Showing 1–12 of 57 results
Assessment of Nucleation Kinetic Mechanisms in Gas Hydrate Crystallization Processes
Nucleation is one ofرایگان!
Nucleation is one of the most important steps in the process of crystallization of gas hydrates. In the present work the nucleation mechanism of gas hydrate formation process using the propane as a sII gas hydrate former is investigated at isothermal operating conditions. Effects of variations of supersaturation and impeller speed on the kinetics of hydrate nucleation are also presented. Differente expressions for dependence of induction time with degree of supersaturation are employed. The accuracy of the predicted induction times for the case of progressive nucleation are always much higher than those obtained through instantaneous nucleation assumption at all ranges of impeller speeds. It is found that the heterogeneous progressive nucleation is the most probable nucleation mechanism at the early stages of gas hydrate formation processes
Characterization and Identification of Gas Hydrate Bearing Sediments of Oman Sea Using Seismic Methods
Gas hydrates attractرایگان!
Gas hydrates attracted worldwide attention due to their potential as huge energy resource in the recent decades. Therefore identifying and prospecting them is essential for strategic hydrocarbon reservoir management. Seismic methods are known as a powerful gas hydrate exploration methodology. In this research pre-stack seismic attributes have been used to identify elastic properties and qualitative hydrate saturation of sediments. Using AVO analysis on pre-stack seismic data, occurrence of gas hydrate has been confirmed in the Oman Sea. Also post-stack seismic meta-attributes (applying pattern recognition and classification methods on several attribute planes) have been successfully used to make separation between hydrate and non-hydrate sediments. Joint use of pre- and post-stack seismic attributes will be a good evaluation techniques for confirmation of this study.
Computational Modeling of Natural Gas Production From Hydrate Dissociation
This paper providesرایگان!
This paper provides an overview of computational modeling of hydrate dissociation. A simplified axisymmetric model for natural gas roduction rom the dissociation of methane hydrate in a confined reservoir by a depressurizing well was first described. During the hydrate dissociation, the heat and mass transfer in the reservoir were analyzed, assuming a sharp dissociation front. The system of governing
equations was solved by a finite difference scheme, and the distributions of temperature and pressure in the reservoir, as well as the natural gas production from the well were evaluated. The numerical results were compared with those obtained by the linearization method. Hydrate dissociation in a porous sandstone core was then studied using a kinetic model. The ANSYSFLUENT code was used for analyzing hydrate dissociation in an axisymmetric core. When the core was opened exposing the core to low pressure, the hydrate in the core dissociates and the methane gas and liquid water begin to flow in the pores. A Users’ Defined function (UDF) for analyzing hydrate dissociation was developed and included in the FLUENT code. The New UDF used the Kim-Bishnoi kinetic model for hydrate dissociation. Variations of relative permeability of the core were included in the model. Sample simulation results were presented and discussed
Determination of Structure and Formation Conditions of Gas Hydrate by Using TPD Method and Flash Calculations
In this work, satbilرایگان!
In this work, satbility calculations and determination of gas hydrate structure in equilibrium conditions by using minimization of TPD function for ethane-water system (SI), propane-water system (SII) and methane-methyl cyclo pentane-water system (SH) were performed. Based on results, at 274 K and 275 K temperatures, the liquid phase of methane-water system at 27 bar and 30 bar pressures, propane-water system at .7 bar and 2.5 bar pressures and methane-methyl cyclo pentane-water system at 9.6 bar and 10.1 bar pressures was decomposed. As a result of decomposition of liquid phase for these systems, two new phases, a new liquid phase and hydrate phase were formed. Subsequently, multiphase flash calculations in order to determine the amount and composition of stable phases in equilibrium state were performed. For minimization of TPD function, Algorithm Genetic was used. The results Show good accuracy with data of Heriot Watt university hydrate model (HWHYD)
Effect of Additives on Gas Hydrate Formation and Stability
This study examinesرایگان!
