SCO2-Flex Final Event: The Role of sCO2 cycles in Europe’s future energy system

SCO2-Flex Final Event: The Role of sCO2 cycles in Europe’s future energy system

On the 16th June 2021 the Sco2-Flex project will host its final event to present the results of the project and also introduce 5 other Horizon 2020 projects working with sco2 technology. 

In the context of the EU’s energy transition, the last few years have seen the potential of supercritical CO2 (carbon dioxide) cycles emerge as an efficient replacement of steam in the cycles converting heat into power, leading to a more flexible and lower-emission electricity production.

 

Indeed, since they can be adapted to any type of production (from conventional production to heat recovery, including nuclear and renewable energy), sCO2 cycles offer very interesting prospects in terms of increased efficiency, flexibility, cost control and reduced environmental impact.

 

All over the world, numerous research projects and demonstrators are being set up, and Europe is positioning itself as one of the players in this area. The number of research projects on sCO2, financed by the European Commission, has been increasing for more than 6 years and demonstrates the dynamics of European academic and industrial actors.

 

Given this fact, the event proposed within the framework of the sCO2-flex project aims to show the versatility of sCO2 cycles in energy production as well as the objectives and results obtained by the actors of these European projects.

In addition to a presentation by the European Commission, 6 projects will present their vision of the potential of sCO2 cycles. They are:

 

Check out the full Agenda and to register please click HERE

 

The event will take place online from 2pm to 5pm CET.

 

Registrations will close on the 15th June or until hosting capacity is reached. After registering, you will be sent a link to join the online session the day before the event.

Carbon Dioxide mixtures at the 4th European sCO2 Conference for Energy Systems, Prague

The 4th edition of the European sCO2 Conference for Energy Systems, held virtually on March 23-24, gathered some forty excellent works presented by international authors. The number of attendees and quality of works presented confirmed that the sCO2 community is vibrant and the future of the technology looks bright.

A number of very interesting papers dedicated to CO2 blends triggered the interest of the SCARABEUS consortium:

  • 1 Valencia Chapi, R., Fierros-Peraza, O., Coco-Enríquez, L., Muñoz-Antón, J., Modeling and study of a printed circuit heat exchanger for Brayton power cycles using supercritical CO2 mixtures as working fluid (Universidad Politécnica de Madrid)
  • 2 Ayub, A., Di Marcoberardino, G., Invernizzi, C.M., Iora, P., Advanced thermodynamic power cycles utilizing carbon dioxide based mixtures as working fluids for high temperature waste heat recovery (University of Brescia)
  • 3 Rath, S., Mickoleit, E., Gampe, U., Breitkopf, C., Jäger, A., Study of the influence of additives to CO2 on the performance parameters of a sCO2-cycle (TU Dresden)

These added to two works by University of Seville and City, University of London, presented on behalf of the consortium:

  • Aqel, O., White, M., Sayma, A., Binary interaction uncertainty in the optimization of a transcritical cycle: consequences on cycle and turbine design (City, University of London)
  • Crespi, F., Rodríguez-de Arriba, P., Sánchez, D., Ayub, A., Di Marcoberardino, G., Invernizzi, C.M., Martínez, G.S., Iora, P., Di Bona, D., Binotti, M., Manzolini, G.,  Thermal efficiency gains enabled by using supercritical CO2 mixtures in Concentrated Solar Power applications (University of Seville, Politecnico di Milano, University of Brescia, LEAP)

Different CO2 mixtures were proposed for Concentrated Solar Power and Waste Heat Recovery applications. Rath et al. performed a vast screening of 135 candidates out which five were selected: Krypton, Xenon, Carbonyl sulfide (COS), Propane and Sulfur hexafluoride for WHR systems. For the same application, Ayub et al. studied CO2-Novec mixtures in three different layouts, concluding that a 3 percentage point gain with respect to pure CO2 seems possible. Regarding CSP, Crespi et al. investigated the use of CO2-C6F6 and CO2-TiCl4 mixtures, coming to the conclusion that it is possible for the power block to achieve and even exceed 50% thermal efficiency even under semi-arid boundary conditions, provided that the suitable cycle layout is selected for each working fluid-was achievable. Also for CSP plants, Valencia-Chapi et al. modelled a printed circuit heat exchanger and studied its performance for different CO2 mixtures, noting that heat transfer coefficients of the mixtures were higher than those of pure CO2; this favours lower heat exchang areas. Finally, the turbine of large power blocks running on CO2-C6F6, CO2-H2S and CO2-NOD (non-organic dopant) were studied by Aqel, White & Sayma.

