Integrated computational fluid dynamics and 1D process modelling for superheater region in recovery boiler

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Insinööritieteiden korkeakoulu | Master's thesis
Mechanical Engineering
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Master's Programme in Mechanical Engineering (MEC)
Superheaters are the last heat exchangers on the steam side in recovery boilers. Their performance is accountable for proficient recovery boiler operation. The objective of this work is to obtain thorough knowledge about the superheating process and material temperature distribution for superheater platens. The study includes the effects of 3D flue gas flow field in superheater region and generated steam properties in steam cycle. The detailed analysis for flue gas side and steam side is important for improving recovery boilers' energy efficiency, cost efficiency, safety and contribution for carbon neutral energy production. In this work, for the first time, a comprehensive 1D-process model (1D-PM) for superheated steam cycle is developed and linked with a full-scale 3D-CFD model of the superheater region flue gas flow. The developed 1D-PM is validated using reference data including mass and energy balance calculations, and measurements. The results reveal that first; the geometrical structures of headers, connecting pipes and superheater platens affect platen-wise steam distribution. Second, the integrated solution of the 3D flue gas flow field and platen heat flux distribution with the 1D-PM substantially affect both generated superheated steam properties and material temperature distribution. It is also found that the commonly used uniform heat flux distribution approach for superheating process is not accurate because it does not consider the effect of flue gas flow field in superheater region. This novel integration modelling approach is advantageous for trouble shooting, optimizing the performance of superheaters in recovery boiler and selecting their design margins for the future. It could also be applied for other large scale energy production units including industrial biomass fired boilers.
Vuorinen, Ville
Thesis advisor
Maakala, Viljami
computational fluid dynamics (CFD), 1D process modelling (1D-PM), integrated CFD/1D-PM simulations, heat transfer, recovery boiler
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