Study On Thermodynamic Model And The Calculation Of Process For CO₂ Capture By Hydrate Based Gas Separation

The world excessing 60%of global warming effect derives from CO2,i.e.belonging to catalog of greenhouse gas.But CO2 also a precious resource which would be used for oil recovery,making fertilizer,cooling food,refrigeration,production of carbonated drinks,fire extinguisher,aerosol and the metal processing.Therefore,worldwide efforts are underway to capture COZ from fossil fuel related power plant or chemistry plants.By far three methods are generally accepted as the main approaches to capturing carbon explained as pre-combustion,post-combustion and oxy-fiuel for capture.Specifically,chemical wet scrubbing,physical wet scrubbing,membrane separation and finally low-temperature separation are mainly included for capture.It is most promising that the hydrate based gas separation as one of the low-temperature separation technology will be posed as its main part for future capture assigned by easy-operation,low-energy consumption,absent of specific absorbents,and free of corrosion as well as the solid captured-posed CO2 phase.However the research and development efforts associated with hydrate based gas separation related CO2 separation still of essence because of the non-precise thermodynamic model and limitation of experimental stage for hydrate based gas separation process.To fill this blank,this work focuses on the thermodynamic model for hydrate based gas separation to precisely expect for the post-combustion CO2 capture and pre-combustion CO2 capture.Additionally,this work simulates the hydrate based gas separation processes with the new developed thermodynamic model,respectively.In this work,the CPA-SRK EoS was utilized to perform the phase behavior of gas phase and liquid phase in the gas hydrate system.In the new developed thermodynamic model,H2O was regared as an association component and modeled by the 4C association scheme which involves two proton donors and two proton acceptors.And CO2 was considered as solvent with one proton acceptor site,which was only able to cross associate with water.In addition,N2 was modeled as inert compound with no self-associating or cross-associating interactions.On this basis,the CPA-SRK EoS was re-derived.Additionally,new experimental data of dissociation pressure of CO2+N2 mixtures,with CO2 concentration of 20.03%,36.24%,45.24%and 85.32%,were generated.For the post-combustion Co2 capture,the energy parameters a of H2O and CO2 in CPA-SRK EoS were re-fitted with the saturated liquid density and the saturated vapor pressure value from DiPPR database.The energy parameter ?0.5 of water was developed as a cubic function of(1-(T/Tc)0.5),and the ?0.5 of CO2 was developed as a function of(1-(T/Tc)0.5).With the solubility data of binary system CO2-H2O and binary system N2-H2O,temperature dependent binary interaction parameters%were proposed and verified,respectively.Additionally,the Langumir absorption constant of P-P model and Chen-Guo model were also developed.With the assumption of 0.5 liquid fraction of feed,this work made a Comparison between the prediction results and the experimental value.The results show that improved accuracy were noticed with the new developed P-P model+CPA-SRK EoS and Chen-Guo model+CPA-SRK EoS.And the Chen-Guo model+CPA-SRK EoS performed higher accuracy than P-P model+CPA-SRK EoS.This work also simulated the post-combustion CO2 capture by hydrate based gas separation prosess with Chen-Guo model+CPA-SRK EoS.With the calculation results under the phase equilibrium situation,the effect of the feed concentration and temperature on the dissociation pressure and the number of stage was obtained.In addition,this work also simulated hydrate based gas separation process for the flue gas with 17%CO2 and 83%N2 under actual operation situation.The throughput of flue gas was 4.576 × 105Nm3/h.With the results of three phase isothermal flash calculation,this work calculated the liquid fraction of feed in each stage and analyzed the effect of operation pressure on the composition of hydrate phase,gas phase and the separation efficiency.Then,a four-stage hybrid hydrate-membrane separation process for post-combustion CO2 capture from 17%CO2+83%N2 flue gas was developed.For the pre-combustion CO2 capture,a temperature dependent binary interaction parameter kij of the binary system H2-H2O was obtained with the solubility data.And the result was verified with the literatures reported value.Additionally,the Langumir absorption constant of P-P model and Chen-Guo model were also developed.With the assumption of 0.5 liquid fraction of feed,a Comparison between the prediction results and the experimental value was proposed.The results show that improved accuracy were noticed with the new developed P-P model+CPA-SRK EoS and Chen-Guo model+CPA-SRK EoS.Meanwhile,the Chen-Guo model+CPA-SRK EoS performed higher accuracy than P-P model+CPA-SRK EoS.Additionally,this work simulated the pre-combustion CO2 capture by hydrate based gas separation prosess with Chen-Guo model+CPA-SRK EoS.Under the phase equilibrium situation.With the calculation results,the effect of the feed concentration and temperature on the dissociation pressure and the number of stage was obtained.Additionally,this work also simulated hydrate based gas separation process for 5×105Nm3/h syngas with 40%CO2 and 60%H2 under actual operation situation.With the results of three phase isothermal flash calculation,this work calculated the liquid fraction of feed in each stage and analyzed the effect of operation pressure on the composition of hydrate phase,gas phase and the separation efficiency.Lastly,a second-stage hybrid hydrate-membrane separation process for pre-combustion CO2 capture from 40%CO2+60%H2 syngas was proposed.