A method to measure the tube-wall temperature in CFB boilers. (5th May 2019) - Yao, Yuge
Highlights: A new method was proposed to measure the tube-wall temperature in CFB boilers. Three designs of deposition shapes were provided. Temperature increase of the measuring point was numerically estimated. Influencing factors of measurement accuracy were assessed. Reliability under different working conditions was theoretically proved. Abstract: It is very important to accurately measure the tube-wall temperature of the high-temperature heating surface in the boilers with high steam parameters such as supercritical circulating fluidized bed (CFB) boilers. However, the severe abrasion problem caused by high solid concentration in CFB boilers hinders a direct tube-wall temperature measurement in CFB boilers. In this paper, a new method which embeds thermocouples in deposited metal on the heating surface was proposed to solve this problem. Three different designs of metal deposition shapes were also provided for this method. Finite element method (FEM) was applied to compute the tube-wall temperature field of the superheater and estimate the temperature increase of the measuring point, which was caused by deposited metal and thermocouples. Factors, such as the working conditions, deposition shapes, and thermal conductivities were assessed by their impacts on the measurement reliability. The simulated results showed that the maximum temperature increases of the three designs were acceptable in engineering practice. The effect of small dimension deviations in the deposited metal on the temperature increase could be neglected. This method is also applicable for tubes and deposited metals with various thermal conductivity, as well as membrane tubes and single tubes. This study concluded that this method is technically reliable for tube-wall temperature measurements in the main loop of circulating fluidized bed boilers.