Application of TESPy for a combined heat and power ORC using a geothermal high temperature heat source. This repository only contains the geothermal ORC simulation models, the district heat system itself is not simulated.
A time series of geothermal production temperature for different geothermal mass flows, i.e. 30 kg/s, 40 kg/s and 50 kg/s, is provided in quarterly data, assuming constant geothermal production for three months.
The simulation model calculates the power output of the geothermal ORC following a heat demand curve. For that, the maximum monthly heat demand is mapped to the design heat production of the plant and the heat production for the other months is scaled respectively. The waste heat from the ORC is discharged into the lake.
The ORC plant has the following topology - "hybrid parallel" - as suggested by the researchers (Habka & Ajib, 2014) and (Van Erdeweghe et al., 2018).
Habka, M., & Ajib, S. (2014). Investigation of novel, hybrid, geothermal-energized cogeneration plants based on organic Rankine cycle. Energy, 70, 212–222. https://doi.org/10.1016/j.energy.2014.03.114
Van Erdeweghe, S., Van Bael, J., Laenen, B., & D’haeseleer, W. (2018). Optimal combined heat-and-power plant for a low-temperature geothermal source. Energy, 150, 396–409. https://doi.org/10.1016/j.energy.2018.01.136
The reinjection of the geothermal fluid is constrained to a minimum temperature value of 90 °C (for the case studies conducted here). Its value can be modified in the input file.
In the design, the Temperature values at 24 and 26 are set to this temperature value. The evaporation temperature/pressure inside the orc power cycle is then calculated based on the heat demand specification in the input file. The relationship between design heat demand and evaporation pressure as well as power generation is shown in the figure below. The lake pump is controlled in a way, that temperature increase in the condenser is 10 °C at all times. That means that the lake water mass flow changes with the power production of the ORC power cycle. The design parameters of the cycle are listed in the table below the figure. The remaining design parameters are controlled with the input file (see Usage section).
| Parameter | Value | Unit | |
|---|---|---|---|
| turbine | efficiencies (is, el) | 90, 97 | % |
| pumps | efficiencies (is, el) | 75, 97 | % |
| condenser | temperature difference | 10 | °C |
| pressure ratio hot side | 1 | - | |
| evaporator | pinch point | 10 | °C |
| pressure ratio cold side | 1 | - | |
| preheater | approach point | 3 | °C |
| heat exchangers | pressure ratios | 0.98 | - |
| lake water | temperature increase | 10 | °C |
Partload operation is simulated by applying characteristic curves for the efficiency of heat transfer and turbines as well as pumps. The temperatures 24 and 26 are fixed to the minimum reinjection temperature. However, in case the ORC power cycle is overloaded, the temperature value 26 increases to values higher than the minimum reinjection temperature. This occurs, when the working fluid mass flow increases with lower heat demand. The turbine then requires higher pressure at the inlet to deal with the increased mass flow and therefore the pressure ratio over the valve becomes larger than 1, which is physically impossible. In this case the pressure ratio is set to 1 instead of setting the temperature 26 (valve is fully opened).
Please note, that the district heating system temperature does not influence the other components of the plant in this control strategy. By keeping temperature 24 value constant at the reinjection temperature, the feed temperature of the district heating system cannot be controlled within the district heating heat exchanger anymore. However, partially bypassing the heat exchanger and mixing the cold return flow with the too hot feed flow from the heat exchanger, the temperature value can be brought down to the appropriate level without changing the overall heat input. The district heating water circulation is therefore increased. Since this does not affect the operation of the ORC system, it is not part of the simulation.
Clone the repository and build a new python3.8 environment and install the
requirements to it.
pip install -r ./requirements.txtTo run the simulation type
python run.py input/inputfile.jsonin your console.
Please exchange the "inputfile.json" with the respective scenario you want to simulate, e.g. "high_temp_dh_1500.json". It is possible to specify the working fluid of the ORC, some design parameters like heat production and geothermal source temperature as well as the reinjection temperature constraint.
The tool is quite flexibile in parameter settings, if you want to learn more on how to change parameters, please contact us.
Copyright (c) 2022 Francesco Witte, Nicholas Fry
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