Innovative Thermodynamic Solutions: effective and efficient coupling of CSP and desalination technologies

Innovative Thermodynamic Solutions: effective and efficient coupling of CSP and desalination technologies

Discover our groundbreaking work over the past year in advancing CO2 mixtures for thermodynamic cycles, pushing the boundaries of energy efficiency and sustainability.

The research team from the Energy Department at Politecnico di Milano (POLIMI), DESOLINATION project coordinator, has successfully simulated large-scale Concentrated Solar Power (CSP) plants using innovative CO2 mixtures, enhancing their efficiency and performance. Additionally, they introduced the CO2+SiCl4 mixture in literature for trans-critical cycles, showcasing its potential in improving cycle efficiency.

Our Journey in Thermodynamic Cycle Development

Over the past year, POLIMI has made significant strides in the development and simulation of thermodynamic cycles using CO2 mixtures. Here are some of the key milestones and achievements.

Introduction of CO2+SiCl4 Mixture Research

Introducing the CO2+SiCl4 mixture into the literature for transcritical cycles

With regard to the application of CO2 mixtures in thermodynamic cycles, the work was developed both on the simulation of the large-scale CSP plant with innovative CO2 mixtures, introducing the CO2+SiCl4 mixture into the literature for transcritical cycles, and adding details on the simulations and design of the DESOLINATION project’s demonstration plant, the 1.8 MWel cycle operating with the CO2+SO2 mixture.

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Experimental investigation of the CO2+SiCl4 mixture as innovative working fluid for power cycles: Bubble points and liquid density measurementsv- Energy Journal

In this perspective, complete off-design simulations have been carried out, including the behavior of the real heat exchangers that will be installed and including the management of the inventory of the cycle in off-design.

Learn more of the effect of supercritical CO2 Fluid Properties on Heat Exchanger Design…

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Effects of Supercritical CO2 Fluid Properties on Heat Exchanger Design

Simulation of the large scale CSP plant with CO2+SiCl4 mixture

POLIMI combined CSP with CO2-mixtures power cycles and forward osmosis desalination system, performing simulations in Dubai.

Using these innovative technologies, our CSP plant showed high solar-to-electric efficiencies (around 19% on yearly basis) and very low freshwater specific thermal consumption (about 10 kWhth/m3) when the PABG2000 is used as draw agent.

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Characterization of the physical properties of the thermoresponsiveblock-copolymer PAGB2000 and numerical assessment of its potentialities in Forward Osmosis desalination

Specifically, when comparing the CSP (concentrated solar power) +FO (forward osmosis) studied in DESOLINATION with the CSP+MED assuming the same solar plant and power cycles, the freshwater production is incremented by more than 50%.

When the solution of DESOLINATION is compared with a PV+RO plant, a reduction of reflective area of 28% is foreseen, if both freshwater and electricity are produced with the PV+RO plant.

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Simulations of CSP combined with CO2 mixed power cycles and a forward osmosis desalination system in Dubai

Finally, POLIMI also conducted an experimental campaign on the coalescer using a solution of water and PAGB2000, obtaining an expression of the separation efficiency, to be deployed in the simulations.

The research team from the Energy Department at Politecnico di Milano will shortly be publishing an article on the results of its Experimental study on coalescer efficiency for liquid-liquid separation.

Saty tuned!

Simulations of CSP combined with CO2 mixed power cycles and a forward osmosis desalination system in Dubai

Simulations of CSP combined with CO2 mixed power cycles and a forward osmosis desalination system in Dubai

This year, our project coordinator, Politecnico di Milano (POLIMI) carried out simulations at its CSP (concentrated solar power) plant in Dubai to combine CSP with CO2-mixed electric cycles and a forward osmosis (FO) desalination system.

Using innovative technologies, POLIMI’s CSP plant has demonstrated high solar-electric efficiencies (around 19% on an annual basis) and very low specific thermal consumption of fresh water (around 90 kWhth/m3) when PABG2000 is used as the drawing agent. The synergy between electricity and freshwater production was effective.

