Improvement of CO2 hydrate formation and flow using chemical additives in a slurry loop and a stirred reactor: applications to refrigeration and CO2 capture

Secondary refrigeration and thermal energy storage techniques could be interesting solutions to improve refrigerating system performances and to reduce power consumption and propagation of refrigerants in the atmosphere. In order to combine a more efficient secondary loop and fluids with higher energy storage capacity, a phase change material (PCM) slurry, also called phase change slurry (PCS), could be used as secondary refrigerant. In addition, hydrate-based processes could be an interesting option to separate the CO2 from various gas mixtures. In these two applications, the flow properties of the CO2 hydrate slurry are of paramount importance. In the present study, small amounts of Sodium Dodecyl Sulfate (SDS) were added to the aqueous phase, and this system was tested under CO2 pressure both in a dynamic flow loop and in a stirred reactor. The results obtained with the flow loop demonstrate that SDS has anti-agglomerant properties for the CO2 hydrate: SDS significantly decreases agglomeration and thus improves flowing capacities of the slurry. The results obtained in the reactor shows that the presence of SDS increases the kinetics of the hydrate growth rate both in agitated and in quiescent hydrate forming conditions. Consequently, the addition of SDS could be very promising in industrial applications, such as secondary refrigeration or gas separation, where hydrate slurries must be easily handled and where the hydrate formation rate is of great importance

Etude thermique d'une boucle de réfrigération secondaire par coulis d'hydrates

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Experimental and modelling study of energy efficiency of CO 2 hydrate slurry in a coil heat exchanger

International audienceCold production is now facing important energy and environmental issues related to energy consumption and greenhouse gas emissions. Innovative and sustainable emerging technologies are highly needed to enhance the energy efficiency and reduce environmental impacts of refrigeration systems. Secondary loops using phase change material slurries are high-performance systems able to store and deliver high energy density fluid for refrigeration and air conditioning applications. CO2 hydrate slurries are promising due to their significant latent heat and their capacity to store and transport energy with relatively low viscosity and high heat exchange coefficients. Nevertheless, to be attractive, the thermal performance in a heat exchanger of such hydrate-based system needs to be proven. This article studies the behavior of CO2 hydrate slurry in a coil heat exchanger with both experimental and numerical approaches. The experimental approach evaluates the impact of hydrates on the heat exchanger efficiency under various operating conditions (hydrate fraction and flowrate). The results show that the use of CO2 hydrate slurries has beneficial impact on the heat exchanger efficiency and pressure drops under appropriate conditions. For example, CO2 hydrate slurry at 25 kg h(-1) and 8% hydrate mass fraction presents half the pressure drop of water at 100 kg h(-1), with higher heat exchange. A numerical model of the heat exchanger was also developed and validated by experimental data. Furthermore, an optimization study was proposed in order to find the hydrate fraction range that can deliver the required power (400-1100 W) without degrading the pumping power

Dynamic modelling of secondary refrigeration loop with CO2 hydrate slurry

International audienceSecondary refrigeration is an often used solution to reduce the amount of refrigerant leakage and the impact of refrigerants on global warming. The use of two-phase fluids in refrigeration systems is known to increase the quantity of stored energy. In this work, the impact of gas hydrates on the energy release of a heat exchanger is quantified thanks to the dynamic modelling of a secondary refrigeration system. The system is composed of a chiller, a stirred tank reactor (hydrate formation), a loop and a heat exchanger (hydrate dissociation). The model validated by experimental data can be used to simulate various operating conditions in transient and permanent regimes (various slurry mass flow rate, various thermodynamic conditions) and to compare their energy performances. The numerical and experimental results showed better heat exchanger efficiency with hydrate slurry than with water alone

Thermodynamic modelling of formation/dissociation cycles of two-phase slurries in secondary refrigeration system

International audienceThe thermodynamic modelling of the formation/dissociation cycles of two-phase refrigerants such as ice and hydrate slurries is developed. Ice slurries are already used for industrial applications but their generation requires mechanical processes (scraping or brushing surface exchangers) which increase exergy losses. Hydrates are ice-like crystalline structures composed of water molecules linked together by hydrogen bonds, forming cages in which are trapped guest molecules (CH4, CO2, salt…). Hydrate slurries composed of a suspension of hydrate crystals in aqueous solution can also be used as secondary refrigerants and have the advantage of being able to form without mechanical processes. The originality of this study is to characterize the heat and the gas transfer (in hydrate case) in these systems and to evaluate the impact of these transfers on cold storage and distribution efficiency. A higher performance is obtained by hydrate slurries because of their higher temperature level and energy density

Improvement of CO2 hydrate formation and flow using chemical additives in a slurry loop and a stirred reactor: applications to refrigeration and CO2 capture

International audienceSecondary refrigeration and thermal energy storage techniques could be interesting solutions to improve refrigerating system performances and to reduce power consumption and propagation of refrigerants in the atmosphere. In order to combine a more efficient secondary loop and fluids with higher energy storage capacity, a phase change material (PCM) slurry, also called phase change slurry (PCS), could be used as secondary refrigerant. In addition, hydrate-based processes could be an interesting option to separate the CO2 from various gas mixtures. In these two applications, the flow properties of the CO2 hydrate slurry are of paramount importance. In the present study, small amounts of Sodium Dodecyl Sulfate (SDS) were added to the aqueous phase, and this system was tested under CO2 pressure both in a dynamic flow loop and in a stirred reactor. The results obtained with the flow loop demonstrate that SDS has anti-agglomerant properties for the CO2 hydrate: SDS significantly decreases agglomeration and thus improves flowing capacities of the slurry. The results obtained in the reactor shows that the presence of SDS increases the kinetics of the hydrate growth rate both in agitated and in quiescent hydrate forming conditions. Consequently, the addition of SDS could be very promising in industrial applications, such as secondary refrigeration or gas separation, where hydrate slurries must be easily handled and where the hydrate formation rate is of great importance

Rheological study of CO 2 hydrate slurry in the presence of Sodium Dodecyl Sulfate in a secondary refrigeration loop

ACLInternational audienceSecondary refrigeration and thermal energy storage are promising solutions to enhance the performance of refrigeration systems and reduce the impact of refrigerants on the environment. To improve the energy efficiency of secondary refrigeration loops, phase change material (PCM) slurries with a high energy density, such as CO2 hydrate slurries, can be used as a secondary refrigerant. In addition, hydrate-based processes could be an innovative option to capture CO2 from flue gas. In both applications, the rheological properties of the CO2 hydrate slurry have to be controlled. In the present study, CO2 hydrate slurry in the presence of Sodium Dodecyl Sulfate (SDS) was studied in a dynamic flow loop. The results show that SDS used at concentrations of 1500–2000 ppm significantly decreases agglomeration and improves the flow properties of the slurry. Moreover, SDS helps decrease the viscosity of the CO2-hydrate slurry at high fraction (>10 vol%) and therefore could be suitable for use in industrial applications such as secondary refrigeration, in which hydrate slurries must be easy to handle