the dissolved moisture may reach saturation point and liquid water will condense within the fluid, forming a liquid-liquid mixture.

If allowed to occur, such liquid water may evaporate as the fluid mixture heats up the next day to form pockets of high-pressure steam, potentially causing physical damage to the plant.

This risk can only be averted by the continuous online monitoring of the dissolved moisture to enable effective drying processes within the heat transfer liquid loop.

Michell’s Liquidew moisture-in-liquid analyser was chosen because of its wide measurement range – from 0.0001ppmW to saturation levels – as well as its reliability.

The instrument uses a moisture sensor that is resilient in chemically aggressive media and reliable for continuous long-term operation in dense liquid phase sample flows.

The sensor is part of Michell’s calibration exchange programme, which ensures continued accurate measurements with the minimum of disruption for maintenance.

The supplied sampling system was designed to meet Extresol’s specifications by the company’s dedicated systems engineering department.

Michell Instruments

Michell Instruments is an international leader in high-precision sensing with over 35 years’ experience in the field, specialising in instrumentation for dew point, relative humidity and oxygen analysis. The company serves industries as diverse as petrochemical and pharmaceutical to power generation and food processing. The product range includes:

  • High-precision ceramic moisture sensors to measure trace moisture in process applications.
  • Relative humidity transmitters and sensors for use in HVAC applications, pharmaceutical storage and other production processes where controlled environmental conditions are crucial.
  • Humidity calibration systems and reference dew-point hygrometers enable customers to carry out the calibration of portable hygrometers and relative humidity instruments in-house, saving on downtime and costs.
  • Zirconia and thermo-paramagetic oxygen analysers for combustion optimisation, maintaining gas purity, controlling levels of CO2 in breweries and many other applications.
  • Condumax II Hydrocarbon dew point analysers ensure the quality of natural gas at custody transfer, prevent gas burner failure and the prolong the life of process equipment, helping companies save millions of dollars on repairs and downtime.
  • Trace moisture in hydrocarbon liquids analysers are available in explosion-proof and instrinsically safe versions and allow the continuous measurement of moisture content in a wide range of applications from transformer oil, petrochemical factions and pure hydrocarbons.
  • Process moisture analysers provide continuous on-line measurements of trace moisture in process gases and are available as explosion-proof, instrinsically safe and laboratory versions.

Michell Instruments has three manufacturing locations: Oosterhout, The Netherlands; Lyon, France and Ely, UK. The company has an extensive network of factory-trained application engineers, subsidiaries and distributors stretching across 56 countries.

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