In particular, if the CSP+FO solution studied in DESOLINATION is compared with the CSP+MED solution, assuming the same solar power plant and energy cycles, freshwater production is increased by over 40%.

The DESOLINATION project aims to develop an innovative desalination system combining direct osmosis and membrane distillation, using a draw-off solution. Forward osmosis means that seawater is extracted from the sea, the water is drawn through the membrane by the draw solution and the remaining minerals (brine) are rejected.

When the DESOLINATION solution is compared with a PV+RO plant, a 47% reduction in reflective surface is predicted, if the PV+RO plant produces both fresh water and electricity.

We have also carried out an experimental campaign on the coalescer* using a solution of water and PAGB2000, the aim being to obtain an expression for the separation efficiency, which will then be used in simulations.

*Coalescer: used to separate elements from an emulsion (i.e. liquid water and oil from compressed air using a coalescing effect)

TEMISTh has launched the manufacture of DESOLINATION heat exchanger core!

TEMISTh has launched the manufacture of DESOLINATION heat exchanger core!

The DESOLINATION project has reached an important milestone: after an initial design and simulation phase carried out by our project partner TEMISTh, the first heat exchanger model has now been printed!

Heat Exchangers can take different forms depending on many parameters: temperatures, pressures, chemical properties of the fluids, etc. But they are critical to the heat transfer within the CSP cycles to recover heat from the sun and make the turbine work.

In DESOLINATION, specific work will be on exchanging heat between the power cycle (air in the existing plant, CO2 in the innovative one) and the desalination draw solution (highly concentrated solution). New Printed Circuit Heat Exchangers (PCHEs) and Printed Fin Heat Exchangers (PFHEs) will thus be produced.

Following a simulation and design phase for supercritical CO2 and molten salt, our project partner TEMISTh has launched the manufacture of the Heat Exchanger core (system used to transfer heat between a source and a working fluid).

The aim of this first mock-up is to answer technical questions such as powder removal, assembly and design validation.

The next step is to test the mock-up on an sCO2 loop for validation.

Effects of Supercritical CO2 Fluid Properties on Heat Exchanger Design

Supercritical CO2 (sCO2) in industrial applications is a promising solution for the reduction of equipment size and for the potential increasement of overall efficiency. The characteristics of CO2 near the critical point are advantageous for the heat transfer, with high specific heat capacity when compared to conventional liquid or gas coolants. Moreover, dopants can be mixed to CO2, in a blend, to further increase the heat transfer and elevate the critical point of the fluid. Under the framework of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, a heat exchanger was designed using CO2 and blend as working fluids in an innovative power cycle bank of a concentrated solar power (CSP) plant coupled to a water desalination system. In this paper, the innovative heat exchanger is evaluated in terms of the geometry, focusing on heat transfer and turbulence, using computational fluid dynamic (CFD) simulations with SST k-ω turbulence model and real-gas models with REFPROP library for thermodynamic and transport properties. Within each fluid, the diameter of the channels varied from 1.8–2.2 mm and the results are compared to analytical models. The geometry with 1.8 showed a larger pressure drop, but also larger overall heat transfer coefficient. It is observed that both pressure drop and heat transfer decrease with the diameter. Blend as the hot fluid resulted in higher average temperature and heat transfer coefficient, but in lower pressure drop than pure CO2. Nusselt number correlations were compared, showing the decrease of its values with the diameter for pure CO2, while for the blend it was observed higher values for 2.0 mm of diameter, except for Fang and Xu correlation that showed the same trend as the CO2.

 

Keywords: supercritical CO2; heat exchanger; gas cooler; computational fluid dynamics

Authors:

Afonso Lugo
Lappeenranta-Lahti University of Technology, Lappeenranta, Finland
Jonna Tiainen
The Switch, Lappeenranta, Finland