A Network Approach Applied in Modelling the Heat Transfer and Fluid Flow in a Superheater Heat Exchanger

Excellent Z. Gwebu and Pieter G. Rousseau


Boiler tube failures, anomalies, flow maldistribution


A 1-D thermo-fluid model for a superheater in coal-fired boilers was developed using the network approach encapsulated in the commercial software Flownex. This model brings to light the relationship between the boiler operations, the thermo-fluid processes and the metal temperatures, since it captures the fluid flow as well as the heat transfer. An understanding of this relationship is crucial at both the design and operational stages of a boiler. At the design stage, the model can be used to minimize the material cost while ensuring adequate performance. For an operational boiler, such a model can be combined with condition monitoring and finite element analysis techniques. In turn be used to improve predictive and preventative maintenance of the plant, to analyse the performance of the heat exchanger as well as doing root cause analyses in case of a failure. In order to qualify the model, three boiler operation anomalies were modelled using a tubesheet of superheater with a complex geometry and flow arrangement. For each of these anomalies; outer fouling, inner fouling and flow blockage, three cases were studied. The model successfully predicted that the performance of the heat exchanger drops if the outer fouling layer increases. It also showed that the tube metal temperatures increases if the inner fouling layer increases or the flow throttling increases due to the reduction in the amount of coolant (steam) flowing in the tubes.

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