Hydrogen concentration measurement in high temperature applications using hydrogen permeation

Abstract

With the increasing use of hydrogen in energy process engineering and as chemical reactant, the importance of hydrogen sensors is rising. However, there are few established methods to measure the hydrogen concentration of a gas-mixture at high temperatures. Also the in situ measurement at these temperatures in chemical reactors is challenging. A sensor, which is based on hydrogen permeation, could be a cheap and practical solution for the in situ measurement at high temperatures.A permeation hydrogen sensor for the measurement of the hydrogen partial pressure was developed and built. The concept of the sensor is a small, hermetically sealed nickel tube working as a hydrogen permeable membrane filled with pure hydrogen. It is in contact with the measurement gas and connected to a pressure sensor. Under stationary conditions a equilibrium between the hydrogen partial pressure of the tube and the measurement gas will be established. Since the tube is filled only with hydrogen, the pressure sensor connected with the nickel-tube measures the hydrogen partial pressure of the measurement gas.Such a sensor was modeled, developed, built and characterized. The most important calculations, the general design of the sensor as well as the most important results of the experiments are presented in this paper. The sensor worked with a good accuracy and showed a response time of about 1000 s at 60 °C and 200 s at 900 °C. A response time lower than 200 s for temperatures above 600 °C is possible with an improved sensor design. Also, an in-situ measurement of the steam content inside a shift reactor was conducted, the results matched the calculated steam contents from a reactor balance very precisely.