Natural gas combined cycles are expected to operate in a flexible manner in the future energy markets to complement the increasing variable renewable electricity generation. Stresses in thick-walled components and gas turbine load ramps are the main limitations in the dynamic operation of NGCCs. This work presents two different modelling approaches of the thermal and mechanical stresses originated in the high-pressure drum and steam turbine rotor, and compares four different formulations, two linear and two nonlinear, of the optimization problem included in the model predictive control strategy. A case study shows the capability of the proposed control methodology to optimally operate the NGCC without exceeding the maximum allowable stress in the critical components.
Keywords gas turbine combined cycle, thermal and mechanical stress, optimal control strategy, flexible thermal power plant, dynamic modelling and simulation, dynamic optimization.