Heat sensitivity of vertical water wall at low mass velocity in supercritical pressure W-shaped flame boiler

Abstract

The vertical water wall of the once-through boiler is sensitive to heat disturbance because of its smaller water volume compared with the drum boiler. This paper deduced formulas of the sensitivity coefficient of flow and output enthalpy, and made a heat sensitivity analysis for the vertical water wall of a 600 MW supercritical pressure W-shaped flame boiler at a low mass velocity when heat disturbance occurs. It was found that the flow sensitivity coefficient decreases and the outlet enthalpy sensitivity coefficient increases with increasing steam quality. Increasing mass velocity weakens the flow sensitivity and enhances the outlet enthalpy sensitivity. When the mass velocity exceeds a certain value, the flow sensitivity coefficient is less than zero. Increasing heat flux leads to an increase in the flow sensitivity coefficient and a decrease in the outlet enthalpy sensitivity coefficient. In the condition of low steam quality, the flow sensitivity weakens and outlet enthalpy sensitivity strengthens when the pressure is up to 22 MPa. Moreover, when the quality is high, rising pressure strengthens the flow sensitivity and weakens the outlet enthalpy sensitivity. The study has provided some instructive findings, which may be helpful for the safety operation of the 600 MW supercritical pressure W-shaped flame boiler.