The sulfate-methane interface is an important biogeochemical identification interface for the areas with high methane flux and containing gas hydrate. Above the sulfate-methane interface, the sulfate concentration in ...The sulfate-methane interface is an important biogeochemical identification interface for the areas with high methane flux and containing gas hydrate. Above the sulfate-methane interface, the sulfate concentration in the sediment is consumed progressively for the decomposition of the organic matter and anaerobic methane oxidation. Below the sulfate-methane interface, the methane concentration increases continuously with the depth. Based on the variation characters of the sulfate and methane concentration around the sulfate-methane interface, it is feasible to estimate the intensity of the methane flux, and thereafter to infer the possible occurrence of gas hydrate. The geochemical data of the pore water taken from the northern slope of the South China Sea show the sulfate-methane interface is relatively shallow, which indicates that this area has the high methane flux. It is considered that the high methane flux is most probably caused by the occurrence of underlying gas hydrate in the northern slope of the South China Sea.展开更多
The dissociation rates of methane hydrates formed with and without the presence of sodium dodecyl sulfate （methane-SDS hydrates）, were measured under atmospheric pressure and temperatures below ice point to investig...The dissociation rates of methane hydrates formed with and without the presence of sodium dodecyl sulfate （methane-SDS hydrates）, were measured under atmospheric pressure and temperatures below ice point to investigate the influence of the hydrate production conditions and manners upon its dissociation kinetic behavior. The experimental results demonstrated that the dissociation rate of methane hydrate below ice point is strongly dependent on the manners of hydrate formation and processing. The dissociation rate of hydrate formed quiescently was lower than that of hydrate formed with stirring; the dissociation rate of hydrate formed at lower pressure was higher than that of hydrate formed at higher oressure; the comoaction of hydrate after its formation lowered its stability, i.e., increased＇its dissociation rate.The stability of hydrate could beincreased by prolonging the time period for which hydrate was held at formation temperature and pressure before it was cooled down, or by prolonging the time period for which hydrate was held at dissociation temperature and formation pressure before it was depressurized to atmospheric pressure. It was found that the dissociation rate of methane hydrate varied with the temperature （ranging from 245.2 to 272.2 K） anomalously as reported on the dissociation of methane hydrate without the presence of surfactant as kinetic promoter. The dissociation rate at 268 K was found to be the lowest when the manners and conditions at which hydrates were formed and processed were fixed.展开更多
Kinetic data of methane hydrate formation in the presence of purewater, brines with single salt and mixed salts, and aqueous solutionsof ethylene glycol (EG) and salt + EG were measured. A new kineticmodel of hydrate ...Kinetic data of methane hydrate formation in the presence of purewater, brines with single salt and mixed salts, and aqueous solutionsof ethylene glycol (EG) and salt + EG were measured. A new kineticmodel of hydrate formation for the methane + water systems wasdeveloped based on a four-step formation mechanism and reactionkinetics approach. The proposed kinetic model predicts the kineticbehavior of methane hydrate formation in pure water with goodaccuracy. The feasibility of extending the kinetic model to salt (s)and EG containing systems was explored.展开更多
The porous medium has an important effect on hydrate formation.In this paper,the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (...The porous medium has an important effect on hydrate formation.In this paper,the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (SDS) existing in the system.The results show that A-type zeolite can influence methane hydrate formation.At the temperature of 273.5 K and pressure of 8.3 MPa,the distilled water with A-type zeolite can form methane hydrate with gaseous methane in 12 hours.The formation process of the system with A-type zeolite was quite steady and the amount of A-type zeolite can influence the gas storage capacity significantly.The adding of A-type zeolite with 0.067 g·(g water)-1 into 2×10-3 g·g-1 SDS-water solution can increase the gas storage capacity,and the maximum increase rate was 31%.Simultaneously the promotion effect on hydrate formation of 3A-type zeolite is much more obvious than that of 5A-type zeolite when the water adding amounts are 0.033 g·g-1 and 0.067 g·g-1 at the experimental conditions.展开更多
