Molecular dynamic simulation of carbon dioxide,methane,and nitrogen adsorption on Faujasite zeolite

Removing impurities such as carbon dioxide and nitrogen from natural gas is a technical challenge and one of the major concerns in natural gas treatment process.In this study,adsorption of CH_(4),N_(2),and CO_(2)on the Faujasite(FAU)zeolite has been studied using molecular dynamics simulation at temperatures of 293,308,and 323 K and pressures up to 1 MPa.COMPASS force field was used to model the interactions between zeolite and guest molecules.Ewald and atom-based summation methods were used for the calculation of electrostatic and van der Waals forces,respectively.Simulated results were modeled using Langmuir,Freundlich,Toth,and Sips adsorption isotherms.Sips isotherm for CO_(2),and Toth isotherm for CH_(4)and N_(2)pure compounds showed the best performance.Heat of adsorption for CH_(4),CO_(2),and N_(2)were calculated to be-15.48,-24.1,and-13.31 kJ·mol^(-1),respectively.A comparative study showed that the simulation model was successful in predicting the overall trend of the adsorption with acceptable accuracy.

Using S-statistic for investigating the effect of temperature on hydrodynamics of gas-solid fluidization

The influence of temperature on fluidization was investigated by a statistical chaotic attractor comparison test known as S-statistic, After calibration of the variables used in this method, the S-test was applied to the radioactive particle tracking （RPT） data obtained from a lab-scale fluidized bed. Experiments were performed with sand as fluidized particles and in temperatures from ambient up to 600 ℃ with superficial gas velocities of 0.29, 0.38 and 0.52 m/s. Considering the behavior of bubbles and comparing with frequency domain analysis, it was concluded that S-statistic is a reliable method for characterization of fluidization process behavior at different temperatures.

Vibration time series analysis of bubbling and turbulent fluidization

A non-intrusive vibration monitoring technique was used to study the hydrodynamics of a gas-solid fluidized bed. Experiments were carried out in a 15 cm diameter fluidized bed using 226,470 and 700 um sand particles at various gas velocities, covering both bubbling and turbulent regimes. Auto correlation function, mutual information function, Hurst exponent analysis and power spectral density function were used to analyze the fluidized bed hydrodynamics near the transition point from bubbling to turbulent fluidization regimes. The first pass of the autocorrelation function from one half and the time delay at which it becomes zero, and also the first minimum of the mutual information, occur at a higher time delay in comparison to stochastic systems, and the values of time delays were maximum at the bubbling to turbulent transition gas velocity. The maximum value of Hurst exponent of macro structure occurred at the onset of regime transition from bubbling to turbulent. Further increase in gas velocity after that regime transition velocity causes a decrease in the Hurst exponent of macro structure because of breakage of large bubbles to small ones. The results showed these methods are capable of detecting the regime transition from bubbling to turbulent fluidization conditions using vibration signals.