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The boiler economizer is a tube heat exchanger located in the final part of the convective duct. In the economizer, water flowing into the boiler is preheated by flue gases. The paper presents the boiler economizer mathematical model with distributed parameters, which can be used to simulate its operation. The developed mathematical model makes it possible to determine temperatures of the tube and working medium of the boiler economizer. In addition, the non-linear mathematical model of the entire boiler allows to analyze the influence of ash fouling of individual boiler heating surfaces on the economizer operation. The proposed model can also be used for monitoring heat and flow parameters of the economizer in on-line mode.

The aim of the paper is Computational Fluid Dynamics (CFD) analysis of Wall Heat Transfer Coefficient (WHTC) of pressurized pipe as a part of super-heater of the OP210 boiler. The object of the investigation is convection from saturated steam to the wall of the pipe, which works under high pressure and high temperature. The analysis is an approach to obtain exact solutions of WHTC according to the third type boundary condition compared to direct results from CFD analysis. The paper consists of three-step approach typical for CFD analysis: (i) Pre-Processing, the most elaborated part of the analysis where knowledge about super-heaters, turbulence, velocity profile is important to 3D model, mesh and boundary condition definition. (ii) Simulation of steady state turbulent flow until convergence criteria are met. (iii) Post-Processing where different approaches to the WHTC are shown in comparison. Also, the investigation includes two different types of meshes (where a different number of inflation layers are used) and comparison between k-epsilon and Solid Shear Stress (SST) turbulence model.

Nowadays, industry requirements referring to the optimization, not only demand better efficiency ordurability but also the lower total cost of the project. Maximum temperatures, allowablestress and economics determine materials used during the engineering process. Moreover, different materials in different parts of superheater can be used. Regarding the steady–state, calculations can be derived without major difficulties but transient–state is a much more complex issue, where Computational Fluid Dynamics can be applied. CFD as an engineering tool, that gives a better understanding of the problem, is more and more popular during the optimization process. Appropriate knowledge about heat transfer, fluid dynamics, finite element method is required to find the solution to the given question. The paper presents a CFD analysis of the transient-state of the steam boiler superheater when attemperator is running. Temperature distribution of the steam, flue gas and maximum wall temperature were determined.

Following Rankine’s cycle efficiency, steam with ever-higher parameters is used to improve the efficiency of advanced ultra-supercritical power plants. The high steam parameters require the use of expensive high-alloy steels. Therefore, design concepts with reduced investment costs are more and more popular. In the power industry, the use of thermal barrier coatings to protect components exposed to high temperatures is becoming ever more common. The innovative concept is a double-pipe system with a thermal barrier that provides insulation for the primary pipe, in which ultra-supercritical steam flows. On the outside, the pipe is cooled by lower performance steam. The following paper presents a two-dimensional mathematical model of the proposed solution. A set of heat transfer equations allows the determination of the temperature field in the steady and transient-state operation of such a system. The numerical model is compared with the CFD one. The temperature gradient in the inner pipe wall with and without coating was determined. In addition, the response of the wall temperature to the step-change of the steam temperature was investigated. The paper shows that the use of TBCs allows reducing high-alloy steels and improving the handling properties of thick-walled components.