Improved Reliability of Dew Point Measurements of Furnace Atmosphere on a Continuous Basis

Dew point is a function of the furnace atmosphere composition.  In a metal processing continuous furnace, maintaining appropriate atmosphere composition in each zone is critical to achieving the desired gas/metal reactions and quality and consistency of the sintered product.  Continuous monitoring of dew point is always challenging because of particulates and vapor-phase contaminants in sampled gas stream which can potentially accumulate in filtering systems and on sensors, as well as temperature variations within the sampling unit.  As a result, dew point readings can drift significantly, necessitating frequent cleaning, recalibration, and sensor replacement. Air Products developed a dew point monitoring system and tested it at one customer site.  Drifts/changes of dew point readings on the calibration gas were not observed after more than one year of operation, without any maintenance.  The contamination and drift issues have been mitigated by incorporating an automated self-cleaning and sensor calibration process after pre-set measurement periods.  Temperature control of the sensor and the sampling system are also essential to maintain consistency, and can be achieved via various design features.  Drifts/changes in dew point that are reported through local monitoring/alarms or remotely through Cloud server access can also help to address furnace operational issues quickly and efficiently.