Computational simulation of flow, heat transfer and combustion in a vertical tube heat recovery system generator (HRSG) with a single angel roof, a dual angle roof and an air flow optimized evase are studied. Existing theoretical models for flow and gas combustion [1] are used to predict how the three kinds of roof shapes influence the flue gas and temperature distribution in the whole HRSG System, and particularly the flue gas distribution upstream of first heat exchanger bundles (superheater 3 and reheater 2) and duct burner as well as the temperature distribution downstream of the duct burner. The gas phase conservation equations of momentum, enthalpy and mixture fraction are solved utilizing the k-(epsilon) turbulence model. A Finite Rate/Eddy Dissipation model and the P-1 radiation mode are used to predict gas combustion and radiative heat transfer, respectively. The simulation results show the air flow optimized evase not only provides a more uniform velocity profile upstream of the first heat exchanger bundle, but is also able to reduce the pressure drop through the whole HRSG system.

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