COMBINING WASTE-TO-ENERGY STEAM CYCLE WITH GAS TURBINE UNITS

In recent years, interest has been growing in developing new possibilities to maximize the conversion of waste into energy. Technologies allowing for efficient Waste-To-Energy (WTE) conversion are supported in the EU, by the European Waste Framework Directive, suggesting an efficiency criteria aimed at introducing a reference quality standard. Nevertheless, current state-of-the-art WTE plants are typically characterized by low efficiency values, compared to conventional steam power plants using fossil fuels. This is mainly due to limitations in the WTE steam cycle design parameters, in comparison with large fossil fuelled power plants. This paper focuses on an innovative and promising strategy to improve waste conversion through integration of a conventional WTE power plant with a Gas Turbine (GT). The resulting WTE-GT integrated plant requires to conceive a redesign and an optimization of the steam-gas cycle. In particular, this study investigates the feasibility of utilizing the hot gases leaving the GT to superheat the steam leaving the WTE steam generator, as well as heating the feed water returning to the steam generator of the WTE condenser. Parametric analysis of the effect of the GT discharged heat on the steam mass flow production is carried out and the optimum plant match condition in terms of plants capacity ratio is identified. Detailed modifications to the WTE cycle and the resulting enhancement of its performance are presented. Numerical results of a representative WTE plant integrated with different GT commercial units are shown and discussed. Results of the study suggest issues and useful guidelines to: (i) create new advanced WTE-GT integrated power plants or to (ii) repower existing low-performing WTE power plant, in order to increase waste conversion into energy.