Gas turbine cogeneration concepts for the pressureless discharge of high temperature thermal energy storage units

Abstract

Power-to-heat technology allows the leveling of high electrical power production peaks by converting excess electrical energy into high-exergy heat and storing it in a high-temperature thermal energy storage (HTS). When electricity is needed, a gas turbine process can be used for an efficient discharge in decentralized usage scenarios. As a novelty of this work, different configurations of the Brayton cycle are presented and investigated, which permit a pressureless storage discharge and thus a cost-efficient and scalable HTS unit. The processes enable combined heat and power generation (CHP) to increase the total efficiency of the system. Stationary process simulations are conducted with the software EBSILON®Professional to thermodynamically analyze four process designs. The influence of the HTS outlet temperature, process-internal pressure conditions, as well as other component-specific efficiencies are examined in separate parameter studies. Based on state-of-the-art components, the process variants show electrical efficiencies above 29% and total efficiencies about 87% for an HTS outlet temperature of 900 °C. By reducing thermal losses, closed processes can increase the total efficiency to 97%. Two processes can be determined as suitable for CHP. The open externally heated Brayton cycle achieves the highest electrical efficiency of 33.14% at the design point, while the closed inverse Brayton cycle is achieving the highest total energetic and exergetic efficiency.