Common to all work was the emphasis on the suitable fluid modelling of CO2 mixtures. In the work of Ayub et al., binary interaction parameters of different CO2 mixtures (Novec 5110, Novec 649, R134a, HFO1234yf and HFO1234ze(E)) were estimated using experimental VLE data from literature and then applying Peng-Robinson with Van der Walls mixing rule to estimate thermodynamic properties. The same fluid model was used by Crespi et al. for CO2-C6F6 and CO2-TiCl4 mixtures. Valencia-Chapi et al. modelled CO2 mixtures using the Aungier-Redlich-Kwong real gas model. Aqel, White & Sayma studied the influence of four different Equations of State and of the uncertainty in the estimates of binary interaction parameters on cycle performance and turbine geometry. Rath et al. use a predictive model to calculate mixture properties based on the best available EoS for the pure components.

In addition to the works by Aqel et al. and Crespi et al., which describe the latest results obtained by the SCARABEUS consortium, a series of works developed by other projects funded by the European Commission (sCO2 Hero and sCO2 Flex) were presented at the conference. Moreover, several interesting topics regarding sCO2 cycle performance, turbomachinery and heat exchanger design and novel sCO2 cycle configurations have been thoroughly discussed. The entire set of presentations and papers are available online in the conference repository (https://sco2.eu/conference-repository/4th-conference-online/) so, if you wish to take a closer look at some of the works, just follow this link and enjoy!

 

Preliminary heat transfer experiments at TU Wien

One of the major goals of the SCARABEUS project is to show the feasibility of the innovative air cooled condenser (ACC) through experiments in Vienna. This heat exchanger is a crucial component in the proposed technology by enabling dry cooling in warm areas where one would typically find Concentrated Solar Power plants.

For down-sizing and thereby reducing the costs, enhanced finned tubes on the inside (CO2 side) will be used. In the course of the design process of Kelvion, experimental measurements at TU Wien are essential to evaluate the heat transfer coefficients on the CO2 side.

To do so, the existing test rig at TU Wien was modified. Originally, in the former project for which the rig was designed and constructed, this was able to perform a full Rankine cycle at a maximum CO2 temperature of 350 °C and a pressure of up to 240 bar. For the heat transfer measurements, maximum temperature and pressure were temporarily reduced, since only the low pressure side is of interest.  After the expansion valve, which represents the turbine, two heat exchangers are now located: the precooler and the test tube.

The test tube is a tube-in-tube heat exchanger of 1 m length. Water was chosen as the cooling medium. In a numerical study, Kelvion determined two types of fins considering number, height, thickness and angle of the fins. There will be three test tubes tested at TU Wien in total:

  • BARE test tube
    • Used as a reference without fins
  • COOLING test tube
    • Fins designed to enhance the heat transfer when cooling down superheated CO2
  • CONDENSING test tube
    • Fins designed to enhance the heat transfer when condensing the CO2

The precooler´s purpose is to specifically control the conditions of CO2 at the inlet of the test tube. The test conditions will cover a range of conditions we expect at the ACC in the future which will show dependencies of the heat transfer on:

  • 2 pressures
  • 3 CO2 mass flows
  • 2 CO2 inlet temperatures
  • 5 values of inlet vapor content

To show the impact of an additive on the heat transfer, the heat transfer of a blend of CO2 with R1234ze will be examined and compared to pure CO2. Based on the results the ACC will be designed.

SolarPACES 2020: SCARABEUS listed as one of the flagship R&D projects in Europe by Prof. Julián Blanco, Managing Director of the Solar Platform in Almería (PSA-CIEMAT)

 

 

This year, most conferences have made the decision to go virtual in order to circumvent the limitations on mobility brought about by COVID-19. SolarPACES has been no different in this regard but the

 

Wednesday’s plenary session, chaired by Ana María Ruiz Frías (Solar Committee Chile), focused on CSP Technology Innovation. All continents were represented by high-level speakers -Australia, Asia, America and China- who introduced their vision about research priorities in Concentrating Solar Power and the tools and funding schemes to enable their accomplishment.

 

In this session, Europe was represented by Prof. Julián Blanco, Director of Plataforma Solar de Almería (CIEMAT), largest research, development and test centre in Europe for Concentrating Solar technologies. Prof. Blanco’s presentation provided an excellent summary of the current research priorities identified by the European Commission, along with a very informative review of the ongoing research activities and flagship projects in Europe. With the aim to make the presentation comprehensive, the contents were broken down into twelve R&I areas approved by the Steering Group of the Solar Energy Technology (SET) Plan in 2017.

