Low-grade waste heat recovery for wastewater treatment using clathrate hydrate based technology

Effectively recycling low-grade waste heat is crucial for advancing decarbonization and achieving net-zero emissions, yet current methodologies are limited by inefficiencies in extracting energy from sources with low exergy. This study introduces an innovative approach leveraging hydrate formation and dissociation to utilize low-grade waste heat in purifying wastewater. By directly heating (low-grade waste heat) liquid R134a, our method induces bubble formation, thereby enhancing hydrate nucleation and growth. Our system demonstrates exceptional energy efficiencies, reaching up to 23.5%, and exhibits a high removal efficiency for wastewater with high concentrations of organic and heavy metal contaminants, including methylene blue (86.4%), Cr3+ (98.0%), Ni2+ (98.3%), Zn2+ (98.0%), and Cu2+ (97.1%). This approach not only offers a sustainable pathway for waste heat utilization but also addresses critical challenges in wastewater treatment. This technology demonstrates substantial potential in both low-grade waste heat recovery and wastewater treatment

Monitoring gas hydrate formation with magnetic resonance imaging in a metallic core holder

Methane hydrate deposits world-wide are promising sources of natural gas. Magnetic Resonance Imaging (MRI) has proven useful in previous studies of hydrate formation. In the present work, methane hydrate formation in a water saturated sand pack was investigated employing an MRI-compatible metallic core holder at low magnetic field with a suite of advanced MRI methods developed at the UNB MRI Centre. The new MRI methods are intended to permit observation and quantification of residual fluids in the pore space as hydrate forms. Hydrate formation occurred in the water-saturated sand at 1500 psi and 4 °C. The core holder has a maximum working pressure of 4000 psi between -28 and 80 °C. The heat-exchange jacket enclosing the core holder enabled very precise control of the sample temperature. A pure phase encode MRI technique, SPRITE, and a bulk T1-T2 MR method provided high quality measurements of pore fluid saturation. Rapid 1D SPRITE MRI measurements time resolved the disappearance of pore water and hence the growth of hydrate in the sand pack. 3D π-EPI images confirmed that the residual water was inhomogeneously distributed along the sand pack. Bulk T1-T2 measurements discriminated residual water from the pore gas during the hydrate formation. A recently published local T1-T2 method helped discriminate bulk gas from the residual fluids in the sample. Hydrate formation commenced within two hours of gas supply. Hydrate formed throughout the sand pack, but maximum hydrate was observed at the interface between the gas pressure head and the sand pack. This irregular pattern of hydrate formation became more uniform over 24 hours. The rate of hydrate formation was greatest in the first two hours of reaction. An SE-SPI T2 map showed the T2 distribution changed considerably in space and time as hydrate formation continued. Changes in the T2 distribution are interpreted as pore level changes in residual water content and environment

A numerical investigation of bubble growth on and departure from a superheated wall by lattice Boltzmann method

The bubble growth on and departure from a superheated wall has been simulated by an improved hybrid lattice Boltzmann method. The Briant's treatment of partial wetting boundary was introduced and the new hybrid model was validated by the single bubble growth on and departure from the superheated wall. The results showed that parametric dependencies of the bubble departure diameter were in good agreement with the experimental correlation from some recent literatures. This new model was also employed to simulate twin-bubble growth, coalescence on and departure from a horizontal superheated wall. (C) 2010 Elsevier Ltd. All rights reserved

Kinetic Study on the Process of Cyclopentane plus Methane Hydrate Formation in NaCl Solution

In this work, the formation kinetics of cyclopentane (CP) + methane hydrate is studied. CP is used as a promoter to accelerate the hydrate formation. The total methane consumption, the induction time, and the formation rate were investigated under different hydrate formation conditions in NaC1 solution. The results indicated that the pressure driving force could increase the gas consumption and shorten the induction time. Meanwhile, the induction time could be greatly influenced by the pressure driving force at a lower temperature. Especially, it could be shortened to a minimum value of 110 s with the increase of the pressure driving force at a fixed operating condition (CP concentration, 7.45%; NaCl solution concentration, 3.50%; and temperature, 298.15 K). Moreover, the hydrate formation rate would be accelerated with the increase of the stirring rate by its promotion in the dissolution and dispersion of methane. Finally, a higher CP concentration was favorable for the rapid hydrate formation of CP + CH4 binary hydrates. The amount of CP used could determine the amount of methane incorporated into the hydrate phase

The fate of CO₂ bubble leaked from seabed

AbstractA numerical model of an individual CO2 bubble dissolution and ascent in shallow seawater was developed to simulate the fate of CO2 leaked from seabed naturally or artificially. The model consists of a solubility sub-model of CO2 gas in seawater, a CO2 bubble mass transfer sub-model, and a CO2 bubble momentum transfer sub-model. The model is applied to predict the dynamics of leaked CO2 in seawater at various depths from 0–150 m (temperature from 10 ∘C to 25 ∘C) and for initial bubble sizes from 3.0 to 40.0 mm in diameter. A diagram of CO2 ascending distance vs dissolution time is obtained from model simulations. It is found that CO2 bubbles ascend at a mean speed of 16 cm/sec and a mean shrinking rate of 30×10−3 mm/s in diameter approximately if leaked from a shallow ocean (<150 m) seabed. A parameter, named as critical depth, is defined and suggested as a parameter to indicate if the CO2 leaked from seabed can return to atmosphere. This critical depth is approximately linearly related to the initial bobble size with a gradient of −0.68 m/mm under seawater conditions in the simulation ocean

Experimental Research on the Mechanical Properties of Methane Hydrate-Ice Mixtures

The mechanical properties of methane hydrate are important to the stability of borehole and methane extraction from a methane hydrate reservoir. In this study, a series of triaxial compression tests were carried out on laboratory-formed methane hydrate-ice mixtures with various methane hydrate contents. Axial loading was conducted at an axial strain rate of 1.33%/min and a constant temperature of −10 °C. The results indicate that: (1) the deformation behavior is strongly affected by confining pressure and methane hydrate content; (2) the failure strength significantly increases with confining pressure when confining pressure is less than 10 MPa, and decreases with methane hydrate content; (3) the cohesion decreases with methane hydrate content, while the internal friction angle increases with methane hydrate content; (4) the strength of ice specimens are higher than that of methane hydrate-ice mixture specimens; Based on the experimental data, the relationship among failure strength, confining pressure and methane hydrate content was obtained, and a modified Mohr-Coulomb criterion considering the influence of methane hydrate content on shear strength was proposed