scholarly journals Hydrate Production Philosophy and Thermodynamic Calculations

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 672 ◽  
Author(s):  
Bjørn Kvamme ◽  
Jinzhou Zhao ◽  
Na Wei ◽  
Wantong Sun ◽  
Navid Saeidi ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Chemical Potential ◽  
Hot Water ◽  
Thermal Stimulation ◽  
Pressure Reduction ◽  
Free Energies ◽  
Thermodynamic Consideration ◽  
Production Methods ◽  
Hydrate Phase ◽  
Thermodynamic Variables

The amount of energy in the form of natural gas hydrates is huge and likely substantially more than twice the amount of worldwide conventional fossil fuel. Various ways to produce these hydrates have been proposed over the latest five decades. Most of these hydrate production methods have been based on evaluation of hydrate stability limits rather than thermodynamic consideration and calculations. Typical examples are pressure reduction and thermal stimulation. In this work we discuss some of these proposed methods and use residual thermodynamics for all phases, including the hydrate phase, to evaluate free energy changes related to the changes in independent thermodynamic variables. Pressures, temperatures and composition of all relevant phases which participate in hydrate phase transitions are independent thermodynamic variables. Chemical potential and free energies are thermodynamic responses that determine whether the desired phase transitions are feasible or not. The associated heat needed is related to the first law of thermodynamics and enthalpies. It is argued that the pressure reduction method may not be feasible since the possible thermal gradients from the surroundings are basically low temperature heat that is unable to break water hydrogen bonds in the hydrate–water interface efficiently. Injecting carbon dioxide, on the other hand, leads to formation of new hydrate which generates excess heat compared to the enthalpy needed to dissociate the in situ CH4 hydrate. But the rapid formation of new CO2 hydrate that can block the pores, and also the low permeability of pure CO2 in aquifers, are motivations for adding N2. Optimum mole fractions of N2 based on thermodynamic considerations are discussed. On average, less than 30 mole% N2 can be efficient and feasible. Thermal stimulation using steam or hot water is not economically feasible. Adding massive amounts of methanol or other thermodynamic inhibitors is also technically efficient but far from economically feasible.

On reconstitutive phase transitions and the jump of the chemical potential

Analysis ◽  
2008 ◽  
Vol 28 (1) ◽  
Author(s):  
Thomas Blesgen
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Weak Solutions ◽  
Transition Layer ◽  
Chemical Potential ◽  
Sharp Interface ◽  
Free Energies ◽  
Diffusion In Solids ◽  
Existence Of Weak Solutions ◽  
Two Phases

This article studies diffusion in solids in the case of two phases under isothermal conditions where due to plastic effects the number of vacancies changes when crossing a transition layer, i.e. a reconstitutive phase transition. A segregation model is derived and the equations are studied in the limit of a sharp interface. A Gibbs–Thomson law is derived and it is shown that the vacancy component of the chemical potential jumps across the transition layer thereby explaining recent experimental observations. The thermodynamic correctness of the model is shown as well as the existence of weak solutions with logarithmic free energies.

scholarly journals Environmentally Friendly Production of Methane from Natural Gas Hydrate Using Carbon Dioxide

2019 ◽  
Vol 11 (7) ◽  
pp. 1964 ◽  
Author(s):  
Bjørn Kvamme
Keyword(s):  
Free Energy ◽  
Natural Gas ◽  
Gas Hydrate ◽  
Free Water ◽  
Hot Water ◽  
Thermal Stimulation ◽  
Pressure Reduction ◽  
Natural Gas Hydrate ◽  
Transport Barrier ◽  
The World

