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Dynamic simulation of a supercritical ORC using low-temperature geothermal heat.

Author(s) : VETTER C., WIEMER H. J.

Summary

Low temperature heat between 100°C – 160°C can be used for power production via Organic Rankine Cycles (ORC). In order to study the optimization possibilities of ORC processes, the test facility MoNiKa (Modular low-temperature cycle Karlsruhe) is being built at the Karlsruhe Institute of Technology (KIT). It is designed as a small and compact power plant with a thermal power of 1000 kW. The modular structure enables the use and investigation of different components. The geothermal heat source is realized by a conventionally heated water cycle at the site of KIT. Previous investigations showed that supercritical cycles achieved a rise of the net power output up to 44% compared to sub-critical cycles with isopentane, as they enable better adaptation of the temperature profiles in the heat exchanger. The planned test system is therefore designed for a supercritical process with propane as working fluid with live steam parameters of 5.5 MPa and 117 °C. This contribution contains dynamic simulation results of this new ORC at different load cases. In particular, a detailed analysis of the cooling of the cycle at varying cooling air conditions as well as a comparison of different control strategies concerning the achievable net power in part-load operation are presented. The results showed that the air temperature has great influence on the power requirements of the cooler which leads to a power consumption up to one-third of the produced electricity at high ambient temperatures. This problem can be countered by cooling the air by injecting fine water in so called hybrid mode and by an adaption of the desired condensation temperature to the outdoor temperature. The results of the part load simulations illustrate the optimization potential due to the use of appropriate control strategies. While at fixed pressure operation and constant turbine speed, a continuous decrease in the specific net power is inevitable, a constant specific net power can be achieved over a wide load range by using a turbine with variable speed and a frequency converter. Alternatively, a comparably good part load behavior can be realized by adjusting the live steam temperature to the load via a function developed in this study. This detailed analysis of the plant behavior allows for a more accurate prediction of the electricity production to be expected. In addition, requirements for the components to be applied can be derived from the simulation results.

Details

  • Original title: Dynamic simulation of a supercritical ORC using low-temperature geothermal heat.
  • Record ID : 30013507
  • Languages: English
  • Publication date: 2015/04/19
  • Source: Source: In: Proceedings World Geothermal Congress 2015

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