Experimental Study On Enhancement Of Rapid Formation Of CO₂ Hydrate By Combination Thermodynamic Accelerators

As a new phase change energy storage technology,CO2 hydrate has great application potential.It is characterized by high latent heat of phase change,high gas storage density and suitable phase change conditions.It has unique advantages in cold storage,solid state storage and transportation of gas,mixed gas separation and other fields.However,there are some problems in the growth process of CO2 hydrate,such as high phase equilibrium pressure,small gas-liquid interface,and heat and mass transfer obstructed by hydrate shell,which hinder the nucleation and growth of CO2 hydrate and restrict the development of practical application of CO2 hydrate.In this paper,the combined thermodynamic accelerator tetrabutylammonium bromide(TBAB),tetrahydrofuran(THF)combined SDS,and the addition of a new thermodynamic accelerator R134 a were studied.The rapid nucleation and growth characteristics of CO2 hydrate under low and medium temperature conditions,increasing the gas conversion rate of CO2 hydrate and reducing the induction time of hydrate formation were studied by regulating the phase equilibrium pressure.The specific research contents are as follows:(1)In order to solve the problems of difficult formation of CO2 hydrate and low gas consumption,SDS combined with thermodynamic promoter TBAB was used to strengthen the nucleation and growth of CO2 hydrate,and a set of experimental system for strengthening CO2 by SDS combined with thermodynamic promoter was developed.The experimental results showed that(0-20)Wt % TBAB increased CO2 consumption by about 2-4 times compared with pure water.With the increase of TBAB concentration,the gas consumption of CO2 hydrate formation increased gradually,and the gas consumption of 15 Wt% TBAB reached the maximum of 27.84 mmol / mol.When the TBAB concentration was greater than17.5%,the gas consumption decreased.In the range of(0-15)Wt%,TBAB combined with SDS further increased the gas consumption of hydrate formation and shortened the induction time of hydrate formation by about 83%.(2)Based on the relatively mild phase equilibrium conditions of R134 a hydrate(0.1MPa,3 °C).The nucleation and growth of R134a/CO2 mixed gas hydrate were experimentally studied,and the enhanced formation law of R134 a on CO2 hydrate was analyzed.It was found that different concentrations of R134a/CO2 significantly shortened the induction time of CO2 hydrate formation,increased gas consumption,and improved the hydrate formation rate.It was found that R134a/CO2 hydrate showed a horizontal growth trend under pure water conditions,which hindered gas-liquid exchange and prevented the sustainable growth of CO2 hydrate.To solve this problem,stirring and SDS were introduced in the experiment.It was found that under the action of SDS,the gas consumption of hydrate formation further increased by about 60%,and the hydrate formation was uniform through visual observation.The concentration change of R134 a in the mixed gas during the experiment was analyzed by gas chromatography.Finally,it was concluded that R134 a hydrate was first generated.Under the action of SDS,it was mainly deposited on the gas-liquid interface and the reactor wall in the form of porous hydrate.The existence of“capillary driving mechanism” of porous hydrate provides continuous gas-liquid exchange,ensures the continuous growth of CO2 hydrate and improves the gas conversion rate.(3)An innovative method for the rapid formation of CO2 hydrate controlled by trace R134 a was proposed.Firstly,the optimal mixing amount of R134 a was quantified,and then the strengthening formation law was obtained by controlling the inflation time interval and nucleation time.Finally,the strengthening formation effects under different pressures were systematically analyzed,and the growth and enrichment law of CO2 hydrate was obtained by combining visualization.The experimental results show that the hydrate formation can be significantly accelerated when the content of R134 a is higher than 2%.Since the hydrate is preferentially formed by the first-filled R134 a,the formed crystal can trigger the formation of CO2 hydrate.The longer the aeration time interval is,the larger the size and number of R134 a hydrate clusters are,and the more conducive to shortening the formation time of CO2 hydrate.The “switch” effect is achieved by adding R134 a in pure water.This simple and efficient method lays a theoretical and technical support for controlling CO2 hydrate formation and realizing efficient energy storage.