Hydrate-based carbon dioxide capture from simulated integrated gasification combined cycle gas

The equilibrium hydrate formation conditions for CO2/H-2 gas mixtures with different CO2 concentrations in 0.29 mol% TBAB aqueous solution are firstly measured. The results illustrate that the equilibrium hydrate formation pressure increases remarkably with the decrease of CO2 concentration in the gas mixture. Based on the phase equilibrium data, a three stages hydrate CO2 separation from integrated gasification combined cycle (IGCC) synthesis gas is investigated. Because the separation efficiency is quite low for the third hydrate separation, a hybrid CO2 separation process of two hydrate stages in conjunction with one chemical absorption process (absorption with MEA) is proposed and studied. The experimental results show H-2 concentration in the final residual gas released from the three stages hydrate CO2 separation process was approximately 95.0 mol% while that released from the hybrid CO2 separation process was approximately 99.4 mol%. Thus, the hybrid process is possible to be a promising technology for the industrial application in the future.</p

Experimental Study on Methane Hydrate Dissociation by Depressurization in Porous Sediments

Based on currently available data from site measurements in the Shenhu Area of the South China Sea, methane hydrate dissociation behavior by depressurization is studied in a one-dimensional experimental apparatus. According to time variation of temperature, resistance and gas production, the hydrate dissociation process is divided into three stages: free gas release, rapid dissociation and gradual dissociation. The experimental results show that as the hydrate saturation increases the proportion of hydrate decomposed decreases in the rapid dissociation stage. The hydrate dissociation rate and the dissociation heat increase as the dissociation pressure decreases. Furthermore, the decrease of the dissociation pressure works against the secondary formation of the hydrate.</p

Molecular dynamics simulation of methane hydrate dissociation by depressurisation

Methane (CH4) hydrate dissociation and the mechanism by depressurisation are investigated by molecular dynamics (MD) simulation. The hydrate decomposition processes are studied by the vacuum removal method' and the normal method. It is found that the hydrate decomposition is promoted by depressurisation. The quasi-liquid layer is formed in the hydrate surface layer. The driving force of dissociation is found to be controlled by the concentration gradient between the H2O molecules of the hydrate surface layer and the H2O molecules of the hydrate inner layer. The clathrates collapse gradually, and the hydrate decomposes layer by layer. Relative to our previous MD simulation results, this study shows that the rate of the hydrate dissociation by depressurisation is slower than that by the thermal stimulation and the inhibitor injection. This study illustrated that MD simulation can play a significant role in investigating the hydrate decomposition mechanisms

Effect of temperature fluctuation on hydrate-based CO_2 separation from fuel gas

A new method of temperature fluctuation is proposed to promote the process of hydrate-based CO_2 separation from fuel gas in this work according to the dual nature of CO_2 solubility in hydrate forming and non-hydrate forming regions 1. The temperature fluctuation operated in the process of hydrate formation improves the formation of gas hydrate observably. The amount of the gas consumed with temperature fluctuation is approximately 35% more than that without temperature fluctuation. It is found that only the temperature fluctuation operated in the period of forming hydrate leads to a good effect on CO_2 separation. Meanwhile, with the proceeding of hydrate formation, the effect of temperature fluctuation on the gas hydrate gradually reduces, and little effect is left in the completion term. The CO_2 separation efficiencies in the separation processes with the effective temperature fluctuations are improved remarkably

Hydrate-based carbon dioxide capture from simulated integrated gasification combined cycle gas

The equilibrium hydrate formation conditions for CO2/H2 gas mixtures with different CO2 concentrations in 0.29 mol% TBAB aqueous solution are firstly measured.The results illustrate that the equilibrium hydrate formation pressure increases remarkably with the decrease of CO2 concentration in the gas mixture.Based on the phase equilibrium data,a three stages hydrate CO2 separation from integrated gasification combined cycle (IGCC) synthesis gas is investigated.Because the separation efficiency is quite low for the third hydrate separation,a hybrid CO2 separation process of two hydrate stages in conjunction with one chemical absorption process (absorption with MEA) is proposed and studied.The experimental results show H2 concentration in the final residual gas released from the three stages hydrate CO2 separation process was approximately 95.0 mol% while that released from the hybrid CO2 separation process was approximately 99.4 mol%.Thus,the hybrid process is possible to be a promising technology for the industrial application in the future

Study on the Application of Modified Sn-Based Solder in Cable Intermediate Joints