Temperature gradient and cooling rate have an obvious effect on formation of methane hydrate. The process for formation of methane hydrate in coarse sand is monitored to tmderstand the relationship between temperature...Temperature gradient and cooling rate have an obvious effect on formation of methane hydrate. The process for formation of methane hydrate in coarse sand is monitored to tmderstand the relationship between temperature gradient and cooling rate and nucleation, growth and distribution of methane hydrate by using the electrical resistivity method. The results show that the change of resistivity can better reflect the nucleation and growth and distribution of methane hydrate. Temperature gradient promotes the nucleation, formation, and formation rate of methane hydrate. At a temperature gradient of 0.11℃/cm, the rate of methane hydrate formation and saturation reaches a maximum. Cooling rate has little effect on the methane hydrate formation process. Judging from the outcome of final spatial distribution of methane hydrate, the cooling rate has an obvious but irregular effect in coarse sand. The effect of tempera^re gradient on distribution of methane hydrate in coarse sand is less than that of cooling rate. At a temperature gradient of 0.07℃/cm, methane hydrate is distributed uniformly in the sample. If the temperature gradient is higher or lower than this value, the hydrate is enriched in the upper layer of sample.展开更多
Phase equilibrium conditions of gas hydrate in several systems were measured by the step-heating method using the cylindrical transparent sapphire cell device.The experimental data for pure CH4 or CO2+deionized water ...Phase equilibrium conditions of gas hydrate in several systems were measured by the step-heating method using the cylindrical transparent sapphire cell device.The experimental data for pure CH4 or CO2+deionized water systems showed good agreement with those in the literatures.This kind of method was then applied to CH4/CO2+sodium dodecyl sulfate(SDS)aqueous solution,CH4/CO2+SDS aqueous solution+silica sand,and(CH4+C2H6+C3H8)gas mixture+SDS aqueous solution systems,where SDS was added to increase the hydrate formation rate without evident influence on the equilibrium conditions.The feasibility and reliability of the step-heating method,especially for porous media systems and gas mixtures systems were determined.The experimental data for CO2+silica sand data shows that the equilibrium pressure will change significantly when the particle size of silica sand is less than 96μm.The formation equilibrium pressure was also measured by the reformation of hydrate.展开更多
The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments ...The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments have predicted that the shielding ice formed on the hydrate surface after initial dissociation of the hydrate plays an important role in the self-preservation effect. We propose ice-shielding models of gas hydrates to investigate the dissociation rates quantitatively, including the self-preservation process, at temperatures below the ice-melting point and at atmospheric pressure. Three general models are constructed for two temperature ranges The rate-determining process for the lower temperature range is hydrate dissociation, and those for the higher range are gas diffusion through ice or hydrate layers, which depend on the thickness of the shielding-ice layer. Our models suggest that the extent of self-preservation depends on temperature, original hydrate size, and guest substances, which can explain the experimental results.展开更多
Internal reformation of low steam methane fuel is highly beneficial for improving the energy efficiency and reducing the system complexity and cost of solid oxide fuel cells(SOFCs).However,anode coking for the Ni-base...Internal reformation of low steam methane fuel is highly beneficial for improving the energy efficiency and reducing the system complexity and cost of solid oxide fuel cells(SOFCs).However,anode coking for the Ni-based anode should be prevented before the technology becomes a reality.A multi-physics fully coupled model is employed to simulate the operations of SOFCs fueled by low steam methane.The multi-physics model produces I-V relations that are in excellent agreement with the experimental results.The multi-physics model and the experimental non-coking current density deduced kinetic carbon activity criterion are used to examine the effect of operating parameters and the anode diffusion barrier layer on the propensity of carbon deposition.The interplays among the fuel utilization ratio,current generation,thickness of the barrier layer and the cell operating voltage are revealed.It is demonstrated that a barrier layer of 400μm thickness is an optimal and safe anode design to achieve high power density and non-coking operations.The anode structure design can be very useful for the development of high efficiency and low cost SOFC technology.展开更多
文摘The sulfate-methane interface is an important biogeochemical identification interface for the areas with high methane flux and containing gas hydrate. Above the sulfate-methane interface, the sulfate concentration in the sediment is consumed progressively for the decomposition of the organic matter and anaerobic methane oxidation. Below the sulfate-methane interface, the methane concentration increases continuously with the depth. Based on the variation characters of the sulfate and methane concentration around the sulfate-methane interface, it is feasible to estimate the intensity of the methane flux, and thereafter to infer the possible occurrence of gas hydrate. The geochemical data of the pore water taken from the northern slope of the South China Sea show the sulfate-methane interface is relatively shallow, which indicates that this area has the high methane flux. It is considered that the high methane flux is most probably caused by the occurrence of underlying gas hydrate in the northern slope of the South China Sea.
