Numerical Simulation on the Hydrodynamic Performance of High-Pressure Evaporator in Once-Through Heat Recovery Steam Generators

The once-through heat recovery steam generator (HRSG) of gas-turbine combined-cycle power plants adopts a triple-pressure reheat evaporator arrangement. To study the overall performance of the evaporator during operation, it's divided into three sections: EVA1, EVA2, and EVA3 along the working fluid flow. In this study, in accordance with the heating load distribution characteristics of the evaporator and in consideration of the system mass, momentum, and energy conservation equations, the nonlinear mass and pressure drop balance equations are directly solved. The flow distribution, pressure drop distribution, profiles of working fluid temperature and outlet steam temperature of evaporator at boiler maximum continuous rating (BMCR), 75 % BMCR, and 30 % BMCR loads are analyzed. The flow distribution of evaporator at each load shows a positive response characteristic. The flow distribution at all levels is relatively reasonable, and there will be no heavy difference in the temperature and steam quality of fluid, which will lead to pulsation. Simulation results demonstrate that the metal properties can meet the requirements of material strength at each working condition, and the evaporator will not experience flow instability, stagnation, and pulsation at low loads. The triple-pressure once-through reheat HRSG can operate safely and reliably and has the advantage of lifting and lowering the load rapidly.