Mobile Hydrogen Monitoring in the Wall of Hydrogenation Reactors

A test technique was developed for in-situ, instantaneous, and nondestructive inspection of the distribution of mobile hydrogen in the wall of a hydrogenation reactor operating at an elevated temperature and high pressure. The base current density of the developed sensor was < 0.6 μA/cm² at cooling water temperatures below 313 K (40°C). The steady current density, i_∞, of atomic hydrogen oxidation needed calibrating from the direct-measuring sensor signal, i_sen. The calibration equation could be expressed as i_∞ = 1.2 i_sen. Its factor 1.2 corrects the difference in the direction change of hydrogen diffusion from one dimension in the steel wall to three dimensions in the space between the steel external surface and the external side of the Pd alloy in the sensor. The temperature of the cooling water of the sensor obviously influenced the steady permeation current density. Results of the study showed that the temperature of the sensor should be kept constant so as to assure measurement accuracy. The specifications of the developed probe available for elevated temperature are presented in this paper. Inspection results of hydrogen concentration obtained from an operating hydrogenation reactor are displayed.