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Paper on off-design operation of ACCs presented by University of Seville at ASME Turbo Expo, Boston (USA)

15 July, 2023/in Conference and journal papers /by jose

Fan power consumption at reduced mass flow rate for different ACC designs The researchers at University of Seville have presented their work assessing the part-load operation of supercritical power cycles running on Carbon Dioxide mixtures. As a continuation of the work presented at the 5th European Conference on Supercritical Carbon Dioxide Energy Systems, where […]

Paper on axial turbine flowpath design presented by City, University of London at ASME Turbo Expo, Boston (USA)

15 July, 2023/in Conference and journal papers /by jose

Turbine flowpath for a 100 MWe SCARABEUS plant running on mixtures of Carbon Dioxide and Hexafluorobenzene The researchers at City, University of London have presented their work on the design of the flowpath of large axial turbines for integration into supercritical power cycles operating with Carbon Dioxide mixtures. This research is framed in Work […]

Paper on off-design operation of ACCs presented by University of Seville at ASME Turbo Expo, Boston (USA)

15 July, 2023/in Conference and journal papers /by jose

Paper on axial turbine flowpath design presented by City, University of London at ASME Turbo Expo, Boston (USA)

15 July, 2023/in Conference and journal papers /by jose

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Paper on off-design operation of ACCs presented by University of Seville at ASME Turbo Expo, Boston (USA)

15 July, 2023/in Conference and journal papers /by jose

Fan power consumption at reduced mass flow rate for different ACC designs

The researchers at University of Seville have presented their work assessing the part-load operation of supercritical power cycles running on Carbon Dioxide mixtures. As a continuation of the work presented at the 5^th European Conference on Supercritical Carbon Dioxide Energy Systems, where the methodology to design ACCs for supercritical CO₂ power cycles developed at University of Seville was presented, this paper explores the operation of the cycle when running in off-design. Emphasis is placed on the operation of the ACC because of the strong impact that a wrong operation of this component has on overall cycle performance.

The paper can be downloaded free of charge from the conference website (link). Check the abstract below:

This manuscript, developed in the framework of SCARABEUS project, presents an assessment of the part-load performance of a transcritical Recompression cycle running on a 80%CO₂-20%SO₂ mixture under different load-control schemes.

The first part of the paper describes the computational platform of the integrated system, implemented in Thermoflex but with profuse use of in-house scripts, in order to accurately describe the off-design performance of key components when operating on CO₂ mixtures with non-ideal gas behaviour. These off-design models make use of performance maps for turbomachinery — provided by the SCARABEUS partners — whereas the Conductance Ratio Method employed to model the counter-current heat exchangers is calibrated with in-house tools. The paper is specifically focused on the Heat Rejection Unit, for which a specific design tool accounting for accurate heat transfer between working fluid and cooling medium (air) and for auxiliary power consumption — both in off-design — has been developed by the authors.

In the second part of the paper, different operating strategies of the power cycle are considered, based on keeping one of the following three parameters constant: turbine inlet temperature, turbine outlet temperature or return temperature of molten salts. Globally, plant operation is constrained by the need to keep the temperature of cold HTF returning to the storage system as close as possible to its rated (design) value and by the need to keep turbine outlet temperature below 450°C to avoid the installation of an external cooling system in the low pressure section of this equipment. Therefore, the trade-off between these two parameters and system net efficiency are assessed in the paper. Regarding the Air-Cooled Condenser, the optimal operation strategy of this component found to be based on a combination of Single-speed and Variable Frequency Driver fans.

The results show that the operation at constant turbine inlet temperature leads to the highest net efficiency of the power block, closely followed by the control scheme based on constant return temperature of the heat transfer fluid. Nevertheless, this latter option enables a perfect control on the other two figures of merit. As a consequence, the identification of the best operation strategy must be addressed in future works by means of a thorough techno-economic assessment considering the annual yield of the plant.

