Energy analysis and operation of steam generators in conventional thermal power plants

The main goal of this work is to develop a suitable method, based on practical data, to determine the temperatures of the combustion gases and the values of relevant parameters related with heat transfer phenomena inside the boilers of conventional thermal power plants. In fact, the knowledge of the flame temperature, the real temperature of the gases in the furnace and the gases temperature between the heat exchangers of the boilers, provides an important tool for the design and operation of this kind of installation. The method is built, through a computer aid calculation model, using the values of the efficiency tests of the fourth steam generator group of the Setubal Thermal Power Plant, whose boiler is a conventional one, with one drum, natural circulation and two chambers. Initially an analysis of the thermal cycle of the power plant is done, with the calculation of an approximate value of its efficiency and of the influence that the feed water regenerative heating, the reheating cycle and the nonisentropic expansion process in the turbine has on that value. The second step is the energy analysis of the steam generator group, with the identification and quantification of the energetic losses and of another relevant parameters of operation. Finally, using a method of iterative cycles, the gases temperatures are estimated through the use of energy balances. The comparison of the calculated temperature at the outlet of the boiler, with the experimental temperature (the only one that is known experimentally) shows the validation of the method. The mean temperature of the tube wall surface, the influence of fouling in that temperature and the height at which the vaporisation of water begins in the furnace walls, are obtained from the heat transfer calculations in the furnace. The flame dimensions and its dependence with the combustion air excess are also determined.