Numeričko-eksperimentalna analiza termomehaničkog stanja strukture plameno-dimnocevnih kotlova pri promenljivim režimima rada

Abstract

The subject of scientific research is hot water fire-tube boilers with a regular and screened reversing chamber. In addition to nominal operating mode, transient operating modes are analyzed, as well as one of the most important transient operating regimes – boiler start-up. The effects of various phenomena which may have impact on boiler safety, reduction of its reliability and its opearting life, are also analysed. The effects of the following phenomena are presented: deposits on fire tube and smoke pipes, thickness of the wall carring pipes of the first reflecting chamber, electrochemical corrosion, stress corrosion, fatigue and creep. Scientific methods of mathemnatical-numerical analysis with application of Ansys software package as well as experimental methods on a real object and minimized boiler model are applied in the research. Operational experiences indicate failures during operation, which represent a consequence of conditions with parameters that are higher than allowed. If such occurs, the security protection system should react in a timely manner and prevent accidents. However, emergency conditions are also possible due to fatigue of the materials of certain elements of the boiler, whose service life is shortened, due to constant exposure to high pressures and stresses. The hot water boiler structure is exposed not only to high pressures but also to high temperatures, which is why thermal stresses are dominant in those elements of the boiler with thicker walls. Thermal stresses are highest at the largest temperature gradients, which occur at variable operating modes. Therefore, the emphasis of this paper is on the variable operating modes of the hot water boiler and their impact on the structure.