Decentralized heat and power (CHP) production constitutes a promising solution to reduce the primary energy consumption and greenhouse gas emissions. Here, micro gas turbine (MGT) based CHP systems are particularly suitable due to their low pollutant emissions without exhaust gas treatment. Typically, the electrical power demand for single houses ranges from 1 to several kWel. However, downsizing turbocharger components of a conventional MGT CHP system can reduce electrical efficiencies since losses like seal and tip leakages, generally do not scale proportionally with size. By introducing an inverted Brayton Cycle (IBC) based MGT this potential can be exploited. The IBC keeps the volumetric flows constant while mass flow and thermodynamic work are scaled by the ratio of pressure level. Since the performance of turbocharger components is mainly driven by the volumetric flow they should be applicable for both cycles. Hence, smaller power outputs can be achieved. The overall aim of this work, is the development of a recuperated inverted MGT CHP unit for a single family house with 1 kWel. This paper presents an experimental study of the applicability and feasibility of a conventional MGT operated in IBC mode. The demonstrator was based on a single shaft, single stage conventional MGT. Reliable start up and stable operation within the entire operating range from 180 000 rpm to 240 000 rpm are demonstrated. The turbine outlet pressure varied between 0,5 bar (part load) and 0,3 bar absolute (full load). All relevant parameters such as pressure losses and efficiencies of the main components are investigated. Moreover, the power output and the mechanical and thermal losses were analyzed in detail. Although the results indicated that the mechanical and heat losses have a high influence on the performance and economic efficiency of the system, the prototype shows great potential for further development.
Renewable energy sources such as wind turbines and photovoltaics are the key to an environmentally friendly energy supply. However, their volatile power output is challenging in regard to supply security. Therefore, flexible energy systems with storage capabilities are crucial for the expansion of renewable energy sources since they allow storing off-demand produced power and reconverting and supplying it on-demand. For this purpose, a novel power plant concept is presented where high-temperature energy storage (HTES) is integrated between the recuperator and the combustor of a conventional micro gas turbine (MGT). It is used to store renewable energy in times of oversupply, which is later used to reduce fuel demand during MGT operation. Hereby, pollutant emissions are reduced significantly, while the power grid is stabilized. This paper presents a numerical process simulation study, aiming to examine the influence of different storage temperatures and load profiles of HTES on the MGT performance (e.g., fuel consumption, efficiency). Furthermore, relevant operating points and their process parameters such as pressures, temperatures, and mass-flow rates are derived. As operation conditions for the combustor are strongly influenced by the HTES, the paper contains a detailed theoretical analysis of the impact on combustor operability and includes an experimental investigation of the first combustor design adapted for the compound and tested under higher inlet temperatures conditions.
Residential buildings account for approximately one fifth of the total energy consumption and 12 % of the overall CO2 emissions in the OECD countries. Replacing conventional boilers by a co-generation of heat and power in decentralized plants on site promises a great benefit. Especially, micro gas turbine (MGT) based combined heat and power systems are particularly suitable due to their low pollutant emissions without exhaust gas treatment. Hence, the overall aim of this work is the development of a recuperated inverted MGT as heat and power supply for a single family house with 1 kWel. First, an inverted MGT on a Brayton cycle MGT was developed and experimentally characterized, in previous work by the authors. This approach allows exploiting the potential of using the same components for both cycles. As a next step, the applicability of the Brayton cycle components operated in inverted mode needs to be evaluated and the requirements for a component optimization need to be defined, both, by pursuing thermodynamic cycle simulations. This paper presents a parametrization and validation of in-house 1D steady state simulation tool for an inverted MGT, based on experimental data from the inverted Brayton cycle test rig. Moreover, a sensitivity analysis is conducted to estimate the influence of every major component on the overall system and to identify the necessary optimizations. Finally, the component requirements for an optimized inverted MGT with 1 kWel and 16 % of electrical efficiency are defined. This work demonstrates the high potential of an inverted MGT for a decentralized heat and power generation when optimizing the system components.
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. This paper presents fundamental, application-independent conceptual studies of thermally coupled micro gas turbines (MGT) and high temperature heat pumps (HTHP). The MGT provides electrical power to drive the compressor of the heat pump, while the heat of the exhaust flow is used as a heat source. This self-sufficient system is expected to provide high thermal output at temperature levels beyond available heat pump technology. In addition, low temperatures can be achieved for cooling processes. Within the scope of this study, several process architectures with different integration of heat sources are analyzed by performing thermodynamic cycle simulations. The results demonstrate attainable temperature levels and it can be shown that heat can be provided at temperatures above 300 °C. Cooling processes can be effectively integrated in some of the investigated cycle configurations so that temperatures below −30 °C can be reached. Thermal coupling enables high utilization rates of primary energy and values over 100% are possible. The present work provides the basis for future studies, which will take the economic feasibility in comparison with competing technologies into consideration.
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