Experimental Study On The Convective Mixing Characteristics Of Impure Carbon Dioxide And Brine

In recent years,CO₂ emissions have increased dramatically due to the large use of fossil fuels,which makes the phenomenon of greenhouse effect worsen.In order to mitigate the greenhouse effect,people pay more and more attention to CO₂ emission reduction.Carbon capture and storage?CCS?is considered to be one of the most effective measures to reduce CO₂ emissions.Because of the wide distribution and large storage capacity of saline aquifers,CO₂ storage in saline aquifers has become the preferred technology for geological CO₂ storage.The CO₂ flow captured from industrial carbon emission sources will contain impurity gases.Purification of CO₂ will greatly increase the cost of CO₂ capture and become an important obstacle to large-scale implementation of CCS.By reducing the purity requirement of CO₂capture,impure CO₂ geological storage can effectively reduce the economic cost of purification and improve the economic benefits of CCS projects.Therefore,it is very important to study impure CO₂ storage in saline aquifer for evaluating CCS projects.In this paper,Hele-Shaw device is used to carry out the visualization experiment of convective mixing.The effects of salt water concentration,impurity gas and temperature on the convective mixing characteristics of CO₂ and fluid are studied.?1?Increasing salinity will increase the viscosity of solution,decrease the density accumulation rate of gas in the diffusion boundary layer,and then increase the stability of the system,delay the starting time of convective mixing,weaken the intensity of convective mixing,and slow down the development speed of finger mixing length.Finally,the transport rate of CO₂ in solution is slowed down,resulting in the reduction of CO₂ solubility.?2?The presence of Ar and SO₂ impurities will accelerate the onset time of convective mixing,increase the development speed of finger diffusive lengths,accelerate the rate of convective mixing,and ultimately increase the solubility of CO₂,but there are differences in the mechanism of action between the two.Among them,the presence of Ar will affect the diffusion performance of mixed gases in water,accelerate the start time of convective mixing,and increase the effective Ra value,which will increase the intensity of convective mixing.On the other hand,SO₂ accelerates the initial time of convective mixing,increases the intensity of convective mixing and increases the mass transfer rate of CO₂ in water by increasing the density difference of solution,thus increasing the solubility of CO₂.?3?The increase of temperature will decrease the viscosity of solution,weaken the stability of the interface between the two phases lower,reduce the difficulty of convective mixing,and accelerate the starting time of convective mixing,and increase the number of fingering.However,as the temperature rises,the solubility of the gas decreases dramatically,slowing down the speed of gas entering the liquid phase and reducing the concentration of the gas contained in the finger,which leads to a decrease in the density difference between the finger and the solution below,thus slowing down the development of finger and leading to a decrease in the final solubility of CO₂.In this paper,the effects of salinity,impurity gas and temperature on the convective mixing characteristics of CO₂ and saline are analyzed through the parameters of initial mixing time,finger mixing length,finger diffusion length and CO₂ concentration of solution,which provides a new reference for evaluating the storage project of impure CO₂ brine layer.