Dynamic simulation of a three pressure level heat recovery steam generator

In many countries the liberalization of the electricity market and the significant increase of the electricity production due to renewable energy sources, forced power plants fed by fossil fuels to change management strategies from base to cycling load. Cycling requirements in terms of fast start-up and number of start-ups per year have considerably increased in the last years. Therefore, nowadays cycling operation is fundamental to be competitive in the electricity market, especially for combined cycle power plants. For this reason a proper procedure is essential to predict the residual life of plant components and assist operators during the planning and production phase. The core of the proposed procedure is the plant dynamic model. The model is used to estimate the variation of thermodynamic parameters during transient condition and start-up/shut-down period. The power plant performances have been evaluated by considering the entire geometry of the heat exchangers and drums. Models are built including the main devices and the mass and energy flows among them and considering the control strategy and the effects of environmental conditions (which can also influence the load of devices). Steady-state and different transient conditions are investigated and the trends of the main thermodynamic parameters are computed. Being Combined Cycle Power Units the most concerned in flexibility the selected test case is a Combined Cycle Gas Turbine unit with a three pressure level Heat Recovery Steam Generator. An estimation of the residual life of the most stressed components, in this case the high pressure superheater, is proposed.