This study examines the effects of two additive including hydroxyethyl cellulose (HEC) and sodium dodecyl sulfate (SDS) for increasing stability and gas content of natural gas hydrates. SDS can used as a hydrate promoter and HEC as a stabilizer. A high-pressure reactor in a laboratory- scale is used for to measure hydrate formation rate and stability. Hydrate stability tests were performed at temperature of -5 °C and pressure 15 bar. Induction time was obtained around 40 minutes at an optimum value of SDS
Effects of DC plasma nitriding parameters on properties of DIN 1.2344 low alloy steel
The aim of this papeرایگان!
The aim of this paper is optimizing of parameters can be affected to depth of nitrided layer for improving the corrosion resistance of DIN 1.2344 low alloy steel by plasma nitriding.In this study, DIN 1.2344 low alloy steel samples were plasma nitrided at 3 level temperatures (450, 500 and 550℃), 3 level time (2, 4, 6 hour) and in 2 level gas compositions (25%N2-75%H2 and 75%N2- 25%H2). Diffusion zone was determined by optical microscopy. Phases formed in these layers were studied by X-ray diffraction method. The XRD pattern reveals that all specimens consist Fe3N, Fe2N and Cr2N phases.Results have shown that depth of diffusion zone increases byincreasing gas compositions from 25% N2 to 75% N2. In addition, thickness of this layer have increased by increasing temperature from 450℃ to 550℃, but It seems that by increasing nitriding time of 2 to 4 hour the depth of the white layer increased but by increasing to 6 hour the depth of this layer decreased sligthly. The optimun condition for plasma nitriding of DIN 1.2344 is 550℃, 4h and 75% N2
Evaluation of various types equations of state for prediction of rate of hydrate formation based on Kashchiev and Firoozabadi model in the presence or absence of kinetic hydrate inhibitors for gasous mixtures in a recirculating systems
This paper comparesرایگان!
This paper compares the effects of using various types of equations of state such as Peng Rabinson(PR), Predictive Soave Ridlich Kowng (PSRK), Benedict–Webb–Rubin-Starling (BWRS), Nasrifar-Boland(NB), and Valderrama -Patel -Teja (VPT) on rate of double gas hydrate formation based on the Kashchiev and Firoozabadi model for gaseous mixtures such as 65% C1/35 %C3, 35% C1/65% C3, 65% C1/35 % i-C4, 35% C1/65% i-C4 with experimental data points obtained in a flow mini-loop apparatus with or without the presence of kinetic inhibitors at various pressures and specified temperature. For the prediction of the gas consumption rate for double gas hydrate formation in a flow mini-loop apparatus, the rate equation based on the Kashchiev and Firoozabadi model for simple gas hydrate formation in bench scale was eveloped. The TAAD% was found to be 18.6 %, 18.8 %, 19.8%, 20.2% and 20.7% for the PR, NB, PSRK, VPT and BWRS equations of state for calculating gas consumption in double gas hydrate formation in the presence and absence of kinetic hydrate inhibitors, respectively. omparison results between the calculated and experimental data points of gas consumption indicate that the PR and NB equations of state have lower errors than the PSRK, VPT and BWRS equations of state for this model
Experimental and Modeling Investigation on Structure H Hydrate Formation Kinetics
In the current work,رایگان!
In the current work, the kinetics of crystal H hydrate formation is modeled by using the chemical affinity model. The experiments were performed at constant temperatures of 274.15, 275.15, 275.65, 276.15 and 277.15 K. Methylcyclopentane (MCP) is used as sH former and methane is used as a help gas. The parameters of model (Ar and tK) are determined and the results show that the parameter of Ar/RT has a constant value at the first step and a different value at second step.These parameters were used to predicting experimental data. The results indicate that this model can predict experimental data very well at several conditions
Experimental investigation of gas consumption for simple gas hydrate formation in a recirculation flow mini-loop apparatus in the presence of modified starch as a kinetic inhibitor
The main objective oرایگان!
