# Analysis of the Impact of Forces in Hanger Rods on Power Boiler Operation
## 1 Introduction  
Devices operating at high temperatures and pressures are designed according to specific standards, and they do not include all the cases of loads to which they are exposed [1]. Boiler pressure parts such as membrane walls [2], collectors, chambers, and pipelines, as well as non-pressure components like suspension brackets and hanger rods, are subject to periodic damage. These components are subject to restrictive regulations, which are implemented as regulations or directives [3]. A boiler, the structure of which is very complex, is often designed using simplified boundary conditions, and the focus is thus only on selected elements [1, 4]. The boiler pressure parts were mainly subjected to strength calculations, which resulted from the action of high pressure and temperature. Unfortunately, it was forgotten that the real stresses in such elements are an effect of the action of all loads, such as the tensile forces from the boiler weight or the bending moments that result from the eccentricity of the boiler mounting, etc. [5, 6]. For a suspended boiler, the loads resulting from its weight are carried by hanger rods. Hanger rods are used to suspend the furnace chamber, circulating fluidized-bed separators and the boiler's other components. Failure to carry the boiler weight in a uniform manner can result in unwanted stresses in the boiler pressure parts, overloads, and changes in geometry due to uncontrolled thermal displacements of the boiler elements, which may finally lead to damage to the boiler pressure part or to the rods [7]. Therefore, such that the loads should be carried uniformly, it is necessary to monitor the force in the rods at the assembly stage and regulate the forces acting in hanger rods systematically, along with a control of the boiler geometry at selected points. The problem of monitoring the forces in the rods and the correct method and approach to numerical analysis is particularlynoticeable in systems where there are no compensators for the non-uniform tension of forces in the rods. Such compensators can be disc springs mounted under nuts or spring suspensions. Of course, these compensating elements also are damaged in cases of a non-uniform load, which consequently leads to the failure of hanger rods and the boiler pressure parts, as well as of the compensating elements themselves. In the age of an extremely high demand for energy, the most important thing is not only the failure-free operation of conventional boilers in terms of their suspension, but also fast diagnostics of the damage and the ability to carry out a lasting and effective repair. In order to perform such diagnostics, appropriate tools, as well as computational methods, are necessary. The current methods described in the literature [8; 9; 10] and in the design requirements [1; 3; 4] focus mainly on the analysis of individual boiler subassemblies, such as superheater banks [11] or small boiler units that are supported from the bottom with a small number of support points [5; 6; 12]; however, the aim of this paper is to analyse large boiler units with a hanging structure that have many suspension points in a steel structure. The described case of boiler damage concerns a global analysis of the entire boiler, which is achieved by taking into account the complex geometry in contrast to individual subassemblies [11], i.e., where the modelling of boundary conditions and geometry does not result in many problems. The example of the boiler analysis conducted using the presented methods was also aimed at presenting the tools, as well as the simplifications that make it possible to assess the impact of a non-uniform distribution of forces in the rods on the boiler global structure. The approach presented in this paper seems to be the most appropriate when considering the available technology for measuring and regulating forces in rods, which is often burdened with measurement inaccuracies of up to 6% [13].