Repowering existing under-utilized WTE power plant with gas turbines

Highlights: • Guidelines for Waste To Energy middle pressure repowering using Gas Turbine are presented. • Two different middle pressure repowering options are proposed and discussed. • Optimum plant match condition in terms of plants capacity ratio is identified. • Repowering results with different commercial GT units are shown. • Performance indexes to quantify efficiency and power output allocation are presented. - Abstract: Several Northern European countries are facing an incineration plant capacity larger than national generation of waste, mainly caused by a reduced availability of waste, economic crisis and over-investments. This is causing several WTE power plants to operate at reduced or under-utilized waste input capacity. In the aforementioned context, this paper focuses on two repowering options to improve waste conversion efficiency of an existing under-utilized Waste-To-Energy (WTE) power plant with a Gas Turbine (GT). In particular, this study investigates the feasibility of middle pressure repowering strategies: additional steam is produced in a simplified Heat Recovery Steam Generator (HRSG) fed by the GT exhaust gas. The proposed repowering options are quite simple and easy to adapt to mid-size under-utilized types of WTE power plant. A thermodynamic evaluation of the system feasibility is presented for a typical WTE. For each investigated repowering option, minimum GT size is identified along with optimum plant match condition in terms of plants capacity. A complete thermodynamic simulation of the steam cycle is performed and different plant configurations are examined under different GT commercial units. Detailed modifications to the WTE cycle and the resulting performance improvements are presented for both analyzed repowering options. Furthermore, different key performance indicators have been taken into account to evaluate, for each investigated configuration, the integrated dual-fuel system performance enhancement in comparison with the under-utilized and the original WTE plant. Both power output and efficiency of the repowered WTE plant compare favorably with those of the original stand-alone system: repowered system power output rise up to three times the original one and first law efficiency can reach up to 36%. Furthermore, the integration with GT can enhance the waste utilization, achieving positive synergy effects, as quantified in this study.