 

The SCARABEUS consortium is grateful to Prof. Julián Blanco for making the presentation available for download (link).

The Institute for Energy Systems and Thermodynamics at TU Wien getting ready for the testing campaign

During the last months, IET concentrated on design tasks according to work package 4, where pre-tests for the design of the air-cooled condenser (ACC) and the recuperator (printed circuit heat exchanger) are planned. Therefor several modifications of the test rig are necessary, see Figure 1:

 

 

Figure 1: Modifications of test rig at IET. Grey: additional heat exchangers (precooler and test tube). Blue: cooling water lines.

 

With the combination precooler and test-test-tubes, desuperheating and condensation experiments at a pressure level of p = 66 bar are planned. For pure CO2 the corresponding condensation temperature is 26,11 °C. Maximum CO2-temperature will be 180 °C, so different desuperheating / condensation tests are possible depending on entrance temperature of CO2 and cooling load of the precooler. In the first step, experiments with pure CO2 will be done, then testing with blended CO2 by adding a refrigerant (R1234ze) will follow. Adding a blend will give a first impression of about the behaviour of a mixture instead of pure CO2 and will help to train the handling of harmless mixtures on the rig, in the perspective of the future planned tests with other blends being developed and tested at UBS and POLIMI.

 

 

Figure 2: Left: Precooler delivered from KELVION. Right: test rig under modification.

 

 

The SCARABEUS team keeps growing at University of Seville

 

The SCARABEUS team at University of Seville keeps growing. USE is very happy to welcome Pablo Rodríguez to support the optimization and integration tasks. Find some more information about him below and follow his activities through LinkedIn here: https://www.linkedin.com/in/pablo-enrique-rodr%C3%ADguez-de-arriba-9088b91b7/

 

 

 

Pablo Rodríguez standing in front of a Ljungström turbine at the lab

 

I’m Pablo Rodríguez, a Sevillian engineer recently graduated from the master’s degree in Industrial Engineering at the Escuela Técnica Superior de Ingeniería (University of Seville). Specialised in Energy Engineering, I’m keen on topics such as energy efficiency, process optimization, power generation, renewable energies, SWRO plants or refrigeration. It’s in the latter of these subjects that I wrote my BSc and MSc theses: performing an analysis about the international regulations of refrigerants (anybody sees the link to some of the dopants used in SCARABEUS?).

 

I just joined the Thermal Power Group (Department of Energy Engineering, University of Seville) as a researcher. I’m sincerely enthusiastic about being part of the SCARABEUS project, in which I promised to put all my commitment and energy to achieve the best results.

 

Recuperator Model with design process using pure CO2

The SCARABEUS concept relies on a recuperative cycle using supercritical carbon dioxide as working fluid. Being supercritical and in order to achieve high efficiency, very high pressures and temperatures are involved and a recuperator becomes mandatory. This is a device which can improve the thermodynamic cycle efficiency by cooling the sCO2 after its expansion and heating it after its compression, without any additional heat exchange with the environment.

 

3D model of the recuperator to be installed in the test rig at TUW

 

The advantage to use printed circuit heat exchanger technology in the recuperator is to withstand high pressure and high temperature with reduced footprint (large area-to-volume ratio). This is why PCHE is the technology of choice in SCARABEUS. The 3D model above represents the recuperator which will be installed in the test rig at TUW. It is designed for a pressure of 220 bar and a temperature of 650°C and the geometry of the internal channel configuration is shown below.

 

 

Internal channels of the PCHE developed by KELVION for SCARABEUS

 

Some CFD calculations will be performed to study new types of internal geometries in order to optimize the thermal-hydraulical performances and to decrease heat exchange area. While this technology is already very compact, the Company is pursuing further reductions of footprint.

Researchers from City pass milestone on the route to PhD

Researchers from City pass milestone on the route to PhD

 

This week two researchers from the SCARABEUS research team at City, University of London, successfully completed their transfer from MPhil to PhD. This milestone, which has been completed just over a year since beginning at City, marks the successful transition from registration as a Master of Philosophy (MPhil) student to a full PhD candidate.

 

For the transfer, Mr Omar Aqel and Ms Salma Salah both prepared a technical report containing a literature review and an update on their work to date, and presented a 30-minute presentation over Microsoft Teams, followed by Q&A, to an internal audience of academics and researchers from City.