The main objective of the present work is to investigate experimentally of simple gas hydrate formation with or without the presence of kinetic inhibitors such as modified starch in a recirculation flow mini-loop apparatus. For this purpose, a laboratory recirculation flow miniloop apparatus was set up to measure the induction time for hydrate formation and gas consumption rate when a hydrate forming substance (such as C1, C3, CO2 and i-C4) is contacted with water in the absence or presence of dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with pure gas is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of the required gas make-up. The effect of pressure on gas consumption during hydrate formation is investigated with or without the presence of poly vinylpyrrolidone (PVP) and modified starch as kinetic inhibitors at various concentrations. Our results were shown that the modified starch can be applied as inhibitors in prevention of simple gas hydrate formation in mini-loop apparatus
Experimental investigation of induction time for binary mixtures during gas hydrate formation in the simultaneous presence of the PVP and L-Tyrosine as kinetic inhibitors in a flow mini-loop apparatus
The main objective oرایگان!
The main objective of the present work is experimental investigation of induction time for double gas hydrate formation in presence or absence of kinetic inhibitors in a flow mini-loop apparatus. For this purpose, a laboratory flow mini-loop apparatus was set up to measure the induction time for hydrate formation when a gaseous mixture (such as 70% C1-30% C3, 30%C1-70% C3,70%C1-30% i-C4 and 30%C1-70% i-C4) is contacted with water in the absence or presence of dissolved inhibitor under suitable temperature and pressure conditions
Experimental Study and Modeling of Methane Hydrate Formation Induction Time in the Presence of Ionic Liquids
Gas hydrate formatioرایگان!
Gas hydrate formation has been referred as unfavorable phenomenon since it leads to blockage of pipelines. To prevent formation of these compounds, several methods are normally pursued including system heating, depressurization, water removal, and use of gas hydrate formation inhibitors. The latter technique may be the most practical method for this purpose. Two types of inhibitors are generally used in the industry: thermodynamic inhibitors and kinetic ones. Thermodynamic inhibitors (such as ethylene glycol and methanol) shift the hydrate-liquid-vapor- (HLV) equilibrium curve to lower temperature and higher-pressure conditions. Kinetic inhibitors (such as PVP, PVCap) delay the hydrate nucleation and growth rates. There are some evidences that ionic liquids have dual inhibition effects. In this communication, we use three ionic liquids including (BMIM-BF4), (BMIM-DCA), and (TEACL). Methane hydrate formation induction time in the presence of different concentrations of these three ionic liquids is kinetically investigated in this work. Consequently, the effects of initial pressure and ionic liquids concentration on the induction time can be evaluated. In addition, a three parameter semi-empirical model is developed on the basis of chemical kinetics theory. Finally, it is shown that the proposed semi-empirical model has a good accuracy in comparison with the experimental data
Gas hydrate formation inhibition using low dosage hydrate inhibitors
Development and utilرایگان!
Development and utilization of Low Dosage Hydrate Inhibitors (LDHI) have been attracted researchers and industry for almost two decades. These inhibitors are known to be more effective, more environmental friendly, less corrosive and havelower capital and operational expenses. These inhibitors are usually classified to Kinetic Inhibitors (KI) and Anti-Agglomerants (AA). While kinetic inhibitors prevent hydrate formation by prolonging induction time of hydrate formation more than the residence time of free water in pipeline, anti agglomerants inhibits pipeline plugging acting as a hydrate emulsifier. Environmental aspects of commercial LDHI’s have encouraged researches to look for more environmentally friendly LDHI’s. Considerable efforts have been made to develop non-ionic surfactants e.g. Alkylamide or zwitterionic surfactants, which can be effective inhibitors or to utilize environmentally friendly materials like starch or anti-freeze proteins. In present paper, these research activities, patents and industrial reports are reviewed, including: chemicals with kinetic or anti agglomeration effects, their mechanism of acts, Compatibility, chemical screening and selecting methods like molecular Dynamics simulations, experimental procedures, data reproductivity, stochasticity, inhibitors synergism, multifunction inhibitors, inhibitors surfactant effects and surface interfacial properties, biodegradability, toxicity and environmental impacts