| Coal-bed methane is an important unconventional natural gas resource.Two-thirds of low-concentration coal-bed methane whose methane concentration is less than 30%is emptied because its calorific value is too low and it is forbidden to use it,which wastes resources and pollutes the environment.The key to the development and utilization of coalbed methane resources is efficient and practical separation and concentration technology.Absorption-hydration separation technology is a new technology with high safety and low pollution,which can be used for the concentration of methane in coalbed methane.At present,the research on the absorption-hydration separation of coalbed methane is still in the preliminary stage of exploration,and there are still a series of problems that need to be solved.In this paper,tetrahydropyran(THP)is used as an absorption-hydration additive to study the influence of tetrahydropyran on the formation of coalbed methane hydrate.Finally,the process and energy consumption of using tetrahydropyran to concentrate coalbed methane are designed and simulated.In this paper,firstly,the constant volume pressure search method is used to measure the hydrate phase equilibrium conditions of CH4,N2 and 20 mol%CH4/N2 mixtures in pure water and THP solutions.The results show that THP has an obvious thermodynamic promotion effect on the formation of hydrates from CH4,N2 and CH4/N2 mixtures.As the THP concentration increases from 1.67 mol%to 5.6 mol%,the phase equilibrium conditions of CH4,N2 and CH4/N2 mixture gas hydrate move to the area of low temperature and high pressure;THP expands the operating range of CH4/N2 mixture for hydrate separation.Secondly,the performance of the absorption-hydration method to separate 20mol%CH4/N2 mixture in the presence of THP was studied,and the effects of temperature,feed pressure,initial gas-liquid ratio and THP concentration on the separation were investigated.Studies have shown that temperature reduction,pressure increase and initial gas-liquid ratio decrease are beneficial to increase the rate of hydrate formation and CH4 recovery,but the liquid phase CH4 concentration decreases.The recovery rate and separation factor of CH4 reached the maximum at 280.15 K and 2.5 MPa in a 5.6 mol%THP solution,which were 72.7%and 6.7respectively;in a 1.67 mol%THP solution at 280.15 K,2 MPa and a gas-liquid ratio of 78,the liquid The CH4 concentration achieved a maximum value of 50.3 mol%.In order to further improve the separation efficiency,the separation of 20 mol%CH4/N2mixed gas by water-in-oil emulsion was also studied,and the influence of different oil phase components,water-oil ratio and stage gas inlet method on the separation effect was investigated.The results show that the separation effect of the water-in-decane emulsion system is better than that of the THP water-in-water emulsion system and the THP solution system;the water-oil ratio of the emulsion increases,the CH4 recovery rate decreases,and the liquid phase CH4concentration increases;The stage gas inlet method can increase the liquid phase CH4concentration from 46.7 mol%to 51 mol%.Finally,the absorption-hydration method to separate low-concentration coalbed methane process was established in HYSYS V10.The energy consumption of the four processes in THP solution and n-decane emulsion was calculated through simulation.The results show that the total energy consumption of the process with product gas of high CH4 concentration is lower,and the n-decane emulsion system can obtain more secondary coalbed methane products.The research in this article provides reference data for the industrialization of low-concentration coalbed methane separation technology by absorption-hydration method. |
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