(530c) Development of An Impedance-Based Sensor for Detection of Catalyst Coking in Fuel Reforming Systems

A novel sensor for detecting the early stages of catalyst coking in fuel reforming systems has been developed at the Colorado School of Mines.  The sensor was manufactured by inkjet printing a colloidal suspension of ceramic powders to create thin (~20 μm) catalytic and conductive elements of the sensor.  The catalytic elements of the sensor are composed of a Ni-YSZ cermet. The Ni-YSZ cermet was prepared with a concentration below the percolation limit (~20 vol%) of nickel, ensuring a low electrical conductivity.  As coke forms on the catalyst material, the nickel nodules in the Ni-YSZ are connected by electrically conductive carbon and the conductivity of the catalyst material increases. 

Sensors were tested in 1% ethylene and methane dry reforming environments to induce coking.  The sensor showed a strong response to coking by producing a signal on the order of hundreds of millivolts.  The mass of the coke load was determined to be below the detection limit of available thermogravimetric analyzers (TGA) ( <10 µg).  The coke load was further examined with a field emmision scanning electron microscope (FESEM) and was found to be primarily carbon nanofibers.  Carbon nanofibers ~10-100 nm in diameter connected nickel nodules in the sensors’ catalyst material resulting in a change in resistance in the catalyst material. 

Tests were also carried out to determine if the sensor was capable of automatically controlling a fuel stream.  Custom electronics were developed to interface the sensor to an Arduino UNO microcontroller.  The Arduino microcontroller was able to read signals from the sensor and control the experimental fuel stream.  Sensors were exposed to a methane dry reforming fuel stream (23% methane, 77% carbon dioxide at 640 °C) to induce coking.  The sensor automatically shut down the coking fuel stream when a coking signal was detected, ~130 s after the sensor was exposed to coking conditions.