Identification of thermal boundary conditions in heat exchangers of fluidized bed boilers

A CFD simulation was carried out for the platen superheater placed in the combustion chamber of the CFB boiler. Velocity, pressure, and temperature of the steam as well as the temperature of the tube wall with the complex cross section were computed using the ANSYS/CFX software. The direct and inverse problems were solved. In the first inverse problem, the heat transfer coefficient on the flue gas side was determined based on the measured steam temperature at the inlet and outlet of the three pass steam superheater. In the second inverse problem, the inlet steam temperature and the heat transfer coefficient on the flue gas side were estimated using measured steam temperatures at selected locations of the superheater. The first inverse problem was solved iteratively using the secant method. The Levenberg-Marquardt method was used to solve the second inverse problem. At every iteration step, a direct conjugate heat transfer problem was solved using the ANSYS/CFX software.