Abstract:In Combined Circle Gas Turbine units (CCGT),in order to raise economic benefits and reduce the non-normal water hammer risk occurred during operation for daily start stop unit(DSS) of circulating water system, and furthermore, intend to overcome the limitation of other methods, which be used to calculate the pumps working points. This paper analyses both physical features and differences between design conditions and the practical two-shift operation model, which the big gradient piping-main circulating water system cater for a grade of 350MW CCGT units in DB power plant. Base on the analysis, there are a number of energy-saving potentials and the best retrofit method would be to adopt frequency conversion. In accordance with a set of pump performance curves in various frequencies provided by manufactory and three kinds of parallel system curves simulated through experimental data, line chart method is used to calculate the work point. Compared with analytic method, line chart method is simple and intuitive and validity has been proved by serials of trials. After retrofit, conserving energy target is obtained; both system safety and controlling logic have been optimized further. On another hand this project also provides means for economical operation of unit.