基金Supported by the National Natural Science Foundation of China （20506016, 20676145, U0633003）, the National High Technology Research and Development Program of China （2006AA09A208）, Program for New Century Excellent Talents in Uni versity of the State Ministry of Education （NCET-07-0842）, and the Foundation for the Authors of National Excellent Doc toral Dissertation of the People＇s Republic of China （200447）.
文摘The dissociation rates of methane hydrates formed with and without the presence of sodium dodecyl sulfate （methane-SDS hydrates）, were measured under atmospheric pressure and temperatures below ice point to investigate the influence of the hydrate production conditions and manners upon its dissociation kinetic behavior. The experimental results demonstrated that the dissociation rate of methane hydrate below ice point is strongly dependent on the manners of hydrate formation and processing. The dissociation rate of hydrate formed quiescently was lower than that of hydrate formed with stirring; the dissociation rate of hydrate formed at lower pressure was higher than that of hydrate formed at higher oressure; the comoaction of hydrate after its formation lowered its stability, i.e., increased＇its dissociation rate.The stability of hydrate could beincreased by prolonging the time period for which hydrate was held at formation temperature and pressure before it was cooled down, or by prolonging the time period for which hydrate was held at dissociation temperature and formation pressure before it was depressurized to atmospheric pressure. It was found that the dissociation rate of methane hydrate varied with the temperature （ranging from 245.2 to 272.2 K） anomalously as reported on the dissociation of methane hydrate without the presence of surfactant as kinetic promoter. The dissociation rate at 268 K was found to be the lowest when the manners and conditions at which hydrates were formed and processed were fixed.
基金Supported by the National Natural Science Foundation(No. 20003010) and Postdoctoral Research Foundation.
文摘Kinetic data of methane hydrate formation in the presence of purewater, brines with single salt and mixed salts, and aqueous solutionsof ethylene glycol (EG) and salt + EG were measured. A new kineticmodel of hydrate formation for the methane + water systems wasdeveloped based on a four-step formation mechanism and reactionkinetics approach. The proposed kinetic model predicts the kineticbehavior of methane hydrate formation in pure water with goodaccuracy. The feasibility of extending the kinetic model to salt (s)and EG containing systems was explored.
基金Supported by the National Natural Science Foundation of China （50876107）, the National Basic Research Program of China （2009CB219504）, NSFC-Guangdong Union Foundation （NSFC-U0733033） and CAS Program （KGCX2-YW-805）.
文摘The porous medium has an important effect on hydrate formation.In this paper,the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (SDS) existing in the system.The results show that A-type zeolite can influence methane hydrate formation.At the temperature of 273.5 K and pressure of 8.3 MPa,the distilled water with A-type zeolite can form methane hydrate with gaseous methane in 12 hours.The formation process of the system with A-type zeolite was quite steady and the amount of A-type zeolite can influence the gas storage capacity significantly.The adding of A-type zeolite with 0.067 g·(g water)-1 into 2×10-3 g·g-1 SDS-water solution can increase the gas storage capacity,and the maximum increase rate was 31%.Simultaneously the promotion effect on hydrate formation of 3A-type zeolite is much more obvious than that of 5A-type zeolite when the water adding amounts are 0.033 g·g-1 and 0.067 g·g-1 at the experimental conditions.
