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SUPERCRITICAL CO2 CYCLE FOR FLEXIBLE AND SUSTAINABLE SUPPORT TO THE ELECTRICITY SYSTEM

Periodic Reporting for period 1 - sCO2-Flex (SUPERCRITICAL CO2 CYCLE FOR FLEXIBLE AND SUSTAINABLE SUPPORT TO THE ELECTRICITY SYSTEM)

Reporting period: 2018-01-01 to 2019-06-30

Current fossil-fuel power plants have been designed to operate in base-load conditions, i.e. to provide a constant power output. However, their role is changing, due to the growing share of renewables, both inside and outside the EU. Fossil-fuel plants will increasingly be expected to provide fluctuating back-up power, to foster the integration of intermittent renewable energy sources and to provide stability to the grid. However, these plants were generally not designed to undergo frequent power output fluctuations.

In this context, sCO2-Flex consortium addresses this challenge by developing and validating (at simulation level the global cycle and at relevant environment boiler, heat exchanger (HX) and turbomachinery) the scalable/modular design of a 25 MWe Brayton cycle using supercritical CO2, able to increase the operational flexibility and the efficiency of existing and future coal and lignite power plants.

sCO2-Flex will develop and optimize the design of a 25MWe sCO2 Brayton cycle and of its main components able to meet long-term flexibility requirements, enabling entire load range optimization with fast load changes, fast start-ups and shut-downs, while reducing environmental impacts and focusing on cost-effectiveness. The project, bringing the sCO2 cycle to TRL6, will pave the way to future demonstration projects (from 2020) and to commercialization of the technology (from 2025). Ambitious exploitation and dissemination activities will be set up to ensure proper market uptake.

The consortium brings together ten partners, i.e. academics, technology providers and a power plant operator, thus constituting an interdisciplinary group of experienced partners covering the whole value chain, each of them providing its specific expertise and contributing to the achievement of the project’s objectives.

During the first 18 months, the project sought to:
• select the 3 most convenient cycle architectures for the project
• start the work of the WPs dedicated to components and cycle flexibility
• set up dissemination and management actions
"The first eighteen-month period of the project was intended to determine the cycle architecture that is expected to meet performance and flexibility requirements (among 21 proposed cycle architectures).

1.Works and Results on WP1:
Three cycle architectures have been selected (among the 21 analysed configurations) regarding the following 3 main criteria:
i) Cycle performance: cycle #16
ii) Boiler integration/integrity: cycle#23,
iii) Cycle simplicity/feasibility (manufacturing constraints, flexibility, control and regulation): cycle #31.
The D1.3 deliverable was significantly updated shortly after its submission. This update was made following the first work of WP 2 and 4, which revealed a more interesting architecture than cycle #13, namely cycle #16. The consortium subsequently decided to update the deliverable and the new version was available at the end 2018.

The WPs for equipment development and flexibility started shortly before the end of WP1 and are still in progress. The work resulting from these WPs is based on the results of WP1 and has already made it possible to choose a cycle configuration among the 3 proposed in the WP1 :Cycle #31 was quickly abandoned because of its too low performance and cycle #23 was abandoned because of the complexity of the boiler and turbomachinery which were not likely to allow the desired flexibility from an operational point of view.

2.WP2: boiler and materials
Boiler calculations and material selection have been done on the selected cycle. Boiler calculation and optimization require a lot of time and cannot be done for a large number of cycles. In this context, it has been decided by the consortium that UJV will do calculations only for a small and specific number of cases.
The procedure of the erosion test on an “air foil-shaped” test sample has been made by CV REZ with recommendation for material selection and coating. The experimental plan has been defined for material testing at CSM.

3.WP3: turbomachines
The preliminary material selection, the conceptual design and the mechanical configuration of turbomachinery have been done.
The fluid model selection and the study of boundary layer behaviour have been investigated by UDE.
BHGE defined compressors and turbine arrangement in order to guarantee the maximum cycle operational flexibility. The compressors are both with variable IGV and equipped with VFD systems; due to a high rotating speed, the turbine is connected through a gear box to the electric generator. This turbomachinery configuration allows to achieve a partial load down to 20% of cycle rated power.
A full-scale prototype compressor is under design phase. Prototype performance tests are expected within 2020 to verify aerodynamics and performance prediction in proximity of the CO2 critical point.

4.WP4: Heat Exchangers
An important work was achieved at FIVES in order to reach higher levels of mechanical resistance of the assembly. A reproducible rupture pressure value of 1200 bar was achieved so far, which is very noteworthy.
USTUTT and CVR built up test sections in order to evaluate thermal and hydraulic performances of sCO2 in respectively plates and fins HXs and printed circuit HXs. HXs prototypes were discussed and defined with FIVES to be tested in these sections, and are being manufactured.
Moreover, USTUTT investigated the characteristics of sCO2 cooling heat transfer in tubes. Potential materials for HXs manufacturing were selected and prepared by FIVES for corrosion/erosion tests to be run at CSM.

5.WP5: Cycle flexibility:
The static modelling and simulations at system level showed that the part-load range to study is quite large (from 20% to 100% of nominal load). Up to now, simplified correlations have been used by POLIMI to perform calculation. Also, a MATLAB model has been created and benchmarked against the D1.1 results for steady state calculations. These calculations resulted in a review of D1.1 initial hypothesis and led to a pressure optimisation of “cycle family n°2” (partial cooling architectures). Sensitivity analyses have been performed for “cycle family n°1” taking into account different maximum and minimum CO2 temperatures, as well as other system’s parameters variations. All obtained results are in line with previous conclusions of partners studies."
The next few months of the project will be used to continue work on the work packages already in progress, with the construction and testing of the various prototypes.

Different WPs will also start:
• WP6 aims to validate the calculations performed in WP5 taking into account the design criteria defined in WP2/3/4. The consolidated results are used to design a 25 MWe sCO2 cycle with a focus on flexibility and reliability in transient conditions. Finally, the overall concept is extended to other application fields to prove the replicability of the developed concept.
• WP7 aims at performing an economic, environmental and social assessment of the sCO2 Cycle. WP7 will carry out a detailed cost-benefit analysis and financial assessment of the 25 MWe cycle design and study the cost of a 100 MW sCO2 cycle to foster market uptake and industrial deployment from 2025 and prepare and foster the social acceptance of sCO2 technology.