Project title: Innovative ORC Power Systems Technology
Project website: N.A.
Time period: From July 2016 to January 2020
Funder: Siemens Energy
Total budget: Undisclosed
Work Package One
The development of sCO2 power cycle technology is pursued for various applications because early and more recent studies have documented possible advantages in terms of efficiency and turbine compactness. This study on medium and large combined cycle configurations is focused on the preliminary assessment of several solutions based on specific configurations of bottoming units adopting sCO2 as working fluid. The results demonstrate that the optimal bottoming unit layout is that of the so-called dual-rail cycle configuration, where the pinch point problem in the low-temperature recuperator is overcome by splitting the CO2 flow leaving the compressor into two streams. For the heavy-duty gas turbine case, the dual rail power cycle allows for a net conversion efficiency similar to that of a state-of-the-art CCGT power plant with a three pressure-level and reheat steam Rankine bottoming unit. For medium power capacity gas turbines, the dual-rail sCO2 power cycle, instead, overperforms the conventional steam bottoming unit, which generally consists of a two-pressure level steam cycle. This result suggests that high-efficiency distributed power generation may be the target application for the first deployment of sCO2 power technology.
Work Package Two
The main goal of this study is to investigate concepts that improve the bottoming cycle efficiency of small- and medium-sized gas turbine power plants in comparison with current technology. In addition, the proposed solutions should be as simple as possible to avoid high CAPEX. The sought performance improvement should be based on the overall CCPP (combined cycle power plant) efficiency and not on the bottoming cycle efficiency. The goal is therefore to utilize the maximum thermal power discharged from the GT exhaust in order to obtain the highest electrical power output of the bottoming cycle.
This study considered as exemplary application the bottoming cycle for the following Siemens gas turbines:
- SGT-A65 TR
The ambient temperature considered for the air-cooled condenser is set to 30 °C. The study is complemented by an evaluation of the variation of the ambient temperature between 10 °C and 40 °C. Various pure fluids and mixtures are considered, whereby typical aspects like thermal stability, flammability, toxicity, environmental impact, cost, availability have been taken into account during the initial screening.
Work Package Three
This study investigates the technical and economic viability of the ISORCC (Integrated Solar Organic Rankine Combined Cycle) concept under different operating scenarios and technical configurations and investigates whether there is an optimum solar field size for the power plant configurations under study.
Notably, the study provides evaluations by means of modeling and simulations of:
- The maximum power output achievable across a 24-hour period given the power output limitations of the gas turbine(s), and the variable thermal input to the bottoming cycle of the solar field.
- The variation in the overall power plant efficiency as the contribution of the solar field to the ORC system rises and the gas turbine load is reduced accordingly, in order to maintain the overall power output of the plant constant.
- The variation in overall power plant efficiency by following a given daily load profile and making maximum use of the solar thermal energy contribution to the bottoming cycle over the course of a 24 hours period.
The following economic factors for the proposed technical configurations have been estimated:
- Overall installed capital cost;
- Internal Rate of Return on the investment (IRR); and,
- Cost of the produced electricity (COE).