Ultrasound Measurements of Temperature Profile in Solids: Pilot Scale Monitoring of Temperature Distribution across Refractory of Oxy-Fuel Combustor

摘要

A novel ultrasound temperature measurement method was developed and tested during the operation of a pilot-scale Oxy-fuel combustor. By using noninvasive ultrasound probing, the temperature distribution across containments of extreme environments can be obtained in real time. This is accomplished by measuring the time of flight (TOF) of ultrasound echoes, calculating changes in the speed of sound (SOS), and estimating the corresponding temperature changes based on empirical or theoretical correlation between the SOS and the temperature. To improve the accuracy of the estimated temperature distribution, the ultrasound waveguide was engineered to have multiple internal partial ultrasound reflectors along the length of the ultrasound propagation. These refractors create multiple echoes, the TOF of which gives the indication of the temperature distribution in different segments of the waveguide. In this pilot test, a high purity, nonporous alumina rod, capable of withstanding temperatures up to 1,700°C, was selected as the waveguide. Partial ultrasound reflections were created by drilling small holes along its length. A single ultrasonic transducer/receiver with the central frequency of 5MHz was used to produce ultrasound pulses and detects ultrasound echoes. The waveguide was installed into one of the available ports on the oxy-fuel combustor. Its distal end was positioned to be flush with the internal surface of the refractory. The transducer was attached outside the combustor to the proximal end of the waveguide, which was cooled by water to maintain its temperature below the Curie point of the transducer. Thermocouples were attached to the waveguide to provide independent temperature measurements.