With the increasing use of underground cables, the quantity and quality of intermediate joints demanded are also increasing. The quality of the traditional crimping intermediate joint is easily affected by the actual process of the operator, which may lead to the heating of the crimping part of the wire core, affecting the insulation performance of the cable, and finally causing the joint to break. However, aluminothermic reactive technology has some problems, such as a high welding temperature and an uncontrollable reaction. In order to solve these problems, according to the brazing principle and microalloying method, the optimal content of In in Sn-1.5Cu-based solder was explored, and then the connection of the middle joint of a 10 kV cable was completed using a connecting die and electrical connection process. The contact resistance and tensile strength of the joint were tested to verify the feasibility of this method. The results show that the maximum conductivity of the solder with 3.8% and 5% In content can reach 3.236 × 106 S/m, and the highest wettability is 93.6%. Finally, the minimum contact resistance of the intermediate joint is 7.05 μΩ, which is 43% lower than that of the aluminothermic welded joint, and the tensile strength is close to that of the welded joint, with a maximum of 7174 N

Molecular dynamics simulation of the intercalation behaviors of methane hydrate in montmorillonite

The formation and mechanism of CH4 hydrate intercalated in montmorillonite are investigated by molecular dynamics (MD) simulation. The formation process of CH4 hydrate in montmorillonite with 1 similar to 8 H2O layers is observed. In the montmorillonite, the "surface H2O" constructs the network by hydrogen bonds with the surface Si-O ring of clay, forming the surface cage. The "interlayer H2O" constructs the network by hydrogen bonds, forming the interlayer cage. CH4 molecules and their surrounding H2O molecules form clathrate hydrates. The cation of montmorillonite has a steric effect on constructing the network and destroying the balance of hydrogen bonds between the H2O molecules, distorting the cage of hydrate in clay. Therefore, the cages are irregular, which is unlike the ideal CH4 clathrate hydrates cage. The pore size of montmorillonite is another impact factor to the hydrate formation. It is quite easier to form CH4 hydrate nucleation in montmorillonite with large pore size than in montmorillonite with small pore. The MD work provides the constructive information to the investigation of the reservoir formation for natural gas hydrate (NGH) in sediments

Effect of temperature fluctuation on hydrate-based CO2 separation from fuel gas

A new method of temperature fluctuation is proposed to promote the process of hydrate-based CO2 separation from fuel gas in this work according to the dual nature of CO2 solubility in hydrate forming and non-hydrate forming regions [1]. The temperature fluctuation operated in the process of hydrate formation improves the formation of gas hydrate observably. The amount of the gas consumed with temperature fluctuation is approximately 35% more than that without temperature fluctuation. It is found that only the temperature fluctuation operated in the period of forming hydrate leads to a good effect on CO2 separation. Meanwhile, with the proceeding of hydrate formation, the effect of temperature fluctuation on the gas hydrate gradually reduces, and little effect is left in the completion term. The CO2 separation efficiencies in the separation processes with the effective temperature fluctuations are improved remarkably

Carbon dioxide hydrate separation from Integrated Gasification Combined Cycle (IGCC) syngas by a novel hydrate heat-mass coupling method

A novel hydrate heat-mass coupling separation (HHMCS) method was studied to reduce the energy consumption of CO2 hydrate separation from Integrated Gasification Combined Cycle (IGCC) syngas in this work. Tetra-n-butyl ammonium bromide (TBAB) is used as a hydrate promoter and pure TBAB hydrate is used as a phase change heat-mass coupling additive. The heat-mass coupling effect, CO2 separation characteristics and influence factors were studied by continuous separation experiments in a bubble column reactor. Compared to conventional gas hydrate separation method, the HHMCS process exhibits a higher energy-saving potential, less temperature and TBAB concentration fluctuation due to pure TBAB hydrate phase change. Increase inlet gas rate, the accumulated gas consumption decreased slightly, but the average gas consumption rate increased. Increase operating pressure and decrease gas phase volume increased the average gas consumption rate and CO2 separation efficiency. After continuous separation of simulated syngas, the average CO2 concentration in H-2-rich gas decreased to 17.45 mol %, and that in CO2-rich gas increased to 86.44 mol%. The CO2 split fraction and separation factor reached 0.80 and 8.15, respectively. The work provided a new idea to integrally utilize the phase change enthalpy, improve the operating flexibility and heat transfer in large device. (C) 2020 Elsevier Ltd. All reserved