Abstract:

The safety of equipment under flexible operation is an important issue in the deep peak shaving process of coal-fired power plants. As large-scale, high-temperature and pressure-bearing heat exchangers, high-pressure heaters play an important role in the flexibility regulation of the unit. However, safety problems are severe. Therefore, a three-dimensional finite element model was established for the No.1 high-pressure heater of a 660 MW supercritical coal-fired power plant, to assess the distributions of transient temperature fields, thermal stress fields, mechanical stress fields and coupling stress fields of the heater under different feedwater bypass regulations. Moreover, the stress variations were carried out in four key areas including water chamber outlet, steam inlet pipe, the upper side of the tube sheet and the lower side of the tube sheet. The results show that as the bypass degree increases, the fluctuation range of thermal stresses, mechanical stresses and coupling stresses increases. The maximum thermal stress locates at the steam inlet pipe, the maximum mechanical stress locates at the lower side of tube sheet and the maximum coupling stress corresponds to the upper side of tube sheet. The upper side of tube sheet is the most dangerous part of the high-pressure heater, which needs to be paid attention to and repaired in advance.

Key words: supercritical coal-fired power plant, high pressure heater, stress analysis, feedwater bypass