Experimental Study On Gas Hydrate Exploitation By Combining N₂ And CO₂ Mixture Replacement And Heat Injection

The CO₂ replacement method is currently considered as one of the most promising hydrate production techniques that can both obtain clean energy and sequester greenhouse gases as solid hydrates without undermine the stability of the geographic structure.However,the source of pure CO₂ is rare.The CO₂+N₂ mixture replacement exploitation can increase the recovery rate.The CO₂+N₂ mixture is the main component of the flue gas.The use flue gas of power plant combined with heat can reduce raw material costs and increase the recovery rate.Meanwhile,the CO₂ can be stored as CO₂ hydrates.Therefore,in this paper,to simulate the flue gas of coal-fired power plant,the CO₂+N₂ mixture gas,is used as a gas source to conduct hydrate exploitation by replacement combined with heat method.The influence of combined exploitation process parameters,the methane recovery rate and energy consumption are discussed.In this paper,the hydrate reservoir was simulated by using ice powder and methane in the quartz sand system.The experiment was carried out to simulate the replacement process of the methane production from methane hydrate by injecting 53%CO₂+47%N₂ combined with hot deionized water at the temperature of 1¹4℃and the pressure of 8¹4 MPa.The experiment results of the combined exploitation show that for the experiments of methane hydrate production by 53%CO₂+47%N₂ at temperature of 1¹4℃and injection pressure of 8¹4MPa,with the water injection volume of 20ml and water injection temperature of20⁶0℃,the methane recovery ratio increased with pressure rising、temperature increasing and the water injection temperature increasing.When the injection pressure is 14 MPa,the injection volume is 20 ml,the water injection temperature is 60℃,the temperature is 1℃,the methane recovery ratio can reach 91.6%.Meanwhile,thermal decomposition experiments of methane hydrates at 1¹4℃were carried out.The extraction mechanism and kinetics of methane hydrate with 53%CO₂+47%N₂ gas mixture combined with heat were analyzed.To analyze material condition and energy efficiency,two schemes of methane recovery method were simulated and calculated by Aspen software,based on the replacement process of the methane production from methane hydrate by injecting 53%CO₂+47%N₂ gas mixture with/without heat.At the temperature of 1¹2℃and injection pressure of 3¹6MPa,,simulation results show that under the temperature of 1°C and the replacement pressure range of 6MPa,the two methods have the lowest energy consumption.The unit energy consumption of 53%CO₂+47%N₂mixture with heat combination method is 0.59 kWh/Kg-CH₄;the unit energy consumption of53%CO₂+47%N₂ mixture replacement is 0.66 kWh/Kg-CH₄.Uder the same condition,the EROI of combined method is 18.49²4.44,and the EROI of replacement method is14.81²2.25.The energy efficiency of combined method is higher than that of replacement.