Michell Instruments Ltd. - PRODUCT NEWS


Choose how to control moisture in your hydrogen coolant with a Michell hygrometer

Michell Instruments' on-line and portable dew point hygrometers provide a complete solution to monitor moisture levels and reduce the risk of explosion in hydrogen-cooled electricity generators.

Using hydrogen as a coolant in the power generation industry is common practice: it has an extremely high heat transfer capacity and is more efficient than any other medium. However, this efficiency has its price, as hydrogen is also highly flammable. The higher the moisture level is, the higher the potential for corrosion of the generator internals. High moisture levels lower the thermal conductivity (and therefore efficiency) of the hydrogen. Also, condensed moisture within the system increases the risk of the hydrogen in the system simultaneously igniting - a phenomenon known as 'flashover'. The risk of this is avoided by ensuring that the dew point of the moisture in the hydrogen is kept to a safe margin below the minimum temperature of the casing, typically around 0°C, to avoid condensation.

As it is not possible to hermetically seal the generator casings, there is potential for moisture to ingress from the surrounding air. The heat exchanger itself will also become more prone to leakage due to corrosion with age, allowing moisture to seep into the hydrogen, so constant measurement is vital to ensure that the dew point remains at a safe level below ambient temperature. There are two options: either continual monitoring or regular spot-checks of the system.

Continuous measurement ensures that the current dew point of the system is always available and alarms can be triggered if it rises above the ambient level. ATEX certified dew-point transmitters, such as Michell's Easidew PRO I.S. and Easidew TX I.S. are well suited to this application as they can be used to measure the dew-point of flammable gases within the hazardous area. As hydrogen constitutes an explosion risk, a digital indicator, if required, should be installed in a safe location, remote from the generator set. Both transmitters provide a 4-20 mA output signal covering the range -100 to +20°C.

A portable dew-point hygrometer, such as Michell's MDM300 I.S., may be used for making spot-checks of moisture in the system. This can either provide a fail-safe for the online moisture analyzers, or as the main method of measuring moisture. Portable instruments can be highly cost-effective as they can be used for spot checks in more than one location in a plant, eg also for transformer drying applications.

About Michell Instruments
Michell Instruments is the international leader in the field of moisture and humidity measurement solutions. With over 30 years experience, Michell designs and manufactures a wide range of transmitters, instruments and system solutions capable of measuring trace moisture, humidity and dew point in a vast range of applications and industries ranging from compressed air, power generation, process, oil and gas, pharmaceutical and many more. With a fast growing international subsidiary and distribution network, Michell provides solutions in moisture and humidity to the most demanding customers across the globe.

About Rense Instruments
Rense Instruments is an industry leader in the development and production of humidity and temperature measuring sensors, humidity portable and laboratory instruments and calibration transfer standards. Rense Instruments was acquired by Michell in January 2006 and completes Michell Instruments product range in humidity solutions. Rense instruments expertise spans over three decades focusing on serving customers with solutions for HVAC, energy management, storage and many other general industry and OEM applications.

Michell Instruments Limited
48 Lancaster Way Business Park,
Ely, Cambridgeshire CB6 3NW. UK
Tel: +44(0) 1353 658031 Fax: +44(0) 1353 658199
website: www.michell-instruments.co.uk

November 2011

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