 

Mr Omar Aqel presented his report entitled “Optimization of cycle and turbine design for small-scale solar power plants employing CO2-based working fluids”. Within Omar’s work he has investigated the effect of candidate dopants on optimal cycle conditions within CSP applications, with a particular focus on the expansion process. Results highlighted the change in working fluid properties such as molecular weight, speed of sound, density, and the adiabatic coefficient. Having also explored the sensitivity of turbine design to dopant type and amount, Omar will now focus on the application of CO2-based working fluids in small-scale power plants. He aims to investigate their feasibility using an integrated system approach which accounts for turbomachinery design restrictions that are unique to small-scale installations.

 

 

 

Ms Salma Salah presented her report entitled “Advanced design optimisation methods for supercritical CO2 multi-stage axial turbines”. Within Salma’s work she discussed the various aspects of axial turbine design including design methodology, previous preliminary and computational fluid dynamic (CFD) studies on sCO2 turbines, in addition to existing prototypes and conceptual designs for sCO2 turbomachinery. In this work, 100 kW and 100 MW design models have been developed and a parametric study has been conducted to examine the effect of various design parameters on the performance of a small-scale sCO2 turbine. This work was concluded by detailing the future steps for her research.

 

 

New Open Access publication by University o Brescia and Politecnico di Milano provides information about characterisation of supercritical CO 2 blends

In the last Open Access paper published by UNIBS and POLIMI, a new methodology for
the thermal stability test of CO2 blends have been developed and tested.
The method proposed relies on the study of the thermodynamic behaviour of the
working fluid from the variation of the van der Waals coefficients. The comparison of
the estimated coefficients a, b and the molar mass (MM) from the regression of the
experimental data (in the gas phase), starting from the virgin fluid isochoric line, and
after different thermal stress test, can be representative of potential decomposition of
the investigated fluid. As a consequence of the thermal stress, the substance
decomposes in a mixture of different unknown species that, for simplicity, is assumed
as a pure fluid characterised by different coefficients a, b and MM. Moreover, starting
from the obtained parameters, the isothermal compressibility k T can be used as a
proper index to highlight the impact of the thermal degradation on the power cycle.

An example of the new method is briefly discussed for a mixture of carbon dioxide and
perfluorohexane, with molar fractions of 80% and 20% respectively. In Figure 1 , the
virgin fluid measurements are along mixture density value of 99.4 kg/m 3 , in the gas
phase, while measured p-T points after each thermal stress are represented. The best
fit of the experimental values, using the van der Waals equation of state, yields the
values in Table 1 , assuming a pure fluid behaviour of the mixture, while Table 2 shows
the resulting isothermal compressibility k T at different temperatures. Since
measurements at 250°C and 300°C are in agreement with the fresh mixture, the values
were included for the calculation of the virgin mixture parameters.
Although the van der Waals parameters are slightly different after the thermal stress
tests at 350°C and 400°C, the mixture can be considered thermally stable up to 400°C:
this behaviour is also confirmed by the parameter k T . Decomposition phenomena occur
from 450°C where not only the isothermal compressibility increases by more than 50%
with respect to the virgin mixture but also a strong deviation of the van der Waals
parameters from initial values can be observed

 

 

Figure 1 Results of P-T measurements for the mixture CO 2 +C6F 14 .

Table 1 Parameters a, b and MM of the van der Waals equation of state of the mixture carbon dioxide and perfluorohexane.

  a

(MPam6kmol-2)

b

(m3kmol-1)

MM

(kgkmol-1)

Virgin mixture 0.818 0.086 102.4
350°C 0.901 0.087 102.9
400°C 0.924 0.088 101.0
450°C 0.016 0.360 158.7
500°C 0.004 0.584 176.1

 

Table 2 The estimated isothermal compressibility kT of carbon dioxide and perfluorohexane at 120°C for the virgin and the decomposed mixture using the van der Waals coefficients and MM of Table 4.

  1/kT

(MPa)

u(kT)

(MPa)

Virgin mixture 2.246 0.052
350°C 2.084 0.054
400°C 2.072 0.057
450°C 3.435 0.122
500°C 4.149 0.247

 

PS: For more information, follow this link to the online article: link.

Hydraulic testing of heat exchangers tube completed at Kelvion

With a few weeks of delay due to the COVID-19 outbreak, the tubes used to determine the heat transfer coefficient to design the Air-Cooled Condenser have successfully undergone hydrostatic testing at KELVION. They will soon be installed in the test rig at TUW.