The combined cycle plants installed in the mid-nineties to early 2000s were mainlydesigned to operate at base load with a limited number of planned starts. However, withderegulation of the power industry and the resultant volatility in the natural gas market,operation of many plants shifted to almost daily cycling. This operational mode changecaused much concern among the owners and operators of combined cycle plants becausenot only was it not possible to operate according to OEM operating manuals, but it was alsonot clear what kind of damage could occur if the units were ramped up faster thanrecommended.The plants built later for cycling operations did not fare much better because the OEM lifecycle calculations were based on very specific operating procedures that were often toodifficult to maintain or too impractical to follow.This paper describes various historical damaging mechanisms encountered in HeatRecovery Steam Generators (HRSGs) during operation and the impact of cycling,including the effect of these damaging mechanisms on various HRSG components. Basedon available analysis techniques, correlations can be evolved to estimate the lifeconsumption or damage factor of various HRSG components. Using these correlations andthe expected number and type of life cycles, it is possible to calculate the life of the mostcritical components of any HRSG.The correlations can be used to develop dynamic software which can estimate the lifeconsumption of critical components on a continual basis. The dynamic software can use thedata directly from the plant Data Acquisition system, thus eliminating the tedious task ofmanual data transmission. The necessity to strictly adhere to the operating procedures maybe reduced, as long there are some safeguards to avoid exceeding the very high transients.The damage factor and the life consumption thus calculated can be used on a continual basisto gauge the economic benefits of the aggressive operations as the unit is operating. Thecalculations can also be used to foresee when focused inspection is necessary and todetermine which components need repair and when.The paper will also present examples of usage of such dynamic software using the actualplant data.
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