This invention concerns the temperature measurement of hot gases within a vessel having a hot surface which radiates microwave energy. The method is particularly suited to gases laden with entrained solids.
Generally temperatures inside of furnaces, reactors, incinerators, and the like are measured by optical or infrared pyrometers since the temperatures involved may exceed the capabilities of, e.g., thermocouples. These optical or infrared pyrometers are aimed at the point of interest through a sight hole or inspection door. In the case of modern coal gasification reactors which operate under significant pressure, transparent windows of quartz and the like, can be used. However the harsh environment within the reactor makes it extremely difficult to keep these transparent windows clear for extended periods.
Many of the problems of such prior art are overcome by the use of a microwave radiometer to sense microwave energy emitted from a heated vessel. As described, e.g., in U.S. 4,568,199, incorporated herein by reference, the sensed energy is converted into a signal indicative thereof, and the amplitude of the signal is measured as an indication of the general temperature inside the vessel. This signal measures not only the temperature of the gases within the vessel, but is influenced by the temperature and microwave absorption properties of any suspended solids, and also by the radiation from any refractory or slag lining in the vessel which will have a temperature which will decrease as the distance increases from the hottest surface of the refractory. These influences tend to dampen the ability to measure rapid temperature fluctuations as may occur within the vessel, not only with regard to actual temperature of the gases, but also in creating a time lag as the temperatures within the entrained solids and in the refractory equilibrate with the temperature of the gases at their surface. For some applications, such as chemical conversion processes, it would be highly desirable to obtain a signal that would indicate the temperature of the gases and just the surface, of any entrained solids in contact with such gases (which surfaces would virtually be at the same temperature), and wherein such signal is capable of tracking rapid fluctuations in said temperature. Such a method has now been found.