Huge amounts of natural gas hydrate are trapped in an ice-like structure (hydrate). Most of these hydrates have been formed from biogenic degradation of organic waste in the upper crust and are almost pure methane hydrates. With up to 14 mol% methane, concentrated inside a water phase, this is an attractive energy source. Unlike conventional hydrocarbons, these hydrates are widely distributed around the world, and might in total amount to more than twice the energy in all known sources of conventional fossil fuels. A variety of methods for producing methane from hydrate-filled sediments have been proposed and developed through laboratory scale experiments, pilot scale experiments, and theoretical considerations. Thermal stimulation (steam, hot water) and pressure reduction has by far been the dominating technology platforms during the latest three decades. Thermal stimulation as the primary method is too expensive. There are many challenges related to pressure reduction as a method. Conditions of pressure can be changed to outside the hydrate stability zone, but dissociation energy still needs to be supplied. Pressure release will set up a temperature gradient and heat can be transferred from the surrounding formation, but it has never been proven that the capacity and transport ability will ever be enough to sustain a commercial production rate. On the contrary, some recent pilot tests have been terminated due to freezing down. Other problems include sand production and water production. A more novel approach of injecting CO2 into natural gas hydrate-filled sediments have also been investigated in various laboratories around the world with varying success. In this work, we focus on some frequent misunderstandings related to this concept. The only feasible mechanism for the use of CO2 goes though the formation of a new CO2 hydrate from free water in the pores and the incoming CO2. As demonstrated in this work, the nucleation of a CO2 hydrate film rapidly forms a mass transport barrier that slows down any further growth of the CO2 hydrate. Addition of small amounts of surfactants can break these hydrate films. We also demonstrate that the free energy of the CO2 hydrate is roughly 2 kJ/mol lower than the free energy of the CH4 hydrate. In addition to heat release from the formation of the new CO2 hydrate, the increase in ion content of the remaining water will dissociate CH4 hydrate before the CO2 hydrate due to the difference in free energy.

scholarly journals Enthalpies of Hydrate Formation from Hydrate Formers Dissolved in Water

Energies ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 1039 ◽  
Author(s):  
Bjørn Kvamme
Keyword(s):  
Experimental Data ◽  
Phase Transitions ◽  
Reduction Method ◽  
Hydrate Formation ◽  
Alternative Methods ◽  
Pressure Reduction ◽  
Hydrate Dissociation ◽  
Enthalpy Changes ◽  
Hydrate Phase ◽  
Hydrocarbon Sources

The international interest in the energy potential related to the huge amounts of methane trapped in the form of hydrates is rapidly increasing. Unlike conventional hydrocarbon sources these natural gas hydrate deposits are widely spread around the world. This includes countries which have limited or no conventional hydrocarbon sources, like for instance Japan. A variety of possible production methods have been proposed during the latest four decades. The pressure reduction method has been dominant in terms of research efforts and associated investments in large scale pilot test studies. Common to any feasible method for producing methane from hydrates is the need for transfer of heat. In the pressure reduction method necessary heat is normally expected to be supplied from the surrounding formation. It still remain, however, unverified whether the capacity, and heat transport capabilities of surrounding formation, will be sufficient to supply enough heat for a commercial production based on reduction in pressure. Adding heat is very costly. Addition of limited heat in critical areas (regions of potential freezing down) might be economically feasible. This requires knowledge about enthalpies of hydrate dissociation under various conditions of temperature and pressure. When hydrate is present in the pores then it is the most stable phase for water. Hydrate can then grow in the concentration range in between liquid controlled solubility concentrations, and the minimum concentration of hydrate in water needed to keep the hydrate stable. Every concentration in that range off concentrations results unique free energy and enthalpy of the formed hydrate. Similarly for hydrate dissociation towards water containing less hydrate former than the stability limit. Every outside liquid water concentration results in unique enthalpy changes for hydrate dissociation. There are presently no other available calculation approaches for enthalpy changes related to these hydrate phase transitions. The interest of using CO2 for safe storage in the form of hydrate, and associated CH4 release, is also increasing. The only feasible mechanism in this method involves the formation of new CO2 hydrate, and associated release of heat which assist in dissociating the in situ CH4 hydrate. Very limited experimental data is available for heats of formation (and dissociation), even for CH4. And most experimental data are incomplete in the sense that associated water/hydrate former rate are often missing or guessed. Thermodynamic conditions are frequently not precisely defined. Although measured hydrate equilibrium pressure versus temperature curves can be used there is still a need for additional models for volume changes, and ways to find other information needed. In this work we propose a simple and fairly direct scheme of calculating enthalpies of formation and dissociation using residual thermodynamics. This is feasible since also hydrate can be described by residual thermodynamics though molecular dynamics simulations. The concept is derived and explained in detail and also compared to experimental data. For enthalpy changes related to hydrate formation from water and dissolved hydrate formers we have not found experimental data to compare with. To our knowledge there are no other alternative methods available for calculating enthalpy changes for these types of hydrate phase transitions. And there are no limits in the theory for which hydrate phase transitions that can be described as long as chemical potentials for water and hydrate formers in the relevant phases are available from theoretical modeling and/or experimental information.

