Experiment And Theoretical Research For Formation Of Coal-bed Methane Hydrate In Porous Media+THF+TBAB System

Coal-bed methane(CBM) is a clean unconventional gas resource with high calorific value. But there is a large proportion of C BM which would be directly discharged for low methane concentration. The purification of CBM using hydrate formation utilizes the different formation pressure of each gas component in CBM. In an attempt to reach the separation of coal-bed methane, hydrate formation for low-concentration coal-bed methane has been performed mainly being based on CH4?N2?O2 which are used for formatting hydrate under different temperature and pressure conditions. Recovery of methane from low concentration coal-bed gas could be a breakthrough point in the effort to mitigate greenhouse effect and air pollution, also optimize energy structure.The development of hydrate technology is restricted due to the stiff synthesis conditions of gas hydrates and long induction time. Therefore, it is necessary to study how to improve the thermodynamics for gas-hydrate separation, shortens the induction time and improve the hydrate storage capability. This paper investigated the effect of the compounded system of chemical accelerators(TBAB + THF) on the hydrate formation in porous medium. Using water fugacity model combined with UNIFAC group contribution method and eN RTL model, we predict phase equilibrium of the low concentration coal-bed methane hydrate in the presence of TBAB or THF in porous medium. These can provide the theoretical basis for industrialization of hydrate technology. Specific work content includes: This experiment 9 groups(1) According to orthogonal experiment method, we have designed experiment which include nine groups in porous media + THF + TBAB system, and have measured data of phase equilibrium, induction time and hydrate storage capability of low concentration coal-bed gas hydrate. The experimental result has indicated that our experiment system can remarkably reduce the phase equilibrium pressure of low concentration coal-bed gas hydrate. When THF(or TBAB) concentration has been fixed, the promotion of mixed additives on hydrate phase equilibrium was strengthened and then weakened with the gradual increasing concentration of TBAB(or THF). So there is an optimal concentration for the mixed additives. Though the analysis of orthogonal experiment data, the result has indicated that the order about the influence of various factors on phase equilibrium is THF > TBAB > glass sand.(2) Utilizing the water fugacity model and PRSV equation of state, we have predicted hydrate phase equilibrium of one-component gas(CH4 and N2) and multi- component gas(CH4 + N2). The results got by comparing the model values and experiment values shows that the fugacity model is a reliable thermodynamic model to calculate hydrate phase equilibr ium. Based on this model, using UNIFAC group contribution method and eNRTL model, considering the influence of capillary force on hydrate fugacity in porous media, we have researched the thermodynamic model of low concentration coal-bed gas hydrate with the presence of THF or TBAB in porous medium. The result shows that fugacity model can predict the formation conditions for low concentration coal-bed gas hydrate in porous media; Porous medium hinders the formation of hydrate, the smaller the pore radius of porous medium is, the greater the inhibition is; The pressure of hydrate formation of low concentration coal-bed methane in porous media + additives system is significantly lower than it in pure water system, and the pressure reduces by more than 90%.