基金supported by the Chinese Academy of Sciences Action-plan for Western Project(No.KZCX2-XB3-03)the National Natural Science Foundation of China(No.41001038,51266005)the National Natural Science Foundation of China(No.41101070,1106ZBB007)
文摘Temperature gradient and cooling rate have an obvious effect on formation of methane hydrate. The process for formation of methane hydrate in coarse sand is monitored to tmderstand the relationship between temperature gradient and cooling rate and nucleation, growth and distribution of methane hydrate by using the electrical resistivity method. The results show that the change of resistivity can better reflect the nucleation and growth and distribution of methane hydrate. Temperature gradient promotes the nucleation, formation, and formation rate of methane hydrate. At a temperature gradient of 0.11℃/cm, the rate of methane hydrate formation and saturation reaches a maximum. Cooling rate has little effect on the methane hydrate formation process. Judging from the outcome of final spatial distribution of methane hydrate, the cooling rate has an obvious but irregular effect in coarse sand. The effect of tempera^re gradient on distribution of methane hydrate in coarse sand is less than that of cooling rate. At a temperature gradient of 0.07℃/cm, methane hydrate is distributed uniformly in the sample. If the temperature gradient is higher or lower than this value, the hydrate is enriched in the upper layer of sample.
基金Supported by the National Natural Science Foundation of China （20676145, U0633003）, the National Basic Research Program of China （2009CB219504） and the Program for New Century Excellent Talents in University of the State Ministry of Education.
文摘Phase equilibrium conditions of gas hydrate in several systems were measured by the step-heating method using the cylindrical transparent sapphire cell device.The experimental data for pure CH4 or CO2+deionized water systems showed good agreement with those in the literatures.This kind of method was then applied to CH4/CO2+sodium dodecyl sulfate(SDS)aqueous solution,CH4/CO2+SDS aqueous solution+silica sand,and(CH4+C2H6+C3H8)gas mixture+SDS aqueous solution systems,where SDS was added to increase the hydrate formation rate without evident influence on the equilibrium conditions.The feasibility and reliability of the step-heating method,especially for porous media systems and gas mixtures systems were determined.The experimental data for CO2+silica sand data shows that the equilibrium pressure will change significantly when the particle size of silica sand is less than 96μm.The formation equilibrium pressure was also measured by the reformation of hydrate.
文摘The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments have predicted that the shielding ice formed on the hydrate surface after initial dissociation of the hydrate plays an important role in the self-preservation effect. We propose ice-shielding models of gas hydrates to investigate the dissociation rates quantitatively, including the self-preservation process, at temperatures below the ice-melting point and at atmospheric pressure. Three general models are constructed for two temperature ranges The rate-determining process for the lower temperature range is hydrate dissociation, and those for the higher range are gas diffusion through ice or hydrate layers, which depend on the thickness of the shielding-ice layer. Our models suggest that the extent of self-preservation depends on temperature, original hydrate size, and guest substances, which can explain the experimental results.
基金supported by the National Natural Science Foundation of China (No.11574284 abd No.11774324)the National Basic Research Program of China (No.2012CB215405)Collaborative Innovation Center of Suzhou Nano Science and Technology
文摘Internal reformation of low steam methane fuel is highly beneficial for improving the energy efficiency and reducing the system complexity and cost of solid oxide fuel cells(SOFCs).However,anode coking for the Ni-based anode should be prevented before the technology becomes a reality.A multi-physics fully coupled model is employed to simulate the operations of SOFCs fueled by low steam methane.The multi-physics model produces I-V relations that are in excellent agreement with the experimental results.The multi-physics model and the experimental non-coking current density deduced kinetic carbon activity criterion are used to examine the effect of operating parameters and the anode diffusion barrier layer on the propensity of carbon deposition.The interplays among the fuel utilization ratio,current generation,thickness of the barrier layer and the cell operating voltage are revealed.It is demonstrated that a barrier layer of 400μm thickness is an optimal and safe anode design to achieve high power density and non-coking operations.The anode structure design can be very useful for the development of high efficiency and low cost SOFC technology.