SS - Gas Hydrate: Gas production from methane hydrate sediment layer by thermal stimulation with hot water injection

2010 ◽  
Author(s):  
Kyuro Sasaki ◽  
Shinzi Ono ◽  
Yuichi Sugai ◽  
Norio Tenma ◽  
Takao Ebinuma ◽  
...  
Keyword(s):  
Gas Hydrate ◽  
Methane Hydrate ◽  
Water Injection ◽  
Gas Production ◽  
Hot Water ◽  
Thermal Stimulation ◽  
Sediment Layer

scholarly journals Heat conduction and thermal convection on thermal front movement during natural gas hydrate thermal stimulation exploitation

2018 ◽  
Vol 73 ◽  
pp. 40 ◽  
Author(s):  
Yongmao Hao ◽  
Xiaozhou Li ◽  
Shuxia Li ◽  
Guangzhong Lü ◽  
Yunye Liu ◽  
...  
Keyword(s):  
Heat Conduction ◽  
Thermal Convection ◽  
Thermal Model ◽  
Hot Water ◽  
Thermal Stimulation ◽  
Analytical Models ◽  
Natural Gas Hydrate ◽  
Thermal Front ◽  
Transfer Mode ◽  
Front Movement

Natural Gas Hydrate (NGH) has attracted increasing attention for its great potential as clean energy in the future. The main heat transfer mode that controls the thermal front movement in the process of NGH exploitation by heat injection was discussed through NGH thermal stimulation experiments, and whether it is reliable that most analytical models only consider the heat conduction but neglect the effect of thermal convection was determined by the comparison results between experiments and Selim’s thermal model. And the following findings were obtained. First, the movement rate of thermal front increases with the rise of hot water injection rate but changes little with the rise of the temperature of the injected hot water, which indicated that thermal convection is the key factor promoting the movement of thermal front. Second, the thermal front movement rates measured in the experiments are about 10 times that by the Selim’s thermal model, the reason for which is that the Selim’s thermal model only takes the heat conduction into account. And third, theoretical calculation shows that heat flux transferred by thermal convection is 15.56 times that by heat conduction. It is concluded that thermal convection is the main heat transfer mode that controls the thermal front movement in the process of NGH thermal stimulation, and its influence should never be neglected in those analytical models.

Symmetrization of interface dynamics equations

1992 ◽  
Vol 3 (3) ◽  
pp. 283-297 ◽  
Author(s):  
Leonid K. Antanovskii
Keyword(s):  
Chemical Potential ◽  
General Procedure ◽  
Unsteady Motion ◽  
Free Boundaries ◽  
Piecewise Constant ◽  
Mass Transfer Processes ◽  
Construction Of Self ◽  
Thermodynamic Variables ◽  
Capillary Fluid ◽  
Similar Solutions

The system of conservation laws governing heat and mass transfer processes in a continuous medium is obtained in a symmetric form on the basis of the successive application of fundamental thermodynamic principles. This approach involves reformulating the problem in intensive thermodynamic variables such as the temperature and chemical potential. The equations of capillary fluid mechanics and phase transitions with moving free boundaries are analysed in detail. The unsteady motion of a drop driven by buoyancy forces in an unbounded ambient fluid with dilute surfactants is investigated where the LeChatelier principle is established for an arbitrary surfactant. The general procedure for construction of self-similar solutions for the thermodiffusive Stefan problem with piecewise constant matrices of coefficients is described

scholarly journals Solid-to-liquid phase transitions of sub-nanometer clusters enhance chemical transformation

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Juan-Juan Sun ◽  
Jun Cheng
Keyword(s):  
Phase Transitions ◽  
Liquid Phase ◽  
Active Sites ◽  
Catalyst Activity ◽  
Ab Initio Molecular Dynamics ◽  
Free Energies ◽  
Elementary Reactions ◽  
Au Clusters ◽  
Calculate Temperature Dependence ◽  
Entropic Effects

AbstractUnderstanding the nature of active sites is crucial in heterogeneous catalysis, and dynamic changes of catalyst structures during reaction turnover have brought into focus the dynamic nature of active sites. However, much less is known on how the structural dynamics couples with elementary reactions. Here we report an anomalous decrease in reaction free energies and barriers on dynamical sub-nanometer Au clusters. We calculate temperature dependence of free energies using ab initio molecular dynamics, and find significant entropic effects due to solid-to-liquid phase transitions of the Au clusters induced by adsorption of different states along the reaction coordinate. This finding demonstrates that catalyst dynamics can play an important role in catalyst activity.

Sign in / Sign up

Export Citation Format

Share Document