Session: 06-02 Power to Heat Solutions

Paper Number: 81959

81959 - Conceptual Study of Thermally Coupled Micro Gas Turbines and High Temperature Heat Pumps for Trigeneration 

In the context of climate change low-emission technologies need to be developed to cover the high thermal energy demand of the industrial sector. Because of the ongoing transition to renewable energy sources and their limited availability, combustion-based technologies will be required to support this transition and ensure an economically feasible energy supply.

High temperature heat pumps (HTHP) are potentially a key technology for the electrification of process heat for future energy systems at temperature levels up to 500 °C. However, there is a high need for research in this area as the majority of current market-ready technologies operate only up to approximately 120 °C - 150 °C. The economic and environmental performance of electrically driven HTHPs strongly depends on the generation mix of the local electric grid and the availability of on-site heat sources. As the use of renewable energy is still limited, utilizing state-of-the-art cogeneration plants is more favorable compared to the energy mix of many countries. Micro gas turbines (MGT) are a promising technology for cogeneration of energy in the industrial sector of small and medium-sized companies. The advantages of MGTs are high total efficiency (heat and power), low emissions as well as high part-load capability and reliability. Their fuel flexibility makes MGTs easily adaptable to energy grids based on hydrogen and renewable fuels. For these reasons, the potential of combining gas turbines with innovative heat pump concepts based on the reverse Brayton cycle is investigated in the scope of this work.

This paper presents concepts with thermally coupled cycles, which are based on using residual heat of the exhaust flow of MGTs as heat source for the heat pump while part of the generated electricity drives the HTHP-compressor. The combined system is expected to provide high thermal output at temperature levels beyond available heat pump technology and potentially high load flexibility. In addition, low temperatures can be achieved for cooling processes. Within the scope of this study, several process architectures are analyzed by performing thermodynamic cycle simulations. Parametric studies are performed to determine system boundaries in terms of temperature and power levels. To study the technological potential, design methods to optimize process architecture and cycle parameters for cogeneration (CHP) and trigeneration (CCHP) scenarios are applied.

Furthermore, a design mode for heat exchanger modules of the performance solver is introduced, that allows for variable effectiveness as a function of inlet conditions and prevents oversizing of heat exchangers.

The results demonstrate attainable temperature levels for different cycle architectures and it can be shown that heat sink temperatures higher than 300 °C are achievable. Cooling processes can be effectively integrated in some of the investigated process architectures so that temperatures below -20 °C can be reached. For low temperatures at least one recuperator is used in the heat pump cycle to keep pressure ratios in a moderate range.

Scenario based studies are performed with boundary conditions for heating and cooling processes that are transferable to the food industry. The technological potential of various cycle concepts for CHP and CCHP applications is outlined by optimizing the cycle parameters for the objectives electric output and cooling rate. Furthermore, a comparison is drawn to conventional technologies in terms of utilization rate of primary energy. With combined cycles the overall utilization rate of primary energy can reach values higher than 95%.

Presenting Author: Jens Gollasch German Aerospace Center (DLR), Institute of Low-Carbon Industrial Processes

Presenting Author Biography: - studied mechanical engineering at the Leibniz University in Hannover (Germany) with focus on energy technology and on aerodynamic simulations of axial turbomachinery<br/>- motivation to work on the development of technologies that contribute to the transition of our energy system <br/>- research associate at the Institute of Low-Carbon Industrial Processes (German Aerospace Center) since 02/2020 <br/>- working on simulations of Brayton cycle high temperature heat pumps and preliminary design of turbomachinery<br/>- project manager for DLR-project in cooperation with Institute of Combustion Technology to investigate combined cycles of micro gas turbines and high temperature heat pumps

Authors:

Jens Gollasch German Aerospace Center (DLR), Institute of Low-Carbon Industrial Processes
Eleni Agelidou German Aerospace Center (DLR), Institute of Combustion Technology
Martin Henke German Aerospace Center (DLR), Institute of Combustion Technology
Panagiotis Stathopoulos German Aerospace Center (DLR), Institute of Low-Carbon Industrial Processes