Paper on axial turbine flowpath design presented by City, University of London at ASME Turbo Expo, Boston (USA)

15 July, 2023/in Conference and journal papers /by jose

Turbine flowpath for a 100 MWe SCARABEUS plant running on mixtures of Carbon Dioxide and Hexafluorobenzene

The researchers at City, University of London have presented their work on the design of the flowpath of large axial turbines for integration into supercritical power cycles operating with Carbon Dioxide mixtures. This research is framed in Work Package 3 – Turbomachinery Design of the project.

The composition of the working fluid has a strong influence on turbine design, as a consequence of two effects. The first one is the impact of working fluid composition on the operating conditions of the cycle that attain peak thermal efficiency. The second one is the impact on the characteristics of the working fluid that are relevant to turbine design. Meanline design codes and CFD tools are combined to assess these effects and to produce optimum flowpath designs.

Impact of loading and flow coefficient on total-to-total efficiency of the turbine

The paper can be downloaded free of charge from the conference website (link). Check the abstract below:

Supercritical CO₂ (sCO₂) mixtures have been found to be promising for enhancing the performance of power cycles for concentrated solar power (CSP) applications, with up to a 6% enhancement in cycle efficiency compared to a simple recuperated CO₂ cycle depending upon the mixture and cycle configuration chosen. Given that turbine efficiency significantly affects the overall plant performance, it is important to confirm whether turbines operating with CO₂ mixtures can achieve the same efficiencies compared to pure CO₂, whilst exploring whether the use of mixtures introduces any differences in the turbine design. This study aims to investigate the differences in turbine flow path designs produced for pure CO₂ compared to CO₂ mixtures, whilst taking into account aerodynamic, rotordynamic and mechanical design aspects, as assessed during the mean-line design process. The aim of this study extends to evaluating the effect of key turbine design variables, such as the loading coefficient, flow coefficient and degree of reaction, on the flow path design and overall aerodynamic performance. Multiple flow path designs have been produced for axial turbines operating with pure CO₂ and mixtures of CO₂ with titanium tetrachloride (TiCL₄), hexafluorobenzene (C₆F₆) and sulphur dioxide (SO₂) for installation in a 100 MWe CSP plant. It is found that turbines operating with either pure CO₂ or CO₂ mixtures result in overall total-to-total efficiencies in excess of 92.5%; where the highest turbine efficiency is achieved for the turbine operating with pure CO₂, whilst this reduces by a maximum of 1.1 percentage points for the CO₂/TiCL₄ mixture. This reduction in efficiency is because the CO₂/TiCL₄ turbine is limited to a maximum of six design stages in order to meet the imposed mechanical design criteria, whilst the pure CO₂ turbine can accommodate thirteen stages leading to higher aerodynamic efficiency. The difference between the two cases is the result of a higher mass-flow rate for the CO₂/TiCL₄ mixture (66% greater than for pure CO₂), which results in high rotor bending stresses and limits the number of stages to comply with the design criteria. It is also found that designing the turbine at loading and flow coefficients of 0.8 and 0.6 respectively, whilst fixing the degree of reaction and pitch-to-chord ratio to values of 0.5 and 0.85 respectively, resulted in an efficiency enhancement of 0.2% with respect to a baseline design produced at loading and flow coefficients of 1.0 and 0.5. This increase is due to being able to increase the number of stages from eleven to fifteen. This indicates that there is not much benefit in modifying key design parameters to improve the turbine efficiency as the 0.2% efficiency enhancement is considered within the margin of accuracy of mean-line flow path design.

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Paper on off-design operation of ACCs presented by University of Seville at ASME Turbo Expo, Boston (USA)

Paper on axial turbine flowpath design presented by City, University of London at ASME Turbo Expo, Boston (USA)

Paper on off-design operation of ACCs presented by University of Seville at ASME Turbo Expo, Boston (USA)

Paper on axial turbine flowpath design presented by City, University of London at ASME Turbo Expo, Boston (USA)

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Paper on off-design operation of ACCs presented by University of Seville at ASME Turbo Expo, Boston (USA)

Paper on axial turbine flowpath design presented by City, University of London at ASME Turbo Expo, Boston (USA)

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