Effect of exhaust gas flow rate in heat recovery steam generator duct using computational fluid dynamic approach

Depletion of fossil fuels motivates energy sectors to recover waste heat and utilize the energy using a heat recovery steam generator (HRSG). In the past, the effect of EG flow rate at the gas side of HRSG incorporated with the thermal spreader and supplementary firing was not explored. Therefore, the novelty of the study resides in the effect of exhaust gas (EG) flow rate at gas side HRSG incorporated with thermal spreader and supplementary firing. The impacts of EG flow rate on EG velocity, EG turbulence kinetic energy (TKE), and EG temperature were studied using computational fluid dynamics (CFD). The CFD analysis predicted increased velocity and temperature at the HRSG duct as the EG flow rate increased. The velocity contour showed an increase in velocity from 27.8 to 58.5 m/s. Temperature at the midplane showed an increase from 1092.7 to 1134.0 K when there was an increase in EG flow rate from 36.49 to 76.79 kg/s. The TKE showed a rise in two sections, which were the thermal spreader and duct burner. TKE at thermal spreader and duct burner was 53–227 m2/s2 and 33–154 m2/s2, respectively. Besides, the simulated CFD HRSG duct model was validated using the cogeneration plant data with only a 4% discrepancy, which indicated that the model is reliable for fluid and thermal study. This study's findings aid engineers in understanding EG flow behavior and the impact on HRSG parameters without modifying plant geometry under varied operating conditions.