A study of the hydrodynamic characteristics of a vertical water wall in a 2953t/h ultra-supercritical pressure boiler

Abstract

A simulation was carried out to study the hydrodynamic characteristics of a vertical water wall in a 2953t/h ultra-supercritical pressure boiler. A hydrodynamic model was established by using the Chebyshev polynomial fitting method. The restriction orifice at the entrance of the water wall was designed at 50% of the boiler maximum continuous rating (BMCR) to minimize the differences in outlet fluid temperature. The hydrodynamic characteristics, including the distributions of the mass flows and pressure drops and the temperature of the metal of the water wall tubes, were studied. It was found that the mass flow within the water wall can be designed to match the heat absorption from the surface that is transferring heat from the furnace at different boiler loads when using this restriction orifice. The variation in the total drops in pressure is related to the variation in the boiler load. However, the proportions of the main components of the overall pressure drop are different at different boiler loads. For weakly heated circuits, the gravitational pressure drop forms a greater part of the total pressure drop than the frictional pressure drop. However for heavily heated circuits, the frictional pressure drop is larger than the gravitational pressure drop, making forced circulation inevitable. The pressure drop induced by the restriction orifice is more pronounced in weakly heated circuits, indicating that it is necessary to use the restriction orifice to adjust the mass flow in weakly heated circuits. Under the normal working conditions of the boiler, the temperatures of the metals did not exceed their safety limitations, suggesting that the reliability of the boiler unit can be ensured.