(328a) Noninvasive Ultrasound Measurements of Temperature Profile Across Containments of Energy Conversion Processes

Process temperature is the primary characteristic that must be monitored in many energy conversion processes, such as gasification and nuclear fission. These processes are often characterized by extreme operating conditions. For example, gasification of coal and biomass is conducted at some of the most extreme temperatures, chemical aggressiveness, mechanical abrasion, and pressure conditions. Several technological challenges impact the reliability and economics of gasification, one of which is the complete lack of temperature and other sensors that perform reliably in the harsh gasification environment over an extended period of operation. The conventional approach of developing hardened conventional insertion sensors has proven to be largely unsuccessful. This is especially true for entrained flow slagging gasifiers since even the most hardened sensors are unlikely to survive for more than 1 or 2 months as the inner surface of the refractory wall degrades and recesses, exposing sensors directly to the corrosive slagging environment.

To overcome the difficulties in obtaining reliable temperature measurements in extreme environments, we are developing noninvasive ultrasound (US) methods for measuring spatial distribution of temperatures in solid materials[1]and applying the results to the measurements of the temperature distribution across cementitious and ceramic process containments. The physical basis of the approach is the temperature dependence of the speed of sound (SOS) in solids. By measuring the time it takes an acoustic signal to travel a known distance between a transducer and a receiver (the time of flight, TOF), the indication about the temperature distribution along the path of the ultrasound (US) propagation may be obtained. However, when temperature along the path of US propagation is non-uniform, as in the case of process containments, the measured TOF depends on the temperature distribution in a complex and unknown way. To overcome this difficulty, the US propagation path inside material of interest is engineered to incorporate partial ultrasound reflectors (back scatterers) at known locations. In this arrangement, measurements of temperature distribution begin with US pulse generated by an ultrasound transducer placed outside the containment.  This pulse will be partially reflected from each scatterer in the US propagation path in the containment wall and returns to the receiver as a train of partial echoes, the TOF of which is used to estimate the temperature distribution across the containment.

In this presentation, we will discuss experimental validation of the described approach[2], the achievable accuracy and spatial resolution of the measured temperature profile, and the application of this method to the monitoring and control of energy conversion processes.