Development And Mechanism Research Of CO₂ Absorption System For Phase Change Nanofluids

CO₂ capture technology is a technology to recover CO₂ from coal-fired power plants,chemical plants,cement plants,iron and steel plants,and is one of the key technologies for carbon emission reduction.The flue gas of coal-fired power plant is the main emission source of CO₂.Among many capture methods,the organic amine chemical absorption method is the main technology to realize industrial application at present.CO₂capture absorbent is the core of chemical absorption method,which determines the research and design of absorption tower,regeneration tower and heat exchange equipment,the heat integration of waste heat recovery process of capture system,and the design and development of public works.At present,there are many problems in CO₂ capture absorbers,such as high regeneration energy consumption,low mass transfer rate and large operation loss,which seriously restrict the large-scale transformation and application of CO₂ capture technology.Aiming at low energy consumption,high mass transfer rate,large absorption capacity,low corrosion and low degradation rate,a phase-change nanofluid absorption system suitable for low partial pressure CO₂ capture has been developed and its mechanism has been studied.The main research work is divided into the following aspects:（1）A phase-change nano absorption system composed of base solution,lower critical amine and nano particles was developed.The absorption and regeneration properties of five kinds and 18 kinds of organic amine absorbents with good water solubility were evaluated,and AEP was selected as the best absorbent.The energy consumption of 10 kinds of lipophilic amine absorbers in the presence of lower critical solution temperature was evaluated.DPA was selected as the best lipophilic amine with lower critical temperature,which was used as the stratification agent and consumption reducing agent of phase change absorption system.The optimum ratio of AEP-DPA to lipophilic amines is 6:4.The mass transfer enhancement effect of five kinds of 10 nm nanoparticles was analyzed.It was found that CuO promoted the performance of AEP-DPA the most.The formula of phase-change nanofluid is 0.6 mol/LAEP+0.4 mol/LDPA+0.05wt%CuO.（2）The reaction products and mechanism of AEP-DPA-CuO phase change nanofluid were studied.The"self extraction"mechanism of regeneration process was revealed,and the principle of enhanced mass transfer of nanoparticles was discussed.The H and DEPTQ spectra of NMR were used to analyze the molecular structure of carbamate,and GC-MS was used to analyze the structure and composition of heat stable products before and after the reaction.Based on the product analysis,the absorption and regeneration mechanism of phase-change nanofluids were studied,and the phenomenon of"self extraction"in the regeneration process was revealed.The particle size distribution,dispersion and agglomeration of nanoparticles in solution were studied.The mechanism of nanoparticle enhanced absorption was analyzed,and five laws,Brownian motion,Marangoni effect,large specific surface enhancement,bubble coalescence and heterogeneous catalysis were revealed.（3）The physical parameters and reaction kinetics of the phase change absorption system were studied,and the influencing factors of CO₂absorption rate of the phase change system were analyzed.Based on the principle of zwitterion reaction and the fast pseudo first order reaction model,a general kinetic model was established.On the basis of modeling,the boundary conditions and important parameters are defined,and the total reaction rate constant of the mass transfer process of phase change absorption system is derived.The total reaction rate constant is verified by using the fast pseudo first-order reaction,and the model parameters are tested and verified by numerical calculation.（4）The thermodynamic behaviors such as gas-liquid equilibrium and reaction heat of CO₂ absorption by phase-change nanofluids were studied.The phase equilibrium data of CO₂absorption process under different temperature and partial pressure are studied by using the gas-liquid phase equilibrium experimental device,and the principle of gas-liquid phase equilibrium is analyzed.A theoretical model of absorption reaction heat and regeneration reaction heat is proposed.The reaction heat of the base solution and lower critical amine is measured.The reaction heat of AEP-DPA-CuO phase change absorption system is studied under different ratio,absorption temperature,reaction concentration and reaction pressure,and compared with MEA reaction heat.（5）The corrosion and degradation of phase change nanofluids were studied,and corrosion inhibitors and anti degradation agents were developed.The corrosion characteristics of the system with temperature and load were summarized,and the application effects of six kinds of synthesized inhibitors in phase change nanofluids were investigated.Through the analysis of thermal degradation and oxidative degradation,it is found that the products include thermal degradation and oxidative degradation.The effects of CO₂ loading,O₂,temperature and Fe³⁺on the degradation rate were studied,and the degradation inhibition rates of six antioxidants were analyzed.（6）The continuous experiment of capturing CO₂ in industrial AEP-DPA-CuO phase change system was carried out,and the performance of phase change absorption system was further evaluated.Compared with AEP-DPA-CuO phase change absorption system,lmea solution has the advantages of high absorption rate,large absorption load,low regeneration temperature and large regeneration amount.The high-efficiency inhibitor and antioxidant have good application effect.