Search for a Solution to the Problem of Flow-Accelerated Corrosion in Heat-Recovery Steam Generators

The design and operating conditions of the low-pressure circut of Ep-258/310/35-15.0/3.14/0.44- 540/535/263 (P-132) heat-recovery steam generator (HRSG) as part of 795 MW CCGT were studied to reduce the wear of its tubes. Reliable and effective operating conditions of the natural-circulation loop are presented. The design of the low-pressure loop of P-132 is described. Modifications of the operating conditions to reduce the velocity of steam-water mixture in the natural-circulation loop, which, in turn, reduces the flow-accelerated corrosion, are described. In particular, the effect of changes in the drum pressure at constant and variable feedwater temperature on the velocity of the steam-water mixture is described. Methods and designs for eliminating gas shunts to equalize the heat absorption by the evaporator tubes in the HRSG are proposed. Several modifications of the HRSG design intended to reduce flow-accelerated corrosion are considered: a new evaporator design with outlet bends replaced with straight tubes; a new design of the riser system with more independent movement of the mixture from the evaporator; a different longitudinal spacing of evaporator tubes. The combined effect of modifications to the design and operating conditions on the reliability of the low-pressure loop is studied. It is concluded that the optimal solutions to reduce flow-accelerated corrosion are to increase the pressure in the low-pressure drum, to redesign the outlet section of the low-pressure evaporator and the low-pressure riser system, and to install anti-shunt partitions in the heating surfaces. These measures will allow steel 20 to be used to manufacture evaporation and riser tubes of the low-pressure loop due to the reduction of the velocity of steam-water mixture.