Integrated Optimization and Control of a Hybrid Gas Turbine/sCO2 Power System
During phase-I, the project team led by Echogen Power Systems (EPS) had two primary objectives based on investigating the application of gas turbines with supercritical carbon dioxide (sCO2) power cycles. The first objective was to improve the overall efficiency and performance of a hybrid gas turbine/sCO2 power system through a joint optimization of the two subsystems (gas turbine and sCO2 power cycle) using non-linear optimization techniques that simultaneously evaluate thermal performance of the combined cycle. The hybrid power system included several points of interaction, including (but not limited to) gas turbine exhaust, fuel heating, inlet chilling and turbine cooling. The second objective was to establish a baseline transient response model of the hybrid power system and a notional microgrid and begin steps to integrate the control systems of the three major elements (gas turbine, sCO2 cycle and grid controller). The project team established a baseline performance for a combined cycle power plant using a production gas turbine and scaled sCO2 power cycle only utilizing exhaust heat recovery. Echogen’s non-linear techno-economic optimization code was extended by adding gas turbine component models derived from a in-house developed gas turbine design code. With the two cycles coupled by the gas turbine exhaust, design parameters of both cycles were allowed to vary simultaneously to determine performance opportunity versus isolated designs. Returning to the baseline gas turbine/sCO2 power cycle transient models: Echogen had in-house developed sCO2 cycle transient model in GT-Suite system simulation software, and had partnered with Siemens Finspång for gas turbine transient model, and Siemens PTI group to provide micro-grid load profile as well as hybrid power cycle generated load (power and frequency) analysis. The transient model for the SGT-750 Siemens gas turbine was a “black-box” functional mock-up interface (FMI) model developed by Siemens Industrial Turbomachinery in Finspång, Sweden. The SGT-750 is a twin-shaft gas turbine that produces 40 MW electricity with an efficiency of about 40% at ISO conditions. At 100% gas turbine throttle (load), the SGT-750 has average exhaust conditions of 114.6 kg/s and 469.8°C. The transient model for sCO2 power cycle was developed by Echogen in GT-SUITE 1D system simulation software platform. The basic CO2 flow circuit has single-shaft turbomachinery with net 11.5 MW electrical power output at design conditions. The power turbine has a double-ended shaft with one end connected to synchronous generator through a fixed-ratio gearbox. The other end of power turbine is connected to the compressor through a continuously variable transmission. The major components of the sCO2 power cycle modeled include air cooled condenser/cooler, CO2 compressor, recuperator, two waste heat exchanger coils, power turbine, continuous variable transmission, gearbox and generator. Integration of SGT-750 transient model and sCO2 power cycle transient model was done in Matlab Simulink. In the integrated model, the gas turbine and sCO2 power cycle interacted at two points, first one being the gas turbine exhaust gas flow rate and temperature, which were inputs to sCO2 power cycle model. The second point was the distribution of micro-grid load demand signal between the SGT-750 generator and sCO2 cycle generator. For a given combined-cycle load demand, the gas turbine load demand was equal to the total demand minus the sCO2 cycle power generated. In the present study the integrated model was simulated for two cases of grid load demand: (i) for a step change, both positive-step and negative-step, in grid load demand (ii) for a micro-grid load demand curve provided by Siemens PTI group. Finally, the time series plots representing load demand versus integrated system response were presented including the sCO2 power cycle control system performance plots. The actual generated power and frequency of both the generators, gas turbine and sCO2 power cycle, was supplied to Siemens PTI group for dynamic grid assessment, results of which are provided in appendices.
- Research Organization:
- Echogen Power Systems, Akron, OH (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- FE0031621
- OSTI ID:
- 1670695
- Report Number(s):
- DOE-EPS-FE31621
- Country of Publication:
- United States
- Language:
- English
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