Available from AMS Instrumentation and Calibration , Michell Instruments’ on-line and portable dew point hygrometers are designed to monitor moisture levels and reduce the risk of explosion in hydrogen-cooled electricity generators.
Used commonly as a coolant in the power generation industry, hydrogen offers benefits such as an extremely high heat transfer capacity and better efficiency than any other medium. The downside of using hydrogen is its high flammability.
High moisture levels lead to greater potential for corrosion of the generator internals. High moisture levels lower the thermal conductivity (and therefore efficiency) of the hydrogen. Additionally, condensed moisture within the system increases the risk of the hydrogen simultaneously igniting.
One can avoid this risk 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 0ºC to avoid condensation.
Since the generator casings cannot be hermetically sealed, there is potential for moisture to ingress from the surrounding air. The heat exchanger will also become more prone to leakage due to corrosion with age, allowing moisture to seep into the hydrogen.
Constant measurement is therefore vital to ensure that the dew point remains at a safe level below ambient temperature. This can be done either through continual monitoring or conducting 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.
Michell’s Easidew PRO I.S. and Easidew TX I.S. are ATEX certified dew point transmitters 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 should preferably be installed in a safe location, remote from the generator set. Both transmitters provide a 4-20 mA output signal covering the temperature range of -100ºC to +20ºC.
Michell’s MDM300 I.S. portable dew point hygrometers can be used for making spot checks of moisture in the system. These can either function as a fail-safe for the online moisture analysers, or as the main method of measuring moisture.
Portable dew point hygrometers are highly cost-effective as they can be used for spot checks in more than one location in a plant.